1.
Electromagnetic radiation
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In physics, electromagnetic radiation refers to the waves of the electromagnetic field, propagating through space carrying electromagnetic radiant energy. It includes radio waves, microwaves, infrared, light, ultraviolet, X-, classically, electromagnetic radiation consists of electromagnetic waves, which are synchronized oscillations of electric and magnetic fields that propagate at the speed of light through a vacuum. The oscillations of the two fields are perpendicular to other and perpendicular to the direction of energy and wave propagation. The wavefront of electromagnetic waves emitted from a point source is a sphere, the position of an electromagnetic wave within the electromagnetic spectrum can be characterized by either its frequency of oscillation or its wavelength. Electromagnetic waves are produced whenever charged particles are accelerated, and these waves can interact with other charged particles. EM waves carry energy, momentum and angular momentum away from their source particle, quanta of EM waves are called photons, whose rest mass is zero, but whose energy, or equivalent total mass, is not zero so they are still affected by gravity. Thus, EMR is sometimes referred to as the far field, in this language, the near field refers to EM fields near the charges and current that directly produced them, specifically, electromagnetic induction and electrostatic induction phenomena. In the quantum theory of electromagnetism, EMR consists of photons, quantum effects provide additional sources of EMR, such as the transition of electrons to lower energy levels in an atom and black-body radiation. The energy of a photon is quantized and is greater for photons of higher frequency. This relationship is given by Plancks equation E = hν, where E is the energy per photon, ν is the frequency of the photon, a single gamma ray photon, for example, might carry ~100,000 times the energy of a single photon of visible light. The effects of EMR upon chemical compounds and biological organisms depend both upon the power and its frequency. EMR of visible or lower frequencies is called non-ionizing radiation, because its photons do not individually have enough energy to ionize atoms or molecules, the effects of these radiations on chemical systems and living tissue are caused primarily by heating effects from the combined energy transfer of many photons. In contrast, high ultraviolet, X-rays and gamma rays are called ionizing radiation since individual photons of high frequency have enough energy to ionize molecules or break chemical bonds. These radiations have the ability to cause chemical reactions and damage living cells beyond that resulting from simple heating, Maxwell derived a wave form of the electric and magnetic equations, thus uncovering the wave-like nature of electric and magnetic fields and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the speed of light. Maxwell’s equations were confirmed by Heinrich Hertz through experiments with radio waves, according to Maxwells equations, a spatially varying electric field is always associated with a magnetic field that changes over time. Likewise, a varying magnetic field is associated with specific changes over time in the electric field. In an electromagnetic wave, the changes in the field are always accompanied by a wave in the magnetic field in one direction
2.
Microwave oven
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A microwave oven is a kitchen appliance that heats and cooks food by exposing it to microwave radiation in the electromagnetic spectrum. This induces polar molecules in the food to rotate and produce energy in a process known as dielectric heating. Percy Spencer is generally credited with inventing the microwave oven after World War II from radar technology developed during the war. Named the Radarange, it was first sold in 1946, Raytheon later licensed its patents for a home-use microwave oven that was first introduced by Tappan in 1955, but these units were still too large and expensive for general home use. The countertop microwave oven was first introduced in 1967 by the Amana Corporation, Microwave ovens are popular for reheating previously cooked foods and cooking a variety of foods. They are also useful for heating of otherwise slowly prepared cooking items, such as hot butter, fats. Unlike conventional ovens, microwave ovens usually do not directly brown or caramelize food, exceptions occur in rare cases where the oven is used to heat frying-oil and other very oily items, which attain far higher temperatures than that of boiling water. Some modern microwave ovens are part of units with built-in extractor hoods. The exploitation of high-frequency radio waves for heating substances was possible by the development of vacuum tube radio transmitters around 1920. By 1930 the application of waves to heat human tissue had developed into the medical therapy of diathermy. At the 1933 Chicago Worlds Fair, Westinghouse demonstrated the cooking of foods between two metal plates attached to a 10 kW,60 MHz shortwave transmitter. The Westinghouse team, led by I. F. Mouromtseff, found that foods like steaks and this patent proposed radio frequency heating, at 10 to 20 megahertz. The invention of the cavity magnetron made possible the production of waves of a small enough wavelength. The magnetron was originally a component in the development of short wavelength radar during World War II. A more high-powered microwave generator that worked at shorter wavelengths was needed, sir Henry Tizard travelled to the U. S. in late September 1940 to offer the magnetron in exchange for their financial and industrial help. An early 6 kW version, built in England by the General Electric Company Research Laboratories, Wembley, contracts were awarded to Raytheon and other companies for mass production of the magnetron. In 1945, the heating effect of a high-power microwave beam was accidentally discovered by Percy Spencer. Employed by Raytheon at the time, he noticed that microwaves from a radar set he was working on started to melt a candy bar he had in his pocket
3.
Microwave transmission
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Microwave transmission is the transmission of information or energy by electromagnetic waves whose wavelengths are measured in small numbers of centimetre, these are called microwaves. This part of the spectrum ranges across frequencies of roughly 1.0 gigahertz to 300 GHz. These correspond to wavelengths from 30 centimeters down to 0.1 cm, communication satellites which transferred data between ground stations by microwaves took over much long distance traffic in the 1960s. This allows nearby microwave equipment to use the same frequencies without interfering with each other, a disadvantage is that microwaves are limited to line of sight propagation, they cannot pass around hills or mountains as lower frequency radio waves can. Microwave radio transmission is used in point-to-point communication systems on the surface of the Earth, in satellite communications. Other parts of the radio band are used for radars, radio navigation systems, sensor systems. Radio waves in this band are usually strongly attenuated by the Earthly atmosphere and particles contained in it, also, in wide band of frequencies around 60 GHz, the radio waves are strongly attenuated by molecular oxygen in the atmosphere. Wireless transmission of power Proposed systems e. g, in microwave radio relay, microwaves are transmitted between the two locations with directional antennas, forming a fixed radio connection between the two points. The requirement of a line of sight limits the distance between stations to 30 or 40 miles. Beginning in the 1950s, networks of microwave links, such as the AT&T Long Lines system in the U. S. carried long distance telephone calls. The first system, dubbed TD-2 and built by AT&T, connected New York and these included long daisy-chained series of such links that traversed mountain ranges and spanned continents. Much of the traffic is now carried by cheaper optical fibers and communication satellites. Antennas must be highly directional, these antennas are installed in elevated locations such as radio towers in order to be able to transmit across long distances. Typical types of antenna used in radio relay link installations are parabolic antennas, dielectric lens, and horn-reflector antennas, highly directive antennas permit an economical use of the available frequency spectrum, despite long transmission distances. Because of the frequencies used, a line-of-sight path between the stations is required. Additionally, in order to avoid attenuation of the beam an area around the beam called the first Fresnel zone must be free from obstacles, obstacles in the signal field cause unwanted attenuation. In the planning process, it is essential that path profiles are produced, multipath fades are usually deep only in a small spot and a narrow frequency band, so space and/or frequency diversity schemes can be applied to mitigate these effects. Rare events of temperature, humidity and pressure profile versus height, may produce large deviations and distortion of the propagation and affect transmission quality
4.
Frazier Mountain
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Frazier Mountain is a broad, pine-forested peak in the Transverse Ranges System, within the Los Padres National Forest in northeastern Ventura County, California. At 8,017 feet, Frazier Mnt. is the sixteenth-highest mountain in the Transverse Ranges of Southern California, the community of Frazier Park and its outlying district of Lake of the Woods are northward of the mountain. The intersection of Ventura, Los Angeles, and Kern Counties lies just to the northeast, interstate 5 runs to the east of the mountain, and Southern California Edisons Path 26500 kV wires are at its eastern foothills. Mount Pinos is 21.5 miles by road west of Frazier Mountain, alamo Mountain and the Sespe Condor Sanctuary are to its south. The summit of the mountain is a Forest Service lookout area with radio tower facilities as well as a fire lookout tower. The highest point is accessible by a forest road that is open there is no snow present on the mountain. Transverse Ranges—related topics 1857 Fort Tejon earthquake — nearby on the San Andreas fault
5.
California
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California is the most populous state in the United States and the third most extensive by area. Located on the western coast of the U. S, California is bordered by the other U. S. states of Oregon, Nevada, and Arizona and shares an international border with the Mexican state of Baja California. Los Angeles is Californias most populous city, and the second largest after New York City. The Los Angeles Area and the San Francisco Bay Area are the nations second- and fifth-most populous urban regions, California also has the nations most populous county, Los Angeles County, and its largest county by area, San Bernardino County. The Central Valley, an agricultural area, dominates the states center. What is now California was first settled by various Native American tribes before being explored by a number of European expeditions during the 16th and 17th centuries, the Spanish Empire then claimed it as part of Alta California in their New Spain colony. The area became a part of Mexico in 1821 following its war for independence. The western portion of Alta California then was organized as the State of California, the California Gold Rush starting in 1848 led to dramatic social and demographic changes, with large-scale emigration from the east and abroad with an accompanying economic boom. If it were a country, California would be the 6th largest economy in the world, fifty-eight percent of the states economy is centered on finance, government, real estate services, technology, and professional, scientific and technical business services. Although it accounts for only 1.5 percent of the states economy, the story of Calafia is recorded in a 1510 work The Adventures of Esplandián, written as a sequel to Amadis de Gaula by Spanish adventure writer Garci Rodríguez de Montalvo. The kingdom of Queen Calafia, according to Montalvo, was said to be a land inhabited by griffins and other strange beasts. This conventional wisdom that California was an island, with maps drawn to reflect this belief, shortened forms of the states name include CA, Cal. Calif. and US-CA. Settled by successive waves of arrivals during the last 10,000 years, various estimates of the native population range from 100,000 to 300,000. The Indigenous peoples of California included more than 70 distinct groups of Native Americans, ranging from large, settled populations living on the coast to groups in the interior. California groups also were diverse in their organization with bands, tribes, villages. Trade, intermarriage and military alliances fostered many social and economic relationships among the diverse groups, the first European effort to explore the coast as far north as the Russian River was a Spanish sailing expedition, led by Portuguese captain Juan Rodríguez Cabrillo, in 1542. Some 37 years later English explorer Francis Drake also explored and claimed a portion of the California coast in 1579. Spanish traders made unintended visits with the Manila galleons on their trips from the Philippines beginning in 1565
6.
Radome
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A radome is a structural, weatherproof enclosure that protects a microwave antenna. The radome is constructed of material that minimally attenuates the signal transmitted or received by the antenna. In other words, the radome is transparent to radar or radio waves, radomes protect the antenna surfaces from weather and conceal antenna electronic equipment from public view. They also protect nearby personnel from being struck by quickly rotating antennas. Radomes can be constructed in several shapes depending upon the application using various construction materials. When found on fixed-wing aircraft with forward-looking radar, the nose cones often additionally serve as radomes, in case of advanced aircraft systems like AEW&C, a rotating radome often called rotodome is mounted on the top of the fuselage for 360 degree coverage. There are newer AEW&C configurations which instead of rotodome uses three antenna modules in triangular configuration inside radome for 360 degree coverage such as Chinese and Indian AEW&Cs, on rotary-wing and fixed-wing aircraft using microwave satellite for beyond-line-of-sight communication, radomes often appear as blisters on the fuselage. In addition to protection, radomes also streamline the antenna system, a radome is often used to prevent ice and freezing rain from accumulating directly onto the metal surface of antennas. In the case of a radar dish antenna, the radome also protects the antenna from debris. Its shape is easily identified by its hardshell, which has strong properties against being damaged and this reflected power goes back to the transmitter, where it can cause overheating. A foldback circuit can act to prevent this, however, one drawback of its use is that it causes the output power to drop dramatically. One of the driving forces behind the development of fibreglass as a structural material was the need during World War II for radomes. When considering structural load, the use of a radome greatly reduces wind load in normal and iced conditions. Many tower sites require or prefer the use of radomes for wind loading benefits, sometimes radomes may be unsightly if near the ground, and heaters could be used instead. Usually running on direct current, the heaters do not interfere physically or electrically with the current of the radio transmission. For radar dishes, a single, large, ball-shaped dome also protects the mechanism and the sensitive electronics. The Menwith Hill electronic surveillance base, which includes over 30 radomes, is believed to regularly intercept satellite communications. At Menwith Hill, the radome enclosures have a use in preventing observers from deducing the direction of the antennas
7.
Attenuation
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In physics, attenuation is the gradual loss in intensity of any kind of flux through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, in electrical engineering and telecommunications, attenuation affects the propagation of waves and signals in electrical circuits, in optical fibers, and in air. Electrical attenuators and optical attenuators are commonly manufactured components in this field, in many cases, attenuation is an exponential function of the path length through the medium. In chemical spectroscopy, this is known as the Beer–Lambert law, in engineering, attenuation is usually measured in units of decibels per unit length of medium and is represented by the attenuation coefficient of the medium in question. Attenuation also occurs in earthquakes, when the waves move farther away from the epicenter. One area of research in which figures strongly is in ultrasound physics. Attenuation in ultrasound is the reduction in amplitude of the beam as a function of distance through the imaging medium. Accounting for attenuation effects in ultrasound is important because a reduced signal amplitude can affect the quality of the image produced. By knowing the attenuation that an ultrasound beam experiences traveling through a medium, ultrasound attenuation measurement in heterogeneous systems, like emulsions or colloids, yields information on particle size distribution. There is an ISO standard on this technique, ultrasound attenuation can be used for extensional rheology measurement. There are acoustic rheometers that employ Stokes law for measuring extensional viscosity, wave equations which take acoustic attenuation into account can be written on a fractional derivative form, see the article on acoustic attenuation or e. g. the survey paper. Attenuation coefficients are used to different media according to how strongly the transmitted ultrasound amplitude decreases as a function of frequency. Attenuation coefficients vary widely for different media, in biomedical ultrasound imaging however, biological materials and water are the most commonly used media. Ultrasound propagation through homogeneous media is associated only with absorption and can be characterized with absorption coefficient only, propagation through heterogeneous media requires taking into account scattering. When the sun’s radiation reaches the sea-surface, the radiation is attenuated by the water. The intensity of light at depth can be calculated using the Beer-Lambert Law, in clear open waters, visible light is absorbed at the longest wavelengths first. Thus, red, orange, and yellow wavelengths are absorbed at higher water depths, because the blue and violet wavelengths are absorbed last compared to the other wavelengths, open ocean waters appear deep-blue to the eye. In near-shore waters, sea water contains more phytoplankton than the very clear central ocean waters, chlorophyll-a pigments in the phytoplankton absorb light, and the plants themselves scatter light, making coastal waters less clear than open waters
8.
Wavelength
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In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the waves shape repeats, and thus the inverse of the spatial frequency. Wavelength is commonly designated by the Greek letter lambda, the concept can also be applied to periodic waves of non-sinusoidal shape. The term wavelength is also applied to modulated waves. Wavelength depends on the medium that a wave travels through, examples of wave-like phenomena are sound waves, light, water waves and periodic electrical signals in a conductor. A sound wave is a variation in air pressure, while in light and other electromagnetic radiation the strength of the electric, water waves are variations in the height of a body of water. In a crystal lattice vibration, atomic positions vary, wavelength is a measure of the distance between repetitions of a shape feature such as peaks, valleys, or zero-crossings, not a measure of how far any given particle moves. For example, in waves over deep water a particle near the waters surface moves in a circle of the same diameter as the wave height. The range of wavelengths or frequencies for wave phenomena is called a spectrum, the name originated with the visible light spectrum but now can be applied to the entire electromagnetic spectrum as well as to a sound spectrum or vibration spectrum. In linear media, any pattern can be described in terms of the independent propagation of sinusoidal components. The wavelength λ of a sinusoidal waveform traveling at constant speed v is given by λ = v f, in a dispersive medium, the phase speed itself depends upon the frequency of the wave, making the relationship between wavelength and frequency nonlinear. In the case of electromagnetic radiation—such as light—in free space, the speed is the speed of light. Thus the wavelength of a 100 MHz electromagnetic wave is about, the wavelength of visible light ranges from deep red, roughly 700 nm, to violet, roughly 400 nm. For sound waves in air, the speed of sound is 343 m/s, the wavelengths of sound frequencies audible to the human ear are thus between approximately 17 m and 17 mm, respectively. Note that the wavelengths in audible sound are much longer than those in visible light, a standing wave is an undulatory motion that stays in one place. A sinusoidal standing wave includes stationary points of no motion, called nodes, the upper figure shows three standing waves in a box. The walls of the box are considered to require the wave to have nodes at the walls of the box determining which wavelengths are allowed, the stationary wave can be viewed as the sum of two traveling sinusoidal waves of oppositely directed velocities. Consequently, wavelength, period, and wave velocity are related just as for a traveling wave, for example, the speed of light can be determined from observation of standing waves in a metal box containing an ideal vacuum. In that case, the k, the magnitude of k, is still in the same relationship with wavelength as shown above
9.
Frequency
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Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as frequency, which emphasizes the contrast to spatial frequency. The period is the duration of time of one cycle in a repeating event, for example, if a newborn babys heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as vibrations, audio signals, radio waves. For cyclical processes, such as rotation, oscillations, or waves, in physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter f or by the Greek letter ν or ν. For a simple motion, the relation between the frequency and the period T is given by f =1 T. The SI unit of frequency is the hertz, named after the German physicist Heinrich Hertz, a previous name for this unit was cycles per second. The SI unit for period is the second, a traditional unit of measure used with rotating mechanical devices is revolutions per minute, abbreviated r/min or rpm. As a matter of convenience, longer and slower waves, such as ocean surface waves, short and fast waves, like audio and radio, are usually described by their frequency instead of period. Spatial frequency is analogous to temporal frequency, but the axis is replaced by one or more spatial displacement axes. Y = sin = sin d θ d x = k Wavenumber, in the case of more than one spatial dimension, wavenumber is a vector quantity. For periodic waves in nondispersive media, frequency has a relationship to the wavelength. Even in dispersive media, the frequency f of a wave is equal to the phase velocity v of the wave divided by the wavelength λ of the wave. In the special case of electromagnetic waves moving through a vacuum, then v = c, where c is the speed of light in a vacuum, and this expression becomes, f = c λ. When waves from a monochrome source travel from one medium to another, their remains the same—only their wavelength. For example, if 71 events occur within 15 seconds the frequency is, the latter method introduces a random error into the count of between zero and one count, so on average half a count. This is called gating error and causes an error in the calculated frequency of Δf = 1/, or a fractional error of Δf / f = 1/ where Tm is the timing interval. This error decreases with frequency, so it is a problem at low frequencies where the number of counts N is small, an older method of measuring the frequency of rotating or vibrating objects is to use a stroboscope
10.
Ultra high frequency
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Ultra high frequency is the ITU designation for radio frequencies in the range between 300 MHz and 3 GHz, also known as the decimetre band as the wavelengths range from one meter to one decimetre. Radio waves with frequencies above the UHF band fall into the SHF or microwave frequency range, lower frequency signals fall into the VHF or lower bands. UHF radio waves propagate mainly by line of sight, they are blocked by hills, the IEEE defines the UHF radar band as frequencies between 300 MHz and 1 GHz. Two other IEEE radar bands overlap the ITU UHF band, the L band between 1 and 2 GHz and the S band between 2 and 4 GHz. Radio waves in the UHF band travel almost entirely by propagation and ground reflection, there is very little reflection from the ionosphere. They are blocked by hills and cannot travel far beyond the horizon, atmospheric moisture reduces, or attenuates, the strength of UHF signals over long distances, and the attenuation increases with frequency. UHF TV signals are generally more degraded by moisture than lower bands, occasionally when conditions are right, UHF radio waves can travel long distances by tropospheric ducting as the atmosphere warms and cools throughout the day. The length of an antenna is related to the length of the radio waves used, the UHF antenna is stubby and short, at UHF frequencies a quarter-wave monopole, the most common omnidirectional antenna is between 2.5 and 25 cm long for example. UHF is widely used in telephones, cell phones, walkie-talkies and other two-way radio systems from short range up to the visual horizon. Their transmissions do not travel far, allowing frequency reuse, public safety, business communications and personal radio services such as GMRS, PMR446, and UHF CB are often found on UHF frequencies as well as IEEE802.11 wireless LANs. The widely adapted GSM and UMTS cellular networks use UHF cellular frequencies, radio repeaters are used to retransmit UHF signals when a distance greater than the line of sight is required. Omnidirectional UHF antennas used on mobile devices are usually short whips, higher gain omnidirectional UHF antennas can be made of collinear arrays of dipoles and are used for mobile base stations and cellular base station antennas. The short wavelengths also allow high gain antennas to be conveniently small, high gain antennas for point-to-point communication links and UHF television reception are usually Yagi, log periodic, corner reflectors, or reflective array antennas. At the top end of the band slot antennas and parabolic dishes become practical, for television broadcasting specialized vertical radiators that are mostly modifications of the slot antenna or helical antenna are used, the slotted cylinder, zig-zag, and panel antennas. UHF television broadcasting fulfilled the demand for additional over-the-air television channels in urban areas, today, much of the bandwidth has been reallocated to land mobile, trunked radio and mobile telephone use. UHF channels are used for digital television. UHF spectrum is used worldwide for mobile radio systems for commercial, industrial, public safety. Many personal radio services use frequencies allocated in the UHF band, major telecommunications providers have deployed voice and data cellular networks in UHF/VHF range
11.
Extremely high frequency
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Extremely high frequency is the International Telecommunications Union designation for the band of radio frequencies in the electromagnetic spectrum from 30 to 300 gigahertz. It lies between the high frequency band, and the far infrared band which is also referred to as the terahertz gap. Radio waves in this band have wavelengths from ten to one millimetre, giving it the name millimetre band or millimetre wave, millimetre-length electromagnetic waves were first investigated in the 1890s by Indian scientist Jagadish Chandra Bose. Compared to lower bands, radio waves in this band have high atmospheric attenuation, therefore, they have a short range and can only be used for terrestrial communication over about a kilometer. Absorption by humidity in the atmosphere is significant except in desert environments, however the short propagation range allows smaller frequency reuse distances than lower frequencies. The short wavelength allows modest size antennas to have a beam width. Millimeter waves propagate solely by line-of-sight paths, they are not reflected by the ionosphere nor do they travel along the Earth as ground waves as lower frequency radio waves do, at typical power densities they are blocked by building walls and suffer significant attenuation passing through foliage. The high free space loss and atmospheric absorption limits useful propagation to a few kilometers, thus they are useful for densely packed communications networks such as personal area networks that improve spectrum utilization through frequency reuse. They show optical propagation characteristics and can be reflected and focused by small metal surfaces around 1 ft. diameter, at millimeter wavelengths, surfaces appear rougher so diffuse reflection increases. Multipath propagation, particularly reflection from indoor walls and surfaces, causes serious fading, doppler shift of frequency can be significant even at pedestrian speeds. In portable devices, shadowing due to the body is a problem. Since the waves penetrate clothing and their small wavelength allows them to reflect from small metal objects they are used in millimeter wave scanners for security scanning. This band is used in radio astronomy and remote sensing. Ground-based radio astronomy is limited to high altitude such as Kitt Peak. Satellite-based remote sensing near 60 GHz can determine temperature in the atmosphere by measuring radiation emitted from oxygen molecules that is a function of temperature and pressure. The ITU non-exclusive passive frequency allocation at 57-59 and it is used commonly in flat terrain. The 71-76, 81-86 and 92–95 GHz bands are used for point-to-point high-bandwidth communication links. These higher frequencies do not suffer from oxygen absorption, but require a license in the US from the Federal Communications Commission
12.
Super high frequency
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Super high frequency is the ITU designation for radio frequencies in the range between 3 GHz and 30 GHz. This band of frequencies is known as the centimetre band or centimetre wave as the wavelengths range from one to ten centimetres. These frequencies fall within the band, so radio waves with these frequencies are called microwaves. This frequency range is used for most radar transmitters, wireless LANs, satellite communication, microwave relay links. Wireless USB technology is anticipated to use approximately one-third of this spectrum, frequencies in the SHF range are often referred to by their IEEE radar band designations, S, C, X, Ku, K, or Ka band, or by similar NATO or EU designations. Microwaves propagate entirely by line of sight, groundwave and ionospheric reflection do not occur, although in some cases they can penetrate building walls enough for useful reception, unobstructed rights of way cleared to the first Fresnel zone are usually required. Wavelengths are small enough at microwave frequencies that the antenna can be larger than a wavelength. Therefore, they are used in point-to-point terrestrial communications links limited by the visual horizon, such high gain antennas allow frequency reuse by nearby transmitters. The size of SHF waves allows strong reflections from objects the size of automobiles, aircraft, and ships. Thus, the narrow beamwidths possible with high gain antennas and the low atmospheric attenuation as compared with higher frequencies make SHF the main frequencies used in radar. Attenuation and scattering by moisture in the increase with frequency. Small amounts of energy are randomly scattered by water vapor molecules in the troposphere. This is used in communications systems, operating at a few GHz. A powerful microwave beam is aimed just above the horizon, as it passes through the some of the microwaves are scattered back to Earth to a receiver beyond the horizon. Distances of 300 km can be achieved and these are mainly used for military communication. The wavelengths of SHF waves are small enough that they can be focused into narrow beams by high gain antennas from a meter to five meters in diameter. Directive antennas at SHF frequencies are mostly aperture antennas, such as antennas, dielectric lens, slot. Large parabolic antennas can produce very narrow beams of a few degrees or less, for omnidirectional applications like wireless devices and cellphones, small dipoles or monopoles are used
13.
C band (IEEE)
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The communications C-band was the first frequency band that was allocated for commercial telecommunications via satellites. The same frequencies were already in use for terrestrial microwave radio relay chains. Nearly all C-band communication satellites use the band of frequencies from 3.7 to 4.2 GHz for their downlinks, note that by using the band from 3.7 to 4.0 GHz, this C-band overlaps somewhat into the IEEE S-band for radars. The C-band communication satellites typically have 24 radio transponders spaced 20 MHz apart, hence, the transponders on the same polarization are always 40 MHz apart. Of this 40 MHz, each transponder utilizes about 36 MHz, the C-band is primarily used for open satellite communications, whether for full-time satellite television networks or raw satellite feeds, although subscription programming also exists. Typical antenna sizes on C-band capable systems ranges from 7.5 to 12 feet on consumer satellite dishes, rain fade – the collective name for the negative effects of adverse weather conditions on transmission – is mostly a consequence of precipitation and moisture in the air. Slight variations in the assignments of C-band frequencies have been approved for use in parts of the world. This latter region is the most populous one, since it includes the Peoples Republic of China, India, Pakistan, Japan and this is known as the 5-centimeter band by amateurs and the C-band by AMSAT. Particle accelerators may be powered by C-band RF sources, the frequencies are then standardized at 5.996 GHz or 5.712 GHz, which is the second harmonic of S-band
14.
X band
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The X band is a segment of the microwave radio region of the electromagnetic spectrum. In some cases, such as in engineering, the frequency range of the X band is rather indefinitely set at approximately 7.0 to 11.2 GHz. In radar engineering, the range is specified by the IEEE at 8.0 to 12.0 GHz. This is also the case pertaining to X band military communications satellites, X band is used in radar applications including continuous-wave, pulsed, single-polarization, dual-polarization, synthetic aperture radar, and phased arrays. X band is used in modern radars. The shorter wavelengths of the X band allow for higher resolution imagery from high-resolution imaging radars for target identification and discrimination, in Ireland, Libya, Saudi Arabia and Canada, the X band 10.15 to 10.7 segment is used for terrestrial broadband. Alvarion, CBNL, and Ogier make systems for this, though each has a proprietary airlink, the Ogier system is a full duplex Transverter used for DOCSIS over microwave. The home / Business CPE has a coaxial cable with a power adapter connecting to an ordinary cable modem. The local oscillator is usually 9750 MHz, the same as for Ku band satellite TV LNB, two way applications such as broadband typically use a 350 MHz TX offset. Portions of the X band are assigned by the International Telecommunications Union exclusively for deep space telecommunications, the primary user of this allocation is the American NASA Deep Space Network. DSN facilities are located in Goldstone, California, near Canberra, Australia and these three stations, located approximately 120 degrees apart in longitude, provide continual communications from the Earth to almost any point in the Solar System independent of Earth rotation. DSN stations are capable of using the older and lower S band deep-space radio communications allocations and it will also detect variations in angular momentum due to the redistribution of masses, such as the migration of ice from the polar caps to the atmosphere. An important use of the X band communications came with the two Viking program landers and these results are some of the best confirmations of the General Theory of Relativity. This is known as the 3-centimeter band by amateurs and the X-band by AMSAT, motion detectors often use 10.525 GHz.10.4 GHz is proposed for traffic light crossing detectors. Comreg in Ireland has allocated 10.450 GHz for Traffic Sensors as SRD, many electron paramagnetic resonance spectrometers operate near 9.8 GHz. Particle accelerators may be powered by X-band RF sources, the frequencies are then standardized at 11.9942 GHz or 11.424 GHz, which is the second harmonic of C-band and fourth harmonic of S-band. The European X-band frequency is used for the Compact Linear Collider. ntia. doc. gov/osmhome/allochrt. pdf http, //www. g3pho. free-online. co. uk/microwaves/wideband. htm
15.
Radio wave
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Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies as high as 300 GHz to as low as 3 kHz, though some definitions describe waves above 1 or 3 GHz as microwaves, at 300 GHz, the corresponding wavelength is 1 mm, and at 3 kHz is 100 km. Like all other electromagnetic waves, they travel at the speed of light, naturally occurring radio waves are generated by lightning, or by astronomical objects. Radio waves are generated by radio transmitters and received by radio receivers, the radio spectrum is divided into a number of radio bands on the basis of frequency, allocated to different uses. Radio waves were first predicted by mathematical work done in 1867 by Scottish mathematical physicist James Clerk Maxwell, Maxwell noticed wavelike properties of light and similarities in electrical and magnetic observations. Radio waves were first used for communication in the mid 1890s by Guglielmo Marconi, different frequencies experience different combinations of these phenomena in the Earths atmosphere, making certain radio bands more useful for specific purposes than others. It does not necessarily require a cleared sight path, at lower frequencies radio waves can pass through buildings, foliage and this is the only method of propagation possible at microwave frequencies and above. On the surface of the Earth, line of propagation is limited by the visual horizon to about 40 miles. This is the used by cell phones, cordless phones, walkie-talkies, wireless networks, FM and television broadcasting. Indirect propagation, Radio waves can reach points beyond the line-of-sight by diffraction, diffraction allows a radio wave to bend around obstructions such as a building edge, a vehicle, or a turn in a hall. Radio waves also reflect from surfaces such as walls, floors, ceilings, vehicles and these effects are used in short range radio communication systems. Ground waves allow mediumwave and longwave broadcasting stations to have coverage areas beyond the horizon, the nonzero resistance of the earth absorbs energy from ground waves, so as they propagate the waves lose power and the wavefronts bend over at an angle to the surface. As frequency decreases, the decrease and the achievable range increases. Military very low frequency and extremely low frequency communication systems can communicate over most of the Earth, and with submarines hundreds of feet underwater. Tropospheric propagation, In the VHF and UHF bands, radio waves can travel somewhat beyond the horizon due to refraction in the troposphere. This is due to changes in the index of air with temperature and pressure. At times, radio waves can travel up to 500 -1000 km due to tropospheric ducting and these effects are variable and not as reliable as ionospheric propagation, below. So radio waves directed at an angle into the sky can return to Earth beyond the horizon, by using multiple skips communication at intercontinental distances can be achieved
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Far infrared
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Far infrared is a region in the infrared spectrum of electromagnetic radiation. Far infrared is defined as any radiation with a wavelength of 15 micrometers to 1 mm. Different sources use different boundaries for the far infrared spectrum, for example, visible light includes radiation with wavelengths between 400 nm and 700 nm, meaning that far infrared photons have less energy than visible light photons. Objects with temperatures between about 5 K and 340 K will emit radiation in the far infrared range and this property is sometimes used to observe interstellar gases where new stars are often formed. This is due to the dust at the center of M82 being heated by an unknown source, as of 2015, recently developed electric or hydronic panel-based longwave infrared heaters are becoming more adopted. Some human proximity sensors use passive infrared sensing in the far infrared wavelength to detect both static and/or moving human bodies. The infrared radiation band covers the range of 700 nm –1 mm, frequency range of 430 THz –300 GHz. Far-infrared fadiation is found on the spectrum at 15–1000 µm with a frequency range of 0. 3–20 THz. They report that this radiant heat can penetrate up to 1.5 inches beneath the skin, biomedical researchers have experimented with the use of FIR emitting ceramics which are embedded into various fibers and woven into the fabric of garments. These researchers noted in subjects a delay in the onset of fatigue induced by muscle contractions and they propose that this ceramic-emitted FIR has the potential to promote cell repair. The American athletic apparel company, Under Armour Under Armour, Inc, far infrared radiation, its biological effects and medical applications
17.
Terahertz radiation
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Photon energy in THz regime is less than band-gap of nonmetallic materials and thus THz beam can traverse through such materials. The transmitted THz beam is used for material characterization, layer inspection, terahertz radiation falls in between infrared radiation and microwave radiation in the electromagnetic spectrum, and it shares some properties with each of these. Like infrared and microwave radiation, terahertz radiation travels in a line of sight and is non-ionizing, like microwave radiation, terahertz radiation can penetrate a wide variety of non-conducting materials. Terahertz radiation can pass through clothing, paper, cardboard, wood, masonry, plastic, the penetration depth is typically less than that of microwave radiation. Terahertz radiation has limited penetration through fog and clouds and cannot penetrate liquid water or metal, THz is not ionizing yet can penetrate some distance through body tissue, so it is of interest as a replacement for medical X-rays. Due to its wavelength, images made using THz are low resolution. However, at distances of ~10 meters the band may still allow many useful applications in imaging and construction of high bandwidth wireless networking systems, terahertz radiation is emitted as part of the black-body radiation from anything with temperatures greater than about 10 kelvin. The opacity of the Earths atmosphere to submillimeter radiation restricts these observatories to very high altitude sites, and electronic oscillators based on resonant tunneling diodes have been shown to operate up to 700 GHz. There have also been solid-state sources of millimeter and submillimeter waves for many years, AB Millimeter in Paris, for instance, produces a system that covers the entire range from 8 GHz to 1000 GHz with solid state sources and detectors. Nowadays, most time-domain work is done via ultrafast lasers, in mid-2007, scientists at the U. S. The group was led by Ulrich Welp of Argonnes Materials Science Division, the device uses high-temperature superconducting crystals, grown at the University of Tsukuba in Japan. This alternating current induces an electromagnetic field, even a small voltage can induce frequencies in the terahertz range, according to Welp. In 2008, engineers at Harvard University achieved room temperature emission of several hundred nanowatts of coherent terahertz radiation using a semiconductor source, THz radiation was generated by nonlinear mixing of two modes in a mid-infrared quantum cascade laser. Previous sources had required cryogenic cooling, which limited their use in everyday applications. In 2009, it was discovered that the act of unpeeling adhesive tape generates non-polarized terahertz radiation, with a peak at 2 THz. In 2011, Japanese electronic parts maker Rohm and a team at Osaka University produced a chip capable of transmitting 1.5 Gbit/s using terahertz radiation. Such an antenna would broadcast in the frequency range. Unlike X-rays, terahertz radiation is not ionizing radiation and its low photon energies in general do not damage tissues, some frequencies of terahertz radiation can penetrate several millimeters of tissue with low water content and reflect back
18.
Ultra-high-frequency
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Ultra high frequency is the ITU designation for radio frequencies in the range between 300 MHz and 3 GHz, also known as the decimetre band as the wavelengths range from one meter to one decimetre. Radio waves with frequencies above the UHF band fall into the SHF or microwave frequency range, lower frequency signals fall into the VHF or lower bands. UHF radio waves propagate mainly by line of sight, they are blocked by hills, the IEEE defines the UHF radar band as frequencies between 300 MHz and 1 GHz. Two other IEEE radar bands overlap the ITU UHF band, the L band between 1 and 2 GHz and the S band between 2 and 4 GHz. Radio waves in the UHF band travel almost entirely by propagation and ground reflection, there is very little reflection from the ionosphere. They are blocked by hills and cannot travel far beyond the horizon, atmospheric moisture reduces, or attenuates, the strength of UHF signals over long distances, and the attenuation increases with frequency. UHF TV signals are generally more degraded by moisture than lower bands, occasionally when conditions are right, UHF radio waves can travel long distances by tropospheric ducting as the atmosphere warms and cools throughout the day. The length of an antenna is related to the length of the radio waves used, the UHF antenna is stubby and short, at UHF frequencies a quarter-wave monopole, the most common omnidirectional antenna is between 2.5 and 25 cm long for example. UHF is widely used in telephones, cell phones, walkie-talkies and other two-way radio systems from short range up to the visual horizon. Their transmissions do not travel far, allowing frequency reuse, public safety, business communications and personal radio services such as GMRS, PMR446, and UHF CB are often found on UHF frequencies as well as IEEE802.11 wireless LANs. The widely adapted GSM and UMTS cellular networks use UHF cellular frequencies, radio repeaters are used to retransmit UHF signals when a distance greater than the line of sight is required. Omnidirectional UHF antennas used on mobile devices are usually short whips, higher gain omnidirectional UHF antennas can be made of collinear arrays of dipoles and are used for mobile base stations and cellular base station antennas. The short wavelengths also allow high gain antennas to be conveniently small, high gain antennas for point-to-point communication links and UHF television reception are usually Yagi, log periodic, corner reflectors, or reflective array antennas. At the top end of the band slot antennas and parabolic dishes become practical, for television broadcasting specialized vertical radiators that are mostly modifications of the slot antenna or helical antenna are used, the slotted cylinder, zig-zag, and panel antennas. UHF television broadcasting fulfilled the demand for additional over-the-air television channels in urban areas, today, much of the bandwidth has been reallocated to land mobile, trunked radio and mobile telephone use. UHF channels are used for digital television. UHF spectrum is used worldwide for mobile radio systems for commercial, industrial, public safety. Many personal radio services use frequencies allocated in the UHF band, major telecommunications providers have deployed voice and data cellular networks in UHF/VHF range
19.
Radio
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When radio waves strike an electrical conductor, the oscillating fields induce an alternating current in the conductor. The information in the waves can be extracted and transformed back into its original form, Radio systems need a transmitter to modulate some property of the energy produced to impress a signal on it, for example using amplitude modulation or angle modulation. Radio systems also need an antenna to convert electric currents into radio waves, an antenna can be used for both transmitting and receiving. The electrical resonance of tuned circuits in radios allow individual stations to be selected, the electromagnetic wave is intercepted by a tuned receiving antenna. Radio frequencies occupy the range from a 3 kHz to 300 GHz, a radio communication system sends signals by radio. The term radio is derived from the Latin word radius, meaning spoke of a wheel, beam of light, however, this invention would not be widely adopted. The switch to radio in place of wireless took place slowly and unevenly in the English-speaking world, the United States Navy would also play a role. Although its translation of the 1906 Berlin Convention used the terms wireless telegraph and wireless telegram, the term started to become preferred by the general public in the 1920s with the introduction of broadcasting. Radio systems used for communication have the following elements, with more than 100 years of development, each process is implemented by a wide range of methods, specialised for different communications purposes. Each system contains a transmitter, This consists of a source of electrical energy, the transmitter contains a system to modulate some property of the energy produced to impress a signal on it. This modulation might be as simple as turning the energy on and off, or altering more subtle such as amplitude, frequency, phase. Amplitude modulation of a carrier wave works by varying the strength of the signal in proportion to the information being sent. For example, changes in the strength can be used to reflect the sounds to be reproduced by a speaker. It was the used for the first audio radio transmissions. Frequency modulation varies the frequency of the carrier, the instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal. FM has the capture effect whereby a receiver only receives the strongest signal, Digital data can be sent by shifting the carriers frequency among a set of discrete values, a technique known as frequency-shift keying. FM is commonly used at Very high frequency radio frequencies for high-fidelity broadcasts of music, analog TV sound is also broadcast using FM. Angle modulation alters the phase of the carrier wave to transmit a signal
20.
Wave
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In physics, a wave is an oscillation accompanied by a transfer of energy that travels through a medium. Frequency refers to the addition of time, wave motion transfers energy from one point to another, which displace particles of the transmission medium–that is, with little or no associated mass transport. Waves consist, instead, of oscillations or vibrations, around almost fixed locations, there are two main types of waves. Mechanical waves propagate through a medium, and the substance of this medium is deformed, restoring forces then reverse the deformation. For example, sound waves propagate via air molecules colliding with their neighbors, when the molecules collide, they also bounce away from each other. This keeps the molecules from continuing to travel in the direction of the wave, the second main type, electromagnetic waves, do not require a medium. Instead, they consist of periodic oscillations of electrical and magnetic fields generated by charged particles. These types vary in wavelength, and include radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, waves are described by a wave equation which sets out how the disturbance proceeds over time. The mathematical form of this varies depending on the type of wave. Further, the behavior of particles in quantum mechanics are described by waves, in addition, gravitational waves also travel through space, which are a result of a vibration or movement in gravitational fields. While mechanical waves can be transverse and longitudinal, all electromagnetic waves are transverse in free space. A single, all-encompassing definition for the wave is not straightforward. A vibration can be defined as a back-and-forth motion around a reference value, however, a vibration is not necessarily a wave. An attempt to define the necessary and sufficient characteristics that qualify a phenomenon as a results in a blurred line. The term wave is often understood as referring to a transport of spatial disturbances that are generally not accompanied by a motion of the medium occupying this space as a whole. In a wave, the energy of a vibration is moving away from the source in the form of a disturbance within the surrounding medium and it may appear that the description of waves is closely related to their physical origin for each specific instance of a wave process. For example, acoustics is distinguished from optics in that sound waves are related to a rather than an electromagnetic wave transfer caused by vibration. Concepts such as mass, momentum, inertia, or elasticity and this difference in origin introduces certain wave characteristics particular to the properties of the medium involved
21.
Line-of-sight propagation
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Line-of-sight propagation is a characteristic of electromagnetic radiation or acoustic wave propagation which means waves which travel in a direct path from the source to the receiver. Electromagnetic transmission includes light emissions traveling in a straight line, the rays or waves may be diffracted, refracted, reflected, or absorbed by atmosphere and obstructions with material and generally cannot travel over the horizon or behind obstacles. In contrast to line-of-sight propagation, at low frequency due to radio waves can travel as ground waves. This enables AM broadcast radio stations to transmit beyond the horizon, however, at frequencies above 30 MHz and in lower levels of the atmosphere, neither of these effects are significant. Thus, any obstruction between the antenna and the receiving antenna will block the signal, just like the light that the eye may sense. The farthest possible point of propagation is referred to as the radio horizon, in practice, the propagation characteristics of these radio waves vary substantially depending on the exact frequency and the strength of the transmitted signal. Broadcast FM radio, at low frequencies of around 100 MHz, are less affected by the presence of buildings. Low-powered microwave transmitters can be foiled by tree branches, or even heavy rain or snow, if a direct visual fix cannot be taken, it is important to take into account the curvature of the Earth when calculating line-of-sight from maps. Designs for microwave used to use 4/3 earth radius to compute clearances along the path, the presence of objects not in the direct visual line of sight can interfere with radio transmission. This is caused by diffraction effects, for the best propagation, reflected radiation from the ground plane also acts to cancel out the direct signal. This effect, combined with the free-space r−2 propagation loss to a r−4 propagation loss and this effect can be reduced by raising either or both antennas further from the ground, the reduction in loss achieved is known as height gain. Although the frequencies used by mobile phones are in the line-of-sight range, for mobile phone services, these problems are tackled using, rooftop or hilltop positioning of base stations many base stations. A phone can typically see at least three, and usually as many as six at any given time, sectorized antennas at the base stations. Instead of one antenna with omnidirectional coverage, the station may use as few as 3 or as many as 32 separate antennas and this allows the base station to use a directional antenna that is pointing at the user, which improves the signal to noise ratio. If the user moves from one sector to another, the base station automatically selects the proper antenna. Electromagnetic radiation is blocked where the wavelength is longer than any gaps and this means that windowless metal enclosures will completely block cell signs, such as elevator cabins, and parts of trains, cars, and ships. The same problem can affect signals in buildings with steel reinforcement. The radio horizon is the locus of points at which direct rays from an antenna are tangential to the surface of the Earth, if the Earth was a perfect sphere and there was no atmosphere, the radio horizon would be a circle
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Surface wave
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In physics, a surface wave is a mechanical wave that propagates along the interface between differing media. A common example is gravity waves along the surface of liquids, gravity waves can also occur within liquids, at the interface between two fluids with different densities. Elastic surface waves can travel along the surface of solids, such as Rayleigh or Love waves, in radio transmission, a ground wave is a guided wave that propagates close to the surface of the Earth. In seismology, several types of waves are encountered. Surface waves, in this sense, are commonly known as either Love waves or Rayleigh waves. A seismic wave is a wave travels through the Earth. Love waves have transverse motion, whereas Rayleigh waves have both longitudinal and transverse motion, seismic waves are studied by seismologists and measured by a seismograph or seismometer. Surface waves span a wide range, and the period of waves that are most damaging is usually 10 seconds or longer. Surface waves can travel around the many times from the largest earthquakes. Surface waves are caused when P waves and S waves come to the surface, the term surface wave can describe waves over an ocean, even when they are approximated by Airy functions and are more properly called creeping waves. Examples are the waves at the surface of water and air, another example is internal waves, which can be transmitted along the interface of two water masses of different densities. In theory of hearing physiology, the wave of Von Bekesy. His theory pretended to explain features of the auditory sensation owing to these passive mechanical phenomena. But Jozef Zwislocki and later David Kemp, showed that that was unrealistic, ground wave refers to the propagation of radio waves parallel to and adjacent to the surface of the Earth, following the curvature of the Earth. This radiative ground wave is known as the Norton surface wave, other types of surface wave are the non-radiative Zenneck surface wave or Zenneck-Sommerfeld surface wave, the trapped surface wave and the gliding wave. See also Dyakonov surface waves propagating at the interface of transparent materials with different symmetry, lower frequency radio space waves, below 3 MHz, travel efficiently as ground waves. In ITU nomenclature, this includes, medium frequency, low frequency, very low frequency, ultra low frequency, super low frequency, ground propagation works because lower-frequency waves are more strongly diffracted around obstacles due to their long wavelengths, allowing them to follow the Earths curvature. The Earth has one refractive index and the atmosphere has another, ground waves propagate in vertical polarization, with their magnetic field horizontal and electric field vertical
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Ionosphere
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The ionosphere is a region of Earths upper atmosphere, from about 60 km to 1,000 km altitude, and includes the thermosphere and parts of the mesosphere and exosphere. It is ionized by radiation, plays an important part in atmospheric electricity. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth. The ionosphere is a shell of electrons and electrically charged atoms and molecules that surrounds the Earth and it owes its existence primarily to ultraviolet radiation from the Sun. The lowest part of the Earths atmosphere, the troposphere extends from the surface to about 10 km, above 10 km is the stratosphere, followed by the mesosphere. In the stratosphere incoming solar radiation creates the ozone layer, at heights of above 80 km, in the thermosphere, the atmosphere is so thin that free electrons can exist for short periods of time before they are captured by a nearby positive ion. The number of free electrons is sufficient to affect radio propagation. This portion of the atmosphere is ionized and contains a plasma which is referred to as the ionosphere, in this process the light electron obtains a high velocity so that the temperature of the created electronic gas is much higher than the one of ions and neutrals. The reverse process to ionization is recombination, in which an electron is captured by a positive ion. Recombination occurs spontaneously, and causes the emission of a photon carrying away the energy produced upon recombination, as gas density increases at lower altitudes, the recombination process prevails, since the gas molecules and ions are closer together. The balance between two processes determines the quantity of ionization present. Ionization depends primarily on the Sun and its activity, the amount of ionization in the ionosphere varies greatly with the amount of radiation received from the Sun. Thus there is an effect and a seasonal effect. The local winter hemisphere is tipped away from the Sun, thus there is less received solar radiation, the activity of the Sun is associated with the sunspot cycle, with more radiation occurring with more sunspots. Radiation received also varies with geographical location, there are also mechanisms that disturb the ionosphere and decrease the ionization. There are disturbances such as flares and the associated release of charged particles into the solar wind which reaches the Earth. At night the F layer is the layer of significant ionization present. During the day, the D and E layers become more heavily ionized, as does the F layer
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Point-to-point (telecommunications)
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In telecommunications, a point-to-point connection refers to a communications connection between two nodes or endpoints. An example is a call, in which one telephone is connected with one other. This is contrasted with a point-to-multipoint or broadcast connection, in which many nodes can receive information transmitted by one node, other examples of point-to-point communications links are leased lines, microwave relay links, and two way radio. Point-to-point is sometimes abbreviated as P2P and this usage of P2P is distinct from P2P referring to peer-to-peer for file sharing networks. A traditional point-to-point data link is a medium with exactly two endpoints and no data or packet formatting. The host computers at either end had to take responsibility for formatting the data transmitted between them. The connection between the computer and the medium was generally implemented through an RS-232 or similar interface. Computers in close proximity may be connected by wires directly between their interface cards, when connected at a distance, each endpoint would be fitted with a modem to convert analog telecommunications signals into a digital data stream. When the connection used a telecommunications provider, the connections were called a dedicated, leased, the ARPANET used leased lines to provide point-to-point data links between its packet-switching nodes, which were called Interface Message Processors. In, the term point-to-point telecommunications relates to fixed wireless communications for Internet or voice over IP via radio frequencies in the multi-gigahertz range. The Telecommunications Industry Associations engineering committees develop U. S. standards for point-to-point communications, online tools help users find if they have such line of sight. The telecommunications signal is typically bi-directional, either time division multiple access or channelized, in hubs and switches, a hub provides a point-to-multipoint circuit which divides the total bandwidth supplied by the hub among each connected client node. Within many switched telecommunications systems, it is possible to establish a permanent circuit, one example might be a telephone in the lobby of a public building, which is programmed to ring only the number of a telephone dispatcher. Nailing down a switched connection saves the cost of running a circuit between the two points. The resources in such a connection can be released when no longer needed, for example, a television circuit from a parade route back to the studio
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Wireless network
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A wireless network is a computer network that uses wireless data connections between network nodes. Wireless telecommunications networks are generally implemented and administered using radio communication and this implementation takes place at the physical level of the OSI model network structure. Examples of wireless networks include cell phone networks, wireless local area networks, wireless networks, satellite communication networks. The first professional wireless network was developed under the brand ALOHAnet in 1969 at the University of Hawaii, the first commercial wireless network was the WaveLAN product family, developed by NCR in 1986. Terrestrial microwaves are in the low range, which limits all communications to line-of-sight. Relay stations are spaced approximately 48 km apart, Communications satellites – Satellites communicate via microwave radio waves, which are not deflected by the Earths atmosphere. The satellites are stationed in space, typically in geosynchronous orbit 35,400 km above the equator and these Earth-orbiting systems are capable of receiving and relaying voice, data, and TV signals. Cellular and PCS systems use several radio communications technologies, the systems divide the region covered into multiple geographic areas. Each area has a transmitter or radio relay antenna device to relay calls from one area to the next area. Radio and spread spectrum technologies – Wireless local area networks use a radio technology similar to digital cellular. Wireless LANs use spread spectrum technology to enable communication between devices in a limited area. IEEE802.11 defines a common flavor of open-standards wireless radio-wave technology known as Wifi, free-space optical communication uses visible or invisible light for communications. In most cases, line-of-sight propagation is used, which limits the physical positioning of communicating devices, Wireless personal area networks interconnect devices within a relatively small area, that is generally within a persons reach. For example, both Bluetooth radio and invisible infrared light provides a WPAN for interconnecting a headset to a laptop, Wi-Fi PANs are becoming commonplace as equipment designers start to integrate Wi-Fi into a variety of consumer electronic devices. Intel My WiFi and Windows 7 virtual Wi-Fi capabilities have made Wi-Fi PANs simpler and easier to set up, a wireless local area network links two or more devices over a short distance using a wireless distribution method, usually providing a connection through an access point for internet access. The use of spread-spectrum or OFDM technologies may allow users to move around within a coverage area. Products using the IEEE802.11 WLAN standards are marketed under the Wi-Fi brand name and it is often used in cities to connect networks in two or more buildings without installing a wired link. A wireless ad hoc network, also known as a mesh network or mobile ad hoc network, is a wireless network made up of radio nodes organized in a mesh topology
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Radar
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Radar is an object-detection system that uses radio waves to determine the range, angle, or velocity of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, Radio waves from the transmitter reflect off the object and return to the receiver, giving information about the objects location and speed. Radar was developed secretly for military use by several nations in the period before, the term RADAR was coined in 1940 by the United States Navy as an acronym for RAdio Detection And Ranging or RAdio Direction And Ranging. The term radar has since entered English and other languages as a common noun, high tech radar systems are associated with digital signal processing, machine learning and are capable of extracting useful information from very high noise levels. Other systems similar to make use of other parts of the electromagnetic spectrum. One example is lidar, which uses ultraviolet, visible, or near infrared light from lasers rather than radio waves, as early as 1886, German physicist Heinrich Hertz showed that radio waves could be reflected from solid objects. In 1895, Alexander Popov, an instructor at the Imperial Russian Navy school in Kronstadt. The next year, he added a spark-gap transmitter, in 1897, while testing this equipment for communicating between two ships in the Baltic Sea, he took note of an interference beat caused by the passage of a third vessel. In his report, Popov wrote that this phenomenon might be used for detecting objects, the German inventor Christian Hülsmeyer was the first to use radio waves to detect the presence of distant metallic objects. In 1904, he demonstrated the feasibility of detecting a ship in dense fog and he obtained a patent for his detection device in April 1904 and later a patent for a related amendment for estimating the distance to the ship. He also got a British patent on September 23,1904 for a radar system. It operated on a 50 cm wavelength and the radar signal was created via a spark-gap. In 1915, Robert Watson-Watt used radio technology to advance warning to airmen. Watson-Watt became an expert on the use of direction finding as part of his lightning experiments. As part of ongoing experiments, he asked the new boy, Arnold Frederic Wilkins, Wilkins made an extensive study of available units before selecting a receiver model from the General Post Office. Its instruction manual noted that there was fading when aircraft flew by, in 1922, A. Hoyt Taylor and Leo C. Taylor submitted a report, suggesting that this might be used to detect the presence of ships in low visibility, eight years later, Lawrence A. Australia, Canada, New Zealand, and South Africa followed prewar Great Britain, and Hungary had similar developments during the war. Hugon, began developing a radio apparatus, a part of which was installed on the liner Normandie in 1935
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Communications satellite
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Communications satellites are used for television, telephone, radio, internet, and military applications. There are over 2,000 communications satellites in Earth’s orbit, Wireless communication uses electromagnetic waves to carry signals. These waves require line-of-sight, and are thus obstructed by the curvature of the Earth, the purpose of communications satellites is to relay the signal around the curve of the Earth allowing communication between widely separated points. Communications satellites use a range of radio and microwave frequencies. To avoid signal interference, international organizations have regulations for which frequency ranges or bands certain organizations are allowed to use and this allocation of bands minimizes the risk of signal interference. The concept of the communications satellite was first proposed by Arthur C. Clarke, building on work by Konstantin Tsiolkovsky and on the 1929 work by Herman Potočnik Das Problem der Befahrung des Weltraums — der Raketen-motor, in October 1945 Clarke published an article titled Extraterrestrial Relays in the British magazine Wireless World. The article described the fundamentals behind the deployment of artificial satellites in geostationary orbits for the purpose of relaying radio signals, thus, Arthur C. Clarke is often quoted as being the inventor of the communications satellite and the term Clarke Belt employed as a description of the orbit. Decades later a project named Communication Moon Relay was a project carried out by the United States Navy. Its objective was to develop a secure and reliable method of communication by using the Moon as a passive reflector. The first artificial Earth satellite was Sputnik 1, put into orbit by the Soviet Union on October 4,1957, it was equipped with an on-board radio-transmitter that worked on two frequencies,20.005 and 40.002 MHz. Sputnik 1 was launched as a step in the exploration of space, while incredibly important it was not placed in orbit for the purpose of sending data from one point on earth to another. And it was the first artificial satellite in the leading to todays satellite communications. The first artificial satellite used solely to further advances in communications was a balloon named Echo 1. Echo 1 was the worlds first artificial communications satellite capable of relaying signals to other points on Earth and it soared 1,600 kilometres above the planet after its Aug.12,1960 launch, yet relied on humanitys oldest flight technology — ballooning. Launched by NASA, Echo 1 was a 30-metre aluminized PET film balloon served as a passive reflector for radio communications. The worlds first inflatable satellite — or satelloon, as they were informally known — helped lay the foundation of todays satellite communications, the idea behind a communications satellite is simple, Send data up into space and beam it back down to another spot on the globe. Echo 1 accomplished this by serving as an enormous mirror,10 stories tall
28.
Remote sensing
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Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object and thus in contrast to on-site observation. It may be split into active remote sensing and passive remote sensing, passive sensors gather radiation that is emitted or reflected by the object or surrounding areas. Reflected sunlight is the most common source of radiation measured by passive sensors, examples of passive remote sensors include film photography, infrared, charge-coupled devices, and radiometers. Active collection, on the hand, emits energy in order to scan objects and areas whereupon a sensor then detects. RADAR and LiDAR are examples of remote sensing where the time delay between emission and return is measured, establishing the location, speed and direction of an object. Remote sensing makes it possible to data of dangerous or inaccessible areas. Remote sensing applications include monitoring deforestation in areas such as the Amazon Basin, glacial features in Arctic and Antarctic regions, military collection during the Cold War made use of stand-off collection of data about dangerous border areas. Remote sensing also replaces costly and slow data collection on the ground, the basis for multispectral collection and analysis is that of examined areas or objects that reflect or emit radiation that stand out from surrounding areas. For a summary of major remote sensing satellite systems see the overview table, conventional radar is mostly associated with aerial traffic control, early warning, and certain large scale meteorological data. Other types of active collection includes plasmas in the ionosphere, interferometric synthetic aperture radar is used to produce precise digital elevation models of large scale terrain. Laser and radar altimeters on satellites have provided a range of data. By measuring the bulges of water caused by gravity, they map features on the seafloor to a resolution of a mile or so, by measuring the height and wavelength of ocean waves, the altimeters measure wind speeds and direction, and surface ocean currents and directions. Ultrasound and radar tide gauges measure sea level, tides and wave direction in coastal, light detection and ranging is well known in examples of weapon ranging, laser illuminated homing of projectiles. Vegetation remote sensing is an application of LIDAR. Radiometers and photometers are the most common instrument in use, collecting reflected and emitted radiation in a range of frequencies. The most common are visible and infrared sensors, followed by microwave, gamma ray and rarely and they may also be used to detect the emission spectra of various chemicals, providing data on chemical concentrations in the atmosphere. Simultaneous multi-spectral platforms such as Landsat have been in use since the 1970s and these thematic mappers take images in multiple wavelengths of electro-magnetic radiation and are usually found on Earth observation satellites, including the Landsat program or the IKONOS satellite. Landsat images are used by agencies such as KYDOW to indicate water quality parameters including Secchi depth, chlorophyll a density
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Radio astronomy
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Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The first detection of radio waves from an object was in 1932. Subsequent observations have identified a number of different sources of radio emission and these include stars and galaxies, as well as entirely new classes of objects, such as radio galaxies, quasars, pulsars, and masers. The discovery of the microwave background radiation, regarded as evidence for the Big Bang theory, was made through radio astronomy. Before Jansky observed the Milky Way in the 1930s, physicists speculated that radio waves could be observed from astronomical sources, in the 1860s, James Clerk Maxwells equations had shown that electromagnetic radiation is associated with electricity and magnetism, and could exist at any wavelength. These attempts were unable to detect any emission due to limitations of the instruments. The discovery of the radio reflecting ionosphere in 1902, led physicists to conclude that the layer would bounce any astronomical radio transmission back into space, Karl Jansky made the discovery of the first astronomical radio source serendipitously in the early 1930s. As an engineer with Bell Telephone Laboratories, he was investigating static that interfered with short wave transatlantic voice transmissions, using a large directional antenna, Jansky noticed that his analog pen-and-paper recording system kept recording a repeating signal of unknown origin. Since the signal peaked about every 24 hours, Jansky originally suspected the source of the interference was the Sun crossing the view of his directional antenna. Continued analysis showed that the source was not following the 24-hour daily cycle of the Sun exactly and he concluded that since the Sun were not large emitters of radio noise, the strange radio interference may be generated by interstellar gas and dust in the galaxy. Jansky announced his discovery in 1933 and he wanted to investigate the radio waves from the Milky Way in further detail, but Bell Labs reassigned him to another project, so he did no further work in the field of astronomy. His pioneering efforts in the field of astronomy have been recognized by the naming of the fundamental unit of flux density. Grote Reber was inspired by Janskys work, and built a radio telescope 9m in diameter in his backyard in 1937. He began by repeating Janskys observations, and then conducted the first sky survey in the radio frequencies, on February 27,1942, James Stanley Hey, a British Army research officer, made the first detection of radio waves emitted by the Sun. Later that year George Clark Southworth, at Bell Labs like Jansky, both researchers were bound by wartime security surrounding radar, so Reber, who was not, published his 1944 findings first. Several other people independently discovered solar radiowaves, including E. Schott in Denmark, at Cambridge University, where ionospheric research had taken place during World War II, J. A. This early research soon branched out into the observation of celestial radio sources. Martin Ryle and Antony Hewish at the Cavendish Astrophysics Group developed the technique of Earth-rotation aperture synthesis, the radio astronomy group in Cambridge went on to found the Mullard Radio Astronomy Observatory near Cambridge in the 1950s
30.
Particle accelerator
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A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to nearly light speed and to contain them in well-defined beams. Large accelerators are used in physics as colliders, or as synchrotron light sources for the study of condensed matter physics. There are currently more than 30,000 accelerators in operation around the world, there are two basic classes of accelerators, electrostatic and electrodynamic accelerators. Electrostatic accelerators use electric fields to accelerate particles. The most common types are the Cockcroft–Walton generator and the Van de Graaff generator, a small-scale example of this class is the cathode ray tube in an ordinary old television set. The achievable kinetic energy for particles in these devices is determined by the accelerating voltage, electrodynamic or electromagnetic accelerators, on the other hand, use changing electromagnetic fields to accelerate particles. Since in these types the particles can pass through the accelerating field multiple times. This class, which was first developed in the 1920s, is the basis for most modern large-scale accelerators, because colliders can give evidence of the structure of the subatomic world, accelerators were commonly referred to as atom smashers in the 20th century. Despite the fact that most accelerators actually propel subatomic particles, the term persists in popular usage when referring to particle accelerators in general. Beams of high-energy particles are useful for both fundamental and applied research in the sciences, and also in many technical and industrial fields unrelated to fundamental research and it has been estimated that there are approximately 30,000 accelerators worldwide. The bar graph shows the breakdown of the number of industrial accelerators according to their applications, for the most basic inquiries into the dynamics and structure of matter, space, and time, physicists seek the simplest kinds of interactions at the highest possible energies. These typically entail particle energies of many GeV, and the interactions of the simplest kinds of particles, leptons and quarks for the matter, the largest and highest energy particle accelerator used for elementary particle physics is the Large Hadron Collider at CERN, operating since 2009. These investigations often involve collisions of heavy nuclei – of atoms like iron or gold – at energies of several GeV per nucleon, the largest such particle accelerator is the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. An example of type of machine is LANSCE at Los Alamos. A large number of light sources exist worldwide. The ESRF in Grenoble, France has been used to extract detailed 3-dimensional images of trapped in amber. Thus there is a demand for electron accelerators of moderate energy. Everyday examples of particle accelerators are cathode ray tubes found in television sets and these low-energy accelerators use a single pair of electrodes with a DC voltage of a few thousand volts between them
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Spectroscopy
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Spectroscopy /spɛkˈtrɒskəpi/ is the study of the interaction between matter and electromagnetic radiation. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, later the concept was expanded greatly to include any interaction with radiative energy as a function of its wavelength or frequency. Spectroscopic data is represented by an emission spectrum, a plot of the response of interest as a function of wavelength or frequency. Spectroscopy and spectrography are terms used to refer to the measurement of radiation intensity as a function of wavelength and are used to describe experimental spectroscopic methods. Spectral measurement devices are referred to as spectrometers, spectrophotometers, spectrographs or spectral analyzers, daily observations of color can be related to spectroscopy. Neon lighting is an application of atomic spectroscopy. Neon and other noble gases have characteristic emission frequencies, neon lamps use collision of electrons with the gas to excite these emissions. Inks, dyes and paints include chemical compounds selected for their characteristics in order to generate specific colors. A commonly encountered molecular spectrum is that of nitrogen dioxide, gaseous nitrogen dioxide has a characteristic red absorption feature, and this gives air polluted with nitrogen dioxide a reddish-brown color. Rayleigh scattering is a spectroscopic scattering phenomenon that accounts for the color of the sky, Spectroscopy is used in physical and analytical chemistry because atoms and molecules have unique spectra. As a result, these spectra can be used to detect, identify and quantify information about the atoms, Spectroscopy is also used in astronomy and remote sensing on earth. The measured spectra are used to determine the composition and physical properties of astronomical objects. One of the concepts in spectroscopy is a resonance and its corresponding resonant frequency. Resonances were first characterized in mechanical systems such as pendulums, mechanical systems that vibrate or oscillate will experience large amplitude oscillations when they are driven at their resonant frequency. A plot of amplitude vs. excitation frequency will have a peak centered at the resonance frequency and this plot is one type of spectrum, with the peak often referred to as a spectral line, and most spectral lines have a similar appearance. In quantum mechanical systems, the resonance is a coupling of two quantum mechanical stationary states of one system, such as an atom, via an oscillatory source of energy such as a photon. The coupling of the two states is strongest when the energy of the matches the energy difference between the two states. The energy of a photon is related to its frequency by E = h ν where h is Plancks constant, spectra of atoms and molecules often consist of a series of spectral lines, each one representing a resonance between two different quantum states
32.
Collision avoidance system
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A collision avoidance system is an automobile safety system designed to reduce the severity of a collision. It is also known as a system, forward collision warning system. It uses radar and sometimes laser and camera to detect an imminent crash, GPS sensors can detect fixed dangers such as approaching stop signs through a location database. Once the detection is done, these systems provide a warning to the driver when there is an imminent collision or take action autonomously without any driver input. Collision avoidance by braking is appropriate at low speeds, while collision avoidance by steering is appropriate at higher vehicle speeds. Cars with collision avoidance may also be equipped with cruise control. In Europe there was an agreement about advanced emergency braking system or autonomous emergency braking in 2012. United Nations Economic Commission for Europe has announced that this kind of system will become mandatory for new heavy vehicles starting in 2015, NHTSA projected that the ensuing acceleration of the rollout of automatic emergency braking would prevent an estimated 28,000 collisions and 12,000 injuries. The first demonstration of forward collision avoidance was performed in 1995 by a team of scientists and engineers at Hughes Research Laboratories in Malibu, the project was funded by Delco Electronics, and was led by HRL physicist Ross D. Olney. The technology was labeled for marketing purposes as Forewarn, the system was radar based - a technology that was readily available at Hughes Electronics, but not commercially elsewhere. A small custom fabricated radar-head was developed specifically for this application at 77 GHz. The forward radar-head, plus the signal processing unit and visual-audio-tactile feedbacks were first integrated into a Volvo S40 and this was a fully functional vehicle, and demonstrations were concurrently being provided by a duplicate vehicle. In the early-2000s, the U. S. National Highway Traffic Safety Administration researched whether to make frontal collision warning systems, in 2011, the European Commission investigated the stimulation of collision mitigation by braking systems. According to the assessment, this might ultimately prevent around 5,000 fatalities and 50,000 serious injuries per year across the EU. A2012 study by the Insurance Institute for Highway Safety examined how particular features of crash-avoidance systems affected the number of claims under various forms of insurance coverage and they found lane departure systems to be not helpful, and perhaps harmful, at the circa 2012 stage of development. A2015 Insurance Institute for Highway Safety study found forward collision warning, in the 2016 Berlin terror attack a truck was driven into the Berlin Christmas market and was brought to a stop by its automatic braking system. Collision avoidance features are rapidly making their way into the new vehicle fleet, in a study of police-reported crashes, automatic emergency braking was found to reduce the incidence of rear-end crashes by 39 percent. A2012 study suggests that if all cars feature the system, it will reduce accidents by up to 27 percent, several features are commonly found across collision avoidance systems
33.
Garage door opener
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A garage door opener is a motorized device that opens and closes garage doors. Most are controlled by switches on the wall, as well as by remote controls carried by the owner. The electric overhead garage door opener was invented by C. G, johnson in 1926 in Hartford City, Indiana. As in an elevator, the motor does not provide most of the power to move a heavy garage door. Instead, most of doors weight is offset by the springs attached to the door. In a typical design, torsion springs apply torque to a shaft, the electric opener provides only a small amount of force to control how far the door opens and closes. In most cases, the door opener also holds the door closed in place of a lock. The typical electric garage door opener consists of a unit that contains the electric motor. The power unit attaches to a track, a trolley connected to an arm that attaches to the top of the garage door slides back and forth on the track, thus opening and closing the garage door. The trolley is pulled along the track by a chain, belt, a quick-release mechanism is attached to the trolley to allow the garage door to be disconnected from the opener for manual operation during a power failure or in case of emergency. Limit switches on the unit control the distance the garage door opens. The entire assembly hangs above the garage door, the power unit hangs from the ceiling and is located towards the rear of the garage. The end of the track on the end of the power unit attaches to a header bracket that is attached to the header wall above the garage door. The power head is supported by punched angle iron. Recently another type of opener, known as the opener, has become more popular. This style of opener was used frequently on commercial doors but in recent years has been adapted for residential use and this style of opener consists of a motor that attaches to the side of the torsion rod and moves the door up and down by simply spinning the rod. These openers need a few extra components to function safely for residential use and these include a cable tension monitor, to detect when a cable is broken, and a separate locking mechanism to lock the door when it is fully closed. These have the advantage that they free up ceiling space that an ordinary opener and these also have the disadvantage that the door must have a torsion rod to attach the motor to
34.
Remote keyless system
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A keyless entry system is an electronic lock that controls access to a building or vehicle without using a traditional mechanical key. The term keyless entry system originally meant a lock controlled by a keypad located at or near the drivers door and these systems, having evolved into a hidden touch-activated keypad, are still available on certain Ford or Lincoln models. Widely used in automobiles, an RKS performs the functions of a car key without physical contact. When within a few yards of the car, pressing a button on the remote can lock or unlock the doors, a remote keyless system can include both a remote keyless entry system, which unlocks the doors, and a remote keyless ignition system, which starts the engine. One of the first introductions was in 1980 on the Ford Thunderbird, Mercury Cougar, Lincoln Continental Mark VI, and Lincoln Town Car and it was a keypad on the driver-side exterior door above the door handle. It consisted of a keypad with five buttons that when the code was entered, would unlock the door, with subsequent code entries to unlock all doors. The feature gained its first widespread availability in the U. S. on several General Motors vehicles in 1989, Keyless remotes contain a short-range radio transmitter, and must be within a certain range, usually 5–20 meters, of the car to work. When a button is pushed, it sends a signal by radio waves to a receiver unit in the car. Most RKEs operate at a frequency of 315 MHz for North America-made cars and at 433.92 MHz for European, Japanese, modern systems since the mid-1990s implement encryption as well as rotating entry codes to prevent car thieves from intercepting and spoofing the signal. Earlier systems used infrared instead of signals to unlock the vehicle, such as systems found on Mercedes-Benz, BMW. A typical setup on cars is to have the horn or other sound chirp twice to signify that the car has been unlocked, for example, Toyota, Scion, and Lexus use a chirp system to signify the car being locked/unlocked. While two beeps means that drivers door is unlocked, four beeps means all doors are unlocked, one long beep is for the trunk or power tailgate. One short beep signifies that the car is locked and alarm is set, the functions of a remote keyless entry system are contained on a key fob or built into the ignition key handle itself. Buttons are dedicated to locking or unlocking the doors and opening the trunk or tailgate, on some minivans, the power sliding doors can be opened/closed remotely. Some cars will also close any open windows and roof when remotely locking the car, some remote keyless fobs also feature a red panic button which activates the car alarm as a standard feature. On cars where the release is electronically operated, it can be triggered to open by a button on the remote. Conventionally, the springs open with the help of hydraulic struts or torsion springs. Premium models, such as SUVs and estates with tailgates, may have a motorized assist that can open and close the tailgate for easy access and remote operation
35.
Electromagnetic spectrum
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The electromagnetic spectrum is the collective term for all known frequencies and their linked wavelengths of the known photons. The electromagnetic spectrum of an object has a different meaning, and is instead the characteristic distribution of radiation emitted or absorbed by that particular object. Visible light lies toward the end, with wavelengths from 400 to 700 nanometres. The limit for long wavelengths is the size of the universe itself, until the middle of the 20th century it was believed by most physicists that this spectrum was infinite and continuous. Nearly all types of radiation can be used for spectroscopy, to study. Other technological uses are described under electromagnetic radiation, for most of history, visible light was the only known part of the electromagnetic spectrum. The ancient Greeks recognized that light traveled in straight lines and studied some of its properties, the study of light continued, and during the 16th and 17th centuries conflicting theories regarded light as either a wave or a particle. The first discovery of electromagnetic radiation other than visible light came in 1800 and he was studying the temperature of different colors by moving a thermometer through light split by a prism. He noticed that the highest temperature was beyond red and he theorized that this temperature change was due to calorific rays that were a type of light ray that could not be seen. The next year, Johann Ritter, working at the end of the spectrum. These behaved similarly to visible light rays, but were beyond them in the spectrum. They were later renamed ultraviolet radiation, during the 1860s James Maxwell developed four partial differential equations for the electromagnetic field. Two of these equations predicted the possibility of, and behavior of, analyzing the speed of these theoretical waves, Maxwell realized that they must travel at a speed that was about the known speed of light. This startling coincidence in value led Maxwell to make the inference that light itself is a type of electromagnetic wave, maxwells equations predicted an infinite number of frequencies of electromagnetic waves, all traveling at the speed of light. This was the first indication of the existence of the electromagnetic spectrum. Maxwells predicted waves included waves at very low compared to infrared. Hertz found the waves and was able to infer that they traveled at the speed of light, Hertz also demonstrated that the new radiation could be both reflected and refracted by various dielectric media, in the same manner as light. For example, Hertz was able to focus the waves using a lens made of tree resin, in a later experiment, Hertz similarly produced and measured the properties of microwaves
36.
Infrared
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It extends from the nominal red edge of the visible spectrum at 700 nanometers, to 1000000 nm. Most of the radiation emitted by objects near room temperature is infrared. Like all EMR, IR carries radiant energy, and behaves both like a wave and like its quantum particle, the photon, slightly more than half of the total energy from the Sun was eventually found to arrive on Earth in the form of infrared. The balance between absorbed and emitted infrared radiation has an effect on Earths climate. Infrared radiation is emitted or absorbed by molecules when they change their rotational-vibrational movements and it excites vibrational modes in a molecule through a change in the dipole moment, making it a useful frequency range for study of these energy states for molecules of the proper symmetry. Infrared spectroscopy examines absorption and transmission of photons in the infrared range, Infrared radiation is used in industrial, scientific, and medical applications. Night-vision devices using active near-infrared illumination allow people or animals to be observed without the observer being detected, Infrared thermal-imaging cameras are used to detect heat loss in insulated systems, to observe changing blood flow in the skin, and to detect overheating of electrical apparatuses. Thermal-infrared imaging is used extensively for military and civilian purposes, military applications include target acquisition, surveillance, night vision, homing, and tracking. Humans at normal body temperature radiate chiefly at wavelengths around 10 μm, Infrared radiation extends from the nominal red edge of the visible spectrum at 700 nanometers to 1 mm. This range of wavelengths corresponds to a range of approximately 430 THz down to 300 GHz. Below infrared is the portion of the electromagnetic spectrum. Sunlight, at a temperature of 5,780 kelvins, is composed of near thermal-spectrum radiation that is slightly more than half infrared. At zenith, sunlight provides an irradiance of just over 1 kilowatt per square meter at sea level, of this energy,527 watts is infrared radiation,445 watts is visible light, and 32 watts is ultraviolet radiation. Nearly all the radiation in sunlight is near infrared, shorter than 4 micrometers. On the surface of Earth, at far lower temperatures than the surface of the Sun, almost all thermal radiation consists of infrared in mid-infrared region, much longer than in sunlight. Of these natural thermal radiation processes only lightning and natural fires are hot enough to produce much visible energy, thermal infrared radiation also has a maximum emission wavelength, which is inversely proportional to the absolute temperature of object, in accordance with Wiens displacement law. Therefore, the band is often subdivided into smaller sections. Due to the nature of the blackbody radiation curves, typical hot objects, such as exhaust pipes, the three regions are used for observation of different temperature ranges, and hence different environments in space
37.
Hertz
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The hertz is the unit of frequency in the International System of Units and is defined as one cycle per second. It is named for Heinrich Rudolf Hertz, the first person to provide proof of the existence of electromagnetic waves. Hertz are commonly expressed in SI multiples kilohertz, megahertz, gigahertz, kilo means thousand, mega meaning million, giga meaning billion and tera for trillion. Some of the units most common uses are in the description of waves and musical tones, particularly those used in radio-. It is also used to describe the speeds at which computers, the hertz is equivalent to cycles per second, i. e. 1/second or s −1. In English, hertz is also used as the plural form, as an SI unit, Hz can be prefixed, commonly used multiples are kHz, MHz, GHz and THz. One hertz simply means one cycle per second,100 Hz means one hundred cycles per second, and so on. The unit may be applied to any periodic event—for example, a clock might be said to tick at 1 Hz, the rate of aperiodic or stochastic events occur is expressed in reciprocal second or inverse second in general or, the specific case of radioactive decay, becquerels. Whereas 1 Hz is 1 cycle per second,1 Bq is 1 aperiodic radionuclide event per second, the conversion between a frequency f measured in hertz and an angular velocity ω measured in radians per second is ω =2 π f and f = ω2 π. This SI unit is named after Heinrich Hertz, as with every International System of Units unit named for a person, the first letter of its symbol is upper case. Note that degree Celsius conforms to this rule because the d is lowercase. — Based on The International System of Units, the hertz is named after the German physicist Heinrich Hertz, who made important scientific contributions to the study of electromagnetism. The name was established by the International Electrotechnical Commission in 1930, the term cycles per second was largely replaced by hertz by the 1970s. One hobby magazine, Electronics Illustrated, declared their intention to stick with the traditional kc. Mc. etc. units, sound is a traveling longitudinal wave which is an oscillation of pressure. Humans perceive frequency of waves as pitch. Each musical note corresponds to a frequency which can be measured in hertz. An infants ear is able to perceive frequencies ranging from 20 Hz to 20,000 Hz, the range of ultrasound, infrasound and other physical vibrations such as molecular and atomic vibrations extends from a few femtoHz into the terahertz range and beyond. Electromagnetic radiation is described by its frequency—the number of oscillations of the perpendicular electric and magnetic fields per second—expressed in hertz. Radio frequency radiation is measured in kilohertz, megahertz, or gigahertz
38.
Photon
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A photon is an elementary particle, the quantum of the electromagnetic field including electromagnetic radiation such as light, and the force carrier for the electromagnetic force. The photon has zero rest mass and is moving at the speed of light. Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, exhibiting properties of both waves and particles. For example, a photon may be refracted by a lens and exhibit wave interference with itself. The quanta in a light wave cannot be spatially localized, some defined physical parameters of a photon are listed. The modern concept of the photon was developed gradually by Albert Einstein in the early 20th century to explain experimental observations that did not fit the classical model of light. The benefit of the model was that it accounted for the frequency dependence of lights energy. The photon model accounted for observations, including the properties of black-body radiation. In that model, light was described by Maxwells equations, in 1926 the optical physicist Frithiof Wolfers and the chemist Gilbert N. Lewis coined the name photon for these particles. After Arthur H. Compton won the Nobel Prize in 1927 for his studies, most scientists accepted that light quanta have an independent existence. In the Standard Model of particle physics, photons and other particles are described as a necessary consequence of physical laws having a certain symmetry at every point in spacetime. The intrinsic properties of particles, such as charge, mass and it has been applied to photochemistry, high-resolution microscopy, and measurements of molecular distances. Recently, photons have been studied as elements of quantum computers, in 1900, the German physicist Max Planck was studying black-body radiation and suggested that the energy carried by electromagnetic waves could only be released in packets of energy. In his 1901 article in Annalen der Physik he called these packets energy elements, the word quanta was used before 1900 to mean particles or amounts of different quantities, including electricity. In 1905, Albert Einstein suggested that waves could only exist as discrete wave-packets. He called such a wave-packet the light quantum, the name photon derives from the Greek word for light, φῶς. Arthur Compton used photon in 1928, referring to Gilbert N. Lewis, the name was suggested initially as a unit related to the illumination of the eye and the resulting sensation of light and was used later in a physiological context. Although Wolferss and Lewiss theories were contradicted by many experiments and never accepted, in physics, a photon is usually denoted by the symbol γ
39.
Energy
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In physics, energy is the property that must be transferred to an object in order to perform work on – or to heat – the object, and can be converted in form, but not created or destroyed. The SI unit of energy is the joule, which is the transferred to an object by the mechanical work of moving it a distance of 1 metre against a force of 1 newton. Mass and energy are closely related, for example, with a sensitive enough scale, one could measure an increase in mass after heating an object. Living organisms require available energy to stay alive, such as the humans get from food. Civilisation gets the energy it needs from energy resources such as fuels, nuclear fuel. The processes of Earths climate and ecosystem are driven by the radiant energy Earth receives from the sun, the total energy of a system can be subdivided and classified in various ways. It may also be convenient to distinguish gravitational energy, thermal energy, several types of energy, electric energy. Many of these overlap, for instance, thermal energy usually consists partly of kinetic. Some types of energy are a mix of both potential and kinetic energy. An example is energy which is the sum of kinetic. Whenever physical scientists discover that a phenomenon appears to violate the law of energy conservation. Heat and work are special cases in that they are not properties of systems, in general we cannot measure how much heat or work are present in an object, but rather only how much energy is transferred among objects in certain ways during the occurrence of a given process. Heat and work are measured as positive or negative depending on which side of the transfer we view them from, the distinctions between different kinds of energy is not always clear-cut. In contrast to the definition, energeia was a qualitative philosophical concept, broad enough to include ideas such as happiness. The modern analog of this property, kinetic energy, differs from vis viva only by a factor of two, in 1807, Thomas Young was possibly the first to use the term energy instead of vis viva, in its modern sense. Gustave-Gaspard Coriolis described kinetic energy in 1829 in its modern sense, the law of conservation of energy was also first postulated in the early 19th century, and applies to any isolated system. It was argued for years whether heat was a physical substance, dubbed the caloric, or merely a physical quantity. In 1845 James Prescott Joule discovered the link between mechanical work and the generation of heat and these developments led to the theory of conservation of energy, formalized largely by William Thomson as the field of thermodynamics
40.
Electronvolt
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In physics, the electronvolt is a unit of energy equal to approximately 1. 6×10−19 joules. By definition, it is the amount of energy gained by the charge of an electron moving across an electric potential difference of one volt. Thus it is 1 volt multiplied by the elementary charge, therefore, one electronvolt is equal to 6981160217662079999♠1. 6021766208×10−19 J. The electronvolt is not a SI unit, and its definition is empirical, like the elementary charge on which it is based, it is not an independent quantity but is equal to 1 J/C √2hα / μ0c0. It is a unit of energy within physics, widely used in solid state, atomic, nuclear. It is commonly used with the metric prefixes milli-, kilo-, in some older documents, and in the name Bevatron, the symbol BeV is used, which stands for billion electronvolts, it is equivalent to the GeV. By mass–energy equivalence, the electronvolt is also a unit of mass and it is common in particle physics, where units of mass and energy are often interchanged, to express mass in units of eV/c2, where c is the speed of light in vacuum. It is common to express mass in terms of eV as a unit of mass. The mass equivalent of 1 eV/c2 is 1 eV / c 2 = ⋅1 V2 =1.783 ×10 −36 kg. For example, an electron and a positron, each with a mass of 0.511 MeV/c2, the proton has a mass of 0.938 GeV/c2. In general, the masses of all hadrons are of the order of 1 GeV/c2, the unified atomic mass unit,1 gram divided by Avogadros number, is almost the mass of a hydrogen atom, which is mostly the mass of the proton. To convert to megaelectronvolts, use the formula,1 u =931.4941 MeV/c2 =0.9314941 GeV/c2, in high-energy physics, the electronvolt is often used as a unit of momentum. A potential difference of 1 volt causes an electron to gain an amount of energy and this gives rise to usage of eV as units of momentum, for the energy supplied results in acceleration of the particle. The dimensions of units are LMT−1. The dimensions of units are L2MT−2. Then, dividing the units of energy by a constant that has units of velocity. In the field of particle physics, the fundamental velocity unit is the speed of light in vacuum c. Thus, dividing energy in eV by the speed of light, the fundamental velocity constant c is often dropped from the units of momentum by way of defining units of length such that the value of c is unity
41.
Gamma ray
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Gamma ray, denoted by the lower-case Greek letter gamma, is penetrating electromagnetic radiation of a kind arising from the radioactive decay of atomic nuclei. It consists of photons in the highest observed range of photon energy, paul Villard, a French chemist and physicist, discovered gamma radiation in 1900 while studying radiation emitted by radium. In 1903, Ernest Rutherford named this radiation gamma rays, Rutherford had previously discovered two other types of radioactive decay, which he named alpha and beta rays. Gamma rays are able to ionize atoms, and are thus biologically hazardous. The decay of a nucleus from a high energy state to a lower energy state. Natural sources of gamma rays on Earth are observed in the decay of radionuclides. There are rare terrestrial natural sources, such as lightning strikes and terrestrial gamma-ray flashes, However, a large fraction of such astronomical gamma rays are screened by Earths atmosphere and can only be detected by spacecraft. Gamma rays typically have frequencies above 10 exahertz, and therefore have energies above 100 keV and wavelengths less than 10 picometers, However, this is not a strict definition, but rather only a rule-of-thumb description for natural processes. Electromagnetic radiation from radioactive decay of nuclei is referred to as gamma rays no matter its energy. This radiation commonly has energy of a few hundred keV, in astronomy, gamma rays are defined by their energy, and no production process needs to be specified. The energies of gamma rays from astronomical sources range to over 10 TeV, a notable example is the extremely powerful bursts of high-energy radiation referred to as long duration gamma-ray bursts, of energies higher than can be produced by radioactive decay. These bursts of gamma rays are thought to be due to the collapse of stars called hypernovae, the first gamma ray source to be discovered historically was the radioactive decay process called gamma decay. In this type of decay, a nucleus emits a gamma ray almost immediately upon formation. Paul Villard, a French chemist and physicist, discovered gamma radiation in 1900, However, Villard did not consider naming them as a different fundamental type. Rutherford also noted that gamma rays were not deflected by a field, another property making them unlike alpha. Gamma rays were first thought to be particles with mass, like alpha, Rutherford initially believed that they might be extremely fast beta particles, but their failure to be deflected by a magnetic field indicated that they had no charge. In 1914, gamma rays were observed to be reflected from crystal surfaces, Rutherford and his coworker Edward Andrade measured the wavelengths of gamma rays from radium, and found that they were similar to X-rays, but with shorter wavelengths and higher frequency. This was eventually recognized as giving them more energy per photon
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. Bibcode:2004mmu..symp..291W. ISBN 0-521-75576-X.
