Wireless power transfer (WPT), wireless power transmission, wireless energy transmission (WET), or electromagnetic power transfer is the transmission of electrical energy without wires as a physical link. In a wireless power transmission system, an electrically powered transmitter device generates a time-varying electromagnetic field that transmits power across space to a receiver device; the receiver device extracts power from the field and supplies it to an electrical load. The technology of wireless power transmission can eliminate the use of the wires and batteries, thereby increasing the mobility, convenience, and safety of an electronic device for all users. Wireless power transfer is useful to power electrical devices where interconnecting wires are inconvenient, hazardous, or are not possible.
Inductive charging pad for a smartphone as an example of near-field wireless transfer. When the phone is set on the pad, a coil in the pad creates a magnetic field which induces a current in another coil, in the phone, charging its battery.
Prototype inductive electric car charging system at 2011 Tokyo Auto Show
Powermat inductive charging spots in a coffee shop. Customers can set their phones and computers on them to recharge.
Wireless powered access card.
In electrical engineering, two conductors are said to be inductively coupled or magnetically coupled when they are configured in a way such that change in current through one wire induces a voltage across the ends of the other wire through electromagnetic induction. A changing current through the first wire creates a changing magnetic field around it by Ampere's circuital law. The changing magnetic field induces an electromotive force (EMF) voltage in the second wire by Faraday's law of induction. The amount of inductive coupling between two conductors is measured by their mutual inductance.
Example of inductive coupling, 1910. The bottom coil is connected to AC power. The alternating magnetic field through the top coil induces current in it which lights the lamp.
Power transformer transfers power from one winding to the other by inductive coupling
Antenna transformer inductively couples antenna of AM radio station to transmitter
clamp ammeter measuring current by inductive coupling