Basics of Wireless Power Transfer

Wireless power transfer, also known as contactless power transfer, wireless power transfer, or contactless power transfer, is the process of transferring electrical energy from one object to another without contact. The main feature is that the electrical energy required for operation is not supplied along electrical wires and by means of electrical contacts, but through non-wired electromagnetic fields. The latter also includes light, for example in the form of a laser beam.

The most widely used method is inductive energy transfer. At close range of a few centimeters, it has a comparatively high efficiency of about 90%. Examples of applications include the charging of batteries in mobile devices such as electric toothbrushes or mobile phones, as well as the transfer of energy between stationary and moving machine parts or between the track and vehicles moving on it.

When it comes to wireless power transmission, a distinction is made between two principles that differ in physical properties:

1. Near-field wireless power transfers, also known as non-radiating coupling. These include, for example, inductive coupling based on magnetic flux. The term wireless power transmission is often used synonymously with inductive power transmission, as it plays a dominant role in practical applications. In the case of non-radiating coupling in the near field, wave phenomena do not play a role.
2. Transmission of energy in the far field, also known as radiant energy transfer, based on electromagnetic waves. In addition to light, this also includes radio technology, which, in addition to the main application in the field of signal or message transmission, can in principle also be used for energy transmission.

The differences between the near-field coupling and the radiating far-field are mainly in the range: Near-field coupling is limited to short distances in the range of a few centimeters to a few meters in technical applications, while energy transmission via the far field can bridge significantly larger distances, but in technical applications is limited to the transmission of comparatively very small powers. The reason for this lies in the so-called free space attenuation, which generally allows a very low efficiency far below 1%.