The wireless energy transfer can be divided into two basic methods: the power transmissions in the near field and the far field. Power transmission in the far field takes place by waves. In many cases these are electromagnetic waves, although acoustic faces are usually used for power transmissions. In order to increase the efficiency, a strong wave bundling to a beam is necessary. The beam builds an unobstructed connection between transmitter and receiver and additionally requires a precise alignment between transmitting and receiving unit. The energy supply of flying objects is provided by a laser beam from the ground. Another example is the collection of energy by solar panels from Peter Edward Glaser (1968). This energy is transported through a direct microwave beam to earth. The advantage of the direct electromagnetic energy transmissions in the far field is, that the range is only attenuated by the propagation medium. This is the reason why very large distances can be bridged through air or even in vacuum.
If the efficiency, a ratio of received and transmitted power, plays a secondary role, a transmitter builded beam can be renounced. In a wide environment this makes the energy supply of micro beneficiaries possible. As an example, the high-frequency RFID variants should be mentioned here.
The transmission method in the far field always have the disadvantage that either a bundle of waves to a beam is necessary, or the efficiency of an energy transfer only achieves very small values. The situation is different in the near field coupling. In this case the energy is transferred directly in the electric or magnetic field. A dispension of an electromagnetic wave ideally will not take place. Because the receiver is powered directly by the generated transmitter field, the unbridgeable distances, in comparison with the transmissions in the far field, are very limited. In contrast, there is a high efficiency, which can be achieved even without a precise alignment of the transmitter and receiver.
A majority of the currently available systems transfers energy in the near field. An inductive transmissions application takes place. The increasing number of these systems, especially in the consumer market, has led to the desire for multi-vendor interoperability. In the future it should be possible, to provide different recipients with only one standardized power station. This desire brought of several consortia. For example the Wireless Power Consortium (WPC, founded 2009), the Power Matters Alliance (PMA, founded 2012) and the Alliance for Wireless Power (A4WP), which also was founded in 2012.
A currently very successful market is the mobile communication sector. For charging mobile phones most of the manufacturers are using a standardized inductive transmission method in the near field. This saves error-prone charging contacts and connectors, while increasing the user’s comfort. As motioned at the beginning, there are also many interesting and lucrative fields of application in medical technology. Thus, for example, implanted support systems could be powered transcutaneously. This has the enormous advantage, that the feeding of the implant without cables, which are guided through the skin, is possible. Hereby, the risk of infections is reduced to a minimum. Also many other devices and tools in the medical field benefit from wireless loading. This facilitates, that the disinfection and chemical sterilization of electronic devices is easier than in the past. For example, they can be easily immersed in an appropriate liquid.