Peak wireless power transfer using magnetically coupled series resonators

Wireless power transfer can create the illusion of portable devices with infinite power supplies. Power transfer using magnetically coupled series resonators is maximized when the load presented to the sender is matched to the series impedance of the source. This determines an optimal separation distance between the sender and the receiver. However, the maximum power transferred only depends on the losses in the system and is independent of this distance and the resonant frequency. Closed-form expressions describe the power transferred and efficiency for all distances and system values. These expressions are validated with systems operating at 23 kHz, 40 kHz and 59 kHz. The performance of resonant magnetic coupling for wireless power applications is bounded to have efficiencies less than 50% at the maximum power distance and beyond. Higher efficiencies are only possible at shorter distances where the load presented to the sender is larger than the series impedance of the source.