Wireless power transfer using weakly coupled magnetostatic resonators

Wireless power transfer can create the illusion of portable devices with infinite power supplies and enable applications that are currently unimaginable because of power constraints. Magnetic induction has been extensively used for wireless power transfer, but its efficiency depends on magnetic coupling that decays as the inverse cube of distance. At long enough distances, the magnetic coupling is weak enough that the effect of the receiver coil on the sender coil can be neglected. In this weakly coupled limit, series resonance in both the sender and the receiver increases the power transfer. Compared to magnetic induction, the power transfer increases by the sum of the quality factors of the sender and the receiver times the quality factor of the sender. Similarly, the efficiency increases by half of the product of the quality factors of the sender and the receiver. However, the overall efficiency of the power transfer is less than 50% for all weakly coupled series resonators. Resonators with a Q of 1,000 should be able to send power over a distance 9 times the radius of the devices with an efficiency of 10%.