Delivering power to an implanted device located deep inside the body is not trivial. This problem is made more challenging if the implanted device is in constant motion. This paper describes two methods of transferring power wirelessly by means of magnetic induction coupling. In the first method, a pair of transmit and receive coils is used for power transfer over a large distance (compared to their diameter). In the second method, an intermediate pair of coils is inserted in between transmit and receive coils. Comparison between the power transfer efficiency with and without the intermediate coils shows power transfer efficiency to be 11.5 % and 8.8 %, respectively. The latter method is especially suitable for powering implanted devices in the eye due to immunity to movements of the eye and ease of surgery. Using this method, we have demonstrated wireless power delivery into an animal eye.

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Wireless powering of a retinal prosthesis is necessary for continuous operation of the implanted device in a blind patient. Inductive link has the potential for transferring power wirelessly to such an implanted device inside the eye. However, constant motion of the eye and changes in electrode-tissue impedance results in a decrease in the inductive link efficiency. In this paper, we present a novel method to improve the efficiency of the inductive link by introducing an intermediate pair of coils to close the gap between two coils with large separation. Based on our theoretical formulation, the power transfer efficiency of the double-pair coil link is estimated to exceed the efficiency of a single-pair coil when the coupling coefficient can be improved by a conservative value of 3 times. We fabricated the double-pair coils using flexible printed circuit board technology. Measurement result confirms our initial expectation. By implementing this design, we aim to provide sufficient power for next generation retinal prosthesis which has electrode count exceeding 1000 and can consume upwards of 50 mW of power.