Closed-loop inductive link for wireless powering of a high density electrode array retinal prosthesis

A retinal prosthesis intended for rehabilitation of vision impaired patients will require continuous power supply in order to achieve real-time moving images. In this work, we explore the use of inductive coils fabricated using flexible circuit technologies for inductive powering of the implanted prosthetic device. We found that manufacturing technologies dictate the optimum operating frequency of the coil. For a minimum track width and spacing of 4 mils, the optimum frequency was found to be 2.9 MHz. We also looked at the distribution of electric and magnetic fields generated by the inductive coils in and surrounding the eye. These simulation results show that there are electric field concentrations around the conductive coils. Apart from the coils, we need to design an efficient circuit to drive the transmit coil and recover the transmitted power. In order to maintain optimal operation of the link, a closed-loop load modulation feedback operation is proposed. Adaptive control using back-telemetry of the induced voltage on the secondary side can close the power supply loop and result in optimum power transfer by boosting the supply voltage on the primary side when load is high and reducing this voltage when load is small.