Physics-based design space analysis for inductive wireless power transfer in cochlear implants

Abstract This work presents a physics-based analytical framework for the systematic design space analysis of inductive wireless power transfer in cochlear implants. A 12-coil library is characterized and calibrated against Maxwell 2D simulations. Transmitter-receiver pairs are evaluated at three ISM bands (6.78, 13.56, and 27.12 MHz) with individually optimized load resistance, across implant depths of 3 to 20 mm. A constraint hierarchy is established where the transmitter power budget binds at 6.78 and 13.56 MHz, while SAR binds at higher frequencies for the highest-efficiency pairs. The temperature rise is shown to be independent of implant depth under regulated power and is never observed to limit operation. Robustness under depth deviation, lateral misalignment, and capacitor tolerance is characterized, and multiplicative gap decomposition is shown to underestimate the retained worst-case efficiency by up to 15.5% relative to direct evaluation, a conservative but pessimistic shortcut. Applied to a fully implantable cochlear implant charging scenario, a phantom-validated thermal scaling of 1.36 mK/mW replaces the Pennes model, which overestimates temperature rise by 7.3 times. The analytically optimal coil pair would improve the additional charging time by 3.8 times by cutting the additional charging time from 45 to 12 minutes compared to the small footprint hardware pair.