An Algorithm for the Computer Aided Design of Coil Couple for a Misalignment Tolerant Biomedical Inductive Powering Unit

Coils misalignments restrain the wider implementation of inductive powering of implantable medical devices. The misalignment problem can be overcome with the help of the coils geometry optimization. Coil couple design implies simultaneous adjustment of the several parameters (coils radii, turns numbers, and pitch). Thus, it is desirable to have the means for computer-aided design of the system. An algorithm for the coil couple design is devised. The key feature of the algorithm is the use of predefined maximum and minimum acceptable values of the load power as a performance metric. The algorithm gives the geometry of the coil which ensures that the inductive powering unit provides the given range of the load power for the given range of the misalignments. A formal method is proposed for the calculation of the initial coils characteristics and consequent adjustment of the transmitting coil external radius, transmitting coil turns number, coils internal radii (simultaneously), and receiving coil turns number. The software implementing the proposed algorithm was developed. Eight design runs were performed in order to evaluate the algorithm performance in various conditions, including different power ranges (10 W, 100 mW, and $300~\mu \text{W}$ ), operating frequencies (0.2 MHz, 1 MHz, 6.78 MHz, and 13.56 MHz), and possible implementations (ventricular assist devices, cochlear implants, and spinal cord stimulators). It was proved that the power drop as low as 10% of the mean load power can be ensured for the lateral misalignments up to the receiving coil external radius. The low-power inductive powering unit was constructed and tested. The experimental results confirm the numerical modeling.