Field Distribution Models of Spiral Coil for Misalignment Analysis in Wireless Power Transfer Systems

This paper presents design and optimization methods for spiral coils utilized for wireless power transfer in wireless medical implant applications. A theoretical model was examined for near-field distributions of spiral-type transmitter antennas in both orthogonal components. Finite-element simulations were performed to verify the theoretical radiation patterns. Receiver antenna voltages were measured at planes of interest as a means to map field distributions. Theoretical, simulation, and experimental results were conducted in free space and they agreed well. Understanding the orthogonal field components and their distributions in various distances between the worn transmitter coil outside the body and the receiver coil of implant that has a much smaller size provides a means to find the optimal location and angle to harvest maximum energy. The analysis method for near-field wireless power transmission can be utilized to determine design strategies of the transmitter spiral coil with considerations also in the amplifier circuit and physical constraints in practical scenarios to obtain maximum power and link efficiency for the implant devices. The method can be extended to investigate field distributions affected by human tissues, which construct a much more complex environment, and will be conducted in future works.