Effects of Coaxial-Lateral and Coaxial-Angular Displacements on Link Efficiency of a Wirelessly Powered Optogenetic Implant: Design, Modeling, and Experimental Validation

Abstract

In recent years, the wireless power transfer (WPT) system has evolved tremendously as a means to deliver power to miniaturized implantable sensors. Efficiently delivering power to implants is a challenge due to the loose coupling between the transmitter and receiver coils because of the various displacements (coaxial, lateral, and angular). The coupling coefficient deteriorates significantly due to the displacements, thus decreasing the overall power transfer efficiency of the system. In this paper, we present an analysis and modeling of the effects of various displacements on the efficiency and the overall performance of a miniaturized WPT system designed for an optogenetic implant. To emulate the tissue media inside a human head, skin, skull, and gray matter layers are theoretically modeled using dielectric properties, and simulation models are developed using Ansys high-frequency structure simulator (HFSS) software. The propagation loss and the link efficiency are modeled and simulated as a function of various displacement combinations. To validate the theoretical and simulation models, the WPT system is characterized in various displacement conditions using chicken breast as the tissue media. The measurement results also show a good agreement with the simulation results, thus providing estimation for the misalignment tolerance range for given specifications. The efficiency performance analysis of the proposed WPT system for various worst-case scenarios also provides a preliminary model for designing a closed-loop wireless power delivery regulation scheme in the future.