Date of Award

Winter 2-2022

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

First Advisor

Arden Moore

Abstract

Inductive charging as a means of power delivery to implanted device is becoming more commonplace as increasingly sophisticated implants with higher power requirements enter clinical use. When such devices undergo inductive charging, losses within the system result in dissipated heat that must be absorbed by the surrounding tissue. The skin-mounted primary antenna and components within the implanted device such as the metal casing, battery, and secondary antenna are all susceptible to temperature increase during a charging cycle. Heating of this kind must be considered when designing modern implants utilizing this mode of power transfer in order to safeguard surrounding tissues from thermal damage, ensure patient comfort, and guarantee device longevity. The transient thermal response of tissues in the vicinity of a primary antenna and inductively charged neuromodulation implant during a charging cycle are presented in this work via a computational model incorporating device heating, tissue cooling due to blood perfusion, and multiple tissue layers. Previous studies utilizing similar numerical techniques have been conducted to investigate tissue heating, however this work seeks to transcend previous results to provide a generalized performance model across a wide range of heating conditions for a generic implanted device geometry. This will provide a useful benchmark for device manufacturers in the design of a wide variety of rechargeable implantable devices. Additionally, to maximize power transfer capability and charging performance, several thermal regulation techniques to mitigate device heating are investigated that incorporate both active and passive cooling schemes. For cases approaching 1 W heat generation within the implanted device and antenna with no applied thermal management, local tissue temperatures did not pose a significant risk of thermal tissue damage after a two-hour charging duration. At high levels of heat dissipation, however, thermal discomfort at the skin’s surface is likely to precede any actual tissue damage, thus being the limiting factor in terms of allowable heat dissipation. Comparisons against tissue temperature results for devices in clinical use proved reliability in the proposed generic model to predict maximum tissue temperatures for similar devices up to 1 W heat generation in the primary antenna and implanted device. For the four thermal regulation techniques investigated, passive standoffs at the antenna base proved most effective, decreasing max tissue temperatures by just over 1 °C.

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