Implant-to-Wearable Communication through the Human Body: Exploring the Effects of Encapsulated Capacitive and Galvanic Transmitters

TL;DR

This study compares encapsulated capacitive and galvanic transmitters for implant-to-wearable human-body communication, demonstrating that galvanic transmitters are more efficient, with in-vivo tests confirming significant signal loss with capacitive encapsulation.

Contribution

The paper provides a comprehensive analysis and experimental validation of implant-to-wearable communication, highlighting the superiority of galvanic transmitters over capacitive ones in this context.

Findings

Galvanic transmitters are more efficient than capacitive ones for implant-to-wearable communication.

Encapsulation thickness significantly affects signal levels, with capacitive transmitters losing over 20 dB per mm.

In-vivo experiments on rats validate the circuit and FEM simulation results.

Abstract

Data transfer using human-body communication (HBC) represents an actively explored alternative solution to address the challenges related to energy-efficiency, tissue absorption, and security of conventional wireless. Although the use of HBC for wearable-to-wearable communication has been well-explored, different configurations for the transmitter (Tx) and receiver (Rx) for implant-to-wearable HBC needs further studies. This paper substantiates the hypothesis that a fully implanted galvanic Tx is more efficient than a capacitive Tx for interaction with a wearable Rx. Given the practical limitations of implanting an ideal capacitive device, we choose a galvanic device with one electrode encapsulated to model the capacitive scenario. We analyze the lumped circuit model for in-body to out-of-body communication, and perform Circuit-based as well as Finite Element Method (FEM) simulations to explore how the encapsulation thickness affects the received signal levels. We demonstrate in-vivo experimental results on live Sprague Dawley rats to validate the hypothesis, and show that compared to the galvanic Tx, the channel loss will be $\approx$ 20 dB higher with each additional mm thickness of capacitive encapsulation, eventually going below the noise floor for ideal capacitive Tx.