Understanding The Role of Magnetic and Magneto-Quasistatic Fields in Human Body Communication

TL;DR

This paper provides a fundamental analysis of Magnetic Human Body Communication (M-HBC), revealing that the human body minimally influences M-HBC signals across a broad frequency range, and compares its performance with EQS HBC.

Contribution

First detailed electromagnetic analysis of M-HBC's underlying principles and its contrast with EQS HBC, guiding future device design and application choices.

Findings

Human body is negligible in M-HBC operation below 30 MHz.

Conductive tissues attenuate magnetic fields at higher frequencies.

Different operational modes of MQS HBC are outlined and compared with EQS HBC.

Abstract

With the advent of wearable technologies, Human Body Communication (HBC) has emerged as a physically secure and power-efficient alternative to the otherwise ubiquitous Wireless Body Area Network (WBAN). Whereas the most investigated nodes of HBC have been Electric and Electro-quasistatic (EQS) Capacitive and Galvanic, recently Magnetic HBC (M-HBC) has been proposed as a viable alternative. Previous works have investigated M-HBC through an application point of view, without developing a fundamental working principle for the same. In this paper, for the first time, a ground up analysis has been performed to study the possible effects and contributions of the human body channel in M-HBC over a broad frequency range (1kHz to 10 GHz), by detailed electromagnetic simulations and supporting experiments. The results show that while M-HBC can be successfully operated as a body area network, the human body itself plays a minimal or negligible role in it's functionality. For frequencies less than about 30 MHz, in the domain of operation of Magneto-quasistatic (MQS) HBC, the human body is transparent to the quasistatic magnetic field. Conversely for higher frequencies, the conductive nature of human tissues end up attenuating Magnetic HBC fields due to Eddy currents induced in body tissues, eliminating the possibility of the body to support efficient waveguide modes. With this better understanding at hand, different modes of operations of MQS HBC have been outlined for both high impedance capacitive and 50 Ohm termination cases, and their performances have been compared with EQS HBC for similar sized devices, over varying distance between TX and RX. The resulting report presents the first fundamental understanding towards M-HBC operation and its contrast with EQS HBC, aiding HBC device designers to make educated design decisions, depending on mode of applications.