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

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

Understanding the Role of Magnetic and Magneto-Quasistatic Fields in Human Body Communication 789 444 IEEE Transactions on Biomedical Engineering (TBME)
Author(s): Mayukh Nath, Alfred Krister Ulvog, Scott Weigand, Shreyas Sen

With the advent of wearable technologies, Human Body Communication (HBC) has emerged as a physically secure and power-efficient alternative to wireless networks such as Bluetooth, Med-Radio or Wi-Fi. HBC uses the human body itself as a medium to communicate between wearable or implantable devices on and around a human body. The most studied way to achieve this is to leverage the conductivity of the body tissues and send electrical signals, using the body as a wire. This study explores the option of using magnetic field instead as a viable and potentially safer alternative for HBC.

We perform a thorough analysis using electromagnetic theory and simulations, to study the effect of the human body over a broad frequency range, namely 1 kHz to 10 GHz. We find that the human body is transparent to magnetic field for frequencies less than 30 MHz. At these frequencies, the signal wavelength is large compared to the human body dimensions, so for our application case, this region of operation can be named as Magneto-Quasistatic HBC (MQS-HBC). However, for higher frequencies, especially frequencies greater than 100 MHz, the body tissues become increasingly conductive and start absorbing magnetic field, hence hurting the performance of M-HBC.

With this understanding at hand, different modes of operations of MQS-HBC are explored for varying application cases.  Their performances are also compared with their electric HBC counterpart over varying distance between TX and RX. We show that unlike electric capacitive HBC, where channel gain becomes constant beyond a certain distance between transmitter and receiver, M-HBC channel gain keeps falling with distance, as well as mis-alignment between transmitter and receiver coils.

The resulting report presents a fundamental understanding towards M-HBC operation and its contrast with Electro-Quasistatic (EQS) HBC, aiding HBC device designers to make educated design choices, depending on mode of applications.

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