Advanced Biophysical Model to Capture Channel Variability for EQS Capacitive HBC

Abstract

Human Body Communication (HBC) has come up as a promising alternative to traditional radio frequency (RF) Wireless Body Area Network (WBAN) technologies. This is essentially due to HBC providing a broadband communication channel with enhanced signal security in the physical layer due to lower radiation from the human body as compared to its RF counterparts. An in-depth understanding of the mechanism for the channel loss variability and associated biophysical model needs to be developed before EQS-HBC can be used more frequently in WBAN consumer and medical applications. Biophysical models characterizing the human body as a communication channel didn't exist in literature for a long time. Recent developments have shown models that capture the channel response for fixed transmitter and receiver positions on the human body. These biophysical models do not capture the variability in the HBC channel for varying positions of the devices with respect to the human body. In this study, we provide a detailed analysis of the change in path loss in a capacitive-HBC channel in the electroquasistatic (EQS) domain. Causes of channel loss variability namely: inter-device coupling and effects of fringe fields due to body's shadowing effects are investigated. FEM based simulation results are used to analyze the channel response of human body for different positions and sizes of the device which are further verified using measurement results to validate the developed biophysical model. Using the bio-physical model, we develop a closed form equation for the path loss in a capacitive HBC channel which is then analyzed as a function of the geometric properties of the device and the position with respect to the human body which will help pave the path towards future EQS-HBC WBAN design.

Bi-Phasic Quasistatic Brain Communication for Fully Untethered Connected Brain Implants

“…Two differential electrodes placed on the sides of the bowl work as the RX electrodes, which are connected to a TI BUF602 buffer configured as a 50 Ω driver. The TI buffer offers capacitive termination at the input of the RX, which is essential for establishing a wideband HBC channel as shown in earlier works 18,31,33,34 (on the other hand, a traditional 50 Ω termination results in a high-pass channel). The output of the buffer goes to a handheld Spectrum Analyzer from RF Explorer.…”

“…Two differential metal electrodes attached to the sides of the bowl work as the RX electrodes, which are connected to a TI BUF602 buffer configured as a 50 Ω driver for measurement instruments. The TI buffer offers ~2 pF capacitive termination at the input of the RX, which helps in establishing a wideband HBC channel as shown in earlier works 18,31,33,34 The mouse was anaesthetized with 2-3% isoflurane throughout the surgery. After shaving the hair, the animal was fixed on a stereotaxic frame, so that the head does not move during the experiment, and the head skin was sterilized.…”

Touchscreen Communication (ToSCom): EQS Body Communication during Touch Sensing

“…1 (e)) has been demonstrated as a physically secure [10,11] low-loss channel that enables high-speed communication [14] strictly through touch [9]. The use of the human body as a communication channel for wearable devices on or around the body is a low-power and energy-efficient methodology [15][16][17][18][19][20][21][22], making it especially suitable for communication in wearable IoB nodes. In ToSCom (Fig.…”

Physically Secure Wearable–Wearable Through-Body Interhuman Body Communication

“…This coupling dominates the return path and thus the channel loss at close distances. This theory is established and modeled by the authors of Datta et al, (2021). However, wearable device measurements are not provided-in this article, we analyze the effects of inter-device coupling and body shadowing on multiple subjects.…”

“…It should be noted that the loss from Experiments 3 and 4 on average was a few dB more than that from Experiment 1. This is can be explained by the theory developed in Datta et al, (2021) where body shadowing has a significant adverse effect on the signal level-interestingly enough, the channel actually improves for the configuration where the devices are further apart-as opposed to the scenario where one of the transmitters or receivers is sandwiched between the two humans.…”