On the Interaction of Biopotential Sensing and Right Leg Drive System with Electro-Quasistatic Human Body Communication

Abstract

Continuous long-term sensing of biopotential signals is vital to facilitate accurate diagnosis. The current state of the art in wearable health monitoring relies on radiative technology for communication. Due to their radiative nature, these systems result in lossy and inefficient transmission, limiting the device's life span. Human Body Communication has emerged as an energy-efficient secure communication modality, and literature has shown body communication to transmit biopotential signals at 100x lower power than traditional radiative technologies. Unlike radiative communication that uses airwaves, HBC, specifically Capacitive Electro-Quasistatic HBC (EQS-HBC), couple signals and confine them within the human body. In Capacitive EQS-HBC, the transmitter uses an electrode to modulate the body potential to transmit data. The modulation of body potential by HBC raises the following concerns. Will HBC transmissions affect the quality of biopotential signals sensed from the body? Additionally, since biopotential sensing systems commonly use Right Leg Drive (RLD) to bias body potential, there is also a concern if RLD can affect the quality of HBC transmissions. For the first time, our work studies the interactions between EQS-HBC and biopotential sensing. Our work is important since understanding HBC-RLD interactions is integral to developing EQS-HBC-based biosensors for Body Area Networks (BANs). For the studies, we conducted lab experiments and developed circuit theoretic models to back the experimental outcomes. We show that due to their higher frequency content and common-mode nature, HBC transmissions do not affect the differential sensing of low-frequency biopotential signals. We show that biopotential sensing using RLD affects HBC. RLD deteriorates the signal strength of HBC transmissions. We thus propose not to use RLD with HBC. We demonstrate our proposed solution by transmitting ECG signals using HBC with 96% correlation compared to the traditional wireless system at a fraction of the power.