Characterization of Human Body Forward Path Loss and Variability Effects in Voltage-Mode HBC

Human body communication (HBC) has recently emerged as a promising modality for connecting ultralow power wearable/implantable devices. The wide variations in HBC channel characteristics in previously reported literature call for an in-depth analysis of the sources of such variations. It is also important to identify whether most of the loss is due to propagation through human body (forward path), or the lack of common ground among the communicating devices. Our experiments show that along with frequency dependence, multiple other factors, such as excitation/termination modality, electrode area, and pressure, significantly affect HBC loss. In this letter, we focus on measuring human body loss with common ground up to 1 MHz (i.e., megabits of data rate using broadband signaling), and investigate the effects of abovementioned variation sources. Our experiments show: 1) high-impedance termination along with voltage-mode communication maximizes received signal; 2) in capacitive HBC, the forward path loss is significantly lower (average: 0.5 dB and variation: 0.5 dB) compared to the return path loss due to noncommon ground; 3) variation in excitation/termination dependent losses explained by a simplified lumped HBC model; and 4) the effect of coupler area/pressure on forward-path channel loss in common ground scenario.