  The emergence of Human Body Communication (HBC) as an alternative to wireless
body area networks (WBAN) has led to the development of small sized, energy
efficient and more secure wearable and implantable devices forming a network in
and around the body. Previous studies claim that though HBC is comparatively
more secure than WBAN, nevertheless, the electromagnetic (EM) radiative nature
of HBC in >10MHz region makes the information susceptible to eavesdropping.
Furthermore, interferences may be picked up by the body due to the human body
antenna effect in the 40-400MHz range. Alternatively, electro-quasistatic (EQS)
mode of HBC forms an attractive way for covert data transmission in the sub
10MHz region by allowing the signal to be contained within the body. However,
there is a gap in the knowledge about the mechanism and sources of interference
in this region (crucial in allowing for proper choice of data transmission
band). In this paper, the interference coupling modality in the EQS region is
explained along with its possible sources. Interferences seen by the wearable
in the actual scenario is a non-trivial problem and a suitable measurement EQS
HBC setup is designed to recreate it by employing a wearable sized measurement
setup having a small ground plane. For the first time, a human biophysical
interference pickup model is proposed and interference measurement results
using a wearable device are presented up to 250kHz in different environmental
settings.
