Multiuser human body communication via inter-user contact: Evaluation of signal propagation with electromagnetic simulations and wearable measurements

Multiuser human body communication (MU-HBC) uses multiple human bodies as a part of the transmission channel and enables intuitive data sharing among users through physical contact. This paper investigates signal propagation in MU-HBC by combining electromagnetic field simulations with measurements using wearable transceivers. In the simulations, a transmitter was attached to the left wrist of a male whole-body model, and two receivers were placed on the left and right wrists of a female model. Electric field distributions and transmission characteristics at 10 MHz were calculated using the finite-difference time-domain method for three inter-user contact conditions: no contact, hand-holding, and arm-linking. In the measurements, two human subjects wore compact, battery-powered spectrum analyzers connected to electrodes on their wrists, and the transmission characteristics were measured for hand-holding and arm-linking. The simulated and measured results consistently showed that the receiver position relative to the transmitter is the dominant factor determining the transmission characteristics, whereas the difference between hand-holding and arm-linking is comparatively small. In particular, the receiver closer to the transmitter exhibited a path loss of 7–15 dB smaller than that of the farther receiver. The measured values agreed with the simulations within 1 dB for the closer receiver and within several decibels for the farther receiver, and the standard deviation over five repeated measurements was at most 2.65 dB. These findings demonstrate that reliable signal propagation through multiple human bodies can be achieved via direct contact and provide design guidelines for wearable transceivers and low-power front-end circuits in MU-HBC systems.