Enhancing Physical Security of Body Resonance Human Body Communication

Electro quasi-static (EQS) human body communication (HBC) offers an energy-efficient and physically secure alternative to traditional radio frequency (RF) communication. To enable high-speed connectivity among body-worn devices, higher-frequency HBC beyond EQS is motivated. As frequency increases, entering body resonance (BR) region, signal wavelength approaches human body dimensions. In this region, the transmitter (TX) signal excites the body and radiates outward, making it susceptible to eavesdropping and compromising physical security. This paper, for the first time, explores BR HBC physical security and proposes Faraday fabric shielding to significantly mitigate its vulnerability. Firstly, the BR HBC TX radiation and the effect of shielding are theoretically explained and simulated across 30 MHz∼300 MHz. Simulations demonstrate that electrode-skin interface leakage increases with frequency and Tx proximity to the body. A wearable-sized shield substantially weakens the leakage without significantly affecting on-body channel gain. Subsequently, measurements with battery-powered wearable devices confirm body-worn Tx enhances leakage by up to 32.4 dB than standalone TX. Shielding reduces leakage around BR peak (at 50∼150 MHz) below the noise floor from 10 cm with <20 dB on-body channel gain loss. The security benefit (SB), difference between leakage and on-body channel gain reductions, varies with Tx positions and body postures, and the greatest SB occurs near the BR peak and peak from radiation (∼120 MHz). Finally, shielding is applied to enhance the physical security of the fingertip-based BR HBC human-machine interface, enabling communication strictly by touch. In conclusion, Faraday fabric shielding effectively mitigates leakage, ensuring robust physical security without significantly compromising on-body channel performance. By addressing physical security challenges in the BR region, this study lays the groundwork for future advancements in high-speed HBC.