Enabling Physically Secure Human Body Communication in Body Resonance Region with Faraday Fabric

Human Body Communication (HBC) is an energy-efficient alternative to conventional radio frequency (RF) communication. The HBC in the Electro-Quasistatic (EQS) region is physically secure as the signal is mostly confined within 5~10 cm around the human body. However, HBC in the body resonance (BR) region suffers greatly from radiation, which makes the signal easily eavesdropped even at a large distance, and there have not been any efficient shielding methods. This paper, for the first time, introduces a method to shield the BR HBC signal and greatly minimize leakage. Firstly, the transmitter-body interface leakage of the BR HBC signal is measured from 10 cm to 30 cm. Then with the Faraday fabric shielding the transmitter, the interface leakage is measured again for comparison. Moreover, the on-body measurements are implemented with and without the Faraday fabric shield. The measurement results show that the Faraday fabric shield can reduce the leakage by 23.1~48.6 dB at 10 cm, and at 20 cm and 30 cm the leakage from the shielded transmitter is lower than −70 dB. The shield can reduce the channel gain of the on-body receiver by up to 20.41~40.88 dB and makes the leakage channel gain decrease by 10.1 ~ 22 dB more than the on-body scenario. The security benefit achieves the largest around the BR peak frequencies. Beyond the BR peak frequencies, the on-body receiver detects similar or even lower power than the off-body ones. Therefore, the human body plays a major role in the BR peak frequencies while beyond that the transmitter radiation is dominant in transmitting information in the BR HBC system.