Channel Loss in Contactless Human Body Communication

Human body communication (HBC) utilizes human body as the transmission medium to facilitate data communications in a wireless body area network (WBAN). It normally uses a pair of transmitting (Tx) and receiving (Rx) electrodes clinging to the body surface to form a low-loss body channel, so a higher energy efficiency can be achieved in comparison to conventional wireless communications. In HBC, the Tx electrode can be shared with vital sign monitoring electrode, such as ECG electrode or EEG electrode, to inject the signal into body. As for the Rx electrode, it can be either in direct contact to body surface or placed in proximity to body surface. The late case forms a contactless HBC communication, which find more applications in the WBAN, e.g. a smart phone in one's pocket to receive ECG signal from the chest electrode. In view of the adverse effect caused by the contactless case, this paper presents a study on the path loss of contactless HBC, which are investigated by finite element method (FEM) and verified by actual measurements. An empirical formula for path loss and contactless space is derived, showing that the path loss is increased by 18 dB when the distance between electrode and body increases from 1 mm to 10 mm. It also shows a 5 dB reduction on path loss with a 50% increase of the electrode size.