Figure 2

(a) Forward and return path for regular intra-body Electro-quasistatic Human Body communication (EQS-HBC). Forward path is formed through the human body, while the return path is formed through parasitic capacitances \(C_{G,Tx}\) and \(C_{G,Rx}\) with environment. (b) Weak Capacitive coupling between an EQS-HBC user and an antenna, ensuring minimal leakage pick-up by that antenna. This implies minimal interference and maximum security towards antenna based devices. (c) Strong capacitive coupling, \(C_C\) between two human bodies pose the question of inter-body signal leakage for EQS HBC. This can potentially allow the 2nd user, the attacker, to sniff EQS HBC signals from the 1st user. If the 2nd person is just a regular user of HBC, the capacitive coupling can cause interference between the EQS HBC Signals from the two bodies. (d) Simplified circuit model for regular intra-body HBC of Fig. 2a, and approximate expression for channel loss. (e) Simplified circuit model for inter-body HBC or HBC leakage, from Fig. 2b, and approximate expression for channel loss. The extra term \(C_C/C_{Body}\) represents an additional loss from inter-body coupling. (f) Comparison of inter-body EQS coupling for capacitive vs Resistive load at the receiver’s end. For capacitive load, the low-frequency region is a flat-band response. For resistive load, the response is a 20 dB/decade rising slope.