Figure 3
From: Enabling Covert Body Area Network using Electro-Quasistatic Human Body Communication
(a–c) EQS-HBC Signal Transmission (VEQS-HBC) and Quasi-static Leakage (VQSL) Signal Measurement with distance in time-domain using an oscilloscope, voltage probe, and an antenna. The transmission signal amplitude is 3.3 V. (a) EQS-HBC Received signal at different on-body locations is ~30 mV (green curve) showing a channel loss of ~40 dB which is almost independent of the distance between the transmitter and receiver. Off-body signal corresponding to each of the human body receiver locations is measured in air with very close proximity from the body (doff–body ~ 0.01 m) (black curve). This shows that the EQS-HBC occurs through the on-body signal transmission, and not through the air. (b) The EQS-HBC signal received at different locations of the body is ~30 mV (green curve). Quasi-static Leakage around the body is measured in air medium from both device hand (red curve) and free hand (blue curve) respectively. The QS leakage (QSL) measurement set-up is shown in Fig. 10. Note that for the EQS-HBC received signal measurement, distance refers to the on-body distance between the transmit device and the receiving electrode. In the case of leakage measurements here, it is the distance between the antenna and the corresponding hand for which the leakage is measured. The free hand, although contains almost the same amount of signal, leaks considerably lesser than the device hand, proving that human body alone does not leak. However, the human body aids the transmit device to leak (device hand leakage) by providing a low impedance closed path with the earth ground, which will be discussed in the next experiments.
