  Data transfer using human-body communication (HBC) represents an actively
explored alternative solution to address the challenges related to
energy-efficiency, tissue absorption, and security of conventional wireless.
Although the use of HBC for wearable-to-wearable communication has been
well-explored, different configurations for the transmitter (Tx) and receiver
(Rx) for implant-to-wearable HBC needs further studies. This paper
substantiates the hypothesis that a fully implanted galvanic Tx is more
efficient than a capacitive Tx for interaction with a wearable Rx. Given the
practical limitations of implanting an ideal capacitive device, we choose a
galvanic device with one electrode encapsulated to model the capacitive
scenario. We analyze the lumped circuit model for in-body to out-of-body
communication, and perform Circuit-based as well as Finite Element Method (FEM)
simulations to explore how the encapsulation thickness affects the received
signal levels. We demonstrate in-vivo experimental results on live Sprague
Dawley rats to validate the hypothesis, and show that compared to the galvanic
Tx, the channel loss will be $\approx$ 20 dB higher with each additional mm
thickness of capacitive encapsulation, eventually going below the noise floor
for ideal capacitive Tx.
