  New medical procedures promise continuous patient monitoring and drug
delivery through implanted sensors and actuators. When over the air wireless
radio frequency (OTA-RF) links are used for intra-body implant communication,
the network incurs heavy energy costs owing to absorption within the human
tissue. With this motivation, we explore an alternate form of intra-body
communication that relies on weak electrical signals, instead of OTA-RF. To
demonstrate the feasibility of this new paradigm for enabling communication
between sensors and actuators embedded within the tissue, or placed on the
surface of the skin, we develop a rigorous analytical model based on galvanic
coupling of low energy signals. The main contributions in this paper are: (i)
developing a suite of analytical expressions for modeling the resulting
communication channel for weak electrical signals in a three dimensional
multi-layered tissue structure, (ii) validating and verifying the model through
extensive finite element simulations, published measurements in existing
literature, and experiments conducted with porcine tissue, (iii) designing the
communication framework with safety considerations, and analyzing the influence
of different network and hardware parameters such as transmission frequency and
electrode placements. Our results reveal a close agreement between theory,
simulation, literature and experimental findings, pointing to the suitability
of the model for quick and accurate channel characterization and parameter
estimation for networked and implanted sensors.
