Multi-Path Model and Sensitivity Analysis for Galvanic Coupled Intra-Body Communication Through Layered Tissue

Abstract

Abstract-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.

Past Results, Present Trends, and Future Challenges in Intrabody Communication

“…In this respect, the main proposals of channel models in IBC have been directed to the definition of both lumped [24,30,33,36,38,130,131] and distributed parameters circuit diagrams [18,35,37,40,132]. These models easily and intuitively incorporate some of the electrical characteristics of the different tissues, such as tissue resistivity and capacitive properties, as well as their dependence on frequency, thus helping obtain simple analytical expressions for both attenuation and dispersion through the human body.…”

“…A work by Swaminathan et al in [130] proposes a lumped circuit model to simulate the galvanic IBC transmission in both on-body and in-body links from 100 kHz to 1 MHz. The proposed model contains six impedances that account for the longitudinal transmission across each individual tissue (skin, fat, muscle, and bone), four transverse impedances emulating the current flow from one tissue to another, and four impedances that simulate the electrode-skin contact.…”

Data Packet Transmission Through Fat Tissue for Wireless IntraBody Networks

“…We vary the signal transmission distance from 20 mm to 100 mm, with a 20 mm step, for the phantom and the ex-vivo setups. These distances were chosen based on the distance between several vital organs such as liver-kidney, pancreas-kidney, and liver-heart and also from the experimental models adopted in previous studies [14,25]. To prove that the fat tissue is a good communication channel compared to the muscle tissue, we compare the results of using the fat tissue as a communication channel against the results obtained when the muscle tissue is used.…”

“…Generally, three different techniques have been used to propagate a signal onto the human body: Galvanic coupling [14][15][16][17][18], capacitive coupling [17][18][19][20][21][22], and RF links [23][24][25][26][27][28][29]. Usually higher frequencies are not suitable for intrabody communication due to the lossy nature of biological tissues [30,31].…”

Characterization of the Fat Channel for Intra-Body Communication at R-Band Frequencies

“…Previous investigators have employed three different physical principles for intra-body communication: galvanic coupling [9][10][11], capacitive coupling [12][13][14], and RF links [15,16]. The Medical Implant Communication Service (MICS) operating over the frequency range 402-405 MHz has been accepted worldwide for data transmission to support medical application associated with medical implant devices.…”