Intra-body Communication Using Galvanic Coupling Meenupriya Swaminathan, Ferran Cabrera*, Gunar Schirner & Kaushik R. Chowdhury {meenu, schirner, krc} @ece.neu.edu,
[email protected] Abstract
Extra-body Network
Proactive Remote care & Lower diagnosis & increased health care care longevity cost
GC Link Sensor
Sensor/Actuator
Data Retrieval
Couple r Groun d
Couple r Groun d
Topology Node B Couple r Groun d
Implanted node On Surface node Relay Controller Relay to Controller GC Link Node to Relay GC Link RF Link
Components and Network Architecture for Galvanic Coupled Body Network
Galvanic Coupling - Background
Signal Propagation Through Tissue – Modeling Method
Outcome: • Fewer Relays • Energy saving • Higher data-rate
Guiding signal through body
Establishing path from node to controller
Physical Protocol Link Quality Analysis
…
CP-BN
& suffer losses We constructed a 2-port equivalent circuit model in MATLAB & FEM based ANSYS HFSS simulation suite of human arm using electrical properties of tissues [1].
Self Adaptation
Synchronization
Protocol Design at Network Layer
The spatio-temporal distribution should be analyzed and leveraged for multiple channel access Eg. TDMA
The network should distinguish critical situations from normal deviations based on correlations derived from routine activities. Eg. Abnormal Heart rate from heavy activity Vs emergency
Existing RF based BNs not suitable for human tissues containing water consume more power does not propagate inside body tissues
10-6 10-5 10-4 10-3 (J)
Optimizing Node Placement
Injects low power electrical signal to the tissues Weak secondary currents carry data to receiver Signal propagates radially across multiple tissues
Why Galvanic Coupling
Galvanic coupled CP-BN mimics body’s natural signalling (low frequency signals) low interference as energy is confined within body consumes two orders of magnitude less energy Galvanic Coupling RF
Studying the impact of realistic noise figures on capacity
Node C Rate Adaptation, Scaling
CSMA & BES
Storage & Fault Detection Queuing
Data Aggregation
RF Link
Intra-body Network
Memory Signal Processi ng
Relays
Signal Processi ng
Relay
Implant
Couple r Groun d
Human Body GC Link
Building transmitter and receiver circuits with suitable modulation schemes that maximizes transfer rate
Node A
Controller
Data Aggregation
Channel Capacity
Implant
Controller
Signal Processi ng
RF Link
Data Transfer
Objective: Establishing reliable & energy efficient CP-BN physical layer
Couple r Groun d
Signal Processi ng
Data Transfer
Future health-care relies on autonomous sensing of physiological signals and controlled drug delivery
Need for implanted cyber –physical body sensor network (CP-BN) that can wirelessly communicate with an external control point
RF Transceive r Memory Signal Processi ng
Access Point
Data Retrieval
Implementation of Physical Layer
Skin Fat Muscle
Multiplexing, Synchronization Channel Access & Topology control
Objective – Networking Body Sensors
Traffic to/from node A Traffic to/from node B Traffic to/from node C
Access Point
Channel Model GC Link, Topology, Modulation
Implanted wireless sensors promise the next generation of health-care by in-situ testing of abnormal physiological conditions, personalized medicine and proactive drug delivery to ensure continued well being. However, these sensors must communicate among themselves and with an external control, which raises questions on how to ensure energy efficient data delivery through the body tissues. Traditional forms of high power radio frequency-based communication find limited use in such scenarios owing the limited penetration of electromagnetic waves through human tissue, and the need for frequent battery replacements. Instead, we propose a radically different form of wireless communication that involves galvanic coupling extremely low power electrical signals, resulting in two orders of energy savings. In this scarcely explored paradigm, there are several interesting challenges that must be overcome including (i) modeling the body propagation channel (ii) identifying the best placements of implants and auxiliary data forwarding nodes (iii) devising scientific methods to characterize and improve channel capacity for information transfer. To model the human tissue propagating characteristics, we developed a theoretical suite using equivalent circuits using MATLAB and validated through extensive simulations using finite element method. Using these models, we estimated the channel gain and obtained an estimate for achievable data rates. We could also identify the optimal transmission frequency and electrode placements for signal propagation. Our results reveal a close agreement with experimental findings. Further development of suitable physical and higher layer networking protocols that are reliable with minimum latency would make galvanic coupling an attractive technology for future intra-body networks.
Future Research Challenges
Obtained an estimate for observed noise and achievable data rates.
Acknowledgement Support: U.S. National Science Foundation (Grant No. CNS-1136027)
Identified optimal transmission frequency and electrode placements under varying tissue dimensions [2]
Galvanic Coupling on Skin (a) Front View (b) Cross Section
Skin to muscle & intra-muscle links showed lower loss than on-skin links
References [1] ICNIRP (International Commission on Non-Ionizing Radiation Protection). 1998. Guidelines for limiting exposure to time-varying electric, magnetic, & electromagnetic fields (up to 300 GHz). Channel gain for on skin links
[2] M Swaminathan, F S Cabrera, G Schirner, and K R Chowdhury, Characterization and Signal Propagation Studies for Wireless Galvanic Coupled Body Sensors, IEEE Journal on Selected Areas in Communications, under review. *Universitat Polit`ecnica de Catalunya, Barcelona, Spain