Channel gain for on skin links

1. Intra-body Communication Using Galvanic Coupling MeenupriyaSwaminathan, FerranCabrera*, GunarSchirner & Kaushik R. Chowdhury {meenu, schirner, krc} @ece.neu.edu, ferran@nomis.es Abstract Future Research Challenges Implementation of Physical Layer • 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 • modeling the body propagation channel • identifying the best placements of implants and auxiliary data forwarding nodes • 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. Traffic to/from node A Objective: Establishing reliable & energy efficient CP-BN physical layer Access Point Traffic to/from node B Channel Capacity Traffic to/from node C • Building transmitter and receiver circuits with suitable modulation schemes that maximizes transfer rate • Studying the impact of realistic noise figures on capacity Extra-body Network Skin Fat Muscle Data Transfer Access Point Coupler RF Transceiver Signal Processing Memory Ground RF Link Data Aggregation Node A Controller Topology Controller Human Body • Outcome: • Fewer Relays • Energy saving • Higher data-rate Optimizing Node Placement Coupler Signal Processing Implant GC Link Ground Relay Data Retrieval Relays Coupler Signal Processing Memory GC Link Ground Guiding signal through body Establishing path from node to controller Sensor/Actuator Node B Coupler Objective – Networking Body Sensors Signal Processing Sensor • 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 Coupler Intra-body Network Ground Signal Processing Implant Ground Rate Adaptation, Scaling Storage & Fault Detection CSMA & BES RF Link Data Transfer Node C Components and Network Architecture for Galvanic Coupled Body Network Physical Protocol Implanted node Galvanic Coupling - Background Signal Propagation Through Tissue – Modeling Method Link Quality Analysis On Surface node Channel Model GC Link, Topology, Modulation Multiplexing, Synchronization Channel Access & Topology control Data Aggregation • Injects low power electrical signal to the tissues • Weak secondary currents carry data to receiver • Signal propagates radially across multiple tissues • & suffer losses Relay CP-BN … Controller Queuing Data Retrieval • Proactive care & increased longevity Relay to Controller GC Link 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]. • Remote diagnosis & care Self Adaptation Synchronization Node to Relay GC Link • Lower • health care • cost RF Link 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 Why Galvanic Coupling Galvanic Coupling RF • Existing RF based BNs • not suitable for human tissues containing water • consume more power • does not propagate inside body tissues • 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 • Obtained an estimate for observed noise and achievable data rates. • Identified optimal transmission frequency and electrode placements • under varying tissue dimensions [2] • Skin to muscle & intra-muscle links showed lower loss than on-skin links 10-6 10-5 10-4 10-3 (J) Acknowledgement Support: U.S. National Science Foundation (Grant No. CNS-1136027) 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). [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. Galvanic Coupling on Skin (a) Front View (b) Cross Section Channel gain for on skin links *UniversitatPolit`ecnica de Catalunya, Barcelona, Spain