Using Body Coupled Communication as a Wireless Body Area Network
- Category: Circuits & Systems, Medical Electronics
- Tags: Charles Sodini, Grant Anderson
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Download as PDFTo achieve comfortable form factors for wireless medical devices, battery size, and thus power consumption, must be curtailed. Often the largest power consumption for wireless medical devices is in storing or transmitting acquired data. Body area networks (BAN) can alleviate power demands by using low-power transmitters to send data “locally” around the body to receivers that are around areas of the body that allow for larger form factors, like the wrist or the waist. These receivers, which have larger power budgets, can then process and store the data or send it elsewhere using higher power transmitters.
Body coupled communication (BCC) shows great potential for forming a BAN. Two-node BCC works by forming two capacitive links between a transmitter and a receiver, creating a circuit loop. One of these links is created by both the transmitter and receiver capacitively coupling to the body, effectively using the body as a low resistance channel between the respective capacitors. The second link is created by both the transmitter and receiver coupling to the environment, or “earth ground,” and using it as a return path. Larger BANs can be made by coupling additional nodes to both the body and the environment.
A model for implantable BCC has been developed in which the electrodes couple to the body and use the body as a lossy transmission line. This model was tested by placing all four electrodes on the skin of a human, simulating how the electrodes would couple to body if they were implanted. Signals were still able to be transmitted and received.
The BCC channel’s attenuation varies with body position and distance between receiver and transmitter. Thus communication schemes that encode data with frequency or phase modulation work best. Both FSK and PM binary signals have been successfully sent and received using both the traditional BCC and the implantable model.
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- Figure 1: (a) The electric field lines made between the transmitter, receiver, body, and environment. (b) The circuit diagram for (a); the red capacitors are parasitic and degrade functionality.
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- Figure 2: The model for using BCC with implants. The parasitic capacitances E and H, from Figure 1 are no longer parasitic but are wanted, replacing capacitors A and D. The body node is no longer modeled as a conductor but a lossy transmission line.
- T. G. Zimmerman, “Personal Area Networks (PAN): Near-field intrabody communication,” M.S. thesis, Massachusetts Institute of Technology, Cambridge, 1995.
- S.-J. Song, N. Cho, S. Kim, J. Yoo, S. Choi, H-J Yoo ., “A 0.9V 2.6mW Body-Coupled Scalable PHY Transceiver for Body Sensor Applications,” ISSCC Dig. Tech. Papers, Feb. 2007, pp. 366-367.
- A. Fazzi, S. Ouzounov, J. Homberg., “A 2.75mW wideband correlation-based transceiver for body-coupled communication,” ISSCC Dig. Tech. Papers, Feb. 2009, pp. 204-205.