An optical telemetry system for wireless transmission of biomedical signals across the skin
Name
42648143-MIT.pdf
Description
Full printable version
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2.82 MB
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Checksum (MD5)
8b117806e64619fd5b6c78a6fa4f78ba
Author(s)
Larson, Bruce C. (Bruce Carl)
Advisor(s)
David J. Edell.
Date Issued
1999
Publisher
Massachusetts Institute of Technology
Abstract
A technology base for optically-coupled systems was developed that permits in-vivo transmission of biomedical signals across the skin. By complete implantation of sensors and instrumentation electronics, problems with percutaneous connectors were eliminated. Optical power and signal transmission was accomplished with smaller and lighter implant structures than previously achieved with radio frequency (RF) coupling techniques. This is particularly valuable in the field of neuroprosthetics, because it may be possible to implant an optical telemeter directly on the surface of the brain to make mechanically stable connections to microelectrode arrays for neuroelectric recordings. Miniature optical power panels (2.5 mm x 2.5 mm) were developed from arrays of photodiodes. Infrared light of 880 nm wavelength was effective for delivering power across the skin. Panels composed of silicon photodiodes were 14% efficient at converting this light to electrical power, and GaAlAs panels were 41% efficient. Tissue heating experiments demonstrated the safety of optical power transmission. An LED was identified that was both electrically efficient (16%) and of appropriate wavelength (660 nm) for transmitting optical signals from the implant. Pulse period encoding was used for transmission of signals because it was robust and required less power than schemes with higher LED duty cycles. Specialized photodetector circuits were developed to receive pulse encoded data, and decoder circuits were built to reconstruct the transmitted signals. Two prototype single-channel neural waveform telemeters (approx. 10 Hz to 7 kHz bandwidth) were constructed and implanted in the visual cortex of rabbits. Both implants successfully transmitted neuroelectric signals. The first implant survived for four weeks before failing due to a flaw in the encapsulation, and the improved second prototype continues to function properly 28 months after implantation. Integrated circuits (ICs) were designed to record and transmit eight channels of neural waveforms. The first IC telemeter functioned properly, although the sensitivity was not as great as needed for the recording of neural waveforms. It required less than 50 mW of electrical power to operate. Efforts to improve this design introduced flaws in the next set of IC designs, so these problems were addressed, and a final set of designs was submitted for fabrication at the conclusion of this research project.
Description
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.
Vita.
Includes bibliographical references (p. 236-239).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Subjects
Electrical Engineering and Computer Science
MIT Department
Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science
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