Transcutaneous power and ultrasonic bloodflow velocity sensors.
Curtis, Philip James
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Ultrasonic flow sensors to monitor blood flow in animals and humans have been in use for many years. This study draws on the experience of past research to solve some of the recurring problems found with implanted sensors. Four areas have been explored, all linked by the contribution each makes toward the development of an improved blood-flow sensor. In the first, the use of transcutaneous power to operate an implanted ultrasonic blood-flow sensor is analyzed. The purpose of such a study is the total elimination of batteries. The theory of transcutaneous power is developed from the basic equations of Maxwell and Stefan and a basic efficiency statement is derived. Design guidelines and graphs are generated from this statement and basic experiments are conducted to indicate the validity of the theory. The conclusion is that a properly designed and applied transcutaneous power-transfer circuit is capable of efficiencies as high as 90%. A high-efficiency low-voltage regulator and a low-voltage reference are developed in the second area. This regulator and reference are compatible with existing low-voltage implantable circuits intended initially to be battery powered. The regulator is capable of delivering 2.7 V (two mercury cells in series) with better than 85% efficiency; the voltage reference operates from less than 100 uA and has a temperature stability better than 200 ppm/°C. The third area details an extensive program involving the design, fabrication and employment of a discrete-component continuous-wave implanted ultrasonic doppler blood-flow velocity sensor. The study includes circuit design and construction, package encapsulation and extensive clinical results obtained from more than 975 functioning implant hours with 12 different flow sensors. Among the conclusions derived is the need for an alternative to batteries as a source of power. In the fourth area, transcutaneous power, low-voltage regulator design and the original ultrasonic blood-flow unit are combined in the first of its kind transcutaneously powered blood-flow velocity sensor. The details of this sensor are described in addition to the results of two implants with a prototype unit. The overwhelming conclusion is that transcutaneous power is an immensely practical alternative to battery power for certain clinical experiments.
Approved for public release; distribution is unlimitedThis thesis document was issued under the authority of another institution, not NPS. At the time it was written, a copy was added to the NPS Library Collection for reasons not now known. It has been included in the digital archive for its historical value to NPS. Not believed to be a CIVINS title.
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