- Browse Repository
- Case Western Reserve University Special Collections
- Judge Ben C. Green Law Library
- 1977-05-17 (x)
- Case Western Reserve University Patents
Case Western Reserve University Patents
Show moreBackground of the invention: The present invention is in the field of diffused strain gauge pressure transducers. More particularly, the present invention relates to miniaturized pressure transducers capable of being implanted within the human or animal body for direct measurement of physiological pressures, such as respiratory, venous, arterial, amniotic, and cerebrospinal fluid pressures. Prior art transducers capable of monitoring physiological pressures in human beings and animals were normally not implanted in the body due to their undesirably large size, fragility, and complexity. These transducers were usually connected to the pressure source monitored by a fluid-filled catheter inserted into the body. This method of monitoring pressure often resulted in unreliable and inaccurate data, due to dynamic response problems associated with the fluid-filled catheter. Attempts to implant miniaturized pressure transducers within the body for direct measurement of internal fluid pressure often resulted in malfunctions due to leakage of body fluid into the critical components of the transducer. Summary of the invention: The present invention provides a miniaturized, fluid-tight pressure transducer capable of being implanted within a human or animal body. All components of the transducer are hermetically bonded together to provide a rugged, reliable sensor package. The transducer is assembled using known microcircuitry techniques, resulting in a finished pressure sensor measuring approximately 1.25 by 3.75 mm. with a depth of 0.250 mm. An N-type, phosphorus-doped, single crystal, silicon base and a single crystal silicon cover are eutectically bonded together by a metallic laminate seal in a vacuum environment to form an evacuated, fluidtight pressure reference chamber which contains piezoresistive bridge sensor elements diffused on a flexible diaphragm formed by preferential etching of the crystal silicon base of specific crystalline orientation. The diaphragm will flex or deform when there is a fluctuation of the pressure differential between the sealed pressure reference chamber and fluid external to the implanted pressure transducer. As the diaphragm flexes, the electrical parameters of the piezoresistive bridge will change proportionately. Electrical conductors lead from the piezoresistive bridge to a set of contacts external to the sealed reference chamber. These electrical conductors take the form of diffused, electrically insulated conductor paths on the surface of the silicon base where the conductors exit the evacuated chamber. Conventional electrical readout circuitry can be connected to the external transducer contacts to monitor and record fluid pressure, represented by the electrical parameters of the piezoresistive bridge. When utilized with an active temperature compensation circuit, the transducer can provide a linear output proportional to pressure that is stable to better than 1 mm. Hg at a 300 mm.
http://www.google.com/patents?vid=USPAT4023562
Show less