Measuring and testing – Specimen stress or strain – or testing by stress or strain... – Specified electrical sensor or system
Patent
1992-08-31
1994-01-04
Myracle, Jerry W.
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
Specified electrical sensor or system
73702, 7386259, 73DIG1, 310309, 318116, G01B 716
Patent
active
052750558
ABSTRACT:
A resonant strain gauge includes a silicon substrate, a polysilicon flexure beam attached at both ends to the substrate, and a polysilicon rigid cover cooperating with the substrate to enclose the flexure beam within a sealed vacuum chamber. An upper bias electrode is formed on the cover, and a lower bias electrode is formed on the substrate directly beneath and spaced apart from the flexure beam. A drive electrode is formed in or on the beam, centered between the upper and lower bias electrodes transversely with respect to the direction of beam elongation. The upper and lower electrodes are biased at constant voltage levels, of equal magnitude and opposite polarity. The drive electrode, ordinarily biased at ground, is selectively charged by applying an oscillating drive voltage, to cause mechanical oscillation of the beam. A piezoresistor element, formed on the beam, senses beam oscillation and provides a position indicating input to the oscillator circuit that drives the beam. The beam tends to oscillate at its natural resonant frequency. The piezoresistor thus provides the natural resonant frequency to the oscillating circuit, adjusting the frequency of the beam drive signal toward coincidence with the natural resonant frequency. A shield electrode can be formed on the flexure beam between the piezoresistor and the drive electrode, to insure against parasitic capacitance. In alternative embodiments, the drive signal is applied to one of the bias electrodes to oscillate the beam, and beam oscillation is sensed capacitively.
REFERENCES:
patent: 3164987 (1965-01-01), Davidson et al.
patent: 3413573 (1968-11-01), Blake et al.
patent: 3470400 (1969-09-01), Weisbord
patent: 3486383 (1969-12-01), Riordan
patent: 3657667 (1972-04-01), Nishikubo et al.
patent: 3769531 (1973-10-01), Elkuch
patent: 4801897 (1989-01-01), Flecken
patent: 5090254 (1992-02-01), Guckel et al.
Burns David W.
Zook James D.
Honeywell Inc.
Myracle Jerry W.
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