Patent EP0301816A2 successfully refreshed from Google Patents.
EP0301816A2
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Accelerometer
Assignee: BAE Systems Electronics Ltd
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Filing: 1988-07-27
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Granted: —
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Expires: 2008-07-27
Abstract
Abstract An accelerometer capable of sensing acceleration in 3 orthogonal directions while being formed in a single silicon wafer comprises 3 cantilever beams (2) etched from the wafer, each having a mass (3) asymmetric to the neutral plane (A) of the beam, and formed by etching away the beam (2) on one face only of the wafer. The beams are arranged at 120° to each other so that their sensing axes (S) are orthogonal or approximately so. Deflection of the beams is measured by piezoelectric, electrostatic or electrodynamic effect and force feedback is preferably employed, again using one of these effects.
Inventors
- 👤 Peter Dudley Church
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-05 20:14
CPC Classifications
G; G01; G01P; G01P15/00; G01P15/02; G01P15/08; G01P15/0802; G01P15/18; G01P2015/0805; G01P2015/0822; G01P2015/0825; G01P2015/0828
Claims Analysis
Total Claims: 23
Claim 1
Independent Claim
118 words
An accelerometer comprising a plurality of cantilever mounted beams (2), characterised in that a longitudinal surface of each beam (2) lies in a common plane (4), the mass distribution of each beam (2) transverse to said surface being such that each beam (2) has a sensing axis (S), along which the beam (2) is preferentially responsive to acceleration, said sensing axis (S) being inclined to said common plane (4), the orientation of the beams (2) in said common plane (4) being such that the sensing axes (S) of the beams (2) are aligned with a set of co-ordinate axes (Figure 3), and including sensing means (9,10) in respect of each beam (2) to determine the acceleration-induced beam deflection.
Claim 2
Dependent Claim
118 words
An accelerometer comprising a plurality of cantilever mounted beams (2), characterised in that a longitudinal surface of each beam (2) lies in a common plane (4), the mass distribution of each beam (2) transverse to said surface being such that each beam (2) has a sensing axis (S), along which the beam (2) is preferentially responsive to acceleration, said sensing axis (S) being inclined to said common plane (4), the orientation of the beams (2) in said common plane (4) being such that the sensing axes (S) of the beams (2) are aligned with a set of co-ordinate axes (Figure 3), and including sensing means (9,10) in respect of each beam (2) to determine the acceleration-induced beam deflection.
Claim 3
Dependent Claim
31 words
An accelerometer according to Claim 1, characterised in that the beams (2) are integral parts of a semiconductor wafer (1), one surface (4) of said wafer lying in said common plane.
Claim 4
Dependent Claim
26 words
An accelerometer according to Claim 1 or Claim 2, characterised in that each beam (2) comprises a support-end section and a substantially thicker free-end section (3).
Claim 5
Dependent Claim
35 words
An accelerometer according to any of Claims 1, 2 and 3, characterised in that each beam (2) comprises a support-end section and a free-end section of substantially greater width across said longitudinal surface (Figure 5).
Claim 6
Dependent Claim
15 words
An accelerometer according to any of Claims 1 to 4, characterised by three beams (2).
Claim 7
Dependent Claim
15 words
An accelerometer according to Claim 5, characterised in that said co-ordinate axes are mutually orthogonal.
Claim 8
Dependent Claim
65 words
An accelerometer according to any preceding claim, characterised by sensing means comprising, in respect of each beam, means (9,9′) for transmitting a surface acoustic wave along said longitudinal surface, and means for timing the transmission of said surface acoustic wave and determining a change in the time of transmission resulting from a change in length of said longitudinal surface resulting from deflection of the beam.
Claim 9
Dependent Claim
53 words
An accelerometer according to Claim 7, characterised in that said means for transmitting a surface acoustic wave comprises a layer of piezoelectric material (7) deposited on said longitudinal surface, a transmitting electrode system (9,9′) and a receiving electrode (10,10′) system spaced apart along said longitudinal surface to define a surface acoustic wave path.
Claim 10
Dependent Claim
66 words
An accelerometer according to Claim 8, characterised by, in respect of each beam (2), two surface acoustic wave paths side by side along said longitudinal surface, the two paths being oppositely directed and the two electrode systems toward the free end of the beam being coupled together to provide two paths in series and having terminal electrode systems toward the support end of the beam (2).
Claim 11
Dependent Claim
50 words
An accelerometer according to any of Claims 1 - 6, characterised in that said sensing means comprises, in respect of each beam (2), a capacitor electrode (C1) mounted on said longitudinal surface, a fixedly mounted capacitor electrode (C3), and means responsive to the capacitance between said electrodes (C1 and C3).
Claim 12
Dependent Claim
53 words
An accelerometer according to Claim 10, characterised in that said sensing means comprises, in respect of each beam (2), two capacitor electrodes (C1,C2) mounted on said longitudinal surface and a fixedly mounted capacitor (C3) electrode confronting the beam mounted capacitor electrodes (C1,C2) to permit capacitor connections to be solely on the beam surface.
Claim 13
Dependent Claim
53 words
An accelerometer according to any of Claims 1-6, characterised in that said sensing means comprises, in respect of each beam (2), an inductive coil (35) mounted on said longitudinal surface, a fixedly mounted inductive coil (39) confronting the beam mounted coil (35), and means responsive to the electromagnetic coupling between said coils (35,39).
Claim 14
Dependent Claim
55 words
An accelerometer according to Claim 12, characterised in that said sensing means comprises, in respect of each beam (2), two inductive coils (35,37) mounted on said longitudinal surface and a fixedly mounted closed inductive coil (39) confronting the beam mounted inductive coils (35,37) to permit coil connections (41) to be solely on the beam surface.
Claim 15
Dependent Claim
49 words
An accelerometer according to any preceding claim characterised by force feedback means (7,11,13) associated with each beam (2) responsive to said sensing means (9,10) to tend to maintain zero deflection of the associated beam (2), an output signal from said force feedback means (7,11,13) providing an indication of acceleration.
Claim 16
Dependent Claim
83 words
An accelerometer according to Claim 14, characterised in that said force feedback means comprises, in respect of each beam (2), a composite deposit on said longitudinal surface, said composite deposit comprising a first electrode layer (11), a layer of piezoelectric material (7) and a second electrode layer (13), and means for applying a potential difference between said first and second electrodes such as to impose a longitudinal stress on said longitudinal surface to oppose stress imposed by acceleration-induced deflection of the beam (2).
Claim 17
Dependent Claim
76 words
An accelerometer according to Claim 15, characterised in that said longitudinal surface lies between recessed longitudinal portions of the beam surface, said layer of piezoelectric material extending over said longitudinal surface and said recessed longitudinal portions and wherein a third electrode is deposited on said recessed portions, said third electrode being isolated from said second electrode to permit different potential differences to be imposed between said first and second electrodes and said first and third electrodes.
Claim 18
Dependent Claim
44 words
An accelerometer according to Claim 15, characterised in that said second electrode is coated with a material having such an expansion coefficient as to produce a differential expansion with said longitudinal surface opposed to that produced between said piezoelectric layer and said longitudinal surface.
Claim 19
Dependent Claim
41 words
An accelerometer according to Claim 15, characterised in that a layer of piezoelectric material on the surface of said beam opposite to said longitudinal layer provides a balancing differential expansion force and substantially zero deflection of the beam with temperature change.
Claim 20
Dependent Claim
41 words
An accelerometer according to Claim 14, characterised in that said force feedback means comprises, in respect of each beam, a capacitor electrode mounted on said longitudinal surface, a fixedly mounted capacitor electrode and means for applying a potential difference between them.
Claim 21
Dependent Claim
35 words
An accelerometer according to Claim 14, wherein said force feedback means comprises, in respect of each beam, an inductive coil mounted on said longitudinal surface, a fixedly mounted inductive coil and means for energising them.
Claim 22
Dependent Claim
62 words
An accelerometer according to Claim 2, characterised in that on each side of said semiconductor wafer (1) a cover plate (17,21) is bonded to said semiconductor wafer (1) so as to cover at least one beam (2), each cover plate (17,21) being spaced from the associated surface of the beam (2) by a distance smaller than the thickness of the wafer (1).
Claim 23
Dependent Claim
57 words
An accelerometer according to Claim 2, characterised in that each said beam (2) has leaf portions (27,29) extending from its opposite surfaces towards the adjacent body of the semiconductor wafer (1), deflection of a beam out of the wafer (1) being limited by obstruction between a said leaf portion (27,29) and said body of semiconductor wafer (1).
References Cited (Backward Citations)
No citation records indexed.
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