Accelerometer with reduced extraneous vibrations owing to improved electrode shape
First Claim
1. An accelerometer with moveable mass (5) and fixed part (2) using variations in capacitance (3, 4) to detect the movement of the mass (5), in which a first series of electrodes (4) solidly connected to the mass (5) is interdigitated with a series of electrodes (3, 7) solidly connected to the fixed part (2), each moveable electrode (4) forming, together with an adjacent fixed electrode (3), a variable capacitance varying as a function of the position of the moveable mass (5), the accelerometer furthermore comprising an electronic circuit that detects the variation in at least one capacitance between moveable mass (5) and fixed part (2), said electronic circuit acting as an indicator of the displacement of the moveable mass characterized in that at least one electrode (3, 4) of the moveable mass (5) and/or of the fixed part (2) each exhibit a finger shape with a wide base and with a profile narrowing in the direction of their free end, and the electronic circuit generates a repetitive electrostatic restoring force and in that the repetitive electrostatic force is specifically chosen so that a mechanical power frequency spectrum (10, 201) of said repetitive electrostatic force exhibits a zone with substantially zero power at a mechanical resonant frequency of the electrodes (4) of the moveable mass (5) and/or of the fixed part (2).
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Abstract
The invention relates to an accelerometer comprising a moving mass (5) and a fixed part (2), which uses variations in capacitance (3, 4) in order to detect the movement of the mass (5). The inventive accelerometer comprises a first series of electrodes (4) which are solidly connected to the mass (5) and which are interdigitated with a series of electrodes (3, 7) which are solidly connected to the fixed part (2). According to the invention, each moving electrode (4), together with an adjacent fixed electrode (3), forms a capacitance which varies according to the position of the moving mass (5). The accelerometer further comprises an electronic circuit which is used to detect the variation in at least one capacitance between the moving mass (5) and the fixed part (2), in the form of a moving mass displacement indicator. The invention is characterised in that one or more or the electrodes (3, 4) or the moving mass (5) and/or the fixed part (2) takes the form of a finger with a large base and a profile which narrows in the direction of the free end thereof. Moreover, the recurring return stress can be selected such that the mechanical power has an essentially zero power zone at the mechanical resonance frequency of the electrodes.
31 Citations
16 Claims
- 1. An accelerometer with moveable mass (5) and fixed part (2) using variations in capacitance (3, 4) to detect the movement of the mass (5), in which a first series of electrodes (4) solidly connected to the mass (5) is interdigitated with a series of electrodes (3, 7) solidly connected to the fixed part (2), each moveable electrode (4) forming, together with an adjacent fixed electrode (3), a variable capacitance varying as a function of the position of the moveable mass (5), the accelerometer furthermore comprising an electronic circuit that detects the variation in at least one capacitance between moveable mass (5) and fixed part (2), said electronic circuit acting as an indicator of the displacement of the moveable mass characterized in that at least one electrode (3, 4) of the moveable mass (5) and/or of the fixed part (2) each exhibit a finger shape with a wide base and with a profile narrowing in the direction of their free end, and the electronic circuit generates a repetitive electrostatic restoring force and in that the repetitive electrostatic force is specifically chosen so that a mechanical power frequency spectrum (10, 201) of said repetitive electrostatic force exhibits a zone with substantially zero power at a mechanical resonant frequency of the electrodes (4) of the moveable mass (5) and/or of the fixed part (2).
Specification