Mechanical resonance, silicon accelerometer
First Claim
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1. A sensor comprising:
- a supporting frame having an opening therein;
a mass disposed in the opening and moveable in directions approximately parallel to a first axis; and
wherein;
the first axis is perpendicular to a plane parallel to the perimeter of said supporting frame; and
a second axis is parallel to the plane;
a flexure coupled between the frame and the mass; and
wherein;
said flexure supports said mass relative to said supporting frame;
said flexure bends a first way upon movement of said mass in a first direction approximately parallel to the first axis; and
said flexure bends a second way upon movement of said mass in a second direction approximately parallel to the first axis; and
a vibratory beam formed on said flexure; and
wherein;
said vibratory beam is stretched in a direction approximately parallel to the second axis when said flexure bends the first way;
said vibratory beam is compressed in a direction approximately parallel to the second axis when said flexure bends the second way;
said vibratory beam has a resonant frequency;
the resonant frequency changes when said vibratory beam is stretched;
the resonant frequency changes when said vibratory beam is compressed; and
the resonant frequency is indicative of a magnitude and direction of acceleration affecting said mass in a direction approximately parallel to the first axis.
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Abstract
A silicon accelerometer includes a plurality of silicon layers. The silicon layers form first and second silicon beams supported by flexure members. An acceleration responsive silicon mass is arranged to bend the flexure members in response to accelerations. The silicon beams are vibrated in vacuum chambers and gas damping is provided for the acceleration responsive mass and the flexure members. A sensor is provided for sensing vibration of the first and second silicon beams.
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Citations
28 Claims
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1. A sensor comprising:
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a supporting frame having an opening therein; a mass disposed in the opening and moveable in directions approximately parallel to a first axis; and wherein; the first axis is perpendicular to a plane parallel to the perimeter of said supporting frame; and a second axis is parallel to the plane; a flexure coupled between the frame and the mass; and wherein; said flexure supports said mass relative to said supporting frame; said flexure bends a first way upon movement of said mass in a first direction approximately parallel to the first axis; and said flexure bends a second way upon movement of said mass in a second direction approximately parallel to the first axis; and a vibratory beam formed on said flexure; and wherein; said vibratory beam is stretched in a direction approximately parallel to the second axis when said flexure bends the first way; said vibratory beam is compressed in a direction approximately parallel to the second axis when said flexure bends the second way; said vibratory beam has a resonant frequency; the resonant frequency changes when said vibratory beam is stretched; the resonant frequency changes when said vibratory beam is compressed; and the resonant frequency is indicative of a magnitude and direction of acceleration affecting said mass in a direction approximately parallel to the first axis. - View Dependent Claims (2)
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3. A sensor comprising:
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a supporting frame having an opening therein; a mass disposed in the opening and moveable in directions approximately parallel to a first axis; wherein; the first axis is perpendicular to a plane approximately parallel to the perimeter of said supporting frame; and a second axis and a third axis are parallel to the plane; a plurality of flexures coupled between said frame and said mass; and wherein; said plurality of flexures support said mass relative to said supporting frame; each flexure of a first portion of said plurality of flexures, bends a first way upon movement of said mass in a first direction approximately parallel to the first axis; each flexure of the first portion of said plurality of flexures, bends a second way upon movement of said mass in a second direction approximately parallel to the first axis; each flexure of a second portion of said plurality of flexures, bends a first way upon movement of said mass in a first direction approximately parallel to the first axis; and each flexure of the second portion of said plurality of flexures, bends a second way upon movement of said mass in a second direction approximately parallel to the first axis; a first vibratory beam formed on each flexure of the first portion of said plurality of flexures; and wherein; said first vibratory beam is stretched in a direction approximately parallel to a plane containing the second and third axes, when said first portion flexure bends the first way; said first vibratory beam is compressed in a direction approximately parallel to the plane containing the second and third axes, when said first portion flexure bends the second way; said first vibratory beam has a first resonant frequency; the first resonant frequency increases when said first vibratory beam is stretched; and the first resonant frequency decreases when said first vibratory beam is compressed; and a second vibratory beam formed on each flexure of the second portion of said plurality of flexures; and wherein; said second vibratory beam is compressed in a direction approximately parallel to the plane containing the second and third axes, when said second portion flexure bends the first way; said second vibratory beam is stretched in a direction approximately parallel to the plane containing the second and third axes, when said second portion flexure bends the second way; said second vibratory beam has a second resonant frequency; the second resonant frequency changes when said second vibratory beam is stretched; and the second resonant frequency changes when said second vibratory beam is compressed; and the first and second resonant frequencies are indicative of a magnitude and direction of an acceleration force affecting said mass in a direction approximately parallel to the first axis. - View Dependent Claims (4)
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5. An accelerometer comprising:
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a first wafer having a thickness, having a first surface, having a second surface approximately parallel to and at a distance equal to the thickness from the first surface, having a recess formed in said first wafer resulting in a proof mass having first and second surfaces, surrounded by a perimeter support structure having first and second surfaces, the proof mass supported by a first plurality of flexures connected to the perimeter support structure and to the proof mass at the first surface of said first wafer, and the proof mass supported by a second plurality of flexures connected to the perimeter support structure and to the proof mass at the second surface of said first wafer, the first and second pluralities of flexures formed from said first wafer; a resonant vibratory microbeam formed on at least one flexure of the first plurality of flexures; a first insulating layer situated next to the first surface of the perimeter support structure; a second insulating layer situated next to the second surface of the perimeter support structure; a second wafer, formed over the first surface of said first wafer and situated next to said first insulating layer, having a recess for permitting movement of the proof mass; a third wafer, formed under the second surface of said first wafer and situated next to said second insulating layer, having a recess for permitting movement of the proof mass; a sensing means, proximate to said resonant vibratory microbeam, for detecting a vibration of said resonant vibratory microbeam; and a force rebalance circuit connected to said first wafer, said second wafer, said third wafer and to said sensing means; and wherein; the proof mass is moveable in first and second directions perpendicular to a plane parallel to the first surface of said first wafer; the proof mass moves in the first direction when said accelerometer is subject to an acceleration force in the first direction, the proof mass moves in the second direction when said accelerometer is subject to an acceleration force in the second direction, and the proof mass is situated in a null position when not subject to an acceleration force; said force rebalance circuit provides an electrostatic force on the proof mass, which has a magnitude equal to a magnitude of an acceleration force simultaneously affecting the proof mass, the electrostatic force having a direction opposite of that of the acceleration force, and the electrostatic force maintaining the proof mass in the null position; an amount of distance that the proof mass moves is proportional to a difference of the magnitudes of the acceleration and electrostatic forces; an amount of bending of the at least one flexure is proportional to the amount of distance that the proof mass moves; said resonant vibratory microbeam has a resonant frequency that increases when the proof mass moves in the first direction and decreases when the proof mass moves in the second direction, wherein a variation of the resonant frequency is due to a change of length of said resonant vibratory microbeam which in turn is due to a bending of the at least one flexure; said first and second wafers form electrodes of a first capacitor and said first and third wafers form electrodes of a second capacitor, such that a first signal on the electrodes of the first capacitor provides an electrostatic force to attract the proof mass towards said second wafer and a second signal on the electrodes of the second capacitor provides an electrostatic force to attract the proof mass towards said third wafer; the resonant frequency of said resonant vibratory microbeam is at a first frequency when the magnitude of the acceleration force is zero, is initially slightly greater than the first frequency when the magnitude of the acceleration force is greater than zero in the first direction, and is initially slightly less than the first frequency when the magnitude of the acceleration force is greater than zero in the second direction; and said force rebalance circuit provides first and second signals to the electrodes of the first and second capacitors, respectively, for maintaining the proof mass in the null position, the first and second signals indicative of magnitude and direction of the acceleration force in the first and second direction. - View Dependent Claims (6)
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7. A sensor comprising:
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a supporting frame having an opening therein; a mass disposed in the opening and moveable in directions approximately parallel to a first axis; and wherein; the first axis is perpendicular to a plane parallel to the perimeter of said supporting frame; and a second axis is parallel to the plane; at least one flexure coupled between the frame and the mass; and wherein; said flexure supports said mass relative to said supporting frame; said flexure bends a first way upon movement of said mass in a first direction approximately parallel to the first axis; and said flexure bends a second way upon movement of said mass in a second direction approximately parallel to the first axis; and a vibratory beam formed on said flexure; and wherein; said vibratory beam is stretched in a direction approximately parallel to the second axis when said flexure bends the first way; said vibratory beam is compressed in a direction approximately parallel to the second axis when said flexure bends the second way; said vibratory beam has a resonant frequency;
the resonant frequency changes when said vibratory beam is stretched;the resonant frequency changes when said vibratory beam is compressed; and the resonant frequency is indicative of a magnitude of acceleration affecting said mass in a direction approximately parallel to the first axis.
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8. A sensor comprising:
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first, second, and third layers, each layer having first and second surfaces wherein all of the first and second surfaces said first, second and third layers are approximately parallel to one another; said second layer fabricated to form an acceleration responsive mass, a supportive structure, a first plurality of flexure members at the first surface of said second layer and a second plurality of flexure members at the second surface of said second layer, wherein the first and second pluralities of flexure members support the acceleration responsive mass relative to the supportive structure, and the acceleration responsive mass is moveable relative to the supportive structure, along an axis approximately perpendicular to the first and second surfaces of said first, second and third layers; said first layer having the second surface proximate to the first surface of said second layer, and having a first recess formed in the second surface of said first layer to permit movement of the acceleration responsive mass along the axis towards said first layer; said third layer having the first surface proximate to the second surface of said second layer, and having a second recess formed in the first surface of said third layer to permit movement of the acceleration responsive mass along the axis towards said third layer; first means, situated on a first flexure member of the first plurality of flexure members, for sensing bending of the first flexure member of the first plurality of flexure members; and wherein; the acceleration responsive mass, when affected by an acceleration force that is in a direction parallel to the axis, results in a bending of the first flexure member of the first plurality of flexure members at an amount indicative of an amount of the acceleration force; said first means for sensing, formed on the first flexure member of the first plurality of flexure members, comprises a vibratory beam, having a first variable resonant frequency that is indicative of an amount of bending of the first flexure member of the first plurality of flexure members and that the bending subjects the vibratory beam to compression or tension and thus results in a change of the first variable resonant frequency; and the first resonant frequency is indicative of the amount of acceleration force affecting the acceleration responsive mass in the direction parallel to the axis. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28)
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Specification