Capacitive accelerometer with liquid dielectric

• US 6,966,225 B1
• Filed: 07/12/2002
• Issued: 11/22/2005
• Est. Priority Date: 07/12/2002
• Status: Expired due to Fees

• Current Assignee: Maxtor Corporation (Seagate Technology Holdings Plc)
• Original Assignee: Maxtor Corporation (Seagate Technology Holdings Plc)
• Inventors: Mallary, Michael
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): SAINT SURIN, JACQUES M
• Application Number:
  US10/194,583
• Time in Patent Office: 1,229 Days
• Field of Search: 735/143.2, 735/141.8, 735/140.5, 735/141.2, 735/140.1, 735/140.6, 732/89, 361/280, 361/283.1, 361/289
• US Class Current: 73/514.32
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 2015/0882 for providing damping of vibrations
• CPC Class Codes: H01G 5/0132 Liquid dielectrics
• CPC Class Codes: H01G 5/145 with profiled electrodes

Abstract

An accelerometer includes a capacitive sensing device and circuitry. The capacitive sensing device has electrode structures spaced by a gap for relative movement in response to a force applied to the capacitive sensing device to produce a displacement of the electrode structures. A liquid is disposed in the gap between the electrode structures. The circuitry is coupled to the capacitive sensing device for determining from the displacement an electric signal indicative of acceleration of the applied force.

Claims

1. An accelerometer comprising:

a capacitive sensing device that includes a movable electrode structure, a stationary electrode structure and a liquid, wherein the movable electrode structure includes a plurality of movable plates, the stationary electrode structure includes a plurality of stationary plates, the movable and stationary plates are asymmetrically interleaved with each other, gaps are disposed between corresponding ones of the movable and stationary plates, the liquid is disposed in the gaps and contacts the movable and stationary plates, the movable electrode structure moves towards the stationary electrode structure in response to a force applied to the capacitive sensing device, the stationary electrode structure remains stationary in response to the applied force, and the gaps decrease in response to the applied force, thereby creating a displacement between the movable and stationary electrode structures in response to the applied force; and

circuitry coupled to the capacitive sensing device for determining from the displacement an electric signal indicative of acceleration of the applied force.

2. The accelerometer of claim 1, wherein the circuitry is configured for passive damping.

3. The accelerometer of claim 2, wherein the circuitry is configured to provide an AC voltage across the capacitive sensing device and measure a resulting AC current.

4. The accelerometer of claim 1, wherein the circuitry is configured for active damping.

5. The accelerometer of claim 4, wherein the circuitry is configured to provide an AC voltage across the capacitive sensing device and produce therefrom a DC voltage proportional to the acceleration.

6. The accelerometer of claim 5, wherein the circuitry is configured to derive a damping signal from the DC voltage.

7. The accelerometer of claim 5, wherein the circuitry is configured to invert the DC voltage and apply the inverted DC voltage across the capacitive sensing device to return the electrode structures to an initial relative position.

8. The accelerometer of claim 7, wherein the liquid has a dielectric constant selected to produce a predetermined increase in an electrostatic force produced between the electrode structures in response to the applied DC voltage.

9. The accelerometer of claim 8, wherein the liquid has a dielectric constant greater than one.

10. The accelerometer of claim 1, wherein the liquid is substantially nonelectrically conductive.

11. The accelerometer of claim 1, wherein the liquid has a resistivity of on the order of 10¹² ohm-cm. or higher.

12. The accelerometer of claim 8, wherein the liquid is chemically stable so as not to substantially dissociate in the presence of an electric field produced between the electrode structures by the applied DC voltage.

13. The accelerometer of claim 8, wherein the liquid has a breakdown voltage sufficient so as not to substantially dissociate in response to the applied DC voltage.

14. The accelerometer of claim 1, wherein the liquid has a viscosity that provides a selected amount of damping of the relative movement of the electrode structures.

15. The accelerometer of claim 1, wherein the liquid has a viscosity of less than 1 poise.

16. The accelerometer of claim 1, wherein the liquid has a viscosity of less than 0.01 poise.

17. The accelerometer of claim 1, wherein the liquid has a vapor pressure on the order of 10⁻

7 mm Hg or lower.

18. The accelerometer of claim 1, wherein the liquid has a melting point of less than 0 degrees F.

19. The accelerometer of claim 1, wherein the liquid is diffusion pump oil.

20. The accelerometer of claim 1, wherein the liquid is a perfluorocarbon or a hydrofluorocarbon.

21. The accelerometer of claim 1, wherein the liquid is a halide.

22. The accelerometer of claim 1, further comprising an envelope in which the electrode structures and the liquid are disposed.

23. The accelerometer of claim 22, wherein the envelope is a flexible mylar film.

24. The accelerometer of claim 23, wherein the liquid is encased within the envelope.

25. The accelerometer of claim 23, wherein first and second leads coupled to the movable and stationary electrode structures, respectively, protrude through the envelope.

26. An accelerometer comprising:

a capacitive sensing device that includes first and second electrode structures and a liquid, wherein the first electrode structure includes a plurality of first plates, the second electrode structure includes a plurality of second plates, the first and second plates are asymmetrically interleaved with each other, gaps are disposed between corresponding ones of the first and second plates, the liquid is disposed in the gaps and contacts the first and second plates, the electrode structures move towards each other in response to a force applied to the capacitive sensing device, and the gaps decrease in response to the applied force, thereby creating a displacement between the electrode structures in response to the applied force; and

circuitry coupled to the capacitive sensing device for determining from the displacement an electric signal indicative of acceleration of the applied force.

27. The accelerometer of claim 26, wherein the circuitry is configured for passive damping.

28. The accelerometer of claim 27, wherein the circuitry is configured to provide an AC voltage across the electrode structures and measure a resulting AC current.

29. The accelerometer of claim 26, wherein the circuitry is configured for active damping.

30. The accelerometer of claim 29, wherein the circuitry is configured to provide an AC voltage across the electrode structures, produce therefrom a DC voltage proportional to the acceleration, invert the DC voltage, apply the inverted DC voltage to the second electrode structure to return the electrode structures to an initial relative position, and isolate the DC voltage from the capacitive sensing device.

31. The accelerometer of claim 26, wherein the liquid is substantially nonelectrically conductive.

32. The accelerometer of claim 26, wherein the liquid provides damping of the relative movement of the electrode structures.

33. The accelerometer of claim 26, wherein the electrode structures have comb-like shapes.

34. The accelerometer of claim 26, wherein the first electrode structure is movable and the second electrode structure is stationary.

35. The accelerometer of claim 26, further comprising a flexible envelope in which the electrode structures and the liquid are disposed, wherein first and second leads coupled to the first and second electrode structures, respectively, protrude through the envelope, and the liquid contacts and is encased within the envelope.

36. An accelerometer comprising:

a capacitive sensing device that includes first and second electrode structures and a liquid, wherein the first electrode structure includes a plurality of first plates, the second electrode structure includes a plurality of second plates, the first and second plates are interleaved with each other and protrude along a first axis, gaps are disposed between corresponding ones of the first and second plates, the liquid is disposed in the gaps and contacts the first and second plates, the electrode structures move towards each other primarily along a second axis perpendicular to the first axis such that the first and second plates are more asymmetrically interleaved with each other in response to a force applied to the capacitive sensing device, and the gaps decrease in response to the applied force, thereby creating a displacement between the electrode structures in response to the applied force; and

circuitry coupled to the capacitive sensing device for determining from the displacement an electric signal indicative of acceleration of the applied force.

37. The accelerometer of claim 36, wherein the circuitry is configured for passive damping.

38. The accelerometer of claim 37, wherein the circuitry is configured to provide an AC voltage across the electrode structures and measure a resulting AC current.

39. The accelerometer of claim 36, wherein the circuitry is configured for active damping.

40. The accelerometer of claim 39, wherein the circuitry is configured to provide an AC voltage across the electrode structures, produce therefrom a DC voltage proportional to the acceleration, invert the DC voltage, apply the inverted DC voltage to the second electrode structure to return the electrode structures to an initial relative position, and isolate the DC voltage from the capacitive sensing device.

41. The accelerometer of claim 36, wherein the liquid is substantially nonelectrically conductive.

42. The accelerometer of claim 36, wherein the liquid provides damping of the relative movement of the electrode structures.

43. The accelerometer of claim 36, wherein the electrode structures have comb-like shapes.

44. The accelerometer of claim 36, wherein the first electrode structure is movable and the second electrode structure is stationary.

45. The accelerometer of claim 36, further comprising a flexible envelope in which the electrode structures and the liquid are disposed, wherein first and second leads coupled to the first and second electrode structures, respectively, protrude through the envelope, and the liquid contacts and is encased within the envelope.

46. An accelerometer comprising:

a capacitive sensing device that includes first and second electrode structures and a liquid, wherein the first electrode structure includes a plurality of first plates, the second electrode structure includes a plurality of second plates, the first and second plates are interleaved with each other, protrude along a first axis and are arranged in corresponding pairs such that each plate in the pair is closer to the other plate in the pair than to any other plate, gaps are disposed between the plates in the pairs, the liquid is disposed in the gaps and contacts the first and second plates, the electrode structures move towards each other primarily along a second axis perpendicular to the first axis such that plates in the pairs move towards each other in response to a force applied to the capacitive sensing device, and the gaps decrease in response to the applied force, thereby creating a displacement between the electrode structures in response to the applied force; and

circuitry coupled to the capacitive sensing device for determining from the displacement an electric signal indicative of acceleration of the applied force.

47. The accelerometer of claim 46, wherein the circuitry is configured for passive damping.

48. The accelerometer of claim 47, wherein the circuitry is configured to provide an AC voltage across the electrode structures and measure a resulting AC current.

49. The accelerometer of claim 46, wherein the circuitry is configured for active damping.

50. The accelerometer of claim 49, wherein the circuitry is configured to provide an AC voltage across the electrode structures, produce therefrom a DC voltage proportional to the acceleration, invert the DC voltage, apply the inverted DC voltage to the second electrode structure to return the electrode structures to an initial relative position, and isolate the DC voltage from the capacitive sensing device.

51. The accelerometer of claim 46, wherein the liquid is substantially nonelectrically conductive.

52. The accelerometer of claim 46, wherein the liquid provides damping of the relative movement of the electrode structures.

53. The accelerometer of claim 46, wherein the electrode structures have comb-like shapes.

54. The accelerometer of claim 46, wherein the first electrode structure is movable and the second electrode structure is stationary.

55. The accelerometer of claim 46, further comprising a flexible envelope in which the electrode structures and the liquid are disposed, wherein first and second leads coupled to the first and second electrode structures, respectively, protrude through the envelope, and the liquid contacts and is encased within the envelope.

56. An accelerometer comprising:

a capacitive sensing device that includes first and second electrode structures and a liquid, wherein the first electrode structure includes a plurality of first plates, the second electrode structure includes a plurality of second plates, the first and second plates are interleaved with each other, protrude along a first axis and are arranged in corresponding pairs such that each plate in the pair is closer to the other plate in the pair than to any other plate, gaps are disposed between the plates in the pairs, the liquid is disposed in the gaps and contacts the first and second plates, the electrode structures move towards each other primarily along a second axis perpendicular to the first axis such that each plate in the pair is even closer to the other plate in the pair than to any other plate in response to a force applied to the capacitive sensing device, and the gaps decrease in response to the applied force, thereby creating a displacement between the electrode structures in response to the applied force; and

circuitry coupled to the capacitive sensing device for determining from the displacement an electric signal indicative of acceleration of the applied force.

57. The accelerometer of claim 56, wherein the circuitry is configured for passive damping.

58. The accelerometer of claim 57, wherein the circuitry is configured to provide an AC voltage across the electrode structures and measure a resulting AC current.

59. The accelerometer of claim 56, wherein the circuitry is configured for active damping.

60. The accelerometer of claim 59, wherein the circuitry is configured to provide an AC voltage across the electrode structures, produce therefrom a DC voltage proportional to the acceleration, invert the DC voltage, apply the inverted DC voltage to the second electrode structure to return the electrode structures to an initial relative position, and isolate the DC voltage from the capacitive sensing device.

61. The accelerometer of claim 56, wherein the liquid is substantially nonelectrically conductive.

62. The accelerometer of claim 56, wherein the liquid provides damping of the relative movement of the electrode structures.

63. The accelerometer of claim 56, wherein the electrode structures have comb-like shapes.

64. The accelerometer of claim 56, wherein the first electrode structure is movable and the second electrode structure is stationary.

65. The accelerometer of claim 56, further comprising a flexible envelope in which the electrode structures and the liquid are disposed, wherein first and second leads coupled to the first and second electrode structures, respectively, protrude through the envelope, and the liquid contacts and is encased within the envelope.

66. An accelerometer comprising:

a capacitive sensing device that includes first and second electrode structures and a liquid, wherein a gap is disposed between the electrode structures, the liquid is disposed in the gap and contacts the electrode structures, the electrode structures move towards each other in response to a force applied to the capacitive sensing device, and the gap decreases to a thickness of at least several molecular layers of the liquid and less than about five molecular layers of the liquid in response to the applied force, thereby creating a displacement between the electrode structures in response to the applied force; and

circuitry coupled to the capacitive sensing device for determining from the displacement an electric signal indicative of acceleration of the applied force.

67. The accelerometer of claim 66, wherein the circuitry is configured for passive damping.

68. The accelerometer of claim 67, wherein the circuitry is configured to provide an AC voltage across the electrode structures and measure a resulting AC current.

69. The accelerometer of claim 66, wherein the circuitry is configured for active damping.

70. The accelerometer of claim 69, wherein the circuitry is configured to provide an AC voltage across the electrode structures, produce therefrom a DC voltage proportional to the acceleration, invert the DC voltage, apply the inverted DC voltage to the second electrode structure to return the electrode structures to an initial relative position, and isolate the DC voltage from the capacitive sensing device.

71. The accelerometer of claim 66, wherein the liquid is substantially nonelectrically conductive.

72. The accelerometer of claim 66, wherein the liquid provides damping of the relative movement of the electrode structures.

73. The accelerometer of claim 66, wherein the electrode structures have comb-like shapes with protruding plates that are asymmetrically interleaved with each other.

74. The accelerometer of claim 66, wherein the electrode structures have comb-like shapes with protruding plates that are interleaved with each other and protrude along a first axis, and the electrode structures move towards each other primarily along a second axis perpendicular to the first axis such that corresponding plates move towards each other and non-corresponding plates move away from each other.

75. The accelerometer of claim 66, further comprising a flexible envelope in which the electrode structures and the liquid are disposed, wherein first and second leads coupled to the first and second electrode structures, respectively, protrude through the envelope, and the liquid contacts and is encased within the envelope.

76. An accelerometer comprising:

a capacitive sensing device that includes first and second electrode structures and a liquid, wherein a gap is disposed between the electrode structures, the liquid is disposed in the gap and contacts the electrode structures, the electrode structures move towards each other in response to a force applied to the capacitive sensing device, and the gap decreases in response to the applied force, thereby creating a displacement between the electrode structures in response to the applied force; and

circuitry coupled to the capacitive sensing device for determining from the displacement an electric signal indicative of acceleration of the applied force, wherein the circuitry is configured for active damping and does not apply a fixed DC bias to the electrode structures.

77. The accelerometer of claim 76, wherein the circuitry is configured to provide an AC voltage to the first electrode structure and a DC path from the first electrode structure to ground.

78. The accelerometer of claim 77, wherein the DC path is a transformer.

79. The accelerometer of claim 77, wherein the circuitry is configured to produce from the AC voltage a DC voltage proportional to the acceleration.

80. The accelerometer of claim 79, wherein the circuitry is configured to invert the DC voltage, apply the inverted DC voltage to the second electrode structure to return the electrode structures to an initial relative position, and isolate the DC voltage from the capacitive sensing device.

81. The accelerometer of claim 76, wherein the liquid is substantially nonelectrically conductive.

82. The accelerometer of claim 76, wherein the liquid provides damping of the relative movement of the electrode structures.

83. The accelerometer of claim 76, wherein the electrode structures have comb-like shapes with protruding plates that are asymmetrically interleaved with each other.

84. The accelerometer of claim 76, wherein the electrode structures have comb-like shapes with protruding plates that are interleaved with each other and protrude along a first axis, and the electrode structures move towards each other primarily along a second axis perpendicular to the first axis such that corresponding plates move towards each other and non-corresponding plates move away from each other.

85. The accelerometer of claim 76, further comprising a flexible envelope in which the electrode structures and the liquid are disposed, wherein first and second leads coupled to the first and second electrode structures, respectively, protrude through the envelope, and the liquid contacts and is encased within the envelope.

86. An accelerometer comprising:

a capacitive sensing device that includes first and second electrode structures and a liquid, wherein a gap is disposed between the electrode structures, the liquid is disposed in the gap and contacts the electrode structures, the electrode structures move towards each other in response to a force applied to the capacitive sensing device, and the gap decreases in response to the applied force, thereby creating a displacement between the electrode structures in response to the applied force; and

circuitry coupled to the capacitive sensing device for determining from the displacement an electric signal indicative of acceleration of the applied force, wherein the circuitry is configured for active damping, provides an AC voltage to the first electrode structure, includes a blocking capacitor connected directly to the second electrode structure, an amplifier connected directly to the blocking capacitor, a diode connected directly to the amplifier, and an inverter connected directly to the diode and the second electrode structure, and the blocking capacitor, the amplifier, the diode and the inverter provide a closed-loop feedback path for the second electrode structure.

87. The accelerometer of claim 86, wherein the circuitry is configured to provide a DC path from the first electrode structure to ground.

88. The accelerometer of claim 87, wherein the DC path is a transformer.

89. The accelerometer of claim 87, wherein the circuitry is configured to provide an AC path from a node between the diode and the inverter to ground.

90. The accelerometer of claim 89, wherein the AC path is an RC filter.

91. The accelerometer of claim 86, wherein the liquid is substantially nonelectrically conductive.

92. The accelerometer of claim 86, wherein the liquid provides damping of the relative movement of the electrode structures.

93. The accelerometer of claim 86, wherein the electrode structures have comb-like shapes with protruding plates that are asymmetrically interleaved with each other.

94. The accelerometer of claim 86, wherein the electrode structures have comb-like shapes with protruding plates that are interleaved with each other and protrude along a first axis, and the electrode structures move towards each other primarily along a second axis perpendicular to the first axis such that corresponding plates move towards each other and non-corresponding plates move away from each other.

95. The accelerometer of claim 86, further comprising a flexible envelope in which the electrode structures and the liquid are disposed, wherein first and second leads coupled to the first and second electrode structures, respectively, protrude through the envelope, and the liquid contacts and is encased within the envelope.

96. An accelerometer comprising:

a capacitive sensing device that includes first and second electrode structures, a liquid and a flexible envelope, wherein a gap is disposed between the electrode structures, the liquid is disposed in the gap and contacts the electrode structures, the electrode structures move towards each other in response to a force applied to the capacitive sensing device, the gap decreases in response to the applied force, thereby creating a displacement between the electrode structures in response to the applied force, the electrode structures and the liquid are disposed within the envelope, first and second leads coupled to the first and second electrode structures, respectively, protrude through the envelope, and the liquid contacts and is encased within the envelope; and

circuitry coupled to the capacitive sensing device for determining from the displacement an electric signal indicative of acceleration of the applied force.

97. The accelerometer of claim 96, wherein the circuitry is configured for passive damping.

98. The accelerometer of claim 97, wherein the circuitry is configured to provide an AC voltage across the electrode structures and measure a resulting AC current.

99. The accelerometer of claim 96, wherein the circuitry is configured for active damping.

100. The accelerometer of claim 99, wherein the circuitry is configured to provide an AC voltage across the electrode structures, produce therefrom a DC voltage proportional to the acceleration, invert the DC voltage, apply the inverted DC voltage to the second electrode structure to return the electrode structures to an initial relative position, and isolate the DC voltage from the capacitive sensing device.

101. The accelerometer of claim 96, wherein the liquid is substantially nonelectrically conductive.

102. The accelerometer of claim 96, wherein the liquid provides damping of the relative movement of the electrode structures.

103. The accelerometer of claim 96, wherein the electrode structures have comb-like shapes with protruding plates that are asymmetrically interleaved with each other.

104. The accelerometer of claim 96, wherein the electrode structures have comb-like shapes with protruding plates that are interleaved with each other and protrude along a first axis, and the electrode structures move towards each other primarily along a second axis perpendicular to the first axis such that corresponding plates move towards each other and non-corresponding plates move away from each other.

105. The accelerometer of claim 96, wherein the envelope is a mylar film.

106. An accelerometer comprising:

a capacitive sensing device that includes first and second electrode structures, a liquid and a thin film envelope, wherein a gap is disposed between the electrode structures, the liquid is disposed in the gap and contacts the electrode structures, the electrode structures move towards each other in response to a force applied to the capacitive sensing device, the gap decreases in response to the applied force, thereby creating a displacement between the electrode structures in response to the applied force, the electrode structures and the liquid are disposed within the envelope, first and second leads coupled to the first and second electrode structures, respectively, protrude through the envelope, and the liquid contacts and is encased within the envelope; and

circuitry coupled to the capacitive sensing device for determining from the displacement an electric signal indicative of acceleration of the applied force.

107. The accelerometer of claim 106, wherein the circuitry is configured for passive damping.

108. The accelerometer of claim 107, wherein the circuitry is configured to provide an AC voltage across the electrode structures and measure a resulting AC current.

109. The accelerometer of claim 106, wherein the circuitry is configured for active damping.

110. The accelerometer of claim 109, wherein the circuitry is configured to provide an AC voltage across the electrode structures, produce therefrom a DC voltage proportional to the acceleration, invert the DC voltage, apply the inverted DC voltage to the second electrode structure to return the electrode structures to an initial relative position, and isolate the DC voltage from the capacitive sensing device.

111. The accelerometer of claim 106, wherein the liquid is substantially nonelectrically conductive.

112. The accelerometer of claim 106, wherein the liquid provides damping of the relative movement of the electrode structures.

113. The accelerometer of claim 106, wherein the electrode structures have comb-like shapes with protruding plates that are asymmetrically interleaved with each other.

114. The accelerometer of claim 106, wherein the electrode structures have comb-like shapes with protruding plates that are interleaved with each other and protrude along a first axis, and the electrode structures move towards each other primarily along a second axis perpendicular to the first axis such that corresponding plates move towards each other and non-corresponding plates move away from each other.

115. The accelerometer of claim 106, wherein the envelope is a mylar film.

116. An accelerometer for use in a disk drive that includes an arm, a transducer and a storage medium, wherein the arm moves the transducer across the storage medium and the transducer exchanges data signals with the storage medium, the accelerometer comprising:

a capacitive sensing device that includes first and second electrode structures and a liquid, wherein a gap is disposed between the electrode structures, the liquid is disposed in the gap and contacts the electrode structures, the electrode structures move towards each other in response to a force applied to the capacitive sensing device, the gap decreases in response to the applied force, thereby creating a displacement between the electrode structures in response to the applied force, and the capacitive sensing device is mounted between the arm and the transducer; and

circuitry coupled to the capacitive sensing device for determining from the displacement an electric signal indicative of acceleration of the applied force.

117. The accelerometer of claim 116, wherein the circuitry is configured for passive damping.

118. The accelerometer of claim 117, wherein the circuitry is configured to provide an AC voltage across the electrode structures and measure a resulting AC current.

119. The accelerometer of claim 116, wherein the circuitry is configured for active damping.

120. The accelerometer of claim 119, wherein the circuitry is configured to provide an AC voltage across the electrode structures, produce therefrom a DC voltage proportional to the acceleration, invert the DC voltage, apply the inverted DC voltage to the second electrode structure to return the electrode structures to an initial relative position, and isolate the DC voltage from the capacitive sensing device.

121. The accelerometer of claim 116, wherein the liquid is substantially nonelectrically conductive.

122. The accelerometer of claim 116, wherein the liquid provides damping of the relative movement of the electrode structures.

123. The accelerometer of claim 116, wherein the electrode structures have comb-like shapes with protruding plates that are asymmetrically interleaved with each other.

124. The accelerometer of claim 116, wherein the electrode structures have comb-like shapes with protruding plates that are interleaved with each other and protrude along a first axis, and the electrode structures move towards each other primarily along a second axis perpendicular to the first axis such that corresponding plates move towards each other and non-corresponding plates move away from each other.

125. The accelerometer of claim 116, further comprising a flexible envelope in which the electrode structures and the liquid are disposed, wherein first and second leads coupled to the first and second electrode structures, respectively, protrude through the envelope, and the liquid contacts and is encased within the envelope.