Capacitive pressure sensor having encapsulated resonating components

• US 20040035211A1
• Filed: 03/18/2003
• Published: 02/26/2004
• Est. Priority Date: 08/06/1999
• Status: Abandoned Application

• Current Assignee: Setra Systems Incorporated (Fortive Corp.)
• Original Assignee: Setra Systems Incorporated (Fortive Corp.)
• Inventors: Vaughan, Kevin, Pinto, Gino A.
• Application Number:
  US10/391,064
• Publication Number:
  US 20040035211A1
• Time in Patent Office: Days
• US Class Current: 73/718
• CPC Class Codes: G01L 9/0072 using variations in capacitance

Abstract

A capacitive pressure sensor for measuring a pressure applied to an elastic member includes a capacitive plate disposed adjacent to the elastic member so as to define a gap between a planar conductive surface of the elastic member and a corresponding planar surface of the capacitive plate. The gap, capacitive plate and elastic member together define a capacitor having a characteristic capacitance. The sensor further includes an elongated electrical conductor characterized by an associated inductance value. The conductor is fixedly attached to and electrically coupled with the capacitive plate. The gap between the capacitive plate and the elastic member varies as a predetermined function of the pressure applied to the elastic member so as to vary the characteristic capacitance. The capacitor and the electrical conductor together form an electrical resonator having a characteristic resonant frequency. Varying the capacitance of this tank circuit varies the resonant frequency of the tank circuit. Thus, the resonant frequency of the tank circuit is indicative of the pressure applied to the elastic member. The close physical proximity of the capacitor and the electrical conductor equalizes the effects of environmental influences such as temperature variations, vibration and shock, thus making such effects more predictable.

Claims

1. A capacitive pressure sensor comprising:

an elastic member having a first side and a second side, said elastic member comprising a conductive surface at said first side;

a support member supporting an edge of said elastic member, wherein said support member and said elastic member separate two pressure regions across said elastic member, a first pressure region contiguous with said first side of said elastic member and a second pressure region contiguous with said second side of said elastic member, wherein a central portion of said elastic member is displaceable along an axis in response to a pressure differential between said two pressure regions across said elastic member;

an electrically conductive, capacitive plate disposed substantially adjacent to said elastic member so as to define a gap between said first side of said elastic member and said capacitive plate, wherein said gap, capacitive plate and elastic member define a capacitor having a characteristic capacitance; and

,

an elongated electrical conductor characterized by an associated inductance value, said conductor being fixedly attached, along a substantial portion of its entire length, to said capacitive plate;

wherein said capacitor and said electrical conductor are electrically coupled to form a resonant tank circuit;

wherein said gap varies as a predetermined function of the pressure differential between said two pressure regions across said elastic member so as to vary said characteristic capacitance, and consequently vary a resonant frequency of said tank circuit.

2. A capacitive pressure sensor according to claim 1, wherein said first pressure region is a sealed region.

3. A capacitive pressure sensor according to claim 2, wherein said first sealed pressure region is vacuum.

4. A sensor according to claim 1, wherein said electrical conductor is disposed in a spiral configuration within a plane substantially parallel to said capacitive plate.

5. A sensor according to claim 1, further including an insulator disposed between and fixedly attached to said capacitive plate and said electrical conductor.

6. A sensor according to claim 1, further including a stiffening element fixedly attached to said electrical conductor.

7. A sensor according to claim 6, wherein said stiffening element includes a ceramic material.

8. A sensor according to claim 1, wherein said electrical conductor includes at least two layers of electrical conductors separated by alternating layers of insulating material, each said at least two layers of electrical conductors being spirally disposed within a plane parallel to other said layers of electrical conductors and being electrically coupled to adjacent layers of electrical conductors.

9. A sensor according to claim 1, wherein said elastic member is electrically conductive.

10. A sensor according to claim 1, wherein said elastic member is non-electrically conductive and includes a plated surface forming said conductive surface.

11. A sensor according to claim 1, wherein said resonant tank circuit includes a parallel coupling of said capacitor and said elongated conductor.

12. A sensor according to claim 1, wherein said resonant tank circuit includes a series coupling of said capacitor and said elongated conductor.

13. A sensor according to claim 1, wherein said first pressure region comprises a chamber having at least one port.

14. A sensor according to claim 1, wherein said second pressure region comprises a chamber having at least one port.

15. A sensor according to claim 1, wherein a central portion of said capacitive plate is supported by a rigid structure extending from said central portion of said elastic member.

16. A sensor according to claim 1, wherein said capacitive plate is supported by way of a rigid structure connected to said support member.

17. A capacitive pressure sensor comprising:

an elastic member having a first side and a second side, said elastic member comprising a conductive surface at said first side;

a housing for supporting said elastic member, said elastic member and said housing forming a first pressure region contiguous with said first side of said elastic member, and a second pressure region contiguous with said second side of said elastic member, wherein said first pressure region and said second pressure region generate a pressure differential across said elastic member, wherein a central portion of said elastic member is displaceable along an axis in response to the pressure differential;

a capacitive plate disposed substantially parallel to said elastic member so as to define a gap between said conductive surface and a corresponding surface of said capacitive plate, said gap, capacitive plate and elastic member defining a capacitor having a characteristic capacitance; and

,

an elongated electrical conductor characterized by an inductance value and fixedly attached, along a substantial portion of its entire length, to said capacitive plate;

wherein said capacitor and said electrical conductor are electrically coupled to form a resonant tank circuit;

wherein said gap varies as a predetermined function of said pressure differential across said elastic member so as to vary said characteristic capacitance, and consequently vary a resonant frequency of said tank circuit.

18. A capacitive pressure sensor according to claim 17, wherein said first pressure region is characterized by a constant and controlled pressure value.

19. A sensor according to claim 17, wherein said electrical conductor is disposed in a spiral configuration within a plane substantially parallel to said capacitive plate.

20. A sensor according to claim 17, further including an insulator disposed between and fixedly attached to said capacitive plate and said electrical conductor.

21. A sensor according to claim 17, further including a stiffening element fixedly attached to said electrical conductor.

22. A sensor according to claim 21, wherein said stiffening element includes a ceramic material.

23. A sensor according to claim 17, wherein said electrical conductor includes at least two layers of electrical conductors separated by alternating layers of insulating material, each said at least two layers of electrical conductors being spirally disposed within a plane parallel to other said layers of electrical conductors and being electrically coupled to adjacent layers of electrical conductors.

24. A sensor according to claim 17, wherein said elastic member is electrically conductive.

25. A sensor according to claim 17, wherein said elastic member is non-electrically conductive and includes a plated surface forming said conductive surface.

26. A sensor according to claim 17, wherein said resonant tank circuit includes a parallel coupling of said capacitor and said elongated conductor.

27. A sensor according to claim 17, wherein said resonant tank circuit includes a series coupling of said capacitor and said elongated conductor.

28. A sensor according to claim 17, wherein said first pressure region comprises a chamber having at least one port.

29. A sensor according to claim 17, wherein said second pressure region comprises a chamber having at least one port.

30. A sensor according to claim 17, wherein a central portion of said capacitive plate is supported by a rigid structure extending from said central portion of said elastic member.

31. A sensor according to claim 17, wherein said capacitive plate is supported by way of a rigid structure connected to said housing.

32. A sensor for measuring a pressure differential across an elastic member having at least a first substantially planar, electrically conductive surface and being supported by at least one edge, comprising:

a housing for supporting said elastic member by said edge, forming (i) a first pressure region disposed on a first side of said elastic member corresponding to said first planar surface, and (ii) a second pressure region disposed on a second side of said elastic member opposite said first side, wherein said first pressure region and said second pressure region generate said pressure differential across said elastic member, and wherein a central portion of said elastic member is displaceable along an axis in response to said pressure differential;

an electrically conductive, capacitive plate disposed substantially adjacent to said elastic member so as to define a gap between said first planar surface and a corresponding planar surface of said capacitive plate, said gap, capacitive plate and elastic member defining a capacitor having a characteristic capacitance; and

,

an elongated electrical conductor characterized by an associated inductance value, disposed, along a substantial portion of its entire length, upon a substrate in a substantially planar configuration;

wherein said capacitor and said electrical conductor are electrically coupled to form a resonant tank circuit;

wherein said gap varies as a predetermined function of said pressure differential so as to vary said characteristic capacitance, and consequently vary a resonant frequency of said tank circuit.

33. A sensor according to claim 32, wherein said capacitive plate is disposed within said housing and said elongated conductor is disposed outside of said housing.

34. A sensor according to claim 32, wherein said capacitive plate and said elongated conductor are each electrically coupled to a conductive post.

35. A sensor according to claim 32, wherein said conductive post extends through and is fixedly attached to said housing via an electrically non-conductive sleeve, said capacitive plate is fixedly attached to a portion of said post extending into said housing, and said elongated conductor is fixedly attached to a portion of said post extending out of said housing.

36. A sensor according to claim 32, wherein said elongated conductor is fixedly attached to an insulating substrate.

37. A sensor according to claim 32, wherein said resonant tank circuit includes a parallel coupling of said capacitor and said elongated conductor.

38. A sensor according to claim 32, wherein said resonant tank circuit includes a series coupling of said capacitor and said elongated conductor.

39. A sensor according to claim 32, wherein said first pressure region comprises a chamber having at least one port.

40. A sensor according to claim 32, wherein said second pressure region comprises a chamber having at least one port.

41. A sensor according to claim 32, wherein a central portion of said capacitive plate is supported by a rigid structure extending from said central portion of said elastic member.

42. A sensor according to claim 32, wherein said capacitive plate is supported by way of a rigid structure connected to said housing.