Capacitive transducer

• US 6,006,386 A
• Filed: 04/30/1998
• Issued: 12/28/1999
• Est. Priority Date: 11/16/1995
• Status: Expired due to Fees

• Current Assignee: International Road Dynamics Incorporated (Quarterhill Inc. (f/k/a Wi-LAN Inc.))
• Original Assignee: International Road Dynamics Incorporated (Quarterhill Inc. (f/k/a Wi-LAN Inc.))
• Inventors: Mohaupt, Udo H.
• Primary Examiner(s): Fuller, Benjamin R.
• Assistant Examiner(s): THOMPSON, JEWEL VERGIE
• Application Number:
  US09/066,462
• Time in Patent Office: 607 Days
• Field of Search: 73/862.041-862.043, 73/862.046, 73/862.626, 73/862.68
• US Class Current: 73/862.68
• CPC Class Codes: G01G 7/06 by electrostatic action
• CPC Class Codes: G01L 1/142 using capacitors

Abstract

A capacitance transducer is provided herein for use in measuring loads. It includes a flexible first electrode, a flexible thin film solid dielectric and a fluid dielectric therebetween. A load which is applied to the transducer presses the first electrode, and the thin film dielectric against the second electrode, thereby squeezing out the fluid dielectric to increase the area of the electrodes that are in close proximity. This provides a capacitance transducer that has a significant linear response and an insignificant non-linear response.

Claims

1. A capacitance transducer comprising:

a first electrode;

a second electrode, said second electrode comprising a dielectric plate including a plurality of separate electrodes thereon, said separate electrodes consisting of a plurality of transversely-spaced-apart, longitudinally-extending strips of electrically-conducting material, wherein said first electrode and said second electrode have overlapping surface areas;

a plurality of transversely-spaced-apart, longitudinally-extending first solid dielectric strips which are disposed between said first electrode and said second electrode; and

a second fluid dielectric which is also disposed between said first electrode and said second electrode;

said first electrode and said second electrode being so-oriented that increasing force which is applied to said transducer resiliently presses an increasing portion of said overlapping surface areas of said first electrode and said second electrode into close proximity, but which are separated by said first solid dielectric strips, while substantially-simultaneously removing said second fluid dielectric from areas of close proximity, thereby to cause a capacitance response that depends significantly on the size of areas which are pressed together relative to any capacitance response resulting from a change in the spacing of said first electrode and said second electrode.

2. A capacitance transducer comprising:

a first electrode;

a second electrode, said second electrode comprising a dielectric plate including a plurality of separate electrodes thereon, said separate electrodes consisting of a plurality of transversely-spaced-apart, longitudinally-extending strips of electrically-conducting material, wherein said first electrode and said second electrode have overlapping surface areas;

a plurality of transversely-spaced-apart, longitudinally-extending first rigid dielectric strips which are disposed between said first electrode and said second electrode;

a second fluid dielectric which is also disposed between said first electrode and said second electrode; and

means for orienting said first electrode with respect to said second electrode so that increasing force which is applied to said transducer resiliently presses an increasing portion of said overlapping surface areas of said first electrode and said second electrode into closer proximity, while being separated by said first rigid dielectric strips, and while substantially-simultaneously removing said second fluid dielectric from areas of close proximity, thereby to cause a capacitance response that depends significantly on the size of said areas which are pressed together relative to any capacitance response resulting from a change in said spacing of said electrodes;

thereby to provide a capacitance transducer that has a significant linear response and an insignificant non-linear response.

3. A capacitance transducer comprising:

a first electrode;

a second electrode, said second electrode comprising a dielectric plate which includes a plurality of separate electrodes thereon, said separate electrodes consisting of a plurality of transversely-spaced-apart, longitudinally-extending strips of electrically-conducting material, wherein said first electrode and said second electrode have overlapping surface areas;

a plurality of transversely-spaced-apart, longitudinally-extending first rigid dielectric strips which are disposed between said first electrode and said second electrode;

a second fluid dielectric which is also disposed between said first electrode and said second electrode; and

means for orienting said first electrode with respect to said second electrode so that increasing force which is applied to said transducer resiliently presses an increasing portion of overlapping surface areas of said first electrode and said second electrode into closer proximity while being separated by said first rigid dielectric strips, and while substantially-simultaneously removing said second fluid dielectric from areas of close proximity, thereby to cause a capacitance response that depends significantly on the size of the areas which are pressed together relative to any capacitance response resulting from a change in said spacing of the electrodes, and wherein portions of said first electrode which are not pressed close to said second electrode are farther from said second electrode, said further portions being separated from said second electrode both by said rigid dielectric strips and by said second fluid dielectric that occupies said space between said electrodes;

thereby to provide a capacitance transducer that has a significant linear response and an insignificant non-linear response.

4. The capacitance transducer according to claim 3 wherein one or both of said first electrode and said second electrode are flexible, thereby to enable them to deflect to press together.

5. The capacitance transducer according to claim 3 wherein said first electrode and said second electrode have two opposing portions which are inclined with respect to one another, whereby an increasingly-greater area is produced as said electrodes are pressed together and deflect towards one another.

6. The capacitance transducer according to claim 5 wherein said inclined portions are provided by appropriate selection of material and dimensions of one or both of said first electrode and said second electrode to cause a linear increase in the effective area as said electrodes are pressed together and deflect towards one another.

7. The capacitance transducer according to claim 3 wherein one or both of said first electrode and said second electrode are constructed to bend towards one another, whereby oppositely-bending curves of each are pressed increasingly together by compression.

8. The capacitance transducer according to claim 3 wherein said first electrode and said second electrode are constructed from different materials, and thereby have different physical characteristics.

9. The capacitance transducer according to claim 8, wherein said first electrode comprises a thin sheet of aluminum, and wherein said second electrode comprises a sheet of flexible, thin, substantially-incompressible insulation material whose underside is coated with a plurality of transversely-spaced-apart, longitudinally-extending strips of copper.

10. The capacitance transducer according to claim 3, wherein said first rigid dielectric comprises thin transversely-spaced-apart strips of dielectric material, the thickness of said thin strips of dielectric material being less than the distance between said first electrode and said second electrode.

11. The capacitance transducer according to claim 9 wherein said solid flexible, thin, substantially-incompressible insulator material comprises nylon which has a gradual change in thickness, thereby creating an effect on capacitance to balance or offset another effect.

12. The capacitance transducer according to claim 9, wherein said solid flexible, thin, substantially-incompressible insulator material comprises fiberglass which has a gradual change in thickness, thereby creating an effect on capacitance to balance or offset another effect.

13. The capacitance transducer according to claim 10, wherein said first electrode or said second electrode are bonded to said flexible, thin, substantially-incompressible insulator material.

14. The capacitance transducer according to claim 3 wherein said second electrode comprises a thin flexible sheet of synthetic plastics material on which a thin film of copper has been deposited, and the transverse spaces between said electrode strips are then etched.

15. The capacitance transducer according to claim 3 wherein said second fluid dielectric occupies the space between said first electrode, between said second electrode and between said first rigid dielectric when said first electrode and said second electrode are not pressed together;

and wherein said second fluid dielectric may move into and out of said space as said first electrode and said second electrode deflect and resiliently deform.

16. The capacitance transducer according to claim 3, wherein said capacitance transducer comprises a closed chamber.

17. The capacitance transducer according to claim 16, wherein said second fluid dielectric comprises air.

18. The capacitance transducer according to claim 16, wherein said second fluid dielectric comprises a compressible fluid, thereby to accommodate for any volume change which results from deflection of said first electrode and said second electrode.

19. The capacitance transducer according to claim 16, wherein said second fluid dielectric comprises a vacuum.

20. The capacitance transducer according to claim 3 wherein said first electrode and said second electrode comprise one set of a plurality of sets of said first electrode and said second electrode.

21. A capacitance mat for use in measuring loads, comprising:

a vertically-stacked sandwich of at least a pair of vertically-spaced-apart, first electrode plate and second electrode plate forming a capacitor, a lower one of said first electrode plate and said second electrode plate comprising a laminate of an insulator dielectric substrate and a plurality of separate electrodes consisting of a plurality of transversely-spaced-apart, longitudinally-extending strips of electrically-conducting material;

a first rigid dielectric, said first rigid dielectric comprising a plurality of laterally-spaced-apart, substantially-rigid, dielectric material separator strips which are disposed between each adjacent pair of said stack of vertically-spaced-apart, first electrode plate and said second electrode plate, thereby to separate said each adjacent pair of said vertically-spaced-apart first and second electrode plates, said substantially-rigid dielectric material separator strips being offset in different levels of said vertically-stacked sandwich, and being disposed to run parallel to one another in said different levels of said vertically-stacked sandwich, said substantially-rigid dielectric material separator strips thereby defining spaces into which at least one of said electrode plates may bend in response to an applied load, so that selected portions of said dielectric material separator strips are in contact with a substantially-horizontal electrode plate which is immediately above it in response to that applied load, and whereby a lower electrode is pressed against an upper electrode, causing capacitance of said mat to change; and

a second fluid dielectric;

thereby to provide a capacitance transducer mat that has a significant linear response and an insignificant non-linear response.

22. The capacitance mat according to claim 21, wherein one or both of said first electrode and said second electrode-coated dielectric plate are flexible, thereby to enable them to press together.

23. The capacitance mat according to claim 21, wherein said first electrode plate and said second electrode plate have two opposing portions which are inclined with respect to one another, whereby an increasingly-greater area is produced as said electrode plates are pressed together and deflect towards one another.

24. The capacitance mat according to claim 23, wherein said inclined portions are provided by appropriate selection of material and dimensions of one or both of said first electrode and said second electrode to cause a linear increase in said effective area as said electrode are pressed together and deflect towards one another.

25. The capacitance mat according to claim 21, wherein one or both of said first electrode plate and said second electrode plate are constructed to bend towards one another, whereby oppositely-bending curves of each are pressed increasingly together by compression.

26. The capacitance mat according to claim 21, wherein said first electrode plate and said second electrode plate are constituted of different materials and thereby have different physical characteristics.

27. The capacitance mat according to claim 21, wherein said first electrode plate is coated with a thin layer of copper and wherein said second electrode plate is coated with a thin layer of transversely-spaced-apart, longitudinally-extending strips of aluminum, said second electrode plate having greater strength and thickness than said first electrode plate.

28. The capacitance mat according to claim 21, wherein said first rigid dielectric comprises a plurality of transversely-spaced-apart thin strips of dielectric material, the thickness of said thin strips of dielectric material being less than said distance between said first electrode plate and said second electrode plate.

29. The capacitance mat according to claim 28, wherein said plurality of transversely-spaced-apart, longitudinally-extending dielectric strips each have a substantially-constant thickness.

30. The capacitance mat according to claim 28, wherein said plurality of transversely-spaced-apart, longitudinally-extending dielectric strips each have a gradual change in thickness, thereby creating a desired effect on capacitance to balance or offset an undesired effect.

31. The capacitance mat according to claim 21, wherein a lower one of said electrode plates comprises a thin flexible sheet of synthetic plastics material on which thin films of transversely-spaced-apart, longitudinally-extending strips of copper have been deposited.

32. The capacitance mat according to claim 31, wherein a uniform film of copper has been first deposited, and said second electrode is then shaped by etching.

33. The capacitance mat according to claim 21, wherein said second fluid dielectric occupies the space between said first electrode plate and said second electrode plate when said first electrode plate and said second electrode plate are not pressed together, and whereby said second fluid dielectric may move into and out of said space as said first electrode plate and said second electrode plate deflect and resiliently deform.

34. The capacitance mat according to claim 21, wherein said capacitor transducer comprises a closed chamber.

35. The capacitance mat according to claim 34, wherein said second fluid dielectric comprises air.

36. The capacitance mat according to claim 34, wherein said second fluid dielectric comprises a compressible fluid, thereby to accommodate for any volume change which results from deflections of said first electrode plate and said second electrode plate.

37. The capacitance mat according to claim 34, wherein said second fluid dielectric comprises a vacuum.

38. A capacitance transducer comprising:

a first electrode and a second electrode, said first electrode and said second electrode having overlapping surface areas which are spaced apart by a first solid dielectric, said first solid dielectric comprising a plurality of transversely-spaced-apart thin strips of dielectric material, the thickness of said thin strips of dielectric material being less than the distance between said first electrode and said second electrode, and by a second fluid dielectric, said second fluid dielectric occupying the space between said first electrode, between said second electrode and between said first solid dielectric when said first electrode and said second electrode are not pressed together, and said second fluid dielectric being movable into and out of said space as said first electrode and said second electrode deflect and resiliently deform; and

means for orienting said first electrode with respect to said second electrode so that increasing force which is applied to said transducer resiliently presses an increasing portion of overlapping surface areas of said first electrode and said electrode into closer proximity while being separated by said first solid dielectric strips and while substantially-simultaneously removing said second fluid dielectric from areas of close proximity, thereby to cause a capacitance response that depends significantly on the size of the areas which are pressed together relative to any capacitance response resulting from a change in the spacing of the electrodes, and wherein further portions of said first electrode which are not pressed close to said second electrode are farther from said second electrode, said further portions being separated from said second electrode by said first solid dielectric strips and also by said second fluid dielectric that occupies said space between said electrodes;

thereby to provide a capacitance transducer that has a significant linear response and an insignificant non-linear response.

39. The capacitance transducer according to claim 38, wherein said capacitance transducer comprises a closed chamber.

40. The capacitance transducer according to claim 39, wherein said second fluid dielectric comprises air.

41. The capacitance transducer according to claim 39, wherein said second fluid dielectric comprises a compressible fluid, thereby to accommodate for any volume change which results from deflections of said first electrode and said second electrode.

42. The capacitance transducer according to claim 39, wherein said second fluid dielectric comprises a vacuum.