Apparatus and methods for measuring the dielectric and geometric properties of materials

• US 5,223,796 A
• Filed: 05/28/1991
• Issued: 06/29/1993
• Est. Priority Date: 05/28/1991
• Status: Expired due to Fees

• Current Assignee: Axiomatics Incorporated (Axiomatics AB)
• Original Assignee: Axiomatics Incorporated (Axiomatics AB)
• Inventors: Waldman, Francis A., von Guttenberg, Philip A.
• Primary Examiner(s): Harvey, Jack B.
• Assistant Examiner(s): Regan, Maura K.
• Application Number:
  US07/706,406
• Time in Patent Office: 763 Days
• Field of Search: 324/686, 324/687, 324/688, 324/663, 324/661, 324/662, 324/670, 324/671, 324/649, 324/652, 73/61 R, 73/61.1 R
• US Class Current: 324/687
• CPC Class Codes: G01R 27/2676 Probes
• CPC Class Codes: H03K 2217/960775 Emitter-receiver or "fringe" type detection, i.e. one or more field emitting electrodes and corresponding one or more receiving electrodes

Abstract

Apparatus and methods for measuring the properties of a material by employing a driven electrode, a sensing electrode and a shunting electrode. The shunting electrode is disposed in proximity to the driven and sensing electrodes and functions to increase the sensitivity of electrical measurements made between the driven and sensing electrodes by influencing the coupling of the imposed electric field to the sensing electrode to a degree related to the properties of the material under test.

Claims

1. A sensor for measuring properties of a material under test, the sensor comprising:

an electrode pair comprising a driven electrode and a sensing electrode disposed in proximity to a material under test;

terminal means for connecting said driven electrode to electrical signal generating means for providing an electrical signal to said driven electrode to generate an electric field which couples to said sensing electrode thereby generating an electrical signal at said sensing electrode;

terminal means for connecting said sensing electrode to electrical signal receiving means for receiving the signal at said sensing electrode; and

a shunting electrode to shunt a portion of said electric field away from said sensing electrode, the shunting electrode having a width greater than that of the driven electrode and of the sensing electrode, disposed at a position in external proximity to said electrode pair and in proximity to the material under test, and held at an electrical potential, the position, width, and electrical potential of said shunting electrode selected to vary the coupling of the electric field to the sensing electrode as a function of the properties of the material under test and to permit measurement of properties of the material under test from the signal at the sensing electrode with a sensitivity significantly greater than that possible in the absence of said shunting electrode.

2. The sensor of claim 1 wherein the electrical signal provided to the driven electrode is an AC signal.

3. The sensor of claim 1 wherein the shunting electrode is maintained at a fixed potential.

4. The sensor of claim 1 wherein the shunting electrode is maintained at ground potential.

5. The sensor of claim 1 wherein the electrodes are substantially flat and the shunting electrode has a substantially greater surface area than the sensing electrode.

6. The sensor of claim 1 wherein the electrodes are formed as parallel strips of a conducting material.

7. The sensor of claim 1 wherein the electrodes are formed as concentric rings of a conducting material.

8. The sensor of claim 6 or 7 wherein the shunting electrode is wider than the sensing electrode and the driven electrode.

9. The sensor of claim 1 wherein one of the electrodes of said electrode pair is formed of two distinct but electrically connected conducting structures disposed on either side of the other electrode of the electrode pair, and wherein said shunting electrode is formed of two distinct but electrically connected conducting structures disposed on either side of the electrode pair.

10. The sensor of claim 1 wherein one of the electrodes of said electrode pair is formed as a first strip of a conducting material and the other electrode of said electrode pair is formed as electrically-connected second and third strips of a conducting material, the second and third strips disposed parallel to said first strip, one on each side of said first strip, and wherein said shunting electrode is formed as electrically-connected fourth and fifth strips of a conducting material, the fourth and fifth strips disposed parallel to the first, second, and third strips, the fourth strip adjacent to the second strip, and the fifth strip adjacent to the third strip.

11. The sensor of claim 10 wherein the first, second, and third strips are approximately the same length, wherein the width of the first strip is approximately twice the widths of the second and third strips, and wherein the distances between the first and the second strips and between the first and the third strips are approximately equal to the width of the second and third strips.

12. The sensor of claim 11 wherein the fourth and fifth strips have approximately the same length as the first, second, and third strips, wherein the fourth and fifth strips are wider than the first, second, and third strips, and wherein the distances between the second and fourth strips and between the third and fifth strips are approximately equal to the width of the second and third strips.

13. The sensor of claim 1 further comprising a ground electrode disposed in proximity to the driven, sensing, and shunting electrodes.

14. The sensor of claim 1 wherein the electrodes are formed on an insulating substrate having a grounded back plane.

15. The sensor of claim 14 wherein said grounded back plane and said shunting electrode are electrically connected.

16. The sensor of claim 14 wherein said grounded back plane and said shunting electrode are formed of a continuous strip of a conducting material.

17. The sensor of claim 1 wherein the driven, sensing, and shunting electrodes are separated from the material under test by an insulating layer.

18. The sensor of claim 1 wherein the shunting electrode is exposed to the material under test.

19. The sensor of claim 1 wherein the shunting electrode is porous and exposed to the material under test, whereby the material under test flows through the shunting electrode.

20. The sensor of claim 1 wherein the driven, sensing, and shunting electrodes are substantially flat and coplanar.

21. The sensor of claim 1 wherein the sensor is flexible.

22. The sensor of claim 1 wherein the driven, sensing, and shunting electrodes are disposed on a wall of a pipe through which the material under test flows.

23. The sensor of claim 1 wherein the driven and sensing electrodes are disposed on and insulated from an inner wall of a conducting pipe through which the material under test flows, whereby the conducting pipe itself functions as the shunting electrode and as a ground plane.

24. The sensor of claim 1 wherein the driven, sensing, and shunting electrodes are disposed on an outer wall of an insulating structure containing the material under test.

25. The sensor of claim 1 wherein said driven and sensing electrodes are disposed in a first plane and said shunting electrode is disposed in a second plane parallel to said first plane.

26. The sensor of claim 1 wherein said driven and sensing electrodes are disposed along a first cylinder and said shunting electrode is disposed along a second cylinder concentric with said first cylinder.

27. The sensor of claim 1 further comprising temperature sensing means for measuring the temperature of the material under test.

28. Apparatus for measuring properties of a material under test, the apparatus comprising:

an electrode pair comprising a driven electrode and a sensing electrode disposed in proximity to a material under test;

electrical signal generating means connected to said driven electrode for providing an electrical signal to said driven electrode to generate an electric field which couples to said sensing electrode thereby generating an electrical signal at said sensing electrode;

electrical signal receiving means connected to said sensing electrode for receiving the signal at said sensing electrode;

a shunting electrode to shunt a portion of said electric field away from said sensing electrode, the shunting electrode having a width greater than that of the driven electrode and of the sensing electrode, disposed at a position in proximity to said electrode pair and in proximity to the material under test, and held at an electrical potential, the position, width, and electrical potential of said shunting electrode selected to vary the coupling of the electric field to the sensing electrode as a function of the properties of the material under test;

measurement apparatus for measuring an electrical parameter or parameters describing the coupling of the electric field between the driven electrode and the sensing electrode, the measurement made in response to the electrical signals at the driven and sensing electrodes; and

computing apparatus for estimating one or more quantities relating to the properties of the material under test from the measured parameters with a sensitivity significantly greater than that possible in the absence of said shunting electrode.

29. The apparatus of claim 28 wherein the shunting electrode is disposed externally to the driven and sensing electrodes of said electrode pair.

30. The apparatus of claim 28 wherein the electrical signal provided to the driven electrode is an AC signal.

31. The apparatus of claim 28 wherein the shunting electrode is maintained at a fixed potential.

32. The apparatus of claim 28 wherein the shunting electrode is maintained at ground potential.

33. The apparatus of claim 28 wherein the electrodes are substantially flat and the shunting electrode has a substantially greater surface area than the sensing electrode.

34. The apparatus of claim 28 wherein the electrodes are formed as parallel strips of a conducting material.

35. The apparatus of claim 28 wherein the electrodes are formed as concentric rings of a conducting material.

36. The apparatus of claim 34 or 35 wherein the shunting electrode is wider than the sensing electrode and the driven electrode.

37. The apparatus of claim 28 wherein one of the electrodes of said electrode pair is formed of two distinct but electrically connected conducting structures disposed on either side of the other electrode of the electrode pair, and wherein said shunting electrode is formed of two distinct but electrically connected conducting structures disposed on either side of the electrode pair.

38. The apparatus of claim 28 wherein one of the electrodes of said electrode pair is formed as a first strip of a conducting material and the other electrode of said electrode pair is formed as electrically-connected second and third strips of a conducting material, the second and third strips disposed parallel to said first strip, one on each side of said first strip, and wherein said shunting electrode is formed as electrically-connected fourth and fifth strips of a conducting material, the fourth and fifth strips disposed parallel to the first, second, and third strips, the fourth strip adjacent to the second strip, and the fifth strip adjacent to the third strip.

39. The apparatus of claim 38 wherein the first, second, and third strips are approximately the same length, wherein the width of the first strip is approximately twice the widths of the second and third strips, and wherein the distances between the first and the second strips and between the first and the third strips are approximately equal to the width of the second and third strips.

40. The apparatus of claim 39 wherein the fourth and fifth strips have approximately the same length as the first, second, and third strips, wherein the fourth and fifth strips are wider than the first, second, and third strips, and wherein the distances between the second and fourth strips and between the third and fifth strips are approximately equal to the width of the second and third strips.

41. The apparatus of claim 28 further comprising a ground electrode disposed in proximity to the driven, sensing, and shunting electrodes.

42. The apparatus of claim 28 wherein the electrodes are formed on an insulating substrate having a grounded back plane.

43. The apparatus of claim 42 wherein said grounded back plane and said shunting electrode are electrically connected.

44. The apparatus of claim 42 wherein said grounded back plane and said shunting electrode are formed of a continuous strip of a conducting material.

45. The apparatus of claim 28 wherein the driven, sensing, and shunting electrodes are separated from the material under test by an insulating layer.

46. The apparatus of claim 28 wherein the shunting electrode is exposed to the material under test.

47. The apparatus of claim 28 wherein the shunting electrode is porous and exposed to the material under test, whereby the material under test flows through the shunting electrode.

48. The apparatus of claim 28 wherein the driven, sensing, and shunting electrodes are substantially flat and coplanar.

49. The apparatus of claim 28 wherein the driven, sensing, and shunting electrodes are flexible.

50. The apparatus of claim 28 wherein the driven, sensing, and shunting electrodes are disposed on a wall of a pipe through which the material under test flows.

51. The apparatus of claim 28 wherein the driven and sensing electrodes are disposed on and insulated from an inner wall of a conducting pipe through which the material under test flows, whereby the conducting pipe itself functions as the shunting electrodes and as a ground plane.

52. The apparatus of claim 28 wherein the driven, sensing, and shunting electrodes are disposed on an outer wall of an insulating structure containing the material under test.

53. The apparatus of claim 28 wherein said driven and sensing electrodes are disposed in a first plane and said shunting electrode is disposed in a second plane parallel to said first plane.

54. The sensor of claim 28 wherein said driven and sensing electrodes are disposed along a first cylinder and said shunting electrode is disposed along a second cylinder concentric with said first cylinder.

55. The apparatus of claim 28 further comprising temperature sensing means for measuring the temperature of the material under test.

56. A method for measuring the properties of a material under test comprising:

disposing an electrode pair in proximity to a material under test, said electrode pair comprising a driven electrode and a sensing electrode;

providing an electrical signal to said driven electrode to generate an electric field which couples to said sensing electrode thereby generating an electrical signal at said sensing electrode;

disposing a shunting electrode having a width greater than that of the driven electrode and of the sensing electrode at a position in proximity to said electrode pair and said material under test, and holding said shunting electrode at an electrical potential to shunt a portion of said electric field away from said sensing electrode, the position, width, and electrical potential of said shunting electrode selected to vary the coupling of the electric field to the sensing electrode as a function of the properties of the material under test;

measuring an electrical parameter or parameters describing the coupling of the electric field between the driven electrode and the sensing electrode, the measurement made in response to the electrical signals at the driven and sensing electrodes; and

estimating one or more quantities relating to the properties of the material under test from the measured parameters with a sensitivity significantly greater than that possible in the absence of said shunting electrode.

57. The method of claim 56 wherein the electrical parameter is a complex transfer admittance measured between the driven electrode and the sensing electrode.

58. The method of claim 56 wherein the electrical parameter is a complex gain measured between the driven electrode and the sensing electrode.

59. The method of claim 56 wherein the electrodes are incorporated in an RLC circuit and wherein the electrical parameters are resonant frequency and Q factor.

60. The method of claim 56 wherein said at least one quantity includes the permittivity of the material under test.

61. The method of claim 56 wherein said at least one quantity includes the conduction and/or dielectric losses of the material under test.

62. The method of claim 56 wherein said at least one quantity includes the thickness of the material under test.

63. The method of claim 56 wherein said at least one quantity includes the spatial relationship of the electrodes relative to the material under test.

64. The method of claim 56 wherein said at least one quantity includes a quantity representative of a property of the material under test that affects the permittivity and/or the conduction and/or dielectric losses of the material under test.

65. The method of claim 64 wherein said quantity is a concentration of a solute in a solvent.

66. The method of claim 64 wherein said quantity is a degree of emulsification.

67. The method of claim 56 further comprising selecting the size of the shunting electrode to provide optimum sensitivity for a measurement of interest.

68. The method of claim 56 further comprising selecting the frequency of the driving electrical signal to provide optimum sensitivity for a measurement of interest.

69. The method of claim 56 wherein the electrical parameter or parameters are measured at a plurality of frequencies to quantify properties of multi-component materials under test.

70. The method of claim 56 wherein said at least one quantity is estimated using parameter estimation techniques.