Eddy current sensor arrays

• US 20030071615A1
• Filed: 03/19/2002
• Published: 04/17/2003
• Est. Priority Date: 03/19/2001
• Status: Active Grant

• Current Assignee: Jentek Sensors, Inc.
• Original Assignee: Jentek Sensors
• Inventors: Goldfine, Neil J., Grundy, David C., Schlicker, Darrell E., Washabaugh, Andrew P., Shay, Ian C., Walrath, Karen E., Windoloski, Mark
• Granted Patent: US 6,784,662 B2
• Time in Patent Office: Days
• US Class Current: 324/242
• CPC Class Codes: G01N 27/82 for investigating the presence of flaws
• CPC Class Codes: G01N 27/9006 Details, e.g. in the structure or functioning of sensors
• CPC Class Codes: G01N 27/902 by moving the sensors
• CPC Class Codes: G01N 27/904 with two or more sensors

Abstract

An apparatus for the nondestructive measurements of materials. Eddy current sensing arrays are described which provide a capability for high resolution imaging of test materials and also a high probabilitity of detection for defects. These arrays incorporate layouts for the sensing elements which take advantage of microfabrication manufacturing capabilities for creating essentially identical sensor arrays, aligning sensing elements in proximity to the drive elements, and laying out conductive pathways that promote cancellation of undesired magnetic flux.

Claims

1. A test circuit comprising:

a primary winding of parallel conducting segments including at least four extended portions to impose a spatially periodic magnetic field of at least two spatial wavelengths in a test material when driven by an electric current;

a plurality of sense elements for sensing the response to the imposed magnetic field, the sensing area of each sensing element positioned between the extended portions of the primary winding, the plurality of sensing elements being aligned with one another to sense the response at incremental areas along a path parallel to the extended portions of the primary winding, and having separate output connections; and

at least one sensing element is a magnetoresistive sensor.

2. A test circuit as claimed in claim 1 wherein at least one of the sensing elements is inductive to sense the time varying magnetic flux.

3. A test circuit as claimed in claim 1 wherein all of the sensing elements are magnetoresistive to sense magnetic field intensity.

4. A test circuit as claimed in claim 1 wherein the at least one sensing element is a giant magnetoresistive sensor.

5. A test circuit as claimed in claim 4 wherein at least one of the sensing elements is inductive to sense the time varying magnetic flux.

6. A test circuit as claimed in claim 4 wherein all the sensing elements are giant magnetoresistive.

7. A test circuit as claimed in claim 4 further comprising a secondary coil that surrounds the at least one giant magnetoresistive sensing element.

8. A test circuit as claimed in claim 7 wherein the secondary coil is in a feedback configuration.

9. A test circuit as claimed in claim 8 wherein the feedback configuration acts to vary the current to the secondary coil to maintain the magnetic field at the giant magnetoresistive sensor at a prescribed condition.

10. A test circuit comprising:

a primary winding of parallel conducting segments having extended portions including at least one central conductor and at least one return conductor positioned on either side of the central conductor to impose a magnetic field in a test material when driven by an electric current;

a plurality of sense elements for sensing the response of the test material to the imposed magnetic field, each sensing element positioned between the extended portions of the primary winding, the sense elements being aligned with one another to sense the response at incremental areas along a path parallel to the extended portions of the primary winding, and having separate output connections.

11. A test circuit as claimed in claim 10 wherein the distance between the central conductors and return conductors are selected to align with features of a component being tested.

12. A test circuit as claimed in claim 10 including two central conductors and two return paths symmetrically located on either side of the central conductors.

13. A test circuit as claimed in claim 12 wherein the distance between the central conductors and return conductors are selected to align with features of a component being tested.

14. A test circuit as claimed in claim 10 further comprising a second plurality of sense elements aligned with one another to sense the response at incremental areas along a path parallel to the extended portions of the primary winding, and having separate output connections.

15. A test circuit as claimed in claim 14 wherein each individual sense element in the first plurality of sense elements is aligned with a sense element in the second plurality of sense elements in a direction perpendicular to the extended portions of the primary winding.

16. A test circuit as claimed in claim 14 wherein the sense elements in the first plurality of sense elements is offset in a direction parallel to the extended portions of the primary winding from the sense elements in the second plurality of sense elements.

17. A test circuit as claimed in claim 16 wherein the offset distance is one-half of the length of a sensing element.

18. A test circuit as claimed in claim 14 wherein the distances from the first plurality of sense elements and the second plurality of sense elements to the central conductor are equal.

19. A test circuit as claimed in claim 18 wherein a differential measurement is taken between a sense element in the first plurality of sense elements and a sense element in the second plurality of sense elements.

20. A test circuit as claimed in claim 10 wherein the sensing elements and the central conductor are in the same plane.

21. A test circuit as claimed in claim 10 wherein the location of the sense elements is non-uniform in the direction parallel to the extended portions of the primary winding.

22. A test circuit as claimed in claim 10 wherein the primary winding and sense elements are fabricated onto a flexible substrate.

23. A test circuit as claimed in claim 10 further comprising a balloon filled with a fluid to maintain contact between the test circuit and a surface under test of the test material.

24. A test circuit as claimed in claim 23 wherein the balloon is attached to a shuttle and the shuttle is shaped to approximately match the shape of the material under test.

25. A test circuit as claimed in claim 24 further comprising a removable cartridge that permits rapid replacement of the sensor and balloon components.

26. A test circuit as claimed in claim 23 wherein the surface under test is inside a bolt hole.

27. A test circuit as claimed in claim 23 wherein the surface under test is inside an engine disk slot.

28. A test circuit as claimed in claim 10 wherein the conductivity and proximity of the sensor to the surface are measured to detect cracks.

29. A test circuit as claimed in claim 10 wherein the proximity is measured at each sensing element to determine surface roughness.

30. A test circuit as claimed in claim 10 wherein each sensing element response is used for health monitoring or condition assessment.

31. A test circuit as claimed in claim 10 wherein the primary winding and sense elements are fabricated onto a rigid substrate.

32. A test circuit as claimed in claim 10 wherein the sensor is not in contact with a surface under test of the test material.

33. A test circuit as claimed in claim 10 wherein at least one of the sense elements includes a magnetoresistive sensor.

34. A test circuit as claimed in claim 10 wherein the at least one of the sense elements includes a giant magnetoresistive sensor.

35. A test circuit as claimed in claim 34 further comprising a secondary coil that surrounds the giant magnetoresistive sensing element.

36. A test circuit as claimed in claim 35 wherein the secondary coil is in a feedback configuration.

37. A test circuit as described in claim 10 wherein the sensor response to a flaw is determined in advance, this response being used to construct a filter, and the filter being applied to a sensor response to search for indications likely to be the flaw of interest and to suppress responses unlikely to be that flaw.

38. A test circuit as described in claim 10 wherein a single encoder is used to record the position of the array in the scan direction during scanning.

39. A test circuit as described in claim 10 wherein a template is used to align incremental scans of the sensor to construct an image of a wide area.

40. A test circuit as described in claim 10 wherein an automated scanner is used to move the sensor across a surface of the material under test.

41. A test circuit as described in claim 10 wherein modular fixtures with position encoders are used to permit manual scanning of complex parts.

42. A test circuit comprising:

a primary winding loop of conducting segments having a pair of parallel extended portions to impose a magnetic field in a test material when driven by an electric current;

a first plurality of sense elements for sensing the response of the test material to the imposed magnetic field, the sense elements being aligned with one another to sense the response at incremental areas along a path parallel to the extended portions of the primary winding, and having separate output connections.

43. A test circuit as claimed in claim 42 wherein the first plurality of sense elements are positioned between the extended portions of the primary winding.

44. A test circuit as claimed in claim 42 wherein the first plurality of sense elements are positioned outside the primary winding loop.

45. A test circuit as claimed in claim 44 wherein the primary winding and sense elements are in the same plane.

46. A test circuit as claimed in claim 44 further comprising a second plurality of sense elements, with the sense elements being aligned with one another to sense the response at incremental areas along a path parallel to the extended portions of the primary winding, and having separate output connections.

47. A test circuit as claimed in claim 46 wherein the second plurality of sense elements are positioned between the extended portions of the primary winding, with both the first and second plurality of sense elements being near a common extended portion of the primary winding.

48. A test circuit as claimed in claim 46 wherein the second plurality of sense elements are positioned outside the primary winding loop on the side opposite that of the first plurality of sense elements.

49. A test circuit as claimed in claim 46 wherein the distances between the first and second plurality of sense elements and the extended portions of the primary winding are equal.

50. A test circuit as claimed in claim 46 wherein the distances between the first and second plurality of sense elements and the extended portions of the primary winding are different.

51. A test circuit as claimed in claim 46 wherein the primary winding and sense elements are in the same plane.

52. A test circuit as claimed in claim 46 wherein each individual sense element in the first plurality of sense elements is aligned with a sense element in the second plurality of sense elements in a direction perpendicular to the extended portions of the primary winding.

53. A test circuit as claimed in claim 46 wherein the sense elements in the first plurality of sense elements is offset in a direction parallel to the extended portions of the primary winding from the sense elements in the second plurality of sense elements.

54. A test circuit as claimed in claim 53 wherein the offset distance is one-half of the length of a sensing element.

55. A test circuit as claimed in claim 42 wherein the location of the sense elements is non-uniform in the direction parallel to the extended portions of the primary winding.

56. A test circuit as claimed in claim 42 wherein the primary winding and sense elements are fabricated onto a flexible substrate.

57. A test circuit as claimed in claim 42 wherein the primary winding and sense elements are fabricated onto a rigid substrate.

58. A test circuit as claimed in claim 42 wherein at least one of the sense elements includes a magnetoresistive sensor.

59. A test circuit as claimed in claim 42 wherein at least one of the sense elements includes a giant magnetoresistive sensor.

60. A test circuit as claimed in claim 59 further comprising a secondary coil that surrounds the giant magnetoresistive sensing element.

61. A test circuit as claimed in claim 59 wherein the secondary coil is in a feedback configuration.

62. A test circuit comprising:

two parallel rows of aligned sense elements for scanning across a material under test surface;

a linear conductor segment positioned parallel to and between the sensing element rows for imposing a magnetic field; and

a first row of sensing elements for detecting cracks on a first side of a feature and a second row of sensing elements for detecting cracks on a second side of a feature.

63. A test circuit as described in claim 62 wherein the feature is a fastener in an aircraft skin.

64. A test circuit as described in claim 62 wherein multiple frequencies are used to remove the interference caused by the feature and isolate the crack response.

65. A test circuit as described in claim 62 wherein a shape filter is used to search the sensor response for shapes that are most likely to be cracks and to suppress responses unlikely to be cracks.

66. A test circuit as described in claim 65 wherein the response from sensing elements on opposite sides of the central conductor are combined to construct a filter representing a flaw of interest, the filter then being used to search the response image for indications likely to be the flaw of interest.

67. A test circuit as claimed in claim 66 wherein the flaw of interest is a crack.

68. A test circuit as claimed in claim 66 wherein the flaw of interest is a buried inclusion.

69. An automated drawing tool for sensors with at least one extended portion and at least one sensing element where the tool takes input information for dimensions and automatically draws the sensor configuration and leads based on predetermined rules for a specific family of sensor designs.