EDDY CURRENT DETECTION

• US 20120019236A1
• Filed: 06/22/2011
• Published: 01/26/2012
• Est. Priority Date: 07/26/2010
• Status: Active Grant

• Current Assignee: Radiation Monitoring Devices, Inc. (Dynasil Corp. of America)
• Original Assignee: Radiation Monitoring Devices, Inc. (Dynasil Corp. of America)
• Inventors: Tiernan, Timothy C., Steinback, Mark, Rensing, Noa M., Weststrate, Evan
• Granted Patent: US 9,678,175 B2
• Time in Patent Office: Days
• US Class Current: 324/234
• CPC Class Codes: G01B 1/00 Measuring instruments characterised by the selection of material therefor
• CPC Class Codes: G01B 2210/00 Aspects not specifically covered by any group under G01B, e.g. of wheel alignment, caliper-like sensors
• CPC Class Codes: G01N 1/00 Sampling; Preparing specimens for investigation
• CPC Class Codes: G01N 2201/00 Features of devices classified in G01N21/00
• CPC Class Codes: G01N 27/9006 Details, e.g. in the structure or functioning of sensors
• CPC Class Codes: G01R 1/00 Details of instruments or arrangements of the types included in groups G01R5/00 - G01R13/00 and G01R31/00 constructional details particular to electromechanical arrangements for measuring the electric consumption G01R11/02
• CPC Class Codes: G01R 33/09 Magnetoresistive devices
• CPC Class Codes: G01R 33/096 anisotropic magnetoresistance sensors

Abstract

Eddy current detection probes and related methods are disclosed. In some embodiments, the eddy current detection probes are hybrid probes, including a solid state sensor and a detection loop. In some embodiments, the eddy current detection probes include a drive coil and a detection loop, with the detection loop having a sensitive axis that is not parallel to principal axis of the drive coil. In some such embodiments, the sensitive axis of the detection loop is perpendicular to the principal axis of the drive coil.

Claims

1. An eddy current detection probe, comprising:

a solid state sensor configured to sense changes in a magnetic field created by perturbations in an eddy current; and

a conductive detection loop configured to receive the magnetic field and generate a voltage in response to variations in the magnetic field.

2. The eddy current detection probe of claim 1, wherein the solid state sensor is a magnetoresistive sensor.

3. The eddy current detection probe of claim 2, wherein the solid state sensor is an anisotropic magnetoresistive (AMR) sensor.

4. The eddy current detection probe of claim 2, wherein the solid state sensor is a giant magnetoresistive (GMR) sensor.

5. The eddy current detection probe of claim 2, wherein the magnetoresistive sensor is sized to be sensitive to magnetic fields along only one axis.

6. The eddy current detection probe of claim 5, wherein a principal direction of sensitivity of the solid state sensor is configured to be parallel to a principal axis of the conductive detection loop.

7. The eddy current detection probe of claim 1, further comprising a drive coil configured to generate a drive magnetic field, wherein the drive coil is oriented substantially perpendicular to the conductive detection loop.

8. The eddy current detection probe of claim 1, wherein the drive coil is configured to generate the drive magnetic field along a first axis, and wherein the conductive detection loop has a principal sensitivity axis oriented substantially perpendicular to the first axis.

9. The eddy current detection probe of claim 8, wherein a principal direction of sensitivity of the solid state sensor is orientated substantially perpendicular to the first axis.

10. The eddy current detection probe of claim 1, wherein the solid state sensor and the conductive detection loop are electrically connected to produce a single output signal.

11. The eddy current detection probe of claim 1, wherein the conductive detection loop is configured to apply to, and read from, the solid state sensor an electrical signal.

12. An eddy current detection probe, comprising:

a substrate having a substantially planar surface;

a drive coil disposed on the substantially planar surface;

an anisotropic magnetoresistive (AMR) sensor disposed on the substantially planar surface of the substrate and positioned within a perimeter of the drive coil; and

a detection loop comprising a first electrical lead and a second electrical lead,

wherein the first electrical lead is connected to a first end of the AMR sensor and the second electrical lead is connected to a second end of the AMR sensor,

wherein the first electrical lead and second electrical lead are positioned at least partially around the substrate to form the detection loop, and

wherein the detection loop is substantially perpendicular to the drive coil.

13. The eddy current detection probe of claim 12, wherein the AMR sensor is configured to be sensitive to magnetic fields along only one axis.

14. The eddy current detection probe of claim 13, wherein the AMR sensor is configured to be sensitive to magnetic fields along only one axis through its geometry.

15. The eddy current detection probe of claim 13, wherein the AMR sensor is configured to have a preferred direction of sensitivity or a linear out put by means of barberpole stripes.

16. An eddy current detection probe, comprising:

a first substrate having a substantially planar surface;

a drive coil disposed on the substantially planar surface of the first substrate;

a second substrate smaller than the first substrate, the second substrate having a substantially planar surface;

an anisotropic magnetoresistive (AMR) sensor disposed on the substantially planar surface of the second substrate and attached to the first substrate within a perimeter of the drive coil; and

a detection loop comprising a first electrical lead and a second electrical lead,

wherein the first electrical lead is connected to a first end of the AMR sensor and the second electrical lead is connected to a second end of the AMR sensor,

wherein the first electrical lead and second electrical lead are positioned at least partially around the first substrate to form the detection loop, and

wherein the detection loop is substantially perpendicular to the drive coil.

17. An eddy current detection probe, comprising:

a drive coil; and

a conductive detection loop oriented substantially perpendicular to the drive coil, wherein the conductive detection loop has a height that is substantially perpendicular to the drive coil and less than 2.5 mm.

18. The eddy current detection probe of claim 17, wherein the drive coil is contained at least substantially within a plane, and wherein the plane is configured to be parallel to a surface of a material specimen probed by the eddy current detection probe.

19. The eddy current detection probe of claim 17, wherein the conductive detection loop has a side disposed in a same plane as that in which the drive coil is disposed.

20. The eddy current detection probe of claim 17, wherein the drive coil is configured to generate a drive magnetic field along a first axis, and wherein the conductive detection loop has a detection axis oriented substantially perpendicular to the first axis

21. The eddy current detection probe of claim 17, further comprising:

a substrate have a substantially planar surface;

wherein the drive coil is disposed on the substantially planar surface, and

wherein the conductive detection loop is wrapped at least partially around the substrate.

22. The eddy current detection probe of claim 17, wherein the conductive detection loop is formed at least partially by a first electrical lead and a second electrical lead.

23. The eddy current detection probe of claim 17, wherein the conductive detection loop encloses an area of less than approximately 0.2 square millimeters.

24. The eddy current detection probe of claim 17, wherein the drive coil is formed on a printed circuit board.

25. The eddy current detection probe of claim 24, wherein the conductive detection loop is formed at least partially on the printed circuit board.

26. A method, comprising:

exciting a drive coil of an eddy current detection probe with an alternating current (AC) signal having a frequency greater than approximately 1 MHz;

applying to a material under test an incident magnetic field generated by the drive coil as a result of exciting the drive coil; and

detecting an induced magnetic field from the material under test using a conductive detection loop oriented substantially perpendicular to the drive coil.

27. The method of claim 26, wherein the conductive detection loop has a height that is substantially perpendicular to the drive coil and less than 1 mm.

28. The method of claim 26, wherein the conductive detection loop has a height that is substantially perpendicular to the drive coil and less than 0.5 mm.

29. The method of claim 26, wherein exciting the drive coil with an AC signal comprises exciting the drive coil with an AC signal having a frequency between approximately 2 MHz and 5 MHz.

30. The method of claim 26, wherein exciting the drive coil with an AC signal comprises exciting the drive coil with an AC signal having a frequency greater than approximately 2 MHz.

31. The method of claim 26, wherein applying to the material under test an incident magnetic field generated by the drive coil as a result of exciting the drive coil comprises orienting the drive coil substantially parallel to a surface of the material under test.

32. The method of claim 31, wherein exciting the drive coil with an AC signal comprises exciting the drive coil with an AC signal having a frequency between approximately 2 MHz and 5 MHz.

33. The method of claim 32, wherein the conductive detection loop has a height that is substantially perpendicular to the drive coil and less than 2.5 mm.

34. The method of claim 26, wherein the detected signal is preconditioned by applying a bucking signal, comprising an inverted reference signal at the drive frequency.

35. The method of claim 34, wherein the reference signal is obtained by making a reference measurement at a point of an article to be tested known to be free of defects.

36. The method of claim 34, wherein the reference signal is obtained by averaging respective signals obtained at several different points of the article to be tested.

37. The method of claim 32, wherein the conductive detection loop has a height that is substantially perpendicular to the drive coil and less than 0.5 mm.

38. A method of manufacturing an eddy current detection probe, comprising:

fabricating a conductive drive coil on a first layer of a multi-layered substrate;

fabricating conductive traces on at least two layers of the multi-layered substrate; and

interconnecting with conductive material the conductive traces on the at least two layers of the multi-layered substrate to form a detection loop substantially perpendicular to the conductive drive coil.

39. The method of claim 38, wherein fabricating the conductive traces comprises fabricating the conductive traces on four or more layers of the multi-layered substrate.

40. The method of claim 38, wherein the multi-layered substrate comprises a printed circuit board.

41. The method of claim 38, wherein fabricating the conductive drive coil comprises photolithographically defining the conductive drive coil.

42. A probe for depth profiling, comprising

a drive coil configured to be positioned proximate a surface of an article being tested such that an axis of the drive coil is perpendicular to the surface of the article;

a magnetoresistive sensor constructed and aligned to respond to electrical conductivity and/or magnetic permeability differences between material in a layer at the surface of the article and material in the interior of the article.

43. The probe of claim 42, wherein the sensor is an AMR sensor.

44. The probe of claim 42, wherein the coil is disposed on a substantially planar surface.

45. The probe of claim 44, wherein the sensor is disposed on the substantially planar surface.

46. The probe of claim 42, wherein the sensor is positioned outside the diameter of the coil.

47. The probe of claim 45, wherein the direction of maximum sensitivity of the probe is tilted with respect to the plane.

48. The probe of claim 42, comprising multiple sensors.

49. The probe of claim 42, wherein the difference between the electrical conductivity and/or magnetic permeability of the material surface layer and the interior material of the part are due to case hardening of the article.

50. The probe of claim 42, wherein the difference between the electrical conductivity and/or magnetic permeability of the surface layer and the interior material of the article are due to a coating applied to the article.