Magnetometer having periodic winding structure and material property estimator

• US 5,453,689 A
• Filed: 12/06/1991
• Issued: 09/26/1995
• Est. Priority Date: 12/06/1991
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Goldfine, Neil J., Melcher, deceased, James R.
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US07/803,504
• Time in Patent Office: 1,390 Days
• Field of Search: 324/225, 324/227, 324/229-233, 324/239-243, 324/262, 324/207.17, 324/207.18, 324/207.19, 324/207.26, 324/202, 364/571.07, 364/578
• US Class Current: 324/239
• CPC Class Codes: G01B 7/105 for measuring thickness of coating
• CPC Class Codes: G01N 27/72 by investigating magnetic variables
• CPC Class Codes: G01N 27/9046 by analysing electrical signals
• CPC Class Codes: G01R 33/1223 Measuring permeability, i.e. permeameters G01R33/14 takes precedence

Abstract

Apparatus and methods are disclosed which provide increased sensitivity, selectivity and dynamic range for non-contact measurement of actual physical and/or kinematic properties of conducting and magnetic materials. The apparatus and methods are based upon various methods for increasing sensitivity, selectivity and dynamic range through proper construction of a magnetometer sensor and for proper selection of operating point parameters for the application. A measurement apparatus for measuring one or more MUT properties includes an electromagnetic winding structure which, when driven by an electric signal, imposes a magnetic field in the MUT and senses an electromagnetic response. An analyzer is provided for applying the electric signal to the winding structure. A property estimator is coupled to the winding structure and translates sensed electromagnetic responses into estimates of one or more preselected properties of the material.

Claims

1. A magnetometer for measuring one or more properties of a material comprising:

an electromagnetic structure capable of imposing a magnetic field in the material when driven by an electric signal and sensing an electromagnetic response to the magnetic field;

an analyzer for applying the electric signal to the structure to define a spatial wavelength of the magnetic field imposed in the material; and

a property estimator coupled to the electromagnetic structure for translating sensed electromagnetic responses into estimates of one or more preselected properties of the material, wherein the sensed responses are obtained at a plurality of proximities to the material and wherein the property estimator comprises an algorithm model providing a prediction of the electromagnetic response for each value of each of the preselected properties of the material based on a set of properties characterizing the electromagnetic structure and the material, wherein the property estimator successively implements the model to produce a property estimation grid for the preselected properties, the property estimator translating sensed electromagnetic responses using the property estimation grid into estimates of said preselected properties.

2. A magnetometer as claimed in claim 1 wherein the property estimator implements the model by computing the magnetic vector potential distribution along the winding plane and subsequently computing surface current density and relevant terminal admittance to obtain a sensor response.

3. A magnetometer for measuring one or more properties of a material comprising:

an electromagnetic structure capable of imposing a magnetic field in the material when driven by an electric signal and sensing an electromagnetic response to the magnetic field;

an analyzer for applying the electric signal to the structure to define a spatial wavelength of the magnetic field imposed in the material; and

P1 a property estimator coupled to the electromagnetic structure for translating sensed electromagnetic responses into estimates of one or more preselected properties of the material, wherein the sensed responses are obtained at a plurality of proximities to the material;

wherein the electric signal has a preselected temporal excitation frequency being proximal to a transverse diffusion effect characteristic frequency for the electromagnetic structure.

4. A magnetometer for measuring one or more properties of a material comprising:

an electromagnetic winding structure capable of imposing a magnetic field in the material, when driven by an electric signal and sensing an electromagnetic response to the magnetic field;

an analyzer for applying the electric signal to the winding structure to define a spatial wavelength of the magnetic field imposed in the material, the electric signal having its temporal excitation frequency being proximal to a transverse diffusion effect characteristic frequency of the winding structure; and

a property estimator providing a property estimation grid for translating sensed electromagnetic responses into estimates of one or more preselected properties of the material, wherein the property estimator comprises an algorithmic model for providing a prediction of a response for each value of each of the preselected material properties based on a set of properties characterizing the winding structure and the material, the property estimator implementing the model successively for obtaining the property estimation grid for the preselected material properties.

5. A magnetometer as claimed in claim 4 wherein the winding structure comprises a plurality of electromagnetic winding elements arranged into a meandering pattern including a primary winding to which the electric signal is applied and a secondary winding which senses the electromagnetic response.

6. A magnetometer as claimed in claim 4 wherein the sensed electromagnetic responses are obtained at a plurality of proximities of the electromagnetic structure relative to the material.

7. A magnetometer as claimed in claim 6 wherein for each proximity the winding structure is capable of being adjusted to vary its position and orientation relative to the material, electromagnetic responses being sensed by the winding structure for each position and orientation of the winding structure relative to the material.

8. A magnetometer as claimed in claim 4 wherein the winding structure is submerged in a magnetic coupling media having a permeability which is different than the permeability of air.

9. A magnetometer as claimed in claim 4 wherein the electromagnetic structure is capable of being adapted to conform to a curved surface of the material.

10. A magnetometer as claimed in claim 4 wherein the model provides a response prediction for each value of each of the preselected material properties based on a set of properties comprising winding structure dimensions, winding structure geometry, winding structure physical properties, winding structure electric signal frequency, winding structure proximity to the material, material dimensions and material physical properties.

11. A magnetometer for measuring an affected zone conductivity and thickness of a processed metal comprising:

an electromagnetic winding structure capable of imposing a magnetic field in the processed metal when driven by an electric signal and sensing an electromagnetic response, the winding structure comprising a primary winding including a conductor and a secondary winding including a conductor which is separated from the primary winding by a gap, the primary winding conductor width being substantially greater than the gap width;

an analyzer for applying the electric signal having a preselected temporal excitation frequency to the winding structure; and

a property estimator coupled to the winding structure for translating each sensed response into substantially independent conductivity and thickness estimates.

12. A magnetometer as claimed in claim 11 wherein the winding structure is capable of being adjusted to vary its position and orientation relative to the heat treated metal, electromagnetic responses being sensed by the winding structure for each position and orientation of the winding structure relative to the heat treated metal.

13. A magnetometer as claimed in claim 11 wherein the electromagnetic structure is capable of being adapted to conform to a curved surface of the heat treated metal.

14. A magnetometer as claimed in claim 11 wherein the electric signal has a preselected temporal excitation frequency being proximal to a transverse diffusion effect characteristic frequency for the electromagnetic structure.

15. A magnetometer as claimed in claim 11 wherein operating point parameters and winding geometry, dimensions and configuration for the winding structure are adjusted to satisfy material property estimation requirements for substantially independent heat affected zone conductivity and thickness estimates.

16. A magnetometer for measuring proximity to and conductivity of a material comprising:

a periodic electromagnetic winding structure capable of imposing a magnetic field in the material when driven by an electric signal and sensing an electromagnetic response to the magnetic field;

an analyzer for applying the electric signal to the winding structure to define a spatial wavelength of the magnetic field imposed in the material which is associated with the periodic winding structure, the electric signal having a preselected temporal excitation frequency; and

a property estimator coupled to the winding structure for receiving sensed responses, the property estimator accessing a property estimation grid for translating sensed responses into substantially independent proximity and conductivity estimates at the single preselected temporal excitation frequency.

17. A magnetometer as claimed in claim 16 wherein the property estimator generates the property estimation grid by successively implementing an algorithmic model, which for each implementation provides a prediction of an electromagnetic response for a proximity and conductivity based on a set of properties characterizing the winding structure and the material.

18. A magnetometer as claimed in claim 17 wherein the property estimator implements the model by computing the magnetic vector potential distribution along the winding plane and subsequently computing surface current density and relevant terminal admittance to obtain a sensor response.

19. A magnetometer as claimed in claim 16 wherein the property estimator further comprises a processor for locating cracks in the material by detecting changes in conductivity for conductivity estimates obtained at plural locations along the material.

20. A magnetometer as claimed in claim 16 wherein the property estimator further comprises a processor for locating cracks and monitoring aging at locations of the material by detecting changes in conductivity for multiple conductivity estimates obtained at various times for each location.

21. A magnetometer as claimed in claim 16 wherein the winding structure is formed of a plurality of electromagnetic winding elements arranged into a meandering pattern.

22. A magnetometer as claimed in claim 16 wherein the electric signal has a preselected temporal excitation frequency being proximal to a transverse diffusion effect characteristic frequency for the winding structure.

23. A magnetometer as claimed in claim 16 wherein operating point parameters and winding geometry, dimensions and configuration for the winding structure are adjusted to satisfy material property estimation requirements for substantially independent proximity and conductivity estimates.

24. A magnetometer as claimed in claim 16 wherein the winding structure is capable of being adjusted to vary its position and orientation relative to the material, electromagnetic responses being sensed by the winding structure for each position and orientation of the winding structure relative to the material.

25. A magnetometer as claimed in claim 16 wherein the winding structure is capable of being adapted to conform to a curved surface of the material.

26. A magnetometer as claimed in claim 16 wherein the analyzer applies multiple electric signals each having a single preselected temporal excitation frequency to the winding structure for measuring the dependence of conductivity on temporal excitation frequency.

27. A magnetometer as claimed in claim 16 wherein the analyzer applies multiple electric signals each having a single preselected temporal excitation frequency to the winding structure for measuring the dependence of the conductivity estimates on temporal excitation frequency to characterize shape, size, depth and number of cracks in the material.

28. A magnetometer for measuring complex permeability of a material comprising:

an electromagnetic winding structure capable of imposing a magnetic field in the material and sensing an electromagnetic response to the magnetic field, the winding structure comprising a plurality of meandering electromagnetic windings;

an analyzer for applying an electric signal to the winding structure to define a spatial wavelength the magnetic field imposed in the material, the electric signal having a preselected temporal excitation frequency; and

a property estimator coupled to the winding structure for receiving sensed responses, the property estimator providing a response prediction table for translating sensed responses into complex permeability estimates of the material, the property estimator generating the prediction table by successively implementing an algorithmic model which provides for each implementation a prediction of a response for a value of complex permeability based on a set of properties characterizing the winding structure and the material.

29. A magnetometer as claimed in claim 28 wherein the electric signal has a preselected temporal excitation frequency being proximal to a transverse diffusion effect characteristic frequency for the winding structure.

30. A magnetometer as claimed in claim 28 wherein the model provides a response prediction for a proximity and conductivity based on a set of properties comprising winding structure dimensions, winding structure geometry, winding structure physical properties, the temporal excitation frequency of the electric signal, winding structure proximity to the material, material dimensions and material physical properties.

31. A magnetometer as claimed in claim 28 wherein the winding structure is capable of being adapted to conform to a curved surface of the material.

32. A magnetometer as claimed in claim 28 for measuring dispersive complex permeability properties of a layered material

an electromagnetic structure capable of imposing a magnetic field in the layered material when driven by an electric signal and sensing an electromagnetic response;

an analyzer for applying the electric signal to the electromagnetic structure to define a spatial wavelength associated with the imposed magnetic field in the material, the electric signal having a preselected temporal excitation frequency; and

wherein the property estimator coupled to the structure translates sensed electromagnetic responses into estimates of dispersive complex permeability properties of each layer of the layered material.

33. A magnetometer as claimed in claim 32 wherein one layer of the layered material is air.

34. An apparatus as claimed in claim 32 wherein the electromagnetic structure comprises a plurality of electromagnetic windings forming a meandering pattern.

35. An apparatus for measuring one or more properties of a material comprising:

a pair of meandering electromagnetic winding structures positioned on opposite sides of the material, each meandering winding structure being capable of posing a magnetic field in the material when driven by an electric signal and sensing an electromagnetic response to the magnetic filed;

an analyzer for applying electric signals in plural modes of phase relationship to the meandering winding structures to define respective spatial wavelengths of the magnetic fields imposed in the material; and

a property estimator coupled to the winding structures for translating electromagnetic responses from each of the pair of meandering winding structures in the plural modes of phase relationship into estimates of one or more properties of the material.

36. An apparatus as claimed in claim 35 wherein the property estimator provides estimates of one or more anisotropic properties of the material.

37. A magnetometer for measuring one or more preselected properties of a material having a curved surface comprising:

an electromagnetic winding structure capable of being adapted to conform to the curved surface of the material, the winding structure comprising a plurality of meandering electromagnetic windings for imposing a magnetic field in a material when driven by an electric signal and sensing an electromagnetic response to the magnetic field;

an analyzer for applying an electric signal to the winding structure to define a spatial wavelength of the magnetic field imposed in the material, the electric signal having a preselected temporal excitation frequency; and

a property estimator providing a property estimation grid for translating sensed electromagnetic responses into estimates of one or more preselected properties of the material, wherein the property estimator comprises an algorithmic model for providing a prediction of a response for each value of each of the preselected material properties based on a set of properties characterizing the winding structure and the material, the property estimator implementing the model successively for obtaining the property estimation grid for the preselected material properties.

38. A magnetometer as claimed in claim 37 wherein the winding structure is capable of being adapted to surround the material.

39. A magnetometer as claimed in claim 37 wherein the winding structure is capable of being spiralled around the material.

40. A magnetometer as claimed in claim 37 wherein the winding structure is spiralled around a magnetic or insulating core to obtain measurements on a separate material.

41. A magnetometer for measuring one or more properties of a material comprising;

an electromagnetic winding structure comprising a primary winding including a conductor capable of imposing a magnetic field in the material when driven by an electric signal and one or more secondary windings including conductors for sensing an electromagnetic response, the secondary winding conductors being separated from the primary winding conductor by a gap and the primary winding conductor having a width which is substantially greater than the gap width;

an analyzer for applying an electric signal to the primary winding for imposing the magnetic field in the material; and

a property estimator coupled to the winding structure for translating sensed electromagnetic responses into estimates of one or more preselected properties of the material.

42. A magnetometer as claimed in claim 41 wherein the primary winding has a thickness which is substantially smaller than a primary width.

43. A magnetometer as claimed in claim 41 wherein the primary and secondary windings form a meandering pattern in a single plane.

44. A magnetometer as claimed in claim 41 wherein for the preselected material properties, operating point parameters and winding geometry, dimensions and configuration for the winding structure are adjusted to satisfy material property estimation requirements.

45. A magnetometer as claimed in claim 41 wherein for each of a plurality of temporal excitation frequencies of the electric signal the property estimator converts sensed responses to property estimates.

46. A magnetometer as claimed in claim 41 wherein the winding structure is capable of being adjusted to vary its position and orientation relative to the material, electromagnetic responses being sensed by the winding structure for each position and orientation of the winding structure relative to the material.

47. A magnetometer as claimed in claim 41 wherein the sensed responses are obtained with the winding structure being maintained at a single proximity and a single orientation relative to the material.

48. A magnetometer as claimed in claim 41 wherein the electric signal has a temporal excitation frequency being proximal to a transverse diffusion effect characteristic frequency of the electromagnetic structure.

49. A magnetometer as claimed in claim 41 wherein the winding structure further comprises a plurality of layered primary and secondary windings capable of imposing magnetic fields in the material and sensing electromagnetic responses.

50. A magnetometer as claimed in claim 41 wherein the secondary windings sense electromagnetic responses for each of a plurality of temporal excitation frequencies of the electric signals.

51. An apparatus for measuring one or more properties of a material comprising:

a deposited electromagnetic winding structure comprising a meandering primary winding which imposes a magnetic field in the material when driven by an electric signal for exciting multiple spatial surface current density modes, the meandering primary winding providing a prescribed spatial wavelength associated with the winding structure, the winding structure further comprising a secondary winding which senses fields produced by a dominant spatial wavelength surface current density mode and at least one shorter wavelength mode for obtaining electromagnetic response;

an analyzer for applying the electric signal to the winding structure; and

a property estimator coupled to the winding structure for translating electromagnetic responses at the dominant and at least one shorter wavelength modes into estimates of one or more properties of the material.

52. An apparatus as claimed in claim 51 wherein the primary and secondary windings forming a meandering pattern.

53. An apparatus as claimed in claim 51 wherein the winding structure further comprises a conducting back-plane located adjacent to the primary and secondary windings.

54. An apparatus as claimed in claim 51 wherein the winding structure further comprises a permeable substrate located adjacent to the primary and secondary windings.

55. An apparatus as claimed in claim 51 further comprising a plurality of additional secondary windings each independently sensing multiple spatial wavelength surface current density modes.

56. An apparatus as claimed in claim 55 wherein the additional secondary windings are located in a different plane than the primary winding.

57. A magnetometer for measuring proximity to and a second property of a material comprising:

a periodic electromagnetic winding structure capable of imposing a magnetic field in the material when driven by an electric signal and sensing an electromagnetic response to the magnetic field;

an analyzer for applying the electric signal to the winding structure to define a spatial wavelength of the periodic winding structure and the magnetic field imposed in the material, the electric signal having a preselected temporal excitation frequency; and

a property estimator coupled to the winding structure for receiving sensed responses, the property estimator accessing a property estimation grid for translating sensed responses into substantially independent proximity and second property estimates at the single preselected temporal excitation frequency.

58. A magnetometer as claimed in claim 57 wherein the property estimator generates the property estimation grid by successively implementing an algorithmic model, which for each implementation provides a prediction of an electromagnetic response for a proximity and second property based on a set of properties characterizing the winding structure and the material.

59. A magnetometer as claimed in claim 57 wherein the second property is conductivity.

60. A magnetometer for measuring conductivity and a second property of a material comprising:

a periodic electromagnetic winding structure capable of imposing a magnetic field in the material when driven by an electric signal and sensing an electromagnetic response to the magnetic filed;

an analyzer for applying the electric signal to the winding structure to define a spatial wavelength of the periodic winding structure and the magnetic field imposed in the material, the electric signal having a preselected temporal excitation frequency; and

a property estimator coupled to the winding structure for receiving sensed responses, the property estimator accessing a property estimation grid for translating sensed responses into substantially independent conductivity and second property estimates at the single preselected temporal excitation frequency.

61. A magnetometer as claimed in claim 60 wherein the property estimator generates the property estimation grid by successively implementing an algorithmic model, which for each implementation provides a prediction of an electromagnetic response for a conductivity and second property based on a set of properties characterizing the winding structure and the material.