Generating highly uniform electromagnetic field characteristics

• US 5,642,087 A
• Filed: 10/25/1994
• Issued: 06/24/1997
• Est. Priority Date: 10/25/1994
• Status: Expired due to Fees

• Current Assignee: Sandia Corporation (Martin Marietta Corporation)
• Original Assignee: Sandia Corporation (Martin Marietta Corporation)
• Inventors: Crow, James T.
• Primary Examiner(s): DONOVAN, LINCOLN D
• Application Number:
  US08/328,849
• Time in Patent Office: 973 Days
• Field of Search: 335/216, 335/299, 335/300, 335/306, 324/318, 324/324
• US Class Current: 335/216
• CPC Class Codes: G01R 33/3875 using correction coil assemblies, e.g. active shimming
• CPC Class Codes: G01R 33/421 of main or gradient magnetic field
• CPC Class Codes: H05H 7/04 Magnet systems , e.g. undulators, wigglers free-electron laser H01S3/0903; Energisation thereof

Abstract

An apparatus and method for generating homogenous electromagnetic fields within a volume. The homogeneity provided may be for magnetic and/or electric fields, and for field magnitude, radial gradient, or higher order radial derivative. The invention comprises conductive pathways oriented mirror symmetrically about a desired region of homogeneity. A corresponding apparatus and method is provided for substantially cancelling the electromagnetic field outside of the apparatus, comprising a second set of conductive pathways placed outside the first set.

Claims

1. An apparatus for generating an electromagnetic field having a region of homogeneity of a characteristic of said electromagnetic field, said apparatus comprising:

a central axis of said apparatus; and

at least a minimum number of conductive pathways disposed about and substantially parallel to said central axis, azimuthal locations of said conductive pathways being substantially defined by locations selected from the group consisting of an x-axis, solutions to

space="preserve" listing-type="equation">cos(3φ

.sub.n)+cos(3φ

.sub.n-1)+ . . . +cos(3φ

.sub.1)+w=0,

said solutions divided by a positive integer, and said solutions divided by a positive integer reflected about a plane of reflection, where n is a number of conductive pathways per quadrant and w is selected from the group consisting of 0 and 0.5;

wherein said characteristic comprises a characteristic selected from the group consisting of rate of rotation, field magnitude, radial gradient, and higher order radial derivatives of field magnitude and said minimum number of conductive pathways is 18 where said characteristic comprises radial gradient and is 10 otherwise.

2. The apparatus of claim 1 wherein azimuthal locations of said conductive pathways are substantially defined by locations selected from the group consisting of an x-axis, solutions to a set of equations comprising one or more of the group consisting of

3. The apparatus of claim 1 wherein said conductive pathways define an approximately biconic volume having a long axis parallel to said central axis.

4. The apparatus of claim 1 wherein said electromagnetic field comprises a magnetic field.

5. The apparatus of claim 4 wherein each of said conductive pathways comprises a substantially identical line current magnitude.

6. The apparatus of claim 4 wherein not all conductive pathways comprise a substantially identical line current magnitude, thereby producing a transverse gradient in said magnetic field.

7. The apparatus of claim 6 wherein said central axis is curved.

8. The apparatus of claim 1 wherein said electromagnetic field comprises an electric field.

9. The apparatus of claim 8 wherein each of said conductive pathways comprises a substantially identical line charge.

10. The apparatus of claim 8 wherein not all conductive pathways comprise a substantially identical line charge, thereby producing a transverse gradient in said electric field.

11. The apparatus of claim 10 wherein said central axis is curved.

12. The apparatus of claim 1 additionally comprising means for substantially canceling said electromagnetic field external to said apparatus, said means for substantially canceling comprising a plurality of conductive lines equal in number to said conductive pathways.

13. The apparatus of claim 12 wherein said conductive lines are located at the same azimuthal positions as said conductive pathways.

14. The apparatus of claim 1 additionally comprising means for pulsing current through said conductive pathways.

15. The apparatus of claim 14 wherein said means for pulsing current comprises means selected from the group consisting of homopolar generators, rotating flywheel energy storage systems, capacitive electrical storage and discharge systems, and high-current power supplies operating directly from electrical mains.

16. The apparatus of claim 1 wherein said conductive pathways comprise clusters of wires.

17. The apparatus of claim 16 wherein each of said clusters of wires comprises a plurality of wires disposed around a central wire.

18. The apparatus of claim 17 additionally comprising means for adjusting current in said plurality of wires so as to tune a field centroid of said cluster of wires.

19. The apparatus of claim 1 wherein said conductive pathways comprise current sheets.

20. The apparatus of claim 1 additionally comprising an electromagnetic shield surrounding said conductive pathways.

21. The apparatus of claim 1 wherein pairs of conductive pathways of opposite charge are joined at an end of said apparatus by a member selected from the group consisting of loops of conductive material, current sheets, and conductive plates.

22. The apparatus of claim 1 wherein said apparatus comprises a device selected from the group consisting of magnetic resonance imager, pulsed magnetic resonance imager, magnetic resonance microscope, nuclear magnetic resonance spectroscope, charged particle beam steerer, charged particle momentum analyzer, high-field pulsed-beam charged particle momentum analyzer, time-resolved charged-particle momentum analyzer, atomic clock, isotope separator, charged particle beam focuser, separator for removing ferromagnetic material from fluids, charged particle beam guider, charged particle energy analyzer, separator of fluids having different dielectric properties, and separator of particles from fluids.

23. A method for generating an electromagnetic field having a region of homogeneity of a characteristic of the electromagnetic field, the method comprising the steps of:

a) establishing a central axis;

b) situating at least a minimum number of conductive pathways, disposed about and substantially parallel to the central axis, at azimuthal locations substantially defined by locations selected from the group consisting of an x-axis, solutions to

space="preserve" listing-type="equation">cos(3φ

.sub.n)+cos(3φ

.sub.n-1)+ . . . +cos(3φ

.sub.1)+w=0,

the solutions divided by a positive integer, and the solutions divided by a positive integer reflected about a plane of reflection, where n is a number of conductive pathways per quadrant and w is selected from the group consisting of 0 and 0.5; and

c) generating the electromagnetic field comprising a region of homogeneity of a characteristic selected from the group consisting of rate of rotation, field magnitude, radial gradient, and higher order radial derivatives of field magnitude, and said minimum number of conductive pathways is 18 where said characteristic comprises radial gradient and is 10 otherwise.

24. The method of claim 23 wherein the situating step comprises situating the conductive pathways at azimuthal locations substantially defined by locations selected from the group consisting of an x-axis, solutions to a set of equations comprising one or more of the group consisting of

25. The method of claim 23 wherein the situating step comprises situating conductive pathways defining an approximately biconic volume having a long axis parallel to the central axis.

26. The method of claim 23 wherein the generating step comprises generating a magnetic field.

27. The method of claim 26 wherein the generating step comprises passing through each of the conductive pathways a substantially identical line current magnitude.

28. The method of claim 26 wherein the generating step comprises passing through fewer than all conductive pathways a substantially identical line current magnitude, thereby producing a transverse gradient in the magnetic field.

29. The method of claim 28 wherein the establishing step comprises establishing a curved central axis.

30. The method of claim 23 wherein the generating step comprises generating an electric field.

31. The method of claim 30 wherein the generating step comprises placing on each of the conductive pathways a substantially identical line charge.

32. The method of claim 30 wherein the generating step comprises placing on fewer than all conductive pathways a substantially identical line charge, thereby producing a transverse gradient in the electric field.

33. The method of claim 32 wherein the establishing step comprises establishing a curved central axis.

34. The method of claim 23 additionally comprising the step of substantially canceling the electromagnetic field external to a volume, by providing a plurality of conductive lines defining the volume and equal in number to the conductive pathways.

35. The method of claim 34 wherein the step of substantially canceling comprises situating conductive lines located at the same azimuthal positions as the conductive pathways.

36. The method of claim 23 wherein the generating step comprises pulsing current through the conductive pathways.

37. The method of claim 36 wherein the pulsing step comprises utilizing a member selected from the group consisting of homopolar generators, rotating flywheel energy storage systems, capacitive electrical storage and discharge systems, and high-current power supplies operating directly from electrical mains.

38. The method of claim 23 wherein the situating step comprises situating conductive pathways comprising clusters of wires.

39. The method of claim 38 wherein the situating step comprises situating clusters of wires each of which comprises a plurality of wires disposed around a central wire.

40. The method of claim 39 additionally comprising the step of adjusting current in the plurality of wires so as to tune a field centroid of the cluster of wires.

41. The method of claim 23 wherein the situating step comprises situating current sheets.

42. The method of claim 23 additionally comprising the step of situating an electromagnetic shield surrounding the conductive pathways.

43. The method of claim 23 additionally comprising the step of joining pairs of conductive pathways of opposite charge at ends thereof by a member selected from the group consisting of loops of conductive material, current sheets, and conductive plates.

44. The method of claim 23 wherein the generating step comprises generating the electromagnetic field within a device selected from the group consisting of magnetic resonance imager, pulsed magnetic resonance imager, magnetic resonance microscope, nuclear magnetic resonance spectroscope, charged particle beam steerer, charged particle momentum analyzer, high-field pulsed-beam charged particle momentum analyzer, time-resolved charged-particle momentum analyzer, atomic clock, isotope separator, charged particle beam focuser, separator for removing ferromagnetic material from fluids, charged particle beam guider, charged particle energy analyzer, separator of fluids having different dielectric properties, and separator of particles from fluids.

45. An apparatus for generating an electromagnetic field internal to said apparatus and a substantially reduced electromagnetic field external to said apparatus, said apparatus comprising a first plurality of conductive pathways generating a cylindrical core volume of electromagnetic field and a second plurality of conductive pathways for substantially cancelling said electromagnetic field external to said second plurality.

46. The apparatus of claim 45 wherein said first and said second plurality of conductive pathways comprise a plurality of current sheets.

47. The apparatus of claim 45 wherein each of said second plurality of conductive pathways is located at an identical azimuthal position from a center of said core volume as a corresponding pathway of said first plurality of conductive pathways.

48. The apparatus of claim 47 wherein a current passing through each of said second plurality of conductive pathways is approximately equal to a current passing through each of said first plurality of conductive pathways multiplied by a ratio of a distance of said second plurality of conductive pathways from said center to a distance of said first plurality of conductive pathways from said center.

49. The apparatus of claim 48 wherein each of said second plurality of conductive pathways comprises n conductive lines and each of said first plurality of conductive pathways comprises m conductive lines, n/m being approximately equal to said ratio.

50. A method for generating an electromagnetic field internal to a device and a substantially reduced electromagnetic field external to the device, the method comprising the steps of:

a) situating a first plurality of conductive pathways;

b) generating a cylindrical core volume of electromagnetic field within a volume defined by the first plurality of conductive pathways; and

c) situating a second plurality of conductive pathways for substantially canceling the electromagnetic field external to the second plurality.

51. The method of claim 50 wherein the situating steps comprise situating a plurality of current sheets.

52. The method of claim 50 wherein the step of situating a second plurality of conductive pathways comprises situating each of the second plurality of conductive pathways at an identical azimuthal position from a center of the core volume as a corresponding pathway of the first plurality of conductive pathways.

53. The method of claim 52 additionally comprising the step of passing a current through each of the second plurality of conductive pathways approximately equal to a current passing through each of the first plurality of conductive pathways multiplied by a ratio of a distance of the second plurality of conductive pathways from the center to a distance of the first plurality of conductive pathways from the center.

54. The method of claim 53 wherein the situating steps comprise forming each of the second plurality of conductive pathways of n conductive lines and each of the first plurality of conductive pathways of m conductive lines, n/m being approximately equal to the ratio.

55. A method for producing an apparatus for generating a region of a substantially uniform electromagnetic field characteristic, said apparatus comprising a central axis, the method comprising the steps of:

a) determining initial sites for a plurality of conductive pathways about and substantially parallel to the central axis;

b) simulating the siting of the plurality of conductive pathways;

c) plotting B_x =0 contours resulting from the simulation;

d) altering the sites of one or more of the plurality of conductive pathways; and

e) repeating the simulating, plotting, and altering steps until desired B_x =0 contours are achieved.

56. The method of claim 55 wherein the repeating step comprises repeating until a predetermined plurality of B_x =0 contour crossings of an origin are achieved.

57. An apparatus for magnetic resonance imaging, said apparatus comprising a plurality of conductive pathways generating a core volume of magnetic field substantially homogenous in both magnitude and direction, said apparatus being substantially open to an ambient environment of a patient.

58. The apparatus of claim 57 wherein said apparatus comprises a side opening along the long axis of said apparatus through which the patient may pass into and out of said apparatus.

59. The apparatus of claim 57 additionally comprising means for substantially cancelling said magnetic field external to said apparatus, said means for substantially cancelling comprising a plurality of conductive lines external to said plurality of conductive pathways.

60. The apparatus of claim 59 wherein said conductive lines are located at the same azimuthal positions as said plurality of conductive pathways.

61. An apparatus for generating an electromagnetic field having a substantially uniform radial gradient, said apparatus comprising eighteen or more conductive pathways generating a cylindrical core volume of electromagnetic field substantially uniform in radial gradient.

62. The apparatus of claim 61 wherein said conductive pathways are each placed on a circle about a long axis of said cylindrical core volume and are substantially parallel to said long axis.

63. The apparatus of claim 62 wherein said conductive pathways define an approximately biconic volume having a long axis parallel to said long axis of said cylindrical core volume.

64. The apparatus of claim 62 wherein said conductive pathways are placed on said circle mirror symmetrically about both x and y axes of said circle.

65. The apparatus of claim 61 wherein said electromagnetic field comprises a magnetic field.

66. The apparatus of claim 65 wherein each of said conductive pathways comprises a substantially identical line current magnitude.

67. The apparatus of claim 61 wherein said electromagnetic field comprises an electric field.

68. The apparatus of claim 67 wherein each of said conductive pathways comprises a substantially identical line charge.

69. The apparatus of claim 61 additionally comprising means for substantially cancelling said electromagnetic field external to said apparatus, said means for substantially cancelling comprising a plurality of conductive lines equal in number to the number of said conductive pathways.

70. The apparatus of claim 69 wherein said conductive lines are located at the same azimuthal positions as said plurality of conductive pathways.

71. An apparatus for generating an electromagnetic field having a directional rotation in time, said apparatus comprising a plurality of conductive pathways generating a cylindrical core volume of electromagnetic field substantially uniform in magnitude or radial gradient and causing said electromagnetic field to rotate.

72. The apparatus of claim 71 additionally comprising means to cause said electromagnetic field to rotate substantially continuously.

73. The apparatus of claim 71 additionally comprising means to cause said electromagnetic field to rotate by steps.

74. The apparatus of claim 71 wherein said conductive pathways are each placed on a circle about a long axis of said cylindrical core volume and said conductive pathways are substantially parallel to said long axis.

75. The apparatus of claim 71 wherein said plurality of conductive pathways comprises a first and a second set of conductive pathways rotated 90 degrees with respect to each other and wherein a current in said first set varies as sin(a) and a current in said second set varies as cos(a), where a is a variable.

76. The apparatus of claim 71 wherein said plurality of conductive pathways comprises a first and a second set of conductive pathways rotated 90 degrees with respect to each other and wherein a peak current in said first set differs from a peak current in said second set, thereby generating an electromagnetic field whose magnitude varies as said electromagnetic field rotates.

77. The apparatus of claim 71 additionally comprising a solenoid placed around said conductive pathways to provide to said electromagnetic field a field vector having a constant component in the longitudinal direction.

78. The apparatus of claim 71 additionally comprising means for substantially cancelling said electromagnetic field external to said apparatus, said means for substantially cancelling comprising a plurality of conductive lines equal in number to said plurality of conductive pathways.

79. The apparatus of claim 78 wherein said conductive lines are located at the same azimuthal positions as said conductive pathways.

80. The apparatus of claim 71 wherein said apparatus comprises a quadrupole magnet rotating rapidly compared to a transit time of a stream of particles, whereby said stream of particles is focused.

81. An apparatus for generating a homogenous electromagnetic field, said apparatus comprising a plurality of conductive pathways generating a cylindrical core volume of both magnetic and electric field substantially homogenous in both magnitude and direction.

82. The apparatus of claim 81 wherein said conductive pathways are each placed on a circle about a long axis of said cylindrical core volume, said conductive pathways being substantially parallel to said long axis.

83. The apparatus of claim 81 wherein line charges of each of said conductive pathways are substantially identical.

84. An apparatus for generating an electromagnetic field having a substantially uniform nth derivative of field magnitude, said apparatus comprising a plurality of conductive pathways generating a core volume of said electromagnetic field, where n is an integer greater than 1.

85. The apparatus of claim 84 wherein said conductive pathways are each placed on a circle about a long axis of said cylindrical core volume, said conductive pathways being substantially parallel to said long axis.

86. An apparatus for separating substances in mixture or solution comprising means for generating an electric field having a substantially uniform nth derivative of field magnitude, said apparatus comprising a plurality of conductive pathways generating a core volume of said electric field, where n is an integer greater than 1.

87. The apparatus of claim 86 wherein said conductive pathways are each placed on a circle about a long axis of said cylindrical core volume, said conductive pathways being substantially parallel to said long axis.