Generating highly uniform electromagnetic field characteristics

• US 5,717,371 A
• Filed: 05/31/1995
• Issued: 02/10/1998
• 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 Terry
• Primary Examiner(s): DONOVAN, LINCOLN D
• Application Number:
  US08/455,819
• Time in Patent Office: 986 Days
• Field of Search: 335/216, 335/296, 335/297, 335/299, 335/300, 335/301, 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 canceling 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 eight conductive pathways disposed about and substantially parallel to said central axis, azimuthal locations, current or charge magnitudes, and distances from said central axis of said conductive pathways being substantially defined by;

solutions to one or more equations selected from the group consisting of ##EQU11## where N is a number of conductive pathways per quadrant, φ

_n are the azimuthal locations of said conductive pathways, R_n are the distances from said central axis of said conductive pathways, I_n are the current or charge magnitudes, w is selected from the group consisting of 0 and 0.5, J is an integer equal to 2(N+w)-1, C is a collection of J equations to be solved, all identical except that running index j changes from 1 to J from equation to equation, Σ

is a sum of N terms in each equation over index n, m is an integer greater than 0, and either not all current or charge magnitudes are substantially equal in absolute value or not all distances from said central axis are substantially equal;

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.

2. 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, separator of particles from fluids, and a rasterizer.

3. 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 eight conductive pathways disposed about and substantially parallel to the central axis, azimuthal locations, current or charge magnitudes, and distances from the central axis of the conductive pathways being substantially defined by;

solutions to one or more equations selected from the group consisting of ##EQU12## where N is a number of conductive pathways per quadrant, φ

_n are the azimuthal locations of said conductive pathways, R_n are the distances from said central axis of said conductive pathways, I_n are the current or charge magnitudes, w is selected from the group consisting of 0 and 0.5, J is an integer equal to 2(N+w)-1, C is a collection of J equations to be solved, all identical except that running index j changes from 1 to J from equation to equation, Σ

is a sum of N terms in each equation over index n, m is an integer greater than 0, and either not all current or charge magnitudes are substantially equal in absolute value or not all distances from said central axis are substantially equal; 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.

4. The method of claim 3 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, separator of particles from fluids, and a rasterizer.

5. 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;

shield means at a uniform radius R_s from said central axis; and

at least four conductive pathways disposed about and substantially parallel to said central axis, azimuthal locations, current or charge magnitudes, and distances from said central axis of said conductive pathways being substantially defined by;

solutions to one or more equations selected from the group consisting of ##EQU13## where N is a number of conductive pathways per quadrant, φ

_n are the azimuthal locations of said conductive pathways, R_n are the distances from said central axis of said conductive pathways, I_n are the current or charge magnitudes, w is selected from the group consisting of 0 and 0.5, J is an integer equal to 2(N+w)-1, C is a collection of J equations to be solved, all identical except that running index j changes from 1 to J from equation to equation, Σ

is a sum of N terms in each equation over index n, and m is an integer greater than 0;

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.

6. The apparatus of claim 5 wherein said shield means comprises a member selected from the group consisting of ferromagnetic shields and conducting shields.

7. 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) locating a shield at a uniform radius R_s from the central axis;

c) situating at least four conductive pathways disposed about and substantially parallel to the central axis, azimuthal locations, current or charge magnitudes, and distances from the central axis of the conductive pathways being substantially defined by;

solutions to one or more equations selected from the group consisting of ##EQU14## where N is a number of conductive pathways per quadrant, φ

_n are the azimuthal locations of the conductive pathways, R_n are the distances from the Central axis of the conductive pathways, I_n are the current or charge magnitudes, w is selected from the group consisting of 0 and 0.5, J is an integer equal to 2(N+w)-1, C is a collection of J equations to be solved, all identical except that running index j changes from 1 to J from equation to equation, Σ

is a sum of N terms in each equation over index n, and m is an integer greater than 0; and

d) 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.

8. The method of claim 7 wherein the locating step comprises locating a shield selected from the group consisting of ferromagnetic shields and conducting shields.