Variable permeability magnetic field sensor and method

• US 20050146326A1
• Filed: 10/20/2004
• Published: 07/07/2005
• Est. Priority Date: 01/15/2002
• Status: Active Grant

• Current Assignee: National University of Singapore
• Original Assignee: National University of Singapore
• Inventors: Li, Xiaoping
• Granted Patent: US 7,196,514 B2
• Time in Patent Office: Days
• US Class Current: 324/250
• CPC Class Codes: G01R 33/04 using the flux-gate principle

Abstract

A magnetic field sensor relies on variations in permeability of magnetic material to detect an external field. An exemplary magnetic field sensor includes a lengthwise extending sensing element, and a coil wound about the sensing element. The sensing element may be formed as a number of geometrically and magnetically similar or identical sensing elements driven by an AC magnetic field. An external magnetic field changes the magnetic characteristics of the sensing element and induces a change in electric potential of the induction coil. The sensor output is proportional to the number of components of the sensing element.

Claims

1. A magnetic field sensor, comprising:

a conductive core, surrounded by a magnetic layer;

a coil wound about said magnetic layer;

a source of electrical energy, providing electrical energy to said conductive core to establish a magnetic field in said magnetic layer, said magnetic field having a magnitude at which there is a linear relationship between said magnetic field and permeability of said magnetic layer;

a sensor for detecting changes in voltage across said coil, resulting from changes in said permeability of said magnetic layer, attributable to an external magnetic field.

2. The sensor of claim 1, further comprising a plurality of parallel, lengthwise extending conductive cores connected in parallel, and wherein said coil is wound about said plurality of conductive cores.

3. The sensor of claim 2, wherein said plurality of conductive cores are geometrically identical.

4. The sensor of claim 2, wherein each of said plurality of conductive cores comprises a ferromagnetic wire.

5. The sensor of claim 2, wherein said each of said plurality of conductive cores is a ferromagnetic thin film.

6. The sensor of claim 2, wherein each of said plurality of conductive cores comprises a conductive wire core coated with a layer of ferromagnetic materials.

7. The sensor of claim 2, wherein said plurality of conductive cores are formed within a lengthwise extending multilayer composite thin film block with each of said conductive cores surrounded by high permeability material.

8. The sensor of claim 7, further comprising insulating material between said high permeability material.

9. The sensor of claim 8, wherein each of said conductive cores is formed as a conductive strip.

10. The sensor of claim 2, wherein said changes in voltage across said coil are proportional to the number of said conductive cores.

11. A method of sensing a low frequency external magnetic field comprising:

exciting a magnetic element with a time varying magnetic field parallel to the longitudinal extent of the said magnetic element, said magnetic field having a frequency and amplitude to maximize the sensitivity of the permeability of said magnetic element to magnetic field in said magnetic element;

sensing said external magnetic field by measuring variation of said permeability of said magnetic element, resulting from said external magnetic field by measuring an induced voltage in a coil coiling said magnetic element.

12. The method of claim 11, wherein said frequency and amplitude are selected in dependence on magnetic properties of said magnetic element.

13. The method of claim 11, wherein said magnetic element comprises a plurality of lengthwise extending conductive elements, each coated with a magnetic layer.

14. A magnetic field sensor, comprising:

a sensing element formed at least in part of a magnetic material;

a coil wound about said sensing element;

a source of electrical energy, providing electrical energy to said sensing element to establish a magnetic field in said sensing element, said magnetic field having a magnitude at which there is a linear relationship between said magnetic field and permeability of said magnetic material in said sensing element;

a circuit for detecting changes in voltage across said coil, resulting from changes in said permeability of said sensing element, attributable to an external magnetic field.

15. The sensor of claim 14, wherein said sensing element comprises a plurality of parallel, lengthwise extending conductive cores, each surrounded by a magnetic layer.

16. The sensor of claim 15, wherein said plurality of conductive cores are geometrically identical.

17. The sensor of claim 16, wherein each of said plurality of conductive cores comprises a ferromagnetic wire.

18. The sensor of claim 17, wherein said each of said plurality of conductive cores is a ferromagnetic thin film.

19. The sensor of claim 18, wherein each of said plurality of conductive cores comprises a conductive wire core coated with a layer of ferromagnetic materials.

20. The sensor of claim 14, wherein said plurality of conductive cores are formed within a lengthwise extending multilayer composite thin film block with each of said conductive cores surrounded by high permeability material.

21. The sensor of claim 20, further comprising insulating material between said high permeability material.

22. The sensor of claim 14, wherein each of said conductive cores is formed as a conductive strip.

23. The sensor of claim 14, wherein said changes in voltage across said coil are proportional to the number of said conductive cores.