Faraday effect continuous circuit flux concentrating magnetic field sensor

• US 5,483,161 A
• Filed: 12/11/1992
• Issued: 01/09/1996
• Est. Priority Date: 12/11/1992
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Commerce
• Original Assignee: THE GOVERNMENT OF THE UNITED STATES OF AMERICA, AS REPRESENTED BY THE SECRETARY OF COMMERCE
• Inventors: Deeter, Merritt N., Manheimer, Marc A., Beahn, Thomas J., Day, Gordon W.
• Primary Examiner(s): O'Shea, Sandra L.
• Assistant Examiner(s): Patidar, Jay M.
• Application Number:
  US07/989,990
• Time in Patent Office: 1,124 Days
• Field of Search: 324/96, 324/244, 324/244.1, 324/117 R, 324/117 H, 324/260-262, 324/251-253, 359/280, 359/281, 359/282, 359/283, 250/225, 385/6, 385/12, 385/14, 356/364, 356/368
• US Class Current: 324/244.1
• CPC Class Codes: G01R 33/0322 using the Faraday or Voigt effect

Abstract

A general-purpose magnetic field sensor capable of sensitively measuring uniform magnetic fields includes a magneto-optic (Faraday-effect) sensor and a flux concentrator. Both the magneto-optic sensor and the flux concentrator have high magnetic permeability. The magneto-optic sensor is positioned in close proximity to the flux concentrator. The combination of the high-permeability magneto-optic material and the flux concentrator creates a magnetic circuit which efficiently concentrates the magnetic field into the magneto-optic sensor, and greatly enhances the measurement sensitivity. The preferred embodiment uses a pair of cylindrical flux concentrators in axial alignment. A sensing beam passes through a central axis hole in the cylindrical flux concentrators. The Faraday effect sensor is co-axially aligned with the holes in the cylindrical flux concentrators. The concentrators and Faraday effect sensor create a continuous flux concentrating magnetic circuit.

Claims

1. A magneto-optic magnetic field sensor comprising:

a high-permeability magnetic flux concentrator;

a high-permeability magneto-optic material located in physical contact with said magnetic concentrator and providing a continuous path of high-permeability between the magneto-optic material and the magnetic flux concentrator;

said magnetic concentrator further comprising a cross-sectional area substantially greater than the cross-sectional area of said magneto-optic material;

an optical detector;

a sensing beam of light; and

said magnetic flux concentrator further including a channel therethrough allowing the sensing beam of light to transmit through the channel and simultaneously through the magneto-optic material, and then to the optical detector.

2. The magnetic field sensor of claim 1 wherein said magnetic flux concentrator further comprises a pair of cylindrical members located co-axially one on each end of said magneto-optic material and co-axial to the longitudinal axis of the magneto-optic material.

3. The magnetic field sensor of claim 2 wherein said pair of cylindrical members further comprise a tapered end adjacent said magneto-optic material.

4. The magnetic field sensor of claim 2 wherein said pair of cylindrical members is selected from the group consisting of nickel-zinc ferrite and magnesium-zinc ferrite compositions.

5. The magnetic field sensor of claim 2 wherein said magneto-optic material further comprises a cylindrical shape with the ends of the cylinder partially inserted into said respective channels in said pair of cylindrical members, thereby leaving a gap between said pair of cylindrical members.

6. The magnetic field sensor of claim 1 wherein said magneto-optic material further comprises a ferromagnetic iron garnet crystal.

7. The magnetic field sensor of claim 1 wherein said optical sensing beam further comprises a plane polarized beam formed by the use of a laser beam in conjunction with a collimating lens and a polarizer.

8. A magneto-optic magnetic field sensor comprising:

a high permeability magneto-optic sensor having a longitudinal axis;

a pair of cylindrical high-permeability magnetic flux concentrators aligned on each end of said magneto-optic sensor and in co-axial alignment with said magneto-optic sensor;

said pair of flux concentrators each further comprising a hole along its longitudinal axis and a cross-sectional area substantially greater than said magneto-optic sensor;

said magneto-optic sensor further comprising partial insertion into each of said flux concentrator holes leaving a gap between said flux concentrators;

a linearly-polarized sensing beam passing through one of said flux concentrator holes then said magneto-optic sensor then the other of said flux concentrator holes; and

a detector sensing changes in the sensing beam intensity caused by changes in the Faraday rotation of the sensing beam as the sensing beam passes through the magneto-optic sensor and a polarizer.