Magneto-optic Kerr effect stress sensing system

• US 5,493,220 A
• Filed: 03/05/1993
• Issued: 02/20/1996
• Est. Priority Date: 03/05/1993
• Status: Expired due to Fees

• Current Assignee: Northeastern University
• Original Assignee: Northeastern University
• Inventors: Oliver, Steven A., DiMarzio, Charles A., McKnight, Stephen W.
• Primary Examiner(s): O'Shea, Sandra L.
• Assistant Examiner(s): EDMONDS, WARREN
• Application Number:
  US08/026,589
• Time in Patent Office: 1,082 Days
• Field of Search: 324/244, 324/244.1, 324/96, 324/260, 324/209, 324/212, 324/226, 324/225, 324/223, 324/72, 250/225, 250/227.17, 250/231.14, 340/631, 340/665, 73/862.33, 73/862.34, 73/862.36, 350/374-378, 356/33, 356/32, 356/35.5, 359/280-284
• US Class Current: 324/209
• CPC Class Codes: G01B 11/18 using photoelastic elements
• CPC Class Codes: G01D 5/344 using polarisation G01D5/35303 takes precedence
• CPC Class Codes: G01R 33/0325 using the Kerr effect

Abstract

A sensor system including a magnetooptic sensing element, a light source, at least one polarizer and at least one detector disposed about the sensing element. The sensing element has a first characteristic such that the sensing element provides a response to an applied external stress.

Claims

1. A magneto-optic Kerr effect stress sensing system comprising:

a light source;

a magneto-optic Kerr effect stress sensor;

a polarizer disposed between said light source and said magnetooptic Kerr effect stress sensor wherein said light source directs a light beam toward said polarizer and said polarizer passes light having a first predetermined polarization said such that the light having the first predetermined polarization is incident upon said magneto-optic Kerr effect stress sensor;

a polarization splitter disposed to intercept light specularly reflected from said stress sensor wherein said polarization splitter passes at least a portion of the light incident thereon and reflects at least a portion of the light incident thereon wherein said polarization splitter is oriented to mix in a predetermined manner portions of the light signal having the first polarization with portions of the light signal having a second different polarization;

a first detector disposed to receive the portion of the light signal which passes through said polarization splitter; and

a second detector disposed to receive the portion of the light signal which is reflected by said polarization splitter.

2. The sensing system of claim 1 wherein said magneto-optic Kerr effect stress sensor includes a plurality of layers wherein at least one of said plurality of layers is a magnetic thin film.

3. The sensing system of claim 1 further comprising a magnetic shield disposed about said magneto-optic Kerr effect stress sensor.

4. The sensing system of claim 1 wherein said magneto-optic Kerr effect stress sensor includes at least one magnetic layer having an in-plane uniaxial magnetic anisotropy and at least one magnetic domain having a magnetization that rotates coherently in response to an externally applied stress.

5. The sensing system of claim 4 wherein said at least one magnetic layer of said magneto-optic Kerr effect field sensor is provided from a magnetic thin film having at least one of:

a ferri-magnetic layer; and

a ferro-magnetic layer.

6. The sensing system of claim 5 wherein said magneto-optic Kerr effect stress sensor further comprises a dielectric layer over which said thin film is disposed.

7. The sensing system of claim 6 wherein said magneto-optic Kerr effect field sensor includes at least one magnetic layer having a saturation magnetostriction constant in the range of 25×

10^-6 to 60×

10^-6.

8. The sensing system of claim 4 wherein:

said magnetic thin film is provided having a thickness in the range of 5 nanometers to 500 nanometers.

9. The sensing system of claim 5 wherein at least one of the magnetic layers of said thin film is comprised of iron and boron.

10. A stress sensing system comprising:

a light source;

a magneto-optic Kerr effect stress sensor wherein said magnetooptic Kerr effect stress sensor comprises a magnetic film having first and second opposing surfaces and having a uniaxial anisotropy field characteristic of a predetermined intensity, wherein the magnetic film has at least one domain having a magnetization characteristic which rotates in response to application of an applied stress;

a polarizer disposed between said light source and said magnetooptic Kerr effect stress sensor wherein said light source directs a light beam toward said polarizer and said polarizer passes light having a first predetermined polarization said such that the light having the predetermined polarization is incident upon said magnetooptic Kerr effect stress sensor; and

a first detector disposed to receive the portion of the light signal reflected from said magneto-optic Kerr effect stress sensor.

11. The stress sensing system of claim 10 wherein:

said magnetic film is provided having a thickness typically in the range of 5 nanometers to 500 nanometers and is provided from a first one of;

a single layer of a ferro-magnetic material; and

a single layer of a ferri-magnetic material.

12. The sensor system of claim 11 wherein said single layer is comprised of iron and boron.

13. The stress sensing system of claim 10 wherein said stress sensor is disposed such that a hard axis of said magnetic film is disposed at an angle 45 degrees relative to a light plane of incidence and such that a magnetization orientation for no applied stress lies transverse to the hard axis and at a 45 degree angle relative to the light plane of incidence.

14. The stress sensing system of claim 13 further comprising a polarization splitter disposed to intercept light specularly reflected from said stress sensor wherein said polarization splitter passes at least a portion of the light incident thereon and reflects at least a portion of the light incident thereon wherein said polarization splitter is oriented to mix in a predetermined manner portions of the light signal having the first polarization with portions of the light signal having a second different polarization and wherein portions of the lights signal which pass through said polarization splitter are detected by said first detector.

15. The stress sensing system of claim 14 further comprising a second detector disposed to receive the portion of the light signal which is reflected by said polarization splitter.

16. The stress sensing system of claim 13 further comprising a second polarizer disposed to intercept at least a portion of the light signal reflected from said stress sensor wherein said second polarizer attenuates the intensity of light having the first polarization wherein said detector is disposed to detect light which passes through said second polarizer.

17. The stress sensing system of claim 13 further comprising a magnetic shield disposed about said magneto-optic Kerr effect stress sensor.

18. The stress sensing system of claim 13 wherein said magneto-optic Kerr effect stress sensor includes at least one magnetic layer having a saturation magnetostriction constant greater than 25×

10^-6.

19. The stress sensing system of claim 10 wherein said magneto-optic Kerr effect stress sensor is disposed on a coupler half-block.