Fiber optic grating corrosion and chemical sensor

• US 6,144,026 A
• Filed: 10/16/1998
• Issued: 11/07/2000
• Est. Priority Date: 10/17/1997
• Status: Expired due to Fees

• Current Assignee: Blue Road Research, Inc., The Boeing Co.
• Original Assignee: Blue Road Research, Inc., The Boeing Co.
• Inventors: Trego, Angela, Haugse, Eric D., Udd, Eric
• Primary Examiner(s): Allen, Stephone B.
• Application Number:
  US09/174,023
• Time in Patent Office: 753 Days
• Field of Search: 250/227.14, 250/227.17, 250/227.18, 250/227.23, 250/231.19, 356/32, 356/35.5, 73/800, 385/37, 385/11, 385/12
• US Class Current: 250/227.14
• CPC Class Codes: G01D 5/35383 using multiple sensor devices using multiplexing techniques
• CPC Class Codes: G01M 3/047 with photo-electrical detection means, e.g. using optical fibres
• CPC Class Codes: G01N 17/00 Investigating resistance of materials to the weather, to corrosion, or to light

Abstract

A fiber grating corrosion sensor system which includes fiber grating corrosion and/or chemical sensors formed by writing one or more fiber gratings that are transverse load sensitive so that when corrosion occurs to a transverse stress applying sleeve there over, the transverse loading is relieved. The spectral signals from the fiber grating sensors change with variations in transverse strain providing a measurement of the degree of corrosion or change in chemical content.

Claims

1. A fiber grating sensor including:

a fiber grating element, having;

a fiber grating therein; and

a covering positioned about said fiber grating element to apply transverse stress to said fiber grating, said covering being constructed from material that weakens to reduce the transverse stress applied to said fiber grating when subjected to an environment whose effect is to be sensed.

2. The fiber grating sensor as defined in claim 1 wherein said fiber grating element includes:

a birefringent fiber with said fiber grating written into said birefringent fiber.

3. The fiber grating sensor as defined in claim 1 wherein said fiber grating includes:

a first fiber grating having a first spacing; and

a second fiber grating having a second spacing, and wherein said fiber grating element includes;

a birefringent fiber with said first and second fiber gratings written into said birefringent fiber at essentially the same place.

4. The fiber grating sensor as defined in claim 1 wherein said fiber grating includes:

a first fiber grating having a first spacing; and

a second fiber grating having a second spacing, and wherein said first and second fiber gratings are written into said fiber grating element at essentially the same place.

5. The fiber grating sensor as defined in claim 1 wherein said fiber grating element includes:

a sidehole optical fiber with said fiber grating written into said sidehole optical fiber.

6. The fiber grating sensor as defined in claim 1 wherein said fiber grating includes:

a first fiber grating having a first spacing; and

a second fiber grating having a second spacing, and wherein said fiber grating element includes;

a sidehole optical fiber with said first and second fiber gratings written into said sidehole optical fiber at essentially the same place.

7. The fiber grating sensor as defined in claim 1 wherein said fiber grating includes:

a first fiber grating having a first spacing; and

a second fiber grating having a second spacing, and wherein said fiber grating element includes;

a birefrigent sidehole optical fiber with said first and second fiber gratings written into said birefrigent sidehole optical fiber at essentially the same place.

8. The fiber grating sensor as defined in claim 1 wherein said fiber grating element includes:

a first semi-cylindrical element positioned between said covering and said fiber grating; and

a second semi-cylindrical element positioned between said covering and said fiber grating opposite said first semi-cylindrical element, whereby said covering forces said first and second semi-cylindrical elements together about said fiber grating.

9. The fiber grating sensor as defined in claim 8 wherein said fiber grating element includes:

a birefringent fiber with said fiber grating written into said birefringent fiber.

10. The fiber grating sensor as defined in claim 8 wherein said fiber grating includes:

a first fiber grating having a first spacing; and

a second fiber grating having a second spacing, and wherein said fiber grating element includes;

a birefringent fiber with said first and second fiber gratings written into said birefringent fiber at essentially the same place.

11. The fiber grating sensor as defined in claim 8 wherein said fiber grating includes:

a first fiber grating having a first spacing; and

a second fiber grating having a second spacing, and wherein said first and second fiber gratings are written into said fiber grating element at essentially the same place.

12. The fiber grating sensor as defined in claim 8 wherein said fiber grating element includes:

a sidehole optical fiber with said fiber grating written into said sidehole optical fiber.

13. The fiber grating sensor as defined in claim 8 wherein said fiber grating includes:

a first fiber grating having a first spacing; and

a second fiber grating having a second spacing, and wherein said fiber grating element includes;

a sidehole optical fiber with said first and second fiber gratings written into said sidehole optical fiber at essentially the same place.

14. The fiber grating sensor as defined in claim 8 wherein said fiber grating includes:

a first fiber grating having a first spacing; and

a second fiber grating having a second spacing, and wherein said fiber grating element includes;

a birefrigent sidehole optical fiber with said first and second fiber gratings written into said birefrigent sidehole optical fiber at essentially the same place.

15. A fiber grating sensor system including:

a first fiber grating element, having;

a first fiber grating therein; and

a covering positioned about said first fiber grating element to apply transverse stress to said first fiber grating, said covering being constructed from material that weakens to reduce the transverse stress applied to said first fiber grating when subjected to an environment whose effect is to be sensed.

16. The fiber grating sensor system as defined in claim 15 further including:

a light source for producing a first light beam;

a beamsplitter operatively connected to said light source and said first fiber grating element to transmit the first light beam to said first fiber grating; and

detector means to monitor changes in reflection spectra of said first light beam from said first fiber grating, whereby changes in said reflection spectra indicate reduced transverse stress applied to said first fiber grating.

17. The fiber grating sensor system as defined in claim 16 further including:

a second fiber grating element operatively connected to said beamsplitter to receive said first light beam, said detector means also monitoring reflection spectra of said first light beam from said second fiber grating, the reflection spectra from said second fiber grating being a measure of axial strain and temperature, transverse strain, corrosion, hydrogen presence, ice presence, pressure, or multiaxis strain.

18. The fiber grating sensor system as defined in claim 17 wherein said light source produce the first light beam in a series of spaced pulses, and wherein said first and second fiber grating elements are spaced from each other further than half the distance light can travel during the length of each pulse.

19. The fiber grating sensor system as defined in claim 16 wherein said first fiber grating element includes:

a birefringent fiber with said first fiber grating written into said birefringent fiber.

20. The fiber grating corrosion sensor as defined in claim 16 wherein said first fiber grating has a first spacing and wherein said first fiber grating also includes:

a second fiber grating having a second spacing, and wherein said first fiber grating element includes an optical fiber chosen from the group consisting of

a birefringent fiber; and

a sidehole optical fiber.