Pressure sensor based on illumination of a deformable integrating cavity

• US 5,917,180 A
• Filed: 07/16/1997
• Issued: 06/29/1999
• Est. Priority Date: 07/16/1997
• Status: Expired due to Term

• Current Assignee: Canadian Space Agency (Government of Canada)
• Original Assignee: Canadian Space Agency (Government of Canada)
• Inventors: Reimer, Ernest M., Danisch, Lee
• Primary Examiner(s): LE, QUE TAN
• Application Number:
  US08/895,268
• Time in Patent Office: 713 Days
• Field of Search: 250/227.14, 250/227.16, 250/227.18, 250/231.1, 340/541, 340/555-557, 73/768, 73/774, 73/783, 356/32-35
• US Class Current: 250/227.14
• CPC Class Codes: G01L 1/24 by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet

Abstract

A pressure sensor relies on detecting multiply scattered light within an optical cavity. Changes in the volume of the cavity are sensed by the change in sampled light intensity. Pressure sensitive mats with a high density of sensor are assembled using optical fiber technology.

Claims

1. A pressure sensor comprising:

(1) a compressible carrier medium of wave energy transmitting material having an outer boundary;

(2) a wave energy source coupled to said carrier medium;

(3) wave energy scattering centers dispersed within said carrier medium to create a scattered energy volume containing scattered wave energy;

(4) a wave energy receiver responding to the integrated intensity of scattered wave energy by producing a signal; and

(5) signal coupling means connected to the wave energy receiver for transferring the signal therefrom to a pressure indicator,

wherein, upon displacement of the outer boundary, the dimensional volume of the scattered energy volume changes in response to changes in an externally applied pressure to provide a change in the intensity of the scattered wave energy so that a signal is thereby produced to permit the pressure indicator to provide a measure of the applied pressure.

2. A pressure sensor as in claim 1 wherein:

(1) the compressible carrier medium is of light-transmitting material;

(2) the wave energy source is a light source;

(3) the scattering centers dispersed within said carrier medium are light scattering centers; and

(4) the wave energy receiver is a light detector for sensing scattered light within said carrier medium.

3. A pressure sensor as in claim 2 wherein the light detector does not intercept light or originating directly from the light source.

4. A pressure measuring system comprising:

(1) a source of illumination;

(2) a compressible light scattering medium or hollow compressible structure defining an integrating cavity within which light from the source of illumination is diffused and integrated through scattering,

(3) a light sensing means directed in a viewing direction to sample diffused and integrated light arising from multiple scattering within the integrating cavity and provide a signal indicative of the intensity of the diffused and integrated light; and

(4) signal coupling means connected to the light sensing means for transferring the signal to a pressure indicator,

wherein the volume of the integrating cavity changes in response to changes in externally applied pressure to provide a variation in the intensity of the diffused and integrated light so that a signal is thereby produced to permit the pressure indicator to provide a measure of the applied pressure.

5. A pressure measuring system as in claim 4 wherein the volume of the integrating cavity is responsive to external pressure applied in a lateral direction to the viewing direction.

6. A pressure measuring system as in claim 5 wherein the source of illumination is outside the viewing direction.

7. A pressure measuring system comprising:

(1) a source of illumination providing a field of illumination;

(2) a light scattering body positioned within the field of illumination to provide an illuminated region that is illuminated by multiply-reflected scattered light, such illuminated region having a volume which is compressible under the application of pressure to the light scattering body;

(3) a light sensing means directed to view multiply-reflected scattered light from the illuminated region to thereby provide a signal indicative of the intensity of the scattered light within the illuminated region; and

(4) signal coupling means connected to the light sensing means for transferring the signal to a pressure indicator

wherein, upon pressure being applied to the light scattering body to effect a change in the volume of the illuminated region a change in the intensity of scattered light within the illuminated region will occur, and the light sensing means provides a signal that corresponds to the amount of the applied pressure to permit the pressure indicator to provide a measure of the applied pressure.

8. A pressure measuring system as in claim 7 wherein the light scattering body is in the form of a flexible sheet having a surface and the illuminated region is a cavity defined in part by a surface of such sheet.

9. A pressure measuring system as in claim 7 wherein the light scattering body is a self-supporting, matrix that is translucent and the illuminated region includes a zone within the matrix wherein light from the source of illumination is being scattered.

10. A pressure measuring system as in claim 7 wherein the light sensing means comprises an optical fiber with a terminal, viewing end directed to receive said scattered light.

11. A pressure measuring system as in claim 10 wherein the source of illumination comprises an optical fiber.

12. A pressure measuring system as in claim 11 wherein the light sensing means and source of illumination both share the same optical fiber.

13. A pressure measuring system as in claims 4, 5, 6, 7, 8, 9, 10, 11 or 12 wherein the source of illumination and light sensing means comprise an array of individual illumination means and individual light sensors to respectively provide:

(1) multiple localized portions of the field of illumination formed as illuminated locations associated with the light scattering body; and

(2) multiple individual signals indicative of the intensity of scattered light arising from the associated illuminated locations of the reflecting body

to permit the pressure indicator to provide a measure of applied pressure at a plurality of discrete locations associated with the array.

14. A pressure measuring system as in claim 13 wherein the array is planar.

15. A pressure measuring system as in claim 13 wherein the array is a first array, formed in a first plane, in combination with a second array of individual illumination means and individual light sensors formed in a second plane wherein:

(1) the first and second arrays are positioned adjacent to each other with their respective planes parallel or coincident; and

(2) the individual illuminated locations for which each array provides a measure of applied pressure are laterally displaced from each other so as to be independently exposed to receive applied pressure.

16. A pressure measuring system as in claim 7 further comprising

an elastically resilient, planar, cover sheet having a light scattering lower surface overlying and at least partially lying within the field of illumination and illuminated region

wherein, upon downward deflection within said field of illumination of the cover sheet and said light scattering lower surface under the effect of pressure applied thereto, the apparent brightness of illumination detected by the light sensing means changes as a measure of applied pressure and provides the corresponding signal output from said light sensing means.

17. A pressure sensor as in claim 16 wherein the planar cover sheet is non-transmissive of light to exclude ambient light from entering the field of view.

18. A pressure sensor as in claim 16 wherein the source and detector of illumination are contiguous.

19. A pressure sensor as in claim 16 wherein the cover sheet is formed of a solid elastomeric material.

20. A pressure sensor as in claim 16 wherein the cover sheet comprises a translucent, elastically resilient, light scattering medium that is compressible in the sense of being volumetrically compactable, positioned within the field of view of the detector and the zone of illumination.

21. A pressure measuring system as claim in claim 13 wherein said sensors each comprise an optical fiber and said array of sensors is characterized by a distribution arrangement for sensing a pressure pattern impinging on said apparatus and the signal output from each of said sensors is arranged in an output array corresponding with said distribution arrangement for optical scanning display or viewing for reconstruction of said pressure pattern.

22. A pressure measuring system as claimed in any of claims 4, 5, 6, 7, 8, 9, 10, 11 or 12 further characterized by an optical-to-electronic signal processor associated with each of said sensors for display by an electronic display.

23. A pressure measuring system as claimed in claim 22 wherein said apparatus includes an array of said sensors having a distribution arrangement for sensing a pressure pattern impinging on said apparatus, and the signal output from each of said sensors is arranged in an output array corresponding with said distribution arrangement for optical scanning display or viewing for reconstruction of said pressure pattern.

24. A pressure measuring system as claimed in any of claims 16, 17, 18, 19 or 20 further characterized by an optical-to-electronic signal processor associated with each of said sensors for display by an electronic display.

25. A pressure measuring system as claimed in claim 24 wherein said apparatus includes an array of said sensors having a distribution arrangement for sensing a pressure pattern impinging on said apparatus, and the signal output from each of said sensors is arranged in an output array corresponding with said distribution arrangement for optical scanning display or viewing for reconstruction of said pressure pattern.