Fiber optic ice detector

• US 5,748,091 A
• Filed: 10/04/1996
• Issued: 05/05/1998
• Est. Priority Date: 10/04/1996
• Status: Expired due to Fees

• Current Assignee: Mcdonnell Douglas Corporation (The Boeing Co.)
• Original Assignee: Mcdonnell Douglas Corporation (The Boeing Co.)
• Inventors: Kim, John Jungwoo
• Primary Examiner(s): Mullen, Thomas
• Assistant Examiner(s): Huang, Sihong
• Application Number:
  US08/726,102
• Time in Patent Office: 578 Days
• Field of Search: 340/583, 340/962, 340/580, 356/381, 356/382, 73/170.26, 244/134 F
• US Class Current: 340/583
• CPC Class Codes: G08B 19/02 Alarm responsive to formation or anticipated formation of ice

Abstract

The thickness of a semi transparent layer, such as ice, is determined by supporting the layer atop or above a light transmissive window and directing multiple light beams through the light transmissive window and into the layer. The light transmissive window has a higher index of refraction than the layer or any intermediate layer directly above the semi-transparent layer. Light beams are directed at an angle to the surface that results in total internal reflection from the outer surface of the supported semi-transparent layer. The light reflected to the rear of the window at the same but opposite angle is monitored and correlates to the thickness of the monitored layer. The spatial distribution of reflected light along the longitudinal axis of the window changes in dependence upon the thickness of the supported layer. Quantitative indications of that thickness are displayed and should that thickness exceed a prescribed level an alarm may be generated. The monitoring system has application as a non-intrusive ice detection system for aircraft airfoil surfaces.

Claims

1. Apparatus for monitoring the thickness of a semi-transparent material within a gaseous environment, comprising:

a detector window, having front and back sides, and being of a first predetermined thickness;

said front side of said detector window for supporting the semi-transparent material whose thickness is to be monitored;

light beam directing means for directing a plurality of individual light beams at said detector window at a first predetermined angle to said back side of said detector window;

said light beam directing means comprising a plurality of first optical fibers displaced in position relative to one another so as to be distributed longitudinally along the back side of said detector window;

light beam detector array means spaced from said light beam directing means;

said light beam detector array means comprising;

a plurality of second optical fibers for receiving light propagating at a second predetermined angle to said back side of said detector window, said second predetermined angle being opposite in direction relative to said back side of said detector window as said first predetermined angle; and

said second optical fibers being displaced in position from one another relative to said back side of said detector window so as to be distributed longitudinally along said detector window; and

at least a plurality of longitudinally displaced light detectors optically coupled to respective ones of said plurality of second optical fibers whereby light propagating into a second optical fiber is coupled to a corresponding one of said light detectors;

each said light detector producing an electrical output signal in dependence upon the intensity of incident light; and

means for monitoring the spatial distribution of light represented by said light detectors to indicate the thickness of said semi-transparent material.

2. The apparatus as defined in claim 1, wherein said first predetermined angle is equal and opposite in direction to said second predetermined angle.

3. The apparatus as defined in claim 1, further comprising alarm means coupled to said monitoring means for providing a perceptible indication when the thickness of said semi-transparent material achieves a predetermined level.

4. The apparatus as defined in claim 1, wherein each said light detector comprises a photodetector array.

5. The apparatus as defined in claim 1, wherein said detector window comprises the material fused quartz.

6. The apparatus as defined in claim 1, wherein said detector window comprises laminate layers of glass and fused quartz.

7. The apparatus as defined in claim 1, wherein the ends of said first and second optical fibers and said window are integrally attached.

8. The apparatus as defined in claim 1 wherein said semi-transparent material is of a first index of refraction, n1, where n1 is greater than the index of refraction of said gaseous environment;

and said detector window is of an index of refraction, n2, wherein n2 is greater than n1.

9. The apparatus as defined in claim 8, wherein said first predetermined angle is equal and opposite in direction to said second predetermined angle and further comprising:

alarm means coupled to said monitoring means for providing a perceptible indication when the thickness of said semi-transparent material achieves a predetermined level.

10. A method of determining the thickness of a light transmissive layer of material in a gaseous medium, said light transmissive layer having a first index of refraction, n1, that is greater than the index of refraction of said gaseous medium, comprising the steps of:

placing said layer of material upon the upper surface of a light transmissive window, said light transmissive window having an index of refraction, n2, greater than n1;

concurrently directing a plurality of beams of light into said light transmissive window from a number of longitudinally distributed locations along a back surface of said window;

said beams being directed at a predetermined angle to said upper surface, α

, at which said light beams propagate through said window and said layer of material, and at which total reflection occurs at the juncture between said upper surface of said light transmissive window and said gaseous medium, whereby a plurality of beams of light are reflected back through said light transmissive window;

inspecting the spatial distribution of said reflected light beams at least along a longitudinal axis of said window, said spatial distribution being correlated to the thickness of said light transmissive layer.

11. The method as defined in claim 10, wherein said light beams comprise light of a single wavelength.

12. The method as defined in claim 10, wherein said light beam comprise light having multiple wavelengths.

13. Apparatus for monitoring the thickness of a light transmissive layer, comprising:

a detector window, said detector window being of predetermined thickness and having a front surface and a rear surface;

said front surface of said detector window for supporting said light transmissive layer, the thickness of which is to be monitored;

light beam directing means for directing a plurality of individual light beams into said detector window at a first predetermined angle, α

, to said front surface;

said light beam directing means comprising a plurality of first optical fibers, each of said first optical fibers having an output window for outputting light;

light beam detector array means spaced from said light beam directing means, said light beam detector array means comprising;

a plurality of second optical fibers extending between first and second opposed ends;

wherein a side surface of each of said second optical fibers includes an input window defining a lens for receiving light reflected from within said detector window at a second predetermined angle, β

, to said front surface of said detector window; and

wherein said plurality of second optical fibers are positioned such that said input windows of said plurality of second optical fibers are displaced in position from one another longitudinally relative to said detector window such that said input window of each second optical fiber is exposed to said detector window.

14. The apparatus as defined in claim 13, further comprising:

at least a plurality of longitudinally displaced light detectors, each being optically coupled to a respective one of said plurality of second optical fibers, whereby light propagating into a second optical fiber is coupled to a corresponding one of said light detectors;

each said light detector producing an electrical output signal in dependence upon the intensity of incident light; and

means for monitoring the spatial distribution of light represented by said light detectors to indicate the thickness of said light transmissive layer.

15. The apparatus as defined in claim 14, further comprising alarm means coupled to said monitoring means for providing a perceptible indication when the thickness of said light transmissive layer achieves a predetermined level.

16. The apparatus as defined in claim 13, wherein said detector window comprises the material fused quartz.

17. The apparatus as defined in claim 13, wherein said detector window comprises laminate layers of glass and fused quartz.

18. The apparatus as defined in claim 13, wherein said detector window comprises plastic

19. The apparatus as defined in claim 13, wherein each of said second optical fibers of said light beam detector array means further includes:

light blocking means for preventing passage of light through said side surface and each of said first and second ends, excluding said input window defined by said side surface;

wherein said second optical fibers are stacked atop one another with said second ends thereof being consecutively horizontally staggered in position to expose each of said input windows and form a staircase like end configuration;

wherein a second end of an uppermost one of said second optical fibers is horizontally positioned spaced from the horizontal position of a corresponding second end of an underlying one of said second optical fibers to expose said input window of said underlying one of said second optical fibers.

20. Apparatus for monitoring the thickness of a light transmissive layer, comprising:

a detector window, said detector window being of predetermined thickness and having a front surface and a rear surface;

said front surface of said detector window for supporting said light transmissive layer, the thickness of which is to be monitored;

light beam directing means for directing a plurality of individual light beams into said detector window at a first predetermined angle, α

, to said front surface, said light beam directing means comprising a plurality of first optical fibers extending between a first end and a second end;

wherein a side surface of each first optical fiber light beam detector array means spaced from said light beam directing means, said light beam detector array means comprising a plurality of second optical fibers for receiving light reflected from within said detector window at a second predetermined angle, β

, to said front surface of said detector window.

21. The apparatus as defined in claim 20, wherein said detector window comprises the material plastic;

and wherein said plurality of first and second optical fibers are at least partially encased within said detector window.

22. The apparatus as defined in claim 21, further comprising:

first optical connector means attached to said first end of said plurality of first optical fibers and second optical connector means connected to a first end of said plurality of second optical fibers.