Infrared defect detection via broad-band acoustics

1. The method of detecting defects in structures, comprising the steps of:

inducing mechanical energy in a structure via the emission of a broad-band acoustic signal;

capturing over a time interval a plurality of images of said structure each of said plurality of images comprised of a plurality of pixels arranged in a plurality of rows and columns each of said pixels indicative of an intensity of infrared energy emitted by a portion of said structure; and

computing a curve for each of said plurality of pixels forming said plurality of images whereby each curve is computed from each of said intensities recorded at a single pixel position in said plurality of images at each of said different times.

2. The method of claim 1 wherein said inducing said mechanical energy comprises the steps of:

generating said broad-band acoustic signal; and

introducing said generated acoustic signal to said structure via an acoustic source.

3. The method of claim 2 wherein said introducing said acoustic signal comprises the steps of:

placing said acoustic signal in physical contact with said structure.

4. The method of claim 2 wherein said generating said broad-band acoustic signal comprises the step of generating an acoustic signal having frequencies in the spectrum between 1 KHz and 1 MHz.

5. The method of claim 4 wherein said generating said broad-band acoustic signal comprises the step of generating an acoustic signal comprising a frequency spectrum between 10 KHz and 50 KHz.

6. The method of claim 2 wherein said generating said broad-band acoustic signal comprises generating an acoustic signal comprising at least two non-harmonically related frequencies.

7. The method of claim 6 wherein said generating step comprises generating a signal at a first frequency centered at 20 KHz and at a second frequency centered at 30 KHz.

8. The method of claim 2 wherein said generating said broad-band acoustic signal comprises generating said acoustic signal for a period of time.

9. The method of claim 8 wherein said period of time is between 0.1 and 2 seconds.

10. The method of claim 9 wherein said period of time is approximately 1.5 seconds.

11. The method of claim 2 wherein said capturing said plurality of images comprises the steps of:

capturing a background image of said structure prior to said inducing said mechanical energy; and

capturing at least one additional image each coincident with said background image such that each corresponding pixel in said background image and in each of said at least one additional image possess a value equal to said intensity of infrared light emitted by a portion of said structure at a different time.

12. The method of claim 1 wherein said structure is selected from the group consisting of fan blades, compressor blades, and gas turbine components.

13. The apparatus for detecting defects in structures comprising:

an acoustic frequency generator adapted to generate a broad-band acoustic energy signal;

an acoustic energy source adapted to transmit said broad-band acoustic energy signal to said structure, said acoustic energy source comprises a signal carrier for transmitting said broad-band acoustic energy signal and a tip designed to maximize contact with a structure for receiving said transmitted broad-band acoustic energy signal and transmitting said broad-band acoustic energy signal to said structure;

an optical device for detecting and recording as a plurality of images an amount of infrared energy emitted by said structure at a plurality of locations; and

an image processor for processing said images.

14. The apparatus of claim 13 wherein said tip is in contact with said signal carrier.

15. The apparatus of claim 13 wherein said tip is adapted to pivot about said signal carrier.

16. The apparatus of claim 13 wherein said tip is comprised of a first material substantially similar to a second material from which said structure is formed.

17. The apparatus of claim 16 wherein said first and second material are selected from the group consisting of nickel, nickel alloys, titanium, steel, and titanium alloys.

18. The apparatus of claim 13 wherein said broad-band acoustic energy source is selected from the group consisting of a non-contact and a limited contact source.

19. The apparatus of claim 18 wherein said broad-band acoustic energy source is selected from the group consisting of an air coupled ultrasonic device and an inductively coupled device.

20. The apparatus of claim 13 wherein said optical device is selected from the group consisting of a CCD device and a fiber optic device.

21. The apparatus of claim 13 wherein said broad-band acoustic energy signal spans a spectrum between 1 KHz and 1 MHz.

22. The apparatus of claim 21 wherein said broad-band acoustic energy signal spans a spectrum between 10 KHz and 50 KHz.

23. The apparatus of claim 13 wherein said broad-band acoustic energy signal comprises at least two non-harmonically related frequencies.

24. The apparatus of claim 23 wherein said broad-band acoustic energy signal comprises a first frequency centered at 20 KHz and a second frequency centered at 30 KHz.

25. The apparatus of claim 13 wherein said broad-band acoustic signal has a duration approximating one and a half seconds.

26. The apparatus of claim 13 wherein said structure is selected from the group consisting of fan blades, compressor blades, and gas turbines.

27. The apparatus of claim 13 wherein said tip is adapted to rotate about said signal carrier.

28. The apparatus of claim 13 wherein said tip is shaped to compliment a surface of said structure.