Contaminant detection sytem

• US 5,629,485 A
• Filed: 12/13/1994
• Issued: 05/13/1997
• Est. Priority Date: 12/13/1994
• Status: Expired due to Fees

• Current Assignee: Goodrich Corporation (Rtx Corporation)
• Original Assignee: Goodrich Corporation (Rtx Corporation)
• Inventors: Peterson, Michael T., Pilarski, deceased, Aleksander B., Readio, Philip O., Rose, Joseph L., Hammer, Jeffrey M.
• Primary Examiner(s): Oda, Christine K.
• Application Number:
  US08/355,357
• Time in Patent Office: 882 Days
• Field of Search: 340/580, 340/582, 340/962, 364/563, 244/134 F, 367/13, 73/170.26, 73/579, 73/583, 73/599
• US Class Current: 73/599
• CPC Class Codes: B64D 15/20 Means for detecting icing or initiating de-icing
• CPC Class Codes: G01N 2291/011 Velocity or travel time
• CPC Class Codes: G01N 2291/014 Resonance or resonant frequency
• CPC Class Codes: G01N 2291/023 Solids
• CPC Class Codes: G01N 2291/0251 Solidification, icing, curing composites, polymerisation
• CPC Class Codes: G01N 2291/0427 Flexural waves, plate waves, e.g. Lamb waves, tuning fork, cantilever
• CPC Class Codes: G01N 2291/057 Angular incidence, parallel to surface propagation
• CPC Class Codes: G01N 2291/102 one emitter, one receiver
• CPC Class Codes: G01N 29/11 by measuring attenuation of acoustic waves
• CPC Class Codes: G01N 29/2462 Probes with waveguides, e.g. SAW devices
• CPC Class Codes: G01N 29/2487 Directing probes, e.g. angle probes directing arrangements G01N29/221
• CPC Class Codes: G01N 29/28 providing acoustic coupling , e.g. water impedance matching G10K11/02
• CPC Class Codes: G01N 29/348 with frequency characteristics, e.g. single frequency signals, chirp signals measuring frequency of mechanical vibrations or acoustic waves in general G01H1/06, G01H3/04; measuring frequency or analysing frequency spectra G01R23/00
• CPC Class Codes: G01N 29/4436 with a reference signal amplitude comparison G01N29/48
• CPC Class Codes: G01N 29/4445 Classification of defects
• CPC Class Codes: G01N 29/46 by spectral analysis, e.g. Fourier analysis or wavelet analysis spectral signal processing per se G06F17/14

Abstract

A contaminant detection system includes a transmitter for transmitting a guided wave through the skin at particular resonances, wherein each resonance point utilized will have propagation characteristics sensitive to a condition of interest. A contaminant may then be classified by transmitting several resonances and then carrying out appropriate feature extraction and pattern recognition techniques utilizing a host processor.

Claims

1. A method of detecting contaminants on a skin exposed to the environment comprising the steps of:

disposing a contaminant detection sheet on the skin, wherein the sheet is exposed to the environment and acoustically isolated from the skin;

transmitting a guided wave through the sheet at a phase velocity corresponding to multiple resonances as indicated on a dispersion curve for the sheet;

receiving the wave transmitted through the sheet and providing a received signal indicative thereof, wherein the received signal has a frequency signature; and

extracting features from the frequency signature of said received signal for classifying contaminants on the skin.

2. A method of detecting contaminants on a skin in accordance with claim 1, wherein said extracting step extracts amplitude features from said received signal.

3. A method of detecting contaminants on a skin in accordance with claim 1, further comprising the step of comparing said extracted features of said received signal with said transmitted guided wave.

4. A method of detecting contaminants on a skin in accordance with claim 1, wherein said transmitting and receiving steps are done utilizing different transducers.

5. A method of detecting contaminants on a skin in accordance with claim 1, wherein said transmitting and receiving steps are done utilizing a single transducer.

6. A method of detecting contaminants on a skin in accordance with claim 1, further comprising the steps of repeating said transmitting, receiving and extracting steps a multiplicity of times.

7. A method of detecting contaminants on a skin in accordance with claim 1, further comprising the step of comparing said received signal with a predetermined test signal.

8. A method of detecting contaminants on a skin in accordance with claim 1, wherein said transmitting step transmits ultrasonic guided waves at a nonperpendicular angle to the sheet.

9. The method of claim 1, further comprising the step of exciting a frequency bandwidth of less than 0.5 MHZ·

mm and phase velocity bandwidth of less than 0.5 mm/sec about at least one resonant point indicated on the dispersion curve.

10. An apparatus for detecting contaminants on a skin exposed to the environment comprising:

a contaminant detection sheet disposed on the skin, wherein the sheet is exposed to the environment and is acoustically isolated from the skin;

a transmitter for transmitting a guided wave through the sheet at a phase velocity corresponding to multiple resonances of the sheet;

a receiver for receiving said guided wave transmitted through the sheet;

means for providing a received signal indicative of the received wave, wherein the received wave has a frequency signature; and

a signal processor for extracting features from the frequency signature of said received signal for classifying contaminants on the skin.

11. An apparatus for detecting contaminants on a skin in accordance with claim 10, wherein said signal processor extracts amplitude features from said received signal.

12. An apparatus for detecting contaminants on a skin in accordance with claim 10, wherein said transmitter and receiver are different transducers.

13. An apparatus for detecting contaminants on a skin in accordance with claim 10, wherein said transmitter and receiver are single transducers.

14. An apparatus for detecting contaminants on a skin in accordance with claim 10, wherein said signal processor compares said received signal with a predetermined test signal.

15. An apparatus for detecting contaminants on a skin in accordance with claim 11, wherein said transmitter transmits said guided wave at a nonperpendicular angle to the sheet.

16. An apparatus for detecting contaminants on a skin in accordance with claim 10, wherein said receiver comprises a multiplicity of transducers.

18. An apparatus for detecting contaminants on a skin in accordance with claim 10, wherein said receiver comprises a multiplicity of transducers.

17. An apparatus for detecting contaminants on a skin exposed to the environment, comprising:

a contaminant detection sheet disposed on top of the skin, wherein said sheet is exposed to contaminants from the environment, and is acoustically isolated from the skin;

a transmitter acoustically coupled to said sheet to provide an acoustic guided wave at a non-perpendicular incident angle with respect to said sheet for transmitting a guided wave through said sheet at a substantially constant phase velocity selected to provide multiple resonances in said contaminant detection sheet;

a receiver acoustically coupled to said sheet for receiving said acoustic guided wave transmitted at a non-perpendicular incident angle;

means for providing a received signal indicative of the received wave, wherein the received wave has a frequency signature; and

a signal processor for extracting features from the frequency signature of said received signal for classifying contaminants on said contaminant detection sheet.

19. An apparatus for detecting contaminants on a skin in accordance with claim 17, wherein said signal processor extracts amplitude features from said received signal.

20. An apparatus for detecting contaminants on a skin in accordance with claim 17, wherein said signal processor compares said extracted features of said received signal with said transmitted guided wave.

21. An apparatus for detecting contaminants on a skin in accordance with claim 17, wherein said transmitter and receiver are different transducers.

22. An apparatus for detecting contaminants on a skin in accordance with claim 17, wherein said transmitter and receiver are a single transducers.

23. An apparatus for detecting contaminants on a skin in accordance with claim 17, wherein said signal processor compares said received signal with a predetermined test signal.

24. The apparatus of claim 17, wherein said transmitter is constructed and arranged to excite a frequency bandwidth of less than 0.5 MHz·

mm and a phase velocity bandwidth of less than 0.5 mm/sec about at least one resonant point.

25. The apparatus of claim 24, wherein the transmitter is coupled to said sheet to provide the guided wave at a non-perpendicular incident angle with respect to said sheet on the order of 26°

.