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Air Coupled Ultrasonic Imaging For Non-Destructive Inspection

GTL Ultrasonics David Lavery Mario Malav é Andrew Ray Final Design Report April 23, 2009. Air Coupled Ultrasonic Imaging For Non-Destructive Inspection. Problem Overview Design Alternatives Chosen Design Detail Market Analysis Transducer Performance Circuitry Performance

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Air Coupled Ultrasonic Imaging For Non-Destructive Inspection

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  1. GTL Ultrasonics David Lavery Mario Malavé Andrew Ray Final Design Report April 23, 2009 Air Coupled Ultrasonic ImagingFor Non-Destructive Inspection

  2. Problem Overview • Design Alternatives • Chosen Design Detail • Market Analysis • Transducer Performance • Circuitry Performance • Software Performance • Final Design Specifications • Unresolved Problems • Probable Solutions • Team Performance Review

  3. Air-Coupled Ultrasonics • Device for non-destructive inspection of materials • Using novel polymer foam transducer • Incorporate new transducer material into device to improve performance

  4. Objectives • Develop a working ACU-NDI system using a novel transducer material • Complete • Reduce Cost • Complete • Increase Efficiency • Partially Complete • Mobile System • Incomplete

  5. Unforeseen Obstacles • Electromagnetic Interference • Overcome using circuit timing • Poorly Conductive Transducer Surface • Overcome using compression contacts • Highly Directional Signal • Overcome at cost of mobility • High Impedance Between Air and Imaged Objects • Through Transmission Abandoned • Pulse-Echo Setup Used

  6. Design AlternativesCylindrical Housing • Portability • Limited Circuitry Space • Poor Electrical Connections

  7. Design AlternativesPlate Mounted • Portability • Electrical Connection Issue Resolved • Poor Stability • Highly Variable Performance

  8. Chosen Design • Best Performance • Marginal Portability • Expandable Circuitry

  9. Design Tradeoffs • Excess Wire Length versus Expandability • Potential for unwanted interference • Ease of circuitry redesign/expansion • Portability versus Stability • Highly directional signal • Difficult to obtain useful data in handheld operation

  10. 7.5mm Plexiglas CopperTape BNC Fitting Transducer Foam

  11. Parts List

  12. Transducer Performance • High Quasi-Static Piezoactive coefficient • 25-700pC/N • Low Acoustic Impedance • 0.028MRayl

  13. Transducer Performance • 200V 300kHz 100pulse/sec • Maximum Unimpeded Transmission Distance 356.3mm • Peak-Peak Voltage Received 20mV • Minimal Signal Distortion

  14. Silver Surface Etching • Photolithography Produces Exact Shapes • Proof of Concept • Not Used for Transducers

  15. Circuitry Alternatives • Amplifier and Band Pass Filter • Eliminates Background Noise • High Gain • More Complex Circuitry

  16. Circuitry Alternatives • Amplifier(s) Without Filters • High Gain • Less Complex Circuitry • Noise Amplified With Signal

  17. Performance Comparison Amplifier Filter - Amplifier

  18. Chosen Circuitry • Single Amplifier • 35dB Gain • Less Complex - Fewer Failures • Fewer Points to Introduce Interference

  19. Amplifier Parts List

  20. Connection Alternatives • Single Adhesive Tape Contact • Simple to Construct • Prone to Poor Connection • Impossible to Verify Contact

  21. Connection Alternatives • Double Adhesive Tape Contacts • Simple to Construct • Prone to Poor Connection • Possible to Verify Connection

  22. Connection Alternatives • Double Mechanical Contact • Complex to Construct • Unlikely to Lose Connection • Possible to Verify Contact

  23. Connection Alternatives • Single Mechanical Contact • Less Complex to Construct • Unlikely to Lose Connection • Impossible to Verify Contact

  24. Mechanical Connection

  25. Mechanical Connection

  26. Connection Resistance • Mechanical Connections • 6.3 Ω, 5.8 Ω, 4.5 Ω, 4.9 Ω • Adhesive Connections • 368K Ω, 630 Ω, ∞ Ω, ∞ Ω

  27. Chosen Connection Design • Double Mechanical Contact • Ability to Check Connection • Low Connection Resistance • Higher Performance • Greater Reliability

  28. Wavelet Transform vs. Fourier Transform Advantages of the Wavelet Transform Ultrasonic Applications Analyzing Received Signal Software Performance

  29. Wavelet Transform vs. Fourier Transform • Fourier Transform • Cross products of changing complex exponentials (varying sinusoids) Continuous Wavelet Transform Cross products of a scaled and shifted wavelet

  30. Predefined Wavelets

  31. Scaled Wavelet

  32. Generated Output • Fourier Transform (Spectrum) Wavelet Transform (Scalogram)

  33. Advantages of the Wavelet Transform • Detect transients in a signal • Analyze non-stationary signals • All order statistics of the signal are changing with time • Detect changing statistics even in the presents of noise • If the noise remains constant throughout the process (stationary noise) • Scalogram not depended on a windowing • Short-Time Fourier Transform (STFT) uses window to generate a spectrogram

  34. STFT Example (T=25ms)

  35. STFT Example (T=1000ms)

  36. Wavelet Transform Example 1

  37. Wavelet Transform Example 2

  38. Ultrasonic Applications • Pass through transducers • Received signal will contain frequency components that change with time • Transient region detection • This can be used to characterize different materials • Due to different impedances of the materials

  39. Analyzing Received Signal • LabVIEW Analysis of reflected data • Data extracted from the oscilloscope via Ethernet port • Analyzed with the “Mexican Hat” wavelet (reflection configuration)

  40. Analyzing Received Signal 1

  41. Analyzing Received Signal 2

  42. Results • Emitting on different surfaces using reflection • Wavelet Analysis showed slight statistical changes • Amplitude changes are present in the ultrasonic signal • Wavelet transform results can be improved if a pass through transducer is used

  43. Damping Detection • LabVIEW Analysis of reflected data • Detect amplitude changes with configurable thresholds

  44. Analyzing Received Signal

  45. Final Specifications • Refer to Specs Handout • Key Specifications • 356.3mm transmissible distance • 7mm flaw detected 10 out of 10 times • 2mm flaw detected 2 out of 10 times

  46. Unresolved Issues • Pass-through capability • Leads to software issues • Compact mobile system • As a result of meeting other performance specifications

  47. Probable Solutions • Pass-through • Increase power to transducer • Identify better material • Circuitry design • Mobile System • Add internal storage capacity • Create pass-through capability

  48. Market Analysis • Frequently used couplants used for transmission • Oil, glycerin, and water • Success with air can open a new market of devices • Possible Device Users • Aviation/Aerospace companies; Boeing, Lockheed Martin, NASA • NASA Space Shuttle • Currently uses Laser Dynamic Range Imager (LDRI) • Only provides superficial data • Air Coupled Ultrasonics (ACU) provides information deeper than the surface

  49. Updated Parts Cost Table

  50. Cost Analysis • 60 Engineering hour for each group member • $50/hr give a cost of $9000 in labor • 21.7% profit at a sales price of 2,500 ($541 per unit sold)

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