Self-Diagnosing Transducers and Systems and Methods Therefor

• US 20110029287A1
• Filed: 07/28/2010
• Published: 02/03/2011
• Est. Priority Date: 07/31/2009
• Status: Abandoned Application

• Current Assignee: Carnegie Mellon University
• Original Assignee: Carnegie Mellon University
• Inventors: Lee, Sang Jun, Sohn, Hoon
• Application Number:
  US12/845,401
• Publication Number:
  US 20110029287A1
• Time in Patent Office: Days
• US Class Current: 702/189
• CPC Class Codes: G01R 29/22 Measuring piezoelectric properties
• CPC Class Codes: G01R 31/2829 Testing of circuits in sensor or actuator systems testing of apparatus for measuring electric or magnetic variables G01R35/00; testing of indicating or recording apparatus G01D; in airbag systems B60R21/0173; checking gas analysers G01N33/007; monitoring or fail-safe circuits for electromagnets H01F7/1844
• CPC Class Codes: G01R 31/70 Testing of connections between components and printed circuit boards G01R31/68 takes precedence

Abstract

A transducer system that includes a piezoelectric transducer and a self-diagnosis system electrically connected to the transducer. In one embodiment, the self-diagnosis system is configured to detect when a debonding defect has occurred in the bond between the transducer and a host structure and to detect when a crack has occurred in the transducer itself. The self-diagnosis system implements debonding-detection and crack-detection schemes that can distinguish between debonding and cracking, as well as distinguish these problems from changes arising from temperature variation.

Claims

1. A method, comprising:

monitoring a piezoelectric transducer for a change in capacitance of the piezoelectric transducer; and

implementing, as a function of said monitoring, a baseline-free process to determine if a defect condition is present or if the change in capacitance is due to a change in temperature of the piezoelectric transducer.

2. A method according to claim 1, wherein said monitoring the piezoelectric transducer includes measuring a scaling factor between an input voltage input into the piezoelectric transducer and a corresponding output voltage output from the piezoelectric transducer.

3. A method according to claim 2, wherein said measuring the scaling factor includes measuring the scaling factor as a ratio of the capacitance of the piezoelectric transducer to the summation of the piezoelectric transducer capacitance and the capacitance of a capacitor in electrical series with the piezoelectric transducer.

4. A method according to claim 1, further comprising determining whether the change in capacitance is an increase in the capacitance, wherein said implementing the baseline-free process includes implementing a baseline-free process to determine if the piezoelectric transducer is at least partially debonded from a host structure.

5. A method according to claim 4, wherein said implementing the baseline-free process includes:

inputting an input signal into the piezoelectric transducer;

generating a response signal representing the response of the piezoelectric transducer to the input signal;

time-reversing the response signal to obtain a time-reversed response signal;

inputting the time-reversed response signal into the piezoelectric transducer;

obtaining a reconstructed signal representing the response of the piezoelectric transducer to time-reversed response signal; and

comparing the reconstructed signal to the input signal.

6. A method according to claim 5, wherein said comparing the reconstructed signal to the input signal includes calculating a time-reversal index as a function of the reconstructed signal and the input signal.

7. A method according to claim 6, wherein said calculating the time-reversal index includes calculating the time-reversal index (TR) as follows:

8. A method according to claim 6, wherein said comparing the reconstructed signal to the input signal further includes calculating a symmetry index as a function of the reconstructed signal and the input signal.

9. A method according to claim 8, wherein said implementing the baseline-free process includes determining whether the time-reversal and symmetry indices have changed over time.

10. A method according to claim 9, further comprising, when the time-reversal and symmetry indices have changed over time, determining a debonding defect condition is present in the piezoelectric transducer.

11. A method according to claim 10, further comprising, in response to determining the debonding defect condition is present, taking an action based on the debonding defect condition being present.

12. A method according to claim 5, wherein said comparing the reconstructed signal to the input signal includes calculating a symmetry index as a function of the reconstructed signal and the input signal.

13. A method according to claim 6, wherein said calculating the time-reversal index includes calculating the symmetry index (SYM) as follows:

14. A method according to claim 1, further comprising determining whether the change in the capacitance is a decrease in the capacitance, wherein said implementing the baseline-free process includes implementing a baseline-free process to determine if the piezoelectric transducer contains an internal crack.

15. A method according to claim 14, wherein said implementing the baseline-free process includes:

applying a driving signal to the piezoelectric transducer at a selected frequency;

generating an output signal representing the output of the piezoelectric transducer that corresponds to the driving signal; and

determining a Lamb wave energy ratio index as a function of the driving signal and the output signal.

16. A method according to claim 15, wherein said determining the Lamb wave energy ratio index includes calculating the Lamb wave energy ratio index as follows:

17. A method according to claim 15, wherein said implementing the baseline-free response process includes determining whether the Lamb wave energy ratio index has changed over time.

18. A method according to claim 17, further comprising, when the Lamb wave energy ratio index has changed over time, determining a cracking defect condition is present in the piezoelectric transducer.

19. A method according to claim 18, further comprising, in response to determining the cracking defect condition is present, taking an action based on the cracking defect condition being present.

20. A method, comprising:

repeatingly inputting an input signal into a piezoelectric transducer secured to a host structure;

repeatingly generating a response signal representing the response of the piezoelectric transducer to the input signal;

repeatingly time-reversing the response signal to obtain a time-reversed response signal;

repeatingly inputting the time-reversed response signal into the piezoelectric transducer;

repeatingly obtaining a reconstructed signal representing the response of the piezoelectric transducer to time-reversed response signal;

repeatingly calculating time-reversal and symmetry indices as a function of the reconstructed signal and the input signal;

monitoring the time-reversal and symmetry indices over time to determine when a change occurs in the time-reversal and symmetry indices; and

in response to the change occurring, automatedly taking an action.

21. A method according to claim 20, wherein said automatedly taking an action includes issuing a notification that a debonding defect is present between the piezoelectric transducer and the host structure.

22. A method, comprising:

repeatingly applying a driving signal to the piezoelectric transducer at a selected frequency;

repeatingly generating an output signal representing the output of the piezoelectric transducer that corresponds to the driving signal;

repeatingly determining a Lamb wave energy ratio index as a function of the driving signal and the output signal;

monitoring the Lamb wave energy ratio index over time to determine when a change occurs in the Lamb wave energy ratio index; and

in response to the change occurring, automatedly taking an action.

23. A method according to claim 22, wherein said automatedly taking an action includes issuing a notification that a cracking defect is present in the piezoelectric transducer.

24. A machine-readable medium containing machine-executable instructions for implementing a method of self-diagnosing a piezoelectric transducer, said machine-executable instructions comprising:

a first set of machine-executable instructions for monitoring the piezoelectric transducer for a change in capacitance of the piezoelectric transducer; and

a second set of machine-executable instructions for implementing, as a function of the monitoring, a baseline-free process to determine if a defect condition is present or if the change in capacitance is due to a change in temperature of the piezoelectric transducer.

25. A machine-readable medium according to claim 24, wherein said first set of machine-executable instructions includes machine-executable instructions for measuring a scaling factor between an input voltage input into the piezoelectric transducer and a corresponding output voltage output from the piezoelectric transducer.

26. A machine-readable medium according to claim 25, wherein said machine-executable instructions for measuring the scaling factor includes machine-executable instructions for measuring the scaling factor as a function of the capacitance of the piezoelectric transducer and the capacitance of a capacitor in electrical series with the piezoelectric transducer.

27. A machine-readable medium according to claim 24, further comprising machine-executable instructions for determining whether the change in capacitance is an increase in capacitance, wherein said second set of machine-executable instructions includes machine-executable instructions for implementing a baseline-free process to determine if the piezoelectric transducer is at least partially debonded from a host structure.

28. A machine-readable medium according to claim 27, wherein said machine-executable instructions for implementing the baseline-free process includes machine-executable instructions for:

inputting an input signal into the piezoelectric transducer;

generating a response signal representing the response of the piezoelectric transducer to the input signal;

time-reversing the response signal to obtain a time-reversed response signal;

inputting the time-reversed response signal into the piezoelectric transducer;

obtaining a reconstructed signal representing the response of the piezoelectric transducer to time-reversed response signal; and

comparing the reconstructed signal to the input signal.

29. A machine-readable medium according to claim 28, wherein said machine-executable instructions for comparing the reconstructed signal to the input signal includes machine-executable instructions for calculating time-reversal and symmetry indices as a function of the reconstructed signal and the input signal.

30. A machine-readable medium according to claim 29, wherein said machine-executable instructions for implementing the baseline-free process includes machine-executable instructions for determining whether the time-reversal and symmetry indices have changed over time.

31. A machine-readable medium according to claim 30, further comprising machine-executable instructions for determining a debonding defect condition is present in the piezoelectric transducer when the time-reversal and symmetry indices have changed over time.

32. A machine-readable medium according to claim 26, further comprising machine-executable instructions for taking an action based on the debonding defect condition being present.

33. A machine-readable medium according to claim 24, further comprising machine-executable instructions for determining whether the change in capacitance is an increase in capacitance, wherein said machine-executable instructions for implementing the baseline-free process includes machine-executable instructions for implementing a baseline-free process to determine if the piezoelectric transducer is at least partially debonded from a host structure.

34. A machine-readable medium according to claim 33, wherein said machine-executable instructions for implementing the baseline-free process includes machine-executable instructions for:

applying a driving signal to the piezoelectric transducer at a selected frequency;

generating an output signal representing the output of the piezoelectric transducer that corresponds to the driving signal; and

determining a Lamb wave energy ratio index as a function of the driving signal and the output signal.

35. A machine-readable medium according to claim 34, wherein said machine-executable instructions for implementing the baseline-free response process includes machine-executable instructions for determining whether the Lamb wave energy ratio index has changed over time.

36. A machine-readable medium according to claim 35, further comprising machine-executable instructions for determining a cracking defect condition is present in the piezoelectric transducer when the Lamb wave energy ratio index has changed over time.

37. A machine-readable medium according to claim 36, further comprising machine-executable instructions for taking an action based on the debonding defect condition being present.

38. A machine-readable medium containing machine-executable instructions for implementing a method of self-diagnosing a piezoelectric transducer, said machine-executable instructions comprising:

machine-executable instructions for repeatingly inputting an input signal into a piezoelectric transducer secured to a host structure;

machine-executable instructions for repeatingly generating a response signal representing the response of the piezoelectric transducer to the input signal;

machine-executable instructions for repeatingly time-reversing the response signal to obtain a time-reversed response signal;

machine-executable instructions for repeatingly inputting the time-reversed response signal into the piezoelectric transducer;

machine-executable instructions for repeatingly obtaining a reconstructed signal representing the response of the piezoelectric transducer to time-reversed response signal;

machine-executable instructions for repeatingly calculating time-reversal and symmetry indices as a function of the reconstructed signal and the input signal;

machine-executable instructions for monitoring the time-reversal and symmetry indices over time to determine when a change occurs in the time-reversal and symmetry indices; and

machine-executable instructions for automatedly taking an action in response to the change occurring.

39. A machine-readable medium according to claim 38, wherein said machine-executable instructions for automatedly taking an action includes machine-executable instructions for issuing a notification that a debonding defect is present between the piezoelectric transducer and the host structure.

40. A machine-readable medium containing machine-executable instructions for implementing a method of self-diagnosing a piezoelectric transducer, said machine-executable instructions comprising:

machine-executable instructions for repeatingly applying a driving signal to the piezoelectric transducer at a selected frequency;

machine-executable instructions for repeatingly generating an output signal representing the output of the piezoelectric transducer that corresponds to the driving signal;

machine-executable instructions for repeatingly determining a Lamb wave energy ratio index as a function of the driving signal and the output signal;

machine-executable instructions for monitoring the Lamb wave energy ratio index over time to determine when a change occurs in the Lamb wave energy ratio index; and

machine-executable instructions for automatedly taking an action in response to the change occurring.

41. A machine-readable medium according to claim 340, wherein said machine-executable instructions for automatedly taking an action includes machine-executable instructions for issuing a notification that a cracking defect is present in the piezoelectric transducer.

42. A transducer system, comprising:

a piezoelectric transducer having a capacitance; and

a self-diagnosis system configured for;

monitoring said piezoelectric transducer for a change in the capacitance of said piezoelectric transducer; and

implementing, as a function of the monitoring, a baseline-free process to determine if a defect condition is present or if the change in capacitance is due to a change in temperature of the piezoelectric transducer.

43. A transducer system according to claim 42, wherein said self-diagnosis system includes a self-sensing circuit electrically connected to said piezoelectric transducer, said self-sensing circuit being in the form of a voltage divider having a measurement leg and a capacitor in electrical parallel with the measurement leg.

44. A transducer system according to claim 42, wherein said self-diagnosis system includes a waveform generator electrically connected to said piezoelectric transducer and configured to input a toneburst signal into said piezoelectric transducer.

45. A transducer system according to claim 44, wherein said self-diagnosis system includes a self-sensing circuit for sensing the response of the piezoelectric transducer to the toneburst signal.

46. A transducer system according to claim 45, wherein said sensing circuit includes a measuring leg and a capacitor in electrical parallel with said measuring leg, wherein said capacitor has a capacitance.

47. A transducer system according to claim 45, wherein said self-diagnosis system is configured to measure, using said self-sensing circuit, a scaling factor that is a function of the capacitance of said piezoelectric transducer and the capacitance of said capacitor.

48. A transducer system according to claim 42, wherein said self-diagnosis system is configured to determine, when said piezoelectric transducer is attached to a host structure, if said piezoelectric transducer is at least partially debonded from the host structure.

49. A transducer system according to claim 48, wherein said self-diagnosis system is configured to:

input an input signal into said piezoelectric transducer;

generate a response signal representing the response of said piezoelectric transducer to the input signal;

time-reverse the response signal to obtain a time-reversed response signal;

input the time-reversed response signal into said piezoelectric transducer;

obtain a reconstructed signal representing the response of said piezoelectric transducer to time-reversed response signal; and

compare the reconstructed signal to the input signal.

50. A transducer system according to claim 49, wherein said self-diagnosing system is configured to calculate time-reversal and symmetry indices as a function of the reconstructed signal and the input signal.

51. A transducer system according to claim 50, wherein said self-diagnosing system is configured to determine whether the time-reversal and symmetry indices have changed over time.

52. A transducer system according to claim 51, wherein said self-diagnosing system is configured to determine a debonding defect condition is present in said piezoelectric transducer.

53. A transducer system according to claim 52, wherein said self-diagnosing system is configured to take an action based on the debonding defect condition being present.

54. A transducer system according to claim 42, wherein said self-diagnosing system is configured to determine if the piezoelectric transducer contains an internal crack.

55. A transducer system according to claim 53, wherein said self-diagnosis system is configured to:

apply a driving signal to said piezoelectric transducer at a selected frequency;

generate an output signal representing the output of said piezoelectric transducer that corresponds to the driving signal; and

determine a Lamb wave energy ratio index as a function of the driving signal and the output signal.

56. A transducer system according to claim 55, wherein said self-diagnosis system is configured to determine whether the Lamb wave energy ratio index has changed over time.

57. A transducer system according to claim 56, wherein said self-diagnosis system is configured to determine a cracking defect condition is present in the piezoelectric transducer.

58. A transducer system according to claim 57, wherein said self-diagnosis system is configured to take an action based on the cracking defect condition being present.