Methods and apparatus for extracting first arrival wave packets in a structural health monitoring system

• US 7,946,176 B2
• Filed: 03/14/2008
• Issued: 05/24/2011
• Est. Priority Date: 04/16/2007
• Status: Active Grant

• Current Assignee: Acellent Technologies, Inc.
• Original Assignee: Acellent Technologies, Inc.
• Inventors: Liu, Bao, Beard, Shawn J
• Primary Examiner(s): Williams; Hezron
• Assistant Examiner(s): MILLER, ROSE MARY
• Application Number:
  US12/049,061
• Publication Number:
  US 20080253229A1
• Time in Patent Office: 1,166 Days
• Field of Search: 735/97, 738/659, 73609-612, 702 34- 36, 702/39
• US Class Current: 73/597
• CPC Class Codes: G01N 2291/0427 Flexural waves, plate waves, e.g. Lamb waves, tuning fork, cantilever
• CPC Class Codes: G01N 2291/106 one or more transducer arrays
• CPC Class Codes: G01N 29/041 on the surface of the material, e.g. using Lamb, Rayleigh or shear waves
• CPC Class Codes: G01N 29/36 Detecting the response signal , e.g. electronic circuits specially adapted therefor
• CPC Class Codes: G01N 29/4463 Signal correction, e.g. distance amplitude correction [DAC], distance gain size [DGS], noise filtering

Abstract

Methods and apparatus for extracting the first arrival wave packet of an acoustic signal in a structural health monitoring (SHM) system include receiving an acoustic signal transmitted between two transducers thereof. Electromagnetic cross-talk is removed from the signal. Signal amplitude threshold values used for picking out the first arrival wave packet are chosen based on signal characteristics or chosen adaptively as the value that leads to the minimum variance of the group velocity estimates of all the actuation-sensing transducer pairs. The group velocity is estimated as the known actuator-sensor distance divided by the propagation time of the first wave packet of which the envelope exceeds a candidate threshold value. The first arrival wave packet is determined as the signal segment where the signal envelope first exceeds the chosen amplitude threshold and the segment length exceeds a specified threshold of time width.

Claims

1. A method for detecting the first arrival wave packet of an acoustic signal at a transducer of a structural health monitoring (SHM) system, the method comprising:

selecting a path between a pair of transducers of an array of transducers attached to the structure, each transducer being operable to generate and apply an acoustic signal to the structure in response to the application of an electrical excitation signal thereto, and to detect an acoustic signal in the structure and to generate and output an electrical signal corresponding to the acoustic signal detected;

transmitting an acoustic signal through the structure and along the selected path from a first one of the transducers;

receiving the signal transmitted from the first transducer with the second transducer;

removing electromagnetic cross-talk from the received signal; and

,

detecting the first arrival wave packet of the acoustic signal at the receiving transducer;

wherein the removing of the electromagnetic cross-talk comprises;

specifying an upper bound for a group velocity of an acoustic signal transmitted on the selected path between the first and second transducers;

computing a lower bound of a time of transmission along the selected path by dividing the distance of the selected path by the specified upper bound of the group velocity;

computing a gate time equal to the sum of the lower bound of the transmission time and a trigger time corresponding to the excitation of the signal at the first transducer; and

retaining only the data in a signal waveform corresponding to times greater than the gate time.

2. A method for detecting the first arrival wave packet of an acoustic signal at a transducer of a structural health monitoring (SHM) system, the method comprising:

selecting a path between a pair of transducers of an array of transducers attached to the structure, each transducer being operable to generate and apply an acoustic signal to the structure in response to the application of an electrical excitation signal thereto, and to detect an acoustic signal in the structure and to generate and output an electrical signal corresponding to the acoustic signal detected;

transmitting an acoustic signal through the structure and along the selected path from a first one of the transducers;

receiving the signal transmitted from the first transducer with the second transducer;

removing electromagnetic cross-talk from the received signal; and

,

detecting the first arrival wave packet of the acoustic signal at the receiving transducer;

wherein the detecting of the first arrival wave packet comprises;

specifying an amplitude threshold;

specifying a time width threshold;

computing an envelope of the entire received excitation signal following the removal of the cross-talk from the signal;

determining the time location of all local maxima in the envelope of the signal;

selecting a first local maximum in the envelope with a signal amplitude greater than the specified amplitude threshold;

determining whether the envelope of the local maximum has a duration greater than the specified time width threshold;

setting the first arrival wave packet as the signal segment starting from the time at which the signal envelope exceeds the specified amplitude threshold and ending at the time that equals the starting time plus the time width threshold if the amplitude of the envelope has a duration greater than the specified time width threshold;

repeating the selecting a first local maximum, determining whether, and setting the first arrival wave packet for a next local maximum if the amplitude of the envelope corresponding to the previous local maximum does not exceed the specified amplitude threshold for the specified time width threshold until a signal portion corresponding to a local maximum in the signal is found that exceeds the specified amplitude and time width thresholds; and

,

deciding that no first arrival was detected in the signal if no portion of the signal envelope exceeds the amplitude threshold for the time width threshold specified.

3. The method of claim 2, further comprising repeating the detecting of the first arrival time for all paths in the array.

4. A method for detecting the first arrival wave packet of an acoustic signal at a transducer of a structural health monitoring (SHM) system, the method comprising:

selecting a path between a pair of transducers of an array of transducers attached to the structure, each transducer being operable to generate and apply an acoustic signal to the structure in response to the application of an electrical excitation signal thereto, and to detect an acoustic signal in the structure and to generate and output an electrical signal corresponding to the acoustic signal detected;

transmitting an acoustic signal through the structure and along the selected path from a first one of the transducers;

receiving the signal transmitted from the first transducer with the second transducer;

removing electromagnetic cross-talk from the received signal; and

,

detecting the first arrival wave packet of the acoustic signal at the receiving transducer;

wherein the detecting of the first arrival wave packet comprises;

(A) selecting a set of candidate threshold values based on the range of the amplitude of the detected signals, wherein a counter number is assigned to each candidate in an ascending order corresponding to an increase in the value of the candidate threshold;

(B) computing an envelope of the excitation signal applied to the transmitting transducers and an envelope of each of the entire detected signals following the removal of the cross-talks from the signals;

(C) selecting a candidate threshold;

(D) applying the candidate threshold to the envelope of a detected signal;

(E) setting the propagation time of the first arrival wave packet as the time from the instant of the maximum of the excitation signal envelope to the instant of the first local maximum of the received signal envelope that exceeds the candidate amplitude threshold;

(F) determining the group velocity for the path on the basis of the propagation time of the first arrival wave packet and the known distance;

(G) repeating (D)-(F) for all selected paths between all pairs of transducers in the array;

(H) calculating a cost value corresponding to the candidate threshold value and counter number, wherein the cost value is a variance of the group velocities of all the selected paths corresponding to the candidate threshold;

(I) repeating (C)-(H) for each candidate threshold until all thresholds have been applied;

(J) selecting the threshold corresponding to the smallest cost value obtained; and

,

(K) selecting the wave packet first arrival time on the basis of the threshold corresponding to the smallest cost value.

5. The method of claim 4, wherein the selecting of the set of candidate threshold values is determined on the basis of the minimum and maximum values of the envelopes of the received signals.

6. The method of claim 4, wherein the selecting of the set of candidate threshold values is a fixed set of values in a selected range of values.