Damage Detection Method for Composite Plate Ultrasonic Guided Wave Structures Based on Peak Frequency

Abstract

This invention discloses a method for damage detection of composite plate ultrasonic guided wave structures based on peak frequency, comprising the following steps: establishing a standard test block of the composite plate and simulating damage samples artificially; acquiring normal and damaged ultrasonic guided wave signals of the composite plate using multi-sensor piezoelectric ultrasonic guided wave detection; obtaining an overcomplete modulation dictionary adapted to different dispersion characteristics of the guided wave signal based on the peak value and frequency of the ultrasonic guided wave; extracting the peak position information of the guided wave signal according to the envelope characteristics of the guided wave signal, and using a fast matching and tracking algorithm based on peak information to separate, extract, and identify different modes of the guided wave signal; obtaining the damage index of the guided wave signal using the energy difference between the normal mode and the damaged mode, and obtaining the specific location and structural state of the damage using an elliptic probability imaging algorithm. By combining the fast matching and tracking algorithm based on peak information with the elliptic probability imaging algorithm, the guided wave signal modes are separated, extracted, and identified, and the damage location and structural state of the composite plate are obtained.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing technology, and more specifically, to a method for detecting damage in composite plate ultrasonic guided wave structures based on a peak frequency modulation dictionary. Background Technology

[0002] Composite materials, with their lightweight, high strength, and excellent mechanical properties, are increasingly used in industries such as aerospace, wind power, and automobiles, becoming strategic materials for high-end equipment. However, composite materials are often used in harsh environments, under severe loads, and complex working conditions, leading to significant accelerated erosion and damage accumulation. Therefore, monitoring the overall structural health of composite materials is crucial. With the help of guided wave monitoring technology, structural damage can be detected and addressed promptly, greatly ensuring structural safety. Especially in large plate structures, ultrasonic guided waves can propagate over long distances without significant attenuation.

[0003] Therefore, ultrasonic guided wave technology is well-suited for large-area, remote monitoring of sheet metal structures. Ultrasonic guided wave monitoring is a promising method for health monitoring of composite material structures; however, the separation, extraction, and identification of ultrasonic guided wave modes remain challenging aspects of damage localization. By utilizing an overcomplete atomic library adapted to the different dispersion characteristics of guided wave signals to match, separate, extract, and identify different modes, and then employing an elliptic probability imaging algorithm to obtain the specific location of the damage and the structural state, this method can accurately acquire the modal information of the guided wave signal and the damage location of the composite plate, demonstrating high practical value. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings and deficiencies of the prior art and provide a method for damage detection of composite plate ultrasonic guided wave structures based on peak frequency. The method employs a fast matching and tracking algorithm based on peak information to accurately extract the peak information of the ultrasonic guided wave signal, realize the separation, extraction and identification of ultrasonic guided wave modes, and use elliptic probability imaging to perform damage imaging on the composite plate, accurately obtaining the modal information of the guided wave signal and the damage location of the composite plate.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for damage detection of composite plate ultrasonic guided wave structures based on peak frequency includes the following steps:

[0007] Establish standard test blocks for composite plates and simulate damage samples artificially;

[0008] Multi-sensor piezoelectric ultrasonic guided wave detection technology was used to obtain normal and damaged ultrasonic guided wave signals of composite plates;

[0009] Based on the peak value and frequency of the ultrasonic guided wave, an overcomplete modulation dictionary adapted to different dispersion characteristics of the guided wave signal is obtained;

[0010] Based on the envelope characteristics of the guided wave signal, the peak position information of the guided wave signal of the composite plate is extracted. A fast matching and tracking algorithm based on the peak information is used to separate, extract and identify different modes of the guided wave signal.

[0011] By utilizing the energy difference between the normal mode and the damaged mode, the damage index of the guided wave signal is obtained. Then, using an elliptic probability imaging algorithm, the specific location and structural state of the composite plate damage are obtained.

[0012] Furthermore, the standard test blocks for composite plates are divided into two categories: non-damaged and delamination-damaged. Delamination-damaged plates are simulated by bonding iron blocks to the composite plates.

[0013] Furthermore, multiple piezoelectric sensors were equidistantly attached to the top and bottom ends of the composite plates with and without delamination damage, and guided wave signals between different piezoelectric sensors were collected.

[0014] Furthermore, by analyzing the time-frequency domain characteristics of the guided wave signal, an overcomplete modulation dictionary is constructed by selecting a sinusoidal modulation function to ensure a high degree of matching between the basis functions and the guided wave signal. The basis function ω(t) is expressed as follows:

[0015]

[0016] In the formula, f is the center frequency of the ultrasonic guided wave signal, n is the number of peak values, and t is the wave propagation time.

[0017] To obtain the atomic matrix, for the basic atoms ω δ (t) undergoes a series of shifts, modulations, and phase changes as follows:

[0018]

[0019] In the formula, τ is the time shift. δ represents the phase, c is the scaling factor, i is the imaginary unit, and δ represents the atomic arrangement number.

[0020] Furthermore, the Hilbert transform is used to obtain the extreme values ​​of the waveguide signal envelope, the peak position information of the waveguide signal of the composite plate is searched, and a fast matching and tracking algorithm based on the peak information is used to separate, extract and identify different modes of the waveguide signal.

[0021] Furthermore, the method for obtaining the envelope of the guided wave signal using the Hlibert transform is as follows:

[0022]

[0023] In the formula, τ is the Hilbert transform output of the original signal x(t), where τ is the phase.

[0024] Analyze the signal y(t) composed of x(t) and The composition is as follows:

[0025]

[0026] In the formula, A(t) is the envelope of x(t). The phase is j, and the imaginary unit is j.

[0027] After obtaining the envelope of the guided wave signal, the location of the envelope extremum is found, and the peak value is searched by searching a fixed cyclic distance from the envelope extremum location to both ends.

[0028] Furthermore, a fast matching and tracking algorithm based on peak information includes:

[0029] Construct an atom library Ψ1 = [η1(t), η2(t), η3(t), ..., η] from the dictionary Ф that matches the position of the modal peak. M [(t)], where M represents the number of atoms in the atomic library;

[0030] Select the best atom η1(t) from the atom library Ψ1 to match the original waveguide signal x(t). The best match requires that their inner product [x(t), η1(t)] is the largest inner product of all atoms in the atom library with the waveguide signal x(t).

[0031] After iteration, the guided wave signal x(t) is decomposed into components of the optimal atom η1(t) and the signal residual R1(t);

[0032] The best atom is matched to the residual signal. The iteration stops when the sparse decomposition of the signal is close enough to the signal or the residual signal meets the set threshold.

[0033] The optimal linear combination of atoms for obtaining the guided wave signal is:

[0034]

[0035] In the formula, i is the number of atoms to be decomposed; R i (t) represents the i-th residual signal; η i+1 (t) represents the (i+1)th atom; L represents the number of modes of the guided wave signal.

[0036] Furthermore, by utilizing the energy difference between the matched damaged signal and the matched normal signal, the damage index DI of the guided wave signal is obtained as follows:

[0037]

[0038] In the formula, To match the wave packet energy of the damaged signal, E(t) is the wave packet energy to match the normal signal;

[0039] Damage imaging of the composite plate was performed using the elliptic probability imaging method, and the following results were obtained:

[0040]

[0041] In the formula, p r (x,y) represents the estimated damage probability of a discrete point (x,y) along r ultrasonic guided wave propagation paths; N P W represents the number of propagation paths for all sensors. r (x,y) represents the linear attenuation imaging weight of the discrete point (x,y) along the r-th ultrasonic guided wave propagation path; DI r Let P(x,y) be the damage index of the r-th ultrasonic guided wave propagation path; P(x,y) is the total damage probability of the discrete point (x,y) in all ultrasonic guided wave propagation paths.

[0042] By calculating the damage probability on different propagation paths point-to-point, the location with the highest total damage probability is identified as the damage location of the composite plate.

[0043] An electronic device includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the peak frequency-based composite plate ultrasonic waveguide structure damage detection method as described in any of the preceding claims.

[0044] A computer-readable storage medium storing a computer program that, when executed by a processor, implements the peak frequency-based composite plate ultrasonic waveguide structure damage detection method as described in any of the preceding claims.

[0045] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0046] 1. This invention uses multi-sensor piezoelectric ultrasonic guided wave technology to detect composite plates, and modal identification and damage location identification can be performed simultaneously on a large scale with multiple sets of data.

[0047] 2. This invention constructs a peak-frequency modulation dictionary by analyzing the time-frequency domain characteristics of ultrasonic guided wave signals. The basis functions of this dictionary are highly matched with the guided wave signals.

[0048] 3. This invention employs a fast matching and tracking algorithm based on peak information, which can accurately extract the peak information of ultrasonic guided wave signals and realize the separation, extraction and identification of ultrasonic guided wave modes.

[0049] 4. This invention utilizes the energy difference between the matched damaged signal and the matched normal signal to obtain the damage index, and uses the elliptic probability imaging method to perform damage imaging on the composite plate, which can accurately obtain the modal information of the guided wave signal and the damage location of the composite plate. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the process for detecting damage in composite plate ultrasonic guided wave structures based on peak frequency.

[0051] Figure 2 A schematic diagram of attaching a piezoelectric sensor to a composite board.

[0052] Figure 3 A schematic diagram illustrating the process of constructing a complete peak-frequency modulation dictionary.

[0053] Figure 4 This is a schematic diagram of the fast matching and tracking algorithm based on peak information.

[0054] Figure 5 This is a schematic diagram illustrating the principle of the elliptic probability imaging algorithm. Detailed Implementation

[0055] The present invention provides a further description of the peak frequency-based composite plate ultrasonic guided wave structure damage detection method with reference to the accompanying drawings and specific embodiments.

[0056] Please see Figure 1 This invention discloses a method for damage detection of composite plate ultrasonic guided wave structures based on peak frequency, comprising the following steps:

[0057] Establish standard test blocks for composite plates and simulate damage samples artificially;

[0058] Multi-sensor piezoelectric ultrasonic guided wave detection technology was used to obtain normal and damaged ultrasonic guided wave signals of composite plates;

[0059] Based on the peak value and frequency of the ultrasonic guided wave, an overcomplete modulation dictionary adapted to different dispersion characteristics of the guided wave signal is obtained;

[0060] Based on the envelope characteristics of the guided wave signal, the peak position information of the guided wave signal of the composite plate is extracted. A fast matching and tracking algorithm based on the peak information is used to separate, extract and identify different modes of the guided wave signal.

[0061] By utilizing the energy difference between the normal mode and the damaged mode, the damage index of the guided wave signal is obtained. Then, using an elliptic probability imaging algorithm, the specific location and structural state of the composite plate damage are obtained.

[0062] Specifically, in this embodiment, the composite plate standard test blocks are divided into two categories: no damage and delamination damage. The delamination damage is simulated by artificially attaching an iron block to the middle position of the composite plate.

[0063] Please see Figure 2 Multiple piezoelectric sensors of the same number were equidistantly attached to the top and bottom ends of composite boards with no damage and delamination damage, respectively. Guided wave signals between different piezoelectric sensors were collected. Using multi-sensor piezoelectric ultrasonic guided wave detection technology, normal and damaged ultrasonic guided wave signals of the composite board were obtained.

[0064] Please see Figure 3 By analyzing the time-frequency domain characteristics of the guided wave signal through a complete peak-frequency modulation dictionary, a sinusoidal modulation function is selected to construct the dictionary, ensuring a high degree of matching between the basis functions and the guided wave signal. The basis function ω(t) is expressed as follows:

[0065]

[0066] In the formula, f is the center frequency of the ultrasonic guided wave signal, n is the peak number, and t is the guided wave propagation time. To obtain the atomic matrix, the basic atoms ω... δ (t) Perform a series of appropriate shifts, modulations, and phase changes as follows:

[0067]

[0068] In the formula, τ is the time shift. δ represents the phase, c is the scaling factor, i is the imaginary unit, and δ represents the atomic arrangement number.

[0069] The Hilbert transform is used to obtain the extrema of the guided wave signal envelope, and the peak position information of the composite material guided wave signal is searched. A fast matching pursuit algorithm based on peak information is then employed to separate, extract, and identify different modes of the guided wave signal. The method for obtaining the guided wave signal envelope using the Hilbert transform is as follows:

[0070]

[0071] In the formula, Let be the Hilbert transform output of the original signal x(t), where τ is the phase. Analyze the signal y(t) as a product of x(t) and... The composition is as follows:

[0072]

[0073] In the formula, A(t) is the envelope of x(t). For phase.

[0074] After obtaining the envelope of the guided wave signal, the location of the envelope extrema is found, but the location of the envelope extrema is not consistent with the location of the modal peak. Since the distance between the envelope extrema and the modal peak is very close, the peak is searched by cyclically searching at a fixed distance from the envelope extrema location towards both ends.

[0075] Please see Figure 4 Fast matching and tracking algorithms based on peak information include:

[0076] First, construct a small atom library Ψ1 = [η1(t), η2(t), η3(t), ..., η] from the atom in the dictionary Ф that matches the position of the modal peak. M [(t)], where M represents the number of atoms in the small atom library.

[0077] Then, the best atom η1(t) that matches the original guided wave signal x(t) is selected from the atom library Ψ1. The best match requires that their inner product [x(t), η1(t)] is the largest inner product of all atoms in the atom library with the guided wave signal x(t).

[0078] After iteration, the guided wave signal x(t) is decomposed into components of the optimal atom η1(t) and the signal residual R1(t).

[0079] Then, the residual signal is further matched with the optimal atoms. The iteration stops when the sparse decomposition of the signal sufficiently approximates the signal or the residual signal meets a set threshold. Therefore, the optimal linear combination of atoms for the guided wave signal is:

[0080]

[0081] In the formula, i is the number of atoms to be decomposed; R i (t) represents the i-th residual signal; η i+1 (t) represents the (i+1)th atom; L represents the number of modes of the guided wave signal.

[0082] Using the energy difference between the matched damaged signal and the matched normal signal, the guided wave signal damage index DI is obtained as follows:

[0083]

[0084] In the formula, To match the wave packet energy of the damaged signal, E(t) is the wave packet energy to match the normal signal.

[0085] Please see Figure 5 Damage imaging of the composite plate was performed using the elliptic probability imaging method, and the following results were obtained:

[0086]

[0087] In the formula, p r (x,y) represents the estimated damage probability of a discrete point (x,y) along r ultrasonic guided wave propagation paths; N P W represents the number of propagation paths for all sensors. r(x,y) represents the linear attenuation imaging weight of the discrete point (x,y) along the r-th acoustic wave propagation path, which is determined by the arrival time of the damage signal; DI r Let P(x,y) be the damage index for the r-th ultrasonic wave propagation path; P(x,y) is the total damage probability of the discrete point (x,y) across all ultrasonic wave propagation paths. By calculating the damage probability on different paths point-to-point, the location with the highest total damage probability is identified as the most likely damage location.

[0088] This invention also discloses an electronic device, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the steps of the peak frequency-based composite plate ultrasonic waveguide structure damage detection method as described in any of the preceding claims. The electronic device of this invention can execute the peak frequency-based composite plate ultrasonic waveguide structure damage detection method of this invention, and can execute any combination of the steps of the method embodiments, possessing the corresponding functions and beneficial effects of the method.

[0089] This invention also discloses a computer-readable storage medium storing a computer program. When executed by a processor, the computer program implements the steps of the peak frequency-based composite plate ultrasonic waveguide structure damage detection method as described in any of the preceding claims. The computer-readable storage medium of this invention can execute the peak frequency-based composite plate ultrasonic waveguide structure damage detection method of this invention, and can execute any combination of the steps of the method embodiments, possessing the corresponding functions and beneficial effects of the method.

[0090] Although the invention has been described in the context of functional modules, it should be understood that, unless otherwise stated, one or more of the functions and / or features may be integrated into a single physical device and / or software module, or one or more functions and / or features may be implemented in a separate physical device or software module. It is also understood that a detailed discussion of the actual implementation of each module is unnecessary for understanding the invention. Rather, given the properties, functions, and internal relationships of the various functional modules in the system disclosed herein, the actual implementation of the module will be understood within the scope of conventional art for an engineer. Therefore, those skilled in the art can implement the invention set forth in the claims using ordinary techniques without excessive experimentation. It is also understood that the specific concepts disclosed are merely illustrative and not intended to limit the scope of the invention, which is determined by the full scope of the appended claims and their equivalents.

[0091] If a function is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0092] More specific examples of computer-readable media (a non-exhaustive list) include: electrical connections (electronic devices) having one or more wires, portable computer disk drives (magnetic devices), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Furthermore, computer-readable media can even be paper or other suitable media on which programs can be printed, because programs can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in computer memory.

[0093] Various parts of this invention can be implemented using hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented using software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, it can be implemented using any of the following techniques known in the art, or a combination thereof: discrete logic circuits having logic gates for implementing logical functions on data signals; application-specific integrated circuits (ASICs) having suitable combinational logic gates; programmable gate arrays (PGAs); field-programmable gate arrays (FPGAs); etc.

[0094] In summary, the present invention has the following advantages and beneficial effects:

[0095] 1. This invention uses multi-sensor piezoelectric ultrasonic guided wave technology to detect composite plates, and modal identification and damage location identification can be performed simultaneously on a large scale with multiple sets of data.

[0096] 2. This invention constructs a peak-frequency modulation dictionary by analyzing the time-frequency domain characteristics of ultrasonic guided wave signals. The basis functions of this dictionary are highly matched with the guided wave signals.

[0097] 3. This invention employs a fast matching and tracking algorithm based on peak information, which can accurately extract the peak information of ultrasonic guided wave signals and realize the separation, extraction and identification of ultrasonic guided wave modes.

[0098] 4. This invention utilizes the energy difference between the matched damaged signal and the matched normal signal to obtain the damage index, and uses the elliptic probability imaging method to perform damage imaging on the composite plate, which can accurately obtain the modal information of the guided wave signal and the damage location of the composite plate.

[0099] The above description is a detailed description of the preferred embodiments of the present invention. However, the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modifications made under the technical spirit disclosed in the present invention should fall within the patent scope covered by the present invention.

Claims

1. A method for damage detection of composite plate ultrasonic guided wave structures based on peak frequency, characterized in that, Includes the following steps: Establish standard test blocks for composite plates and simulate damage samples artificially; Multi-sensor piezoelectric ultrasonic guided wave detection technology was used to obtain normal and damaged ultrasonic guided wave signals of composite plates; Based on the peak value and frequency of the ultrasonic guided wave, an overcomplete modulation dictionary adapted to different dispersion characteristics of the guided wave signal is obtained; Based on the envelope characteristics of the guided wave signal, the peak position information of the guided wave signal of the composite plate is extracted. A fast matching and tracking algorithm based on the peak information is used to separate, extract and identify different modes of the guided wave signal. By utilizing the energy difference between the normal mode and the damaged mode, the damage index of the guided wave signal is obtained, and the specific location and structural state of the composite plate damage are obtained using the elliptic probability imaging algorithm. By analyzing the time-frequency domain characteristics of the guided wave signal, a comprehensive modulation dictionary is constructed by selecting sinusoidal modulation functions to ensure a high degree of matching between the basis functions and the guided wave signal. It is expressed as follows: ； In the formula, f is the center frequency of the ultrasonic guided wave signal, n is the number of peak values, and t is the wave propagation time. To obtain the atomic matrix, the basic atoms... A series of shifts, modulations, and phase changes are performed as follows: ； In the formula, τ is the time shift, φ is the phase, c is the scaling factor, i is the imaginary unit, and δ represents the atomic arrangement number; Fast matching and tracking algorithms based on peak information include: Construct an atom library Ψ1=[η1(t), η2(t), η3(t), ..., η] from the dictionary Ф that matches the position of the modal peak. M [(t)], where M represents the number of atoms in the atomic library; Select the best atom η1(t) from the atom library Ψ1 to match the original waveguide signal x(t). The best match requires that their inner product [x(t), η1(t)] is the largest inner product of all atoms in the atom library with the waveguide signal x(t). After iteration, the guided wave signal x(t) is decomposed into components of the optimal atom η1(t) and the signal residual R1(t); The best atom is matched to the residual signal. The iteration stops when the sparse decomposition of the signal is close enough to the signal or the residual signal meets the set threshold. The optimal linear combination of atoms for obtaining the guided wave signal is: ； In the formula, i represents the number of atoms to be decomposed; Let i be the i-th residual signal; For the (i+1)th atom; L is the number of modes of the guided wave signal; The damage index DI of the guided wave signal is obtained by utilizing the energy difference between the matched damaged signal and the matched normal signal: ； In the formula, To match the wave packet energy of the damaged signal, E(t) is the wave packet energy to match the normal signal; Damage imaging of the composite plate was performed using the elliptic probability imaging method, and the following results were obtained: ； In the formula, p r (x, y) represents the estimated damage probability of a discrete point (x, y) along r ultrasonic guided wave propagation paths; N P W represents the number of propagation paths for all sensors. r (x,y) represents the linear attenuation imaging weight of the discrete point (x,y) on the r-th ultrasonic guided wave propagation path; Let be the damage index of the r-th ultrasonic guided wave propagation path; Let (x, y) be the total damage probability of a discrete point (x, y) across all ultrasonic guided wave propagation paths. By calculating the damage probability on different propagation paths point-to-point, the location with the highest total damage probability is identified as the damage location of the composite plate.

2. The method for damage detection of composite plate ultrasonic guided wave structures based on peak frequency according to claim 1, characterized in that, The standard test blocks for composite plates are divided into two categories: non-destructive and delamination-damaged. Delamination-damaged plates are simulated by bonding iron blocks to the composite plates.

3. The method for damage detection of composite plate ultrasonic guided wave structures based on peak frequency according to claim 2, characterized in that, Multiple piezoelectric sensors were equidistantly attached to the top and bottom ends of composite boards with and without delamination damage, and guided wave signals between different piezoelectric sensors were collected.

4. The method for damage detection of composite plate ultrasonic guided wave structures based on peak frequency according to claim 1, characterized in that, The Hilbert transform is used to obtain the extreme values ​​of the waveguide signal envelope, the peak position information of the waveguide signal of the composite plate is searched, and a fast matching and tracking algorithm based on the peak information is used to separate, extract and identify different modes of the waveguide signal.

5. The method for damage detection of composite plate ultrasonic guided wave structures based on peak frequency according to claim 4, characterized in that, The method for obtaining the envelope of a guided wave signal using Hlibert transform is as follows: ； In the formula, τ is the Hilbert transform output of the original signal x(t), where τ is the phase. Analyze the signal y(t) by combining x(t) and The composition is as follows: ； In the formula, A(t) is the envelope of x(t), φ(t) is the phase, and j is the imaginary unit; After obtaining the envelope of the guided wave signal, the location of the envelope extremum is found, and the peak value is searched by searching a fixed cyclic distance from the envelope extremum location to both ends.

6. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the method for detecting damage to composite plate ultrasonic guided wave structures based on peak frequency as described in any one of claims 1 to 5.

7. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the peak frequency-based composite plate ultrasonic guided wave structure damage detection method as described in any one of claims 1 to 5.

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