Anisotropy-compensated MUSIC damage imaging method based on excitation focused scanning

Abstract

The present invention discloses an anisotropy-compensated MUSIC damage imaging method based on excitation-focused scanning, comprising: aiming at the problem of low imaging accuracy on strongly attenuated anisotropic structures, using a self-excitation-self-sensing piezoelectric sensor array, focusing and scanning the array excitation signal, and improving the signal-to-noise ratio of the damage scattering signal; using the waveguide propagation speed in each direction measured in advance, using a dual anisotropy compensation mechanism of scanning direction-array element direction, and adaptively correcting the array direction vector during the MUSIC scanning process; combining the excitation-focused scanning with the MUSIC algorithm to achieve the final damage imaging positioning. The present invention improves the signal-to-noise ratio of the damage scattering array signal, compensates for the array error caused by the structural anisotropy, and has broad application prospects in the damage imaging positioning of strongly attenuated anisotropic structures.

Description

Technical Field

[0001] The invention belongs to the technical field of engineering structure health monitoring, and in particular relates to an anisotropic compensation MUSIC damage imaging method based on excitation focus scanning. Background Art

[0002] Advanced composite materials technology, especially high-strength carbon fiber composite materials technology, is a typical dual-use and military-civilian integration technology. In recent years, the trend of diversification and multi-application is very obvious. The application fields include aerospace, wind power generation, shipbuilding, automotive industry and other fields. Composite materials structures are easily damaged by low-speed impact during manufacturing and service. These internal damages not only greatly reduce the strength of the structure but also cannot be detected by conventional detection methods, which makes the structure have serious safety hazards. Therefore, structural health monitoring technology has important application value and broad application prospects for ensuring the safety of composite materials structures and reducing maintenance costs.

[0003] The array guided wave damage imaging method based on multiple signal classification (MUSIC) is a potential technology in the field of structural health monitoring. It has the advantages of directional scanning, high resolution, and relatively better program accuracy under low signal-to-noise ratio. The MUSIC algorithm models the guided wave propagation of the sensor array, performs eigenvalue decomposition on the covariance matrix of the array signal, and obtains the noise subspace spanned by the eigenvectors corresponding to the small eigenvalues. Then the MUSIC spatial spectrum is defined to represent the orthogonality between the noise subspace and the array flow pattern vector. By scanning the entire monitoring area, the image is drawn with the spatial spectrum as the pixel value, and the peak of the search image is the damage location. However, in practical applications, the amplitude of the guided wave will decay rapidly when propagating on some composite materials, such as large carbon fiber composite panels, resulting in a significant reduction in the signal-to-noise ratio of the damage scattering signal. In addition, composite materials have strong anisotropy, and the propagation speed of the guided wave in different directions varies greatly, while the accuracy of the MUSIC algorithm depends on the accuracy of the array flow pattern vector related to the wave velocity. If a fixed speed is used during the scanning process, the imaging accuracy will decrease.

[0004] Therefore, for damage monitoring of strongly attenuated anisotropic structures, it is necessary to introduce an excitation focusing scanning mechanism in damage imaging based on the MUSIC algorithm to enhance the excitation signal to improve the signal-to-noise ratio and compensate for the array flow pattern vector error caused by structural anisotropy. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide an anisotropy compensated MUSIC damage imaging method based on excitation focusing scanning. Aiming at the problem that the propagation attenuation of guided waves on a strongly attenuated anisotropic structure is serious and the velocity difference in each direction is obvious, which causes the precision of the MUSIC imaging method to decrease, the characteristic of the piezoelectric sensor that can be used as both a driver and a sensor is utilized, and an excitation focusing scanning mechanism of a one-dimensional linear array is introduced, so that the excitation signal of each array element in the array is focused on the damage position, thereby enhancing the amplitude of the damage scattering signal and improving its signal-to-noise ratio; secondly, by utilizing the wave velocity of guided waves in each direction on the structure measured in advance, a dual anisotropy compensation mechanism of scanning direction-array element direction is adopted, and the array flow pattern vector is adaptively corrected during the MUSIC scanning process to compensate for the array error introduced by the structural anisotropy, which can effectively improve the positioning imaging precision and reliability of the MUSIC damage imaging method in the strongly attenuated anisotropic structure.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions.

[0007] A method for anisotropy compensation MUSIC damage imaging based on excitation focus scanning comprises the following steps:

[0008] Step 1: Drive the piezoelectric transducer (PZT) array elements of the linear array in sequence to generate guided waves, collect the guided wave signals received by all other PZT array elements at the same time, and extract the array difference signal between the damaged state and the healthy state, which is the damaged scattering array signal. Specifically: each PZT array element in the array is used as an excitation array element to generate guided waves, and a total of 2M+1 excitations are performed, where 2M+1 is the number of array elements; during each excitation process, the remaining 2M array elements are collected as the guided wave signals received by the sensing array elements; the final array signal dimension is (2M+1)×2M×N, where N is the sampling length; the corresponding signal record under the excitation array element q and the sensing array element p is x p,q (t), the subscript q represents the number of the excitation array element, and the subscript p represents the number of the sensing array element.

[0009] Step 2: Set a scanning position (r, θ) in the monitoring area, and take the central element of the linear array as the reference element to calculate the time delay of each excitation element PZT q from the reference element to the scanning position; obtain the maximum value of the response signal and signal amplitude of each element in the array by delay accumulation, and calculate and record the square sum of the maximum signal amplitude of each element in the array.

[0010] Step 3: Repeat step 2 until the monitoring area is scanned, extract the search step with the largest maximum square sum, and obtain the corresponding enhanced scattering array signal x′ with the excitation focused on the damage position. p (t);

[0011] Step 4, calculate the covariance matrix of the enhanced damaged scattering array signal; and perform eigenvalue decomposition on it to obtain the noise subspace spanned by the eigenvectors corresponding to the small eigenvalues;

[0012] Step 5: Set a scanning position (r, θ) again, calculate the direction from the search position to each array element in the array, and adaptively select the propagation velocity in the corresponding direction of each array element to calculate the array flow pattern vector according to the waveguide velocity measured in each direction on the structure in advance;

[0013] Step 6: Calculate the inverse of the modulus of the product of the noise subspace and the array flow pattern vector of the scanning position, and record it as the spatial spectrum P(r,θ) of the scanning position;

[0014] Step 7: Repeat steps 5-6 until the monitoring area is scanned. Draw an image with the spatial spectrum as the pixel value, and search for the peak of the image, which is the damage location.

[0015] Furthermore, in step 2:

[0016] The time delay from each excitation array element PZT q to the scanning position relative to the reference array element is calculated as:

[0017]

[0018] Where r is the distance from the scanning position to the sensor array, θ is the direction of the scanning position, d is the array element spacing, and c is the propagation speed of the guided wave.

[0019] Then, the delay of the waveguide signal received by PZT p under each excitation array element is accumulated:

[0020]

[0021] Where ω is the waveguide frequency, x p (t, r, θ) is the delayed accumulation result of the signal collected by PZT p under different excitation array elements. The array element number p ranges from -M to M.

[0022] In addition, set the variable S to record the maximum square sum of the signal amplitude of each array element 0 The value is 0, and the sum of the squares of the maximum values ​​of the signals of each element in the recording array is:

[0023]

[0024] If S(r,θ) is greater than S 0 , then the delayed accumulation result x′ of the signal collected by the recording element under different excitation elements p (t) = x p (t,r,θ), and let S 0 =S(r,θ).

[0025] Furthermore, the step 4 specifically includes:

[0026] Step 4.1. Calculate the covariance matrix of the enhanced damaged scattering array signal:

[0027] R = E[X(t)·X H (t)] (4)

[0028] In the formula, X(t) = [x′ -4 (t),…x′ p (t),…x′4(t)],p=-M,…,M, the superscript H indicates the conjugate transpose operation;

[0029] Step 4.2. Perform eigenvalue decomposition on the covariance matrix to obtain the noise subspace spanned by the eigenvectors corresponding to the small eigenvalues.

[0030]

[0031] Where U S , U N They represent the signal subspace formed by the eigenvectors corresponding to the large eigenvalues ​​and the noise subspace formed by the eigenvectors corresponding to the small eigenvalues, respectively. S ,∑ N They are the large eigenvalues ​​corresponding to the signal subspace and the small eigenvalues ​​corresponding to the noise subspace, respectively.

[0032] Furthermore, the step 5 specifically includes:

[0033] Step 5.1. Calculate the array flow vector a corresponding to the scanning position (r,θ) p (r,θ) is

[0034]

[0035] In the above formula, c(θ p ) is along θ p The propagation speed of guided waves in the direction, θ p is the direction from the scanning position (r,θ) to the PZT p element;

[0036] Step 5.2. When calculating the anisotropically compensated array flow pattern vector, the direction θ from the scanning position (r,θ) to the PZT p element is p for:

[0037]

[0038] Furthermore, in step 6, the inverse of the modulus value of the multiplication of the noise subspace and the flow pattern vector of the scanning position array is calculated and recorded as the spatial spectrum P(r,θ) of the scanning position.

[0039]

[0040] Where A(r,θ) is the matrix form of the array flow vector,

[0041] Furthermore, in step 7, an image is drawn using the spatial spectrum as the pixel value, and the peak of the image is searched to be the damage location:

[0042]

[0043] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0044] 1. Aiming at the problem that the guided wave propagation on the strong attenuation anisotropic structure is seriously attenuated and the speed difference in each direction is obvious, which causes the precision of the MUSIC imaging method to decrease, the present invention utilizes the characteristics of the piezoelectric sensor that can be used as both a driver and a sensor, introduces the excitation focusing scanning mechanism of the one-dimensional linear array, so that the excitation signal of each array element in the array is focused on the damage position, thereby enhancing the amplitude of the damage scattering signal and improving its signal-to-noise ratio, so that the signal-to-noise ratio of the damage scattering signal is improved by about 3.4 times.

[0045] 2. The present invention adopts a dual anisotropy compensation mechanism of scanning direction and array element direction, and adaptively corrects the array flow vector during the MUSIC scanning process, thereby improving the positioning accuracy of the MUSIC damage imaging method in strongly attenuated anisotropic structures, with an angle positioning error of less than 2° and a distance error of less than 20 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a method flow chart of an embodiment of the present invention. ;

[0047] Figure 2 FIG. 1 is a schematic diagram of the arrangement of a PZT linear array on a carbon fiber composite material flat plate according to another embodiment of the present invention.

[0048] Figure 3 for Figure 2 Schematic diagram of the locations of three simulated damages on the carbon fiber composite material plate of the illustrated embodiment.

[0049] FIG4 is a diagram of damage scattering signals excited by PZT 0 and sensed by PZT-4, wherein FIG4a is a scattering signal diagram from damage 1 on the composite material plate; FIG4b is a scattering signal diagram from damage 2 on the composite material plate; and FIG4c is a scattering signal diagram from damage 3 on the composite material plate.

[0050] Figure 5 shows the scattering signal of damage 1 on the composite material plate before and after the excitation focus scan, where: Figure 5a To excite the scattered signal of damage 1 before focusing scanning, Figure 5b This is the scattered signal of damage 1 after excitation focus scanning.

[0051] FIG6 is a schematic diagram of the calculation from the scanning position to the direction of each array element, where: Figure 6a For the case where the sensor array element number p ≥ 0; Figure 6b This is the case where the sensor array element number p<0.

[0052] Figure 7 shows the anisotropically compensated MUSIC damage imaging results based on excitation focused scanning of three damages on a carbon fiber composite plate, where: Figure 7a This is the imaging localization result of injury 1; Figure 7b This is the imaging localization result of Lesion 2; Figure 7c This is the imaging localization result of injury 3. DETAILED DESCRIPTION

[0053] The invention discloses an anisotropy-compensated MUSIC damage imaging method based on excitation focus scanning. Aiming at the problem that the propagation attenuation of guided waves on a strongly attenuated anisotropic structure is serious and the velocity difference in each direction is obvious, which causes the precision of the MUSIC imaging method to decrease, the invention utilizes the characteristics of a piezoelectric sensor that can be used as both a driver and a sensor, introduces an excitation focus scanning mechanism of a one-dimensional linear array, so that the excitation signal of each array element in the array is focused on the damage position, thereby enhancing the amplitude of the damage scattering signal and improving its signal-to-noise ratio; secondly, utilizing the wave velocity of guided waves in each direction on the structure measured in advance, adopting a dual anisotropy compensation mechanism of scanning direction-array element direction, adaptively correcting the array flow pattern vector in the MUSIC scanning process, compensating for the array error introduced by the structural anisotropy, thereby effectively improving the positioning imaging precision and reliability of the MUSIC damage imaging method in the strongly attenuated anisotropic structure.

[0054] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0055] like Figure 1 As shown, the present invention provides an anisotropy compensation MUSIC damage imaging method based on excitation focus scanning, comprising the following steps:

[0056] Step 1: sequentially drive the PZT array elements of the linear array to generate guided waves, collect the guided wave signals received by all other PZT array elements, and extract the array difference signal between the damaged state and the healthy state, which is the damaged scattering array signal.

[0057] In step 1, each PZT array element in the array is used as an excitation array element to generate guided waves, and a total of 2M+1 excitations are performed, where 2M+1 is the number of array elements. During each excitation process, the remaining 2M array elements are simultaneously collected as the guided wave signals received by the sensing array elements. The final array signal dimension is (2M+1)×2M×N, where N is the sampling length. The corresponding signal record under the excitation array element q and the sensing array element p is x p,q (t), the subscript q represents the number of the excitation array element, and the subscript p represents the number of the sensing array element.

[0058] Step 2: Set a scanning position (r, θ) in the monitoring area, and take the central element of the linear array as the reference element to calculate the time delay of each excitation element PZT q from the reference element to the scanning position; obtain the maximum value of the response signal and signal amplitude of each element in the array by delay accumulation, and calculate and record the square sum of the maximum signal amplitude of each element in the array.

[0059] Step 2.1. Set a scanning position (r, θ) in the monitoring area, where r is the distance from the scanning position to the sensor array, and θ is the direction of the scanning position; set the variable S that records the maximum square sum of the signals of each array element in the array 0 The value is 0. Calculate the time delay τ of each excitation array element PZT q relative to the reference array element to the scanning position q ,

[0060]

[0061] Where d is the array element spacing, and c is the propagation velocity of the guided wave.

[0062] Step 2.2. Delay and accumulate the waveguide signals received by PZT p under each excitation array element:

[0063]

[0064] Where ω is the waveguide frequency, x p (t, r, θ) is the delayed accumulation result of the signal collected by PZT p under different excitation array elements. The array element number p ranges from -M to M. The sum of the squares of the maximum values ​​of the signals of each array element is recorded S(r, θ).

[0065]

[0066] If S(r,θ) is greater than S 0 , then the delayed accumulation result x′ of the signal collected by the recording element under different excitation elements p (t) = x p (t,r,θ), and let S 0 =S(r,θ).

[0067] Step 3: Repeat step 2 until the monitoring area is scanned, extract the search step with the largest maximum square sum, and obtain the corresponding enhanced scattering array signal x′ with the excitation focused on the damage position. p (t).

[0068] Step 4, calculate the covariance matrix of the enhanced damaged scattering array signal; and perform eigenvalue decomposition on it to obtain the noise subspace spanned by the eigenvectors corresponding to the small eigenvalues;

[0069] Step 4.1. Calculate the covariance matrix of the enhanced damaged scattering array signal,

[0070] R = E[X(t)·X H (t)] (4)

[0071] In the formula, X(t) = [x′ -4 (t),…x′ p (t),…x′4(t)],p=-M,…,M.

[0072] Step 4.2. Perform eigenvalue decomposition on the covariance matrix to obtain the noise subspace spanned by the eigenvectors corresponding to the small eigenvalues.

[0073]

[0074] Where U S , U N They represent the signal subspace formed by the eigenvectors corresponding to the large eigenvalues ​​and the noise subspace formed by the eigenvectors corresponding to the small eigenvalues, respectively. S ,∑ N They are the large eigenvalues ​​corresponding to the signal subspace and the small eigenvalues ​​corresponding to the noise subspace, respectively.

[0075] Step 5: Set a scanning position (r, θ) again, calculate the direction from the search position to each array element in the array, and adaptively select the propagation velocity in the corresponding direction of each array element to calculate the array flow pattern vector according to the waveguide velocity measured in each direction on the structure in advance;

[0076] Step 5.1. Calculate the array flow vector a corresponding to the scanning position (r,θ) p (r,θ) is

[0077]

[0078] In the above formula, c(θ p ) is along θ p The propagation speed of guided waves in the direction, θ p is the direction from the scanning position (r,θ) to the PZT p element;

[0079] In step 5.2, in the step of calculating the anisotropically compensated array flow pattern vector, the scanning position (r, θ) is directed to the direction θ of the PZT p element. p Calculated as:

[0080]

[0081] Step 6: Calculate the inverse of the modulus of the multiplication of the noise subspace and the array flow pattern vector of the scanning position, and record it as the spatial spectrum P(r,θ) of the scanning position.

[0082]

[0083] Where A(r,θ) is the matrix form of the array flow vector,

[0084] Step 7: Repeat steps 5-6 until the monitoring area is scanned. Draw an image with the spatial spectrum as the pixel value, and search for the peak of the image, which is the damage location.

[0085]

[0086] Embodiment 2 of the present invention: A damage localization experiment is conducted using a carbon fiber composite material plate as a strong attenuation anisotropic structure to illustrate its specific implementation process.

[0087] like Figure 2 As shown, the size of the carbon fiber composite material plate is 600mm×500mm×4mm, with a total of 24 layers. The thickness of each layer is 0.125mm, and the ply sequence is [45 / 0 / -45 / 90 / 0 / -45 / 0 / -45 / 0]s. A one-dimensional uniform linear array is arranged on the structure, which contains 9 array elements with an array element spacing of 13mm. The name of each array element is PZT-4 to PZT 4. A polar coordinate system is established with the center of the array, that is, PZT0 as the origin. At the same time, three damages were artificially simulated on the composite material plate by pasting absorbing glue, namely damage 1, damage 2 and damage 3. The positions of the three damages are (180mm, 90°), (130mm, 113°) and (173mm, 57°).

[0088] For damage imaging on strongly attenuated anisotropic structures, the specific process includes:

[0089] S1. Collect array signals scattered by damage

[0090] When the structure is healthy, each PZT array element in the sensor array is driven in turn to generate guided waves, and the guided wave signals received by all other PZT array elements are collected as reference signals. In the damage monitoring process, the same driving method is used to collect the response signal of the sensor array, which is recorded as the monitoring signal; the reference signal is subtracted from the monitoring signal to obtain the damaged scattering array signal. Among them, the three damage scattering signals with PZT0 as the excitation array element and PZT-4 as the sensing array element are as follows: Figure 4a , 4b , as shown in 4c.

[0091] S2. Excitation Focusing Scanning of Array Waveguide

[0092] Set a scanning position (r, θ) within the monitoring area and set the variable S to record the maximum square sum of the signals of each array element. 0 The value is 0. According to the above formula (1), the relative delay τ between PZT q and the reference array element is calculated: q The delay of the waveguide signal received by PZT p under each excitation array element is accumulated and expressed as x p (t, r, θ). Calculate the sum of the squares of the maximum values ​​of the signals of each element in the array S(r, θ) according to formula (3). If S(r, θ) is greater than S 0 , then the delayed accumulation result x′ of the signal collected by the recording element under different excitation elements p (t) = x p (t,r,θ), and let S 0 =S(r,θ).

[0093] S3. Obtaining enhanced damage scattering signal

[0094] Repeat step 2 to perform a two-dimensional scan of the direction and distance of the monitoring area, with the scanning steps of angle and distance being 1° and 1mm respectively, until the scanning of the entire monitoring area is completed, and the enhanced scattering array signal with the corresponding excitation signal focused on the damage position can be obtained. Take damage 1 as an example. Through excitation focusing scanning, the 8 scattering signals received by each PZT array element are delayed and accumulated, as shown in Figure 5. After excitation focusing scanning, the amplitude of the damage scattering signal increases from 0.15V to 0.7V, and the signal-to-noise ratio increases from 5.5dB to 18.8dB, which is about 3.4 times higher than the signal-to-noise ratio.

[0095] S4.MUSIC algorithm preprocessing

[0096] The covariance matrix of the enhanced damaged scattering array signal is calculated according to formula (4), and the covariance matrix R is decomposed by eigenvalue according to formula (5) to obtain the noise subspace U spanned by the eigenvectors corresponding to the small eigenvalues: N .

[0097] S5. Anisotropy compensation of array flow pattern vectors

[0098] Set a scanning position (r, θ) in the monitoring area again, as shown in Figure 6, and calculate the direction from the scanning position (r, θ) to the PZT p element according to formula (7). Adopt the dual anisotropy compensation mechanism of scanning direction-element direction, adaptively select the guided wave velocity in each element direction to calculate the relative delay from the scanning position to each element, and calculate the array flow vector a according to formula (6) p (r,θ).

[0099] S6. Calculation of spatial spectrum

[0100] The inverse modulus of the product of the noise subspace and the array flow pattern vector of the scanning position is calculated according to formula (8) and recorded as the spatial spectrum P (r, θ) of the scanning position.

[0101] S7. Search the monitoring area and locate the damage

[0102] Repeat step 6 to perform a two-dimensional scan of the direction and distance of the monitoring area, with the scanning steps of angle and distance being 1° and 1mm respectively, until the entire monitoring area is scanned, and the damage image is drawn with the spatial spectrum as the pixel value. When the array flow pattern vector matches the true source signal vector, due to its orthogonality with the noise subspace, a peak appears in the spatial spectrum, which is manifested as a bright spot on the damage image, i.e., the damage location, as shown in Figure 7a , 7b As shown in Figure 7c, the positioning results of the three damages are (162mm, 91°), (145mm, 111°) and (179mm, 56°), the angle positioning errors are all less than 2°, and the distance errors are all less than 20mm.

Claims

1. A method for anisotropically compensated MUSIC damage imaging based on excitation focused scanning, characterized in that: The following steps are involved: Step 1: sequentially drive the PZT array elements of the linear array to generate guided waves, collect the guided wave signals received by all other PZT array elements, and extract the array difference signal between the damaged state and the healthy state, which is the damaged scattering array signal; Step 2: Set a scanning position (r, θ) in the monitoring area, and take the central element of the linear array as the reference element, calculate the time delay of each excitation element PZT q from the reference element to the scanning position; obtain the maximum value of the response signal and signal amplitude of each element in the array by delay accumulation, and calculate and record the square sum of the maximum value of the signal amplitude of each element in the array; Step 3: Repeat step 2 until the monitoring area is scanned, extract the search step with the largest maximum square sum, and obtain the corresponding enhanced scattering array signal x′ with the excitation focused on the damage position. p (t); Step 4, calculate the covariance matrix of the enhanced damaged scattering array signal; and perform eigenvalue decomposition on it to obtain the noise subspace spanned by the eigenvectors corresponding to the small eigenvalues; Step 5, set a scanning position (r, θ) again, calculate the direction from the scanning position (r, θ) to each array element in the array, and adaptively select the propagation velocity in the corresponding direction of each array element to calculate the array flow vector according to the waveguide velocity in each direction on the structure measured in advance; Step 6: Calculate the inverse of the modulus of the product of the noise subspace and the array flow pattern vector of the scanning position, and record it as the spatial spectrum P(r,θ) of the scanning position; Step 7: Repeat steps 5-6 until the scanning of the monitoring area is completed; Draw an image with the spatial spectrum as the pixel value, and search for the peak of the image to be the damage location; The step 5 specifically includes: Step 5.

1. Calculate the array flow vector a corresponding to the scanning position (r,θ) p (r,θ) is In the above formula, c(θ p ) is along θ p The propagation speed of guided waves in the direction, θ p is the direction from the scanning position (r,θ) to the PZT p element; Step 5.

2. When calculating the anisotropically compensated array flow pattern vector, the direction θ from the scanning position (r,θ) to the PZT p element is p for:

2. The anisotropy compensation MUSIC damage imaging method based on excitation focus scanning according to claim 1, characterized in that: In step 1, each PZT array element in the array is used as an excitation array element to generate guided waves, and a total of 2M+1 excitations are performed, where 2M+1 is the number of array elements. During each excitation process, the remaining 2M array elements are simultaneously collected as guided wave signals received by the sensing array elements. The final array signal dimension is (2M+1)×2M×N, where N is the sampling length. The corresponding signal record under the excitation array element q and the response array element p is x. p,q (t), the subscript q represents the number of the excitation array element, and the subscript p represents the number of the response array element.

3. The anisotropy compensation MUSIC damage imaging method based on excitation focus scanning according to claim 1, characterized in that: The time delay from each excitation array element PZT q to the scanning position relative to the reference array element is calculated as: Where r is the distance from the scanning position to the sensor array, θ is the direction of the scanning position, d is the array element spacing, and c is the propagation speed of the guided wave.

4. The anisotropy compensation MUSIC damage imaging method based on excitation focus scanning according to claim 1, characterized in that: Accumulate the delay of the waveguide signal received by PZT p under each excitation array element: Where ω is the waveguide frequency, x p (t, r, θ) is the delayed accumulation result of the signal collected by PZT p under different excitation array elements. The array element number p ranges from -M to M.

5. The anisotropy compensation MUSIC damage imaging method based on excitation focus scanning according to claim 1, characterized in that: Set the variable S to record the maximum square sum of the signals of each array element 0 The value is 0, and the sum of the squares of the maximum values ​​of the signals of each element in the recording array is: If S(r,θ) is greater than S 0 , then the delayed accumulation result x′ of the signal collected by the recording element under different excitation elements p (t) = x p (t,r,θ), and let S 0 =S(r,θ).

6. The anisotropy compensation MUSIC damage imaging method based on excitation focus scanning according to claim 1, characterized in that: The step 4 specifically includes: Step 4.

1. Calculate the covariance matrix of the enhanced damaged scattering array signal: R=E[X(t)X H (t)] (4) In the formula, X(t) = [x′ -4 (t),…x′ p (t),…x′4(t)],p=-M,…,M, the superscript H indicates the conjugate transpose operation; Step 4.

2. Perform eigenvalue decomposition on the covariance matrix to obtain the noise subspace spanned by the eigenvectors corresponding to the small eigenvalues. Where U S , U N They represent the signal subspace formed by the eigenvectors corresponding to the large eigenvalues ​​and the noise subspace formed by the eigenvectors corresponding to the small eigenvalues, respectively. S ,∑ N They are the large eigenvalues ​​corresponding to the signal subspace and the small eigenvalues ​​corresponding to the noise subspace, respectively.

7. The anisotropy compensation MUSIC damage imaging method based on excitation focus scanning according to claim 1, characterized in that: In step 6, the inverse of the modulus value of the product of the noise subspace and the flow pattern vector of the scanning position array is calculated and recorded as the spatial spectrum P(r,θ) of the scanning position. Where A(r,θ) is the matrix form of the array flow vector, 8. The anisotropy compensation MUSIC damage imaging method based on excitation focus scanning according to claim 1, characterized in that: In step 7, an image is drawn using the spatial spectrum as the pixel value, and the peak of the image is searched to be the damage location:

Images