Multi-layer medium ultrasonic super-resolution imaging method based on virtual source excitation

Abstract

The invention discloses a multilayer medium ultrasonic super-resolution imaging method based on virtual source excitation, and belongs to the technical field of ultrasonic nondestructive testing. The method comprises the following steps: 1, selecting an ultrasonic linear array probe; 2, virtual source excitation parameters are determined; 3, delay excitation time of the ith array element in the virtual source excitation group is calculated; 4, placing a phased array probe on the surface of the composite structure test piece, and receiving an echo signal by utilizing ultrasonic phased array excitation receiving equipment; step 5, performing one-dimensional Fourier transform on the collected echo signals along a time axis, and then performing singular value decomposition; step 6, calculating a Green function between the target imaging point and the position of the receiving array element; and step 7, calculating the pixel value of the target imaging point based on the step 6, and realizing the multi-layer medium ultrasonic super-resolution imaging based on virtual source excitation. The ultrasonic super-resolution imaging method aims at overcoming the defects of an existing ultrasonic super-resolution imaging method for the internal defects of the multi-layer medium.

Description

Technical Field

[0001] This invention belongs to the field of ultrasonic nondestructive testing technology, specifically relating to a multilayer medium ultrasonic super-resolution imaging method based on virtual source excitation. Background Technology

[0002] With the application of cyclic stress during service, fatigue cracks can be induced around porosity defects inside the workpiece, leading to the failure of components or equipment. Ultrasonic nondestructive testing (NDT) can perform full lifecycle testing on core components of high-end equipment from production to service, which is crucial for the safe and stable operation of the equipment. An ultrasonic phased array consists of linearly arranged piezoelectric crystals, each capable of independently generating and receiving ultrasonic signals. By sequentially exciting individual array elements and acquiring signals received by all elements, full-matrix acquisition data can be obtained. The full-matrix acquisition data-based full-focusing imaging method is a classic linear ultrasonic imaging method. While it can achieve high-precision imaging characterization of defects, it cannot separate two defects when the distance between them is less than the diffraction limit. To improve detection resolution, previous researchers proposed the TR-MUSIC super-resolution imaging method based on full-matrix acquisition data. This method utilizes eigenvalue decomposition and subspace techniques to separate two porosity defects with a distance less than the diffraction limit in the image. However, the limitation of this method is that when the signal-to-noise ratio of the echo signal is low, the signal subspace and noise subspace after eigenvalue decomposition are aliased, which causes the useful signal used for imaging to be aliased by noise, resulting in a large number of artifacts on the image, making it impossible to achieve super-resolution imaging.

[0003] Meanwhile, with industrial development, multilayer dielectric structures are widely used in core equipment in aerospace, rail transportation, and building energy fields, increasing the demand for high-precision detection technology for internal defects in multilayer dielectric structures. Existing imaging methods improve the imaging accuracy of multilayer dielectric defect detection by calculating the acoustic propagation process in the multilayer dielectric and combining it with a full-focusing imaging algorithm. However, due to the theoretical limitations of the full-focusing imaging algorithm, super-resolution imaging cannot be achieved. As for the TR-MUSIC algorithm, although it can theoretically achieve super-resolution imaging of defects, the energy attenuation of sound waves propagating between multilayer dielectrics leads to a significant reduction in the signal-to-noise ratio of the echo signal, thus restricting the realization of the TR-MUSIC method in multilayer dielectric super-resolution imaging. Summary of the Invention

[0004] This invention provides a multi-layer medium ultrasonic super-resolution imaging method based on virtual source excitation, which solves the problems of the current TR-MUSIC method based on full matrix acquisition technology. When this technology is used for multi-layer medium detection, the echo signal has a low signal-to-noise ratio, which seriously affects the resolution capability of the TR-MUSIC method. Secondly, the full matrix acquisition technology has a large amount of data and requires a long post-processing time, which makes it impossible to achieve real-time super-resolution imaging.

[0005] This invention is achieved through the following technical solution: A multilayer medium ultrasound super-resolution imaging method based on virtual source excitation, the method comprising the following steps: Step 1: Select an ultrasonic linear array probe; Step 2: Determine the virtual source excitation parameters; Step 3: Calculate the first virtual source stimulus group. i The delay excitation time of each array element; Step 4: Place the phased array probe on the surface of the composite structure specimen and use the ultrasonic phased array excitation receiving device to receive the echo signal. Step 5: Perform a one-dimensional Fourier transform on the acquired echo signal along the time axis, and then perform singular value decomposition. Step 6: Calculate the Green's function between the target imaging point and the position of the receiving array element; Step 7: Based on Step 6, recalculate the pixel value of the target imaging point to realize multi-layer medium ultrasonic super-resolution imaging based on virtual source excitation.

[0006] Furthermore, the specific calculation formula for step three is as shown in equations (1) - (4): (1) (2) (3) (4) in, T The number of array elements in the virtual source excitation group. D 1 and D 2 are the refraction points of the first layer of medium. P 1 and second layer of medium refraction point P 2. The lateral distance from the center of the virtual source stimulus group. p For the spacing between array elements, c 1. c 2 and c 3 represents the sound velocity of each of the three media layers. h 1 and h 2 represents the thickness of the two upper media layers. h 0 represents the distance between the virtual source and the upper surface of the target detection medium.t i For the virtual source incentive group, the first i The propagation time from an array element to a virtual source. td i For the virtual source incentive group, the first i The delay excitation time of each array element.

[0007] Furthermore, step four specifically involves sequentially exciting the virtual source excitation group according to the delay excitation rule in step three, so that the echo signal received by all array elements simultaneously is... A ( t , a , b ),in t Sampling time, a This is the sequence number of the virtual source stimulus group. b The sequence number of the receiving array element ( a = 1, 2, … , N - T +1; b = 1, 2, …, N ) .

[0008] Furthermore, step five specifically involves collecting the echo signal. A ( t , a , b A one-dimensional Fourier transform along the time axis is: A ( oh 0, a , b As shown in equation (5): (5) in, oh 0 = 2 πf 0; Again A ( oh 0, a , b Singular value decomposition is performed, as shown in equation (6): (6) Where V's column vectors are left singular vectors, U's row vectors are right singular vectors, and the diagonal elements σ of Σ are singular values, V is... N - T A +1 dimensional square matrix, where U is... N A square matrix of dimension Σ is ( N - T +1)× N 3D matrix.

[0009] Furthermore, step six specifically involves calculating the target imaging points. X = ( x , z The Green's function Gr( between the position of the receiving array element and the position of the receiving array element) X , Xr b , oh 0), as shown in equation (7): (7) Where H0 is the zeroth-order Hankel function of the first kind, oh 0 = 2 πf 0, j The imaginary unit, t ( X , Xr b () is from the target imaging point X To the b The propagation time of the receiving array element can be calculated by equations (1) - (3).

[0010] Furthermore, step seven specifically involves calculating the target imaging points. X pixel values I ( X As shown in equation (8): (8) in, number The number of pores in the target detection area.<a,b> Let a be the dot product of vectors a and b, where a T Let ||a||2 be the transpose of a, and let ||a||2 be the L2 norm of vector a.

[0011] The beneficial effects of this invention are: This invention generates a virtual focal point source near the region to be detected by applying a delayed excitation to a specified array group, thereby increasing the signal-to-noise ratio of the echo signal and improving the performance of TR-MUSIC super-resolution imaging. At the same time, due to the high signal-to-noise ratio of the echo signal, redundant excitation can be significantly reduced, and rapid super-resolution imaging of internal defects in multilayer media can be achieved using a small amount of echo data. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the delay calculation of each element in a virtual source array group in a multilayer medium according to the present invention.

[0013] Figure 2 This is a flowchart of the ultrasonic super-resolution imaging algorithm for internal defects in multilayer media based on virtual source excitation, according to the present invention. Detailed Implementation

[0014] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of this application with unnecessary detail.

[0015] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0016] This invention proposes an ultrasound super-resolution imaging method based on virtual source excitation. By applying delayed excitation to a specified array group, a virtual focal point source is generated near the area to be detected, reducing signal attenuation during propagation and thus increasing the signal-to-noise ratio of the echo signal, thereby improving the performance of TR-MUSIC super-resolution imaging. At the same time, since the echo signal has a high signal-to-noise ratio, redundant excitation can be significantly reduced, and rapid super-resolution imaging of multilayer media can be achieved using a small amount of echo data.

[0017] like Figure 1-2 As shown, a multi-medium ultrasound super-resolution imaging method based on virtual source excitation is described, the method comprising the following steps: Step 1: Select an ultrasonic linear array probe; Step 2: Determine the virtual source excitation parameters; Step 3: Calculate the first virtual source stimulus group. i The delay excitation time of each array element; Step 4: Place the phased array probe on the surface of the composite structure specimen and use the ultrasonic phased array excitation receiving device to receive the echo signal. Step 5: Perform a one-dimensional Fourier transform on the acquired echo signal along the time axis, and then perform singular value decomposition. Step 6: Calculate the Green's function between the target imaging point and the position of the receiving array element; Step 7: Based on Step 6, recalculate the pixel value of the target imaging point to realize multi-layer medium ultrasonic super-resolution imaging based on virtual source excitation.

[0018] Furthermore, the specific calculation formula for step three is as shown in equations (1) - (4): (1) (2) (3) (4) in, T The number of array elements in the virtual source excitation group. D 1 and D 2 are the refraction points of the first layer of medium. P 1 and second layer of medium refraction point P 2. The lateral distance from the center of the virtual source stimulus group. p For the spacing between array elements, c 1. c 2 and c 3 represents the sound velocity of each of the three media layers. h 1 and h 2 represents the thickness of the two upper media layers. h 0 represents the distance between the virtual source and the upper surface of the target detection medium. t i For the virtual source incentive group, the first i The propagation time from an array element to a virtual source. td i For the virtual source incentive group, the first i The delay excitation time of each array element.

[0019] Furthermore, step four specifically involves sequentially exciting the virtual source excitation group according to the delay excitation rule in step three, so that the echo signal received by all array elements simultaneously is... A ( t , a , b ),in t Sampling time, a This is the sequence number of the virtual source stimulus group. b The sequence number of the receiving array element ( a = 1, 2, … , N - T +1; b = 1, 2, …, N ) .

[0020] Furthermore, step five specifically involves collecting the echo signal. A ( t , a , b A one-dimensional Fourier transform along the time axis is: A ( oh 0, a , b As shown in equation (5): (5) in, oh 0 = 2 πf 0; Again A ( oh 0, a , b Singular value decomposition is performed, as shown in equation (6): (6) Where V's column vectors are left singular vectors, U's row vectors are right singular vectors, and the diagonal elements σ of Σ are singular values, V is... N - T A +1 dimensional square matrix, where U is... N A square matrix of dimension Σ is ( N - T +1)× N 3D matrix.

[0021] Furthermore, step six specifically involves calculating the target imaging points. X = ( x , z The Green's function Gr( between the position of the receiving array element and the position of the receiving array element) X , Xr b , oh 0), as shown in equation (7): (7) Where H0 is the zeroth-order Hankel function of the first kind, oh 0 = 2 πf 0, j The imaginary unit, t ( X , Xr b () is from the target imaging point X To the b The propagation time of the receiving array element can be calculated by equations (1) - (3).

[0022] Furthermore, step seven specifically involves calculating the target imaging points. X pixel values I ( X As shown in equation (8): (8) in, number The number of pores in the target detection area.<a,b> Let a be the dot product of vectors a and b, where a T Let ||a||2 be the transpose of a, and let ||a||2 be the L2 norm of vector a.

Claims

1. A multi-medium ultrasonic super-resolution imaging method based on virtual source excitation, characterized in that, The method includes the following steps: Step 1: Select an ultrasonic linear array probe; Step 2: Determine the virtual source excitation parameters; Step 3: Calculate the first virtual source stimulus group. i The delay excitation time of each array element; Step 4: Place the phased array probe on the surface of the composite structure specimen and use the ultrasonic phased array excitation receiving device to receive the echo signal. Step 5: Perform a one-dimensional Fourier transform on the acquired echo signal along the time axis, and then perform singular value decomposition. Step 6: Calculate the Green's function between the target imaging point and the position of the receiving array element; Step 7: Based on Step 6, recalculate the pixel value of the target imaging point to realize multi-layer medium ultrasonic super-resolution imaging based on virtual source excitation.

2. The method according to claim 1, characterized in that, The specific calculation formula for step three is as shown in equations (1) to (4): (1) (2) (3) (4) in, T The number of array elements in the virtual source excitation group. D 1 and D 2 are the refraction points of the first layer of medium. P 1 and second layer of medium refraction point P 2. The lateral distance from the center of the virtual source stimulus group. p For the spacing between array elements, c 1. c 2 and c 3 represents the sound velocity of each of the three media layers. h 1 and h 2 represents the thickness of the two upper media layers. h 0 represents the distance between the virtual source and the upper surface of the target detection medium. t i For the virtual source incentive group, the first i The propagation time from an array element to a virtual source. td i For the virtual source incentive group, the first i The delay excitation time of each array element.

3. The method according to claim 2, characterized in that, Step four specifically involves sequentially exciting the virtual source excitation group according to the delayed excitation rule in step three, so that the echo signal received by all array elements simultaneously is... A ( t , a , b ),in t Sampling time, a This is the sequence number of the virtual source stimulus group. b The sequence number of the receiving array element ( a = 1, 2, … , N - T +1; b = 1,2, …, N ) .

4. The method according to claim 1, characterized in that, Step five specifically involves collecting the echo signal. A ( t , a , b A one-dimensional Fourier transform along the time axis is: A ( ω 0, a , b As shown in equation (5): (5) in, ω 0 = 2 πf 0; Again A ( ω 0, a , b Singular value decomposition is performed, as shown in equation (6): (6) Where V's column vectors are left singular vectors, U's row vectors are right singular vectors, and the diagonal elements σ of Σ are singular values, V is... N - T A +1 dimensional square matrix, where U is... N A square matrix of dimension Σ is ( N - T +1)× N 3D matrix.

5. The method according to claim 2, characterized in that, Step six specifically involves calculating the target imaging points. X =( x , z The Green's function Gr( between the position of the receiving array element and the position of the receiving array element) X , Xr b , ω 0), as shown in equation (7): (7) Where H0 is the zeroth-order Hankel function of the first kind, ω 0 = 2 πf 0, j The imaginary unit, t ( X , Xr b () is from the target imaging point X To the b The propagation time of the receiving array element can be calculated by equations (1) - (3).

6. The method according to claim 1, characterized in that, Step seven specifically involves calculating the target imaging points. X pixel values I ( X As shown in equation (8): (8) in, num The number of pores in the target detection area.<a, b> Let a be the dot product of vectors a and b, where a T Let ||a||2 be the transpose of a, and let ||a||2 be the L2 norm of vector a.

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