A method for ultrasonic oblique-incidence subaperture coherent composite diverging wave imaging

Abstract

The present application provides a method for ultrasonic oblique-incident sub-aperture coherent composite diverging wave imaging. The method includes: determining multiple sub-apertures of an ultrasonic phased array probe, and determining the coordinates of a virtual source point corresponding to each sub-aperture; constructing an image reconstruction area for the workpiece to be measured, and dividing the image reconstruction area into multiple grid points; based on the coordinates of the virtual source point corresponding to each sub-aperture, for each focal point, obtaining the acoustic propagation time of the signals received by each of the multiple array elements of the sub-aperture; based on the acoustic propagation time of the signals received by each of the multiple array elements of each sub-aperture, delaying and superimposing the amplitudes of the signals received by the corresponding array elements to obtain the echo amplitudes of each focal point; thereby finally obtaining a focused image. The method of the present invention calculates the acoustic propagation time of the sound wave in different media, delays and superimposes the amplitudes of the received signals, so that the composite diverging wave imaging can also have a good defect detection effect when facing the case of oblique-incident double-layer media.

Description

Technical Field

[0001] The present application relates to the technical field of ultrasonic non-destructive testing, and in particular to a method for ultrasonic oblique-incidence sub-aperture coherent composite diverging wave imaging. Background Art

[0002] Diverging Wave Imaging (DWI) is an imaging method that places a virtual source behind an ultrasonic phased array probe. This involves applying a delay to the array elements of the effective transmitting aperture, creating a virtual focal point (i.e., a virtual source point) behind the ultrasonic phased array probe. Subaperture diverging wave imaging divides the ultrasonic phased array probe into multiple subarrays. The virtual source point behind the subarray changes with the position of the subarray, moving along a line segment parallel to the rear of the ultrasonic phased array probe, thus forming a virtual source array. This concept was initially applied in the medical field and has been proven to improve the resolution and signal-to-noise ratio of B-scan imaging systems.

[0003] In recent years, some people have applied sub-aperture diverging wave imaging in the field of non-destructive testing, and found that by adding a coherence factor to the sub-aperture diverging wave imaging algorithm, a fully focused image with quality comparable to that obtained using full-matrix data can be obtained, and with a higher frame rate imaging efficiency.

[0004] However, the application scenarios of sub-aperture diverging wave imaging are all vertical incidence methods where the ultrasonic phased array probe is in direct contact with the workpiece to be tested. In actual non-destructive testing scenarios, some complex workpieces need to be ultrasonically inspected. If the sound beam cannot cover the entire area to be tested, it may lead to missed detection. In this case, an inclined wedge is usually added between the ultrasonic phased array probe and the workpiece to be tested. In this application scenario, the ultrasonic waves emitted by the ultrasonic phased array probe need to pass through two media, the inclined wedge and the workpiece to be tested, to reach the detection target. During this process, the sound beam will be reflected and refracted at the coupling interface between the inclined wedge and the workpiece to be tested, resulting in the existing delay law of sub-aperture diverging wave imaging being inapplicable. Summary of the Invention

[0005] This application provides a method for ultrasonic oblique-incidence sub-aperture coherent composite diverging wave imaging, which enables diverging wave imaging to achieve good defect detection results even in the case of oblique-incidence double-layer media. The technical solution of this application is as follows:

[0006] The present application provides an ultrasonic oblique-incidence sub-aperture coherent composite diverging wave imaging method, which is characterized by comprising:

[0007] Determining a plurality of subapertures of the ultrasonic phased array probe, and determining the coordinates of a virtual source point corresponding to each of the subapertures based on the inclination angle of the angled wedge;

[0008] An image reconstruction area is constructed for the workpiece to be measured, and the image reconstruction area is divided into a plurality of grid points, each of which corresponds to a focal point; based on the coordinates of the virtual source point corresponding to each sub-aperture, for each focal point, an acoustic propagation time of a signal received by each of the plurality of array elements of the sub-aperture is obtained;

[0009] Based on the acoustic propagation time of the signals received by the multiple array elements of each sub-aperture, delaying and superimposing the amplitudes of the signals received by the corresponding array elements to obtain the echo amplitudes of the respective focus points;

[0010] A focused image is obtained based on the echo amplitudes of the respective focused points.

[0011] In some implementations, determining a plurality of subapertures of the ultrasonic phased array probe includes:

[0012] The multiple sub-apertures of the ultrasonic phased array probe are determined by a first formula, wherein the first formula is expressed as follows:

[0013] L=(NM) / s+1

[0014] Where L is the number of subapertures, N is the number of array elements of the ultrasonic phased array probe, M is the number of array elements contained in each subaperture, and s is the number of array elements in each subaperture step.

[0015] In some implementations, determining the coordinates of the virtual source point corresponding to each sub-aperture based on the inclination angle of the angled wedge includes:

[0016] Establish a coordinate system, wherein the origin of the coordinate system is the intersection of a perpendicular line to the center of the ultrasonic phased array probe and a coupling interface; wherein the coupling interface is the interface between the angled wedge and the workpiece to be measured; the horizontal axis x of the coordinate system is parallel to the coupling interface, and the vertical axis z of the coordinate system is parallel to the normal to the coupling interface;

[0017] The coordinates of the virtual source point corresponding to each sub-aperture are determined by a second formula, wherein the second formula is expressed as follows:

[0018] x vl =-Fsinθ+x l

[0019] z vl =Fcosθ+z l

[0020] Where F is the focal depth, that is, the distance from the virtual source point to the center of the corresponding subaperture; x vl is the virtual source point V corresponding to the lth sub-aperture l The horizontal axis; z vl is the virtual source point V corresponding to the lth sub-aperturel The vertical coordinate of the wedge; θ is the inclination angle of the wedge; (x l ,z l ) is the center point C of the lth (l=1,2,..,L) sub-aperture l coordinates of

[0021] Among them, (x l ,z l ) is represented as follows:

[0022]

[0023] Where d is the center-to-center distance between adjacent array elements, and h is the height from the center of array element No. 1 of the ultrasonic phased array probe to the coupling interface.

[0024] In some implementations, the acquiring, for each of the focusing points, based on the coordinates of the virtual source point corresponding to each of the sub-apertures, the acoustic propagation time of the signals received by each of the plurality of array elements of the sub-aperture includes:

[0025] Based on the coordinates of the virtual source point corresponding to each sub-aperture, for each focusing point, determining the coordinates of the incident points where the signals received by the plurality of array elements of the sub-aperture pass through the coupling interface twice during the propagation process, which are the coordinates of the first incident point and the second incident point respectively;

[0026] Based on the coordinates of the first incident point, obtaining a transmission delay time for the sub-aperture to transmit the sound wave to the corresponding focusing point;

[0027] Based on the coordinates of the second incident point, obtaining a reception delay time from the echo of the corresponding focusing point to the reception of the signal for each of the multiple array elements of the sub-aperture;

[0028] The transmit delay time and the receive delay time are summed to obtain the acoustic propagation time of the signals received by each of the multiple array elements of the sub-aperture.

[0029] In some implementations, determining, for each of the focusing points, based on the coordinates of the virtual source point corresponding to each of the subapertures, the coordinates of the incident points at which signals received by the plurality of array elements of the subaperture pass through the coupling interface twice during propagation includes:

[0030] Based on the coordinates of a virtual source point corresponding to each sub-aperture, a plurality of first sound paths of the sound wave transmitted from the virtual source point to each grid point in a first row of the image reconstruction area is obtained; and a plurality of second sound paths of the sound wave transmitted from each grid point in the first row to each focal point is obtained;

[0031] Based on the multiple first sound paths and the multiple second sound paths, obtaining the shortest sound paths of the sound waves emitted from the virtual source point to each focusing point;

[0032] Determining the coordinates of the first incident point based on the shortest sound path emitted from the virtual source point to each focal point;

[0033] Acquire multiple third sound paths of the sound wave from each focus point to each grid point in the first row, and acquire multiple fourth sound paths of the sound wave from each grid point in the first row to each array element of the subaperture;

[0034] Based on the multiple third sound paths and the multiple fourth sound paths, obtaining the shortest sound paths of the sound waves reflected from each focal point to each array element of the sub-aperture;

[0035] The coordinates of the second incident point are determined based on the shortest sound paths reflected from the respective focus points to the respective array elements of the sub-aperture.

[0036] In some implementations, obtaining, based on the coordinates of the first incident point, a transmission delay time for transmitting the acoustic wave through the sub-aperture to the corresponding focal point includes:

[0037] The third formula is used to determine the transmission delay time t of the sub-aperture transmitting the sound wave and transmitting it to the corresponding focal point. Tl , wherein the third formula is expressed as follows:

[0038]

[0039] Where x is the horizontal coordinate of the focus point, z is the vertical coordinate of the focus point, c1 is the speed of the sound wave in the inclined wedge, and c2 is the speed of the sound wave in the workpiece to be measured. is the coordinate of the first incident point.

[0040] In some implementations, obtaining, based on the coordinates of the second incident point, a reception delay time from the echo of the corresponding focus point to the reception of the signal by each of the multiple array elements of the sub-aperture includes:

[0041] The fourth formula is used to determine the receiving delay time of each of the multiple array elements of the sub-aperture from the corresponding focus point echo to the received signal The fourth formula is expressed as follows:

[0042]

[0043] in, is the coordinate of the second incident point.

[0044] In some implementations, the horizontal coordinates and vertical coordinates of the virtual source points corresponding to the multiple sub-apertures are respectively stored in a one-dimensional matrix; the transmission delay time is stored in a first three-dimensional matrix, wherein the first two dimensions of the first three-dimensional matrix are the number of grid points in the image reconstruction area, and the third dimension is the number of virtual source points; the receiving delay time is stored in a second three-dimensional matrix, wherein the first two dimensions of the second three-dimensional matrix are the number of grid points in the image reconstruction area, and the third dimension is the number of receiving array elements.

[0045] The technical solutions provided by the embodiments of the present application bring at least the following beneficial effects:

[0046] By calculating the acoustic propagation time of acoustic waves in different media and applying a time-delayed superposition to the amplitudes of the received signals, a method for ultrasonic oblique-incidence sub-aperture coherent composite emission wave imaging is implemented. This method enables composite diverging wave imaging to achieve excellent defect detection even in double-layer media with oblique incidence. This solves the problem of existing diverging wave imaging algorithms being unsuitable for the use of oblique wedges in practical industrial inspections using sub-aperture diverging wave imaging.

[0047] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The drawings herein are incorporated into and constitute a part of the specification, illustrate embodiments consistent with the present application, and together with the specification are used to explain the principles of the present application, and do not constitute an improper limitation on the present application.

[0049] Figure 1 The flowchart of a method for ultrasonic oblique-incident sub-aperture coherent composite diverging wave imaging according to an embodiment of the present invention is shown.

[0050] Figure 2 4 is a schematic diagram showing the calculation of the position of the virtual source point of the diverging wave according to an embodiment of the present invention.

[0051] Figure 3 The flowchart of a method for ultrasonic oblique-incident sub-aperture coherent composite diverging wave imaging according to another embodiment of the present invention is shown.

[0052] Figure 4 4 is a schematic diagram showing calculation of a delay rule during image reconstruction according to an embodiment of the present invention.

[0053] Figure 5 FIG. 1 is a schematic diagram of an ultrasonic detection system according to an embodiment of the present invention.

[0054] Figure 6 FIG. 4 is a front view of a test block according to an embodiment of the present invention.

[0055] Figure 7 FIG. 4 is a diverging wave focused ultrasound image according to an embodiment of the present invention.

[0056] In the picture:

[0057] 1- Host, 2- Display, 3- Ultrasonic sampling system, 4- Panel on the ultrasonic sampling system, 5- Ultrasonic phased array probe, 6- Angle wedge, 7- Workpiece to be measured. DETAILED DESCRIPTION

[0058] In order to enable ordinary people in the art to better understand the technical solutions of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings.

[0059] It should be noted that the terms "first," "second," and the like in this application are used to distinguish similar objects and are not necessarily used to describe a specific order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. Instead, they are merely examples of devices and methods consistent with certain aspects of the present application as detailed in the appended claims.

[0060] like Figure 1 As shown, an embodiment of the present application provides an ultrasonic oblique-incidence sub-aperture coherent composite diverging wave imaging method, which may include the following steps:

[0061] S101 : determining a plurality of sub-apertures of an ultrasonic phased array probe, and determining the coordinates of a virtual source point corresponding to each of the sub-apertures based on an inclination angle of an inclined wedge.

[0062] S102: construct an image reconstruction area for the workpiece to be measured, and divide the image reconstruction area into multiple grid points, each of which corresponds to a focal point; based on the coordinates of the virtual source point corresponding to each sub-aperture, obtain, for each focal point, the acoustic propagation time of the signal received by each of the multiple array elements of the sub-aperture.

[0063] S103 , based on the acoustic propagation time of the signals received by the multiple array elements of each sub-aperture, delay and superpose the amplitudes of the signals received by the corresponding array elements to obtain the echo amplitudes of the respective focus points.

[0064] S104: Obtain a focused image based on the echo amplitudes of the respective focused points.

[0065] In step S101, it is necessary to first determine a plurality of sub-apertures of the ultrasonic phased array probe, wherein the number of the plurality of sub-apertures is determined by the following formula:

[0066] L=(NM) / s+1

[0067] Where L is the number of subapertures, N is the number of array elements of the ultrasonic phased array probe, M is the number of array elements contained in each subaperture, and s is the number of array elements in each subaperture step.

[0068] After determining the multiple sub-apertures of the ultrasonic phased array probe, the coordinates of the virtual source point corresponding to each of the sub-apertures are determined. Figure 2 FIG. 1 is a schematic diagram showing the calculation of the position of the virtual source point of the diverging wave according to an embodiment of the present invention. The ultrasonic phased array probe 5 is placed on an inclined wedge 6 with an inclination angle of θ. The center of the array element No. 1 of the ultrasonic phased array probe is at a height h from the coupling interface.

[0069] A coordinate system is established, wherein the origin of the coordinate system is the intersection of a perpendicular line through the center of the ultrasonic phased array probe and the coupling interface; wherein the coupling interface is the interface between the angled wedge and the workpiece to be measured; the horizontal axis x of the coordinate system is parallel to the coupling interface, and the vertical axis z of the coordinate system is parallel to the normal to the coupling interface. That is, the intersection of the perpendicular line through the center of the ultrasonic phased array probe and the coupling interface is the origin O, the horizontal axis x is parallel to the coupling interface, and the vertical axis z is parallel to the normal to the coupling interface.

[0070] The number of array elements of the ultrasonic phased array probe 5 is N, the center distance between adjacent array elements is d, the number of array elements contained in each sub-aperture is M, and the number of array elements in each sub-aperture step is s. Then the center coordinate (x i ,z i ) can be expressed as:

[0071]

[0072] Then the center point C of the lth (l=1,2,..,L) sub-aperture l The coordinates (x l ,z l ) can be expressed as:

[0073]

[0074] If the distance from the virtual source point to the center of the corresponding sub-aperture is the focal depth F, then the virtual source point V corresponding to the lth sub-aperture is l The coordinates (x vl ,z vl ) can be expressed as:

[0075] x vl =-Fsinθ+x l

[0076] z vl=Fcosθ+z l (3)

[0077] The coordinates of the center points of all L sub-apertures can be obtained by the above formula (3).

[0078] In step S102, the acoustic propagation time of the signal received by each of the multiple array elements of the sub-aperture is obtained, such as Figure 3 As shown, the following steps are included:

[0079] S201, based on the coordinates of the virtual source point corresponding to each sub-aperture, for each focusing point, determining the coordinates of the incident points where the signals received by the multiple array elements of the sub-aperture pass through the coupling interface twice during the propagation process, which are the coordinates of the first incident point and the coordinates of the second incident point.

[0080] Because sound waves propagate along the path that takes the shortest time between the sound source and the focal point, the incident point can be determined by calculating the shortest path corresponding to the sound path, thereby obtaining the coordinates of the incident point. As a possible implementation method, determining the coordinates of the incident point where the signals received by multiple array elements of the subaperture pass through the coupling interface twice during propagation includes the following:

[0081] Based on the coordinates of a virtual source point corresponding to each sub-aperture, a plurality of first sound paths of the sound wave transmitted from the virtual source point to each grid point in a first row of the image reconstruction area is obtained; and a plurality of second sound paths of the sound wave transmitted from each grid point in the first row to each focal point is obtained;

[0082] Based on the multiple first sound paths and the multiple second sound paths, obtaining the shortest sound paths of the sound waves emitted from the virtual source point to each focusing point;

[0083] Determining the coordinates of the first incident point based on the shortest sound path emitted from the virtual source point to each focal point;

[0084] Acquire multiple third sound paths of the sound wave from each focus point to each grid point in the first row, and acquire multiple fourth sound paths of the sound wave from each grid point in the first row to each array element of the subaperture;

[0085] Based on the multiple third sound paths and the multiple fourth sound paths, obtaining the shortest sound paths of the sound waves reflected from each focal point to each array element of the sub-aperture;

[0086] The coordinates of the second incident point are determined based on the shortest sound paths reflected from the respective focus points to the respective array elements of the sub-aperture.

[0087] For example, Figure 4The figure shows the delay rule calculation diagram for image reconstruction in the present invention. During image reconstruction, the image reconstruction area is divided into an area with W×E grid points, with a total of U. W represents the number of rows and E represents the number of columns. l The following is an example of propagation along a path with the shortest required time between the focal point P and the focal point.

[0088] Incident point T l It can be determined by calculating the shortest path of this sound path. First, calculate the sound wave from the virtual source point V l The acoustic path Q of each grid point in the first row of the network to the coupling interface, that is, the image reconstruction area le , and then calculate the acoustic path Q of the sound wave from each grid point of the first row of grids in the image reconstruction area to the focal point P ep , the sound wave starts from the lth virtual source point V l The shortest sound path Q from the emission to the focal point P T It can be expressed as follows:

[0089]

[0090] Similarly, the incident point R i It can also be determined by calculating the shortest path of this sound path. First, calculate the sound path Q from the focus point P to each grid point in the first row of the image reconstruction area. ep , and then calculate the distance from each grid point in the first row of the image reconstruction area to the virtual source point V l The acoustic path Q of element i ie After the sound wave is reflected from the focal point P, the shortest sound path of the process received by the array element i is Q R It can be expressed as follows:

[0091]

[0092] In specific implementation, the acoustic path Q1{q 11 ,q 12 ,…,q 1e ;q 21 ,q 22 ,…,q 2e ;q l1 ,q l2 ,…,q le} and the acoustic path Q2{q 11 ,q 12 ,…,q 1u ;q 21 ,q 22 ,…,q 2u ;…,q e1 ,qe2 ,…,q eu}, and sum Q1 and Q2 to get a three-dimensional matrix Q3 of e×u×l, and take the minimum value of the first dimension of Q3 to get Q T {q 11 ,q 12 ,…,q 1u ;q 21 ,q 22 ,…,q 2Y ;q l1 ,q l2 ,…,q lu}, represents the shortest sound path from the lth virtual source point to any focal point in the image reconstruction area, thus, the corresponding incident points T can be determined l .

[0093] After the sound wave reaches the focal point, it is reflected and finally received by the array element i. In this process, the sound wave is incident at the coupling interface point R i When the sound wave reaches all the grid points of the first row of grids in the image reconstruction area from the focus point, the time Q3{q 11 ,q 12 ,…,q 1u ;q 21 ,q 22 ,…,q 2u ;…,q e1 ,q e2 ,…,q eu}, and then calculate the time Q4{q 11 ,q 12 ,…,q 1e ;q 21 ,q 22 ,…,q 2e ;q i1 ,q i2 ,…,q ie}, sum Q3 and Q4 to get a three-dimensional matrix Q5 of e×u×i, and take the minimum value of the first dimension of Q5 to get Q R {T 11 ,T 12 ,…,T 1Y ;T 21 ,T 22 ,…,T 2Y ;T l1 ,T l2 ,…,T lY}, represents the shortest time from the i-th array element to any focus point in the image reconstruction area, thus, the corresponding incident points R i .

[0094] S202: Based on the coordinates of the first incident point, obtain the transmission delay time for the sub-aperture to transmit the sound wave to the corresponding focusing point.

[0095] S203 : Based on the coordinates of the second incident point, obtain a receiving delay time from the echo of the corresponding focusing point to the reception of the signal for each of the multiple array elements of the sub-aperture.

[0096] S204 , summing the transmission delay time and the reception delay time to obtain the acoustic propagation time of the signals received by each of the plurality of array elements of the sub-aperture.

[0097] Next, continue with Figure 4 The sound wave shown is at the virtual source point V l The propagation between the array element and the focal point P is used as an example to illustrate. Calculate the transmission delay time t of the sound wave after it is emitted from the array element, passes through the coupling interface, and finally reaches the focal point P(x,z) Tl , and the sound wave from the focal point P to point R i The time required for the receiving element i to receive the signal is the receiving delay time t Ri .

[0098] According to the virtual source point V l The coordinates (x vl ,z vl ), the incident point T of the acoustic wave passing through the coupling interface l (x Tl ,0), the coordinates of the focal point P (x, z), the speed of sound in the wedge 6 c1, the speed of sound in the workpiece 7 c2, calculate the launch delay time t Tl Since the calculation is based on the virtual source point, but in fact, the sound wave is emitted by the array element in the ultrasonic phased array probe, the time the sound wave spends at the focal depth F needs to be subtracted when calculating t Tl The specific formula is as follows:

[0099]

[0100] Similarly, we can get the incident point R of the acoustic wave at the coupling interface during the process of the acoustic wave reaching the focal point P and being received by the array element i. i (x Ri ,0), and then we can get the sound wave from the focus point P to point R i The receiving delay time t required for the array element i to receive Ri :

[0101]

[0102] Therefore, the total acoustic propagation time from the emission of the sound beam to its transmission to the focal point P and the echo received by the array element i is for:

[0103]

[0104] By using the above method, the acoustic propagation time of the signal received by each of the multiple array elements of each sub-aperture can be obtained for each of the focusing points.

[0105] In step S103, optionally, the signals received by the ultrasonic phased array probe are stored in the form of a three-dimensional matrix, and the amplitudes of the obtained signals are delayed and superimposed to obtain the echo amplitude at the focus point, and finally a focused image is obtained.

[0106] Next, continue with Figure 4 The sound wave shown is at the virtual source point V l Taking the propagation between the focal point P as an example, the echo amplitude I at the focal point P can be obtained by the following formula:

[0107]

[0108] in, is the amplitude of the signal received by array element i.

[0109] The ultrasonic oblique-incidence sub-aperture coherent composite diverging wave imaging method of the embodiment of the present application calculates the incident point of the sound beam at the coupling interface of the oblique wedge and the workpiece to be measured by using the known sound source position and the position of the focal point, calculates the sound propagation time of the sound wave in different media, and then calculates the corresponding total sound propagation time, and delays and superimposes the amplitude of the received signal based on the total sound propagation time, thereby realizing an ultrasonic oblique-incidence sub-aperture coherent composite diverging wave imaging method, so that the composite diverging wave imaging can also have a good defect detection effect when facing the case of oblique-incidence double-layer media.

[0110] Based on the above method, a specific implementation example is given below to further describe the process of the ultrasonic oblique-incidence sub-aperture coherent composite transmission wave imaging method according to an embodiment of the present invention in detail.

[0111] like Figure 5 As shown, the experimental testing device includes a host 1, a display 2, an ultrasonic sampling system 3, a panel 4 on the ultrasonic sampling system, an ultrasonic phased array probe 5, an angled wedge 6, and a workpiece to be tested 7. The darker portion of the ultrasonic phased array probe 5 represents the subaperture array (i.e., subaperture) of a particular transmitted divergent wave. The ultrasonic sampling system 3 is connected to the host 1 and display 2 via cables, and the ultrasonic phased array probe 5 is connected to two ultrasonic transmission / reception 32-channel ports on the panel 4.

[0112] The workpiece 7 to be tested in this example is a steel rectangular test block with three side drilled holes.

[0113] like Figure 6 As shown, the workpiece 7 to be tested is a steel rectangular test block with three side drilled holes. The length, width and height of the test block are 60 mm, 30 mm and 30 mm respectively. Three horizontal holes with a diameter of 2 mm and a buried depth of 12 mm are processed in the test block, and the horizontal spacing between the centers of the horizontal holes is 10 mm.

[0114] In this example, the ultrasonic phased array probe 5 has a center frequency of 5 MHz, 64 array elements N, a center-to-center spacing d of 0.05 mm, and an element width of 0.55 mm. The ultrasonic phased array probe 5 is placed above an angled wedge 6 to perform defect detection on a test block. The angle θ of the angled wedge 6 is 20 degrees, and the height h from the center of element 1 of the ultrasonic phased array probe 5 to the coupling interface is 10 mm. The implementation steps are as follows:

[0115] 1) First, set the detection parameters in the system control program of display 2: the subaperture of each divergent wave is 8 array elements (i.e., the number of array elements M in each subaperture is 8), the array element is stepped by 1 element each time (i.e., the number of array elements s in each subaperture step is 1), and a total of 57 divergent waves are emitted (i.e., the number of subapertures L is 57) for signal acquisition, the number of receiving array elements is 64, the sampling frequency is 100 MHz, and the focal depth F of the virtual source point is 19 mm; in this example, the ultrasonic wave is made of wood. The sound velocity c1 in the grease-filled oblique wedge 6 is 2337 m / s, and the sound velocity c2 in the steel test block is 5900 m / s. The image reconstruction area is 40 mm × 35 mm (i.e., W × E). The ultrasonic phased array probe 5 and the oblique wedge 6 are positioned to start collecting signal data. The collected raw data is named RF_data in MATLAB and displayed as a three-dimensional matrix of divergent waves: number of sampling points × number of receiving array elements × number of divergent waves. The number of divergent waves here is the number of subapertures.

[0116] 2) The collected raw data RF_data is processed and the imaging algorithm is implemented based on MATLAB software. Specifically, the parameters set in the display 2 are substituted into formula (1) to calculate the coordinates (x i ,z i ), and place the calculated horizontal and vertical coordinates in the matrices x_array and z_array respectively.

[0117] 3) Substitute the parameters set in display 2 into formula (2) to calculate the center point C of the subaperture at each emission. l The horizontal and vertical coordinates are placed in x_centre and z_centre respectively.

[0118] 4) According to the virtual source point V lThe vertical distance F to the sub-aperture array and the coordinates of the center of the sub-aperture array are calculated by formula (3) to obtain the virtual source point V l The specific coordinates (x vl ,z vl ), and place the horizontal and vertical coordinates of the centers of the 57 obtained sub-apertures in the one-dimensional matrices Vx and Vz respectively.

[0119] 5) Through the for loop, the transmission delay time and the receiving delay time are calculated according to the formula (5) and formula (6) after substituting the parameters, and the calculation results are placed in the three-dimensional matrices transmit_delay and receive_delay respectively. Among them, the first two dimensions of the three-dimensional matrices transmit_delay and receive_delay are the number of grid points in the image reconstruction area, and the third dimension is the number of virtual sources and the number of receiving array elements respectively.

[0120] 6) The total sound propagation time matrix Delay is obtained by adding the three-dimensional matrices transmit_delay and receive_delay. The collected signals are delayed and superimposed through two for loops. The first for loop obtains the delayed superposition data of the divergent waves emitted by a single virtual source point, and the second for loop superimposes the data obtained in the first for loop. The final result is the data of the divergent waves emitted by all virtual source points after delayed superposition and placed in shifted_data, finally obtaining the focused image, as shown in Figure 7 shown.

[0121] It should also be noted that the exemplary embodiments described herein describe methods or systems based on a series of steps or devices. However, the present invention is not limited to the order of the steps described above. In other words, the steps may be performed in the order described in the embodiments, or in a different order, or several steps may be performed simultaneously.

[0122] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only.

[0123] It should be understood that the present application is not limited to the exact structures described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. A method for ultrasonic oblique-incidence subaperture coherent composite diverging wave imaging, characterized in that: include: Determining a plurality of subapertures of the ultrasonic phased array probe, and determining the coordinates of a virtual source point corresponding to each of the subapertures based on the inclination angle of the angled wedge; The virtual source point is located above the ultrasonic phased array probe; Constructing an image reconstruction area for the workpiece to be measured, and dividing the image reconstruction area into a plurality of grid points, each of the grid points corresponding to a focus point; Based on the coordinates of the virtual source point corresponding to each sub-aperture, for each focusing point, obtaining the acoustic propagation time of the signal received by each of the plurality of array elements of the sub-aperture; Based on the acoustic propagation time of the signals received by the multiple array elements of each sub-aperture, delaying and superimposing the amplitudes of the signals received by the corresponding array elements to obtain the echo amplitudes of the respective focus points; A focused image is obtained based on the echo amplitude of each focused point; wherein the determining of the multiple sub-apertures of the ultrasonic phased array probe includes: The multiple sub-apertures of the ultrasonic phased array probe are determined by a first formula, wherein the first formula is expressed as follows: L=(NM) / s+1 Where L is the number of subapertures, N is the number of array elements of the ultrasonic phased array probe, M is the number of array elements contained in each subaperture; s is the number of array elements per subaperture step; The determining the coordinates of the virtual source point corresponding to each sub-aperture based on the inclination angle of the oblique wedge includes: Establish a coordinate system, wherein the origin of the coordinate system is the intersection of a perpendicular line to the center of the ultrasonic phased array probe and a coupling interface; wherein the coupling interface is the interface between the angled wedge and the workpiece to be measured; the horizontal axis x of the coordinate system is parallel to the coupling interface, and the vertical axis z of the coordinate system is parallel to the normal to the coupling interface; The coordinates of the virtual source point corresponding to each sub-aperture are determined by a second formula, wherein the second formula is expressed as follows: x vl =-Fsinθ+x l With vl =Fcosθ+z l Where F is the focal depth, that is, the distance from the virtual source point to the center of the corresponding subaperture; x vl is the virtual source point V corresponding to the lth sub-aperture l The horizontal axis; z vl is the virtual source point V corresponding to the lth sub-aperture l The vertical coordinate of the wedge; θ is the inclination angle of the wedge; (x l ,z l ) is the center point C of the lth (l=1,2,..,L) sub-aperture l coordinates of Among them, (x l ,z l ) is represented as follows: Where d is the center-to-center distance between adjacent array elements, and h is the height from the center of array element No. 1 of the ultrasonic phased array probe to the coupling interface.

2. The method according to claim 1, characterized in that The acquiring, based on the coordinates of the virtual source point corresponding to each sub-aperture and for each focusing point, the acoustic propagation time of the signal received by each of the plurality of array elements of the sub-aperture, comprises: Based on the coordinates of the virtual source point corresponding to each sub-aperture, for each focusing point, determining the coordinates of the incident points where the signals received by the plurality of array elements of the sub-aperture pass through the coupling interface twice during the propagation process, which are the coordinates of the first incident point and the second incident point respectively; Based on the coordinates of the first incident point, obtaining a transmission delay time for the sub-aperture to transmit the sound wave to the corresponding focusing point; Based on the coordinates of the second incident point, obtaining a reception delay time from the echo of the corresponding focusing point to the reception of the signal for each of the multiple array elements of the sub-aperture; The transmit delay time and the receive delay time are summed to obtain the acoustic propagation time of the signals received by each of the multiple array elements of the sub-aperture.

3. The method according to claim 2, characterized in that The determining, based on the coordinates of the virtual source point corresponding to each sub-aperture and for each focusing point, the coordinates of the incident points at which signals received by the plurality of array elements of the sub-aperture pass through the coupling interface twice during propagation, includes: Based on the coordinates of a virtual source point corresponding to each sub-aperture, a plurality of first sound paths of the sound wave transmitted from the virtual source point to each grid point in a first row of the image reconstruction area is obtained; and a plurality of second sound paths of the sound wave transmitted from each grid point in the first row to each focal point is obtained; Based on the multiple first sound paths and the multiple second sound paths, obtaining the shortest sound paths of the sound waves emitted from the virtual source point to each focusing point; Determining the coordinates of the first incident point based on the shortest sound path emitted from the virtual source point to each focal point; Acquire multiple third sound paths of the sound wave from each focus point to each grid point in the first row, and acquire multiple fourth sound paths of the sound wave from each grid point in the first row to each array element of the subaperture; Based on the multiple third sound paths and the multiple fourth sound paths, obtaining the shortest sound paths of the sound waves reflected from each focal point to each array element of the sub-aperture; The coordinates of the second incident point are determined based on the shortest sound paths reflected from the respective focus points to the respective array elements of the sub-aperture.

4. The method according to claim 2, characterized in that The acquiring, based on the coordinates of the first incident point, a transmission delay time for the sub-aperture to transmit the sound wave to the corresponding focusing point includes: The third formula is used to determine the transmission delay time t of the sub-aperture transmitting the sound wave and transmitting it to the corresponding focal point. Tl , wherein the third formula is expressed as follows: Where x is the horizontal coordinate of the focus point, z is the vertical coordinate of the focus point, c1 is the speed of the sound wave in the inclined wedge, and c2 is the speed of the sound wave in the workpiece to be measured. is the coordinate of the first incident point.

5. The method according to claim 4, characterized in that The acquiring, based on the coordinates of the second incident point, a reception delay time from the corresponding focus point echo to the reception of a signal by each of the plurality of array elements of the sub-aperture, comprises: The fourth formula is used to determine the receiving delay time of each of the multiple array elements of the sub-aperture from the corresponding focus point echo to the received signal The fourth formula is expressed as follows: in, is the coordinate of the second incident point.

6. The method according to claim 2, characterized in that The horizontal coordinates and vertical coordinates of the virtual source points corresponding to the multiple sub-apertures are respectively stored in a one-dimensional matrix; the transmission delay time is stored in a first three-dimensional matrix, wherein the first two dimensions of the first three-dimensional matrix are the number of grid points in the image reconstruction area, and the third dimension is the number of virtual source points; the receiving delay time is stored in a second three-dimensional matrix, wherein the first two dimensions of the second three-dimensional matrix are the number of grid points in the image reconstruction area, and the third dimension is the number of receiving array elements.

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