Method for detecting defects of double-layer plate through delayed focusing ultrasonic phased array

Abstract

The invention relates to a method for detecting defects of a double-layer plate by a delayed focusing ultrasonic phased array, which comprises the following steps of: transmitting ultrasonic waves to the double-layer plate with defects through ultrasonic phased array detection equipment to obtain original echo data; calculating a first propagation time matrix of an upper-layer plate grid through a traditional delay superposition method; through a Newton iteration method, first refraction point coordinates of the ultrasonic waves entering the lower-layer plate from the upper-layer plate and second refraction point coordinates of the ultrasonic waves entering the upper-layer plate from the lower-layer plate after the ultrasonic waves are reflected by the defects of the lower-layer plate are solved; calculating a second propagation time matrix of the lower-layer plate grid based on the first refraction point coordinate and the second refraction point coordinate; and based on the first propagation time matrix, the second propagation time matrix and the processed echo data, imaging the plate defect. The refraction point of ultrasonic waves passing through the middle joint face is calculated according to the Newton iteration method, the delay superposition link precision is improved, and the imaging quality of the lower layer area of the double-layer plate is effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of plate defect detection, and particularly relates to a method for detecting defects in double-layer plates by ultrasonic phased array with delayed focusing. Background Art

[0002] Ultrasonic phased array technology is an imaging technology used in medicine, aerospace and other fields, which uses the propagation characteristics of ultrasonic waves inside the object to be measured for imaging.

[0003] In the prior art, the ultrasonic phased array full focusing algorithm can effectively detect defects existing in a single-layer medium. However, for double-layer plates, such as polystyrene-aluminum alloy workpieces, since ultrasonic waves will refract when entering the lower layer medium from the upper layer medium, it will cause problems such as low detection accuracy and image deviation when using traditional focusing methods to detect defects in the lower layer area of double-layer plates.

[0004] In view of the above problems, it is very necessary to research and design a method for detecting defects in the lower layer area of double-layer plates by phased array to overcome the problems existing in the detection of internal defects in the lower layer area of double-layer plates by the existing ultrasonic phased array full focusing algorithm. The present invention proposes a method for detecting defects in double-layer plates by ultrasonic phased array with delayed focusing, which is an improvement on the basis of the traditional ultrasonic phased array full focusing detection of single-layer plates. Aiming at the problems of image deviation and low accuracy in the detection of the lower layer area of double-layer plates by the traditional full focusing imaging algorithm, the present invention combines the ray acoustics theory to propose a delayed focusing strategy for double-layer media. This strategy uses the Newton iteration method to calculate the refraction point of ultrasonic waves passing through the middle joint surface, and then calculates the delay time according to the coordinates of the refraction point, improving the accuracy of the later delay superposition link and effectively improving the imaging quality of the lower layer area of double-layer plates; aiming at the problem that the echo of the middle joint surface in the traditional phased array detection of double-layer plates affects the later imaging, the present invention proposes a "region zeroing" processing method. This method calculates the positioning matrix according to the thickness, sound velocity of the upper layer medium and the transducer element spacing, obtains the position of the middle joint surface echo of each group of echoes, and then clears the data in a specific area range of this position to avoid the influence of this part of the data on the later imaging, and can effectively reduce the problems of the middle blind area and artifacts caused by the participation of the middle joint surface echo data in the later operation. Summary of the Invention

[0005] In order to overcome the problem that the existing ultrasonic phased array using the full focusing algorithm cannot effectively detect defects in the lower layer area of double-layer plates, a method for detecting defects in double-layer plates by ultrasonic phased array with delayed focusing is provided.

[0006] The technical means adopted by the present invention are as follows:

[0007] A method for detecting defects in double-layer plates by ultrasonic phased array with delayed focusing includes the following steps:

[0008] S1. Transmit ultrasonic waves to the defective double-layer plate through an ultrasonic phased array detection device to obtain original echo data;

[0009] S2. Preprocess the original echo data to obtain processed echo data;

[0010] S3. Establish a rectangular coordinate system for the plate in the detection area, and divide the plate within the detection range into a number of upper-layer plate grids and a number of lower-layer plate grids;

[0011] S4. Calculate the first propagation time matrix of the upper-layer plate grid through the traditional delay superposition method;

[0012] S5. Solve the coordinates of the first refraction point where the ultrasonic wave enters the lower-layer plate from the upper-layer plate and the coordinates of the second refraction point where the ultrasonic wave is reflected by the defect of the lower-layer plate and enters the upper-layer plate from the lower-layer plate through the Newton iteration method;

[0013] S6. Calculate the second propagation time matrix of the lower-layer plate grid based on the coordinates of the first refraction point and the second refraction point obtained in S5;

[0014] S7. Based on the first propagation time matrix, the second propagation time matrix, and the processed echo data, find the echo amplitudes corresponding to the upper-layer plate grid and the lower-layer plate grid, and image the plate defect according to the echo amplitudes.

[0015] Further, the specific steps of S2 include:

[0016] First, calculate the positioning matrix, which is used to represent the positions where the echo data needs to be zeroed in the region. The calculation formula of the positioning matrix is as follows:

[0017]

[0018] L i，j = T i，i + T′ i，j

[0019] where L is the positioning matrix, and L i，j represents the element in the i-th row and j-th column of the positioning matrix. T i，i is the time it takes for the ultrasonic wave to reach the plate joint surface from the transmitting acoustic element i. T′ i，j is the time it takes for the ultrasonic wave to be reflected from the plate joint surface to the receiving acoustic element j. N represents the number of elements in the ultrasonic phased array detection device.

[0020] T i，i is calculated using the following formula:

[0021]

[0022] where Ti，i is the time it takes for ultrasonic waves to reach the plate joint surface from the acoustic wave transmitting element i, Y 1 is the thickness of the upper layer of the plate, c 1 is the sound velocity of the upper layer of the plate, i = 0, 1, 2…N,

[0023] T′ i，j is calculated using the following formula:

[0024]

[0025] n = |i - j|

[0026] where T′ i，j is the time it takes for the ultrasonic waves emitted by element i to reach the plate joint surface and then be reflected from the plate joint surface and received by element j. a is the distance between adjacent elements, Y 1 is the thickness of the upper layer of the plate, c 1 is the sound velocity of the upper layer of the plate, n = 0, 1, 2…N - 1, i = 0, 1, 2…N, j = 0, 1, 2…N,

[0027] Secondly, according to the pulse width and proportionality coefficient of the echo signal received by the ultrasonic phased array detection device, the regional zeroing range is obtained. The calculation formula for the size of the regional zeroing range is as follows:

[0028] R = W * γ

[0029] where W is the pulse width of the echo signal, γ is the proportionality coefficient, and R is the regional zeroing range,

[0030] Finally, according to the regional zeroing range and the positioning matrix, the original echo data is zeroed to obtain the processed echo data.

[0031] Furthermore, the specific steps of S4 include:

[0032] Construct a line segment connecting the upper layer of the plate grid and the element. Based on the line segment connecting the upper layer of the plate grid and the element, the acoustic path matrix is calculated using the Pythagorean theorem. The calculation formula for the acoustic path matrix is as follows:

[0033]

[0034] where F n is the acoustic path matrix, x n is the abscissa of the element, x t is the abscissa of the upper layer of the plate grid, y t is the ordinate of the upper layer of the plate grid, and N represents the number of elements in the ultrasonic phased array detection device,

[0035] According to the acoustic path matrix and the longitudinal wave sound velocity in the upper layer of the plate, the first propagation time matrix is obtained. The formula for the first propagation time matrix is as follows:

[0036]

[0037] Among them, c 1 is the longitudinal wave sound velocity in the upper layer of the plate, T 1 is the first propagation time matrix, F i is the sound path matrix from the acoustic wave transmitting element to the grid of the upper layer of the plate, F j is the sound path matrix from the grid of the upper layer of the plate to the acoustic wave receiving element, and N represents the number of elements in the ultrasonic phased array detection device.

[0038] Furthermore, step S5 specifically includes:

[0039] Calculate the propagation time of the acoustic wave emitted by the transmitting element to reach the grid of the lower layer of the plate. The calculation formula is as follows:

[0040]

[0041] Among them, f(x m ) is the propagation time of the acoustic wave emitted by the transmitting element to reach the grid of the lower layer of the plate, c 1 is the sound velocity of the upper layer of the plate, c 2 is the sound velocity of the lower layer of the plate, x m is the abscissa of the first refraction point of the acoustic wave at the joint surface, x i is the abscissa of the acoustic wave transmitting element, x p is the abscissa of the grid of the lower layer of the plate, y p is the ordinate of the grid of the lower layer of the plate, Y 1 is the thickness of the upper layer of the plate, and N represents the number of elements in the ultrasonic phased array detection device.

[0042] Take the derivative of the formula for the propagation time of the acoustic wave emitted by the transmitting element to reach the grid of the lower layer of the plate, and set the derivative to 0. Use the Newton iteration method to solve the derivative of the propagation time of the acoustic wave emitted by the transmitting element to reach the grid of the lower layer of the plate, and obtain the coordinates of the first refraction point;

[0043] Calculate the propagation time of the acoustic wave reflected by the grid of the lower layer of the plate to reach the receiving element. The calculation formula is as follows:

[0044]

[0045] Among them, g(x n ) is the propagation time of the acoustic wave emitted by the transmitting element to reach the grid of the lower layer of the plate, c 1 is the sound velocity of the upper layer of the plate, c 2 is the sound velocity of the lower layer of the plate, x n is the abscissa of the second refraction point of the acoustic wave at the joint surface, x j is the abscissa of the acoustic wave receiving element, xp is the abscissa of the lower-layer plate grid, y p is the ordinate of the lower-layer plate grid, Y 1 is the thickness of the upper-layer plate, and N represents the number of array elements in the ultrasonic phased array detection device.

[0046] Derive the formula for the propagation time of the sound wave reflected by the lower-layer plate grid reaching the receiving array element, and set the derivative to 0. Use the Newton iteration method to solve the derivative of the propagation time of the sound wave reflected by the lower-layer plate grid reaching the receiving array element to obtain the coordinates of the second refraction point.

[0047] Furthermore, step S6 specifically includes:

[0048] Calculate the upper-layer path sound path and the lower-layer path sound path according to the coordinates of the first refraction point and the coordinates of the second refraction point. The calculation formulas are as follows:

[0049] The upper-layer path sound path is:

[0050]

[0051] Among them, F 1 is the upper-layer path sound path, x j is the abscissa of the receiving sound wave array element, x i is the abscissa of the transmitting sound wave array element, x m is the abscissa of the first refraction point, x n is the abscissa of the second refraction point, y 1 is the ordinate of the first refraction point,

[0052] The lower-layer path sound path is:

[0053]

[0054] Among them, F 2 is the lower-layer path sound path, x m is the abscissa of the first refraction point, x n is the abscissa of the second refraction point, y p is the ordinate of the lower-layer plate grid,

[0055] Calculate the second propagation time matrix according to the upper-layer path sound path and the lower-layer path sound path. The calculation formula of the second propagation time matrix is:

[0056]

[0057] Among them, F 1 is the upper-layer path sound path, F 2 is the lower-layer path sound path, c1 is the sound speed of the upper-layer plate, c 2 is the sound speed of the lower-layer plate, x m is the abscissa of the first refraction point, x nis the abscissa of the second refraction point, x j is the abscissa of the acoustic receiving array element, x i is the abscissa of the acoustic transmitting array element, y 1 is the ordinate of the first refraction point, y p is the ordinate of the lower layer plate grid.

[0058] Further, step S7 specifically includes:

[0059] Splice the first propagation time matrix and the second propagation time matrix to obtain a complete propagation time matrix. The calculation formula of the complete propagation time matrix is as follows:

[0060]

[0061] where T is the complete propagation time matrix, T 1 is the first propagation time matrix, T 2 is the second propagation time matrix,

[0062] According to the complete propagation time matrix, obtain the complete echo amplitude matrix of the plates in the detection area. Extract the envelope from the complete echo amplitude matrix to obtain envelope data. Normalize the envelope data. According to the normalized envelope data, use a heat map to perform full-focus imaging on the defects of the lower layer plates.

[0063] Further, obtaining the complete echo amplitude matrix of the plates in the detection area according to the complete propagation time matrix includes:

[0064] According to the complete propagation time matrix, find the echo amplitude corresponding to each plate grid in the detection area in the processed echo data. After superimposing all the echo amplitudes, obtain the complete echo amplitude matrix of the plates in the detection area. The calculation formula of the complete echo amplitude matrix is as follows:

[0065]

[0066] where I (x，y) is the complete echo amplitude matrix, x is the abscissa of the plate grid, y is the ordinate of the plate grid, N represents the number of array elements in the ultrasonic phased array detection device, i is the serial number of the acoustic transmitting array element, i = 0, 1, 2...N, j is the serial number of the acoustic receiving array element, j = 0, 1, 2...N, E i，j is the processed echo data, is the index of the echo data E i，j where f s is the system sampling frequency, is the complete propagation time matrix for the i-th array element to transmit acoustic waves and the j-th array element to receive acoustic waves corresponding to the plate grid.

[0067] Compared with the prior art, the present invention has the following advantages:

[0068] 1. Considering that when the ultrasonic phased array system detects double-layer plates, the sound wave will deflect when entering the lower medium from the upper medium, the present invention combines the ray acoustics theory to propose a delay focusing rule for double-layer media, improves the detection accuracy of the lower layer area, and avoids the problem of image offset.

[0069] 2. In the present invention, the Newton iteration method is used to improve the process of solving the refraction point, greatly reducing the amount of computation required for imaging and improving the imaging efficiency of the system.

[0070] 3. Aiming at the problem that the echo of the middle joint surface affects the full-focus imaging, the present invention proposes a "region zeroing" strategy. By calculating the positioning matrix, the echo of the middle joint surface in each group of echo data is cleared, avoiding the influence of this part of data on the later imaging, enabling the improved system to effectively detect defects near the middle joint surface, and reducing the problem of artifacts in the imaging results.

[0071] For the above reasons, the present invention can be widely promoted in the fields such as plate defect detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0073] Figure 1 It is the main flow chart of the present invention.

[0074] Figure 2 It is the schematic diagram of the calculation method of Z in the positioning matrix of the present invention n of the present invention.

[0075] Figure 3 It is the schematic diagram of the region zeroing algorithm of the present invention.

[0076] Figure 4 It is the schematic diagram of the propagation path of ultrasonic waves passing through the grid points in the upper and lower layers of media in the embodiment of the present invention.

[0077] Figure 5 It is the schematic diagram of solving the refraction point of ultrasonic waves in the embodiment of the present invention.

[0078] Figure 6 It is the imaging result of the improved phased array system in the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0079] To enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0080] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily need to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0081] As Figure 1 shown, the present invention provides a method for detecting defects in double-layer plates by delayed focusing of an ultrasonic phased array, which includes the following steps:

[0082] S1. Transmit ultrasonic waves to the defective double-layer plate through an ultrasonic phased array detection device to obtain the original echo data received by each element.

[0083] In S1, the ultrasonic detection device used in the experiment includes: a 16-element ultrasonic probe with an element center distance of 1 mm and a nominal center frequency of 2.5 MHz, a phased array control platform, a computer with a phased array detection host computer program running environment, a defect-free double-layer plate test block, and a double-layer plate test block with defects in the lower layer area.

[0084] Transmit ultrasonic waves to the double-layer plate through the ultrasonic detection device, and the original echo data reflected from the upper layer plate and the lower layer plate by the probe.

[0085] S2. Preprocess the original echo data to obtain the processed echo data.

[0086] Specifically, first, calculate the positioning matrix. The ultrasonic phased array detection device used in this embodiment has a 16-element ultrasonic probe, and the calculation formula of its positioning matrix is as follows:

[0087]

[0088] Li，j = T i，i + T' i，j

[0089] Wherein, L is the positioning matrix, and L i，j represents the element at the i-th row and j-th column of the positioning matrix, and is used to represent the position where the echo data needs to be zeroed in the region. T i，i is the time it takes for the ultrasonic wave to reach the plate joint surface from the transmitting acoustic element i, and T' i，j is the time it takes for the ultrasonic wave to be reflected from the plate joint surface to the receiving acoustic element j.

[0090] As Figure 2 shown, T i，i is calculated using the following formula:

[0091]

[0092] Wherein, T i，i is the time it takes for the ultrasonic wave to reach the plate joint surface from the transmitting acoustic element i, Y 1 is the thickness of the upper layer plate, c 1 is the sound velocity of the upper layer plate, and i = 0, 1, 2... 16.

[0093] T' i，j is calculated using the following formula:

[0094]

[0095] n = |i - j|

[0096] Wherein, T' i，j is the time it takes for the ultrasonic wave emitted by the element i to reach the plate joint surface and then be reflected from the plate joint surface to be received by the element j, and Z n is as Figure 2 shown, which is the time it takes for the ultrasonic wave to reach the plate joint surface from the transmitting acoustic element i and then be reflected from the plate joint surface to the receiving acoustic element. a is the adjacent element spacing, Y 1 is the thickness of the upper layer plate, c 1 is the sound velocity of the upper layer plate, n = 0, 1, 2... 15, i = 0, 1, 2... 16, j = 0, 1, 2... 16.

[0097] In specific implementation, there is no limit to the number of elements in the ultrasonic phased array detection device. Using an ultrasonic phased array detection device with 16 elements is only a preferred solution of the present invention.

[0098] Secondly, according to the pulse width and proportional coefficient of the echo signal received by the ultrasonic phased array detection device, the region zeroing range is obtained. The calculation formula for the size of the region zeroing range is as follows:

[0099] R = W * γ

[0100] Among them, W is the pulse width of the echo signal, γ is the proportionality coefficient, and R is the regional zeroing range.

[0101] The positioning matrix and range size used for regional zeroing act as Figure 3 (a) shown. The reason for the need for the proportionality coefficient γ is that the amplitudes on both sides of the echo of the joint surface are relatively low, and the amplitude is higher closer to the middle. Therefore, when performing regional zeroing, only the data of the region with a larger amplitude of the middle joint surface echo needs to be zeroed, and the data on both sides can be ignored. So, the proportionality coefficient γ is required to limit the range, which can avoid affecting the defect echo data during regional zeroing. Through experimental tests, when γ is in the range of 80% - 85%, the imaging effect is relatively good.

[0102] Finally, according to the regional zeroing range and the positioning matrix, the original echo data is zeroed to obtain the processed echo data as shown in Figure 3 (b).

[0103] S3. Establish a rectangular coordinate system for the plates in the detection area, and divide the plates within the detection range into several upper - layer plate grids and several lower - layer plate grids.

[0104] Specifically, according to information such as the number of array elements and the array element spacing, determine the detection range and imaging resolution, establish a rectangular coordinate system for the detection area, and divide the actual detection range into X*(Y1 + Y2) grids.

[0105] S4. Use the traditional delay - and - sum method to calculate the first propagation time matrix of the upper - layer plate grids.

[0106] Specifically, the acoustic wave propagation process in the upper - layer plate is as shown in Figure 4 (a). From the i - th array element to the focus P(x, y) and then to the receiving array element j after reflection, the propagation time matrix can be obtained according to the detection of the traditional single - layer medium. Connect the grid P(x p , y p ) and N array elements into N line segments, and use the Pythagorean theorem to calculate the acoustic path matrix of size 1*N, which respectively corresponds to the acoustic path from the n - th array element to the grid P. The formula for the acoustic path matrix is as follows:

[0107]

[0108] Among them, F n is the acoustic path matrix, x n is the abscissa of the array element, x t is the abscissa of the upper - layer plate grid, and y t is the ordinate of the upper - layer plate grid.

[0109] According to the acoustic path matrix and the longitudinal wave sound speed in the upper - layer plate, the first propagation time matrix is obtained. The formula for the first propagation time matrix is as follows:

[0110]

[0111] Wherein, c 1 is the longitudinal wave sound velocity in the upper layer of the plate, T 1 is the first propagation time matrix, F i is the sound path matrix from the acoustic wave transmitting element to the grid of the upper layer of the plate, and F j is the sound path matrix from the grid of the upper layer of the plate to the acoustic wave receiving element.

[0112] The longitudinal wave sound velocity of the plate can be obtained through experimental measurement or directly inferred from the material of the material. For example, the sound velocity of aluminum alloy is generally 6349 m / s.

[0113] S5. Use the Newton iteration method to solve the coordinates of the first refraction point where the ultrasonic wave enters the lower layer of the plate from the upper layer of the plate and the coordinates of the second refraction point where the ultrasonic wave is reflected by the defect of the lower layer of the plate and enters the upper layer of the plate from the lower layer of the plate.

[0114] Specifically, this step uses the Newton iteration method to calculate the refraction point k 1 (x m , y 1 ) of the ultrasonic wave passing through the joint surface of the double-layer plate, and k 2 (x n , y 1 ).

[0115] Let f(x m ) be the propagation time of the acoustic wave emitted by the element i(x i , 0) to reach the grid P(x p , y p ). Calculate the propagation time of the acoustic wave emitted by the acoustic wave transmitting element to reach the grid of the lower layer of the plate. The calculation formula is as follows:

[0116]

[0117] Wherein, f(x m ) is the propagation time of the acoustic wave emitted by the transmitting element to reach the grid of the lower layer of the plate, c 1 is the sound velocity of the upper layer of the plate, c 2 is the sound velocity of the lower layer of the plate, x m is the abscissa of the first refraction point of the acoustic wave at the joint surface, x i is the abscissa of the acoustic wave transmitting element, x p is the abscissa of the grid of the lower layer of the plate, y p is the ordinate of the grid of the lower layer of the plate, Y 1 is the thickness of the upper layer of the plate, and N represents the number of elements in the ultrasonic phased array detection device.

[0118] According to Fermat's theorem, ultrasonic waves always propagate along the path with the shortest time, and the path with the shortest time among the refraction paths connecting two points is unique. To find the minimum value of f(x), the derivative of the propagation time of the sound wave emitted by the transmitting acoustic element reaching the grid of the lower plate is calculated and set to 0. The calculation formula is as follows:

[0119]

[0120] Among them, f′(x) is the derivative of the propagation time of the sound wave emitted by the transmitting acoustic element reaching the grid, c 1 is the sound speed of the upper plate, c 2 is the sound speed of the lower plate, x is the abscissa of the refraction point of the sound wave at the joint surface, x i is the abscissa of the transmitting acoustic element, x p is the abscissa of the grid of the lower plate, y p is the ordinate of the grid of the lower plate, Y 1 is the thickness of the upper plate.

[0121] Let x k be the abscissa of the minimum point (i.e., the refraction point) of f(x). According to the ray tracing theory analysis, when x is on both sides of the refraction point, f(x) gradually increases. Therefore, it can be inferred that f(x) is a concave function, and f′(x) is a monotonic function passing through the refraction point. For the solution of the equation f′(x) = 0, the Newton iteration method can be used. The iteration formula is as follows:

[0122]

[0123] In the formula, x n represents the nth solution of the formula f′(x) = 0, x n+1 represents the intersection of the tangent line of the function f′(x) at the point (x n , f′(x n )) and the x-axis. The solution x n+1 is continuously iterated. When x n+1 - x n is less than a certain value, it can be considered that x n+1 ≈ x k .

[0124] In the above iteration formula, an initial value x 0 is required. To further reduce the computational load of the imaging system, a reasonable initial value needs to be selected to reduce the number of iterations. When the sound speed c 1 of medium 1 is less than the sound speed c 2 of medium 2, the propagation path is as shown in Figure 5 (a). At this time, the intersection x a of the direct connection line between the element i and the grid P and the medium interface, and the projection of the element i gives xb , according to geometric knowledge, the refraction point x k must be between x a and x b . Therefore, the initial point x 0 can be set as x a . Moving x to the right will surely obtain the refraction point within fewer iteration times. Similarly, when the sound speed c 1 of medium 1 is greater than the sound speed c 2 of medium 2, moving x along the left direction in Figure 5 (b) can also obtain the refraction point.

[0125] Similarly, let g(x n ) be the propagation time for the sound wave emitted by the transmitting element to reach the grid of the lower-layer plate. Its calculation formula is as follows:

[0126]

[0127] where g(x n ) is the propagation time for the sound wave emitted by the transmitting element to reach the grid of the lower-layer plate, c 1 is the sound speed of the upper-layer plate, c 2 is the sound speed of the lower-layer plate, x n is the abscissa of the second refraction point of the sound wave at the joint surface, x j is the abscissa of the receiving sound wave element, x p is the abscissa of the grid of the lower-layer plate, y p is the ordinate of the grid of the lower-layer plate, Y 1 is the thickness of the upper-layer plate, and N represents the number of elements in the ultrasonic phased array detection device.

[0128] Derive the formula for the propagation time of the sound wave reflected by the grid of the lower-layer plate to reach the receiving element, and set the derivative to 0. Use the Newton iteration method to solve the derivative of the propagation time of the sound wave reflected by the grid of the lower-layer plate to reach the receiving element, and obtain the coordinates of the second refraction point.

[0129] S6. Calculate the second propagation time matrix of the grid of the lower-layer plate based on the coordinates of the first refraction point and the coordinates of the second refraction point obtained in S5.

[0130] The sound path propagation process of the lower-layer plate is as shown in Figure 4 (b). Calculating the focal time matrix of the lower-layer area is relatively complex. The sound wave needs to pass through the joint surface when transferring from the upper-layer area to the lower-layer area. Since the sound speeds on both sides of the joint surface are different, the sound wave will refract when passing through this interface. The ultrasonic wave will pass through four paths from emission, being reflected by the lower-layer defect, and then to reception, that is, Figure 4 (b) the path a→b→c→d, which respectively correspond to the propagation paths of the ultrasonic wave in the two media.

[0131] Calculate the propagation time of the lower layer grid according to the sound path from the upper layer board to the joint surface, the sound path from the joint surface to the lower layer board, the sound path refracted from the lower layer board to the joint surface, and the sound path refracted from the joint surface to the upper layer board. The specific formula is as follows:

[0132]

[0133] Among them, t is the propagation time of the lower layer grid, c 1 is the sound velocity of the upper layer board, c 2 is the sound velocity of the lower layer board, l a is the sound path from the upper layer board to the joint surface, l b is the sound path from the joint surface to the lower layer board, l c is the sound path refracted from the lower layer board to the joint surface, l d is the sound path refracted from the joint surface to the upper layer board.

[0134] Calculate the sound path of the upper layer path and the lower layer path according to the coordinates of the first refraction point and the second refraction point. The calculation formula is as follows:

[0135] The sound path of the upper layer path (path a + path d) is:

[0136]

[0137] Among them, F 1 is the sound path of the upper layer path, x j is the abscissa of the receiving acoustic wave element, x i is the abscissa of the emitting acoustic wave element, x m is the abscissa of the first refraction point, x n is the abscissa of the second refraction point, y 1 is the ordinate of the first refraction point.

[0138] The sound path of the lower layer path (path b + path c) is:

[0139]

[0140] Among them, F 2 is the sound path of the lower layer path, x m is the abscissa of the first refraction point, x n is the abscissa of the second refraction point, y p is the ordinate of the lower layer board grid.

[0141] Calculate the second propagation time matrix according to the sound path of the upper layer path and the lower layer path. The calculation formula of the second propagation time matrix is:

[0142]

[0143] F 1is the sound path of the upper layer, F 2 is the sound path of the lower layer, c 1 is the sound speed of the upper layer plate, c 2 is the sound speed of the lower layer plate, x m is the abscissa of the first refraction point, x n is the abscissa of the second refraction point, x j is the abscissa of the receiving acoustic wave array element, x i is the abscissa of the transmitting acoustic wave array element, y 1 is the ordinate of the first refraction point, y p is the ordinate of the grid of the lower layer plate.

[0144] S7. Image the defects of the lower layer plate based on the first propagation time matrix, the second propagation time matrix, and the processed echo data.

[0145] Specifically, splice the first propagation time matrix and the second propagation time matrix to obtain the complete propagation time matrix. The calculation formula of the complete propagation time matrix is as follows:

[0146]

[0147] where T is the complete propagation time matrix, T 1 is the first propagation time matrix, T 2 is the second propagation time matrix.

[0148] Find the echo amplitude corresponding to each plate grid in the detection area in the processed echo data according to the complete propagation time matrix. After superimposing all the echo amplitudes, the complete echo amplitude matrix of the plates in the detection area is obtained. The calculation formula of the complete echo amplitude matrix is as follows:

[0149]

[0150] where I (x，y) is the complete echo amplitude matrix, x is the abscissa of the plate grid, y is the ordinate of the plate grid, N represents the number of array elements in the ultrasonic phased array detection device, i is the serial number of the transmitting acoustic wave array element, i = 0, 1, 2... N, j is the serial number of the receiving acoustic wave array element, j = 0, 1, 2... N, E i，j is the processed echo data, is the index of the echo data E i，j where f s is the system sampling frequency, is the propagation time matrix of the acoustic wave transmitted by the i-th array element and received by the j-th array element corresponding to the plate grid.

[0151] As can be seen from the above formula, the calculated propagation time matrix is used to find the echo amplitude corresponding to the grid coordinates in the echo data matrix. Since each grid P is superimposed N*N times, random Gaussian noise and electronic noise introduced by the hardware circuit can be effectively suppressed, and the data has a high fault tolerance.

[0152] The echo amplitude obtained through the above steps is a modulated signal. Then, the envelope of the complete echo amplitude is extracted to obtain envelope data. The envelope data is normalized. According to the normalized envelope data, a heat map is used for full-focus imaging of the defects in the lower-layer plate. The imaging results of the phased array system in the embodiments of the present invention are as Figure 6 (b) shown, Figure 6 (a) is the imaging result of the phased array system before improvement.

[0153] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for detecting defects of double-layer plates using a delayed focusing ultrasonic phased array, characterized in that: The following steps are involved: S1. Using ultrasonic phased array testing equipment to transmit ultrasonic waves to the defective double-layer plate to obtain original echo data; S2. Preprocessing the raw echo data to obtain processed echo data; S3. Establish a rectangular coordinate system for the plates in the detection area, and divide the plates within the detection range into a number of upper plate grids and a number of lower plate grids; S4. Calculate the first propagation time matrix of the upper plate grid by a conventional time-delay superposition method; S5. By Newton's iteration method, the coordinates of the first refraction point where the ultrasonic wave enters the lower plate from the upper plate and the coordinates of the second refraction point where the ultrasonic wave enters the upper plate from the lower plate after being reflected by the defect of the lower plate are solved; S6. Calculate the second propagation time matrix of the lower plate grid based on the first refraction point coordinates and the second refraction point coordinates obtained in S5; S7. Based on the first propagation time matrix, the second propagation time matrix and the processed echo data, find the echo amplitudes corresponding to the upper plate grid and the lower plate grid, and image the plate defects according to the echo amplitudes.

2. The method for detecting double-layer plate defects by using delayed focusing ultrasonic phased array according to claim 1 is characterized in that: The S2 step specifically includes: First, calculate the positioning matrix. The positioning matrix is ​​used to indicate the location where the echo data needs to be zeroed. The positioning matrix calculation formula is as follows: L i，j =T i，i +T′ i，j Among them, L is the positioning matrix, L i，j represents the element in the i-th row and j-th column of the positioning matrix, T i，i is the time taken for the ultrasonic wave to reach the joint surface of the plate from the transmitting acoustic wave array element i, T′i, j is the time taken for the ultrasonic wave to be reflected from the joint surface of the plate to the receiving acoustic wave array element j, N represents the number of array elements in the ultrasonic phased array detection equipment, T i，i Use the following formula to calculate: Among them, T i，i is the time taken for the ultrasonic wave to reach the joint surface of the plate from the transmitting sound wave array element i, Y1 is the thickness of the upper plate, c1 is the sound velocity of the upper plate, i = 0, 1, 2...N, T′ i，j Use the following formula to calculate: n=|ij| Among them, T′ i，j is the time taken for the ultrasonic wave emitted by array element i to reach the joint surface of the plate, reflect from the joint surface of the plate and be received by array element j, a is the distance between adjacent array elements, Y1 is the thickness of the upper plate, c1 is the sound velocity of the upper plate, n=0,1,2…N-1, i=0,1,2…N, j=0,1,2…N, Secondly, according to the pulse wave width and proportional coefficient of the echo signal received by the ultrasonic phased array detection equipment, the regional zeroing range is obtained. The regional zeroing range size calculation formula is as follows: R=W*γ Where W is the pulse width of the echo signal, γ is the proportional coefficient, and R is the area zeroing range. Finally, the original echo data is zeroed according to the regional zeroing range and the positioning matrix to obtain processed echo data.

3. The method for detecting defects of double-layer plate using delayed focusing ultrasonic phased array according to claim 1, characterized in that: The S4 step specifically includes: A line segment connecting the upper plate grid and the array element is constructed. Based on the line segment connecting the upper plate grid and the array element, the acoustic path matrix is ​​calculated using the Pythagorean theorem. The acoustic path matrix calculation formula is as follows: Among them, F n is the sound path matrix, x n is the horizontal coordinate of the array element, x t is the horizontal coordinate of the upper plate grid, y t is the ordinate of the grid of the upper plate, N represents the number of array elements in the ultrasonic phased array detection equipment, According to the sound path matrix and the longitudinal wave velocity in the upper plate, the first propagation time matrix is ​​obtained. The formula of the first propagation time matrix is ​​as follows: Where c1 is the longitudinal wave speed in the upper plate, T1 is the first propagation time matrix, and F i is the acoustic path matrix of the transmitting acoustic wave array element to the upper plate grid, F j is the acoustic path matrix from the upper plate grid to the receiving acoustic wave array element, and N represents the number of array elements in the ultrasonic phased array detection equipment.

4. The method for detecting defects of double-layer plate using delayed focusing ultrasonic phased array according to claim 1, characterized in that: Step S5 specifically includes: Calculate the propagation time of the sound wave emitted by the transmitting array element to reach the grid of the lower plate. The calculation formula is as follows: Among them, f(x m ) is the propagation time of the sound wave emitted by the transmitting array element to reach the grid of the lower plate, c1 is the sound velocity of the upper plate, c2 is the sound velocity of the lower plate, x m is the abscissa of the first refraction point of the sound wave at the joint surface, x i is the horizontal coordinate of the acoustic wave array element, x p is the horizontal coordinate of the grid of the lower plate, y p is the ordinate of the grid of the lower plate, Y1 is the thickness of the upper plate, N represents the number of array elements in the ultrasonic phased array detection equipment, The formula of the propagation time of the sound wave emitted by the transmitting sound wave array element to the grid of the lower plate is derived, and the derivative is set to 0. The derivative of the propagation time of the sound wave emitted by the transmitting sound wave array element to the grid of the lower plate is solved by using the Newton iteration method to obtain the coordinates of the first refraction point; Calculate the propagation time of the sound wave reflected by the lower plate grid to reach the receiving array element. The calculation formula is as follows: Among them, g(x n ) is the propagation time of the sound wave emitted by the transmitting array element to reach the grid of the lower plate, c1 is the sound velocity of the upper plate, c2 is the sound velocity of the lower plate, x n is the horizontal coordinate of the second refraction point of the sound wave at the joint surface, x j is the horizontal coordinate of the receiving acoustic wave array element, x p is the horizontal coordinate of the grid of the lower plate, y p is the ordinate of the grid of the lower plate, Y1 is the thickness of the upper plate, N represents the number of array elements in the ultrasonic phased array detection equipment, The formula of the propagation time of the sound wave reflected by the lower plate grid to the receiving array element is derived, and the derivative is set to 0. The derivative of the propagation time of the sound wave reflected by the lower plate grid to the receiving array element is solved using the Newton iteration method to obtain the coordinates of the second refraction point.

5. The method for detecting defects of double-layer plate using delayed focusing ultrasonic phased array according to claim 1, characterized in that: Step S6 specifically includes: According to the coordinates of the first refraction point and the second refraction point, the upper path sound path and the lower path sound path are calculated. The calculation formula is as follows: The upper path sound path is: Among them, F1 is the upper path sound path, x j is the horizontal coordinate of the receiving acoustic wave array element, x i is the horizontal coordinate of the acoustic wave array element, x m is the horizontal coordinate of the first refraction point, x n is the horizontal coordinate of the second refraction point, y1 is the vertical coordinate of the first refraction point, The lower path sound path is: Among them, F2 is the lower path sound path, x m is the horizontal coordinate of the first refraction point, x n is the horizontal coordinate of the second refraction point, y p is the ordinate of the grid of the lower plate, The second propagation time matrix is ​​calculated according to the upper layer path sound path and the lower layer path sound path. The calculation formula of the second propagation time matrix is: Among them, F1 is the sound path of the upper layer, F2 is the sound path of the lower layer, c1 is the sound velocity of the upper plate, c2 is the sound velocity of the lower plate, x m is the horizontal coordinate of the first refraction point, x n is the horizontal coordinate of the second refraction point, x j is the horizontal coordinate of the receiving acoustic wave array element, x i is the horizontal coordinate of the acoustic wave array element, y1 is the vertical coordinate of the first refraction point, and y p is the vertical coordinate of the grid of the lower plate.

6. The method for detecting defects of double-layer plate using delayed focusing ultrasonic phased array according to claim 1, characterized in that: Step S7 specifically includes: The first propagation time matrix and the second propagation time matrix are concatenated to obtain the complete propagation time matrix. The calculation formula of the complete propagation time matrix is ​​as follows: Where T is the complete propagation time matrix, T1 is the first propagation time matrix, T2 is the second propagation time matrix, According to the complete propagation time matrix, the complete echo amplitude matrix of the plate in the detection area is obtained, the envelope of the complete echo amplitude matrix is ​​extracted to obtain the envelope data, the envelope data is normalized, and according to the normalized envelope data, the defects of the lower plate are fully focused on imaging using a heat map.

7. The method for detecting defects of double-layer plate using delayed focusing ultrasonic phased array according to claim 1, characterized in that: According to the complete propagation time matrix, the complete echo amplitude matrix of the plate in the detection area is obtained, including: According to the complete propagation time matrix, find the echo amplitude corresponding to each plate grid in the detection area in the processed echo data, and after superimposing all the echo amplitudes, obtain the complete echo amplitude matrix of the plates in the detection area. The calculation formula of the complete echo amplitude matrix is ​​as follows: Among them, I (x，y) is the complete echo amplitude matrix, x is the horizontal coordinate of the plate grid, y is the vertical coordinate of the plate grid, N represents the number of array elements in the ultrasonic phased array detection equipment, i is the serial number of the transmitting acoustic wave array element, i = 0, 1, 2...N, j is the serial number of the receiving acoustic wave array element, j = 0, 1, 2...N, E i，j For the processed echo data, E is the echo data E i，j The index of f s is the system sampling frequency, It is the complete propagation time matrix of the sound wave transmitted by the i-th array element and received by the j-th array element corresponding to the plate grid.

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