A fan scan imaging method based on physical acoustic field of an ultrasonic phased array

Abstract

The application discloses a kind of fan scanning imaging methods based on ultrasonic phased array physical acoustic field, first establish the coordinate system of ultrasonic phased array physical acoustic field and set basic structure, then define circular defect and widen, and then the normal direction of each sampling point is calculated;Then according to the incident direction of each sampling point, it is judged whether each sampling point is in the range of effective reflection direction, and then the incident direction of each sampling point is corrected, and then the overall propagation time required for the ultrasonic wave received by each sampling point to be transmitted from the center of the element to be reflected to the center of the element is calculated, finally, the propagation time t of each sampling point is converted into discrete sampling index, and the acoustic field of each beam angle is traversed, the A-scan signal of each angle is obtained, and finally interpolation imaging is realized.

Description

Technical Field

[0001] This invention belongs to the field of nondestructive testing technology, and more specifically, relates to a sector scanning imaging method based on the physical acoustic field of an ultrasonic phased array. Background Technology

[0002] Ultrasonic phased array technology is an advanced defect detection technique in ultrasonic testing. Compared to conventional ultrasonic probes, phased arrays offer the advantage of obtaining multiple beam detection signals through beam deflection and focusing without moving the probe, enabling multi-angle scanning and two-dimensional imaging. Sub-fields of this technology include sector scanning imaging, total focusing imaging, and linear scanning imaging.

[0003] This invention focuses on the sector scanning imaging technology. Ultrasonic phased array sector scanning is usually used in conjunction with a wedge block, which allows the longitudinal wave to exceed the critical angle and only the transverse wave to enter the test piece, avoiding mutual interference between the longitudinal and transverse waves. It has a better imaging effect and is very suitable for weld defect detection, making it a very important detection method.

[0004] However, the shape and size of defects in sector scan images do not correspond to their true shape and size. It is difficult to determine the true characteristics of defects directly from scanned images, and even experienced inspectors are prone to misjudgment. With the further development of artificial intelligence, many researchers are now using neural networks for automatic defect detection and characterization. This achieves automated detection, saving manpower, and leverages the powerful reasoning capabilities of neural networks to reduce misjudgments in defect assessment. However, the effectiveness of neural network models is highly dependent on the dataset. Using only real and artificial defect data is insufficient in terms of data volume and diversity, and the time and economic costs of creating datasets are prohibitive. Some researchers use commercial finite element simulation software to create ultrasound datasets. This method has shown good results, generating rich datasets to train neural network models. However, the computational demands of such simulation software are enormous, and generating datasets of tens of thousands of images requires significant time investment. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a sector scanning imaging method based on the physical acoustic field of an ultrasonic phased array, which can quickly obtain simulated images of defects.

[0006] To achieve the above-mentioned objectives, the present invention provides a sector scanning imaging method based on the physical acoustic field of an ultrasonic phased array, characterized by comprising the following steps:

[0007] (1) Establish the coordinate system of the physical sound field of the ultrasonic phased array;

[0008] Let H be the center of the ultrasonic phased array element, and let O be the intersection point of the interface between the center of the array element and the test piece. Let the vertical direction be the Z-axis and the horizontal direction be the X-axis to construct a coordinate system.

[0009] (2) Set up the basic structure of the physical sound field of the ultrasonic phased array;

[0010] N crystals are placed at equal intervals on the wedge of the ultrasonic phased array. The wedge is placed on the surface of the test piece. The N crystals emit ultrasonic beams together, which is equivalent to the beams emitted from the center H of the array element.

[0011] (3) Define circular defects;

[0012] With point O as the upper left endpoint, a rectangular area of ​​size m×n is defined on the surface of the test piece as the detection area. Then, p circular defects with radius r are randomly defined on the detection area.

[0013] (4) Widen the circular defect and calculate the normal direction of each point on the annulus of the defect;

[0014] (4.1) On each circular defect, draw an axis parallel to the X-axis through the center of the circular defect, and divide each circular defect into upper and lower semicircles. Set multiple sampling points on the upper and lower semicircles.

[0015] (4.2) On the upper semicircular arc of each circular defect, the line connecting each sampling point on the upper semicircular arc to the center of the circle is taken as the normal vector. Then the angle between the normal vector and the X-axis is calculated, and the normal direction of each sampling point is represented by this angle. The normal direction of each sampling point on the lower semicircular arc is set to 0.

[0016] (4.3) Defect widening;

[0017] Set the widening step Δr;

[0018] Using the upper semicircular arc of each circular defect as a reference, first draw a semicircular arc at the center of each circular defect according to r+Δr, r+2Δr, ..., r+kΔr, then draw a semicircular arc according to r-Δr, r-2Δr, ..., r-kΔr, where k is a positive integer; then calculate the normal direction of each sampling point on the 2k semicircular arcs according to step (4.2);

[0019] (5) Define the weights of each sampling point on the 2k+1 semicircles;

[0020] Set the weight of each sampling point on the upper semicircular arc of the reference in step (4.3) to 1, and then decrease the weight of each sampling point on the inner and outer semicircular arcs by Δw in sequence, where Δw is a constant less than 1.

[0021] (6) Calculate the incident direction of each sampling point on the 2k+1 semicircles;

[0022] Find the incident point of each sampling point on each semicircle, then connect the corresponding incident point with the sampling point with a straight line, and finally take the angle between the straight line and the X-axis as the incident direction of each sampling point.

[0023] (7) Define the occlusion array for each circular defect;

[0024] Calculate the occlusion parameters for each circular defect: low limit angle, high limit angle, and defect center depth; where the defect center depth is the perpendicular distance from the center of the circular defect to the X-axis; after widening each circular defect, find the maximum and minimum values ​​of the incident direction of each sampling point on 2k+1 semicircles, and then use the maximum value as the low limit angle and the minimum value as the high limit angle.

[0025] The occlusion parameters of each circular defect are combined into an occlusion array;

[0026] (8) Calculate the time required for the ultrasonic beam to propagate from the center of the array element to each sampling point on each semicircle.

[0027] For each sampling point on each semicircle, first calculate the distance between each sampling point and the corresponding incident point, denoted as L1; then calculate the distance from the center of the array element to the incident point, denoted as L2; ​​finally calculate the propagation time t1.

[0028] t1 = L1 / c1 + L2 / c2

[0029] Where c1 and c2 represent the propagation speeds of the ultrasonic beam in the test piece and the wedge, respectively;

[0030] (9) Set the effective reflection direction range for each sampling point;

[0031] For any sampling point on 2k+1 semicircular arcs, when the ultrasonic beam propagates to the sampling point, the sampling point will reflect the ultrasonic beam onto the ultrasonic phased array chip. When the first chip in the ultrasonic phased array physical acoustic field can receive the reflected beam, the angle between the reflected beam and the X-axis in the test piece is taken as the maximum reflection direction of the sampling point; at the same time, when the last chip in the ultrasonic phased array physical acoustic field can receive the reflected beam, the angle between the reflected beam and the X-axis in the test piece is taken as the minimum reflection direction of the sampling point.

[0032] Finally, the region between the minimum reflection direction and the maximum reflection direction is defined as the effective reflection direction range of the sampling point;

[0033] (10) Determine whether each sampling point is within the effective reflection direction range;

[0034] For any sampling point on 2k+1 semicircular arcs, calculate the reflection direction of the sampling point based on the incident direction and the normal direction of the sampling point. The incident direction and the reflection direction are symmetrical about the normal direction.

[0035] Iterate through each sampling point and determine whether the incident direction of each sampling point is within the corresponding effective reflection direction range. If it is within the effective reflection direction range, the reflection direction of the sampling point remains unchanged; otherwise, the reflection direction of the sampling point is set to 0. In addition, for sampling points where the angle between the incident direction and the normal direction exceeds 90 degrees, their reflection direction is also set to 0.

[0036] (11) Check the obstruction of each sampling point;

[0037] Traverse the occlusion array. For any sampling point on any of the 2k+1 semicircles, if the vertical distance from the sampling point to the X-axis is greater than the depth of a certain defect center, and the incident direction of the sampling point is between the corresponding high limit angle and low limit angle, then the sampling point is determined to be occluded, and the reflection direction of the sampling point is set to 0.

[0038] (12) Calculate the time required for the reflected beam to travel from the sampling point to the center of the array element;

[0039] For any sampling point on the 2k+1 semicircular arcs, first find the incident point of the reflected beam at the interface between the wedge and the test piece, then calculate the distance L3 between the sampling point and the corresponding incident point, and the distance L4 from the center of the array element to the incident point; finally, calculate the propagation time t2.

[0040] t2 = L3 / c2 + L4 / c1

[0041] (13) Calculate the total propagation time t required for the ultrasonic waves received at each sampling point to travel from the center of the array element to the center of the array element;

[0042] For any sampling point on 2k+1 semicircular arcs, first determine whether the reflection direction of the sampling point is 0. If it is 0, then set the overall propagation time t of the sampling point to 0; otherwise, set the overall propagation time of the sampling point to t = t1 + t2.

[0043] (14) Traverse the sound field at each beam angle and obtain the A-scan signal at each angle;

[0044] (14.1) Convert the propagation time t of each sampling point into a discrete sampling index;

[0045] Set the sampling interval d. For any sampling point on 2k+1 semicircles, divide the propagation time t of the sampling point by the sampling interval d and then round down to obtain the sampling index.

[0046] (14.2) Calculate the acoustic amplitude of each sampling point at different scanning angles;

[0047] The scanning angle range of the physical sound field of the ultrasonic phased array is set to 30° to 65°, with a beamline set at 1° intervals.

[0048] By traversing each scanning angle, the sound field distribution map of the corresponding angle is obtained. These sound field distribution maps are composed of the sound wave amplitude of each sampling point under different scanning angles.

[0049] (14.3) Filter the sound field distribution map;

[0050] Set a filtering threshold. For each sound field distribution map, set the sampling points with sound wave amplitude less than the filtering threshold to 0, and keep the sound wave amplitude of the remaining sampling points unchanged.

[0051] (14.4) Integrate A-scan signals;

[0052] For each sound field distribution map, traverse each sampling point in the sound field distribution map, find the sampling point whose propagation time t is not 0, then multiply the sound wave amplitude of the sampling point by its corresponding weight, and save it into a two-dimensional array according to its corresponding discrete point index, thus obtaining 36 A-scan signals at different angles.

[0053] (15) Fan-shaped imaging is achieved using A-scan signals at different angles.

[0054] The objective of this invention is achieved as follows:

[0055] This invention discloses a sector-scan imaging method based on the physical acoustic field of an ultrasonic phased array. First, a coordinate system for the physical acoustic field of the ultrasonic phased array is established and its basic structure is set. Then, a circular defect is defined and widened, and the normal direction of each sampling point is calculated. Next, based on the incident direction of each sampling point, it is determined whether each sampling point is within the effective reflection direction range, and the incident direction of each sampling point is corrected. Then, the overall propagation time required for the ultrasonic wave received at each sampling point to travel from the center of the array element to its reflection at the center of the array element is calculated. Finally, the propagation time t of each sampling point is converted into a discrete sampling index, and the acoustic field at each beam angle is traversed to obtain the A-scan signal at each angle, ultimately achieving interpolated imaging.

[0056] Meanwhile, the sector scanning imaging method based on the physical acoustic field of an ultrasonic phased array, as described in this invention, also has the following beneficial effects:

[0057] (1) The present invention can simulate the defect occlusion situation during real ultrasonic phased array detection.

[0058] (2) This invention can simulate many characteristics of real phased array sector scanning imaging, such as: the signal of low-angle defects is strong, while the signal of high-angle defects is weak; for circular defects, they are all elliptical in the image, and the major axis of the ellipse at low angles is relatively flat, while the major axis of the ellipse at high angles is relatively steep; for defects far from the focal point, the images are relatively blurry; through the sector scanning imaging method of the physical sound field of ultrasonic phased array, the shape and size of the defects in the sector scanning image can be made consistent with the real shape and size of the defects, and the real characteristics of the defects can be accurately determined, so that the inspectors can easily judge the defects.

[0059] (3) The present invention can obtain a simulated image with a near-real scanning effect in a short time by using ultrasonic phased array sector scanning imaging, thereby generating a diverse and rich dataset. Attached Figure Description

[0060] Figure 1 This is a flowchart of a sector scanning imaging method based on the physical acoustic field of an ultrasonic phased array according to the present invention.

[0061] Figure 2 This is a coordinate diagram;

[0062] Figure 3 This is a diagram illustrating defect widening;

[0063] Figure 4 This is a schematic diagram of the effective reflection direction range;

[0064] Figure 5 This is a schematic diagram of defect occlusion;

[0065] Figure 6 These are imaging diagrams under conditions of complete occlusion, partial occlusion, and no occlusion.

[0066] Figure 7 It is a sound field distribution diagram from a single angle;

[0067] Figure 8 This is a schematic diagram of the integration of a single A-scan signal at a single angle;

[0068] Figure 9 It is a comparison image of the defect fan after imaging and the real defect image; Detailed Implementation

[0069] The specific embodiments of the present invention will now be described with reference to the accompanying drawings to enable those skilled in the art to better understand the invention. It should be particularly noted that in the following description, detailed descriptions of known functions and designs that might obscure the main content of the invention will be omitted here.

[0070] Example

[0071] Figure 1This is a flowchart of a sector scanning imaging method based on the physical acoustic field of an ultrasonic phased array according to the present invention.

[0072] This invention provides a sector scanning imaging method based on the physical acoustic field of an ultrasonic phased array, comprising the following steps:

[0073] S1. Establish the coordinate system of the physical acoustic field of the ultrasonic phased array;

[0074] like Figure 2 As shown, let H be the center of the ultrasonic phased array element, and let O be the intersection point of the interface between the center of the array element and the test piece. Let the vertical direction be the Z-axis and the horizontal direction be the X-axis to construct a coordinate system.

[0075] S2. Set the basic structure of the physical sound field of the ultrasonic phased array;

[0076] like Figure 2 As shown, 32 wafers are placed at equal intervals on the wedge of the ultrasonic phased array. The wedge is placed on the surface of the test piece. The 32 wafers emit ultrasonic beams together, which is equivalent to the beams emitted from the center H of the array element.

[0077] S3. Define circular defects;

[0078] With point O as the upper left endpoint, a rectangular area of ​​1000*500 is defined on the surface of the test piece as the detection area. Then, three circular defects with a radius of 0.5mm are randomly defined on the detection area.

[0079] S4. Widen the circular defect and calculate the normal direction of each point on the annulus of the defect;

[0080] S4.1. For each circular defect, draw an axis parallel to the X-axis through the center of the circular defect, and divide each circular defect into upper and lower semicircles. Set multiple sampling points on the upper and lower semicircles.

[0081] S4.2 On the upper semicircular arc of each circular defect, the line connecting each sampling point on the upper semicircular arc to the center of the circle is taken as the normal vector. Then, the angle between the normal vector and the X-axis is calculated, and this angle represents the normal direction of each sampling point. The normal direction of each sampling point on the lower semicircular arc is set to 0.

[0082] S4.3, Defect widening;

[0083] Set the widening step Δr;

[0084] like Figure 3As shown, taking the upper semicircular arc of each circular defect as a reference, a semicircular arc is first drawn at the center of each circular defect according to r+Δr, r+2Δr, ..., r+kΔr, and then a semicircular arc is drawn according to r-Δr, r-2Δr, ..., r-kΔr, where k is a positive integer. In this embodiment, k = 7 and Δr = 0.01. Then, the normal direction of each sampling point on the 2k semicircular arcs is calculated according to step S4.2.

[0085] S5. Define the weights of each sampling point on 2k+1 semicircles;

[0086] In step S4.3, the weight of each sampling point on the upper semicircle of the reference is set to 1, and then the weight of each sampling point on the inner and outer semicircles is decreased by 0.1 in turn. In this embodiment, since k=7, the weight of the sampling points on the innermost and outermost circles is 0.3.

[0087] S6. Calculate the incident direction of each sampling point on 2k+1 semicircles;

[0088] Each sampling point on the semicircular arc corresponds to an acoustic beam. This beam is emitted from the center H of the array element, passes through the interface between the wedge and the test piece, and reaches the sampling point. The intersection of the beam and the interface is the incident point. Based on this principle, we can find the incident point of each sampling point on each semicircular arc, then connect the corresponding incident point with the sampling point with a straight line, and finally take the angle between the straight line and the X-axis as the incident direction of each sampling point.

[0089] S7. Define the occlusion array for each circular defect;

[0090] Calculate the occlusion parameters for each circular defect: low limit angle, high limit angle, and defect center depth; where the defect center depth is the perpendicular distance from the center of the circular defect to the X-axis; after widening each circular defect, find the maximum and minimum values ​​of the incident direction of each sampling point on 2k+1 semicircles, and then use the maximum value as the low limit angle and the minimum value as the high limit angle.

[0091] The occlusion parameters of each circular defect are combined into an occlusion array;

[0092] S8. Calculate the time required for the ultrasonic beam to propagate from the center of the array element to each sampling point on each semicircle.

[0093] For each sampling point on each semicircle, first calculate the distance between each sampling point and the corresponding incident point, denoted as L1; then calculate the distance from the center of the array element to the incident point, denoted as L2; ​​finally calculate the propagation time t1.

[0094] t1 = L1 / c1 + L2 / c2

[0095] Where c1 and c2 represent the propagation speeds of the ultrasonic beam in the test piece and the wedge, respectively;

[0096] S9. Set the effective reflection direction range for each sampling point;

[0097] In this embodiment, when the sound wave encounters a defect, it will be reflected, but only a portion of the signal can be reflected back to the sensor and received. This effective range is the range of reflection directions that can be received.

[0098] The sensor consists of 32 vibrating crystals. The maximum reflection direction is the direction in which the first crystal can receive the signal; the minimum reflection direction is the opposite direction in which the last crystal can receive the signal.

[0099] Therefore, for any sampling point on one of the 2k+1 semicircular arcs, when the ultrasonic beam propagates to the sampling point, the sampling point will reflect the ultrasonic beam onto the ultrasonic phased array chip, such as... Figure 4 As shown, when the first crystal in the ultrasonic phased array physical acoustic field can receive the reflected beam, the angle between the reflected beam and the X-axis in the test piece is taken as the maximum reflection direction of the sampling point; at the same time, when the last crystal in the ultrasonic phased array physical acoustic field can receive the reflected beam, the angle between the reflected beam and the X-axis in the test piece is taken as the minimum reflection direction of the sampling point.

[0100] Finally, the region between the minimum reflection direction and the maximum reflection direction is defined as the effective reflection direction range of the sampling point;

[0101] S10. Determine whether each sampling point is within the effective reflection direction range;

[0102] For any sampling point on 2k+1 semicircular arcs, calculate the reflection direction of the sampling point based on the incident direction and the normal direction of the sampling point. The incident direction and the reflection direction are symmetrical about the normal direction.

[0103] Iterate through each sampling point and determine whether the incident direction of each sampling point is within the corresponding effective reflection direction range. If it is within the effective reflection direction range, the reflection direction of the sampling point remains unchanged; otherwise, the reflection direction of the sampling point is set to 0. In addition, for sampling points where the angle between the incident direction and the normal direction exceeds 90 degrees, their reflection direction is also set to 0.

[0104] S11. Check the obstruction status of each sampling point;

[0105] Traverse the occlusion array. For any sampling point on any of the 2k+1 semicircles, if the vertical distance from the sampling point to the X-axis is greater than the depth of a certain defect center, and the incident direction of the sampling point is between the corresponding high limit angle and low limit angle, then the sampling point is determined to be occluded, and the reflection direction of the sampling point is set to 0.

[0106] In this embodiment, as Figure 5 As shown in the figure, the depths of defects 1, 2, and 3 are all higher than that of defect 0. All points on the surface of defect 1 are within the limit angle range, so it is completely occluded. Defect 2 is partially occluded, and defect 3 is not occluded. At the same time, defects 1, 2, and 3 also have their own occlusion arrays, which are used to determine whether they will cause occlusion of other defects. For example, defect 2 will occlude part of the surface of defect 3.

[0107] Subsequently, when calculating the reflection direction at each point, the three parameters in the array will be traversed. If the depth of the point is higher than the depth of a defect center in the array, and the incident direction of the sound wave is between the lower and higher limit angles, it means that the point is occluded and will not be calculated. In this way, the cases of complete occlusion, partial occlusion, and no occlusion can be simulated, similar to the actual phased array imaging situation, such as... Figure 6 As shown.

[0108] S12. Calculate the time required for the reflected beam to travel from the sampling point to the center of the array element;

[0109] For any sampling point on the 2k+1 semicircular arcs, first find the incident point of the reflected beam at the interface between the wedge and the test piece, then calculate the distance L3 between the sampling point and the corresponding incident point, and the distance L4 from the center of the array element to the incident point; finally, calculate the propagation time t2.

[0110] t2 = L3 / c2 + L4 / c1

[0111] S13. Calculate the total propagation time t required for the ultrasonic waves received at each sampling point to travel from the center of the array element to the center of the array element after being emitted and reflected back to the center of the array element.

[0112] For any sampling point on 2k+1 semicircular arcs, first determine whether the reflection direction of the sampling point is 0. If it is 0, the sampling point will not be calculated, and the overall propagation time t of the sampling point will be set to 0; otherwise, the overall propagation time of the sampling point will be set to t = t1 + t2.

[0113] S14. Traverse the sound field at each beam angle and obtain the A-scan signal at each angle;

[0114] S14.1 Convert the propagation time t of each sampling point into a discrete sampling index;

[0115] Set the sampling interval d. For any sampling point on 2k+1 semicircles, divide the propagation time t of the sampling point by the sampling interval d and then round down to obtain the sampling index.

[0116] S14.2 Calculate the acoustic amplitude of each sampling point at different scanning angles;

[0117] In this embodiment, the ultrasonic phased array uses the commonly used multi-line element ultrasonic model as the basic sound field model, and then uses the phased array focusing law to superimpose the sound fields of each array element to obtain the phased array sound field model. The calculation steps of this model are very complicated, and the model has long been perfected, so it will not be described in detail here.

[0118] We need to set the scanning angle range of the physical acoustic field of the ultrasonic phased array to 30° to 65°, and set a beamline at 1° intervals;

[0119] Then, by traversing each scanning angle, the corresponding sound field distribution map can be obtained. The size of the sound field distribution map is exactly the same as the widened defect map. These sound field distribution maps are composed of the sound wave amplitude of each sampling point under different scanning angles.

[0120] like Figure 7 As shown, the two figures below are the sound field distribution diagrams of the equivalent beam at 30° (left) and 65° (right), respectively. The figures show the sound wave amplitude at each point in the detection area.

[0121] S14.3 Filter the sound field distribution diagram;

[0122] Beam signals at various angles will generate a relatively large sound field near the beamline corresponding to that angle, while the amplitude will be weaker in other areas. Ideally, a beam at a certain angle should only detect defects on that beamline, and defects outside that beamline should not affect it. However, since a beam at any angle will generate a sound field throughout the entire detection area, defects in other areas will inevitably affect the signal at that angle, which is especially noticeable in numerical simulation models. Therefore, filtering of the detection signal is necessary.

[0123] Set a filtering threshold. For each sound field distribution map, set the sampling points with sound wave amplitude less than the filtering threshold to 0, and keep the sound wave amplitude of the remaining sampling points unchanged.

[0124] S14.4, Integrate A-scan signals;

[0125] For each sound field distribution map, traverse each sampling point in the sound field distribution map, find the sampling point whose propagation time t is not 0, then multiply the sound wave amplitude of the sampling point by its corresponding weight, and save it into a two-dimensional array according to its corresponding discrete point index, thus obtaining 36 A-scan signals at different angles.

[0126] In this embodiment, a two-dimensional array is used to represent the 36 A-scan signals, such as... Figure 8 As shown in the figure, the integration process of an A-scan signal is illustrated.

[0127] S15. Use interpolation imaging to achieve fan-shaped imaging of A-scan signals at different angles.

[0128] In this embodiment, the specific process of interpolation imaging will not be described in detail here. For details, please refer to the title: A Real-time Interpolation Imaging Method for Sector-Shaped Ultrasonic Phased Array.

[0129] In this embodiment, after performing a simulation scan on the test piece using the above method, the image obtained after defect fan imaging is as follows: Figure 9 As shown in the right image, the actual image of the defect is as follows: Figure 9 As shown in the left figure, a comparison reveals that the present invention can accurately and quickly obtain a simulated image identical to the real image.

[0130] Although the illustrative specific embodiments of the present invention have been described above to enable those skilled in the art to understand the invention, it should be understood that the invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of the present invention are protected.

Claims

1. A method of fan scan imaging based on the physical acoustic field of an ultrasonic phased array, characterized in that, The method comprises the following steps: (1) establishing a coordinate system of the physical sound field of the ultrasonic phased array; Taking the center of the array element of the ultrasonic phased array as H, taking the intersection point of the interface between the ultrasonic phased array and the tested piece directly below H as the coordinate origin O, and taking the vertical downward direction as the Z axis and the horizontal direction as the X axis, a coordinate system is constructed; (2) setting the basic structure of the physical sound field of the ultrasonic phased array; N wafers are placed at equal intervals on the inclined wedge block of the ultrasonic phased array, the inclined wedge block is placed on the surface of the tested piece, and the N wafers together emit an ultrasonic beam, which is equivalent to being emitted from the array element center H; (3) defining a circular defect; Taking point O as the left upper corner endpoint, a rectangular region with a size of m x n is defined on the surface of the tested piece as a detection region, and then p circular defects are randomly defined on the detection region, and the radius of each circular defect is r; (4) widening the circular defect and calculating the normal direction of each point on the circular ring of the defect; (4.1) on each circular defect, an axis parallel to the X axis is drawn through the center of the circular defect, and each circular defect is divided into upper and lower semicircles, and a plurality of sampling points are arranged on the upper and lower semicircles; (4.2) on the upper semicircle of each circular defect, the connecting line between each sampling point on the upper semicircle and the center of the circular defect is taken as a normal vector, and then the included angle between the normal vector and the X axis is calculated, and the normal direction of each sampling point is represented by the angle; the normal direction of each sampling point on the lower semicircle is set to 0; (4.3) defect widening; a widening step Δr is set; taking the upper semicircle of each circular defect as a reference, a semicircle is first drawn at the center of each circular defect according to r+Δr, r+2Δr, …, r+kΔr, and then a semicircle is drawn according to r-Δr, r-2Δr, …, r-kΔr, k being a positive integer; then the normal direction of each sampling point on the 2k semicircles is calculated according to step (4.2); (5) defining the weight of each sampling point on the 2k+1 semicircles; the weight of each sampling point on the reference upper semicircle in step (4.3) is set to 1, and then the weight of each sampling point on the inner and outer semicircles is sequentially decreased by Δw, Δw being a constant less than 1; (6) calculating the incident direction of each sampling point on the 2k+1 semicircles; the incident point of each sampling point on each semicircle is found, then a straight line connecting the corresponding incident point and the sampling point is connected, and finally the included angle between the straight line and the X axis is taken as the incident direction of each sampling point; (7) defining a shielding array of each circular defect; the shielding parameters of each circular defect, i.e. the low limit angle, the high limit angle and the center depth of the defect, are calculated; wherein the center depth of the defect is the vertical distance from the center of the circular defect to the X axis; after widening each circular defect, the maximum and minimum values of the incident direction of each sampling point on the 2k+1 semicircles are found, and then the maximum value is taken as the low limit angle and the minimum value is taken as the high limit angle; the shielding parameters of each circular defect are combined to form a shielding array; (8) calculating the time required for the ultrasonic beam to propagate from the array element center to each sampling point on each semicircle; For each sampling point on each semicircular arc, first calculate the distance between the sampling point and the corresponding incident point, denoted as L1; then calculate the distance between the center of the array element and the incident point, denoted as L2; finally calculate the propagation time t1: t1=L1 / c1+L2 / c2 Wherein, c1, c2 respectively represent the propagation speed of the ultrasonic beam in the tested member and the wedge; (9) Set the effective reflection direction range of each sampling point; For any one sampling point on the 2k+1 semicircular arcs, when the ultrasonic beam propagates to the sampling point, the sampling point will reflect the ultrasonic beam to the ultrasonic phased array wafer, when the first wafer in the ultrasonic phased array physical sound field can receive the reflected beam, the angle between the reflected beam in the tested member and the X axis is the maximum reflection direction of the sampling point; at the same time, when the last wafer in the ultrasonic phased array physical sound field can receive the reflected beam, the angle between the reflected beam in the tested member and the X axis is the minimum reflection direction of the sampling point; Finally, define the area between the minimum reflection direction and the maximum reflection direction as the effective reflection direction range of the sampling point; (10) Judge whether each sampling point is in the effective reflection direction range; For any one sampling point on the 2k+1 semicircular arcs, according to the incident direction and the normal direction of the sampling point, the reflection direction of the sampling point is calculated, and the incident direction and the reflection direction are symmetrical about the normal direction; Traverse each sampling point, judge whether the incident direction of each sampling point is located in the corresponding effective reflection direction range, if it is located in the effective reflection direction range, the reflection direction of the sampling point remains unchanged; otherwise, set the reflection direction of the sampling point to 0; in addition, for the sampling point whose angle between the incident direction and the normal direction exceeds 90 degrees, the reflection direction is also set to 0; (11) Check the shielding condition of each sampling point; Traverse the shielding array, for any one sampling point on the 2k+1 semicircular arcs, if the vertical distance from the sampling point to the X axis is greater than a certain defect center depth, and the incident direction of the sampling point is located between the corresponding high limit angle and low limit angle, it is judged that the sampling point is shielded, and then the reflection direction of the sampling point is set to 0; (12) Calculate the time required for the reflected beam to transmit from the sampling point to the center of the array element; For any one sampling point on the 2k+1 semicircular arcs, first find the incident point of the reflected beam on the interface between the wedge and the tested member, then calculate the distance L3 between the sampling point and the corresponding incident point and the distance L4 between the center of the array element and the incident point; finally, calculate the propagation time t2: t2=L3 / c2+L4 / c1 (13) Calculate the overall propagation time t of the ultrasonic sound wave received by each sampling point from the center of the array element to the reflection to the center of the array element; For any one sampling point on the 2k+1 semicircular arcs, first judge whether the reflection direction of the sampling point is 0, if it is 0, set the overall propagation time t of the sampling point to 0; otherwise, set the overall propagation time of the sampling point as t=t1+t2; (14) Traverse the sound field of each beam angle to obtain the A-scan signal of each angle; (14.1) Convert the propagation time t of each sampling point into discrete sampling index; Setting sampling interval d, for any one sampling point on 2k+1 semicircular arc, the propagation time t of the sampling point is divided by the sampling interval d, and then the integer part is obtained, to obtain the sampling index; (14.2), calculating the sound wave amplitude of each sampling point at different scanning angles; The scanning angle range of the physical acoustic field of the ultrasonic phased array is θ1~θ h Each interval of 1 ° sets a beam line, a total of h beams; Traverse each scanning angle to obtain the corresponding angle sound field distribution map, which is composed of the sound wave amplitude of each sampling point at different scanning angles; (14.3), filtering the sound field distribution map; Setting the filtering threshold, for each sound field distribution map, setting the sampling point with sound wave amplitude less than the filtering threshold to 0, and keeping the sound wave amplitude of the remaining sampling point unchanged; (14.4), integrating A-scan signal; For each sound field distribution map, traverse each sampling point in the sound field distribution map, find out the sampling point with the propagation time t not being 0, then multiply the sound wave amplitude of the sampling point by its corresponding weight, and then save it to a two-dimensional array according to its corresponding discrete point index, that is, obtain h A-scan signals at different angles; (15), realizing fan imaging by using A-scan signals at different angles.

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