A curved surface synthetic aperture imaging method based on ultrasonic phased array leaky surface wave

Abstract

The application discloses a curved surface synthetic aperture imaging method based on an ultrasonic phased array leaky surface wave and comprises four steps of constructing a water immersion type ultrasonic phased array leaky surface wave detection system, curved surface self-adaptive profiling and feedback, leaky surface wave signal excitation and collection and curved surface synthetic aperture focusing imaging. The technical effect of the application is that a motion device composed of an X / Y double-shaft guide rail and a four-shaft mechanical hand controls the phased array probe to generate leaky surface waves, so that adaptive detection imaging of surface or near-surface defects of complex curved surface parts can be realized in a non-contact and high-efficiency manner, the problem of poor coupling of traditional contact detection is solved, and high-precision curved surface synthetic aperture imaging is realized through phased array multi-element focusing imaging, so that the imaging quality is improved and the imaging rate is improved.

Description

Technical Field

[0001] This invention belongs to the field of nondestructive testing technology, specifically relating to a surface synthetic aperture imaging method based on ultrasonic phased array leak surface waves. Background Technology

[0002] During the manufacturing and service of mechanical equipment, defects such as cracks, surface pores, scratches, and fatigue cracks may occur on its metal surface. These defects can expand rapidly under harsh conditions such as high temperature and corrosion, which will seriously affect the mechanical properties and load-bearing capacity of the components. Therefore, the detection of metal surface defects is of great significance to ensuring its service safety.

[0003] Currently, ultrasonic testing is one of the most widely used non-destructive testing technologies for surface damage in mechanical equipment. With technological advancements, the types of testing methods are increasing, and testing efficiency is continuously improving. For example, a Chinese patent (CN107917958B, authorized on January 24, 2020) discloses a method for detecting micro-damage on material surfaces using opposing surface waves. This invention uses two surface wave probes and an inclined wedge to simultaneously excite surface wave signals with a phase difference of π from both ends of the specimen along opposite directions. The surface wave signals are then received in the middle of the specimen to characterize the degree of micro-damage. This method employs traditional contact ultrasonic testing, thus requiring extremely high coupling performance between the probe and the component. Furthermore, the surface quality of the sample, the coupling medium, and the clamping force of the testing device all affect the quality of the ultrasonic testing, resulting in limitations due to the contact-based nature of the method and low testing efficiency.

[0004] Leaking surface waves (SSWs) can be used to detect surface structural defects and evaluate material properties, offering advantages such as non-contact operation and high sensitivity. Compared to wedge-type SSW detection, it is less affected by the surface shape of the material and can be automated. For example, Chinese patent CN 111751448 B, published on July 7, 2023, discloses an ultrasonic synthetic aperture focusing imaging method for leaking surface waves. This invention uses a four-axis motion detection device to control a water immersion focusing probe to obliquely incident on the workpiece surface to generate leaking surface waves. Then, it collects the leaking surface wave pulse echo signals and finally performs synthetic aperture focusing imaging on the pulse echo signals to achieve defect identification. The technical advantage of this method is that it can achieve non-contact and efficient imaging of surface or near-surface defects of parts, improving detection efficiency and imaging resolution. However, the above detection methods are only applicable to damage detection of planar workpieces. When the surface of the workpiece to be inspected is a complex curved surface, such as a curved workpiece with different curvature cross-sectional geometric features, this method cannot successfully complete the detection of surface damage defects, and its automation level is not high.

[0005] Furthermore, current methods primarily utilize single-crystal transducers to generate surface leakage waves, resulting in insufficient detection efficiency and accuracy. Ultrasonic phased arrays, employing multi-element focusing imaging, offer superior defect characterization capabilities and higher detection accuracy. Moreover, for complex curved surfaces, ultrasonic phased array flexible probes or curved surface array probes are typically used. These probes employ contact-based detection, leading to unstable coupling conditions and low detection efficiency. In contrast, water immersion ultrasonic phased array testing offers superior coupling, is suitable for complex curved surfaces with varying curvature, and enables rapid automated scanning, making it widely used in industry.

[0006] Therefore, to solve the above problems, it is urgent to design a surface synthetic aperture imaging method based on ultrasonic phased array leaky surface waves to achieve high-efficiency, high-resolution imaging detection of complex curved surface parts. The method involves synchronously combining the motion control of an X / Y dual-axis guide rail and a four-axis manipulator to achieve contour mapping of the workpiece surface using a water-immersed phased array probe, and feeding the contour results back to a computer. Then, by adjusting the posture of the four-axis manipulator, the phased array probe is obliquely incident on the workpiece surface to generate leaky surface waves, and the focal point is moved sequentially along the surface contour to excite and acquire the leaky surface wave pulse signal. Finally, synthetic aperture imaging is performed on the leaky surface wave signal. The technical advantage of this invention is that by controlling the phased array probe with a motion device consisting of an X / Y dual-axis guide rail and a four-axis manipulator, it can achieve non-contact, high-efficiency adaptive detection and imaging of surface or near-surface defects of complex curved surface parts, solving the problem of poor coupling in traditional contact detection. Furthermore, by using phased array multi-element focusing imaging to achieve high-precision synthetic aperture imaging of curved surfaces, it improves both imaging quality and imaging speed. This paper presents an effective non-destructive testing method for evaluating the surface quality of metal components with complex curved shapes. Summary of the Invention

[0007] To address the aforementioned problems, this invention discloses a surface synthetic aperture imaging method for curved surfaces based on ultrasonic phased array leaky surface waves. By constructing a water-immersion ultrasonic phased array automated inspection system, high-resolution, rapid ultrasonic synthetic aperture imaging of curved metal parts with different curvature cross-sectional geometric features can be achieved. The key feature of this invention is that, firstly, a water-immersion phased array probe is used to contour the workpiece surface via synchronous combined motion control of an X / Y dual-axis guide rail and a four-axis manipulator, and the contouring result is fed back to a computer. Then, the pose of the four-axis manipulator is adjusted to control the phased array probe to obliquely incident on the workpiece surface, generating leaky surface waves. The focal point is then moved sequentially along the surface contour to excite and acquire the leaky surface wave pulse signal. Finally, synthetic aperture focusing imaging is performed on the leaky surface wave signal to identify defects on the curved workpiece surface. This method solves the problem of poor coupling in traditional wedge-type contact detection and achieves high-precision synthetic aperture imaging of curved surfaces through phased array multi-element focusing imaging, improving both imaging quality and imaging speed.

[0008] A surface synthetic aperture imaging method based on surface waves leaking from an ultrasonic phased array, characterized by comprising the following steps:

[0009] Step 1: Constructing a water-immersion ultrasonic phased array surface wave detection system: The system includes a motion control system and an ultrasonic phased array detection system; the motion control system includes a motion control device, a water-immersion ultrasonic detection device, an X / Y dual-axis guide rail, and a four-axis robot; the ultrasonic phased array detection system includes a phased array probe, a phased array detector, and an industrial computer; the workpiece to be tested is placed on the detection stage, and according to the different surface shapes of the workpiece, the motion control device drives the ultrasonic phased array probe to complete different scanning trajectories to achieve damage detection through synchronous combined motion control of the X / Y dual-axis guide rail and the four-axis robot.

[0010] Step 2: Ultrasonic Phased Array Surface Adaptive Contouring and Feedback: The X / Y dual-axis guide rails are moved to position the phased array probe at a suitable location directly above one side of the workpiece end, serving as the initial position. The Y-axis stepper motor is driven to rotate the ball screw, causing a four-axis robotic arm connected to the motion slider to hold the phased array probe and move along the Y direction in steps of Δy. Different positions are scanned sequentially, and the scanned positions are numbered, with the initial detection position marked as 1 and the final position as M. At each detection position, the earliest set of waveforms is extracted using interface wave detection, and the transit time t in the nth set of A-scan data is determined. n The corresponding shortest distance d from the array element to the surface of the workpiece under test n Then we have: With array element center c n With the center of the circle, d n Draw a circle Φ with radius Φ n Then the circle Φ n Tangent to the surface being measured at point q n That is, the surface curve of the workpiece being measured is tangent to all circles; for a probe with a total number of array elements of I, a total of I-1 tangent points can be obtained. By fitting the tangent points, the surface shape corresponding to the scanning range of the detection position point can be obtained; repeat the above steps until the Mth group of scanning is completed; fit the scanning data results of different position areas to obtain the surface curvature and contour shape of the workpiece being measured, and feed the workpiece surface contour information back to the computer. Adjust the pose of the four-axis manipulator through the motion control device to obtain the scanning motion trajectory of the phased array probe along the surface of the workpiece being measured;

[0011] Step 3: Excitation and Acquisition of Surface Wave Signals: Place the workpiece under test on the testing platform parallel to the X-axis guide rail along the generatrix of the acoustic wave incident point. The detection trajectory is a rotational movement within the plane formed by the Y-axis and Z-axis along the contour scanning point trajectory established in Step 2, while always maintaining the scanning center line of the phased array probe perpendicular to the tangent direction of the surface at the incident point. Based on the acoustic characteristics of the workpiece under test and water, determine the Rayleigh angle during water immersion testing using Snell's Law. C w Let C be the speed of longitudinal waves propagating in water. g The surface wave propagation velocity of the workpiece being measured; controlling the four-axis robot to make the water immersion phased array probe move at an angle greater than Rayleigh angle α. R An incident angle α is obliquely incident on the workpiece surface, generating a leaky surface wave along the workpiece surface. The incident angle α is the angle between the scanning center line of the phased array probe and the normal to the incident point of the workpiece. The underwater acoustic distance h of the phased array probe is adjusted by a four-axis robot, and the sound beam is focused onto a point on the surface of the workpiece by delaying the excitation pulses of each element of the phased array probe, thus controlling the focusing error. The water immersion phased array probe is moved along the contour patterned in step two by a motion control device that synchronizes the X / Y dual-axis guide rail and the four-axis manipulator. It rotates at equal arc length intervals of Δl on the workpiece surface. The scanning positions of the phased array probe are numbered sequentially, with the initial detection position marked as 1 and the final position as N. At each scanning position, the phased array detector excites the water immersion phased array probe to generate an ultrasonic pulse signal and collects the surface wave pulse echo signal. The collected echo signal is stored as S(j) and transmitted to the computer, where j is the scanning position number.

[0012] Step 4: Perform surface synthetic aperture focusing imaging on the leaky surface wave pulse echo signal acquired in Step 3 to achieve imaging of surface or near-surface defects of the workpiece.

[0013] The surface synthetic aperture imaging method based on ultrasonic phased array leak surface waves, wherein step four of the leak surface wave surface synthetic aperture focusing imaging includes the following steps:

[0014] Step 1: Divide the imaging area into equally spaced grids, and focus the workpiece surface D on the surface being measured. j (x j y j If the secondary sound source generated diffuses at a certain angle θ, then the number of effective detection positions for the target imaging point A participating in the focusing of the surface wave synthesis aperture is k.

[0015] Step 2: Calculate the distance r from the focal point to the target imaging point A(a, b) of the phased array leaky surface wave generated at each scanning position on the surface of the workpiece under test. j , Where -k / 2≤j≤k / 2;

[0016] Step 3: The total vertical distance R0 from the probe directly opposite point A to the target imaging point A is R0 = F + (ax) j ), calculate the total distance R of the sound beam propagating from the water immersion phased array probe to the target imaging point A on the surface of the workpiece being measured. j =F+r j , where F is the focal length of the water immersion phased array probe;

[0017] Step 4: Repeat steps 2 to 3 until j = k / 2;

[0018] Step 5: The vertical distance and propagation time of the sound beam from the water immersion phased array probe directly opposite point A to the target imaging point A on the surface of the workpiece being measured. Based on the vertical distance propagation time, calculate the relative delay time at each scanning position:

[0019] Step 6: Extract the amplitude of the surface wave pulse echo signal collected at each scanning position point along the contour direction of the workpiece surface in the YZ plane, and assign it to S. j (l A ±j·Δl,t0±τ j The average amplitude of the acquired surface wave pulse echo signals was calculated by superimposing the time delay values, resulting in the phased array surface wave surface synthetic aperture imaging signal: Assign the signal sound pressure to A(a, b).

[0020] Because the present invention adopts the above technical solutions, compared with the prior art, the beneficial effects of this application are as follows:

[0021] 1. Introducing a motion control system consisting of a synchronous combination of X / Y dual-axis guide rails and a four-axis robot into the inspection of curved workpieces offers advantages such as high flexibility, low cost, and high precision, enabling efficient automated inspection.

[0022] 2. The application of ultrasonic phased array probe can realize the rapid extraction of surface contour information of curved workpieces, complete the surface contouring of the workpiece under test, and feed back to the motion control device to adjust the position of the robot arm, which can realize the rapid and automated scanning of surface defects of complex curved workpieces.

[0023] 3. The leak surface wave is generated by the ultrasonic phased array probe. The multi-element focusing has better defect characterization ability and higher detection accuracy. Moreover, the leak surface wave has the advantages of non-contact and high sensitivity, which can avoid the problem of poor coupling of contact detection. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the water immersion ultrasonic phased array detection device disclosed in this invention;

[0026] Figure 2 This is a schematic diagram of the adaptive contouring of the phased array surface disclosed in this invention;

[0027] Figure 3 This is a schematic diagram of surface wave propagation in a phased array leak disclosed in this invention;

[0028] Figure 4 This is a schematic diagram of the synthetic aperture imaging of the surface wave curve of the phased array leak disclosed in this invention;

[0029] Figure 5 This is a schematic diagram of the detection method disclosed in this invention;

[0030] Figure 6 This is a schematic diagram of the imaging effect of the detection method disclosed in this invention;

[0031] Figure Labels

[0032] 1. Motion control device; 2. Working condition computer; 3. Phased array detector; 4. X-axis guide rail; 5. Y-axis guide rail; 6. Motion slider; 7. Stepper motor; 8. Ball screw; 9. Four-axis robot; 10. Phased array probe; 11. Water immersion ultrasonic testing device; 12. Water medium; 13. Curved surface workpiece to be tested; 14. Testing table; 15. Defect; 16. Scanning point trajectory; Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Step 1: Construct a water-immersion ultrasonic phased array leak surface wave detection system: See [link / reference] Figure 1The testing system of this invention comprises a motion control device, a water immersion ultrasonic testing device, an X / Y dual-axis guide rail, a four-axis manipulator, an IMASONIC 5MHz-64elts13007 1007 phased array probe, a Vantage 64LE phased array detector, and an industrial computer; a curved workpiece made of steel with four linearly distributed drill holes of 1mm diameter and a distance of 3mm between the holes, and dimensions of 180mm*120mm*60mm (length*width*height) is selected as the workpiece to be tested;

[0035] Step 2: Perform contouring on the curved workpiece: See Figure 2 The phased array probe is initially positioned directly above one side of the end of the workpiece by moving along the X / Y dual-axis guide rails. A Y-axis stepper motor drives a ball screw to rotate, causing a four-axis robotic arm connected to a motion slider to hold the phased array probe and move it along the Y direction in steps of Δy = 10mm. The probe is then scanned sequentially at different positions, and the scan positions are numbered, with the initial detection position marked as 1 and the final position as 12. At each detection position, the earliest waveform is extracted using interface wave detection, and the transit time t in the nth group of A-scan data is determined. n The corresponding shortest distance d from the array element to the surface of the workpiece being measured. n Then we have: With array element center c n With the center of the circle, d n Draw a circle Φ with radius Φ n Then the circle Φ n Tangent to the surface of the workpiece at point q n That is, the surface curve of the workpiece being measured is tangent to all circles; for a probe with a total of 64 array elements, a total of 63 tangent points can be obtained. By fitting the tangent points, the surface shape corresponding to the scanning range of the detection position point can be obtained; repeat the above steps until the 12th group of scans is completed; fit the scanning data results of different position areas to obtain the surface curvature and contour shape of the workpiece being measured, and feed the workpiece surface contour information back to the computer. By adjusting the pose of the robot arm through the motion control device, the scanning motion trajectory of the phased array probe along the surface of the workpiece being measured can be obtained;

[0036] Step 3: Excite and acquire surface wave signals from the surface of the curved workpiece: See [link / reference] Figure 3 The workpiece to be tested is placed on a testing platform parallel to the X-axis guide rail along the generatrix of the acoustic wave incident point. The testing trajectory is a rotational movement within the plane formed by the Y and Z axes along the contour scanning point trajectory defined in step two, while always maintaining the scanning center line of the phased array probe perpendicular to the tangent direction of the surface at the incident point. Based on the acoustic characteristics of the workpiece and water, the Rayleigh angle for water immersion testing is determined using Snell's law. Cw =1497m / s is the propagation speed of longitudinal waves in water, C g =2964 m / s is the surface wave propagation velocity of the steel workpiece being tested; the four-axis manipulator controls the water immersion phased array probe to propagate at an angle greater than Rayleigh angle α. R An incident angle α = 31° is used to incident the sound beam onto the workpiece surface at an angle, generating a surface wave along the surface. The incident angle α is the angle between the scanning center line of the phased array probe and the normal to the incident point on the workpiece. To ensure accurate focusing of the sound beam onto the workpiece surface, a four-axis manipulator is used to adjust the underwater acoustic distance h = 40mm of the phased array probe. By delaying the excitation pulses of each element of the phased array probe, the sound beam is focused onto a single point on the surface of the workpiece. The focal length F of the water-immersed phased array probe is 41mm, and focusing error is controlled. The water immersion phased array probe is moved along the contour outlined in step two by a motion control device through synchronous combined motion control of the X / Y dual-axis guide rail and the four-axis robot. It rotates at equal arc length intervals of Δl = 5mm on the workpiece surface. The scanning positions of the phased array probe are numbered sequentially, with the initial detection position marked as 1 and the end position as 40. At each scanning position, the phased array detector excites the water immersion phased array probe to generate ultrasonic pulse signals and collect surface wave pulse echo signals. The collected echo signals are stored as S(j) and transmitted to the computer, where j is the scanning position number.

[0037] Step 4: Perform synthetic aperture focusing imaging on the leaky surface wave pulse echo signal acquired in Step 2 to achieve imaging of surface or near-surface damage defects of complex curved workpieces.

[0038] The surface synthetic aperture imaging method based on ultrasonic phased array leak surface waves, wherein step four of the leak surface wave surface synthetic aperture focusing imaging includes the following steps:

[0039] Step 1, see Figure 4 The imaging area is divided into equally spaced grids, and the focal point D on the surface of the workpiece under test is... j (x j y j If the secondary sound source generated diffuses at a certain angle θ, then the number of effective detection positions for the target imaging point A participating in the focusing of the surface wave synthesis aperture is k.

[0040] Step 2: Calculate the distance r from the focal point to the target imaging point A(a, b) of the phased array leaky surface wave generated at each scanning position on the surface of the workpiece under test. j , Where -k / 2≤j≤k / 2;

[0041] Step 3: The total vertical distance R0 from the probe directly opposite point A to the target imaging point A is R0 = F + (ax) j), calculate the total distance R of the sound beam propagating from the water immersion phased array probe to the target imaging point A on the surface of the workpiece being measured. j =F+r j , where F is the focal length of the water immersion phased array probe;

[0042] Step 4: Repeat steps 2 to 3 until j = k / 2;

[0043] Step 5: The vertical distance and propagation time of the sound beam from the water immersion phased array probe directly opposite point A to the target imaging point A on the surface of the workpiece being measured. Based on the vertical distance propagation time, calculate the relative delay time at each scanning position:

[0044] Step 6: Extract the amplitude of the surface wave pulse echo signal collected at each scanning position point along the contour direction of the workpiece surface in the YZ plane, and assign it to S. j (l A ±j·Δl,t0±τ j The average amplitude of the acquired surface wave pulse echo signals was calculated by superimposing the time delay values, resulting in the phased array surface wave surface synthetic aperture imaging signal: Assign the signal sound pressure to A(a, b).

[0045] Figure 6 The diagram shows the imaging effect of the ultrasonic phased array leak surface wave surface synthetic aperture method of the present invention. It can be seen that the method can accurately identify the surface and near-surface defect shapes of complex curved workpieces in the image, with high imaging resolution and effectively reducing the impact of noise on imaging.

[0046] The above is a detailed description of the present invention. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A surface synthetic aperture imaging method based on surface waves leaking from an ultrasonic phased array, characterized in that, Includes the following steps: Step 1: Constructing a water-immersion ultrasonic phased array surface wave detection system: The system includes a motion control system and an ultrasonic phased array detection system; the motion control system includes a motion control device, a water-immersion ultrasonic detection device, an X / Y dual-axis guide rail, and a four-axis robot; the ultrasonic phased array detection system includes a phased array probe, a phased array detector, and an industrial computer; the workpiece to be tested is placed on the detection table; according to the different surface shapes of the workpiece, the motion control device drives the ultrasonic phased array probe to complete different scanning trajectories to achieve damage detection through synchronous combined motion control of the X / Y dual-axis guide rail and the four-axis robot. Step 2, Adaptive Contouring and Feedback on Curved Surfaces: The phased array probe is initially positioned directly above one side of the end of the workpiece by moving the X / Y dual-axis guide rails. The Y-axis stepper motor drives the ball screw to rotate, causing the four-axis robotic arm connected to the motion slider to hold the phased array probe and move along the Y direction in steps of Δy, sequentially scanning and imaging at different positions. The scanning positions are numbered, with the initial detection position marked as 1 and the final position as M. At each detection position, the earliest set of waveforms is extracted using interface wave detection, and the transit time in the nth set of A-scan data is determined. Corresponding to the shortest distance from the array element to the surface of the workpiece being measured. Then we have: With the array element as the center With the center of the circle, Draw a circle with radius 1. Then the circle has Tangent to the surface being measured at the point That is, the surface curve of the workpiece being measured is tangent to all circles; for a probe with a total number of array elements of I, a total of I-1 tangent points can be obtained. By fitting the tangent points, the surface shape corresponding to the scanning range of the detection position point can be obtained; repeat the above steps until the Mth group of scanning is completed; fit the scanning data results of different position areas to obtain the surface curvature and contour shape of the workpiece being measured, and feed the workpiece surface contour information back to the computer. Adjust the pose of the four-axis manipulator through the motion control device to obtain the scanning motion trajectory of the phased array probe along the surface of the workpiece being measured; Step 3: Excitation and Acquisition of Surface Wave Signals: Place the workpiece under test on the testing platform parallel to the X-axis guide rail along the generatrix of the acoustic wave incident point. The detection trajectory is a rotational movement within the plane formed by the Y-axis and Z-axis along the contour scanning point trajectory established in Step 2, while always maintaining the phased array probe scanning center line perpendicular to the surface tangent direction at the incident point. The Rayleigh angle during water immersion testing is determined using Snell's law. , , The speed of longitudinal waves in water. To measure the surface wave propagation velocity of the workpiece, a four-axis robot is controlled to make the water immersion phased array probe move at an angle greater than Rayleigh's angle. An incident angle α is obliquely incident on the workpiece surface, generating a surface wave along the workpiece surface. The incident angle α is the angle between the scanning center line of the phased array probe and the normal to the incident point of the workpiece. The underwater acoustic distance h of the phased array probe is adjusted by a four-axis robot, and the sound beam is focused onto a point on the surface of the workpiece by delaying the excitation pulses of each element of the phased array probe, thus controlling the focusing error. Where F is the focal length of the water immersion phased array probe; the water immersion phased array probe moves along the contour described in step two by the synchronous combined motion control of the X / Y dual-axis guide rail and the four-axis manipulator through the motion control device, and rotates at equal arc length intervals of Δl on the workpiece surface, and the scanning positions of the phased array probe are numbered sequentially, with the initial detection position marked as 1 and the end position as N; at each scanning position, the water immersion phased array probe is excited by the phased array detector to generate ultrasonic pulse signals and collect surface wave pulse echo signals, and the collected echo signals are stored as S(j) and transmitted to the computer, where j is the scanning position number; Step 4: Perform surface synthetic aperture focusing imaging on the leaky surface wave pulse echo signal acquired in Step 3 to achieve imaging of surface or near-surface defects of the workpiece. This includes the following steps: Step 1: Divide the imaging area into equally spaced grids, and focus the points on the surface of the workpiece being measured. If the generated secondary sound source diffuses at a certain angle θ, then the number of effective detection positions for the target imaging point A participating in the focusing of the surface wave synthesis aperture is k; Step 2: Calculate the propagation of the phased array leaky surface wave generated at each scanning position point from the focal point to the target imaging point on the surface of the workpiece under test. distance , ,in ; Step 3: The total vertical distance of the sound beam from the probe directly opposite point A to the target imaging point A. Calculate the total distance of the sound beam propagating from the water immersion phased array probe to the target imaging point A on the surface of the workpiece being measured. ; Step 4: Repeat steps 2 to 3 until j = k / 2; Step 5: The vertical distance and propagation time of the sound beam from the water immersion phased array probe directly opposite point A to the target imaging point A on the surface of the workpiece being measured. Using the vertical distance propagation time as a benchmark, calculate the relative delay time at each scanning position: ; Step 6: Extract the amplitude of the surface wave pulse echo signal collected at each scanning position point along the contour direction of the workpiece surface in the YZ plane, and assign it to... The average amplitude of the acquired surface wave pulse echo signals was calculated by superimposing the time delay values, resulting in the phased array surface wave surface synthetic aperture imaging signal: Assigning the signal sound pressure level to .

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