A method and system for virtual synthesis of omnidirectional ultrasound for complex profile ultrasonic testing

Abstract

The application provides a complex surface ultrasonic detection method and system for synthesizing virtual omnidirectional ultrasonic waves. The method comprises the following steps: synthesizing a virtual sound beam with full directivity through a focused ultrasonic probe, and collecting ultrasonic echo signals of a complex surface through the virtual sound beam under the condition of stable acoustic coupling; reconstructing the surface profile of the complex surface according to the ultrasonic echo signals; calculating the relative position relationship between the focal point of the virtual sound beam and the surface profile to select an imaging algorithm related to sound line tracing; predicting the propagation time of the ultrasonic signal through the complex surface to reach the imaging point by using the selected imaging algorithm, and then outputting a high-resolution focused display image of the internal defects of the complex surface. The application is suitable for the scene where the profile information of the complex surface is unknown. The virtual omnidirectional sound field is used for scanning, and the post-processing algorithm is used to accurately realize the surface real profile reconstruction and internal defect imaging, so that the full-depth synchronous focusing imaging in the complex surface coupling scene is realized.

Description

Technical Field

[0001] The present application relates to the field of ultrasonic detection of complex surfaces, and more specifically, to a method and system for ultrasonic detection of complex surfaces using virtual synthetic omnidirectional ultrasound. Background Art

[0002] Complex curved structures are widely used in key industrial sectors such as aerospace, energy, rail transportation, and pressure vessels. During the manufacturing process, these structures are prone to voids and cracks. Furthermore, their service environments often face extreme conditions, such as alternating stress, high temperature, and high pressure. Under these harsh conditions, material aging and defect propagation are accelerated, significantly weakening the performance of the structure. Therefore, developing efficient and accurate nondestructive testing technologies to accurately detect internal defects in complex curved structures is of great engineering value for ensuring the safe service performance of key components, extending product life cycles, improving manufacturing processes, and preventing potential failure risks.

[0003] Ultrasonic testing has always been an important method for detecting internal defects in engineering materials due to its advantages such as wide applicability, high resolution and accurate defect location. However, complex surfaces bring challenges to ultrasonic testing, such as difficulty in acoustic coupling, difficult conformal scanning control, and difficult ultrasonic incident reception.

[0004] In existing technology, automated scanning of complex surfaces is commonly performed using a multi-degree-of-freedom robotic arm holding an ultrasonic probe. This approach uses computer programming to automatically plan a conformal scanning path based on the surface contour of the structure being inspected, while also adjusting the transducer's position at each scanning point in real time to ensure vertical ultrasonic coverage of the entire complex surface. Furthermore, a pressure sensor can be installed at the end of the robotic arm to assist in dynamically adjusting the probe's orientation and distance relative to the structure being inspected. For real structures, design drawings may be missing, or the actual geometry may deviate due to manufacturing errors and deformation during service. In such cases, a laser profilometer is often used as an auxiliary tool to reconstruct the unknown surface contour. Laser ultrasonic technology enables completely non-contact scanning along a pre-set trajectory on curved surfaces. The orientation of the vibrometer, which receives the laser-excited ultrasonic waves, must be adjusted in real time based on the contour of the test surface to maximize the capture of the laser signal reflected from the surface and achieve the optimal signal-to-noise ratio. After acquiring complete ultrasonic data, synthetic aperture focusing or total focusing algorithms can be used to achieve ultrasonic imaging of internal defects.

[0005] However, this virtual source imaging technology requires the pre-determination of the relative position of the focus and the inspected surface, and the contour-matching scanning control of the inspected object contour is difficult, requiring high-precision coordinated control of the robotic arm and the ultrasonic acquisition system.

[0006] Therefore, there is a need for an ultrasonic detection solution that can synchronously realize ultrasonic detection of complex surfaces with unknown contours. Summary of the Invention

[0007] This application provides a method and system for ultrasonic detection of complex surfaces using virtual synthetic omnidirectional ultrasound. The specific solution is as follows:

[0008] A complex surface ultrasonic detection method using virtual synthetic omnidirectional ultrasound, comprising the following steps:

[0009] A virtual acoustic beam with omnidirectionality is synthesized by a preset focused ultrasonic probe, and ultrasonic echo signals of surface and internal defects of complex surfaces are collected by the virtual acoustic beam under the condition of stable acoustic coupling;

[0010] reconstructing the surface contour of the complex surface according to the ultrasonic echo signal;

[0011] calculating a relative positional relationship between the focus of the virtual acoustic beam and the surface contour, and selecting an imaging algorithm for acoustic ray tracing based on the relative positional relationship;

[0012] The selected imaging algorithm is used to predict the propagation time of the ultrasonic signal through the complex surface to reach the imaging point, and then a high-resolution focused display image of the internal defects of the complex surface is output.

[0013] In some specific embodiments, the imaging algorithm is based on delaying and superimposing the original time-domain ultrasonic echo signal, and calculates the propagation time of the sound line from the focused ultrasonic probe through the complex acoustic impedance mismatch surface to the imaging point, thereby generating a high-resolution full-depth synchronous focused image that focuses on the internal defects of the complex surface.

[0014] In some specific embodiments, selecting an imaging algorithm for acoustic ray tracking based on the relative position relationship specifically includes:

[0015] When the relative position relationship indicates that the focus is located on the complex surface, selecting a virtual source synthetic aperture focusing imaging algorithm based on Fermat's theorem;

[0016] When the relative position relationship indicates that the focus is located below the complex surface, a virtual source synthetic aperture focusing imaging algorithm based on Snell's law is selected.

[0017] In some specific embodiments, by rotating a focused ultrasound probe of a single small-opening-angle acoustic beam, small-opening-angle acoustic beams with the same beam shape but different directions are superimposed to form a large-opening-angle virtual acoustic beam with omnidirectionality;

[0018] Alternatively, multiple focused ultrasound probes with fixed directions are arranged to realize a virtual sound beam with omnidirectionality by synchronously or step-by-step collecting ultrasound signals from different directions.

[0019] In some specific embodiments, during the process of reconstructing the surface contour, when the virtual acoustic beam scans the complex surface along a straight linear grid, the propagation distance of the surface echo incident and reflected along the surface normal direction is quantitatively corresponded with the target surface contour point with the help of the inverse boundary scattering transform, and abnormal surface points that appear during reconstruction are eliminated based on the quantitative correspondence.

[0020] In some specific embodiments, the quantitative correspondence expression is as follows:

[0021]

[0022] in, is the coordinate of the synthetic virtual beam focus in the scanning direction, is the physical focal length of the focusing probe used to synthesize the virtual sound beam, i.e., the rotation radius; and , is the speed of longitudinal waves in water, is the surface echo round trip time.

[0023] In some specific embodiments, the expression of the virtual source synthetic aperture focusing imaging algorithm based on Fermat's theorem is:

[0024]

[0025]

[0026] in, Represents the imaging point The echo signal amplitude at is the total number of scanning steps, For the The time domain signal amplitude collected in the step is recorded as follows, and the position of the corresponding virtual sound beam focus in the horizontal scanning direction is recorded as , It represents the propagation time of the sound line from the probe through the complex shape of the acoustic impedance mismatch surface to the imaging point. are the surface point coordinates for reconstructing the surface contour, is the number of discrete surface points, is the physical focal length of the focusing probe used to synthesize the virtual sound beam, i.e., the rotation radius. is the speed of longitudinal waves in water, is the longitudinal wave speed in the test block, and are weight coefficients respectively.

[0027] In some embodiments, the weight coefficient and The calculation expression is:

[0028]

[0029]

[0030] in, is a step function, is the angle between the incident surface point and the horizontal scanning direction determined by Fermat’s theorem, The vertical direction of the imaging point corresponds to the reconstructed surface point Axis coordinates, is the maximum imaging depth.

[0031] In some specific embodiments, the expression of the virtual source synthetic aperture focusing algorithm based on Snell's law is:

[0032]

[0033]

[0034] in, Represents the imaging point The echo signal amplitude at is the total number of scanning steps, For the The time domain signal amplitude collected in the step is recorded as follows, and the position of the corresponding virtual sound beam focus in the horizontal scanning direction is recorded as , It represents the propagation time of the sound line from the probe through the complex shape of the acoustic impedance mismatch surface to the imaging point. are the surface point coordinates for reconstructing the surface contour, is the number of discrete surface points, is the physical focal length of the focusing probe used to synthesize the virtual sound beam, i.e., the rotation radius. is the speed of longitudinal waves in water, is the longitudinal wave speed in the test block, and are weight coefficients respectively.

[0035] In some specific embodiments, based on a series of candidate surface points obtained by reconstruction , the structure makes the incident angle and refraction angle The objective function satisfies Snell's law;

[0036] By traversing all candidate points, the point where the objective function obtains the minimum value is selected as the true incident point;

[0037] After selecting the real incident point, the propagation paths of the sound wave in the two media are divided into: the path from the focused ultrasound probe to the surface incident point in water, and the path from the surface point to the imaging point in the complex surface;

[0038] The objective function The expression is:

[0039]

[0040] in, / are the angles between the incident sound ray and the negative / positive vector of the tangent line, / is the angle between the refracted sound ray and the negative / positive vector of the tangent line, is the speed of longitudinal waves in water, is the longitudinal wave speed in the test block.

[0041] In some embodiments, the focused ultrasound probe transmits and receives sound waves limited to a beam angle Within the defined narrow sector area;

[0042] The focused ultrasound probe is controlled to rotate with its curvature center as the center, so as not to exceed the beam angle. Angular step length From the initial position Clockwise rotation Second to the end position At each rotation position, the complex surface ultrasonic signal is collected in pulse-echo mode, and then the collected signals at each position are accumulated to synthesize a beam with an equivalent opening angle of Virtual sound beam.

[0043] A complex surface ultrasonic detection system using virtual synthetic omnidirectional ultrasound, comprising:

[0044] A scanning unit is used to synthesize a virtual acoustic beam with omnidirectionality through a preset focused ultrasonic probe, and to collect ultrasonic echo signals of surface and internal defects of complex surfaces through the virtual acoustic beam under the condition of stable acoustic coupling;

[0045] A contour reconstruction unit, configured to reconstruct a surface contour of a complex surface according to the ultrasonic echo signal;

[0046] a position unit, configured to calculate a relative positional relationship between the focus of the virtual acoustic beam and the surface contour, and select an imaging algorithm for acoustic ray tracing based on the relative positional relationship;

[0047] The output unit is used to use the selected imaging algorithm to predict the propagation time of the ultrasonic signal through the complex surface to reach the imaging point, and then output a high-resolution focused display image of the internal defects of the complex surface.

[0048] Beneficial effects: This application proposes a complex surface ultrasonic detection method and system using virtual synthetic omnidirectional ultrasound. For scenarios where the contour information of complex surfaces is unknown, the virtual omnidirectional sound field synthesized by a focused ultrasonic probe is used for scanning, and the true surface contour reconstruction and internal defect imaging are accurately achieved with the help of post-processing algorithms. There is no need to determine the relative position relationship between the virtual sound beam focus and the measured surface in advance. Different imaging algorithms are adaptively selected to achieve virtual source synthetic aperture focused imaging, and full-depth synchronous focused imaging is achieved in complex surface coupling scenarios, which provides a powerful means for the visual detection of complex surface defects and is of great value to improving the manufacturing quality and service safety of such components.

[0049] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0051] Figure 1 It is a flowchart of the application method;

[0052] Figure 2 This is an example diagram of the principle of the present application method;

[0053] Figure 3 It is a schematic diagram of generating an omnidirectional ultrasonic sound field by rotating a single focused probe;

[0054] Figure 4 This is a schematic diagram of the virtual source synthetic aperture focusing algorithm based on Fermat's theorem;

[0055] Figure 5 This is a schematic diagram of the virtual source synthetic aperture focusing algorithm based on Snell's law;

[0056] Figure 6 It is a schematic diagram of the incident and refraction process of ultrasound at a certain surface point when the virtual acoustic beam focus is below the sample surface;

[0057] Figure 7a It is the ultrasonic B-scan image after multi-angle data superposition when the virtual acoustic beam focus is located above the sample surface;

[0058] Figure 7b It is an ultrasonic B-scan image acquired at an incident angle of 90° when the virtual acoustic beam focus is located above the sample surface;

[0059] Figure 7c It is an ultrasonic B-scan image acquired at an incident angle of 75° when the virtual acoustic beam focus is located above the sample surface;

[0060] Figure 7d It is an ultrasonic B-scan image acquired at an incident angle of 105° when the virtual acoustic beam focus is located above the sample surface;

[0061] Figure 8 It is a comparison diagram between the reconstructed profile and the real profile when the virtual acoustic beam focus is located above the sample surface;

[0062] Figure 9a It is the synthetic aperture focusing imaging result obtained by taking the ultrasonic reconstruction profile as input when the virtual acoustic beam focus is located above the sample surface;

[0063] Figure 9b It is the synthetic aperture focusing imaging result obtained with the actual surface profile as input when the virtual acoustic beam focus is located above the sample surface;

[0064] Figure 10a It is an ultrasonic B-scan image after multi-angle data superposition when the virtual acoustic beam focus is located between the concave and convex surfaces;

[0065] Figure 10b It is an ultrasonic B-scan image acquired at an incident angle of 90° when the virtual acoustic beam focus is located between the concave and convex surfaces;

[0066] Figure 10c It is an ultrasonic B-scan image acquired at an incident angle of 75° when the virtual acoustic beam focus is located between the concave and convex surfaces;

[0067] Figure 10d It is an ultrasound B-scan image acquired at an incident angle of 105° when the virtual acoustic beam focus is located between the concave and convex surfaces;

[0068] Figure 11 It is a comparison diagram between the reconstructed contour and the real contour when the virtual acoustic beam focus is located between the concave and convex surfaces;

[0069] Figure 12a It is the synthetic aperture focusing imaging result obtained by taking the ultrasound reconstruction contour as input when the virtual acoustic beam focus is located between the concave and convex surfaces;

[0070] Figure 12b It is the synthetic aperture focusing imaging result obtained by taking the actual surface contour as input when the virtual acoustic beam focus is located between the concave and convex surfaces;

[0071] Figure 13 It is a schematic diagram of the system modules of this application.

[0072] Reference numerals: 1 - scanning unit; 2 - contour reconstruction unit; 3 - position unit; 4 - output unit. DETAILED DESCRIPTION

[0073] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0074] This application proposes a complex surface ultrasonic detection method using virtual synthetic omnidirectional ultrasound. By using the virtual omnidirectional sound field generated by the focused ultrasonic probe, the reconstruction of the surface contour of the complex surface and the imaging of internal defects can be achieved under stable acoustic coupling conditions, thereby improving the ultrasonic receiving efficiency, eliminating the need for complex conformal scanning trajectory planning, and significantly reducing the difficulty of technical implementation. The flow chart of the method is shown in the attached figure. Figure 1 The principle example is shown in the attached Figure 2 The specific plan is as follows:

[0075] A complex surface ultrasonic detection method using virtual synthetic omnidirectional ultrasound, comprising the following steps:

[0076] 101. Synthesize a virtual acoustic beam with omnidirectionality by presetting a focused ultrasonic probe, and obtain ultrasonic echo signals of surface and internal defects of complex surfaces through the virtual acoustic beam under the condition of stable acoustic coupling;

[0077] 102. Reconstruct the surface contour of complex surfaces based on ultrasonic echo signals;

[0078] 103. Calculate the relative positional relationship between the focus of the virtual acoustic beam and the surface contour, and select an imaging algorithm for acoustic ray tracing based on the relative positional relationship;

[0079] 104. The selected imaging algorithm is used to predict the propagation time of the ultrasonic signal through the complex surface to reach the imaging point, and then a high-resolution focused display image of the internal defects of the complex surface is output.

[0080] In the prior art, obtaining the surface contour of the inspected structure and performing ultrasonic imaging of internal defects have always been the focus of research. Based on the reconstruction of the unknown contour of the complex surface, this application realizes full-depth synchronous focusing imaging in the complex surface coupling scenario, which provides a powerful means for the visual detection of complex surface defects and is of great value to improving the manufacturing quality and service safety of such components. Stable acoustic coupling is achieved under liquid immersion conditions, and the virtual omnidirectional sound field synthesized by the ultrasonic probe with a small beam angle is used to linearly scan and collect the echo signals of the complex surface components. The unknown surface contour is reconstructed by the inverse boundary scattering transform and the nearest neighbor search algorithm. The ultrasonic signal is then post-processed again, the relative distance between the rotation center and the surface contour is calculated, and two different virtual source synthetic aperture focusing imaging technologies are applied to the corresponding imaging area to finally output the full-focus imaging results of internal defects.

[0081] In some embodiments, liquid immersion or flexible acoustically transparent materials are used to stabilize the acoustic coupling conditions. This application uses liquid immersion as an example for illustration.

[0082] In some embodiments, the focused ultrasound probe is selected from one or more focused ultrasound probes. The spherical focused ultrasound probe is made of a spherical piezoelectric ceramic piece, and its sound wave transmission and reception are limited to a beam angle. A limited open-angle sound beam is naturally focused within the defined narrow sector area, i.e., at the center of curvature of the probe. When a spherical focused ultrasound probe with a small beam angle is arranged, the small open-angle sound beams with the same beam shape but different directions are superimposed into a large open-angle virtual sound beam with omnidirectionality by rotating the focused ultrasound probe with a single small open-angle sound beam; or, multiple focused ultrasound probes with fixed directions are arranged, and a virtual sound beam with omnidirectionality is achieved by synchronously or step-by-step collecting ultrasound signals from different directions. When two or more focused ultrasound probes with fixed directions are arranged on the same scanning platform, full coverage similar to that of a rotating probe is achieved by synchronously or step-by-step collecting ultrasound signals from different directions;

[0083] Furthermore, a virtual omnidirectional ultrasound is synthesized for rotating a single small beam angle spherical focused ultrasound probe. By rotating the probe around the center of curvature, the single focused probe can maintain equivalent sensitivity in a wider range of azimuths. The emission and reception of sound waves from the focused ultrasound probe are limited to the beam angle. The focused ultrasound probe is controlled to rotate with its curvature center as the center within the narrow sector area defined by the beam angle. Angular step length From the initial position Clockwise rotation Second to the end position At each rotation position, the complex surface ultrasonic signal is collected in pulse-echo mode, and then the collected signals at each position are accumulated to synthesize a beam with an equivalent opening angle of At this time, the center of curvature, that is, the center of rotation, is defined as the virtual beam focus. Since the virtual large-angle beam is composed of multiple small-angle beams with the same beam shape but different directions, arrive In all directions of coverage, the transmit and receive sensitivities remain consistent, achieving an approximately omnidirectional sound beam distribution. The increased equivalent beam opening angle not only enhances the echo response from complex curved surfaces and internal defects, but also enriches the ultrasonic data required for subsequent surface contour reconstruction and image reconstruction. Even if the surface curvature of the inspected part varies, the probe only needs to rotate repeatedly while scanning along a straight trajectory, without the need to obtain the surface contour in advance, to complete omnidirectional sound field coverage of complex structures. The schematic diagram of generating an omnidirectional ultrasonic sound field by rotating a single-focus probe is shown in the attached figure. Figure 3 shown.

[0084] In step 102, echo signals from a complex surface component are collected through linear scanning, and the unknown surface profile is reconstructed using an inverse boundary scattering transform (IBST) and a nearest neighbor search algorithm. In some embodiments, during the surface profile reconstruction process, as a virtual acoustic beam scans the complex surface along a linear grid, the propagation distance of the surface echo incident and reflected along the surface normal is quantitatively correlated with the target surface profile points using the inverse boundary scattering transform (IBST). This quantitative correlation is then used to eliminate anomalous surface points that appear during reconstruction.

[0085] In some specific embodiments, the quantitative correspondence expression is as follows:

[0086]

[0087] in, is the coordinate of the synthetic virtual beam focus in the scanning direction, is the physical focal length of the focusing probe used to synthesize the virtual sound beam, i.e., the rotation radius; and , is the speed of longitudinal waves in water, is the surface echo round trip time.

[0088] Regardless of whether the virtual beam focus is above or below the surface, the above quantitative correspondence expression always holds true. right The rate of change of the target surface contour point Therefore, when When a small disturbance occurs, Fluctuations will be amplified, which is especially common in actual working conditions with rough surfaces or strong echo noise. In order to automatically remove abnormal surface points that appear during reconstruction, a nearest neighbor search algorithm is introduced. The specific steps are as follows:

[0089] Step 1: Reconstruct formula (1) to obtain The surface discrete points are divided into two subsets, the set : Points that have been determined to be true surface contours (initially empty); set : Other points to be judged;

[0090] Step 2: From the collection Manually select a point ( ) as the initial surface point;

[0091] Step 3: Set it as the current point and calculate its difference from all points in set B that satisfy point The Euclidean distance between

[0092] Step 4: Select the candidate points from the above points. Recent , determine it as the new current point, and the original current point Transfer from set B to set ;

[0093] Step 5: Repeat steps 3 and 4 until all the elements in set B satisfy All points are transferred to .

[0094] After the iteration is completed, The local weighted scattered point smoothing method is used for smoothing to obtain the reconstructed true surface contour point set.

[0095] In some specific embodiments, the imaging algorithm is based on delay-sum post-processing of the original time-domain ultrasonic echo signal, and calculates the propagation time of the sound line from the focused ultrasonic probe through the complex acoustic impedance mismatch surface to the imaging point, thereby generating a fully focused imaging image reflecting the internal defects of the complex surface. Specifically, based on the reconstructed surface contour, along The positive direction of the axis divides the imaging area into discrete areas. Compare the reconstructed contour with the virtual beam focus at The coordinate difference in the axial direction can clarify the spatial relative positions of the two, thereby adaptively selecting the matching virtual source synthetic aperture focusing imaging algorithm.

[0096] Furthermore, selecting an imaging algorithm based on the relative position relationship specifically includes: when the relative position relationship indicates that the focus is located above a complex surface, selecting a virtual source synthetic aperture focusing imaging algorithm based on Fermat's theorem; when the relative position relationship indicates that the focus is located below the complex surface, selecting a virtual source synthetic aperture focusing imaging algorithm based on Snell's law.

[0097] Virtual source synthetic aperture focusing imaging technology is to perform delay-sum post-processing on the acquired original time domain echo signal to generate a high-resolution fully focused image. Its expression is as follows:

[0098]

[0099] in, Represents the imaging point The echo signal amplitude at is the total number of scanning steps, For the The time domain signal amplitude collected in the step is recorded as follows, and the position of the corresponding virtual sound beam focus in the horizontal scanning direction is recorded as The key to synthetic aperture focusing imaging technology is to calculate the propagation time of the sound line from the probe through the complex shape of the acoustic impedance mismatch surface to the imaging point, which is expressed as .

[0100] The schematic diagram of the virtual source synthetic aperture focusing algorithm based on Fermat's theorem when the virtual acoustic beam focus is above the sample surface is shown in the attached figure. Figure 4 As shown in Figure 2, the expression of the virtual source synthetic aperture focusing imaging algorithm based on Fermat’s theorem is:

[0101]

[0102]

[0103] in, Represents the imaging point The echo signal amplitude at is the total number of scanning steps, For the The time domain signal amplitude collected in the step is recorded as follows, and the position of the corresponding virtual sound beam focus in the horizontal scanning direction is recorded as , It represents the propagation time of the sound line from the probe through the complex shape of the acoustic impedance mismatch surface to the imaging point. are the surface point coordinates for reconstructing the surface contour, is the number of discrete surface points, is the physical focal length of the focusing probe used to synthesize the virtual sound beam, i.e., the rotation radius. is the speed of longitudinal waves in water, is the longitudinal wave speed in the test block, and The weight coefficients are introduced to select the sound beam that participates in delay-sum imaging only when the incident sound ray direction falls within the beam angle coverage range and to compensate the signal amplitude of the imaging area at different depths. and .

[0104] In some embodiments, the weight coefficient and The calculation expression is:

[0105]

[0106]

[0107] in, is a step function, is the angle between the incident surface point and the horizontal scanning direction determined by Fermat’s theorem, The vertical direction of the imaging point corresponds to the reconstructed surface point Axis coordinates, is the maximum imaging depth.

[0108] The schematic diagram of the virtual source synthetic aperture focusing algorithm based on Snell's law when the virtual beam focus is below the sample surface is shown in the figure. Figure 5 As shown. Figure 6 The schematic diagram shows the incident and refraction process of ultrasound at a certain surface point when the virtual acoustic beam focus is located below the sample surface. A series of candidate surface points obtained based on reconstruction , the structure makes the incident angle and refraction angle An objective function that satisfies Snell's law is developed. By traversing all candidate points, the point that minimizes the objective function is selected as the true incident point. After selecting the true incident point, the propagation paths of the sound wave in the two media are divided into: the path from the focused ultrasound probe to the surface incident point in water, and the path from the surface point to the imaging point within the complex surface.

[0109] Objective function The expression is:

[0110]

[0111] in, / are the angles between the incident sound ray and the negative / positive vector of the tangent line, / is the angle between the refracted sound ray and the negative / positive vector of the tangent line, is the speed of longitudinal waves in water, is the longitudinal wave speed in the test block.

[0112] The expression of the virtual source synthetic aperture focusing algorithm based on Snell's law is:

[0113]

[0114]

[0115] in, Represents the imaging point The echo signal amplitude at is the total number of scanning steps, For the The time domain signal amplitude collected in the step is recorded as follows, and the position of the corresponding virtual sound beam focus in the horizontal scanning direction is recorded as , It represents the propagation time of the sound line from the probe through the complex shape of the acoustic impedance mismatch surface to the imaging point. are the surface point coordinates for reconstructing the surface contour, is the number of discrete surface points, is the physical focal length of the focusing probe used to synthesize the virtual sound beam, i.e., the rotation radius. is the speed of longitudinal waves in water, is the longitudinal wave speed in the test block, and are weight coefficients respectively.

[0116] For imaging defects inside complex surfaces, this application's solution eliminates the need for prior knowledge of the surface profile of the object being measured. Instead, it utilizes a virtual omnidirectional sound field synthesized by simple mechanical rotation of a small-beam angular spherical focused ultrasonic probe. Ultrasonic echo signals from complex surfaces are collected through linear scanning under liquid immersion conditions, and the true surface profile is reconstructed using the inverse boundary scattering transform and nearest neighbor search algorithm. Based on this profile, the ultrasonic signal is subjected to delay-sum post-processing imaging. Depending on whether the virtual beam focus is above or below the surface, a virtual source synthetic aperture focusing imaging algorithm based on Fermat's theorem and Snell's law is employed, ultimately achieving full-depth, synchronously focused, high-resolution imaging of the interior of complex surfaces.

[0117] In order to verify the feasibility of the method proposed in this application, the following experiments were conducted:

[0118] A 5 MHz focused ultrasound probe was used under immersion conditions to conduct ultrasonic testing on an acrylic sample with a concave-convex wavy surface. The sample had twelve transverse through holes with a radius of 1.5 mm at different depths, a surface curvature radius of 21.21 mm, and a maximum surface inclination angle of 45°. Two sets of virtual acoustic beam focus settings were used: one above the surface and the other between the concave and convex surfaces, to verify the feasibility and effectiveness of the proposed virtual source synthetic aperture focusing imaging algorithm.

[0119] When the virtual acoustic beam focus is above the surface, a virtual source synthetic aperture focusing imaging algorithm based on Fermat's theorem is employed. First, a focused ultrasound probe is fixed on a linear motion stage and can rotate around the focus within a physical focal radius of 15.6 mm. To achieve full coverage of the sample surface, the probe rotation angle is set between 45° and 135°, with 5° intervals, covering a total of 19 azimuths. Linear scanning is performed from left to right with evenly spaced 0.1 mm steps. The scan length is set to 190 mm, and a total of 1900 ultrasonic A-scan signals are acquired. The signal sampling frequency is 100 MHz, and the sampling duration is 60 μs. To improve the signal-to-noise ratio, each A-scan signal is first averaged over 30 repetitions and then bandpass filtered in the 1-8 MHz frequency range. The 1900 A-scan signals are then combined into a single B-scan image. The velocity of longitudinal waves in water is 1480 m / s, while the velocity of longitudinal waves in acrylic is 2680 m / s. The B-scan signals collected from each azimuth linear scan are summed up according to the position, and finally the B-scan signal of the sample with complete echo information in the omnidirectional sound field is obtained. Figure 7b 、 Figure 7c 、 Figure 7d As shown in the figure, in the ultrasound B-scan image collected at a single incident angle (such as 90°, 75°, and 105°), only some echoes of the local wavy surface and the internal transverse through-hole can be observed. However, after the B-scan image after multi-angle data superposition, as shown in the figure, Figure 7a As shown. Among them, α is the probe rotation angle, defined as the azimuth angle relative to the horizontal scanning direction x The counterclockwise angle of the axis. The echo signals of the wavy surface and the internal transverse through-holes can be fully presented. Moreover, when the virtual beam focus scans the concave area on the wavy specimen surface, the surface echo shows three folds, indicating that at a certain linear scanning position and when the virtual beam focus is above the specimen surface, up to three surface points can receive vertically incident ultrasound at the same time. The echoes of all internal transverse through-holes are shown as multiple curved long lines in the figure, indicating that each transverse through-hole is covered by ultrasound from multiple directions, and its echo signals can be fully captured. The above results verify that the virtual omnidirectional ultrasonic beam synthesized by probe rotation can significantly broaden the coverage of the unit focusing probe, providing rich ultrasonic data information for subsequent surface contour reconstruction and internal defect imaging. From Figure 7a The surface echo propagation delay is extracted and applied to the inverse boundary scattering transform and the nearest neighbor search algorithm to reconstruct the surface profile of the acrylic sample and compare it with the CAD model. The results are as follows: Figure 8 As shown in the figure, the final reconstructed surface profile is highly consistent with the actual sample surface, with an average absolute error of only 0.14 mm, which verifies the feasibility of using a virtual omnidirectional ultrasonic beam to reconstruct complex surfaces with high precision. The axis coordinates start at zero and are located below the reconstructed contour, so the entire imaging area is processed using the virtual source synthetic aperture focusing algorithm based on Fermat's theorem. Figure 9a and Figure 9b Synthetic aperture focusing (SAF) imaging results obtained using both ultrasound-reconstructed and actual surface profiles as input are presented. All images are amplitude-normalized. The actual locations of all internal SDHs are marked with white circles. In both cases, all SDHs were successfully detected, with their imaging results displaying distinct circular boundaries that closely coincide with the circular edges of their respective tops. Because SDHs scatter ultrasound in all directions, their location accuracy was quantified by measuring the difference between the straight-line distance from the maximum amplitude point in the SDH imaging result to the actual center and the SDH radius. Using the ultrasound-reconstructed surface profile for imaging, all SDHs were accurately imaged, with a maximum absolute error of 0.32 mm and an average absolute error of 0.18 mm. Using the actual surface profile for imaging, the maximum absolute error was 0.31 mm and the average absolute error was 0.14 mm. This demonstrates that the virtual source SAF algorithm based on Fermat's theorem significantly improves the imaging amplitude and location accuracy of internal defects, and that minor deviations between the ultrasound-reconstructed surface profile and the actual profile do not significantly affect the final image quality.

[0120] When the virtual beam focus is between the concave and convex surfaces, the virtual source synthetic aperture focusing imaging algorithm based on Fermat's theorem is used for the imaging area above the surface, and the virtual source synthetic aperture focusing imaging algorithm based on Snell's law is used for the imaging area below the surface. The other experimental settings are the same as the previous experiment. The experimental results are shown in Figure 2. Figure 10a 、 10b As shown in Figures 10c and 10d, after the B-scan images of 19 different probe orientations are superimposed, the echo signals of the surface and the SDH are clearly visible in the new image, while at a single angle, only the local surface and SDH echoes can be observed due to the limited coverage angle of the sound beam. α is the probe rotation angle, defined as the azimuth angle relative to the horizontal scanning direction x The B-scan image shows a continuous wave pattern on the specimen surface without any folding, indicating that only a single surface point is covered by the perpendicularly incident ultrasound at each linear scan position. These experimental results demonstrate that, regardless of the relative distance between the virtual acoustic focus and the specimen surface, the omnidirectional ultrasound beam synthesized by probe rotation significantly enhances the effective coverage of a single focused probe. Figure 11The comparison results between the ultrasound reconstructed contour and the CAD model are shown: the reconstructed contour is highly consistent with the actual sample surface in terms of geometry, with an average absolute error of only 0.12 mm. When the ordinate of the reconstructed contour is greater than zero, the virtual source synthetic aperture focusing imaging algorithm based on Fermat's theorem is used for imaging in that area; while in areas where the ordinate is less than or equal to zero, the virtual source synthetic aperture focusing imaging algorithm based on Snell's law is used. The imaging results based on the ultrasound reconstructed contour and the CAD contour are shown in Figure 2. Figure 12a and 12b As shown, all SDHs are imaged in the correct locations, exhibiting a more complete circular outline that is highly consistent with the actual geometry, while also achieving slightly improved positioning accuracy. When using ultrasound to reconstruct the outline, the maximum absolute error for all SDH images is 0.25 mm, with an average absolute error of 0.15 mm. When using the actual outline, the maximum absolute error is 0.28 mm, with an average absolute error of 0.14 mm.

[0121] Based on the above results, it can be seen that the method of the present invention is feasible and practical.

[0122] This application provides a complex surface ultrasonic detection system using virtual synthetic omnidirectional ultrasound, which systematizes the above method. The module diagram of the system is shown in the attached figure. Figure 13 The specific plan is as follows:

[0123] A complex surface ultrasonic detection system using virtual synthetic omnidirectional ultrasound, comprising:

[0124] Scanning unit 1 is used to synthesize a virtual acoustic beam with omnidirectionality through a preset focused ultrasonic probe, and to collect ultrasonic echo signals of surface and internal defects of complex surfaces through the virtual acoustic beam under the condition of stable acoustic coupling;

[0125] A contour reconstruction unit 2 is used to reconstruct the surface contour of the complex surface according to the ultrasonic echo signal;

[0126] Position unit 3, used for calculating the relative position relationship between the focus of the virtual acoustic beam and the surface contour, and selecting an imaging algorithm for acoustic ray tracing based on the relative position relationship;

[0127] The output unit 4 is used to predict the propagation time of the ultrasonic signal through the complex surface to reach the imaging point using the selected imaging algorithm, and then output a high-resolution focused display image of the internal defects of the complex surface.

[0128] The present application provides a computer program product comprising computer instructions stored in a computer-readable storage medium. A processor of a computer device reads the computer instructions from the computer-readable storage medium and executes the computer instructions, causing the computer device to perform a method for ultrasonic detection of complex surfaces using virtual synthetic omnidirectional ultrasound. The method for ultrasonic detection of complex surfaces using virtual synthetic omnidirectional ultrasound is applied to a computer program product to facilitate execution.

[0129] The present application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the complex surface ultrasonic detection method using virtual synthetic omnidirectional ultrasound as described above.

[0130] The computer storage medium of this application may adopt any combination of one or more computer-readable media. The computer-readable medium may be a computer-readable signal medium or a computer-readable storage medium. The computer-readable storage medium may be, for example, but not limited to: an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, device or component, or any combination thereof. More specific examples (a non-exhaustive list) of computer-readable storage media include: an electrical connection with one or more wires, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination thereof. In this document, a computer-readable storage medium may be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, device or component. This application applies a complex surface ultrasonic detection method using virtual synthetic omnidirectional ultrasound to a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, it implements the steps of the clothing simulation method provided in this application, which is simple, fast, easy to store, and not easily lost.

[0131] This application proposes a complex surface ultrasonic detection method and system using virtual synthetic omnidirectional ultrasound. For scenarios where the contour information of complex surfaces is unknown, a virtual omnidirectional sound field synthesized by a focused ultrasonic probe is used for scanning. With the help of a post-processing algorithm, the true contour of the surface and the imaging of internal defects are accurately achieved. There is no need to determine the relative position relationship between the virtual sound beam focus and the surface being measured in advance. Different imaging algorithms are adaptively selected to achieve virtual source synthetic aperture focused imaging, and full-depth synchronous focused imaging is achieved in complex surface coupling scenarios. This provides a powerful means for the visual detection of complex surface defects and is of great value to improving the manufacturing quality and service safety of such components.

[0132] Those skilled in the art will appreciate that the modules of the present application described above can be implemented using a general-purpose computing system. They can be centralized on a single computing system or distributed across a network of multiple computing systems. Alternatively, they can be implemented using program code executable by a computer system, so that they can be stored in a storage system and executed by the computing system. Alternatively, they can be fabricated into separate integrated circuit modules, or multiple modules or steps can be fabricated into a single integrated circuit module for implementation. Thus, the present application is not limited to any specific combination of hardware and software.

[0133] Note that the above are only preferred embodiments of the present application and the technical principles employed. Those skilled in the art will understand that the present application is not limited to the specific embodiments herein, and that various obvious changes, readjustments, and substitutions can be made by those skilled in the art without departing from the scope of protection of the present application. Therefore, although the present application has been described in more detail through the above embodiments, the present application is not limited to the above embodiments and may include many other equivalent embodiments without departing from the scope of the present application. The scope of the present application is determined by the scope of the appended claims.

[0134] The above disclosure only describes several specific implementation scenarios of the present application. However, the present application is not limited thereto, and any changes that can be conceived by those skilled in the art should fall within the scope of protection of the present application.

Claims

1. A complex surface ultrasonic detection method using virtual synthetic omnidirectional ultrasound, characterized in that: These include: A virtual acoustic beam with omnidirectionality is synthesized by a preset focused ultrasonic probe, and ultrasonic echo signals of surface and internal defects of complex surfaces are collected by the virtual acoustic beam under the condition of stable acoustic coupling; reconstructing the surface contour of the complex surface according to the ultrasonic echo signal; calculating a relative positional relationship between the focus of the virtual acoustic beam and the surface contour, and selecting an imaging algorithm for acoustic ray tracing based on the relative positional relationship; The selected imaging algorithm is used to predict the propagation time of the ultrasonic signal through the complex surface to the imaging point, and then a high-resolution focused display image of the internal defects of the complex surface is output; When the relative position relationship indicates that the focus is located on the complex surface, a virtual source synthetic aperture focusing imaging algorithm based on Fermat's theorem is selected; the expression of the virtual source synthetic aperture focusing imaging algorithm based on Fermat's theorem is: in, Represents the imaging point The echo signal amplitude at is the total number of scanning steps, and the corresponding position of the virtual beam focus in the horizontal scanning direction is recorded as , It represents the propagation time of the sound line from the probe through the complex shape of the acoustic impedance mismatch surface to the imaging point. are the surface point coordinates for reconstructing the surface contour, is the number of discrete surface points, is the physical focal length of the focusing probe used to synthesize the virtual sound beam, i.e., the rotation radius. is the speed of longitudinal waves in water, is the longitudinal wave speed in the test block, and are weight coefficients, K The total number of rotations of the preset probe scan, k is the number of the current rotation, Imaging point In the i The scanning step position and k When the probe rotates, the signal amplitude corresponding to its propagation time; When the relative position relationship indicates that the focus is located below the complex surface, a virtual source synthetic aperture focusing imaging algorithm based on Snell's law is selected; the expression of the virtual source synthetic aperture focusing algorithm based on Snell's law is: in, Represents the imaging point The echo signal amplitude at is the total number of scanning steps, and the corresponding position of the virtual beam focus in the horizontal scanning direction is recorded as , It represents the propagation time of the sound line from the probe through the complex shape of the acoustic impedance mismatch surface to the imaging point. are the surface point coordinates for reconstructing the surface contour, is the physical focal length of the focusing probe used to synthesize the virtual sound beam, i.e., the rotation radius. is the speed of longitudinal waves in water, is the longitudinal wave speed in the test block, and are weight coefficients, K The total number of rotations of the preset probe scan, k is the number of the current rotation, Imaging point In the i The scanning step position and k The signal amplitude corresponding to the propagation time when the probe rotates.

2. The complex surface ultrasonic detection method according to claim 1, characterized in that: The imaging algorithm is based on delaying and superimposing the original time-domain ultrasonic echo signals, and calculates the propagation time of the sound line from the focused ultrasonic probe through the complex acoustic impedance mismatch surface to the imaging point, thereby generating a high-resolution full-depth synchronous focused image that focuses on the internal defects of complex surfaces.

3. The complex surface ultrasonic detection method according to claim 1, characterized in that: By rotating a focused ultrasound probe with a single small-opening-angle acoustic beam, small-opening-angle acoustic beams with the same beam shape but different directions are superimposed to form a large-opening-angle virtual acoustic beam with omnidirectionality; Alternatively, multiple focused ultrasound probes with fixed directions are arranged to realize a virtual sound beam with omnidirectionality by synchronously or step-by-step collecting ultrasound signals from different directions.

4. The complex surface ultrasonic detection method according to claim 1, characterized in that: In the process of reconstructing the surface contour, when the virtual acoustic beam detects the complex surface in a straight linear grid scanning manner, the inverse boundary scattering transform is used to establish a quantitative correspondence between the propagation distance of the surface echo incident and reflected along the surface normal direction and the target surface contour point, and abnormal surface points that appear during reconstruction are eliminated based on the quantitative correspondence.

5. The complex surface ultrasonic detection method according to claim 4, characterized in that: The quantitative correspondence expression is as follows: in, is the coordinate of the synthetic virtual beam focus in the scanning direction, is the physical focal length of the focusing probe used to synthesize the virtual sound beam, i.e., the rotation radius; and , is the longitudinal wave velocity of the acoustic coupling material, is the surface echo round trip time.

6. The complex surface ultrasonic detection method according to claim 1, characterized in that: Weight coefficients in the expression of virtual source synthetic aperture focusing imaging algorithm based on Fermat's theorem and The calculation expression is: in, is a step function, is the angle between the incident surface point and the horizontal scanning direction determined by Fermat’s theorem, The vertical direction of the imaging point corresponds to the reconstructed surface point Axis coordinates, is the maximum imaging depth, is the initial orientation, is the angular step length, k is the number of the current rotation, is the beam angle.

7. The complex surface ultrasonic detection method according to claim 1, characterized in that: A series of candidate surface points obtained based on ultrasound reconstruction , the structure makes the incident angle and refraction angle The objective function satisfies Snell's law; By traversing all candidate points, the point that minimizes the objective function is selected as the true incident point. After the true incident point is selected, the propagation paths of the sound wave in the two media are divided into: a path from the focused ultrasound probe to the surface incident point in water, and a path from the surface point to the imaging point within the complex surface. Objective function The expression is: in, / are the angles between the incident sound ray and the negative / positive vector of the tangent line, / is the angle between the refracted sound ray and the negative / positive vector of the tangent line, is the speed of longitudinal waves in water, is the longitudinal wave speed in the test block.

8. The complex surface ultrasonic detection method according to claim 1, characterized in that: The focused ultrasound probe's acoustic wave transmission and reception are limited to the beam angle Within the defined narrow sector area; The focused ultrasound probe is controlled to rotate with its curvature center as the center, so as not to exceed the beam angle. Angular step length From the initial position Clockwise rotation Second to the end position At each rotation position, the complex surface ultrasonic signal is collected in pulse-echo mode, and then the collected signals at each position are accumulated to synthesize a beam with an equivalent opening angle of Virtual sound beam.

9. A complex surface ultrasonic detection system with virtual synthetic omnidirectional ultrasound, characterized in that: The method for ultrasonic detection of complex surfaces using virtual synthetic omnidirectional ultrasound as claimed in any one of claims 1 to 8 comprises the following steps: A scanning unit is used to synthesize a virtual acoustic beam with omnidirectionality through a preset focused ultrasonic probe, and to collect ultrasonic echo signals of surface and internal defects of complex surfaces through the virtual acoustic beam under the condition of stable acoustic coupling; A contour reconstruction unit, configured to reconstruct a surface contour of a complex surface according to the ultrasonic echo signal; a position unit, configured to calculate a relative positional relationship between the focus of the virtual acoustic beam and the surface contour, and select an imaging algorithm for acoustic ray tracing based on the relative positional relationship; The output unit is used to use the selected imaging algorithm to predict the propagation time of the ultrasonic signal through the complex surface to reach the imaging point, and then output a high-resolution focused display image of the internal defects of the complex surface.

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