Ultrasonic phased array full-focusing imaging method for acoustic wave multi-path propagation compensation of layered composite material

Abstract

The invention relates to an ultrasonic phased array full-focusing imaging method for acoustic wave multi-path propagation compensation of a layered composite material, which is characterized by comprising the following steps of: arranging an ultrasonic phased array probe with N array elements on a composite material piece to be detected, obtaining complete echo data by taking each array element as a transmitting array element and taking all array elements as receiving array elements in sequence in a full-matrix acquisition mode; a two-dimensional pixel grid is established in an imaging area, a Monte-Carlo perturbation mechanism used for representing the acoustic wave propagation uncertainty in the layered composite material is introduced into a propagation model for each emission array element-receiving array element-pixel point combination, and the acoustic beam emission direction, the propagation path and the equivalent acoustic velocity are subjected to random perturbation, so that the acoustic wave propagation uncertainty in the layered composite material can be represented. Generating a plurality of equivalent sound wave propagation paths, calculating two-way propagation time of each path, and performing weighted statistics on energy contributions of different paths according to array element sound beam directivity to obtain equivalent propagation time delays of pixel points; and performing delay correction on a full-matrix echo signal by using the equivalent propagation time delay, and performing coherent superposition on signals of all transmitting-receiving array element combinations to realize dynamic focusing of a full-pixel grid, and finally reconstructing an ultrasonic full-focusing imaging image with high resolution and high signal-to-noise ratio. The time delay error caused by propagation path deviation and sound velocity non-uniformity in the layered composite material can be effectively compensated, the focusing precision and spatial resolution of full-focusing imaging are improved, meanwhile, an existing TFM imaging frame does not need to be changed, and the method has good engineering implementability and popularization and application value.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of phased ultrasonic imaging technology, in particular to an ultrasonic phased array full focusing imaging method for sound wave multi-path propagation compensation of layered composite materials. BACKGROUND

[0002] The ultrasonic phased array imaging technology has been widely applied in the field of nondestructive testing of carbon fiber reinforced plastics (CFRP) due to its high spatial resolution, flexible electronic scanning capability and strong defect quantitative analysis capability. The full focusing imaging method (Total Focusing Method, TFM) based on full matrix capture (Full Matrix Capture, FMC) can dynamically focus on any pixel point in the detection area, and in theory can obtain the optimal spatial resolution and imaging consistency, so it has become an important imaging means in the ultrasonic testing of composite materials. However, in layered composite materials, due to the existence of a large number of resin-fiber interfaces, layer interfaces and anisotropic structures inside the material, the ultrasonic wave will undergo multiple refraction, scattering and mode conversion during propagation, and there is a significant deviation between the real propagation path and the ideal straight line path. At the same time, the spatial variation of the local equivalent sound speed caused by different layer directions and interface distributions also makes the real propagation time of the ultrasonic wave random and uncertain, and the complex propagation mechanism makes the propagation time between the array elements and the imaging pixels no longer satisfy the geometric straight line model under a single sound speed.

[0003] However, the existing TFM imaging method usually assumes that the medium is a homogeneous isotropic material when calculating the propagation time delay, and uses the straight line propagation path and fixed sound speed model between the array elements and the pixels to determine the propagation time. This simplifying assumption is basically valid in homogeneous materials such as metals, but it will produce systematic time delay errors in layered anisotropic materials such as CFRP. When the focused time delay does not match the real propagation time, the echo signals of each array element channel cannot be truly coherent at the pixel point, resulting in the expansion of the main lobe, the enhancement of the side lobe and the synchronous amplification of the structure noise, which seriously restricts the detectability and positioning accuracy of internal defects, making it difficult to clearly image.

[0004] Therefore, in the ultrasonic phased full focusing imaging of composite materials, the inaccuracy of the propagation time delay model has become a core bottleneck that limits the performance of TFM imaging. Under the premise of maintaining the existing imaging framework, introducing a time delay correction mechanism that can characterize the uncertainty of the propagation path in multi-layer media, so as to obtain a statistical equivalent propagation time delay that is closer to the real physical propagation process, has become a key technical problem that needs to be solved in the field of ultrasonic imaging of composite materials. SUMMARY

[0005] In view of this, the present invention designs an ultrasonic phased array full-focusing imaging method for acoustic wave multipath propagation compensation in layered composite materials, in order to overcome the problems existing in the prior art.

[0006] Based on the above objectives, this invention proposes an ultrasonic phased array full-focusing imaging method for acoustic multipath propagation compensation in layered composite materials, the specific contents of which include:

[0007] This invention, based on FMC ultrasonic phased array data, introduces a Monte Carlo (MC) statistical multipath propagation modeling and equivalent time delay compensation mechanism within the traditional TFM imaging framework. By randomly perturbing the beam emission direction, propagation path, and equivalent sound velocity, a set of physically meaningful equivalent propagation paths are constructed around the ideal propagation path to simulate the multipath propagation behavior caused by multi-layer interfaces, anisotropy, and scattering effects in layered composite materials. For each combination of transmitting array element, receiving array element, and imaging pixel, the two-way propagation time of the sound wave along each perturbed path is calculated. The energy contribution of different paths is weighted statistically based on the beam directivity of the array elements. This suppresses the influence of large-angle scattering paths while highlighting the effective propagation path consistent with the main beam direction, ultimately obtaining an equivalent propagation time delay that more closely approximates the real physical propagation process. This time delay is then used for delay correction and coherent superposition of the full matrix echo data, thereby achieving more accurate dynamic focusing within the imaging region and obtaining high-resolution, high signal-to-noise ratio ultrasonic phased array full-focus imaging results.

[0008] Compared with conventional ultrasonic phased array imaging methods, the advantages of this invention are as follows: This invention proposes an ultrasonic phased array full-focusing imaging method for acoustic wave multipath propagation compensation in layered composite materials. By introducing MC-based multipath propagation modeling and equivalent time delay statistics, it effectively characterizes the propagation uncertainty caused by refraction, scattering, and sound velocity fluctuations in layered composite materials, thereby compensating for the systematic time delay error caused by the traditional linear sound velocity model. By replacing the traditional geometric time delay with statistical equivalent propagation time delay, the echo signals of each array element achieve more accurate phase alignment at the imaging pixel, thereby significantly suppressing sidelobes and false focusing, enhancing the focusing energy of real defect echoes, and improving the spatial resolution and imaging quality of full-focusing imaging. At the same time, this method only improves the propagation time delay calculation method, and can be directly embedded in the application without changing the existing FMC-TFM imaging framework and hardware system, which has good engineering feasibility and promotional application value. Attached Figure Description

[0009] The accompanying drawings are only used to provide a further understanding of the present invention and are not part of the specification. They are used together with the embodiments of the present invention to explain the present invention and do not constitute a limitation thereof.

[0010] Figure 1 This is a schematic diagram of the TFM imaging principle.

[0011] Figure 2 A schematic diagram illustrating the principle of MC correction for sound wave propagation.

[0012] Figure 3 This is a flowchart of an imaging method for detecting internal defects in layered composite materials. Detailed Implementation

[0013] The present invention will be further described below with reference to specific embodiments and accompanying drawings, thereby making the beneficial effects of the present invention clearer.

[0014] An ultrasonic phased array full-focusing imaging method for acoustic wave multipath propagation compensation in layered composite materials, the specific operation steps of which are as follows:

[0015] Step S1: Using N An ultrasonic phased array probe with one array element performs full-matrix data acquisition on the object under test, sequentially using the i-th array element as the transmitting element and all array elements as the receiving elements to acquire the echo signal. , where i, j=1,2,…,N, constitute a complete full matrix acquisition dataset containing each combination of transmit-receive array elements;

[0016] Step S2: Establish a two-dimensional imaging grid within the imaging area, represented by the horizontal coordinate x and the depth coordinate z. For any imaging pixel P(x, z), determine the position of its corresponding emission element. With the position of the receiving array element ;

[0017] Step S3: For each combination of transmitting array element i, receiving array element j and imaging pixel P(x, z), a propagation perturbation mechanism is introduced into the sound wave propagation model to characterize the uncertainty of sound wave propagation in layered composite materials. By perturbing the sound beam exit direction and equivalent sound velocity, multiple equivalent sound wave propagation paths distributed around the ideal straight line path are generated to describe the various propagation modes that may exist in the layered medium.

[0018] Step S4: For each equivalent sound wave propagation path, calculate the two-way propagation time of the sound wave from the transmitting array element i through the imaging pixel point P(x, z) to the receiving array element j.

[0019] Step S5: For the same imaging pixel under the same combination of transmitting element – ​​imaging pixel – receiving element Propagation time of all equivalent sound wave propagation paths We performed weighted statistics to obtain the equivalent propagation time. ;

[0020] Step S6: Utilize the equivalent propagation time Echo signals in full matrix acquisition data Time delay correction is performed, and the correction signals of all transmit-receive array element combinations are coherently superimposed according to the delay summation method to obtain the focusing amplitude of the imaging pixel P(x, z). ;

[0021] Step S7: Repeat steps two through six for all imaging pixels within the imaging area to reconstruct a complete ultrasonic phased array full-focus imaging image. This achieves the compensation of the deviation between the actual propagation path of sound waves and the ideal propagation model in the layered medium through multi-path equivalent propagation time, thereby improving the focusing accuracy, resolution, and signal-to-noise ratio of full-focus imaging.

[0022] Step S31: The specific process of the propagation perturbation mechanism for the uncertainty of sound wave propagation is as follows: For any transmitting array element i, receiving array element j, and pixel point P(x, z), based on its straight propagation path, random angle perturbation is applied to the sound beam output direction, random fluctuations are introduced to the equivalent sound speed of the medium, and joint perturbation modeling is performed on the propagation starting point and path direction. A set of physically meaningful equivalent propagation paths are generated around the ideal straight path to simulate multiple possible propagation modes caused by interlayer refraction, scattering, and anisotropy in layered composite materials. At the same time, a directional weighting function is constructed according to the deflection angle of each perturbation path relative to the straight path, and different contribution degrees are assigned to different paths. Finally, the propagation time of multiple perturbation paths is weighted and averaged using the Monte Carlo statistical integration method to obtain the equivalent statistical propagation delay of the array element pair (i, j) at pixel point p, thereby realizing the unified modeling of multi-path propagation and sound speed uncertainty.

[0023] Step S41: The propagation time is determined by the sound wave propagation distance corresponding to the path and its equivalent sound speed, and the calculation formula is as follows: , where represents the k-th random disturbance propagation path, and represents the equivalent sound speed distribution along this path.

[0024] Step S51: The aforementioned propagation time Weighted statistics are performed, with the specific weighting mechanism being: the aforementioned weighting of propagation time. Weighted statistics are performed, with the specific weighting mechanism as follows: for the k-th Monte Carlo perturbation propagation path between transmitting element i and receiving element j, the total propagation time is... The path length is The local refraction or deflection angles along each segment of the path are The statistical weight of this path is defined as follows: in Number of segments for the path For the propagation attenuation coefficient, the function The probability density representing local deviations from the main propagation direction can be expressed as a small-angle decay function, such as... To reflect the physical feasibility of the perturbation path, the statistical propagation time from transmitting element i to receiving element j is obtained by weighted averaging of all N perturbation paths. This method enhances the contribution of the physically feasible main propagation path in a statistical sense, while suppressing non-main effective paths that are too long or deviate at large angles, thus achieving Monte Carlo correction of the propagation time.

[0025] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. An ultrasonic phased array full-focusing imaging method for acoustic wave multipath propagation compensation in layered composite materials, characterized in that, The method includes the following steps: Step S1: Using N An ultrasonic phased array probe with one array element performs full matrix capture (FMC) on the object under test, sequentially using the i-th array element as the transmitting element and all array elements as the receiving elements to acquire the echo signal. , where i, j=1,2,…,N, constitute a complete full matrix acquisition dataset containing each combination of transmit-receive array elements; Step S2: Establish a two-dimensional imaging grid within the imaging area, represented by the horizontal coordinate x and the depth coordinate z. For any imaging pixel P(x, z), determine the position of its corresponding emission element. With the position of the receiving array element ; Step S3: For each transmitting array element i and receiving array element j With the imaging pixel P(x, z) The combination of these methods introduces a propagation perturbation mechanism into the sound wave propagation model to characterize the uncertainty of sound wave propagation in layered composite materials. By perturbing the sound beam exit direction and equivalent sound velocity, multiple equivalent sound wave propagation paths distributed around an ideal straight path are generated to describe the various propagation modes that may exist in the layered medium. Step S4: For each equivalent sound wave propagation path, calculate the two-way propagation time of the sound wave from the transmitting array element i through the imaging pixel point P(x, z) to the receiving array element j. Step S5: For the same imaging pixel under the same combination of transmitting element – ​​imaging pixel – receiving element Propagation time of all equivalent sound wave propagation paths We performed weighted statistics to obtain the equivalent propagation time. ; Step S6: Utilize the equivalent propagation time Time delay correction is performed on the echo signals in the full matrix acquisition data, and the correction signals of all transmit-receive array element combinations are coherently superimposed according to the delay summation method to obtain the focusing amplitude of the imaging pixel P(x, z). ; Step S7: Repeat steps two through six for all imaging pixels within the imaging area to reconstruct a complete ultrasonic phased array full-focus imaging image. This achieves the compensation of the deviation between the actual propagation path of sound waves and the ideal propagation model in the layered medium through multi-path equivalent propagation time, thereby improving the focusing accuracy, resolution, and signal-to-noise ratio of full-focus imaging.

2. The ultrasonic phased array full-focusing imaging method for acoustic multipath propagation compensation of layered composite materials according to claim 1, characterized in that: In step S3, the specific process of the propagation perturbation mechanism for the uncertainty of sound wave propagation is as follows: For any transmitting array element i, receiving array element j, and pixel point P(x, z), based on its straight propagation path, random angle perturbation is applied to the sound beam output direction, random fluctuations are introduced to the equivalent sound speed of the medium, and joint perturbation modeling is performed on the propagation starting point and path direction. A set of physically meaningful equivalent propagation paths are generated around the ideal straight path to simulate multiple possible propagation modes caused by interlayer refraction, scattering, and anisotropy in layered composite materials. At the same time, a directional weighting function is constructed according to the deflection angle of each perturbation path relative to the straight path, and different contribution degrees are assigned to different paths. Finally, the propagation time of multiple perturbation paths is weighted and averaged using the Monte Carlo statistical integration method to obtain the equivalent statistical propagation delay of the array element pair (i, j) at pixel point p, thereby realizing the unified modeling of multi-path propagation and sound speed uncertainty.

3. The ultrasonic phased array full-focusing imaging method for acoustic multipath propagation compensation of layered composite materials according to claim 1, characterized in that: In step S4, the propagation time is determined by the sound wave propagation distance corresponding to the path and its equivalent sound speed, and the calculation formula is as follows: ,in This represents the k-th random perturbation propagation path. This represents the equivalent sound speed distribution along the path.

4. The ultrasonic phased array full-focusing imaging method for acoustic multipath propagation compensation of layered composite materials according to claim 1, characterized in that: In step S5, the propagation time is... Weighted statistics are performed, with the specific weighting mechanism as follows: for the k-th Monte Carlo perturbation propagation path between transmitting element i and receiving element j, the total propagation time is... The path length is The local refraction or deflection angles along each segment of the path are The statistical weight of this path is defined as follows: ,in Let be the number of path segments, and be the propagation attenuation coefficient, and be the function. The probability density representing local deviations from the main propagation direction can be expressed as a small-angle decay function, such as... To reflect the physical feasibility of the perturbation path, the statistical propagation time from transmitting element i to receiving element j is obtained by weighted averaging of all N perturbation paths. This method enhances the contribution of the physically feasible main propagation path in a statistical sense, while suppressing non-main effective paths that are too long or deviate at large angles, thus achieving Monte Carlo correction of the propagation time.

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