Reinforced concrete structure improvement time domain synthetic aperture imaging fast algorithm

Abstract

The application discloses a reinforced concrete structure improvement time domain synthetic aperture imaging fast algorithm, and steps are as follows: a reinforced concrete two-dimensional finite element simulation model is established, and a half diffusion angle is calculated; simulation testing is carried out on an ultrasonic probe in the reinforced concrete two-dimensional finite element simulation model, and full matrix data are formed; the reinforced concrete two-dimensional finite element simulation model is pixelated, and a diffusion angle factor is calculated; whether synthetic aperture processing is carried out is compared according to the half diffusion angle in step one and the diffusion angle factor in step three; and imaging processing is carried out on the full matrix data in step two according to a time domain synthetic aperture full focusing algorithm. The application has the beneficial effects that the application determines the diffusion angle factor of each pixel point to each transmission ultrasonic probe, the area outside the diffusion angle of the ultrasonic probe is not subjected to sound path calculation and amplitude superposition, the algorithm efficiency is greatly improved, meanwhile, imaging of the pseudo defects outside the diffusion angle is avoided. The smaller the diffusion angle is, the more the data quantity is, and the more obvious the algorithm acceleration effect is.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic nondestructive testing, specifically to a fast algorithm for improving time-domain synthetic aperture imaging of reinforced concrete structures. Background Technology

[0002] Ultrasonic testing generally refers to the process where an ultrasonic probe emits ultrasonic waves, which interact with the acoustic interface inside the object being tested, generating reflected, transmitted, and scattered waves. The ultrasonic probe then receives the echoes, and the received echoes are analyzed to determine macroscopic defects, measure geometric characteristics, and analyze the microstructure and mechanical properties of the object being tested. Ultrasonic testing is one of the five conventional testing techniques and is currently the most widely used and fastest-growing non-destructive testing technique. It has many advantages, including safety, wide applicability to a wide range of materials, low cost, good ultrasonic directional guidance, and high testing speed.

[0003] Ultrasonic testing was first applied to the detection of internal defects in metals in the late 1920s. In the 1940s, the world's first pulse-echo ultrasonic testing instrument was developed in Britain, and the accuracy of ultrasonic testing has continued to improve since then. With technological advancements and interdisciplinary integration, ultrasonic testing has developed more and more new technologies, such as diffraction time-of-flight ultrasonic testing, ultrasonic phased array testing, guided wave technology, electromagnetic ultrasound, and laser ultrasound, demonstrating its strong vitality and continuously improving detection accuracy.

[0004] The basic idea of ​​array ultrasonic testing technology originates from electromagnetic radar technology. Its fundamental approach involves the delay and superposition of multi-aperture signals. Depending on the number of ultrasonic probes receiving the signals, testing methods include single-transmitter single-receiver synthetic aperture methods and single-transmitter multi-receiver total focusing methods. The greatest advantage of array ultrasonic testing lies in overcoming the lateral resolution limitations of traditional ultrasonic testing methods. Traditional ultrasonic lateral resolution is limited by two factors: the detection frequency and the size of the ultrasonic probe. With a sufficient number of array probes, the lateral resolution of array ultrasonic testing is half the size of the ultrasonic probe. Therefore, higher detection frequencies can be used to detect materials with high viscosity and significant sound velocity attenuation. Higher frequencies also allow for the detection of smaller defects, thereby improving image resolution.

[0005] The disadvantages of array ultrasound lie in its slow algorithm speed and high processor processing power requirements. Taking the one-to-many full-focusing algorithm as an example, if the number of ultrasound probes in the array is 12, each ultrasound probe's excitation signal will be received by 12 ultrasound probes, resulting in a total of 144 echo signals acquired after each ultrasound probe in the array is excited. However, existing array ultrasound detection systems have reached 64 or even 128 array elements, which can receive up to 16384 signals. Depending on the signal sampling interval, each signal may have hundreds, thousands, or even more sampling points. High sampling rate and high array element number improve image quality, but each detection data point participates in the imaging processing of each pixel, which also greatly increases the algorithm's running time. At the same time, in order to obtain a better image signal-to-noise ratio, some point-by-point correction algorithms may be used during signal processing. For an ultrasound array composed of 12 ultrasound probes, when imaging a detection area with pixels of 300×200 mm, the imaging algorithm needs a total of 12×12×300×200 array signal analysis operations. This algorithm eliminates most structural noise and improves the signal-to-noise ratio, but its detection speed is very slow, which is a problem that urgently needs to be solved in array ultrasound imaging algorithms. Summary of the Invention

[0006] The purpose of this invention is to provide a fast algorithm for improving temporal synthetic aperture imaging of reinforced concrete structures. Addressing the need for rapid imaging in ultrasonic array detection algorithms, this accelerated algorithm calculates and sets the diffusion angle factor of pixels in the detection area. By calculating the diffusion angle factor, the entire area is avoided from participating in the imaging calculation, reducing the computational load of temporal synthetic aperture full-focus imaging. This can improve the problems of long detection time and low efficiency of ultrasonic array algorithms such as temporal synthetic aperture full-focus imaging, and has significant practical application value.

[0007] The technical solution of this invention: a fast algorithm for improving temporal synthetic aperture imaging of reinforced concrete structures, the specific steps of which are as follows:

[0008] Step 1: Establish a two-dimensional finite element simulation model of reinforced concrete and calculate the half-diffusion angle;

[0009] Step 2: Conduct simulation tests on the ultrasonic probe in the two-dimensional finite element simulation model of reinforced concrete according to the synthetic aperture detection method to form full matrix data;

[0010] Step 3: Pixelate the two-dimensional finite element simulation model of reinforced concrete and calculate the diffusion angle factor from each pixel to each aperture.

[0011] Step 4: Compare the half-diffusion angle in Step 1 with the diffusion angle factor in Step 3, and determine which pixels in the full matrix data in Step 2 meet the pixel requirements for synthesized aperture processing.

[0012] Step 5: Based on the temporal synthetic aperture full focusing algorithm and the judgment results in Step 4, perform imaging processing on the full matrix data in Step 2.

[0013] Furthermore, in step one, a two-dimensional finite element simulation model of reinforced concrete is established, and the half-diffusion angle is calculated. This two-dimensional finite element simulation model of reinforced concrete is established using multiphysics simulation software (COMSOL), specifically as follows:

[0014] Two air defects are set in the upper part of the two-dimensional finite element simulation model of reinforced concrete. The two air defects are a circular air defect and a square air defect. At the same time, four steel bars are set in the middle of the two-dimensional finite element simulation model of reinforced concrete. A detection array composed of 12 ultrasonic probes is set at the bottom of the two-dimensional finite element simulation model of reinforced concrete. The center of the 12 ultrasonic probes is used as the part for transmitting and receiving ultrasonic signals. The half-diffusion angle is calculated according to formula (1):

[0015] ;

[0016] In the formula, It is the half-diffusion angle. D is the wavelength of the longitudinal wave emitted by the ultrasonic probe in reinforced concrete. s The diameter is the ultrasonic probe.

[0017] Furthermore, in step one, a two-dimensional finite element simulation model of reinforced concrete with a height of 240mm and a width of 360mm is established. The diameter of the circular air defect is 40mm, the side length of the square air defect is 40mm, the diameter of the four steel bars is 20mm, the frequency of the longitudinal wave emitted by the ultrasonic probe is 200kHz, and the longitudinal wave velocity in the reinforced concrete is set to 4000 m / s. The half-diffusion angle is calculated using the half-diffusion angle formula (1). It is 37.5°.

[0018] Furthermore, in step two, simulation tests are conducted on the ultrasonic probe in the two-dimensional finite element simulation model of reinforced concrete according to the synthetic aperture detection method to form full matrix data; specifically:

[0019] Twelve ultrasonic probes were sequentially excited to emit ultrasonic signals. Each time, one ultrasonic probe was excited to emit an ultrasonic signal, which was then received and detected by all twelve ultrasonic probes. After completing one round of simulation testing with the twelve ultrasonic probes, a total of 144 aperture simulation detection signal data were collected. Each ultrasonic probe collected 12 aperture simulation detection signal data, forming a full matrix of data, which was then saved to the computer.

[0020] Furthermore, in step three, the two-dimensional finite element simulation model of reinforced concrete is pixelated, and the diffusion angle factor from each pixel to each aperture is calculated; specifically:

[0021] Each small square is considered a pixel, with the origin of the pixel coordinates set to O(0,0). The coordinates of each ultrasound probe are set to its emission position, and the coordinates of the nth ultrasound probe are S. n (x) n ,0), calculate the diffusion angle factor according to formula (2):

[0022] ;

[0023] In the formula, For any pixel point P and S n The angle between the two points, i.e., the diffusion angle factor, is the coordinate of any pixel P, which is (x, y). p ,y p ),Right now Let y be the x-coordinate of any pixel point P. p Let S be the vertical coordinate of any pixel point P. n Let x represent the coordinates of the nth ultrasound probe. n For S n The x-coordinate.

[0024] Furthermore, in step three, each small square is considered as a pixel, and the area of ​​each small square is 1 mm. 2 It is divided into 360×240 pixels.

[0025] Furthermore, in step four, the half-diffusion angle in step one and the diffusion angle factor in step three are compared to determine which pixels in the full matrix data from step two meet the pixel requirements for synthetic aperture processing; specifically:

[0026] The diffusion angle factor calculated by formula (2) The half-diffusion angle calculated using formula (1) By comparison, a mapping relationship between any pixel P and the ultrasound probe is established;

[0027] diffusion angle factor Less than or equal to half diffusion angle Set to "Yes" to use the received signal from the ultrasonic probe to perform synthetic aperture processing on that pixel.

[0028] Diffusion angle factor Greater than half diffusion angle If set to "No", the received signal from this ultrasonic probe cannot be used for synthetic aperture processing of this pixel.

[0029] Furthermore, in step five, the full matrix data from step two is processed for imaging according to the temporal synthetic aperture total focusing algorithm and the judgment results from step four. The temporal synthetic aperture total focusing algorithm is specifically implemented in the mathematical modeling software (MATLAB).

[0030] Imaging processing was performed on 144 full matrix data points using the temporal synthetic aperture full focusing algorithm. Imaging time calculations were performed for full matrix data without diffusion angle factor and for full matrix data with diffusion angle factor.

[0031] The running time was recorded using the timing function in the mathematical modeling software. Without the diffusion angle factor, the time taken for the time-domain synthetic aperture full focusing algorithm to run four times was 189 seconds, 190 seconds, 187 seconds, and 195 seconds, with an average time of 190.25 seconds.

[0032] With full matrix data of diffusion angle factor, the time-domain synthetic aperture full focusing algorithm took 121 seconds, 119 seconds, 120 seconds and 118 seconds to run four times, with an average time of 119.75 seconds, which improved the calculation speed by 37%.

[0033] The beneficial effects of this invention are:

[0034] (1) Traditional time-domain ultrasonic array imaging algorithms image every pixel in the imaging area. However, in actual detection, most areas outside the diffusion angle receive very little ultrasonic energy, and the echo energy is easily submerged in noise. In addition, the idea behind time-domain ultrasonic array imaging algorithms is to calculate the sound path based on the positions of the transmitting ultrasonic probe, the receiving ultrasonic probe, and the imaging pixel, and then superimpose the corresponding amplitude. According to this idea, when the sound path of the area outside the diffusion angle is the same as that of the area inside the diffusion angle with reflected echoes, it will cause false defects. Therefore, traditional time-domain ultrasonic array imaging algorithms are not only inefficient in calculation, but may also cause false defects.

[0035] (2) To address the above problems, this invention incorporates a diffusion angle control algorithm into the algorithm to determine the diffusion angle factor of each pixel relative to each transmitting ultrasonic probe. Areas outside the diffusion angle of the ultrasonic probe are not subject to sound path calculation or amplitude superposition, which greatly improves algorithm efficiency and avoids the formation of false defects outside the diffusion angle. Furthermore, the smaller the diffusion angle, the larger the data volume, and the more significant the algorithm acceleration effect.

[0036] (3) In actual ultrasonic testing, due to the strong directivity of ultrasound, when the ultrasonic probe emits ultrasound into the object being tested, most of the ultrasonic energy will be concentrated within the diffusion angle. Generally, it is considered that the diffusion angle region is the area where the sound pressure amplitude drops by 12dB, that is, 75.12% of the sound energy is concentrated. Within this region, the diffusion angle can be considered to limit the propagation range of the beam. Taking the ultrasonic probe with a frequency of 3 MHz and a diameter of 10 mm in epoxy resin as an example, its diffusion angle is 6.42°, that is, 75.12% of the ultrasonic energy is concentrated in the area of ​​6.42° near the central axis.

[0037] (4) The average time for the full matrix data without diffusion angle factor was 190.25 seconds; the average time for the full matrix data with diffusion angle factor was 119.75 seconds, which increased the calculation speed by 37%. This is because the algorithm with diffusion angle factor reduced the participation of ultrasonic probe signals that were not within the diffusion angle in the calculation, thereby reducing the actual amount of calculation. At the same time, most pixels have diffusion angle factors greater than half the diffusion angle. In the imaging calculation, these pixels reduced the calculation of invalid signals, thereby reducing the probability of artifact generation. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the reinforced concrete two-dimensional finite element simulation model structure and ultrasonic array test of the present invention.

[0039] Figure 2 This is a schematic diagram showing the angle (diffusion angle factor) between any pixel point and the nth ultrasonic probe in this invention.

[0040] Figure 3 This is an image of the fast algorithm for ultrasonic array detection and imaging of reinforced concrete structures according to the present invention. Detailed Implementation

[0041] This invention works and is implemented as follows: a fast algorithm for improving time-domain synthetic aperture imaging of reinforced concrete structures. When detecting the target area, the ultrasonic diffusion angle is calculated based on detection parameters such as ultrasonic wave length, frequency, and ultrasonic probe size. The diffusion angle factor of each transmitting ultrasonic probe for each pixel in the detection area is established, controlling the signal reception and imaging range of each transmitting ultrasonic probe. This reduces the number of imaging calculations, thereby improving detection efficiency. It also better conforms to the propagation law of ultrasound in objects, reducing the formation of artifacts during imaging.

[0042] The effectiveness and feasibility of this invention are verified by the following simulation experiments. A fast algorithm for improving temporal synthetic aperture imaging of reinforced concrete structures, the specific steps of which are as follows:

[0043] First, a two-dimensional finite element simulation model of reinforced concrete with a height of 240mm and a width of 360mm is built using the multiphysics simulation software COMSOL. Figure 1As shown, a schematic diagram of the two-dimensional finite element simulation model structure and ultrasonic array test of reinforced concrete is presented. Two air defects are set in the upper part of the two-dimensional finite element simulation model of reinforced concrete, namely a circular air defect with a diameter of 40 mm and a square air defect with a side length of 40 mm. At the same time, four steel bars with a diameter of 20 mm are set in the middle of the two-dimensional finite element simulation model of reinforced concrete. A detection array consisting of 12 ultrasonic probes is set at the bottom of the two-dimensional finite element simulation model of reinforced concrete. The diameter of each ultrasonic probe is set to 40 mm, and the center of the ultrasonic probe is used as the part for transmitting and receiving ultrasonic signals. The longitudinal wave frequency is 200 kHz, and the longitudinal wave velocity in reinforced concrete is set to 4000 m / s. The half-diffusion angle is calculated according to formula (1):

[0044] ;

[0045] In the formula, It is the half-diffusion angle. D is the wavelength of the longitudinal wave emitted by the ultrasonic probe in reinforced concrete. s The diameter of the ultrasonic probe is given; the calculated half-diffusion angle is approximately 37.5°.

[0046] After establishing a two-dimensional finite element simulation model of reinforced concrete, simulation tests were conducted. The synthetic aperture full focusing method was selected, and 12 ultrasonic probes were excited sequentially to emit ultrasonic signals. Each time one ultrasonic probe was excited, the detection signals were received by all 12 ultrasonic probes. After completing one simulation test of 12 ultrasonic probes, a total of 144 aperture simulation detection signal data could be collected. Each ultrasonic probe could collect 12 aperture simulation detection signal data, forming a full matrix data, which was then saved to the computer.

[0047] The two-dimensional finite element simulation model of reinforced concrete is pixelated, that is, pixelated to 1 mm. 2 The small square is considered as one pixel, and the system can be divided into 360×240 pixels. The coordinates of the lower left pixel are set as the origin O(0,0). Each ultrasound probe uses its emission position as its coordinate point, such as... Figure 2 The diagram shows the angle (diffusion angle factor) between any pixel and the nth ultrasound probe. The angle between each pixel and each ultrasound probe can be calculated. For example, if the coordinates of the nth ultrasound probe are S... n (x) n ,0), calculate the diffusion angle factor according to formula (2):

[0048] ;

[0049] In the formula, For any pixel point P and S n The angle between the two points, i.e., the diffusion angle factor, is the coordinate of any pixel P, which is (x, y). p ,yp ),Right now Let y be the x-coordinate of any pixel point P. p Let S be the vertical coordinate of any pixel point P. n Let x represent the coordinates of the nth ultrasound probe. n For S n The x-coordinate.

[0050] According to formula (2), establish the diffusion angle factor of each pixel point and each ultrasonic probe, and compare it with the half diffusion angle of 37.5° to establish a mapping relationship between each pixel point and the ultrasonic probe. If it is less than the half diffusion angle, it is set to "yes", that is, the received signal of the ultrasonic probe can be used to process the synthetic aperture of the pixel point; if it is greater than the half diffusion angle, it is set to "no", that is, the received signal of the ultrasonic probe cannot be used to process the synthetic aperture of the pixel point.

[0051] Finally, in the mathematical modeling software (MATLAB), the 144 full matrix data were imaged using the temporal synthetic aperture total focusing algorithm. Imaging time was calculated for both methods with and without a diffusion angle factor. The running time was recorded using the timing function in MATLAB. The algorithm without a diffusion angle factor took 189 seconds, 190 seconds, 187 seconds, and 195 seconds for four runs, with an average time of 190.25 seconds. The algorithm with a diffusion angle factor took 121 seconds, 119 seconds, 120 seconds, and 118 seconds for four runs, with an average time of 119.75 seconds, representing a 37% speed improvement. This is because the algorithm with a diffusion angle factor reduces the involvement of ultrasonic probe signals outside the diffusion angle in the calculation, thus reducing the actual computational load. Furthermore, most pixels have a diffusion angle factor greater than half the diffusion angle; these pixels reduce the calculation of invalid signals during imaging calculations, thereby reducing the probability of artifacts.

[0052] This invention improves upon the slow computation speed of traditional ultrasonic array synthetic aperture full focusing algorithms and their derivatives, solving the problem of slow imaging speed. Based on actual ultrasonic testing conditions, a diffusion angle control factor is added to the algorithm, controlling it to only calculate pixels within the emission diffusion angle, reducing computation time and eliminating the problem of false defects in imaging outside the diffusion angle caused by the algorithm's calculation method. This improves computational efficiency and ensures image quality. Figure 3 The image shown is an image obtained from a fast algorithm for ultrasonic array detection and imaging of reinforced concrete structures.

Claims

1. A fast algorithm for time-domain synthetic aperture imaging of reinforced concrete structures, characterized in that: The specific steps are as follows: Step one: establish a two-dimensional finite element simulation model of reinforced concrete, calculate the half diffusion angle; Step two: according to the synthetic aperture detection method, carry out simulation test on the ultrasonic probe in the two-dimensional finite element simulation model of reinforced concrete, and form full matrix data; Step three: pixelize the two-dimensional finite element simulation model of reinforced concrete, calculate the diffusion angle factor of each pixel point to each aperture; Step four: compare the half diffusion angle in step one with the diffusion angle factor in step three, and judge whether the full matrix data in step two meets the pixel point requirement for synthetic aperture processing; Step five: according to the time domain synthetic aperture full focusing algorithm and combined with the judgment result in step four, carry out imaging processing on the full matrix data in step two; In step one, a two-dimensional finite element simulation model of reinforced concrete is established, and the half diffusion angle is calculated; specifically: Two air defects are set on the upper half of the two-dimensional finite element simulation model of reinforced concrete, which are circular air defects and square air defects respectively. Four steel bars are set in the middle of the two-dimensional finite element simulation model of reinforced concrete. The bottom of the two-dimensional finite element simulation model of reinforced concrete is provided with a detection array composed of 12 ultrasonic probes, and the centers of the 12 ultrasonic probes are used as the positions for transmitting and receiving ultrasonic signals. The half diffusion angle is calculated according to formula (1): （1）； In the formula, θ is a half diffusion angle, λ is a wavelength of a longitudinal wave emitted by an ultrasonic probe in the reinforced concrete, D s is a diameter of the ultrasonic probe; In step three, the two-dimensional finite element simulation model of reinforced concrete is pixelized, and the diffusion angle factor of each pixel point to each aperture is calculated; specifically: With each small box as a pixel point, set the pixel point coordinate origin as O (0, 0), and take the emission position of each ultrasonic probe as a coordinate point, the coordinate of the nth ultrasonic probe is S n (x n , 0), and the diffusion angle factor is calculated according to formula (2): （2）； In the formula, For any pixel point P and S n The angle between the two points, i.e., the diffusion angle factor, is the coordinate of any pixel P, which is (x, y). p ,y p ),Right now Let y be the x-coordinate of any pixel point P. p Let S be the vertical coordinate of any pixel point P. n Let x represent the coordinates of the nth ultrasound probe. n For S n The x-coordinate.

2. The improved time-domain synthetic aperture imaging fast algorithm for a reinforced concrete structure according to claim 1, characterized in that: In step one, a two-dimensional finite element simulation model of reinforced concrete with a height of 240mm and a width of 360mm is established. The diameter of the circular air defect is 40mm, the side length of the square air defect is 40mm, the diameter of the four steel bars is 20mm, the frequency of the ultrasonic probe transmitting longitudinal wave is 200kHz, and the longitudinal wave speed in the reinforced concrete is set to 4000m / s. The half diffusion angle θ calculated by formula (1) is 37.5°.

3. The improved time-domain synthetic aperture imaging fast algorithm for a reinforced concrete structure according to claim 2, characterized in that: In step two, according to the synthetic aperture detection method, the ultrasonic probe in the two-dimensional finite element simulation model of reinforced concrete is tested, and full matrix data is formed; specifically: The 12 ultrasonic probes are sequentially excited to emit ultrasonic signals. Each time one ultrasonic probe emits ultrasonic signals, the detection signals are received by the 12 ultrasonic probes. After one simulation test of the 12 ultrasonic probes is completed, a total of 144 aperture simulation detection signal data are collected, including 12 aperture simulation detection signal data collected by each ultrasonic probe. Full matrix data is formed and saved to the computer.

4. The improved time-domain synthetic aperture imaging fast algorithm for a reinforced concrete structure according to claim 3, characterized in that: In step three, each small square is taken as a pixel point, and the area of the small square is 1 mm 2 , and the total number of pixel points is 360 x 240.

5. The improved time-domain synthetic aperture imaging fast algorithm for a reinforced concrete structure according to claim 4, characterized in that: In step four, the half diffusion angle in step one is compared with the diffusion angle factor in step three, and the full matrix data in step two that meets the pixel point requirement for synthetic aperture processing is judged; specifically: The diffusion angle factor θ calculated by formula (2) np The mapping relationship between any pixel point P and the ultrasonic probe is established by comparing the half diffusion angle θ calculated by formula (1). diffusion angle factor θ np less than or equal to half the diffusion angle θ, set to "yes", the pixel point is synthesized aperture processed with the receiving signal of the ultrasonic probe; diffusion angle factor θ np greater than half the diffusion angle θ, set to "no", the pixel point can not be used with the ultrasound probe receiving signal for the synthesis aperture processing.

6. The improved time-domain synthetic aperture imaging fast algorithm for a reinforced concrete structure according to claim 5, characterized in that: In step five, according to the time domain synthetic aperture full focusing algorithm and combined with the judgment result in step four, the full matrix data in step two is imaged; specifically: According to the time domain synthetic aperture full focusing algorithm, the 144 full matrix data are imaged, and the imaging time is calculated for the full matrix data without diffusion angle factor and the full matrix data with diffusion angle factor respectively; The running time is recorded by using the timing function in the mathematical modeling software. The running time of the full matrix data without the diffraction angle factor is 189 s, 190 s, 187 s and 195 s, respectively, and the average time is 190.25 s. The running time of the full matrix data with the diffraction angle factor is 121 s, 119 s, 120 s and 118 s, respectively, and the average time is 119.75 s, and the operation speed is increased by 37%.

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