Plane wave imaging method and system of nonlinear ultrasonic guided wave phased array, and electronic equipment

Abstract

The invention relates to a non-linear ultrasonic guided wave phased array plane wave imaging method, system and electronic equipment, a fundamental wave phased array plane wave excitation mode and harmonic wave phased array element receiving mode are adopted, and visual representation of spatial distribution is carried out on micro-damage through plane wave reverse time migration imaging. The non-linear harmonic response in the pulse echo signal can be effectively improved, micro-damage positioning imaging with higher contrast and fewer artifacts is realized, and a new research thought is provided for solving the micro-damage positioning problem of a large-area plate structure.

Description

Technical Field

[0001] The present invention relates to the technical field of defect detection, and in particular to a plane wave imaging method, system and electronic equipment of a nonlinear ultrasonic guided wave phased array. Background Art

[0002] Under long-term extremely harsh operating conditions such as high load, stress concentration and chemical corrosion, the surface and interior of plate structures are prone to various damages such as cracks and holes. Timely detection and identification of these potential defects is crucial to prevent catastrophic accidents. Ultrasonic guided waves have become one of the important technical means for health monitoring and non-destructive testing and evaluation of plate structures due to their long propagation distance, sensitivity to internal defects, simple operation and harmlessness to the human body.

[0003] Traditional ultrasonic guided wave technology usually locates and characterizes the shape, size and position of macro defects within the wavelength range by analyzing the characteristics of damage scattered waves. However, fatigue cracks are one of the early signs of performance degradation of plate structures, and early detection of fatigue cracks is crucial to avoid further failures and major accidents. However, since the crack interface is usually very tight and it is difficult to form a significant scattering field, the traditional imaging method based on ultrasonic guided wave phased array is limited in the sensitivity of crack detection and imaging, and faces many technical challenges.

[0004] In summary, there is currently a lack of an ultrasonic guided wave detection method that can effectively solve or partially alleviate the above problems, which also provides an important research direction for the development of related technologies. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a plane wave imaging method, system, and electronic equipment of a nonlinear ultrasonic guided wave phased array to solve or partially solve the problem of unsatisfactory sensitivity of crack detection and imaging.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] In one aspect of the present invention, a method for plane wave imaging of a nonlinear ultrasonic guided wave phased array is provided, comprising the following steps:

[0008] Obtaining a focusing angle, and calculating a transmission phase difference of each array element in the first array based on a pre-constructed phased array beam deflection relationship;

[0009] Based on the transmission phase difference, controlling each array element in the first array to simultaneously excite the nonlinear ultrasonic guided wave to form a first fundamental plane wave incident at the focusing angle;

[0010] acquiring a first pulse echo signal received by a second array in response to the first fundamental plane wave;

[0011] Using the anti-phase transmission phase difference to excite a second fundamental plane wave, and acquiring a second pulse echo signal received by a second array in response to the second fundamental plane wave;

[0012] After superimposing the first pulse echo signal and the second pulse echo signal, extracting a forward second harmonic signal;

[0013] Calculating a first distance between a focus and an array element of the first array, and a second distance between a focus and an array element of the second array in the discretized imaging area;

[0014] Based on the first distance and the second distance, obtaining a reverse second harmonic signal by reversely propagating the first fundamental plane wave;

[0015] Based on the forward second harmonic signal and the reverse second harmonic signal, the pixel value of each focus is calculated through plane wave reverse time migration imaging to achieve positioning imaging of sub-wavelength scale micro-damages of the plate-like structure.

[0016] As a preferred technical solution, the transmission phase difference is:

[0017]

[0018] in, represents the transmission phase difference of the i-th array element in the first array, d represents the array element spacing of the first array, θ s represents the focusing angle, c 1 represents the phase velocity of the fundamental wave.

[0019] As a preferred technical solution, the first fundamental plane wave is:

[0020]

[0021] Where T(x, y, t) represents the wave field of the first fundamental plane wave arriving at the focus (x, y) at time t, and u 1 (t) is the excitation signal, k 1 (ω) is the fundamental wave number of ultrasonic guided waves that excites a single mode, L 1 (x, y) is the first distance.

[0022] As a preferred technical solution, the second fundamental plane wave is:

[0023]

[0024] Among them, R j (x, y, t) is the second harmonic wave field corresponding to the focal point (x, y) at time t when it is received by the jth element of the second array, k2 (ω) is the wave number of the corresponding second harmonic generated by the fundamental wave due to nonlinear effect, r j (t) is the signal received by the j-th element of the second array, is the second distance.

[0025] As a preferred technical solution, the calculation of the pixel value of each focus by plane wave reverse time migration imaging is implemented by the following formula:

[0026]

[0027] Wherein, I(x, y) represents the pixel value at the focus (x, y), N is the number of array elements of the second array, T is the sampling time of the signal, T(x, y, t) is the wave field of the first fundamental plane wave reaching the focus (x, y), R j (x, y, t) is the second harmonic wave field corresponding to the focus (x, y) at time t when received by the j-th array element of the second array.

[0028] As a preferred technical solution, after calculating the pixel value of each focus, the method further includes:

[0029] The pixel values ​​are normalized to the maximum value and logarithmized to the base 10 to achieve visualization within the preset value range.

[0030] Another aspect of the present invention provides a plane wave imaging system of a nonlinear ultrasonic guided wave phased array, characterized in that, for implementing the aforementioned plane wave imaging method of a nonlinear ultrasonic guided wave phased array, the system comprises a first array and a second array arranged on a plate-like structure to be measured.

[0031] As a preferred technical solution, the first array includes a plurality of piezoelectric array elements whose center frequency is the center frequency of the fundamental wave of the ultrasonic guided wave.

[0032] As a preferred technical solution, the second array includes a plurality of piezoelectric array elements whose center frequency is the center frequency of the second harmonic of the ultrasonic guided wave.

[0033] Another aspect of the present invention provides an electronic device, comprising: one or more processors and a memory, wherein the memory stores one or more programs, and the one or more programs include instructions for executing the aforementioned plane wave imaging method of the nonlinear ultrasonic guided wave phased array.

[0034] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0035] (1) Enhanced response to nonlinear harmonics: The present invention combines fundamental wave phased array excitation of plane waves and harmonic wave phased array reception to achieve a significant enhancement of the nonlinear harmonic response in the pulse echo signal, breaking through the limitations of traditional single excitation or reception modes and improving detection sensitivity and signal quality.

[0036] (2) High sensitivity: The present invention combines plane wave reverse time migration imaging to perform high-contrast, low-artifact visualization of the spatial distribution of microdamages, solving the problem of high difficulty in locating subwavelength-scale microdamages in large-area plate-like structures, and providing a new approach for nondestructive detection of microdamages in complex structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a flow chart of the plane wave imaging method of the nonlinear ultrasonic guided wave phased array in the embodiment;

[0038] Figure 2 Schematic diagram of defect positions in the aluminum alloy plate to be tested and fundamental wave phased array and harmonic wave phased array in the embodiment;

[0039] Figure 3 The spectrum diagram of the signal obtained by the plane wave incident method and the one-transmit-one-receive full-matrix data acquisition method in the embodiment;

[0040] Figure 4 Schematic diagram of typical nonlinear ultrasonic guided wave plane wave imaging results obtained in the embodiment;

[0041] Figure 5 Schematic diagram of typical nonlinear ultrasonic guided wave total focusing imaging results obtained in the embodiment;

[0042] Figure 6 Schematic diagram of an electronic device in an embodiment. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0044] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0045] Example 1

[0046] In view of the defects of the aforementioned prior art, this embodiment takes into account that nonlinear ultrasonic guided waves can produce nonlinear mechanical interactions with microstructures such as dislocations, grains, precipitates, and tiny defects such as microcracks and micropores. However, the existing nonlinear ultrasonic guided wave detection technology usually requires high-energy excitation, and the received harmonic signal is still weak, resulting in the imaging effect being prone to artifacts and poor image contrast. A plane wave imaging method of a nonlinear ultrasonic guided wave phased array is provided to achieve micro-damage enhanced imaging based on a nonlinear ultrasonic guided wave phased array.

[0047] See also Figure 1 , the method comprises the following steps:

[0048] Step S1, calculating the transmission phase difference of each fundamental wave array element (ie, the array element of the first array) according to the phased array beam deflection formula and the focusing angle.

[0049] The fundamental wave phased array is composed of piezoelectric array elements whose center frequency is the center frequency of the fundamental wave of the ultrasonic guided wave, and the harmonic array elements are composed of piezoelectric array elements whose center frequency is the center frequency of the second harmonic of the ultrasonic guided wave.

[0050] The transmitting phase difference of the fundamental wave array element is:

[0051]

[0052] Where i represents the i-th fundamental wave array element, d represents the array element spacing of the fundamental wave phased array, and θ s represents the focusing angle, c 1 represents the phase velocity of the fundamental wave.

[0053] Step S2: Based on the transmission phase difference, the ultrasonic guided wave is excited simultaneously according to the transmission phase difference of each fundamental wave array element to form a forward fundamental wave plane wave (ie, a first fundamental wave plane wave) incident at a focusing angle.

[0054] Among them, the excitation signal of the i-th fundamental wave array element is:

[0055]

[0056] Where, τ is the pulse width of the excitation signal, f 1 is the frequency of the incident fundamental wave.

[0057] The forward propagation fundamental plane wave field is:

[0058]

[0059] Where T(x, y, t) represents the incident plane wave field reaching the focus (x, y), u 1 (t) is the excitation signal, k1 (ω) is the fundamental wave number of ultrasonic guided waves that excites a single mode, L 1 (x, y) is the propagation distance of the plane wave from the fundamental phased array to the focus.

[0060] Step S3: using harmonic array elements (ie, array elements of the second array) to receive the pulse echo signal of the ultrasonic guided wave (ie, the first pulse echo signal).

[0061] Step S4, using the excitation signal with an opposite phase to excite the fundamental plane wave again (i.e., the second fundamental plane wave), and simultaneously recording the pulse echo signal with an opposite phase (i.e., the second pulse echo signal);

[0062] The time-reversed second harmonic wave field is:

[0063]

[0064] Among them, R j (x, y, t) is the second harmonic wave field corresponding to the reception of the jth harmonic phased array element at the focus (x, y) at time t, k 2 (ω) is the wave number of the corresponding second harmonic generated by the fundamental wave due to nonlinear effect, r j (t) is the signal received by the jth harmonic phased array element, is the distance between each focus and the jth harmonic phased array element.

[0065] Step S5, based on the pulse echo signal, adding the signals collected twice, and then extracting the second harmonic signal through a bandpass filter.

[0066] Step S6, respectively calculating the propagation distance of the fundamental plane wave in the discretized imaging area (ie, the first distance) and the distance from the focus to each receiving array element (ie, the second distance).

[0067] Step S7, based on the distance, forwardly propagate the fundamental plane wave according to the distance, and reversely propagate the received second harmonic signal.

[0068] Step S8, based on the forward propagating fundamental plane wave and the backward propagating second harmonic signal, the plane wave reverse time migration imaging formula is used to calculate the pixel value of each focus to achieve positioning imaging of sub-wavelength scale micro-damages in the plate-like structure.

[0069] Preferably, after calculating the pixel value of each focus, the pixel value is normalized according to the maximum value and the logarithm is taken with a base of 10 and then displayed within a preset value range.

[0070] Specifically, the plane wave reverse time migration imaging formula is:

[0071]

[0072] Where I(x, y) represents the pixel value at the focus (x, y), N is the number of elements of the harmonic phased array, T is the sampling time of the signal, T(x, y, t) is the incident plane wave field reaching the focus (x, y), R j (x, y, t) is the harmonic wave field at the focus (x, y) at time t when received by the jth harmonic phased array element.

[0073] The following is an example of an aluminum alloy plate to be tested to illustrate this method. Figure 2 The size of the aluminum plate is 200mm×300mm×2mm; there is a through hole with a diameter of 6mm at (100,155), and there is a closed microcrack on the left side of the through hole, which is about 2mm long and less than 50μm wide. The fundamental phased array consists of 6 piezoelectric sheets with a diameter of 10mm arranged linearly, and the harmonic phased array consists of 10 piezoelectric sheets with a diameter of 6mm arranged linearly.

[0074] Step 1: The excitation signal of each fundamental phased array element is a 10-cycle sinusoidal pulse signal modulated by a certain delay Hanning window with a frequency of 300kHz. The formula is:

[0075]

[0076] Where t is time, τ is the total duration of the pulse signal, and f 1 is the center frequency of the pulse signal, i is the i-th phased array element, d is the fundamental phased array element spacing, θ s is the focusing angle, c 1 is the phase velocity of the fundamental wave.

[0077] Step 2: All elements of the fundamental wave phased array are excited simultaneously, forming an incident angle of θ s The harmonic phased array receives the pulse echo signal, the signal sampling frequency is 50MHz, and the sampling time is 20ms.

[0078] Step 3: The imaging area is a 100mm×100mm area in the center of the plate, and the discretized pixel spacing is 1mm. The propagation distance of the fundamental plane wave in the discretized imaging area and the distance from the focus to each harmonic phased array element are calculated respectively.

[0079] Step 4: Use the ultrasonic guided wave propagation model to calculate the fundamental plane wave field T(x, y, t) reaching the focus (x, y). The formula is as follows:

[0080]

[0081] Among them, u 1 (t) is the excitation signal, k 1(ω) is the fundamental wave number of ultrasonic guided waves that excites a single mode, L 1 (x, y) is the propagation distance of the plane wave from the fundamental phased array to the focus.

[0082] Step 5: By time-reversing the received harmonic signal, the harmonic wave field R at each focus can be obtained. j (x, y, t), the formula is as follows:

[0083]

[0084] Among them, R j (x, y, t) is the second harmonic wave field corresponding to the reception of the jth harmonic phased array element at the focus (x, y) at time t, k 2 (ω) is the wave number of the corresponding second harmonic generated by the fundamental wave due to nonlinear effect, r j (t) is the signal received by the jth harmonic phased array element, is the distance between each focus and the jth harmonic phased array element.

[0085] Step 6, for each focus, the pixel value of the image is calculated by the plane wave reverse time migration imaging formula, which is as follows:

[0086]

[0087] Where I(x, y) represents the pixel value at the focus (x, y), N is the number of harmonic phased array elements, and T is the sampling time of the signal.

[0088] Reference Figure 3 The spectrum diagram of the signal obtained by the method provided in the embodiment is compared with the spectrum diagram of the signal obtained by the one-pitch-one-catch full-matrix data acquisition method. It can be seen that the second harmonic response obtained by the plane wave excitation method is about 15dB higher than that based on the one-pitch-one-catch full-matrix data acquisition method.

[0089] Reference Figure 4 This is a typical imaging result diagram obtained by the method provided in this embodiment. In the figure, the pixel value is normalized to the maximum value and the logarithm with base 10 is taken and displayed in the range of -20 to 0 dB. The brighter the color bar on the right, the higher the pixel value and the stronger the nonlinear response.

[0090] Reference Figure 5 This is a typical imaging result diagram of a nonlinear ultrasonic guided wave phased array based on full matrix data acquisition and full focusing imaging algorithm. In the figure, the pixel value is normalized to the maximum value and displayed in the range of -20 to 0 dB. The brighter the color bar on the right, the higher the pixel value and the greater the probability of the defect. It can be seen that the microcrack imaging diagram obtained by the method provided in this embodiment has fewer artifacts and better imaging effect.

[0091] This method is based on the fundamental wave phased array excitation plane wave and harmonic wave phased array element reception. It uses plane wave reverse time migration imaging to visualize the spatial distribution of micro-damages. It can effectively improve the nonlinear harmonic response in the pulse echo signal and achieve micro-damage localization imaging with higher contrast and fewer artifacts, providing a new research idea for solving the problem of micro-damage localization in large-area plate structures.

[0092] The present invention has the following characteristics:

[0093] (1) Fundamental plane wave excitation method: This method combines the fundamental phased array excitation plane wave and harmonic phased array reception technology to achieve a significant enhancement of the nonlinear harmonic response in the pulse echo signal. This innovative design breaks through the limitations of traditional single excitation or reception modes and improves detection sensitivity and signal quality.

[0094] (2) Application of plane wave reverse time migration imaging: By introducing plane wave reverse time migration imaging technology, the spatial distribution of micro-damages can be visualized with high contrast and low artifacts, solving the problem of high difficulty in locating sub-wavelength-scale micro-damages in large-area plate-like structures, and providing new ideas for non-destructive detection of micro-damages in complex structures.

[0095] Example 2

[0096] See also Figure 6 This embodiment provides an electronic device, including: one or more processors and a memory, wherein one or more programs are stored in the memory, and the one or more programs include instructions for executing the nonlinear ultrasonic guided wave phased array imaging method based on hybrid array elements and time reversal as described in Example 1.

[0097] like Figure 2 As mentioned above, at the hardware level, the electronic device includes a processor, an internal bus, a network interface, a memory, and a non-volatile memory, and may also include other hardware required for the business. The processor reads the corresponding computer program from the non-volatile memory into the memory and then runs it to achieve the above Figure 1 Of course, in addition to the software implementation, the present invention does not exclude other implementations, such as logic devices or a combination of software and hardware, etc., that is, the execution subject of the following processing flow is not limited to each logic unit, but can also be hardware or logic devices.

[0098] The memory may include non-permanent storage in a computer-readable medium, random access memory (RAM) and / or non-volatile memory in the form of read-only memory (ROM) or flash RAM. The memory is an example of a computer-readable medium.

[0099] Computer readable media include permanent and non-permanent, removable and non-removable media that can be implemented by any method or technology to store information. Information can be computer readable instructions, data structures, program modules or other data. Examples of computer storage media include, but are not limited to, phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disk read-only memory (CD-ROM), digital versatile disk (DVD) or other optical storage, magnetic cassettes, magnetic disk storage or other magnetic storage devices or any other non-transmission media that can be used to store information that can be accessed by a computing device. As defined herein, computer readable media does not include temporary computer readable media (transitory media), such as modulated data signals and carrier waves.

[0100] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A plane wave imaging method of a nonlinear ultrasonic guided wave phased array, characterized in that: The steps include: Obtaining a focusing angle, and calculating a transmission phase difference of each array element in the first array based on a pre-constructed phased array beam deflection relationship; Based on the transmission phase difference, controlling each array element in the first array to simultaneously excite the nonlinear ultrasonic guided wave to form a first fundamental plane wave incident at the focusing angle; acquiring a first pulse echo signal received by a second array in response to the first fundamental plane wave; Using the anti-phase transmission phase difference to excite a second fundamental plane wave, and acquiring a second pulse echo signal received by a second array in response to the second fundamental plane wave; After superimposing the first pulse echo signal and the second pulse echo signal, extracting a forward second harmonic signal; Calculating a first distance between a focus and an array element of the first array, and a second distance between a focus and an array element of the second array in the discretized imaging area; Based on the first distance and the second distance, obtaining a reverse second harmonic signal by reversely propagating the first fundamental plane wave; Based on the forward second harmonic signal and the reverse second harmonic signal, the pixel value of each focus is calculated through plane wave reverse time migration imaging to achieve positioning imaging of sub-wavelength scale micro-damages of the plate-like structure.

2. The plane wave imaging method of a nonlinear ultrasonic guided wave phased array according to claim 1, characterized in that: The transmission phase difference is: in, represents the transmission phase difference of the i-th array element in the first array, d represents the array element spacing of the first array, θ s represents the focusing angle, and c1 represents the phase velocity of the fundamental wave.

3. The plane wave imaging method of a nonlinear ultrasonic guided wave phased array according to claim 1, characterized in that: The first fundamental plane wave is: Where T(x,y,t) represents the wave field of the first fundamental plane wave reaching the focus (x,y) at time t, u1(t) is the excitation signal, k1(ω) is the fundamental wave number of the ultrasonic guided wave that excites a single mode, and L 1 (x, y) is the first distance.

4. The plane wave imaging method of a nonlinear ultrasonic guided wave phased array according to claim 1, characterized in that: The second fundamental plane wave is: Among them, R j (x, y, t) is the second harmonic wave field corresponding to the reception of the jth second array element at the focus (x, y) at time t, k2(ω) is the wave number of the corresponding second harmonic generated by the fundamental wave due to the nonlinear effect, r j (t) is the signal received by the j-th element of the second array, is the second distance.

5. The plane wave imaging method of a nonlinear ultrasonic guided wave phased array according to claim 1, characterized in that: The calculation of the pixel value of each focus by plane wave reverse time migration imaging is implemented by the following formula: Wherein, I(x,y) represents the pixel value at the focus (x,y), N is the number of array elements of the second array, Τ is the sampling time of the signal, T(x,y,t) is the wave field of the first fundamental plane wave reaching the focus (x,y), R j (x, y, t) is the second harmonic wave field corresponding to the focus (x, y) at time t when it is received by the j-th array element of the second array.

6. The plane wave imaging method of a nonlinear ultrasonic guided wave phased array according to claim 1, characterized in that: After calculating the pixel value of each focus, the method further includes: The pixel values ​​are normalized to the maximum value and logarithmized to the base 10 to achieve visualization within the preset value range.

7. A plane wave imaging system of a nonlinear ultrasonic guided wave phased array, characterized in that: A method for plane wave imaging of a nonlinear ultrasonic guided wave phased array as described in any one of claims 1 to 6, wherein the system comprises a first array and a second array arranged on a plate-like structure to be measured.

8. The plane wave imaging system of a nonlinear ultrasonic guided wave phased array according to claim 7, characterized in that: The first array includes a plurality of piezoelectric array elements whose center frequency is the center frequency of the fundamental wave of the ultrasonic guided wave.

9. The nonlinear ultrasonic guided wave phased array plane wave imaging system according to claim 7, characterized in that: The second array includes a plurality of piezoelectric array elements whose center frequency is the center frequency of the second harmonic of the ultrasonic guided wave.

10. An electronic device, characterized in that: include: One or more processors and a memory, wherein the memory stores one or more programs, and the one or more programs include instructions for executing the plane wave imaging method of the nonlinear ultrasonic guided wave phased array as described in any one of claims 1-6.

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