Nonlinear ultrasonic guided wave phased array imaging method based on mixed array elements and time reversal

Abstract

The invention relates to a nonlinear ultrasonic guided wave phased array imaging method based on mixed array elements and time reversal. The method comprises the following steps: exciting a fundamental wave and receiving a second harmonic wave at piezoelectric array elements of the fundamental wave and the second harmonic wave of an ultrasonic guided wave by using a center frequency respectively; full-matrix data of ultrasonic guided wave signals in the detected workpiece are obtained in a one-transmitting and one-receiving mode; a fundamental wave signal is suppressed and a second harmonic signal is enhanced by adopting a pulse inversion mode; for the full-matrix data after pulse inversion, utilizing continuous wavelet transform filtering to extract a second harmonic signal; respectively calculating the distance from the discretized imaging area to the excitation array element and the distance from the discretized imaging area to the receiving array element; and for each discrete pixel point, according to an excitation signal of a distance forward propagation fundamental wave and a received second harmonic signal back propagation, a pixel value is calculated by using a time domain topology energy equation, and local acoustic nonlinear imaging of the plate-shaped structure is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrasonic guided wave detection, and in particular to a nonlinear ultrasonic guided wave phased array imaging method based on hybrid array elements and time reversal. Background Art

[0002] Under extremely harsh operating conditions such as long-term 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 of great significance for preventing catastrophic accidents. Ultrasonic guided waves have become one of the important technical means for health monitoring, non-destructive testing and evaluation of plate structures due to their long propagation distance, sensitivity to internal structural defects, convenient operation and harmlessness to the human body.

[0003] Traditional ultrasonic guided wave technology locates and characterizes the shape, size and position of wavelength-level macro defects by analyzing the amplitude change, phase deviation, flight time, reflection / transmittance ratio, energy attenuation and mode conversion of damage scattered waves. However, fatigue cracks are one of the early signs of performance degradation of plate structures, and their early detection is crucial to prevent further failures and major accidents. However, since the crack interface is usually relatively tight and it is difficult to form a significant scattering field, the imaging method based on traditional ultrasonic guided wave phased array has low sensitivity for crack detection and imaging, and faces great technical challenges.

[0004] Compared with linear ultrasonic guided waves, nonlinear ultrasonic guided waves have been applied to nondestructive detection and assessment of early damage because they can produce nonlinear mechanical interactions with microstructures such as dislocations, grains, and precipitates, as well as micro defects such as microcracks and micropores. However, the existing nonlinear ultrasonic guided wave detection technology can only characterize the cumulative degree of damage in the acoustic channel, and it is difficult to accurately characterize the spatial distribution of local damage that causes acoustic nonlinear effects. In addition, the nonlinear ultrasonic guided wave signal is weak, has a dispersion effect, and is difficult to focus.

[0005] In summary, there is currently a lack of an ultrasonic guided wave detection method to solve or partially solve the above-mentioned problems. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a nonlinear ultrasonic guided wave phased array imaging method based on hybrid array elements and time reversal, so as to solve or partially solve the problems of inaccurate pickup of nonlinear ultrasonic guided wave signals and strong defect imaging intensity.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] The present invention provides a nonlinear ultrasonic guided wave phased array imaging method based on hybrid array elements and time reversal, comprising the following steps:

[0009] In a single-element transmission and multi-element reception mode, in response to the nonlinear ultrasonic guided wave fundamental wave transmitted by the transmitting array element, the receiving array element receives the second harmonic to obtain full matrix data corresponding to the multiple transmitting array elements;

[0010] enhancing the second harmonic component in the full matrix data by pulse inversion;

[0011] Extracting the second harmonic component in the full matrix data by continuous wavelet transform to obtain a second harmonic signal;

[0012] Obtain the distance from the discrete imaging area to the transmitting array element and the receiving array element;

[0013] Based on the distance, forwardly propagate the excitation signal of the nonlinear ultrasonic guided wave fundamental wave, and backward propagate the second harmonic signal;

[0014] The pixel value of each pixel is obtained through time-domain topological energy calculation to achieve imaging.

[0015] As a preferred technical solution, the center frequency of the transmitting array element is configured as the fundamental wave of the nonlinear ultrasonic guided wave, and the center frequency of the receiving array element is configured as the second harmonic of the nonlinear ultrasonic guided wave.

[0016] As a preferred technical solution, each transmitting array element transmits excitation individually, and multiple receiving array elements receive together, thereby achieving the acquisition of full matrix data corresponding to the multiple transmitting array elements.

[0017] As a preferred technical solution, the process of enhancing the second harmonic component in the full matrix data by pulse inversion comprises the following steps:

[0018] The full matrix data corresponding to the excitation after inversion is obtained, and the full matrix data before and after inversion are superimposed to enhance the second harmonic component in the full matrix data.

[0019] As a preferred technical solution, the filtering center frequency band of the continuous wavelet transform is the frequency band of the second harmonic.

[0020] As a preferred technical solution, the nonlinear ultrasonic guided wave fundamental wave excitation signal of the transmitting array element is:

[0021]

[0022] Where u(t) is the excitation signal, t is time, τ is the total duration of the pulse signal, and f1 is the center frequency of the pulse signal.

[0023] As a preferred technical solution, the excitation signal of the forward propagating nonlinear ultrasonic guided wave fundamental wave is:

[0024]

[0025] Among them, U i (x, y, t) represents the incident fundamental wave field emitted by the i-th transmitting array element at the pixel point (x, y) at time t, k1(ω) is the fundamental wave number of the ultrasonic guided wave that excites a single mode, d i (x, y) is the distance between each focus and the i-th transmit element.

[0026] As a preferred technical solution, the reverse propagation of the second harmonic signal is:

[0027]

[0028] Among them, S ij (x, y, t) is the second harmonic wave field corresponding to the focal point (x, y) at time t when it is transmitted by the i-th transmitting array element and received by the j-th receiving array element. k2(ω) is the second harmonic wave number generated by the fundamental wave due to the nonlinear effect. s ij (t) is a signal transmitted by the i-th transmitting array element and received by the j-th receiving array element, obtained based on the full matrix data, j (x, y) is the distance between each focus and the jth receiving element.

[0029] As a preferred technical solution, the pixel value of each pixel is calculated by the following formula:

[0030]

[0031] Where I(x, y) represents the pixel value at the focus (x, y), M and N are the number of transmitting and receiving array elements, T is the sampling time of the signal, and U i (x, y, t) is the incident fundamental wave field emitted by the i-th transmitting array element at the focal point (x, y) at time t, S ii (x, y, t) is the harmonic wave field emitted by the i-th transmitting array element and received by the j-th receiving array element at the focus (x, y) at time t.

[0032] As a preferred technical solution, after calculating the pixel value of each focus, it also includes:

[0033] The pixel value is normalized to the maximum value and the logarithm is taken to the base 10 and then displayed within the preset value range.

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

[0035] (1) Enhancement and extraction of nonlinear ultrasonic guided wave signals: The present invention uses array elements with a center frequency of the fundamental wave to transmit and detect the fundamental wave and array elements with a center frequency of the second harmonic wave to receive the nonlinear ultrasonic guided wave response, and further suppresses the fundamental wave signal through pulse inversion technology, enhances the second harmonic response, and finally uses continuous wavelet transform filtering to extract the second harmonic signal. This effectively enhances the pickup of nonlinear ultrasonic guided wave signals.

[0036] (2) Subwavelength scale defect imaging: The present invention performs spatial characterization of micro-damage based on acoustic nonlinear effects, utilizes time-reversal refocusing of the second harmonic wave field, and combines the time-domain topological energy equation to calculate the pixel value of each focus, thereby achieving subwavelength scale defect imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a flow chart of a nonlinear ultrasonic guided wave phased array imaging method based on hybrid array elements and time reversal in an embodiment;

[0038] Figure 2 Schematic diagram of defect positions in the aluminum alloy plate to be tested and the arrangement of a hybrid array element phased array consisting of 6 fundamental wave transmitting array elements and 5 harmonic wave receiving array elements in the embodiment;

[0039] Figure 3 Schematic diagram of typical nonlinear ultrasonic guided wave imaging results obtained in the embodiment;

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

[0041] Figure 5 Schematic diagram of an electronic device in an embodiment. DETAILED DESCRIPTION

[0042] 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.

[0043] Example 1

[0044] In view of the problems existing in the above-mentioned prior art, this embodiment provides a nonlinear ultrasonic guided wave phased array imaging method based on hybrid array elements and time reversal to realize sub-wavelength level defect detection based on ultrasonic guided waves. Figure 1 , including the following steps:

[0045] Step S1: using the piezoelectric array elements with center frequencies at the fundamental wave and the second harmonic of the ultrasonic guided wave to respectively excite the fundamental wave and receive the second harmonic.

[0046] Preferably, this step is implemented using a hybrid array element phased array, which is composed of a fundamental wave transmitting array element whose center frequency is the fundamental wave of the ultrasonic guided wave and a harmonic receiving array element whose center frequency is the second harmonic of the ultrasonic guided wave.

[0047] Step S2: Acquire the full matrix data of the ultrasonic guided wave signal in the inspection workpiece by adopting a one-transmit-one-receive method.

[0048] The full matrix data is acquired by sequentially stimulating the single fundamental wave transmitting array element and receiving the remaining harmonic receiving array elements.

[0049] Step S3: suppress the fundamental signal and enhance the second harmonic signal by pulse inversion.

[0050] Preferably, the pulse inversion is to excite the ultrasonic guided wave in an anti-phase manner, and then obtain the anti-phase signal of the pulse inversion by full-matrix data acquisition.

[0051] Step S4: Extract the second harmonic signal using continuous wavelet transform filtering.

[0052] Preferably, the central frequency band of the continuous wavelet transform filter is the intermediate frequency band of the second harmonic.

[0053] Step S5: respectively calculating the distance from the discretized imaging area to the excitation array element and the distance from the imaging area to the receiving array element.

[0054] Step S6: forwardly propagate the excitation signal of the fundamental wave according to the distance, and reversely propagate the received second harmonic signal.

[0055] Specifically, the forward propagation fundamental signal is:

[0056]

[0057] Among them, U i (x, y, t) represents the incident fundamental wave field emitted by the ith fundamental wave transmitting array element at the pixel point (x, y) at time t, k1(ω) is the fundamental wave number of the ultrasonic guided wave that excites a single mode, d i (x, y) is the distance between each focus and the i-th transmit element.

[0058] The time-reversed second harmonic wave field is:

[0059]

[0060] Among them, S ii(x, y, t) is the second harmonic wave field corresponding to the fundamental wave transmitted by the i-th fundamental wave transmitting element and received by the j-th harmonic wave receiving element at the focus (x, y) at time t, k2(ω) is the second harmonic wave number generated by the fundamental wave due to the nonlinear effect, s ij (t) is the signal transmitted by the i-th array element and received by the j-th array element obtained based on the full matrix data, d j (x, y) is the distance between each focus and the jth receiving element.

[0061] Step S7: Calculate the pixel value of each pixel using the time domain topological energy equation.

[0062] Specifically, the pixel value of each pixel is calculated by the following formula:

[0063]

[0064] Where I(x, y) represents the pixel value at the focus (x, y), M and N are the number of fundamental wave transmitting elements and the number of harmonic wave receiving elements of the hybrid array element phased array, T is the sampling time of the signal, and U i (x, y, t) is the incident fundamental wave field emitted by the i-th fundamental wave transmitting array element reaching the focus (x, y) at time t, S ij (x, y, t) is the harmonic wave field at the focus (x, y) at time t when it is transmitted by the i-th array element and received by the j-th harmonic receiving array element.

[0065] Preferably, after calculating the pixel value of each focus, the method further includes:

[0066] The pixel value is normalized to the maximum value and the logarithm is taken to the base 10 and then displayed within the preset value range.

[0067] 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 350mm×420mm×2mm; there are two through holes with a diameter of 6mm, and the center coordinates are (175, 205) and (235, 230) respectively; there is a closed microcrack on the left side of the through hole at (175, 205), which is about 2mm long and less than 50μm wide. The hybrid element phased array consists of 6 fundamental wave transmitting elements and 5 harmonic receiving elements, and the fundamental wave transmitting elements and the harmonic receiving elements are arranged alternately.

[0068] Step 1: The excitation signal uses a 10-cycle sine pulse signal modulated by a Hanning window with a frequency of 300kHz. The formula is:

[0069]

[0070] Where t is time, τ is the total duration of the pulse signal, and f1 is the center frequency of the pulse signal.

[0071] Step 2: The phased array is excited by the single fundamental wave transmitting array element in sequence, and the other five harmonic receiving array elements are used to receive the data, so as to acquire the full matrix data. In this way, a total of 30 groups of time domain signals are acquired. The signal sampling frequency is 50MHz, and the sampling time is 20ms.

[0072] Step 3, the imaging area is a 200mm×200mm area in the center of the board, and the discretized pixel spacing is 1mm. First, the distance from the grid to each phased array element is calculated based on the coordinates of each focus and the coordinates of the sensor. The distance calculation formula from the i-th fundamental wave transmitting element to the focus with coordinates (x, y) is as follows:

[0073]

[0074] Among them, (x i ,y i ) is the coordinate of the ith fundamental wave transmitting array element. Similarly, the distance calculation formula from the jth harmonic receiving array element to the focal point with coordinates (x, y) is as follows:

[0075]

[0076] Among them, (x j , yj) is the coordinate of the jth harmonic receiving array element.

[0077] Step 4: Use the ultrasonic guided wave propagation model to calculate the incident fundamental wave field U emitted by the i-th fundamental wave transmitting array element reaching the focus (x, y). i (x, y, t), the formula is as follows:

[0078]

[0079] Where k1(ω) is the wave number of the fundamental wave, d i (x, y) is the distance between each focus and the i-th fundamental wave transmitting array element.

[0080] Step 5: By time-reversing the received harmonic signal, the harmonic wave field S at each focus can be obtained. ij (x, y, t), the formula is as follows:

[0081]

[0082] Among them, s ij (t) is the signal transmitted by the i-th fundamental wave transmitting array element and received by the j-th harmonic receiving array element, d j (x, y) is the distance between each focus and the jth harmonic receiving array element.

[0083] Step 6, for each focus, the pixel value of the image is calculated by the time domain topological energy equation, the formula is as follows:

[0084]

[0085] Among them, M and N are the number of fundamental wave transmitting array elements and the number of harmonic wave receiving array elements respectively, and T is the sampling time of the signal.

[0086] Reference Figure 3 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 -6 to 0 dB. The brighter the color bar on the right, the higher the pixel value and the stronger the nonlinear response.

[0087] Reference Figure 4 This is a typical imaging result diagram of a linear ultrasonic guided wave phased array based on a full-focus imaging algorithm. In the figure, the pixel value is normalized to the maximum value and displayed in the range of -6 to 0 dB. The brighter the color bar on the right, the higher the pixel value and the greater the probability of a defect. It can be seen that the traditional method can only image through holes and cannot detect closed microcracks. The method provided in this embodiment can effectively locate and image closed microcracks.

[0088] In summary, this method is based on hybrid array elements and time reversal strategy, and uses nonlinear ultrasonic guided wave phased array to image micro-damages. It can effectively realize the efficient excitation and enhanced picking of nonlinear harmonic signals, and can realize the positioning imaging of subwavelength scale defects, providing a new research idea for solving the problem of micro-damage positioning in large-area plate structures.

[0089] Example 2

[0090] Based on Example 1, see Figure 5 This embodiment provides an electronic device, including: 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 nonlinear ultrasonic guided wave phased array imaging method based on hybrid array elements and time reversal described in Example 1.

[0091] 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 1Of 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.

[0092] 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.

[0093] 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.

[0094] 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 nonlinear ultrasonic guided wave phased array imaging method based on hybrid array elements and time reversal, characterized in that: The steps include: In a single-element transmission and multi-element reception mode, in response to the nonlinear ultrasonic guided wave fundamental wave transmitted by the transmitting array element, the receiving array element receives the second harmonic to obtain full matrix data corresponding to the multiple transmitting array elements; enhancing the second harmonic component in the full matrix data by pulse inversion; Extracting the second harmonic component in the full matrix data by continuous wavelet transform to obtain a second harmonic signal; Obtain the distance from the discrete imaging area to the transmitting array element and the receiving array element; Based on the distance, forwardly propagate the excitation signal of the nonlinear ultrasonic guided wave fundamental wave, and backward propagate the second harmonic signal; The pixel value of each pixel is obtained through time-domain topological energy calculation to achieve imaging.

2. The nonlinear ultrasonic guided wave phased array imaging method based on hybrid array elements and time reversal according to claim 1, characterized in that: The center frequency of the transmitting array element is configured as the fundamental wave of the nonlinear ultrasonic guided wave, and the center frequency of the receiving array element is configured as the second harmonic of the nonlinear ultrasonic guided wave.

3. The nonlinear ultrasonic guided wave phased array imaging method based on hybrid array elements and time reversal according to claim 1, characterized in that: Each transmitting array element transmits excitation independently, and multiple receiving array elements receive together, thereby realizing the acquisition of full matrix data corresponding to multiple transmitting array elements.

4. The nonlinear ultrasonic guided wave phased array imaging method based on hybrid array elements and time reversal according to claim 1, characterized in that: The process of enhancing the second harmonic component in the full matrix data by pulse inversion comprises the following steps: The full matrix data corresponding to the excitation after inversion is obtained, and the full matrix data before and after inversion are superimposed to enhance the second harmonic component in the full matrix data.

5. The nonlinear ultrasonic guided wave phased array imaging method based on hybrid array elements and time reversal according to claim 1, characterized in that: The filtering center frequency band of the continuous wavelet transform is the frequency band of the second harmonic.

6. The nonlinear ultrasonic guided wave phased array imaging method based on hybrid array elements and time reversal according to claim 1, characterized in that: The nonlinear ultrasonic guided wave fundamental wave excitation signal of the transmitting array element is: Where u(t) is the excitation signal, t is time, τ is the total duration of the pulse signal, and f1 is the center frequency of the pulse signal.

7. The nonlinear ultrasonic guided wave phased array imaging method based on hybrid array elements and time reversal according to claim 1, characterized in that: The excitation signal of the forward propagating nonlinear ultrasonic guided wave fundamental wave is: Among them, U i (x, y, t) represents the incident fundamental wave field emitted by the i-th transmitting array element at the pixel point (x, y) at time t, k1(ω) is the fundamental wave number of the ultrasonic guided wave that excites a single mode, and d i (x,y) is the distance between each focus and the i-th transmitting element.

8. The nonlinear ultrasonic guided wave phased array imaging method based on hybrid array elements and time reversal according to claim 1, characterized in that: The reverse propagation of the second harmonic signal is: Among them, S ij (x, y, t) is the second harmonic wave field corresponding to the second harmonic wave emitted by the i-th transmitting element and received by the j-th receiving element at the focus (x, y) at time t, k2(ω) is the second harmonic wave number generated by the fundamental wave due to the nonlinear effect, s ij (t) is a signal transmitted by the i-th transmitting array element and received by the j-th receiving array element, obtained based on the full matrix data, j (x,y) is the distance between each focus and the jth receiving element.

9. The nonlinear ultrasonic guided wave phased array imaging method based on hybrid array elements and time reversal according to claim 1, characterized in that: The pixel value of each pixel is calculated by the following formula: Where I(x,y) represents the pixel value at the focus (x,y), M and N are the number of transmitting and receiving array elements, T is the sampling time of the signal, and U i (x, y, t) is the incident fundamental wave field emitted by the i-th transmitting array element reaching the focus (x, y) at time t, S ij (x, y, t) is the harmonic wave field emitted by the i-th transmitting array element and received by the j-th receiving array element at the focus (x, y) at time t.

10. The nonlinear ultrasonic guided wave phased array imaging method based on hybrid array elements and time reversal according to claim 1, characterized in that: After calculating the pixel value of each focus, the method further includes: normalizing the pixel value according to the maximum value and taking the logarithm with a base of 10 and then displaying the pixel value within a preset value range.

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