A solid defect imaging method based on the static component of ultrasonic longitudinal waves

Abstract

This invention discloses a solid defect imaging method based on the static component of ultrasonic longitudinal waves. The method includes: applying a positive-phase excitation signal to a dual-frequency ultrasonic transducer array to acquire a first echo signal; inverting the excitation signal to the dual-frequency ultrasonic transducer array to acquire a second echo signal; processing the first and second echo signals using pulse inversion and low-pass filtering techniques to obtain the time-domain signal of the ultrasonic longitudinal wave static component echo; and calculating imaging parameters based on an imaging algorithm using the time-domain signal of the ultrasonic longitudinal wave static component echo, and using the imaging parameters as pixel values ​​to obtain the imaging result. This method can realize defect imaging in solids and has good application prospects and value.

Description

Technical Field

[0001] This invention belongs to the field of ultrasonic nondestructive testing technology, and specifically relates to a solid defect imaging method based on the static component of ultrasonic longitudinal waves. Background Technology

[0002] The static component of ultrasound is generated when ultrasound propagates in a solid due to material nonlinearity, defects, etc., and its carrier frequency is zero. Compared with the traditional fundamental frequency component and higher harmonic components, the static component of ultrasound has the advantages of lower sound attenuation and longer propagation distance, making it a promising method for nondestructive testing and structural health monitoring.

[0003] The information disclosed in the background section is only intended to enhance the understanding of the background of the present invention, and therefore may contain information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0004] To further broaden the ideas of ultrasonic solid defect imaging methods, this invention proposes a solid defect imaging method based on the static component of ultrasonic longitudinal waves.

[0005] The objective of this invention is achieved through the following technical solution: a solid defect imaging method based on the static component of ultrasonic longitudinal waves includes the following steps:

[0006] Step S100: Apply a positive phase excitation signal to enable the dual-frequency ultrasonic transducer array to acquire the first echo signal;

[0007] Step S200: Invert the excitation signal so that the dual-frequency ultrasonic transducer array can acquire the second echo signal;

[0008] Step S300: Process the first echo signal and the second echo signal using pulse inversion and low-pass filtering techniques to obtain the time-domain signal of the ultrasonic longitudinal wave static component echo;

[0009] Step S400: Based on the imaging algorithm, the imaging index is calculated using the time-domain signal of the echo of the static component of the ultrasonic longitudinal wave, and the imaging index is used as the pixel value to obtain the imaging result.

[0010] Preferably, the dual-frequency ultrasonic transducer includes a matching layer, a high-frequency piezoelectric crystal, a frequency-selective isolation layer, a low-frequency piezoelectric crystal, and an acoustic backing.

[0011] Preferably, the dual-frequency ultrasonic transducer array acquires the first echo signal and the second echo signal by exciting each array element individually and receiving all array elements simultaneously.

[0012] Preferably, the first echo signal contains defect features.

[0013] Preferably, the array element excitation refers to the high-frequency piezoelectric element in the dual-frequency transducer being excited to generate high-frequency ultrasonic longitudinal waves.

[0014] Preferably, the array element receiving includes a high-frequency fundamental wave being received by a high-frequency piezoelectric crystal in a dual-frequency ultrasonic transducer.

[0015] Preferably, the array element receiving further includes the reception of the static component of the ultrasonic longitudinal wave by a low-frequency piezoelectric crystal in the dual-frequency ultrasonic transducer.

[0016] Preferably, when using a low-frequency piezoelectric crystal to receive static components, the condition that the main lobe of the frequency envelope of the high-frequency excitation signal must overlap with the amplitude-frequency curve of the low-frequency transducer must be met. This can be achieved by adjusting the duration of the high-frequency ultrasonic excitation signal.

[0017] Preferably, the imaging algorithm includes a total focusing imaging algorithm.

[0018] Preferably, the ultrasonic longitudinal wave static component is a signal with a carrier frequency of zero, generated when a high-frequency ultrasonic longitudinal wave propagates in a solid due to material nonlinearity and other factors. Furthermore, the frequency range commonly used in experiments in this invention is 1-10MHz, but theoretically, higher frequencies can also generate ultrasonic longitudinal wave static components.

[0019] The present invention has the following beneficial effects:

[0020] This invention discloses a solid defect imaging method based on the static component of ultrasonic longitudinal waves, which utilizes the advantages of low attenuation of the ultrasonic static component and no need for phase velocity matching, and can realize the localization imaging of defects in high acoustic attenuation solid materials. Attached Figure Description

[0021] Various other advantages and benefits of the present invention will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0022] In the attached diagram:

[0023] Figure 1 This is a schematic diagram of the location of defects in the aluminum block under test and the arrangement of a uniform linear array containing 8 elements, which is an embodiment of the ultrasonic longitudinal wave static component imaging method of the present invention.

[0024] Figure 2 This is a schematic diagram of a dual-frequency ultrasonic transducer in one embodiment of the present invention;

[0025] Figure 3This is the time-domain signal generated each time the high-frequency piezoelectric element is excited, as described in one embodiment of the present invention.

[0026] Figure 4 This is a flowchart illustrating one embodiment of the ultrasonic longitudinal wave static component imaging method of the present invention.

[0027] Figure 5 In one embodiment of the present invention, the phase (0°) and phase (180°) time-domain signals are excited by array element 1 and received by array element 2;

[0028] Figure 6 This is a time-domain signal of the static component of the ultrasonic longitudinal wave after the received signal has undergone pulse inversion and low-pass filtering in one embodiment of the present invention;

[0029] Figure 7 This is a schematic diagram of a typical imaging result obtained from one embodiment of the ultrasonic longitudinal wave static component imaging method of the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Therefore, the following applies to the appendix Figures 1 to 7 The detailed description of the embodiments of the present invention provided herein is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0032] Phased array imaging uses multiple array elements for signal excitation and reception, enabling the acquisition of richer information about the test piece. Compared to single-element detection, it offers higher detection accuracy and signal-to-noise ratio. Existing ultrasonic phased array imaging methods mainly fall into two categories: linear ultrasound and nonlinear ultrasound second harmonic methods. Higher frequencies experience greater attenuation, while the static component of the ultrasonic longitudinal wave has a zero carrier frequency, exhibiting relatively low attenuation. Typically, high-frequency fundamental and higher harmonic signals are completely attenuated, while the static component can still be observed. The ultrasonic static component combines the advantages of nonlinear ultrasound, low attenuation, no need for phase velocity matching, and good directivity, making it necessary to develop defect imaging methods based on the ultrasonic static component.

[0033] Reference Figure 1This diagram illustrates the location of defects in the solid under test and the position of the dual-frequency transducer array in this embodiment, used to implement a solid defect imaging method based on the static component of ultrasonic longitudinal waves. D represents a through-hole defect with a diameter of 2 mm, and its center position is shown below. Figure 1 As shown. Figure 2 As shown, D is the high-frequency piezoelectric crystal in the dual-frequency transducer, which is a piezoelectric crystal with a resonant frequency (thickness direction) of 5MHz (thickness of 0.4mm, corresponding to half a wavelength of 5MHz); B is the low-frequency piezoelectric crystal in the dual-frequency transducer, which is a piezoelectric crystal with a resonant frequency (thickness direction) of 0.5MHz (thickness of 4mm, corresponding to half a wavelength of 0.5MHz); an isolation layer C is provided between the high and low frequency crystals, which is epoxy resin with a thickness of 0.06mm (corresponding to a quarter wavelength of the high frequency 5MHz, to suppress the backward propagation of high-frequency ultrasound waves, while the low frequency sound waves have a larger wavelength and can propagate backward); A is an acoustic backing to suppress excess oscillations; E is a matching layer for the high-frequency piezoelectric crystal D (its acoustic impedance matches the acoustic impedance at the interface between the piezoelectric material inside the transducer and the object being detected, thereby reducing the reflection and refraction of ultrasound waves and allowing more energy to be invested in the object being detected). The dual-frequency transducer array is a uniform linear array containing 8 elements with an element spacing of 0.27 mm (the element spacing is generally no greater than one-quarter of the element diameter). Figure 1 As shown. The dual-frequency transducer array sequentially excites one element at a time, while the remaining seven elements receive data to acquire the full matrix capture data. This yields a total of 7 × 8 = 56 time-domain signals. The excitation signal is a 15-cycle sinusoidal pulse signal modulated by a Hanning window with a center frequency of 5 MHz, as shown... Figure 3 As shown. The structure under test is an aluminum block with a thickness of 100 mm, a length and a width of 70 mm, and the propagating ultrasonic longitudinal wave velocity is 6198 m / s.

[0034] Figure 4 This is a flowchart illustrating one embodiment of the ultrasonic longitudinal wave static component imaging method of the present invention, which includes the following steps:

[0035] Step S1: Positive phase excitation, dual-frequency ultrasonic transducer acquires echo signal, specifically:

[0036] The dual-frequency ultrasonic transducer array acquires echo signals containing defect features by exciting each array element individually and receiving all array elements simultaneously.

[0037] Step S2: Inverting excitation, dual-frequency ultrasonic transducer acquires echo signals, specifically:

[0038] Invert the excitation signal and repeat step S1 to acquire the echo signal under inverted excitation.

[0039] Step S3: Pulse inversion and low-pass filtering are used to process the echo signal. Specifically:

[0040] The captured echo signal (e.g.) is processed using pulse inversion and low-pass filtering techniques (cutoff frequency of 2MHz). Figure 5 The signals shown are 0° in phase and 180° out of phase. The first signal is a direct signal, and the second signal is the echo signal generated by the defect (the attached figure is a partial magnified view of the echo signal generated by the defect). The final ultrasonic longitudinal wave static component signal is as follows. Figure 6 As shown;

[0041] Step S4: Based on the imaging algorithm, calculate the imaging parameters to obtain the imaging results, specifically:

[0042] Imaging indicators are calculated based on imaging algorithms, and the imaging results are obtained by using the imaging indicators as pixel values.

[0043] The static component of the ultrasonic longitudinal wave is a signal with a carrier frequency of zero, generated when the high-frequency ultrasonic longitudinal wave propagates in a solid due to material nonlinearity and other factors.

[0044] The array element excitation refers to the high-frequency piezoelectric element in the dual-frequency transducer being excited to generate a high-frequency ultrasonic longitudinal wave, and the array element receiving refers to the high-frequency fundamental wave and static component echo signals being received by the high-frequency and low-frequency piezoelectric crystals in the dual-frequency ultrasonic transducer, respectively.

[0045] When using a low-frequency piezoelectric crystal to receive the static component, the main lobe of the high-frequency excitation signal envelope must overlap with the amplitude-frequency curve of the low-frequency transducer. This can be achieved by adjusting the duration of the high-frequency ultrasonic excitation signal. In this embodiment, it was found that the low-frequency piezoelectric crystal received the maximum static component signal response when the number of cycles was 15.

[0046] The imaging algorithm mentioned includes, but is not limited to, full-focus imaging. This embodiment uses a full-focus imaging algorithm, which discretizes the imaging area into a series of rectangular imaging points with a length of 0.25 mm and a width of 0.25 mm. The amplitude is used as the imaging index, i.e., it is calculated according to the following formula:

[0047]

[0048] Among them, I TFM Here are the imaging parameters at the current imaging point position; the elements of the excitation (tx) and receiver (rx) array elements are denoted as i and j, respectively; the x-coordinate represents the lateral position; the z-coordinate represents the longitudinal dimension; c is the wave velocity of ultrasound propagating in a solid, with an exemplary longitudinal wave velocity of 6198 m / s; N is the number of array elements, with an exemplary N = 8; h(t) represents the static component signal of the ultrasonic longitudinal wave (e.g., ... Figure 6 The Hilbert transform (as shown) is used to smooth the image.

[0049] Reference Figure 7 This is an image showing the imaging result of a solid circular through-hole defect obtained by the traditional full-focusing imaging method based on ultrasonic static components, as provided in an embodiment of the present invention. It should be noted that... Figure 7 This is the image result after normalizing the pixel values ​​to their maximum values. From Figure 7 As can be seen, since the static component of the ultrasonic longitudinal wave has the same duration and group velocity as the high-frequency fundamental wave, imaging solid defects using the static component of the ultrasonic longitudinal wave has the same axial resolution as the high-frequency fundamental wave, while the lateral resolution of the static component of the ultrasonic longitudinal wave is also good. Furthermore, when imaging solid defects using the static component of the ultrasonic longitudinal wave, the color is only dark near the defect, while other areas are very light, resulting in a good signal-to-noise ratio. Therefore, the results of this embodiment demonstrate that the method described in this invention has good signal-to-noise ratio and resolution when imaging solid defects.

[0050] Although embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art can make many other forms based on the guidance of this specification and without departing from the scope of protection of the claims of the present invention, and all of these are within the scope of protection of the present invention.

Claims

1. A method for imaging solid defects based on the static component of ultrasonic longitudinal waves, characterized in that, The method includes the following steps: Step S100: Apply a positive phase excitation signal to enable the dual-frequency ultrasonic transducer array to acquire the first echo signal; Step S200: Invert the excitation signal so that the dual-frequency ultrasonic transducer array can acquire the second echo signal; Step S300: Process the first echo signal and the second echo signal using pulse inversion and low-pass filtering techniques to obtain the time-domain signal of the static component echo of the ultrasonic longitudinal wave. Step S400: Based on the imaging algorithm, the imaging index is calculated using the time-domain signal of the echo of the static component of the ultrasonic longitudinal wave, and the imaging index is used as the pixel value to obtain the imaging result. in, The dual-frequency ultrasonic transducer array acquires the first echo signal and the second echo signal by exciting each array element one by one and receiving all array elements simultaneously. The array element excitation finger in the dual-frequency transducer is excited to generate high-frequency ultrasonic longitudinal waves. The array element receiving includes a high-frequency fundamental wave being received by a high-frequency piezoelectric crystal in a dual-frequency ultrasonic transducer. The array element receiving also includes the reception of the static component of the ultrasonic longitudinal wave by the low-frequency piezoelectric crystal in the dual-frequency ultrasonic transducer. When using a low-frequency piezoelectric crystal to receive static components, the main lobe of the envelope of the high-frequency excitation signal must overlap with the amplitude-frequency curve of the low-frequency transducer. This can be achieved by adjusting the duration of the high-frequency ultrasonic excitation signal.

2. The solid defect imaging method based on the static component of ultrasonic longitudinal waves according to claim 1, characterized in that, The static component of the ultrasonic longitudinal wave is a signal with a carrier frequency of zero, generated when the high-frequency ultrasonic longitudinal wave propagates in a solid due to material nonlinearity and other factors.

3. The solid defect imaging method based on the static component of ultrasonic longitudinal waves according to claim 1, characterized in that, The dual-frequency ultrasonic transducer includes a matching layer, a high-frequency piezoelectric crystal, a frequency-selective isolation layer, a low-frequency piezoelectric crystal, and an acoustic backing.

4. The solid defect imaging method based on the static component of ultrasonic longitudinal waves according to claim 1, characterized in that, The first echo signal contains defect features.

5. The solid defect imaging method based on the static component of ultrasonic longitudinal waves according to claim 1, characterized in that, The imaging algorithm mentioned includes a total focusing imaging algorithm.

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