Solid defect imaging method based on ultrasonic longitudinal wave static component

Abstract

The invention discloses a solid defect imaging method based on an ultrasonic longitudinal wave static component, and the method comprises the steps: giving a normal-phase excitation signal, and enabling a dual-frequency ultrasonic transducer array to carry out the collection of a first echo signal; inverting the excitation signal to enable the dual-frequency ultrasonic transducer array to acquire a second echo signal; processing the first echo signal and the second echo signal by using a pulse phase inversion and low-pass filtering technology to obtain an ultrasonic longitudinal wave static component echo time domain signal; and based on an imaging algorithm, an imaging index is calculated by using the ultrasonic longitudinal wave static component echo time domain signal, and an imaging result is obtained by taking the imaging index as a pixel value. The method can realize defect imaging in the solid, and has good application prospect and value.

Description

Technical Field

[0001] The invention belongs to the technical field of ultrasonic nondestructive testing, and in particular relates to a solid defect imaging method based on the static component of ultrasonic longitudinal waves. Background Art

[0002] The ultrasonic static component is generated by the nonlinearity of the material, defects, etc. when the ultrasonic wave propagates in the solid, and its carrier frequency is zero. Compared with the traditional fundamental frequency component and high-order harmonic component, the ultrasonic static component has the advantages of smaller sound attenuation and longer propagation distance, and is a non-destructive testing and structural health monitoring method with good application prospects.

[0003] The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Summary of the invention

[0004] In order to further broaden the idea of ​​ultrasonic solid defect imaging method, the present invention proposes a solid defect imaging method based on the static component of ultrasonic longitudinal wave.

[0005] The objective of the present invention is achieved through the following technical scheme: a solid defect imaging method based on the static component of ultrasonic longitudinal wave comprises the following steps:

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

[0007] Step S200: inverting the excitation signal so that the dual-frequency ultrasonic transducer array collects a second echo signal;

[0008] Step S300: Processing the first echo signal and the second echo signal by pulse inversion and low-pass filtering technology to obtain an ultrasonic longitudinal wave static component echo time domain signal;

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

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

[0011] Preferably, the dual-frequency ultrasonic transducer array collects the first echo signal and the second echo signal in a manner of exciting array elements one by one and receiving all array elements simultaneously.

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

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

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

[0015] Preferably, the array element reception also includes the static component of the ultrasonic longitudinal wave being received by a low-frequency piezoelectric chip in the dual-frequency ultrasonic transducer.

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

[0017] Preferably, the imaging algorithm comprises a full-focus imaging algorithm.

[0018] Preferably, the ultrasonic longitudinal wave static component is a signal with a carrier frequency of zero, which is induced by material nonlinearity when a high-frequency ultrasonic longitudinal wave propagates in a solid. Furthermore, the frequency range commonly used in the present invention in experiments is 1-10 MHz, and theoretically, a higher frequency can also generate an ultrasonic longitudinal wave static component.

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

[0020] The 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 positioning imaging of defects in high acoustic attenuation solid materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] By reading the detailed description of the preferred specific embodiments below, various other advantages and benefits of the present invention will become clear to those of ordinary skill in the art. The drawings in the specification are only used for the purpose of illustrating the preferred embodiments and are not considered to be limitations of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative work.

[0022] In the attached picture:

[0023] Figure 1 It is a schematic diagram of the defect position in the aluminum block to be tested and the arrangement of a uniform linear array containing 8 array elements according to an embodiment of the ultrasonic longitudinal wave static component imaging method of the present invention;

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

[0025] Figure 3A time domain signal generated each time a high-frequency piezoelectric sheet is excited in one embodiment of the present invention;

[0026] Figure 4 It is a flow chart of an embodiment of the method for imaging based on static component of ultrasonic longitudinal wave in the present invention;

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

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

[0029] Figure 7 The figure is a schematic diagram of typical imaging results obtained according to an embodiment of the ultrasonic longitudinal wave static component imaging method of the present invention. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described in combination with 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 are within the scope of protection of the present invention.

[0031] Therefore, the following Figures 1 to 7 The detailed description of the embodiments of the present invention provided in the present invention is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0032] Phased array uses multiple array elements for signal excitation and reception, which can collect more abundant information about the test piece and has higher detection accuracy and signal-to-noise ratio than single array element detection. Among the existing ultrasonic phased array imaging methods, there are two main categories: linear ultrasonic and nonlinear ultrasonic second harmonic methods. The higher the frequency, the greater the attenuation, while the carrier frequency of the static component of the ultrasonic longitudinal wave is zero and has a smaller attenuation. Usually, the high-frequency fundamental wave and high-order harmonic signals have been completely attenuated, while the static component can still be observed. The ultrasonic static component has the advantages of nonlinear ultrasound and low attenuation, no need for phase velocity matching, and good directivity. It is necessary to develop a defect imaging method based on the ultrasonic static component.

[0033] Reference Figure 1, which is a schematic diagram of the position of the defect in the solid to be measured and the position of the dual-frequency transducer array for implementing a solid defect imaging method based on the static component of ultrasonic longitudinal waves in this embodiment, wherein D is a through-hole defect with a diameter of 2 mm, and its center position is as shown in FIG. Figure 1 As shown. Figure 2 As shown in the figure, D is a high-frequency piezoelectric chip in the dual-frequency transducer, and the high-frequency piezoelectric chip is a piezoelectric chip with a resonance frequency (thickness direction) of 5MHz (thickness is 0.4mm, corresponding to half wavelength of 5MHz); B is a low-frequency piezoelectric chip in the dual-frequency transducer, and the low-frequency piezoelectric chip is a piezoelectric chip with a resonance frequency (thickness direction) equal to 0.5MHz (thickness is 4mm, corresponding to half wavelength of 0.5MHz); an isolation layer C is arranged between the high and low frequency chips, which is an epoxy resin with a thickness of 0.06mm (corresponding to a quarter wavelength of high frequency 5MHz, to suppress the backward propagation of high-frequency ultrasonic waves, while the wavelength of low-frequency sound waves is larger and can propagate backward); A is an acoustic backing to suppress unnecessary oscillations; E is a matching layer of the high-frequency piezoelectric chip D (its acoustic impedance matches the acoustic impedance of the ultrasonic wave at the interface between the piezoelectric material inside the transducer and the detected object, thereby reducing the reflection and refraction of the ultrasonic wave and allowing more energy to be input into the detected object). The dual-frequency transducer array is a uniform linear array, including 8 array elements, and the array element spacing is 0.27mm (the array element spacing is generally not greater than one-fourth of the array element diameter). Figure 1 As shown. The dual-frequency transducer array excites a single array element in turn, and the remaining 7 array elements receive to acquire full matrix capture data. In this way, a total of 7×8=56 time domain signals are obtained. The excitation signal is a 15-cycle sinusoidal pulse signal with a center frequency of 5MHz modulated by a Hanning window, as shown Figure 3 The structure under test is an aluminum block with a thickness of 100 mm and a length and width of 70 mm. The propagating ultrasonic longitudinal wave has a sound velocity of 6198 m / s.

[0034] Figure 4 The figure is a flow chart of an embodiment of the method for imaging the static component of ultrasonic longitudinal waves in the present invention, which comprises the following steps:

[0035] Step S1: positive phase excitation, dual-frequency ultrasonic transducer collects echo signals, specifically:

[0036] The dual-frequency ultrasonic transducer array collects the echo signal containing defect characteristics by exciting each array element one by one and receiving all array elements simultaneously;

[0037] Step S2: anti-phase excitation, dual-frequency ultrasonic transducer collects echo signals, specifically:

[0038] Invert the excitation signal, repeat step S1, and collect the echo signal under the inverted excitation;

[0039] Step S3: Pulse inversion and low-pass filtering to process the echo signal, specifically:

[0040] The captured echo signal (such as Figure 5 The first signal is a through signal, and the second signal is an echo signal generated by a defect. The attached figure is a partial enlarged 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, the imaging index is calculated to obtain the imaging result, specifically:

[0042] An imaging index is calculated based on an imaging algorithm, and an imaging result is obtained by using the imaging index as a pixel value.

[0043] The static component of the ultrasonic longitudinal wave is a signal with a carrier frequency of zero, which is induced by material nonlinearity when the high-frequency ultrasonic longitudinal wave propagates in the solid.

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

[0045] When the low-frequency piezoelectric chip is used to receive the static component, the condition that the frequency main lobe of the envelope of the high-frequency excitation signal must overlap with the amplitude-frequency curve of the low-frequency transducer can be met, which can be achieved by adjusting the duration of the high-frequency ultrasonic excitation signal. This embodiment finds through adjustment that when the number of cycles is 15, the static component signal response received by the low-frequency piezoelectric chip is the largest.

[0046] The imaging algorithm includes but is not limited to full focus imaging, etc. This embodiment adopts the full focus imaging algorithm, 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, and uses the amplitude as the imaging index, that is, according to the following formula:

[0047]

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

[0049] Reference Figure 7 , is a solid round through hole defect imaging result diagram obtained by the traditional full-focus imaging method based on the ultrasonic static component provided by the embodiment of the present invention. It should be noted that, Figure 7 It is the imaging result after the pixel value is normalized according to the maximum value. Figure 7 It can be seen that, since the static component of the ultrasonic longitudinal wave has the same duration and group velocity as the high-frequency fundamental wave, the ultrasonic longitudinal wave static component has the same axial resolution as the high-frequency fundamental wave when imaging solid defects, and the lateral resolution of the ultrasonic longitudinal wave static component is also good; on the other hand, when the ultrasonic longitudinal wave static component is used to image solid defects, only the color near the defect is darker, and the color of other places is very light, which has a good signal-to-noise ratio. Therefore, from the results of this embodiment, it can be seen that the method of the present invention has a good signal-to-noise ratio and resolution when imaging solid defects.

[0050] Although the embodiments of the present invention are described above in conjunction with the accompanying drawings, the present invention is not limited to the above specific embodiments and application fields, and the above specific embodiments are only illustrative and instructive, rather than restrictive. A person of ordinary skill in the art can also make many forms under the guidance of this specification and without departing from the scope of protection of the claims of the present invention, all of which belong to the protection of the present invention.

Claims

1. A solid defect imaging method based on the static component of ultrasonic longitudinal waves, characterized in that: The method comprises the following steps: Step S100: providing a positive phase excitation signal to enable the dual-frequency ultrasonic transducer array to collect a first echo signal; Step S200: inverting the excitation signal so that the dual-frequency ultrasonic transducer array collects a second echo signal; Step S300: Processing the first echo signal and the second echo signal by pulse inversion and low-pass filtering technology to obtain an ultrasonic longitudinal wave static component echo time domain signal; Step S400: Based on an imaging algorithm, an imaging index is calculated using the time domain signal of the ultrasonic longitudinal wave static component echo, and an imaging result is obtained using the imaging index as a pixel value.

2. The solid defect imaging method based on the static component of ultrasonic longitudinal wave according to claim 1, characterized in that: Preferably, the static component of the ultrasonic longitudinal wave is a signal with a carrier frequency of zero, which is induced by material nonlinearity when the high-frequency ultrasonic longitudinal wave propagates in a solid.

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

4. The solid defect imaging method based on the static component of ultrasonic longitudinal wave according to claim 1, characterized in that: The dual-frequency ultrasonic transducer array collects the first echo signal and the second echo signal in a manner of exciting array elements one by one and receiving all array elements simultaneously.

5. The solid defect imaging method based on the static component of ultrasonic longitudinal wave according to claim 1, characterized in that: The first echo signal includes a defect signature.

6. The solid defect imaging method based on the static component of ultrasonic longitudinal wave according to claim 4, characterized in that: The array element excitation refers to the high-frequency piezoelectric sheet in the dual-frequency transducer being excited to generate high-frequency ultrasonic longitudinal waves.

7. The solid defect imaging method based on the static component of ultrasonic longitudinal wave according to claim 4, characterized in that: The array element receiving includes the high-frequency fundamental wave being received by the high-frequency piezoelectric chip in the dual-frequency ultrasonic transducer.

8. The solid defect imaging method based on the static component of ultrasonic longitudinal wave according to claim 4, characterized in that: The array element receiving also includes the static component of the ultrasonic longitudinal wave being received by the low-frequency piezoelectric chip in the dual-frequency ultrasonic transducer.

9. The solid defect imaging method based on the static component of ultrasonic longitudinal waves according to claim 8, characterized in that: in, When using a low-frequency piezoelectric chip to receive a static component, the condition that the frequency main lobe of the 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.

10. The solid defect imaging method based on the static component of ultrasonic longitudinal wave according to claim 1, characterized in that: The imaging algorithm includes an all-focus imaging algorithm.

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