An ultrasonic harmonic imaging device and method for defect detection

Abstract

The present invention relates to the technical field of industrial ultrasonic non-destructive testing, and particularly to an ultrasonic harmonic imaging device and method for defect detection; it includes the following steps: S1. An ultrasonic transducer scans a workpiece. The ultrasonic transducer emits ultrasonic waves to the workpiece, and defects on the workpiece reflect the ultrasonic waves. A receiver receives the ultrasonic signals reflected by the defects, which are recorded as received ultrasonic signals; S2. The received ultrasonic signals are processed to obtain original ultrasonic signals, and then the original ultrasonic signals are processed to obtain harmonic signals; S3. The back-projection method is used to image the harmonic signals obtained in step S2. The harmonic signals at each angle are overlapped and superimposed in the corresponding direction to obtain a reconstructed image of the defects; this improves the accuracy of ultrasonic defect detection and the clarity of defect imaging.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial ultrasonic non-destructive testing, and particularly to an ultrasonic harmonic imaging device and method for defect detection. Background Art

[0002] In the field of industrial non-destructive testing, the detection of micro defects is crucial for ensuring the integrity of materials and structures; especially in some demanding applications, such as the aerospace, nuclear energy, and high-end manufacturing fields, any micro defect may cause serious consequences. Therefore, it becomes particularly important to accurately and reliably detect micro defects in materials and those existing on the contact interfaces of interference-fit workpieces.

[0003] Ultrasonic imaging technology is widely used in the process of defect detection, but traditional ultrasonic imaging technology has some obvious drawbacks and deficiencies in detecting micro defects: First, there is side lobe interference, and the side lobe signals will mask the reflection signals of real defects, resulting in false negative results. Second, there is the problem of imaging artifacts. During the ultrasonic imaging process, the multi-path propagation of reflected waves may cause false defects or signals to appear in the image, and these artifacts often mislead the detection results and reduce the reliability of detection. In addition, traditional ultrasonic imaging technology usually exhibits the disadvantages of low contrast and low resolution. In the imaging of micro defects, due to insufficient signal intensity, the contrast of the image is often not enough to clearly distinguish the defects from the background, resulting in micro defects being unable to be accurately identified. Moreover, due to the limitation of resolution, when the size of the defect is close to or smaller than the acoustic wavelength, the ultrasonic imaging system may simply not be able to distinguish these micro defects.

[0004] Therefore, there is an urgent need to provide an ultrasonic harmonic imaging device and method for defect detection, which can improve the accuracy of ultrasonic detection of micro defects and the clarity of micro defect imaging compared with the prior art. Summary of the Invention

[0005] The present invention solves the technical problems existing in the prior art, and provides an ultrasonic harmonic imaging device and method for defect detection.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] An ultrasonic harmonic imaging method for defect detection includes the following steps:

[0008] S1. The ultrasonic transducer scans the workpiece, the ultrasonic transducer emits ultrasonic waves to the workpiece, the defects of the workpiece reflect the ultrasonic waves, and the receiver receives the ultrasonic signals reflected by the defects, which are recorded as received ultrasonic signals;

[0009] S2. Processing the received ultrasonic signal to obtain an original ultrasonic signal, and then processing the original ultrasonic signal to obtain a harmonic signal, specifically comprising the following steps:

[0010] S21, preprocessing the received ultrasonic signal to obtain an original ultrasonic signal;

[0011] S22, decomposing the original ultrasonic signal into K modal components, thereby obtaining a set of center frequencies, and obtaining modal boundaries according to the center frequencies;

[0012] S23, based on the modal boundaries obtained in step S22, design an empirical wavelet filter bank to obtain a harmonic signal;

[0013] S3. Use the back-projection method to image the harmonic signal obtained in step S2, overlap the harmonic signal of each angle in the corresponding direction, and obtain a reconstructed image of the defect.

[0014] Furthermore, S22 specifically includes the following steps:

[0015] S221. Decomposing the original ultrasonic signal into K modal components using a successive variational modal decomposition method;

[0016] S222. For each modal component, construct a constrained variational problem;

[0017] S223. Use a quadratic penalty function and Lagrangian operator to transform the constrained variational problem constructed in step S222 into an unconstrained minimization problem, and then use the alternating direction multiplier method to transform it into a sub-optimization problem and solve it to obtain the center frequency of each modal component.

[0018] S224. Record all the center frequencies obtained in step S223 as a center frequency set, expressed as θ, θ={ω1,…,ω K}, where ω1 represents the first center frequency, ω K Represents the Kth center frequency; ω1 and ω in the center frequency set K Take out the calculation and get the modal boundaries.

[0019] Furthermore, the constrained variation problem in step S222 is expressed as follows:

[0020]

[0021] stu i (t)+u r (t) = x(t);

[0022]

[0023] In the above formula, α represents the penalty factor, which ranges from 0 to αmax , u i (t) represents the i-th modal component, and u r represents the residue. J1 is the compact bandwidth of all modal components at their respective center frequencies, J2 represents the minimized spectral overlap between u i and u r . J3 represents the minimized energy spectrum at the center frequencies of all modal components. x(t) represents the original ultrasonic signal; * represents the convolution operator, ω i represents the center frequency of u i (t), ω i ranges from ω1 to ω K , j represents the imaginary unit, δ(t) represents the Dirac function, and β i (t) represents the time-domain impulse response of the filter (1 / α(ω - ω i )) 2 ), and β l (t) represents the time-domain impulse response of the filter (1 / α(ω - ω l )) 2 ), ω l represents the l-th center frequency, where l takes values 1, 2,..., i;

[0024] α max is specifically calculated by the following formula:

[0025]

[0026] In the above formula, α max represents the maximum value of the penalty factor, f BW represents the frequency bandwidth of the prior knowledge signal, and f s represents the sampling frequency.

[0027] Furthermore, the update method of the center frequency of the i-th modal component in step S223 during the solution process is represented by the following formula:

[0028]

[0029] In the above formula, represents the Fourier transform value of x(t), represents the Fourier transform value of u i (t), represents the Fourier transform value of λ i (t), λ i (t) represents the Lagrange multiplier, ω i represents the i-th power of ω, ω represents the frequency of the input signal, and τ represents the step size for minimizing λ i (t) in the frequency domain using the double ascent method, represents The (n + o)-th power, where n takes values from 1, 2,..., N and o takes values from 1, 2,..., l, denotes the (n + 1)-th power.

[0030] Furthermore, the modal boundary in step S224 is specifically calculated by the following formula:

[0031]

[0032] In the above formula, ω n denotes the modal boundary, w1 denotes the energy ratio corresponding to ω1, and w2 denotes the energy ratio corresponding to ω K .

[0033] Furthermore, S23 specifically includes the following steps:

[0034] S231. Define the scaling function and the empirical wavelet function

[0035] S232. Obtain the detail coefficients W x (0, t) and the approximation coefficients W x (n, t);

[0036] S233. Reconstruct the original ultrasonic signal based on the detail coefficients and the approximation coefficients to obtain the reconstructed ultrasonic signal. The expression of the reconstructed ultrasonic signal is:

[0037]

[0038] The expression of the harmonic signal is:

[0039]

[0040] In the above formula, x(t) ′ denotes the reconstructed ultrasonic signal, and N denotes the total number of modal boundaries;

[0041] S234. Extract the harmonic signal corresponding to the original ultrasonic signal from the reconstructed ultrasonic signal. The expression of the harmonic signal is:

[0042]

[0043] In the above formula, D t denotes the harmonic signal.

[0044] Furthermore, the expressions of the scaling function and the empirical wavelet function in step S231 are respectively:

[0045]

[0046] In the above formula, π represents the pi, and γ and β are both set parameters.

[0047] Furthermore, the expressions for the detail coefficient and the approximation coefficient in step S232 are respectively:

[0048]

[0049] In the above formula, W x (0,t) represents the detail coefficient, x(τ) represents the convolution symbol, and W x (n,t) represents the approximation coefficient.

[0050] Further, S3 specifically includes the following steps:

[0051] S31. Perform counting projection, specifically obtained through the following formula:

[0052] P(θ h ,r h ) = D h (t);

[0053] In the above formula, P(θ h ,r h ) represents the projection at angle θ h , θ h represents the corresponding angle of r h , r h represents the depth of the defect from the ultrasonic transducer, h represents the h-th point scanned by the ultrasonic probe, and h takes 1, 2, 3,..., n;

[0054] S32. For each angle θ h , replay the corresponding projection P(θ h ,r h ) along the corresponding angle to obtain the reconstructed image I(X,Y), and the reconstructed image is specifically represented as:

[0055]

[0056] In the above formula, δ represents the Dirac function, X represents the abscissa of the reconstructed image, and Y represents the ordinate of the reconstructed image.

[0057] An ultrasonic harmonic imaging device applied to defect detection includes an ultrasonic transducer, a host computer, a slave computer, and a four-degree-of-freedom motion device. The four-degree-of-freedom motion device drives the ultrasonic transducer to scan the workpiece. The ultrasonic transducer is electrically connected to the slave computer, the slave computer is electrically connected to the host computer, the slave computer is used to obtain harmonic signals, and the host computer is used to obtain the reconstructed image.

[0058] Compared with the prior art, the beneficial effects of the present invention are:

[0059] In the present invention, ultrasonic scanning is performed on a defect, and the original ultrasonic signal reflected by the defect is received. The original ultrasonic signal is processed using the successive variational mode decomposition method and the empirical wavelet transform method to obtain the harmonic signal corresponding to the original ultrasonic signal. Based on the harmonic signal, the reconstruction image of the defect is obtained using the back-projection method. By removing the fundamental wave signal in the original ultrasonic signal and only retaining the harmonic signal, the specific position of the defect can be accurately obtained from the image constructed based on the harmonic signal. At the same time, the problem of artifacts can be avoided, and the reliability, contrast, and resolution of the detection are improved, making the defect relatively clearer than the background, thereby improving the accuracy of ultrasonic defect detection and the clarity of defect imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 is a schematic structural diagram of the device of the present invention.

[0061] Figure 2 is a schematic diagram of a scanning method of the ultrasonic transducer of the present invention.

[0062] Figure 3 is the ultrasonic energy transducer of the present invention and Figure 2 is a schematic diagram of another different scanning method in

[0063] Figure 4 is a schematic diagram of the spiral motion scanning method of the ultrasonic transducer of the present invention.

[0064] Figure 5 is a schematic diagram of the circular motion scanning method of the ultrasonic transducer of the present invention.

[0065] DESCRIPTION OF THE REFERENCE NUMERALS:

[0066] 1. Four-degree-of-freedom motion device; 2. Coupling agent; 3. Transducer incident positioner; 4. Ultrasonic transducer; 5. Workpiece; 51. Defect; 6. Placing table. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0067] The technical solution of the present invention will be clearly described below in conjunction with the drawings. Obviously, the described embodiments are not all the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention. It should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0068] As Figure 1As shown in the figure, the present invention provides an ultrasonic harmonic imaging device for defect detection, which includes an ultrasonic transducer 4, a host computer and a slave computer. The ultrasonic transducer 4 is arranged on a four-degree-of-freedom motion device 1. The four-degree-of-freedom motion device 1 drives the ultrasonic transducer 4 to move in the X-axis direction, Y-axis direction and Z-axis direction. A transducer incident positioner 3 is connected to the four-degree-of-freedom motion device 1. The transducer incident positioner 3 is set to adjust the incident angle of the ultrasonic transducer 4 according to the spatial position and detection requirements of different workpieces. The ultrasonic transducer 4 is connected to the transducer incident positioner 3. A placement table is arranged at the inner bottom of the four-degree-of-freedom motion device 1, and a workpiece 5 is placed on the placement table. The placement table can rotate. A coupling agent 2 is arranged inside the four-degree-of-freedom motion device 1. The coupling agent 2 is preferably water. The slave computer includes a receiver and a hardware circuit. The receiver uses an FPGA receiver. The hardware circuit includes a power supply circuit, a transmitting circuit, a receiving circuit and a motion control circuit. The FPGA receiver is electrically connected to the four-degree-of-freedom motion device 1 through the motion control circuit. The ultrasonic transducer is electrically connected to the FPGA receiver through the transmitting circuit and the receiving circuit. An acquisition circuit is also connected between the receiving circuit and the FPGA receiver. The power supply circuit is used to provide electric energy; the FPGA receiver is electrically connected to the host computer. The ultrasonic transducer 4 emits ultrasonic waves to the workpiece 5, and the defect 51 on the workpiece 5 reflects the ultrasonic waves. The FPGA receiver receives the reflected signal and processes the reflected signal into a harmonic signal. The host computer obtains an imaging image of the defect 51 according to the harmonic signal processed by the FPGA receiver; the ultrasonic transducer 4 uses a 5MHz / 30MHz ultrasonic probe.

[0069] Place the workpiece 5 on the placement table, and control the four-degree-of-freedom motion device 1 to drive the ultrasonic transducer to scan the workpiece 5. When the ultrasonic transducer scans the workpiece 5, the ultrasonic transducer is placed above the workpiece 5 and perpendicular to the surface of the workpiece 5 (as Figure 2 shown). When there is a hollow inner hole inside the workpiece 5, the ultrasonic transducer can extend into the inner hole of the workpiece 5 to make the ultrasonic transducer perpendicular to the inner wall of the workpiece 5 (as Figure 3 shown); the motion scanning method of the four-degree-of-freedom motion device 1 driving the ultrasonic transducer can be a spiral type (as Figure 4 shown) or a square type (as Figure 5 shown).

[0070] The present invention also provides an ultrasonic harmonic imaging method for defect detection, which includes the following steps:

[0071] S1. The four-degree-of-freedom motion device 1 drives the ultrasonic transducer to perform motion scanning, and at the same time controls the ultrasonic transducer to emit ultrasonic waves. The defect 51 on the workpiece 5 reflects the ultrasonic waves. The FPGA receiver receives the ultrasonic signal reflected by the defect 51, which is recorded as the received ultrasonic signal.

[0072] S2. Preprocess the received ultrasonic signal to obtain the original ultrasonic signal, and then process the original ultrasonic signal to obtain the harmonic signal of the original ultrasonic signal, specifically including the following steps:

[0073] S21. Preprocess the received ultrasonic signal to obtain the original ultrasonic signal. The preprocessing includes removing the spectral trend and smoothing to reduce the influence of the low-frequency modal energy distribution and noise on the discrimination of local minima.

[0074] S22. Decompose the original ultrasonic signal into K modal components, thereby obtaining the center frequencies of a group of narrowband bandwidth modes, and thus obtaining the modal boundaries, specifically including the following steps:

[0075] S221. Use the successive variational mode decomposition method to decompose the original ultrasonic signal into K modal components. Decompose the original ultrasonic signal x(t) into K intrinsic mode functions (IMFs). The i-th intrinsic mode function is denoted as u i (t). The i-th intrinsic mode function is the i-th modal component, where i takes 1, 2,..., K.

[0076] S222. For each modal component, construct a constrained variational problem. The expression of the constrained variational problem is:

[0077]

[0078] s.t.u i (t)+u r (t)=x(t);

[0079]

[0080]

[0081] In the above formula, α represents the penalty factor, α takes values from 0 to α max , u i (t) represents the i-th modal component, u r represents the residue, J1 is the compact bandwidth of all modal components at their respective center frequencies, J2 represents the minimum spectral overlap of u i and u r , J3 represents the minimum energy spectrum at the center frequencies of all modal components, x(t) represents the original ultrasonic signal; * represents the convolution operator, ω i represents the center frequency of u i (t), j represents the imaginary unit, δ(t) represents the Dirac function, β i (t) represents the time-domain impulse response of the filter (1 / α(ω - ω i )) 2 ), β l(t) represents the time-domain impulse response of the filter (1 / α(ω - ω l ) 2 ) and ω l represents the l-th center frequency, where l takes values 1, 2,..., i.

[0082] α max is calculated by the following formula:

[0083]

[0084] In the above formula, α max represents the maximum value of the penalty factor, f BW represents the frequency bandwidth of the prior knowledge signal, f s represents the sampling frequency, and f s is preferably 100 MHz.

[0085] S223. Use the quadratic penalty function and the Lagrange operator to transform the constrained variational problem constructed in step S222 into an unconstrained minimization problem, and then use the alternating direction multiplier method to transform it into a sub-optimization problem for solution, obtaining the center frequency ω i of each modal component. The update method of the center frequency of the i-th modal component during the solution process is represented by the following formula:

[0086]

[0087] In the above formula, represents the Fourier transform value of x(t), represents the Fourier transform value of u i (t), represents the Fourier transform value of λ i (t), and λ i (t) represents the Lagrange multiplier, ω i represents the i-th power of ω, ω represents the frequency of the input signal, τ represents the step size for minimizing λ i (t) in the frequency domain using the double ascent method, represents to the power of (n + o), where n takes values 1, 2,..., N and o takes values 1, 2,..., l, represents to the power of (n + 1).

[0088] S224. Denote all the center frequencies obtained in step S223 as the center frequency set, represented by θ, θ = {ω1,..., ω i ,..., ω K}, where ω1 represents the first center frequency and ω K represents the K-th center frequency; take ω1 and ω KTake the calculation to obtain the modal boundary. The specific calculation formula is as follows:

[0089]

[0090] In the above formula, ω n represents the modal boundary, w1 represents the energy proportion corresponding to ω1, and w2 represents the energy proportion corresponding to ω K .

[0091] S23. Take the modal boundary obtained in step S22 as the modal boundary of the empirical wavelet transform. Use the empirical wavelet transform (EWT) to design an empirical wavelet filter bank, so as to obtain the harmonic signal of the original ultrasonic signal. The specific steps are as follows:

[0092] S231. Define the scaling function and the empirical wavelet function, specifically:

[0093] The expression of the scaling function is:

[0094]

[0095] The expression of the empirical wavelet function is:

[0096]

[0097] In the above formula, represents the scaling function, ω n represents the nth modal boundary; π represents the pi, represents the empirical wavelet function, and γ and β are both set parameters.

[0098] Among them, γ and β are expressed by the following formula:

[0099]

[0100] In the above formula, ω n+1 represents the (n + 1)th modal boundary.

[0101] S232. According to the scaling function and the empirical wavelet function, obtain the detail coefficients and the approximation coefficients. The expressions are as follows:

[0102]

[0103] In the above formula, W x (0,t) represents the detail coefficient, x(τ) represents the convolution symbol, and W x (n,t) represents the approximation coefficient, and t represents time.

[0104] S233. According to the detail coefficients and the approximation coefficients, reconstruct the original ultrasonic signal to obtain the reconstructed ultrasonic signal. The expression of the reconstructed ultrasonic signal is:

[0105]

[0106] In the above formula, x(t) ′ represents the reconstructed ultrasonic signal, and N represents the total number of modal boundaries.

[0107] S234. Extracting a harmonic signal corresponding to the original ultrasonic signal from the reconstructed original ultrasonic signal. The expression of the harmonic signal is:

[0108]

[0109] In the above formula, D t Indicates a harmonic signal.

[0110] S3, imaging the harmonic signal obtained in step S2 by using a back-projection method, and "projecting" the harmonic signal on the image plane, that is, overlapping the harmonic signal data of each angle in the corresponding direction, specifically comprising the following steps:

[0111] S31, performing counting projection, which is specifically expressed by the following formula:

[0112] P(θ h ,r h )=D h (t);

[0113] In the above formula, P(θ h ,r h ) represents the angle θ h The projection under θ h Represents r h The corresponding angle, r h represents the depth of the defect from the ultrasonic transducer, h represents the hth point scanned by the ultrasonic probe, and h can be 1, 2, ..., n.

[0114] S32, back-project the projections at various angles obtained in step S31 to obtain a reconstructed image of the defect 51. For each angle θ h , the corresponding projection P(θ h ,r h ) is played back along the corresponding angle to obtain the reconstructed image I(X,Y). The reconstructed image is specifically expressed as:

[0115]

[0116] In the above formula, δ represents the Dirac function, X represents the horizontal coordinate of the reconstructed image, and Y represents the vertical coordinate of the reconstructed image.

[0117] In this invention, ultrasonic scanning is performed on the defect 51, and the original ultrasonic signals reflected by the defect 51 are received. The original ultrasonic signals are processed using the successive variational mode decomposition method and the empirical wavelet transform method to obtain the harmonic signals corresponding to the original ultrasonic signals. Based on the harmonic signals, the reconstruction image of the defect 51 is obtained using the back-projection method. By removing the fundamental wave signals in the original ultrasonic signals and only retaining the harmonic signals, the specific position of the defect 51 can be accurately obtained from the image constructed based on the harmonic signals. At the same time, the problem of artifacts can be avoided, and the reliability, contrast, and resolution of the detection are improved, making the defect 51 relatively clearer compared to the background, thereby improving the accuracy of ultrasonic detection of the defect 51 and the clarity of the imaging of the defect 51.

[0118] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than limiting the protection scope of the present invention. Any simple modification or equivalent replacement of the technical solution of the present invention by those of ordinary skill in the art shall not depart from the essence and scope of the technical solution of the present invention.

Claims

1. An ultrasonic harmonic imaging method for defect detection, characterized in that: The following steps are involved: S1. The ultrasonic transducer scans the workpiece, transmits ultrasonic waves to the workpiece, and the defects of the workpiece reflect the ultrasonic waves. The receiver receives the ultrasonic signal reflected by the defect, which is recorded as the received ultrasonic signal; S2. Processing the received ultrasonic signal to obtain an original ultrasonic signal, and then processing the original ultrasonic signal to obtain a harmonic signal, specifically comprising the following steps: S21, preprocessing the received ultrasonic signal to obtain an original ultrasonic signal; S22, decomposing the original ultrasonic signal into K modal components, thereby obtaining a set of center frequencies, and obtaining modal boundaries based on the center frequencies; specifically comprising the following steps: S221. Decomposing the original ultrasonic signal into K modal components using a successive variational modal decomposition method; S222. For each modal component, a constrained variational problem is constructed. The constrained variational problem is expressed as follows: ； ； ； ； ； In the above formula, represents the penalty factor, Take 0 to , represents the i-th modal component, Indicates the margin, The tight bandwidth of all modal components at their respective center frequencies, express and The minimized spectral overlap, represents the minimized energy spectrum at the center frequency of all modal components, represents the original ultrasonic signal; represents the convolution operator, express The center frequency, Pick arrive , j represents the imaginary unit, represents the Dirac function, Represents the filter (1 / )’s time-domain impulse response, Represents the filter (1 / )’s time-domain impulse response, represents the lth center frequency, where l is 1, 2, ..., i; It is calculated by the following formula: ； In the above formula, represents the maximum value of the penalty factor, represents the prior knowledge signal frequency bandwidth, Indicates the sampling frequency; S223. Use the quadratic penalty function and Lagrangian operator to transform the constrained variational problem constructed in step S222 into an unconstrained minimization problem. Then use the alternating direction multiplier method to transform it into a sub-optimization problem and solve it to obtain the center frequency of each modal component. The update method of the center frequency of the i-th modal component during the solution process is expressed as follows: ； ； ； In the above formula, express The Fourier transform value of express The Fourier transform value of express The Fourier transform value of represents the Lagrange multiplier, express to the power of i, represents the frequency of the input signal, Indicates that the double rise method is used to solve in the frequency domain Minimize the step size, , n takes 1, 2, ..., N, o takes 1, 2, ..., l, express of power; S224. All the center frequencies obtained in step S223 are recorded as a center frequency set, which is expressed as , ,in, represents the first center frequency, Represents the Kth center frequency; and Take out the calculation and get the modal boundary; S23, based on the modal boundaries obtained in step S22, design an empirical wavelet filter bank to obtain a harmonic signal; S3. Use the back-projection method to image the harmonic signal obtained in step S2, overlap the harmonic signal of each angle in the corresponding direction, and obtain a reconstructed image of the defect.

2. The ultrasonic harmonic imaging method for defect detection according to claim 1, characterized in that: The modal boundary in step S224 is calculated using the following formula: ； In the above formula, represents the modal boundary, express The corresponding energy density, express The corresponding energy density.

3. The ultrasonic harmonic imaging method for defect detection according to claim 2, characterized in that: S23 specifically includes the following steps: S231. Define scaling function and empirical wavelet function ; S232, according to the scale function and the empirical wavelet function, obtain the detail coefficient and approximate coefficients ; S233. Reconstruct the original ultrasonic signal according to the detail coefficient and the approximation coefficient to obtain a reconstructed ultrasonic signal. The expression of the reconstructed ultrasonic signal is: ； The expression of harmonic signal is: ； In the above formula, represents the reconstructed ultrasonic signal, and N represents the total number of modal boundaries; S234. Extracting a harmonic signal corresponding to the original ultrasonic signal from the reconstructed ultrasonic signal. The expression of the harmonic signal is: ； In the above formula, Indicates a harmonic signal.

4. The ultrasonic harmonic imaging method for defect detection according to claim 3, characterized in that: The expressions of the scaling function and empirical wavelet function in step S231 are: ； ； In the above formula, represents pi, , All of them are setting parameters.

5. The ultrasonic harmonic imaging method for defect detection according to claim 4, characterized in that: The expressions of detail coefficient and approximate coefficient in step S232 are: ； ； In the above formula, represents the detail coefficient, represents the convolution symbol, represents the approximation coefficient.

6. The ultrasonic harmonic imaging method for defect detection according to claim 1, characterized in that: S3 specifically includes the following steps: S31, performing counting projection, specifically obtained by the following formula: ； In the above formula, Indicates angle The projection below, express The corresponding angle, represents the depth of the defect from the ultrasonic transducer, h represents the hth point scanned by the ultrasonic probe, and h can be 1, 2, 3, ..., n; S32. For each angle , the corresponding projection Play back along the corresponding angle to get the reconstructed image , the reconstructed image is specifically expressed as: ； In the above formula, represents the Dirac function, represents the horizontal coordinate of the reconstructed image, and Y represents the vertical coordinate of the reconstructed image.

7. An ultrasonic harmonic imaging device for defect detection, characterized in that: An ultrasonic harmonic imaging method for defect detection according to any one of claims 1 to 6 includes an ultrasonic transducer, a host computer, a slave computer, and a four-degree-of-freedom motion device, wherein the four-degree-of-freedom motion device drives the ultrasonic transducer to scan the workpiece, the ultrasonic transducer is electrically connected to the slave computer, the slave computer is electrically connected to the host computer, the slave computer is used to obtain a harmonic signal, and the host computer is used to obtain a reconstructed image.

Images