Ultrasonic harmonic imaging device and method applied to defect detection

Abstract

The invention relates to the technical field of industrial ultrasonic nondestructive testing, in particular to an ultrasonic harmonic imaging device and method applied to defect detection. Comprising the following steps that S1, an ultrasonic transducer scans a workpiece, the ultrasonic transducer transmits ultrasonic waves to the workpiece, defects of the workpiece reflect the ultrasonic waves, and a receiver receives ultrasonic signals reflected by the defects and records the ultrasonic signals as receiving ultrasonic signals; s2, processing the received ultrasonic signal to obtain an original ultrasonic signal, and then processing the original ultrasonic signal to obtain a harmonic signal; s3, imaging the harmonic signals obtained in the step S2 by adopting a back projection method, and overlapping the harmonic signals at each angle in a corresponding direction to obtain a reconstructed image of the defect; and the defect detection accuracy and the defect imaging definition of ultrasonic waves are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial ultrasonic nondestructive testing, and in particular 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 tiny defects is crucial to ensure the integrity of materials and structures; especially in some demanding applications, such as aerospace, nuclear energy and high-end manufacturing, any tiny defects may cause serious consequences. Therefore, it is particularly important to accurately and reliably detect tiny defects in materials and tiny defects on the contact interface of workpieces with interference fit.

[0003] Ultrasonic imaging technology has been widely used in the process of defect detection, but traditional ultrasonic imaging technology has some obvious shortcomings and deficiencies when detecting tiny defects: First, there is sidelobe interference, and the sidelobe signal will mask the reflected signal of the real defect, resulting in a false negative result. Secondly, the problem of imaging artifacts. During ultrasonic imaging, the multipath propagation of reflected waves may cause false defects or signals in the imaging. These artifacts often mislead the detection results and reduce the reliability of the detection. In addition, traditional ultrasonic imaging technology usually exhibits the disadvantages of low contrast and low resolution. In the imaging of tiny defects, due to insufficient signal strength, the image contrast is often not enough to clearly distinguish between defects and background, resulting in the inability to accurately identify tiny defects. Moreover, due to resolution limitations, when the size of the defect is close to or smaller than the wavelength of the sound wave, the ultrasonic imaging system may not be able to distinguish these tiny defects at all.

[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 tiny defects and the clarity of tiny defect imaging compared with the existing technology. 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 purpose, the technical solution adopted by the present invention is as follows:

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

[0008] S1. The ultrasonic transducer scans the workpiece, transmits 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 boundary 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 at each angle in the corresponding direction, and obtain a reconstructed image of the defect.

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

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

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

[0017] S223, using a quadratic penalty function and a Lagrangian operator to transform the constrained variational problem constructed in step S222 into an unconstrained minimization problem, and then using an alternating direction multiplier method to transform it into a sub-optimization problem for solution 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, u r represents the margin, J1 represents the compact bandwidth of all modal components at their respective center frequencies, and J2 represents u i and u r The minimized spectral overlap, J3 represents the minimized energy spectrum at the center frequency of all modal components, x(t) represents the original ultrasonic signal; * represents the convolution operator, ω i Indicates u i (t) center frequency, ω i Take ω1 to ω K , j represents the imaginary unit, δ(t) represents the Dirac function, β i (t) represents the filter (1 / α(ω-ω i ) 2 )’s time domain impulse response, β l (t) represents the filter (1 / α(ω-ω l ) 2 )’s time domain impulse response, ω l represents the lth center frequency, l is 1, 2, ..., i;

[0024] α max The specific calculation is obtained by the following formula:

[0025]

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

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

[0028]

[0029] In the above formula, represents the Fourier transform value of x(t), Indicates u i The Fourier transform value of (t), Represents λ i The Fourier transform value of (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 double rise method to solve λ in the frequency domain i (t) the minimization step size, express (n+o)th power, n is 1, 2, ..., N, o is 1, 2, ..., l, express to 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 represents the modal boundary, w1 represents the energy proportion corresponding to ω1, and w2 represents ω K The corresponding energy density.

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

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

[0035] S232. According to the scale function and the empirical wavelet function, the detail coefficient W is obtained. x (0,t) and the approximation coefficient W x (n,t);

[0036] S233. Reconstruct the original ultrasonic signal according to the detail coefficient and the approximate coefficient to obtain a reconstructed ultrasonic signal. The expression of the reconstructed ultrasonic signal is:

[0037]

[0038] The expression of harmonic signal is:

[0039]

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

[0041] S234, extracting a harmonic signal corresponding to the original ultrasonic signal from the reconstructed ultrasonic signal, wherein the expression of the harmonic signal is:

[0042]

[0043] In the above formula, D t Indicates a 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 ratio of circumference to circumference, and γ and β are both set parameters.

[0047] Furthermore, the expressions of detail coefficient and 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, W x (n,t) represents the approximation coefficient.

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

[0051] S31, performing counting projection, which is specifically obtained by the following formula:

[0052] P(θ h ,r h )=D h (t);

[0053] 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, 3, ..., n;

[0054] S32. 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:

[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 for defect detection comprises 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 a 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.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] The present invention performs ultrasonic scanning on the defect, receives the original ultrasonic signal reflected by the defect, uses the successive variational modal decomposition method and the empirical wavelet transform method to process the original ultrasonic signal, obtains the harmonic signal corresponding to the original ultrasonic signal, and obtains the reconstructed image of the defect by using the back projection method based on the harmonic signal. The fundamental signal in the original ultrasonic signal is eliminated and only the harmonic signal is retained. The image constructed based on the harmonic signal can accurately obtain the specific position of the defect, and can also avoid the occurrence of artifact problems, thereby improving the reliability, contrast and resolution of detection, making the defect 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 It is a structural schematic diagram of the device of the present invention.

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

[0062] Figure 3 The ultrasonic energy device of the present invention and Figure 2 Schematic diagram of another different scanning method.

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

[0064] Figure 5 It is a schematic diagram of the U-shaped motion scanning method of the ultrasonic transducer of the present invention.

[0065] Description of 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. Placement table. DETAILED DESCRIPTION

[0067] The technical solution of the present invention will be clearly described below in conjunction with the accompanying drawings. Obviously, the described embodiments are not all embodiments of the present invention. All other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention. It should be noted that the orientation or position relationship indicated by the terms "center", "up", "down", "left", "right", "vertical", "horizontal", etc. is based on the orientation or position relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description. It does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0068] like Figure 1As shown, the present invention provides an ultrasonic harmonic imaging device for defect detection, including 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, the Y-axis direction and the Z-axis direction. The four-degree-of-freedom motion device 1 is connected to a transducer incident positioner 3. The transducer incident positioner 3 is arranged 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 bottom of the four-degree-of-freedom motion device 1. The placement table The workpiece 5 is placed on the workpiece 5, and the placement table can rotate. The coupling agent 2 is provided inside the four-degree-of-freedom motion device 1, and the coupling agent 2 is preferably water. The lower computer includes a receiver and a hardware circuit. The receiver adopts an FPGA receiver. The hardware circuit includes a power 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. The receiving circuit and the FPGA receiver are also connected with an acquisition circuit. The power circuit is used to provide electric energy; the FPGA receiver is electrically connected to the upper computer. The ultrasonic transducer 4 transmits ultrasonic waves to the workpiece 5, and the defect 51 reflects the ultrasonic waves. The FPGA receiver receives the reflected signal and processes the reflected signal into a harmonic signal. The upper computer obtains an imaging image of the defect 51 according to the harmonic signal processed by the FPGA receiver; the ultrasonic transducer 4 adopts a 5MHz / 30MHz ultrasonic probe.

[0069] The workpiece 5 is placed on the placement table, and the four-degree-of-freedom motion device 1 is controlled to drive the ultrasonic transducer to scan the workpiece 5. When the ultrasonic transducer scans the workpiece 5, the ultrasonic transducer is placed on the upper part of the workpiece 5 and is perpendicular to the surface of the workpiece 5 (such as Figure 2 As shown), when there is a hollow inner hole inside the workpiece 5, the ultrasonic transducer can be inserted into the inner hole of the workpiece 5 so that the ultrasonic transducer is perpendicular to the inner wall of the workpiece 5 (as shown in FIG. Figure 3 The scanning mode of the ultrasonic transducer driven by the four-degree-of-freedom motion device 1 can be a spiral mode (such as Figure 4 as shown) or in a circle (as shown Figure 5 shown).

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

[0071] S1. The four-degree-of-freedom motion device 1 drives the ultrasonic transducer to perform motion scanning and controls the ultrasonic transducer to emit ultrasonic waves. The defect 51 of 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, preprocessing the received ultrasonic signal to obtain an original ultrasonic signal, and then processing the original ultrasonic signal to obtain a harmonic signal of the original ultrasonic signal, specifically comprising the following steps:

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

[0074] S22, decomposing the original ultrasonic signal into K modal components, thereby obtaining a set of central frequencies of narrow-bandwidth modes, thereby obtaining modal boundaries, specifically comprising the following steps:

[0075] S221, using the successive variational modal decomposition method, decompose the original ultrasonic signal into K modal components, decompose the original ultrasonic signal x(t) into K intrinsic mode functions (IMFs), and the i-th intrinsic mode function is represented as u i (t), the i-th eigenmode function is the i-th modal component, and i is 1, 2, ..., K.

[0076] S222. For each modal component, a constrained variation problem is constructed. The expression of the constrained variation problem is expressed as:

[0077]

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

[0079]

[0080]

[0081] In the above formula, α represents the penalty factor, which ranges from 0 to α max ,u i (t) represents the i-th modal component, u r represents the margin, J1 represents the compact bandwidth of all modal components at their respective center frequencies, and J2 represents u i and u r The minimized spectral overlap, J3 represents the minimized energy spectrum at the center frequency of all modal components, x(t) represents the original ultrasonic signal; * represents the convolution operator, ω i Indicates u i (t), j represents the imaginary unit, δ(t) represents the Dirac function, β i (t) represents the filter (1 / α(ω-ω i ) 2 )’s time domain impulse response, β l(t) represents the filter (1 / α(ω-ω l ) 2 )’s time domain impulse response, ω l represents the lth center frequency, where l is 1, 2, ..., i.

[0082] α max 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 prior knowledge signal frequency bandwidth, f s represents the sampling frequency, f s Preferred is 100 MHz.

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

[0086]

[0087] In the above formula, represents the Fourier transform value of x(t), Indicates u i The Fourier transform value of (t), Represents λ i The Fourier transform value of (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 double rise method to solve λ in the frequency domain i (t) the minimization step size, express (n+o)th power, n is 1, 2, ..., N, o is 1, 2, ..., l, express to the (n+1)th power.

[0088] S224, record all the center frequencies obtained in step S223 as a center frequency set, represented by θ, θ = {ω1, ..., ω i ,…,ω K}, where ω1 represents the first center frequency, ω K Represents the Kth center frequency; ω1 and ω in the center frequency set KTake out the calculation and get the modal boundary. The specific calculation formula is:

[0089]

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

[0091] S23, using the modal boundary obtained in step S22 as the modal boundary of empirical wavelet transform, using empirical wavelet transform (EWT), designing an empirical wavelet filter bank, thereby obtaining a harmonic signal of the original ultrasonic signal, specifically comprising the following steps:

[0092] S231, define the scale 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 mode boundary; π represents pi, Represents the empirical wavelet function, γ and β are 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 scale function and the empirical wavelet function, the detail coefficient and the approximate coefficient are obtained, and 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, W x (n,t) represents the approximation coefficient, and t represents time.

[0104] S233. Reconstruct the original ultrasonic signal according to the detail coefficient and the approximate coefficient to obtain a 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, wherein 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 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 including 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 abscissa of the reconstructed image, and Y represents the ordinate of the reconstructed image.

[0117] The present invention performs ultrasonic scanning on the defect 51, receives the original ultrasonic signal reflected by the defect 51, processes the original ultrasonic signal using a successive variational modal decomposition method and an empirical wavelet transform method, obtains a harmonic signal corresponding to the original ultrasonic signal, and obtains a reconstructed image of the defect 51 using a back-projection method based on the harmonic signal. The fundamental signal in the original ultrasonic signal is eliminated and only the harmonic signal is retained. The image constructed based on the harmonic signal can accurately obtain the specific position of the defect 51, and can also avoid the occurrence of artifact problems, thereby improving the reliability, contrast, and resolution of the detection, so that the defect 51 has a higher clarity than 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 to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate 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, 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; 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 according to the center frequencies; S23, based on the modal boundary 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 at 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: S22 specifically includes the following steps: S221, using a successive variational modal decomposition method, decomposing the original ultrasonic signal into K modal components; S222. For each modal component, construct a constrained variational problem; S223, using a quadratic penalty function and a Lagrangian operator to transform the constrained variational problem constructed in step S222 into an unconstrained minimization problem, and then using an alternating direction multiplier method to transform it into a sub-optimization problem for solution to obtain the center frequency of each modal component; S224. Record all 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.

3. The ultrasonic harmonic imaging method for defect detection according to claim 2, characterized in that: The constrained variational problem in step S222 is expressed as follows: s.t.u i (t)+u r (t)=x(t); In the above formula, α represents the penalty factor, which ranges from 0 to α max ,u i (t) represents the i-th modal component, u r represents the margin, J1 represents the compact bandwidth of all modal components at their respective center frequencies, and J2 represents u i and u r The minimized spectral overlap, J3 represents the minimized energy spectrum at the center frequency of all modal components, x(t) represents the original ultrasonic signal; * represents the convolution operator, ω i Indicates u i (t) center frequency, ω i Take ω1 to ω K，j represents the imaginary unit, δ(t) represents the Dirac function, β i (t) represents the filter (1 / α(ω-ω i ) 2 )’s time domain impulse response, β l (t) represents the filter (1 / α(ω-ω l ) 2 )’s time domain impulse response, ω l represents the lth center frequency, l is 1, 2, ..., i; α max The specific calculation is obtained by the following formula: In the above formula, α max represents the maximum value of the penalty factor, f BW represents the prior knowledge signal frequency bandwidth, f s Indicates the sampling frequency.

4. The ultrasonic harmonic imaging method for defect detection according to claim 3, characterized in that: The update method of the center frequency of the i-th modal component in step S223 during the solution process is expressed by the following formula: In the above formula, represents the Fourier transform value of x(t), Indicates u i The Fourier transform value of (t), Represents λ i The Fourier transform value of (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 double rise method to solve λ in the frequency domain i (t) the minimization step size, express (n+o)th power, n is 1, 2, ..., N, o is 1, 2, ..., l, express to the (n+1)th power.

5. The ultrasonic harmonic imaging method for defect detection according to claim 4, characterized in that: The modal boundary in step S224 is calculated by the following formula: In the above formula, ω n represents the modal boundary, w1 represents the energy proportion corresponding to ω1, and w2 represents ω K The corresponding energy density.

6. The ultrasonic harmonic imaging method for defect detection according to claim 5, characterized in that: S23 specifically includes the following steps: S231. Define the scaling function and the empirical wavelet function S232. According to the scale function and the empirical wavelet function, the detail coefficient W is obtained. x (0, t) and the approximation coefficient W x (n, t); S233. Reconstruct the original ultrasonic signal according to the detail coefficient and the approximate 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, x(t)′ 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, wherein the expression of the harmonic signal is: In the above formula, D t Indicates a harmonic signal.

7. The ultrasonic harmonic imaging method for defect detection according to claim 6, characterized in that: The expressions of the scaling function and the empirical wavelet function in step S231 are: In the above formula, π represents the ratio of circumference to circumference, and γ and β are both set parameters.

8. The ultrasonic harmonic imaging method for defect detection according to claim 7, characterized in that: The expressions of detail coefficient and approximate coefficient in step S232 are: In the above formula, W x (0, t) represents the detail coefficient, x(τ) represents the convolution symbol, W x (n, t) represents the approximation coefficient.

9. 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, which is specifically obtained by the following formula: P(θ h ,r h )=D h (t); 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, 3, ..., n; S32. 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: 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.

10. An ultrasonic harmonic imaging device for defect detection, characterized in that: An ultrasonic harmonic imaging method for defect detection using any one of claims 1 to 9 comprises 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 a 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