Electromagnetic eddy current defect imaging method and system based on parameter level set

Abstract

The invention discloses an electromagnetic eddy current defect imaging method and system based on a parameter level set. The method comprises the following steps: optimizing parameters of an array eddy current sensor; performing data acquisition on the to-be-detected metal component to obtain eddy current response signals under different excitation-receiving conditions, and realizing three-dimensional reconstruction of defects based on a parameter level set reconstruction algorithm; setting the position of a discrete point source, conductivity values of metal and defects and an initial coefficient parameter of a primary function; inputting the eddy current response signal into a level set reconstruction algorithm model to obtain a defect reconstruction objective function based on a parameter level set; calculating a Jacobian matrix and iteratively solving the target function by adopting a Gaussian Newton method, carrying out iterative updating, and judging whether defect reconstruction is converged or not according to whether the deviation of two reconstruction results before and after an iterative process is smaller than a threshold value or not; and a final defect imaging result is obtained. The method is convenient to implement, and can obtain the defect information of the inner surface of the metal component through calculation imaging without the help of a mechanical scanning device.

Description

Technical Field

[0001] The invention relates to the technical field of electromagnetic eddy current nondestructive testing, and in particular to an electromagnetic eddy current defect imaging method and system based on parameter level sets. Background Art

[0002] The working principle of electromagnetic eddy current detection technology is based on Faraday's law of electromagnetic induction. When an alternating current passes through the detection coil, an alternating magnetic field is generated around it. When the conductive material to be detected is placed in the magnetic field, eddy currents will be generated inside the material due to electromagnetic induction. The direction of the eddy current is opposite to the direction of the magnetic field, which will weaken the original magnetic field and generate an induced magnetic field inside the material with a direction opposite to the original magnetic field. This induced magnetic field will change the distribution of the original magnetic field, causing the impedance of the detection coil to change. By measuring and analyzing these impedance changes, it can be inferred whether there are defects or performance changes inside the material. Defect quantitative imaging can accurately measure the size, shape, position and other parameters of the defect, avoiding the subjectivity and uncertainty that may exist in traditional detection methods and improving the accuracy of detection. This method first optimizes the parameters of the array eddy current sensor through orthogonal experiments and response surface methodology to improve the uniformity of the sensitive field. Subsequently, a parametric level set reconstruction algorithm is used to achieve three-dimensional reconstruction of defects. The position and initial coefficient parameters of the basis function in the algorithm are adaptively obtained. The Jacobian matrix is ​​calculated and the Gauss-Newton method is used to iteratively solve the inverse problem of electromagnetic parameter distribution imaging based on the parametric level set. The basis function coefficient parameters are continuously iteratively updated to achieve three-dimensional high-precision imaging of defects in metal components. Summary of the invention

[0003] The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

[0004] To this end, the present invention proposes an electromagnetic eddy current defect imaging method based on parameter level set. Data of the metal component to be tested is collected by an array eddy current sensor to obtain eddy current response signals under different excitation-reception conditions. Three-dimensional reconstruction of defects is achieved based on the parameter level set reconstruction algorithm. In theory, three-dimensional imaging of defects and quantitative evaluation of defects in the damaged state of metal components can be achieved.

[0005] Another object of the present invention is to provide an electromagnetic eddy current defect imaging system based on parameter level sets.

[0006] To achieve the above object, the present invention proposes, on one hand, an electromagnetic eddy current defect imaging method based on parameter level set, comprising:

[0007] S1, construct an array eddy current sensor and optimize the parameters of the array eddy current sensor through orthogonal experiments and response surface methodology;

[0008] S2, using the optimized array eddy current sensor to collect data on the metal component to be tested to obtain eddy current response signals under different excitation-reception conditions, and using the parameter level set algorithm to process the signal to characterize the three-dimensional profile of the defect;

[0009] S3, setting the position of the discrete point source describing the three-dimensional profile of the defect, the metal conductivity value and the defect conductivity value, and the initial coefficient parameters of the basis function;

[0010] S4, constructing a level set reconstruction algorithm model according to the position of the discrete point source describing the three-dimensional contour, the metal conductivity value and the defect conductivity value and the initial coefficient parameters of the basis function, and inputting the eddy current response signal into the level set reconstruction algorithm model to obtain a defect reconstruction objective function based on the parameter level set;

[0011] S5, obtaining the defect imaging result by calculating the Jacobian matrix and iteratively solving the defect reconstruction objective function using the Gauss-Newton method, and iteratively updating the basis function coefficient parameters;

[0012] S6, repeatedly executing S5, judging whether the defect reconstruction has converged according to whether the deviation of the defect imaging results before and after the iteration process is less than a preset threshold;

[0013] S7, outputting the final defect imaging result according to the convergence judgment result to obtain the defect position, size and quantity information.

[0014] The electromagnetic eddy current defect imaging method based on parameter level set in the embodiment of the present invention may also have the following additional technical features:

[0015] In one embodiment of the present invention, an array eddy current sensor is constructed, and parameters of the array eddy current sensor are optimized by orthogonal test and response surface method, including:

[0016] Design a 3×3 planar array eddy current sensor and calculate the sensitivity matrix using finite element numerical solution;

[0017] According to the theoretical model of non-coaxial eddy current sensor, the factors affecting the sensitivity matrix are analyzed and the parameter range is determined;

[0018] Based on the parameter range, the best parameter combination is obtained by using orthogonal experiments;

[0019] Based on the optimal parameter combination, the relationship between the uniformity of the sensitivity matrix and the sensor parameters is obtained by using the response surface method to obtain the final optimized parameters of the array sensor.

[0020] In one embodiment of the present invention, an optimized array eddy current sensor is used to collect data from a metal component to be measured to obtain eddy current response signals under different excitation-reception conditions, and a parameter level set algorithm is used to process the signal to characterize the three-dimensional profile of the defect, including:

[0021] The metal imaging area is equivalent to a measured field containing two kinds of conductivity, where the defect area is the target area R and the metal area is the background area Ω\R. The conductivity changes of the target area R and the background area Ω\R are calculated according to the eddy current response signal; the metal conductivity value Δσ1 and the defect conductivity value Δσ0, the conductivity change of the entire background area Ω, is expressed as:

[0022] σ(x)=σ0(1-H(f(x))-c)+σ1H(f(x)-c)

[0023] Where H(s) is the smooth Heaviside function, expressed as:

[0024]

[0025] f(x) is a parametric level set function that satisfies:

[0026]

[0027] The level set function f(x) is obtained by using N basis functions p i (x) Linear weighted representation:

[0028]

[0029] Among them, μ i are the coefficients of the basis functions.

[0030] In one embodiment of the present invention, the position of the discrete point source describing the three-dimensional profile of the defect, the metal conductivity value and the defect conductivity value, and the initial coefficient parameters of the basis function are set, including:

[0031] The location of the defect is preliminarily determined using the linear back-projection algorithm;

[0032] The position of the basis function is set to the defect position reconstructed by linear back projection;

[0033] The metal conductivity value σ1 is determined according to the material of the metal to be tested, and the initial coefficient parameter [μ1 * ,μ2 * ,…,μ n * ].

[0034] In one embodiment of the present invention, the defect imaging result is obtained by calculating the Jacobian matrix and iteratively solving the defect reconstruction objective function using the Gauss-Newton method, including:

[0035] The inverse problem of electromagnetic parameter distribution imaging in eddy current tomography is expressed as:

[0036]

[0037] Substituting the conductivity distribution σ(x) into the above formula, the inverse problem expression of electromagnetic parameter distribution imaging based on parameter level set is obtained:

[0038] argmin{|λ m -U(σ(x,μ))| 2 +β|I(μ-μ * )|}

[0039] In the formula, λ m Indicates the measurement signal of the eddy current sensor, μ * is the initial coefficient parameter of the basis function, β is the regularization parameter;

[0040] For the optimization problem, the Newton iterative algorithm is used to solve it, and the iterative formula is expressed as:

[0041]

[0042] In the formula, μ k is the k-th iteration time basis function coefficient, λ k is the eddy current response signal calculated at the kth iteration, J k is the Jacobian matrix at the kth iteration, expressed as:

[0043]

[0044] Where, δ() represents the Dirac function;

[0045] According to the iterative coefficient μ, the defect imaging result is obtained.

[0046] To achieve the above object, the present invention provides, on the other hand, an electromagnetic eddy current defect imaging system based on parameter level set, comprising:

[0047] Sensor parameter optimization module, used to construct array eddy current sensors and optimize the parameters of array eddy current sensors through orthogonal experiments and response surface methodology;

[0048] The three-dimensional contour characterization module is used to collect data from the metal component to be tested using the optimized array eddy current sensor to obtain eddy current response signals under different excitation-reception conditions, and use the parameter level set algorithm to process the signal to characterize the three-dimensional contour of the defect;

[0049] A parameter setting module, used to set the position of the discrete point source describing the three-dimensional profile of the defect, the metal conductivity value and the defect conductivity value, and the initial coefficient parameters of the basis function;

[0050] An objective function reconstruction module is used to construct a level set reconstruction algorithm model according to the position of the discrete point source describing the three-dimensional contour, the metal conductivity value and the defect conductivity value and the initial coefficient parameters of the basis function, and input the eddy current response signal into the level set reconstruction algorithm model to obtain a defect reconstruction objective function based on the parameter level set;

[0051] The defect imaging result solving module is used to obtain the defect imaging result by calculating the Jacobian matrix and iteratively solving the defect reconstruction objective function using the Gauss-Newton method, and iteratively updating the basis function coefficient parameters;

[0052] The deviation judgment module is used to judge whether the defect reconstruction has converged according to whether the deviation of the defect imaging results before and after the iteration process is less than a preset threshold;

[0053] The final result output module is used to output the final defect imaging result according to the convergence judgment result to obtain the defect position, size and quantity information.

[0054] The electromagnetic eddy current defect imaging method and system based on parameter level set of the embodiment of the present invention are easy to implement and do not require the aid of a mechanical scanning device. The inner surface defect information of the metal component can be obtained through computational imaging.

[0055] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0057] Figure 1 is a flow chart of an electromagnetic eddy current defect imaging method based on parameter level set according to an embodiment of the present invention;

[0058] Figure 2 is a schematic diagram of an array eddy current sensor according to an embodiment of the present invention;

[0059] Figure 3 is a flow chart of parameter optimization of an array eddy current sensor according to an embodiment of the present invention;

[0060] Figure 4 is a defect three-dimensional imaging result diagram according to an embodiment of the present invention;

[0061] Figure 54 is a structural diagram of an electromagnetic eddy current defect imaging system based on parameter level set according to an embodiment of the present invention. DETAILED DESCRIPTION

[0062] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0063] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0064] The following describes an electromagnetic eddy current defect imaging method and system based on parameter level sets according to an embodiment of the present invention with reference to the accompanying drawings.

[0065] Figure 1 is a flow chart of an electromagnetic eddy current defect imaging method based on parameter level set according to an embodiment of the present invention. Figure 1 As shown, the method includes:

[0066] S1, construct an array eddy current sensor and optimize the parameters of the array eddy current sensor through orthogonal experiments and response surface methodology.

[0067] It can be understood that a planar flat plate array eddy current sensor is constructed, and the parameters of the array eddy current sensor are optimized through orthogonal experiments and response surface methodology to improve the uniformity of the sensitive field.

[0068] The entire optimization flow chart of the embodiment of the present invention is as follows: Figure 3 As shown, a 3×3 planar array eddy current sensor is designed, and the sensitivity matrix is ​​calculated by using the finite element numerical solution; the factors affecting the sensitivity matrix are analyzed according to the theoretical model of the non-coaxial eddy current sensor, and the parameter range is determined; based on the parameter range, the optimal parameter combination is obtained by using the orthogonal experiment; based on the optimal parameter combination, the relationship between the uniformity of the sensitivity matrix and the sensor parameters is obtained by the response surface method, so as to obtain the final optimized parameters of the array sensor.

[0069] Specifically, a 3×3 planar array eddy current sensor is designed, such as Figure 2As shown in the figure, according to the analysis of the analytical theoretical model, the main factors affecting the uniformity of the sensitivity matrix of the array eddy current sensor are the coil radius r and the lift-off distance l0, the coil height h and the coil spacing g, and the excitation frequency f. The range of each factor is determined, specifically the excitation frequency (500-10kHz), the coil outer diameter (5-15mm), the coil height (2-4.5mm), the lift-off distance (0.25-1mm) and the coil spacing (7.5-15mm). The uniformity of the sensitivity matrix can be described and characterized by the variance index. The orthogonal experimental design is used to obtain a better level combination. Based on the best level combination obtained by the orthogonal test, the response surface method is further used to obtain the relationship between the uniformity of the sensitivity matrix and the sensor parameters to obtain the final optimized parameters. The optimized sensor parameters are: the excitation frequency is set to 1000Hz, the coil height is 2.5mm and the lift-off distance is 0.5mm, the coil spacing is 10mm, and the coil radius is 5mm.

[0070] S2, using the optimized array eddy current sensor to collect data on the metal component to be tested to obtain eddy current response signals under different excitation-reception conditions, and using the parameter level set algorithm to process the signal to characterize the three-dimensional contour of the defect.

[0071] It can be understood that, by collecting data from the metal component to be measured through the optimized array eddy current sensor, eddy current response signals under different excitation-reception conditions are obtained, and the parameter level set algorithm is used to characterize the three-dimensional profile of the defect.

[0072] The metal imaging area is equivalent to a measured field containing two kinds of conductivity, where the defect area is the target area R and the metal area is the background area Ω\R. The conductivity changes of the target area R and the background area Ω\R are calculated based on the eddy current measurement data. The conductivity value of the metal Δσ1 and the defect conductivity value Δσ0, the conductivity change of the entire imaging area Ω, can be expressed as:

[0073] σ(x)=σ0(1-H(f(x))-c)+σ1H(f(x)-c)

[0074] Where H(s) is the smooth Heaviside function, which can be expressed as:

[0075]

[0076] f(x) is a parametric level set function that satisfies

[0077]

[0078] Wherein c is a positive number slightly greater than 0, and is set to 0.01 in this embodiment. ε is the Heaviside function smoothing factor, and is set to 0.1 in this embodiment.

[0079] The level set function F(x) can be obtained by using N basis functions p i (x) Linear weighted representation, the basis function can be selected from Gaussian radial basis function, cubic spline interpolation function, B-spline interpolation function, etc.

[0080]

[0081] μ i is the coefficient of the basis function, and different coefficients represent different imaging images. Therefore, by adjusting the coefficient, the reconstructed image can be changed.

[0082] S3, setting the position of the discrete point source describing the three-dimensional contour of the defect, the metal conductivity value and the defect conductivity value, and the initial coefficient parameters of the basis function.

[0083] Specifically, the location of the discrete point source (basis function), the metal conductivity value σ1 and the defect conductivity value σ0, and the initial coefficient parameter of the basis function [μ1 * ,μ2 * ,…,μ n * ].

[0084] The embodiment of the present invention adopts the classical linear back-projection algorithm to roughly determine the defect location;

[0085] The embodiment of the present invention sets the position of the basis function to the defect position reconstructed by linear back projection, thereby reducing the number of basis functions;

[0086] The initial coefficient parameter [μ1 * ,μ2 * ,…,μ n * ] is determined based on the grayscale value of the defect position reconstructed by the linear back projection algorithm.

[0087] The metal conductivity value σ1 of the embodiment of the present invention is determined according to the material of the metal to be tested. In this embodiment, the material of the sample to be tested is copper, and the conductivity is set to 5.8×10 7 S / m. The defect conductivity value σ0 can be set to 1×10 -5 S / m.

[0088] S4, constructing a level set reconstruction algorithm model according to the position of the discrete point source describing the three-dimensional contour, the metal conductivity value and the defect conductivity value and the initial coefficient parameters of the basis function, and inputting the eddy current response signal into the level set reconstruction algorithm model to obtain a defect reconstruction objective function based on the parameter level set.

[0089] Specifically, a level set reconstruction algorithm model is constructed according to the positions of discrete point sources describing the three-dimensional contour, the metal conductivity values ​​and the defect conductivity values, and the initial coefficient parameters of the basis function.

[0090] The eddy current response signal is input into the level set reconstruction algorithm model to obtain the defect reconstruction objective function based on the parameter level set;

[0091] argmin{|λ m -U(σ(x,μ))| 2 +β|I(μ-μ * )|}

[0092] In the formula, λ k Indicates the measurement signal of the eddy current sensor, μ * is the initial coefficient parameter of the basis function, and β is the regularization parameter.

[0093] S5, by calculating the Jacobian matrix and using the Gauss-Newton method to iteratively solve the defect reconstruction objective function to obtain the defect imaging result, and iteratively update the basis function coefficient parameters.

[0094] For the above optimization problem, the Newton iterative algorithm is used to solve it, and the iterative formula can be expressed as:

[0095]

[0096] Where μ k is the k-th iteration time basis function coefficient, λ k is the eddy current response signal calculated at the kth iteration, J k is the Jacobian matrix at the kth iteration, which can be expressed as:

[0097]

[0098] Where δ() represents the Dirac function.

[0099] According to the iterative coefficient μ, the defect imaging result can be obtained. In the whole process, the regularization parameter β is set to 0.1 and the iteration step α is set to 1.

[0100] S6, repeatedly executing S5, judging whether the defect reconstruction has converged according to whether the deviation between the two defect imaging results before and after the iterative process is less than a preset threshold.

[0101] Specifically, whether the defect reconstruction has converged is determined based on whether the deviation between the two reconstruction results before and after the iteration process is less than a preset threshold. If it is less than the preset threshold, then transpose step S7; otherwise, transpose step S6.

[0102] S7, outputting the final defect imaging result according to the convergence judgment result to obtain the defect position, size and quantity information.

[0103] In the embodiment of the present invention, four different defect distributions on the surface of the metal copper plate are specifically including a central single defect, a non-central single defect, two defects and four defects. The eddy current detection device is used to obtain the response signals of different defects. The proposed electromagnetic eddy current defect imaging method based on parameter level set is used to reconstruct the three-dimensional contour of the defect. The results are as follows: Figure 4 shown.

[0104] According to the electromagnetic eddy current defect imaging method based on parameter level set in the embodiment of the present invention, three-dimensional imaging of metal component defects can be achieved based on the signal measured by the eddy current sensor. A planar flat array eddy current sensor is built, and the parameters of the array eddy current sensor are optimized through orthogonal experiments and response surface method to improve the uniformity of the sensitive field. The eddy current response signal is input into the level set reconstruction algorithm model to obtain the defect reconstruction objective function based on the parameter level set. The position and initial coefficients of the basis function are adaptively determined by the imaging results of the traditional LBP algorithm. The Jacobian matrix is ​​calculated and the Gauss-Newton method is used to iteratively solve the objective function, and the basis function coefficient parameters are continuously iteratively updated to achieve three-dimensional imaging of defects. The defect distribution reconstructed by the imaging method proposed in the present invention is consistent with the experimental results, and can achieve accurate positioning and evaluation of the defect position under the damaged state of metal materials without the need for mechanical scanning devices, and has broad application prospects.

[0105] In order to implement the above embodiment, Figure 5 As shown, this embodiment also provides an electromagnetic eddy current defect imaging system 10 based on parameter level set, including:

[0106] A sensor parameter optimization module 100 is used to construct an array eddy current sensor and optimize the parameters of the array eddy current sensor through orthogonal experiments and response surface methodology;

[0107] The three-dimensional profile characterization module 200 is used to collect data from the metal component to be measured using the optimized array eddy current sensor to obtain eddy current response signals under different excitation-reception conditions, and use a parameter level set algorithm to process the signal to characterize the three-dimensional profile of the defect;

[0108] A parameter setting module 300 is used to set the position of the discrete point source describing the three-dimensional profile of the defect, the metal conductivity value and the defect conductivity value, and the initial coefficient parameters of the basis function;

[0109] The objective function reconstruction module 400 is used to construct a level set reconstruction algorithm model according to the position of the discrete point source describing the three-dimensional contour, the metal conductivity value and the defect conductivity value and the initial coefficient parameters of the basis function, and input the eddy current response signal into the level set reconstruction algorithm model to obtain a defect reconstruction objective function based on the parameter level set;

[0110] The defect imaging result solving module 500 is used to obtain the defect imaging result by calculating the Jacobian matrix and iteratively solving the defect reconstruction objective function using the Gauss-Newton method, and iteratively updating the basis function coefficient parameters;

[0111] The deviation judgment module 600 is used to judge whether the defect reconstruction has converged according to whether the deviation between the two defect imaging results before and after the iteration process is less than a preset threshold;

[0112] The final result output module 700 is used to output the final defect imaging result according to the convergence judgment result to obtain the defect position, size and quantity information.

[0113] Furthermore, the sensor parameter optimization module 100 is also used for:

[0114] Design a 3×3 planar array eddy current sensor and calculate the sensitivity matrix using finite element numerical solution;

[0115] According to the theoretical model of non-coaxial eddy current sensor, the factors affecting the sensitivity matrix are analyzed and the parameter range is determined;

[0116] Based on the parameter range, the best parameter combination is obtained by using orthogonal experiments;

[0117] Based on the optimal parameter combination, the relationship between the uniformity of the sensitivity matrix and the sensor parameters is obtained by using the response surface method to obtain the final optimized parameters of the array sensor.

[0118] Furthermore, the three-dimensional contour characterization module 200 is also used for:

[0119] The metal imaging area is equivalent to a measured field containing two kinds of conductivity, where the defect area is the target area R and the metal area is the background area Ω\R. The conductivity changes of the target area R and the background area Ω\R are calculated according to the eddy current response signal; the metal conductivity value Δσ1 and the defect conductivity value Δσ0, the conductivity change of the entire background area Ω, is expressed as:

[0120] σ(x)=σ0(1-H(f(x))-c)+σ1H(f(x)-c)

[0121] Where H(s) is the smooth Heaviside function, expressed as:

[0122]

[0123] f(x) is a parametric level set function that satisfies:

[0124]

[0125] The level set function f(x) is obtained by using N basis functions p i (x) Linear weighted representation:

[0126]

[0127] Among them, μ i are the coefficients of the basis functions.

[0128] Furthermore, the parameter setting module 300 is also used to:

[0129] The location of the defect is preliminarily determined using the linear back-projection algorithm;

[0130] The position of the basis function is set to the defect position reconstructed by linear back projection;

[0131] Determine the metal conductivity value σ1 according to the material of the metal to be tested, and set the defect conductivity value σ0 to 1×10 -5 S / m, and determine the initial coefficient parameters of the basis function [μ1 * ,μ2 * ,…,μ n * ].

[0132] Furthermore, the defect imaging result solving module 500 is also used for:

[0133] The inverse problem of electromagnetic parameter distribution imaging in eddy current tomography is expressed as:

[0134]

[0135] Substituting the conductivity distribution σ(x) into the above formula, the inverse problem expression of electromagnetic parameter distribution imaging based on parameter level set is obtained:

[0136] argmin{|λ m -U(σ(x,μ))| 2 +β|I(μ-μ * )|}

[0137] In the formula, λ k Indicates the measurement signal of the eddy current sensor, μ * is the initial coefficient parameter of the basis function, β is the regularization parameter;

[0138] For the optimization problem, the Newton iterative algorithm is used to solve it, and the iterative formula is expressed as:

[0139]

[0140] In the formula, μ k is the k-th iteration time basis function coefficient, λ k is the eddy current response signal calculated at the kth iteration, J k is the Jacobian matrix at the kth iteration, expressed as:

[0141]

[0142] Where, δ() represents the Dirac function;

[0143] According to the iterative coefficient μ, the defect imaging result is obtained.

[0144] According to the electromagnetic eddy current defect imaging system based on parameter level set of the embodiment of the present invention, three-dimensional imaging of metal component defects can be achieved based on the signal measured by the eddy current sensor. A planar flat array eddy current sensor is built, and the parameters of the array eddy current sensor are optimized through orthogonal experiments and response surface method to improve the uniformity of the sensitive field. The eddy current response signal is input into the level set reconstruction algorithm model to obtain the defect reconstruction objective function based on the parameter level set. The position and initial coefficients of the basis function are adaptively determined by the imaging results of the traditional LBP algorithm. The Jacobian matrix is ​​calculated and the Gauss-Newton method is used to iteratively solve the objective function, and the basis function coefficient parameters are continuously iteratively updated to achieve three-dimensional imaging of defects. The defect distribution reconstructed by the imaging method proposed in the present invention is consistent with the experimental results, and can achieve accurate positioning and evaluation of the defect position under the damaged state of metal materials without the need for mechanical scanning devices, and has broad application prospects.

[0145] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0146] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

Claims

1. An electromagnetic eddy current defect imaging method based on parameter level set, characterized in that: include: S1, construct an array eddy current sensor and optimize the parameters of the array eddy current sensor through orthogonal experiments and response surface methodology; S2, using the optimized array eddy current sensor to collect data on the metal component to be tested to obtain eddy current response signals under different excitation-reception conditions, and using the parameter level set algorithm to process the signal to characterize the three-dimensional profile of the defect; S3, setting the position of the discrete point source describing the three-dimensional profile of the defect, the metal conductivity value and the defect conductivity value, and the initial coefficient parameters of the basis function; S4, constructing a level set reconstruction algorithm model according to the position of the discrete point source describing the three-dimensional contour, the metal conductivity value and the defect conductivity value and the initial coefficient parameters of the basis function, and inputting the eddy current response signal into the level set reconstruction algorithm model to obtain a defect reconstruction objective function based on the parameter level set; S5, obtaining the defect imaging result by calculating the Jacobian matrix and iteratively solving the defect reconstruction objective function using the Gauss-Newton method, and iteratively updating the basis function coefficient parameters; S6, repeatedly executing S5, judging whether the defect reconstruction has converged according to whether the deviation of the defect imaging results before and after the iteration process is less than a preset threshold; S7, outputting the final defect imaging result according to the convergence judgment result to obtain the defect position, size and quantity information.

2. The method according to claim 1, characterized in that: An array eddy current sensor was constructed, and the parameters of the array eddy current sensor were optimized by orthogonal experiments and response surface methodology, including: Design a 3×3 planar array eddy current sensor and calculate the sensitivity matrix using finite element numerical solution; According to the theoretical model of non-coaxial eddy current sensor, the factors affecting the sensitivity matrix are analyzed and the parameter range is determined; Based on the parameter range, the best parameter combination is obtained by using orthogonal experiments; Based on the optimal parameter combination, the relationship between the uniformity of the sensitivity matrix and the sensor parameters is obtained by using the response surface method to obtain the final optimized parameters of the array sensor.

3. The method according to claim 1, characterized in that The optimized array eddy current sensor is used to collect data from the metal component to be tested to obtain eddy current response signals under different excitation-reception conditions, and the parameter level set algorithm is used to process the signal to characterize the three-dimensional profile of the defect, including: The metal imaging area is equivalent to a measured field containing two kinds of conductivity, where the defect area is the target area R and the metal area is the background area Ω\R. The conductivity changes of the target area R and the background area Ω\R are calculated according to the eddy current response signal; the metal conductivity value Δσ1 and the defect conductivity value Δσ0, the conductivity change of the entire background area Ω, is expressed as: σ(x)=σ0(1-H(f(x))-c)+σ1H(f(x)-c) Where H(s) is the smooth Heaviside function, expressed as: f(x) is a parametric level set function that satisfies: The level set function f(x) is obtained by using N basis functions p i (x) Linear weighted representation: Among them, μ i are the coefficients of the basis functions.

4. The method according to claim 1, characterized in that Set the position of the discrete point source describing the three-dimensional contour of the defect, the metal conductivity value and the defect conductivity value, and the initial coefficient parameters of the basis function, including: The location of the defect is preliminarily determined using the linear back-projection algorithm; The position of the basis function is set to the defect position reconstructed by linear back projection; The metal conductivity value σ1 is determined according to the material of the metal to be tested, and the initial coefficient parameter [μ1 * ,μ2 * ,…,μ n * ].

5. The method according to claim 1, characterized in that The defect imaging results are obtained by calculating the Jacobian matrix and iteratively solving the defect reconstruction objective function using the Gauss-Newton method, including: The inverse problem of electromagnetic parameter distribution imaging in eddy current tomography is expressed as: Substituting the conductivity distribution σ(x) into the above formula, the inverse problem expression of electromagnetic parameter distribution imaging based on parameter level set is obtained: argmin{|λ m -U(σ(x,μ))| 2 +β|I(μ-μ * )|} In the formula, λ m Indicates the measurement signal of the eddy current sensor, μ * is the initial coefficient parameter of the basis function, β is the regularization parameter; For the optimization problem, the Newton iterative algorithm is used to solve it, and the iterative formula is expressed as: In the formula, μ k is the k-th iteration time basis function coefficient, λ k is the eddy current response signal calculated at the kth iteration, J k is the Jacobian matrix at the kth iteration, expressed as: Where, δ() represents the Dirac function; According to the iterative coefficient μ, the defect imaging result is obtained.

6. An electromagnetic eddy current defect imaging system based on parameter level set, characterized in that: include: Sensor parameter optimization module, used to construct array eddy current sensors and optimize the parameters of array eddy current sensors through orthogonal experiments and response surface methodology; The three-dimensional contour characterization module is used to collect data from the metal component to be tested using the optimized array eddy current sensor to obtain eddy current response signals under different excitation-reception conditions, and use the parameter level set algorithm to process the signal to characterize the three-dimensional contour of the defect; A parameter setting module, used to set the position of the discrete point source describing the three-dimensional profile of the defect, the metal conductivity value and the defect conductivity value, and the initial coefficient parameters of the basis function; An objective function reconstruction module is used to construct a level set reconstruction algorithm model according to the position of the discrete point source describing the three-dimensional contour, the metal conductivity value and the defect conductivity value and the initial coefficient parameters of the basis function, and input the eddy current response signal into the level set reconstruction algorithm model to obtain a defect reconstruction objective function based on the parameter level set; The defect imaging result solving module is used to obtain the defect imaging result by calculating the Jacobian matrix and iteratively solving the defect reconstruction objective function using the Gauss-Newton method, and iteratively updating the basis function coefficient parameters; The deviation judgment module is used to judge whether the defect reconstruction has converged according to whether the deviation of the defect imaging results before and after the iteration process is less than a preset threshold; The final result output module is used to output the final defect imaging result according to the convergence judgment result to obtain the defect position, size and quantity information.

7. The system according to claim 6, characterized in that The sensor parameter optimization module is also used to: Design a 3×3 planar array eddy current sensor and calculate the sensitivity matrix using finite element numerical solution; According to the theoretical model of non-coaxial eddy current sensor, the factors affecting the sensitivity matrix are analyzed and the parameter range is determined; Based on the parameter range, the best parameter combination is obtained by using orthogonal experiments; Based on the optimal parameter combination, the relationship between the uniformity of the sensitivity matrix and the sensor parameters is obtained by using the response surface method to obtain the final optimized parameters of the array sensor.

8. The system according to claim 6, characterized in that The 3D contour characterization module is also used for: The metal imaging area is equivalent to a measured field containing two kinds of conductivity, where the defect area is the target area R and the metal area is the background area Ω\R. The conductivity changes of the target area R and the background area Ω\R are calculated according to the eddy current response signal; the metal conductivity value Δσ1 and the defect conductivity value Δσ0, the conductivity change of the entire background area Ω, is expressed as: σ(x)=σ0(1-H(f(x))-c)+σ1H(f(x)-c) Where H(s) is the smooth Heaviside function, expressed as: f(x) is a parametric level set function that satisfies: The level set function f(x) is obtained by using N basis functions p i (x) Linear weighted representation: Among them, μ i are the coefficients of the basis functions.

9. The system according to claim 6, characterized in that The parameter setting module is also used to: The location of the defect is preliminarily determined using the linear back-projection algorithm; The position of the basis function is set to the defect position reconstructed by linear back projection; The metal conductivity value σ1 is determined according to the material of the metal to be tested, and the initial coefficient parameter [μ1 * ,μ2 * ,…,μ n * ].

10. The system according to claim 6, characterized in that The defect imaging result solving module is also used for: The inverse problem of electromagnetic parameter distribution imaging in eddy current tomography is expressed as: Substituting the conductivity distribution σ(x) into the above formula, the inverse problem expression of electromagnetic parameter distribution imaging based on parameter level set is obtained: argmin{|λ m -U(σ(x,μ))| 2 +β|I(μ-μ * )|} In the formula, λ m Indicates the measurement signal of the eddy current sensor, μ * is the initial coefficient parameter of the basis function, β is the regularization parameter; For the optimization problem, the Newton iterative algorithm is used to solve it, and the iterative formula is expressed as: In the formula, μ k is the k-th iteration time basis function coefficient, λ k is the eddy current response signal calculated at the kth iteration, J k is the Jacobian matrix at the kth iteration, expressed as: Where, δ() represents the Dirac function; According to the iterative coefficient μ, the defect imaging result is obtained.

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