Novel induction type magneto-thermo-acoustic detection method for conductivity of supercapacitor

Abstract

The invention discloses a novel induction-type magneto-thermo-acoustic detection method for the conductivity of a supercapacitor, and relates to the technical field of nondestructive material detection.The method comprises the steps that a steady-state static magnetic field and a pulse alternating magnetic field are introduced to form a composite excitation field, and a magneto-acoustic effect and a thermo-acoustic effect are simultaneously and cooperatively excited in a solid-state electrode material; the magnetoacoustic-thermoacoustic coupling effect is formed, eddy current induced by a pulse alternating magnetic field in the material not only generates joule heat, but also generates a direct carrier of Lorentz force under the action of a steady-state static magnetic field, the two physical effects are derived from the same electromagnetic excitation process, but the mechanisms for generating acoustic signals are complementary to each other, so that the effect of the magnetoacoustic-thermoacoustic coupling is achieved. The two effects are coupled as a unified sound source item, a sound pressure wave equation is established, the equation describes a sound field excitation process under the combined action of a force source and a heat source, the coupling mechanism remarkably enhances the strength and information abundance of ultrasonic signals, and the inherent defect that a single thermoacoustic detection method is insensitive to a high-conductivity material is overcome.

Description

Technical Field

[0001] This invention relates to the field of non-destructive testing technology, specifically to a novel inductive magnetothermal-acoustic testing method for the conductivity of supercapacitors. Background Technology

[0002] Supercapacitors, as novel energy storage devices, are widely used in new energy vehicles, smart grids, and portable electronic devices due to their advantages such as high power density, fast charging and discharging speed, and long cycle life. Their core performance is determined by the conductivity of the electrode materials, and accurate conductivity detection is crucial for optimizing material formulations and improving device performance. Traditional detection methods, limited by contact-based operations or single-effect excitation, struggle to balance detection accuracy with material integrity, thus hindering the research and development efficiency and application expansion of supercapacitors.

[0003] Among existing detection technologies, the four-probe method measures conductivity through direct contact. Applying pressure can easily damage the electrode material surface and internal structure, and contamination at the contact point can introduce detection errors, failing to meet the non-destructive testing requirements for precision materials. While inductive thermoacoustic detection is non-contact, it relies solely on the thermoacoustic effect, ignoring the magnetoacoustic effect. When the conductivity of the electrode material reaches the order of 100 S / m, the thermoacoustic signal is significantly interfered with by the magnetoacoustic effect, leading to a decrease in detection accuracy. Inductive magnetoacoustic imaging is only suitable for fluid objects such as biological tissues; its model and algorithm are not adapted to solid electrode materials, and without coupling the thermoacoustic effect, it is difficult to achieve quantitative and accurate detection of the conductivity of solid materials.

[0004] In summary, existing detection methods suffer from limitations such as insufficient accuracy in contact-based and non-contact methods, as well as restrictions on applicable scenarios, failing to meet the practical requirements for high-precision, non-destructive testing of the conductivity of supercapacitor electrode materials. Developing a non-contact detection method that integrates multi-physics field effects and adapts to the properties of solid-state materials is of great significance for promoting the upgrading of supercapacitor technology and expanding the application scenarios of energy storage devices. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a novel inductive magneto-thermo-acoustic detection method for the conductivity of supercapacitors. This method introduces a composite excitation field composed of a steady-state static magnetic field and a pulsed alternating magnetic field, simultaneously and synergistically exciting magneto-acoustic and thermo-acoustic effects within the solid electrode material, forming a magneto-acoustic-thermo-acoustic coupling effect. The eddy currents induced in the material by the pulsed alternating magnetic field not only generate Joule heating but also directly carry the Lorentz force generated under the action of the steady-state static magnetic field. These two physical effects originate from the same electromagnetic excitation process, but their mechanisms for generating acoustic signals are complementary. By coupling these two effects as a unified sound source term, a more complete sound pressure wave equation is established. This equation fully describes the sound field excitation process under the combined action of force and heat sources. This coupling mechanism significantly enhances the intensity and information richness of the ultrasonic signal, overcoming the inherent defects of weak signals and insensitivity to high-conductivity materials in single thermo-acoustic detection methods. It provides a more solid physical foundation and more comprehensive raw data for subsequent high-precision inversion.

[0006] To solve the above-mentioned technical problems, this invention provides the following technical solution: a novel inductive magnetothermal-acoustic detection method for the conductivity of supercapacitors, the specific steps of which are as follows:

[0007] S100. The electrode material of the supercapacitor to be tested is placed in a pulsed alternating magnetic field and a steady static magnetic field that coexist, so that the electrode material generates both magnetoacoustic and thermoacoustic effects and excites ultrasonic signals.

[0008] S200: Acquire the ultrasonic signal generated in S100 and preprocess it by an ultrasonic transducer array arranged around the electrode material;

[0009] S300, ultrasonic signals preprocessed based on S200 By combining time reversal method with compressed sensing algorithm, the Lorentz force divergence characterizing magnetoacoustic effect is reconstructed. and the heat function characterizing the thermoacoustic effect Together, they serve as a coupled sound source term;

[0010] The Lorentz force divergence obtained from S400 and reconstruction based on S300. and the heat function A quantitative mapping relationship between the supercapacitor electrode material and its conductivity distribution is established, and the least squares iterative algorithm is used to solve the problem to obtain the spatial conductivity distribution of the supercapacitor electrode material.

[0011] S500: Output and display the image and data of the conductivity distribution obtained by S400 inversion.

[0012] Furthermore, the process of generating the S100 ultrasonic signal includes:

[0013] The voltage amplitude of the pulsed alternating magnetic field is set to 80-120V and the pulse frequency is set to 1-5kHz. The strength of the steady-state static magnetic field is adjusted to 0.15-0.25T so that the two magnetic fields form an orthogonally coupled magnetic field environment in the region where the electrode material is located.

[0014] The pulsed alternating magnetic field induces an eddy current electric field within the electrode material through electromagnetic induction. ,in The electric field intensity vector of the eddy current. This represents the spatial position vector within the electrode material. As a time variable, the eddy current electric field drives charge carriers to form eddy currents. ,in Eddy current, The vector of eddy current density. Let be the conductivity function of the electrode material, and let eddy current be in a steady-state static magnetic field. and pulsed alternating magnetic field In the combined magnetic field, the Lorentz force is generated simultaneously. Joule thermal power ,in, For steady-state static magnetic field, It is a pulsed alternating magnetic field. For Lorentz force, For volumetric Joule heat power, The electric field strength modulus of the eddy current electric field;

[0015] The Lorentz force, changing over time, induces mechanical vibration in the electrode material, generating a magnetoacoustic signal. The Joule heating power causes an instantaneous increase in the material's temperature. ,in, This represents the instantaneous temperature change of the material. The density of the electrode material, The specific heat capacity at constant pressure of the material is used to generate a thermoacoustic signal through thermal expansion. The magnetoacoustic signal and the thermoacoustic signal are superimposed and coupled in the sound propagation medium to form the ultrasonic signal under test. .

[0016] Furthermore, the generation of the ultrasonic signal in S100 satisfies the sound field wave equation: ,in, Represents vector divergence operation. The spatial position vector of the sound source point. The coefficient of volume expansion of the material. The propagation speed of the sound source point in the coupling medium. The Lorentz divergence is a measure of the intensity of a magnetoacoustic sound source. The first derivative of the heat function with respect to time characterizes the intensity of the sound source in the thermoacoustic effect. is a heat function and , The volumetric joule heat power is given.

[0017] Furthermore, the specific steps of the coupling sound source term in S300 are as follows:

[0018] Preparation for sound source reconstruction: This involves processing the acquired ultrasonic signals... Preprocessing is performed, and the ultrasonic signal is inverted in time and propagated in reverse using the time inversion method to focus on and locate the sound source position, and to construct a physical model of sound field propagation.

[0019] Sparse reconstruction solution: Based on the constructed physical model, the inverse problem of the sound pressure wave equation is solved using the compressed sensing algorithm, transforming the problem of reconstructing the sound source term into a sparse optimization problem, and reconstructing the distribution of the Lorentz force divergence characterizing the magnetoacoustic effect and the distribution of the heat function characterizing the thermoacoustic effect, respectively.

[0020] Furthermore, the compressed sensing algorithm is an orthogonal matching pursuit algorithm, and its execution steps include:

[0021] The ultrasonic signal is sampled to construct an observation vector, and the orthogonal basis corresponding to the sound pressure wave equation is selected to construct a sparse matrix.

[0022] An observation matrix is ​​constructed by combining the sound propagation information provided by the time-reversal method.

[0023] The Lorentz force divergence matrix and the heat function matrix are simultaneously output by iteratively solving the problem using the orthogonal matching pursuit algorithm.

[0024] Furthermore, in S400, the relationship between the reconstructed Lorentz force divergence and the conductivity distribution is as follows: ,in Represents vector divergence operation. For the reconstructed Lorentz force divergence, For time variables, Let be the conductivity function of the electrode material. This represents the spatial position vector within the electrode material. The eddy current electric field is determined by combining Maxwell's equations with magnetic field parameters. and Please solve. For steady-state static magnetic field, It is a pulsed alternating magnetic field;

[0025] The relationship between the reconstructed heat function and electrical conductivity is as follows: ,in The reconstructed heat function.

[0026] Furthermore, in S400, the process of solving using the least squares iterative algorithm is as follows:

[0027] Distribution by conductivity For the variable to be determined, construct the objective function. ,in The objective function is used to characterize the deviation between the reconstructed values ​​and the observed values. To reconstruct the Lorentz force divergence, The observed values ​​of the Lorentz force divergence are... The square of the L2 norm, This is a weighting coefficient, ranging from 0.1 to 1.0, used to balance the contributions of the two biases. To reconstruct the heat function, For the observed values ​​of the heat function, the least squares iterative algorithm is used to evaluate the objective function. Optimize and update at each step during the iteration process. ,in For the first Conductivity distribution in the next iteration For the first Conductivity distribution in the next iteration The iteration step size, For the objective function at the th The gradient at each iteration is used until the convergence condition is met. The final conductivity distribution is output.

[0028] Furthermore, in S200, the ultrasonic transducer array consists of multiple planar ultrasonic transducers arranged around the electrode material to collect ultrasonic signals generated by the electrode material. The preprocessing uses a pre-filter and a signal amplifier to condition and amplify the collected ultrasonic signals.

[0029] Compared with existing technologies, this novel inductive magnetothermoacoustic detection method for supercapacitor conductivity has the following advantages:

[0030] This invention introduces a composite excitation field composed of a steady-state static magnetic field and a pulsed alternating magnetic field, simultaneously and synergistically exciting magnetoacoustic and thermoacoustic effects within the solid electrode material, forming a magnetoacoustic-thermoacoustic coupling effect. The eddy currents induced in the material by the pulsed alternating magnetic field not only generate Joule heating but also directly carry the Lorentz force generated under the action of the steady-state static magnetic field. These two physical effects originate from the same electromagnetic excitation process, but their mechanisms for generating acoustic signals are complementary. By coupling these two effects as a unified sound source term, a more complete sound pressure wave equation is established. This equation fully describes the sound field excitation process under the combined action of the force and heat sources. This coupling mechanism significantly enhances the intensity and information richness of the ultrasonic signal, overcoming the inherent defects of weak signals and insensitivity to high-conductivity materials in the single thermoacoustic detection method, and providing more solid physical foundation and more comprehensive original data for subsequent high-precision inversion.

[0031] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0033] Figure 1 A flowchart of a novel inductive magnetothermal acoustic detection method for the conductivity of supercapacitors;

[0034] Figure 2 This is a flowchart illustrating the steps of a novel inductive magnetothermoacoustic detection method for the conductivity of supercapacitors. Detailed Implementation

[0035] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0036] Example 1

[0037] This embodiment provides a novel inductive magnetothermal-acoustic detection method for the conductivity of supercapacitors, such as... Figure 2As shown, in step S100, the electrode material of the supercapacitor under test is placed in a simultaneously existing pulsed alternating magnetic field and a steady static magnetic field, causing magnetoacoustic and thermoacoustic effects to be generated inside the electrode material, thus exciting an ultrasonic signal. In step S200, the ultrasonic signal generated in step S100 is acquired and preprocessed by an array of ultrasonic transducers arranged around the electrode material. In step S300, the ultrasonic signal is preprocessed based on the ultrasonic signal from step S200. By combining time reversal method with compressed sensing algorithm, the Lorentz force divergence characterizing magnetoacoustic effect is reconstructed. and the heat function characterizing the thermoacoustic effect Together, they serve as the coupled sound source term. The Lorentz force divergence reconstructed by S400 based on S300 is... and the heat function A quantitative mapping relationship is established between the conductivity distribution of the supercapacitor electrode material and the conductivity distribution of the electrode material. A least-squares iterative algorithm is used to solve the problem, and the spatial conductivity distribution of the supercapacitor electrode material is obtained through inversion. The S500 outputs and displays the image and data of the conductivity distribution obtained by the S400 inversion. This method integrates multi-physics coupling effects, realizing non-contact, high-precision, non-destructive testing of the conductivity of supercapacitor electrode materials. It effectively solves the problems of contact damage, insufficient accuracy, and limited applicability of traditional testing methods.

[0038] First, the ultrasonic signal generation stage (S100) is entered, where a composite magnetic field environment is constructed and coupled ultrasonic signals are excited. The electrode material of the supercapacitor to be tested is placed in a spatial region where both a pulsed alternating magnetic field and a steady-state static magnetic field exist simultaneously, so that the two magnetic fields form an orthogonally coupled magnetic field environment at the location of the electrode material. Among them, the pulsed alternating magnetic field induces an eddy current electric field inside the electrode material through electromagnetic induction. ,in The electric field intensity vector of the eddy current. This represents the spatial position vector within the electrode material. As a time variable, according to the principle of electromagnetic induction, this eddy current electric field will drive the charge carriers inside the material to form eddy currents. And satisfy ,in Let be the conductivity function of the electrode material. Let be the current density vector of the eddy current, and let eddy current be in the steady-state static magnetic field. With pulsed alternating magnetic field In the resulting composite magnetic field, two key physical effects occur simultaneously: firstly, the interaction between the eddy current and the composite magnetic field generates the Lorentz force. Its expression is ,in The magnetic flux density vector of the pulsed alternating magnetic field. This represents the Lorentz force vector. Because the pulsed alternating magnetic field changes with time, the Lorentz force also changes dynamically with time, thus inducing mechanical vibration in the electrode material. This vibration forms a magnetoacoustic signal in the acoustic propagation medium. On the other hand, eddy currents generate Joule heating power within the electrode material; its volumetric Joule heating power... satisfy ,in The electric field strength modulus of the eddy current electric field, the Joule heat power will cause an instantaneous temperature change in the electrode material, the amount of temperature change. We can obtain the result through integration. ,in The density of the electrode material, Given the material's specific heat capacity at constant pressure, a sudden increase in the material's temperature will induce a thermal expansion effect, thereby generating a thermoacoustic signal. The magnetoacoustic signal and the thermoacoustic signal superimpose and couple with each other in the sound propagation medium, ultimately forming the ultrasonic signal being measured. The generation process of this ultrasonic signal satisfies the acoustic field wave equation: ,in Represents vector divergence operation. The spatial position vector of the sound source point. The coefficient of volume expansion of the material. The propagation speed of the sound source point in the coupling medium. The Lorentz divergence is a measure of the intensity of a magnetoacoustic sound source. The first derivative of the heat function with respect to time characterizes the intensity of the sound source in the thermoacoustic effect. It is a heat function and satisfies , The equation, which represents the volumetric Joule thermal power, fully describes the sound field excitation process under the combined influence of Lorentz force and Joule heat.

[0039] Then, the ultrasonic signal acquisition and preprocessing stage (S200) is entered, which is used to capture and pre-condition the ultrasonic signal. An array of ultrasonic transducers is arranged around the electrode material. This array consists of multiple planar ultrasonic transducers to ensure that the coupled ultrasonic signal generated in stage S100 can be acquired from all directions and from multiple angles. Since ultrasonic signals are subject to environmental noise interference during propagation and the original signal amplitude may be weak, the acquired ultrasonic signals need to be preprocessed. The preprocessing process uses a pre-filter to filter out high-frequency noise and low-frequency interference components in the signal, and then uses a signal amplifier to amplify the amplitude of the filtered effective signal to achieve signal conditioning and optimization, thereby obtaining a preprocessed ultrasonic signal that provides a high-quality signal input for subsequent sound source reconstruction.

[0040] Next, the coupled source term reconstruction stage (S300) begins. This stage uses signal processing algorithms to accurately reconstruct the Lorentz force divergence and heat function. Specifically, it consists of two steps: source term reconstruction preparation and sparse reconstruction solution. In the source term reconstruction preparation step, the ultrasonic signal preprocessed in S200 is used... The ultrasonic signal is inverted in time using the time-reversal method, and the inverted signal is propagated backward in a pre-defined sound field model. The time-reversal method utilizes the reciprocity of the sound field to focus and locate the dispersed ultrasonic signal back to the initial position of the sound source, while simultaneously constructing a physical model of sound field propagation. This model accurately describes the propagation path and attenuation characteristics of the ultrasonic signal from the sound source to the transducer array. In the sparse reconstruction solution step, based on the constructed sound field propagation physical model, the inverse problem of the sound pressure wave equation is solved using a compressed sensing algorithm. This embodiment uses the orthogonal matching pursuit algorithm as the compressed sensing algorithm. Its execution process is as follows: the preprocessed ultrasonic signal is sampled to construct an observation vector; an orthogonal basis corresponding to the sound pressure wave equation is selected; a sparse matrix is ​​constructed, which represents the sound source term in the sparse domain; combined with the sound propagation path information provided by the time-reversal method, an observation matrix is ​​constructed; a mapping relationship between the observation vector and the sparse matrix is ​​established; and the orthogonal matching pursuit algorithm is used for iterative solution, gradually approaching the optimal solution, and simultaneously outputting the Lorentz force divergence characterizing the magnetoacoustic effect. and the heat function characterizing the thermoacoustic effect The distribution matrix, together with the other two, constitutes the coupled sound source term, completing the reconstruction process of the sound source term, where... To reconstruct the Lorentz force divergence, The reconstructed heat function.

[0041] Secondly, the conductivity distribution inversion stage (S400) is entered. By establishing a quantitative relationship between the reconstructed sound source term and the conductivity distribution, the spatial conductivity distribution of the electrode material is obtained. First, the quantitative mapping relationship between the reconstructed sound source term and the conductivity distribution is clarified: the relationship between the reconstructed Lorentz force divergence and the conductivity distribution is as follows: eddy current electric field It can be derived from Maxwell's equations combined with known magnetic field parameters. and The solution yields the following relationship between the reconstructed heat function and electrical conductivity: In terms of conductivity function For the variable to be determined, construct the objective function: ,in The objective function is used to characterize the deviation between the reconstructed values ​​and the observed values. To reconstruct the Lorentz force divergence, The observed values ​​of the Lorentz force divergence are... for The square of the norm, These are weighting coefficients used to balance the contributions of the two biases. To reconstruct the heat function, These are the observed values ​​of the heat function. The least squares iterative algorithm is used to evaluate the objective function. The optimization solution is performed, and the iterative update formula is as follows: ,in For the first Conductivity distribution in the next iteration For the first Conductivity distribution in the next iteration The iteration step size, For the objective function at the th The gradient at the next iteration is used, and the iteration process continues until the convergence condition is met. The output at this time This refers to the spatial conductivity distribution of the supercapacitor electrode material obtained through inversion.

[0042] Finally, the results are output and displayed in stage S500. The spatial conductivity distribution results of the supercapacitor electrode material obtained from the inversion in stage S400 are converted into data formats and rendered into images. The conductivity distribution data is converted into a standardized data format, and an intuitive conductivity distribution image is generated based on the spatial location information. Different colors or gray levels can be used to represent the differences in conductivity in different regions. The conductivity distribution image and the corresponding raw data are simultaneously output and displayed through a display device, which makes it convenient for testing personnel to intuitively obtain the conductivity information of each location of the electrode material, providing accurate data support for material performance evaluation and formulation optimization.

[0043] In summary, this embodiment achieves inductive magneto-thermo-acoustic detection of the conductivity of supercapacitor electrode materials through a complete process from S100 to S500. This method enhances the intensity and information richness of the ultrasonic signal by stimulating the magneto-acoustic-thermo-acoustic coupling effect through a composite magnetic field; it improves the accuracy of sound source reconstruction by combining time-reversal method and compressed sensing algorithm; and it achieves accurate inversion of conductivity distribution through least-squares iterative algorithm. The entire detection process does not require contact with the electrode material, avoiding material damage caused by contact detection, and overcomes the insufficient accuracy problem of single-effect detection. It is suitable for conductivity detection of solid-state supercapacitor electrode materials, providing reliable detection technology support for the research, optimization, and application expansion of supercapacitors.

[0044] Example 2

[0045] Based on Example 1, this example provides a novel inductive magnetothermoacoustic detection method for supercapacitor conductivity. The specific steps for detecting supercapacitor conductivity are as follows: Figure 1 As shown, the specific steps are as follows:

[0046] (1) Sample preparation

[0047] The supercapacitor electrode material sample to be tested is placed in a test water tank filled with insulating oil.

[0048] Ensure that the sample is located within the effective overlap region of the steady static magnetic field generated by the pulsed magnetic field coil and the permanent magnet.

[0049] Adjust the position of the ultrasonic transducer array arranged around the sample to ensure that it can effectively receive ultrasonic signals from the sample.

[0050] (2) Magnetic field excitation

[0051] Set the pulsed magnetic field excitation source parameters: adjust the voltage amplitude to 80-120V and the pulse frequency to 1-5kHz to generate a pulsed alternating magnetic field.

[0052] It was confirmed that the steady-state static magnetic field strength provided by the permanent magnet is in the range of 0.15-0.25T, and is spatially orthogonal to the pulsed alternating magnetic field.

[0053] The pulse excitation source is activated, so that the electrode material is simultaneously subjected to the pulsed alternating magnetic field and the steady-state static magnetic field.

[0054] (3) Generation of eddy current field

[0055] The pulsed alternating magnetic field induces eddy currents inside the electrode material. Under the combined action of the steady-state static magnetic field and the pulsed alternating magnetic field, these eddy currents produce two physical effects:

[0056] Magnetoacoustic effect: Eddy currents are subjected to the force of a magnetic field, which induces microscopic vibrations in the material.

[0057] Thermoacoustic effect: Eddy currents flowing through the material's resistance generate Joule heat, causing localized instantaneous thermal expansion of the material.

[0058] The combined effect of material vibration and thermal expansion generates ultrasonic signals that propagate outwards.

[0059] (4) Ultrasonic signal coupling

[0060] An ultrasonic transducer array receives ultrasonic signals propagating from the surface of an electrode material.

[0061] The weak raw electrical signal collected is denoised by a pre-filter.

[0062] The filtered signal is amplified by a low-noise amplifier to improve the signal-to-noise ratio.

[0063] (5) Time Reversal Focus

[0064] Using the time-inversion method, the acquired ultrasonic signals are inverted over time, and then propagated backward in a computer through numerical simulation, thereby physically focusing and initially locating the sound source.

[0065] (6) Compressed sensing separation

[0066] Accurate reconstruction: Based on the sound propagation information provided by the time-reversal method, the compressed sensing algorithm is used to sparsely reconstruct the undersampled signal data;

[0067] The outputs the distributions of two sound source terms that are separated and precisely quantized: the reconstructed distribution of the Lorentz force divergence characterizing the magnetoacoustic effect and the reconstructed distribution of the heat function characterizing the thermoacoustic effect.

[0068] (7) Inversion calculation of conductivity distribution

[0069] The reconstructed Lorentz force divergence and heat function distribution are used as known inputs.

[0070] Establish a quantitative mathematical relationship between these two sound source terms and the conductivity distribution of the electrode material to be determined.

[0071] Construct an objective function with electrical conductivity as the variable, which simultaneously considers the Lorentz force divergence and the fit between the thermal function and the measured values.

[0072] The objective function is optimized by using a least squares iterative algorithm. The estimated value of the conductivity distribution is updated through multiple iterations until the calculation result meets the preset convergence accuracy.

[0073] The output is the spatial conductivity distribution that finally converges and reflects the internal condition of the material.

[0074] (8) Results output and display

[0075] The conductivity distribution data obtained from the inversion is visualized as a two-dimensional or three-dimensional image and displayed on a computer screen.

[0076] It can also output conductivity values ​​or statistical information at specific points for further performance analysis and quality assessment.

[0077] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A novel inductive magnetothermoacoustic detection method for the conductivity of supercapacitors, characterized in that, The specific steps of this method are as follows: S100. The electrode material of the supercapacitor to be tested is placed in a pulsed alternating magnetic field and a steady static magnetic field that coexist, so that the electrode material generates both magnetoacoustic and thermoacoustic effects and excites ultrasonic signals. S200: Acquire the ultrasonic signal generated in S100 and preprocess it by an ultrasonic transducer array arranged around the electrode material; S300, ultrasonic signals preprocessed based on S200 By combining time reversal method with compressed sensing algorithm, the Lorentz force divergence characterizing magnetoacoustic effect is reconstructed. and the heat function characterizing the thermoacoustic effect Together, they serve as a coupled sound source term; The specific steps for coupling the sound source term in S300 are as follows: Preparation for sound source reconstruction: This involves processing the acquired ultrasonic signals... Preprocessing is performed, and the ultrasonic signal is inverted in time and propagated in reverse using the time inversion method to focus on and locate the sound source position, and to construct a physical model of sound field propagation. Sparse reconstruction solution: Based on the constructed physical model, the inverse problem of the sound pressure wave equation is solved using the compressed sensing algorithm, and the problem of reconstructing the sound source term is transformed into a sparse optimization problem, which reconstructs the distribution of the Lorentz force divergence characterizing the magnetoacoustic effect and the distribution of the heat function characterizing the thermoacoustic effect, respectively. The compressed sensing algorithm is an orthogonal matching pursuit algorithm, and its execution steps include: The ultrasonic signal is sampled to construct an observation vector, and the orthogonal basis corresponding to the sound pressure wave equation is selected to construct a sparse matrix. An observation matrix is ​​constructed by combining the sound propagation information provided by the time-reversal method. The Lorentz force divergence matrix and the heat function matrix are simultaneously output by iteratively solving the orthogonal matching pursuit algorithm. The Lorentz force divergence obtained from S400 and reconstruction based on S300. and the heat function A quantitative mapping relationship between the supercapacitor electrode material and its conductivity distribution is established, and the least squares iterative algorithm is used to solve the problem to obtain the spatial conductivity distribution of the supercapacitor electrode material. S500: Output and display the image and data of the conductivity distribution obtained by S400 inversion.

2. The novel inductive magnetothermoacoustic detection method for supercapacitor conductivity according to claim 1, characterized in that, The process of generating the S100 ultrasonic signal includes: The voltage amplitude of the pulsed alternating magnetic field is set to 80-120V and the pulse frequency is set to 1-5kHz. The strength of the steady-state static magnetic field is adjusted to 0.15-0.25T so that the two magnetic fields form an orthogonally coupled magnetic field environment in the region where the electrode material is located. The pulsed alternating magnetic field induces an eddy current electric field within the electrode material through electromagnetic induction. ,in The electric field intensity vector of the eddy current. This represents the spatial position vector within the electrode material. As a time variable, the eddy current electric field drives charge carriers to form eddy currents. ,in Eddy current, The vector of eddy current density. Let be the conductivity function of the electrode material, and let eddy current be in a steady-state static magnetic field. and pulsed alternating magnetic field In the combined magnetic field, the Lorentz force is generated simultaneously. Joule thermal power ,in, For steady-state static magnetic field, It is a pulsed alternating magnetic field. For Lorentz force, For volumetric Joule heat power, The electric field strength modulus of the eddy current electric field; The Lorentz force, changing over time, induces mechanical vibration in the electrode material, generating a magnetoacoustic signal. The Joule heating power causes an instantaneous increase in the material's temperature. ,in, This represents the instantaneous temperature change of the material. The density of the electrode material, The specific heat capacity at constant pressure of the material is used to generate a thermoacoustic signal through thermal expansion. The magnetoacoustic signal and the thermoacoustic signal are superimposed and coupled in the sound propagation medium to form the ultrasonic signal under test. .

3. The novel inductive magnetothermoacoustic detection method for the conductivity of a supercapacitor according to claim 2, characterized in that, The generation of the ultrasonic signal in S100 satisfies the acoustic field wave equation: ,in, Represents vector divergence operation. The spatial position vector of the sound source point. The coefficient of volume expansion of the material. The propagation speed of the sound source point in the coupling medium. The Lorentz divergence is a measure of the intensity of a magnetoacoustic sound source. The first derivative of the heat function with respect to time characterizes the intensity of the sound source in the thermoacoustic effect. is a heat function and , The volumetric joule heat power is given.

4. The novel inductive magnetothermoacoustic detection method for supercapacitor conductivity according to claim 1, characterized in that, In S400, the relationship between the reconstructed Lorentz force divergence and the conductivity distribution is as follows: ,in Represents vector divergence operation. For the reconstructed Lorentz force divergence, For time variables, Let be the conductivity function of the electrode material. This represents the spatial position vector within the electrode material. The eddy current electric field is determined by combining Maxwell's equations with magnetic field parameters. and Please solve. For steady-state static magnetic field, It is a pulsed alternating magnetic field; The relationship between the reconstructed heat function and electrical conductivity is as follows: ,in The reconstructed heat function.

5. The novel inductive magnetothermoacoustic detection method for the conductivity of a supercapacitor according to claim 4, characterized in that, In the S400, the process of solving using the least squares iterative algorithm is as follows: Using conductivity function For the variable to be determined, construct the objective function. ,in The objective function is used to characterize the deviation between the reconstructed values ​​and the observed values. To reconstruct the Lorentz force divergence, The observed values ​​of the Lorentz force divergence are... The square of the L2 norm, This is a weighting coefficient, ranging from 0.1 to 1.0, used to balance the contributions of the two biases. To reconstruct the heat function, Given the observed values ​​of the heat function, the least squares iterative algorithm is used to evaluate the objective function. Optimize and update at each step during the iteration process. ,in For the first Conductivity distribution in the next iteration For the first Conductivity distribution in the next iteration The iteration step size, For the objective function in the th... The gradient at each iteration is used until the convergence condition is met. The final conductivity distribution is output.

6. The novel inductive magnetothermoacoustic detection method for supercapacitor conductivity according to claim 1, characterized in that, In S200, the ultrasonic transducer array consists of multiple planar ultrasonic transducers arranged around the electrode material to collect ultrasonic signals generated by the electrode material. The preprocessing uses a pre-filter and a signal amplifier to condition and amplify the collected ultrasonic signals.

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