Optimization method of laser-ultrasonic excitation light source parameters based on finite element simulation

Abstract

The application relates to a laser-ultrasonic excitation light source parameter optimization method based on finite element simulation, which comprises the following steps: constructing a finite element simulation model of a target material; based on a laser ablation physical mechanism, converting a phase change and a gasification process induced by incident laser on the surface of the target material into equivalent stress acting on the surface of the finite element simulation model; in the finite element simulation model, a plurality of groups of excitation light source parameters are adjusted coordinately, ultrasonic signal responses excited by the equivalent stress under different excitation light source parameter combinations are solved and obtained; time-frequency characteristics of a target wave mode in the ultrasonic signal responses are extracted, and an optimal excitation light source parameter combination is determined from the plurality of groups of excitation light source parameters by taking improvement of signal signal-to-noise ratio and high-frequency components as an optimization target. Through the equivalent stress conversion mechanism of latent heat of vaporization and the finite element model, the excitation source multi-parameters are determined, so that the detection accuracy and adaptability are improved.

Description

Technical Field

[0001] This invention belongs to the field of laser ultrasound technology, specifically relating to a method for optimizing the parameters of a laser ultrasound excitation source based on finite element simulation. Background Technology

[0002] Laser ultrasound, as a novel non-destructive testing method, has demonstrated enormous application potential in high-resolution imaging and non-destructive evaluation of microscopic defects (such as micropores) within materials, thanks to its significant advantages such as non-contact operation, wide bandwidth, and high spatial resolution. The physical process of laser-induced ultrasound is extremely complex, especially under ablation mechanisms, involving various physical phenomena such as material energy reflection and absorption, local thermal expansion, phase transformation melting, vaporization, and plasma generation. In this process, the light source parameters, such as the pulse energy, pulse width, and spot radius of the incident laser, are key factors determining the characteristics of the ultrasonic field. Coordinated changes in laser pulse width, energy, and spot size directly cause fluctuations in power density, thus significantly altering the final excited ultrasonic field distribution.

[0003] In non-destructive testing of minute internal defects in materials, laser-ultrasonic longitudinal waves (P-waves) are the core carriers of defect characteristic information. To achieve high-resolution detection of micron-level pores, cracks, and other internal defects, it is essential to ensure that the excited P-wave signal possesses an extremely high signal-to-noise ratio and contains abundant high-frequency components. The upper frequency limit of the P-wave directly determines the spatial resolution of the detection system for microscopic defects. However, in practical engineering applications, the selection and synergistic optimization of laser excitation source parameters currently face the following technical bottlenecks: First, theoretical analysis is extremely challenging. The excitation of laser ultrasound involves the complex coupling of multiple physical fields, such as thermal conduction of the temperature field, excitation and conduction of transient stress waves, and the partial differential equations are almost impossible to obtain accurate mathematical analytical solutions, making it difficult to directly derive the light source parameters that can excite the optimal longitudinal wave characteristics from the theoretical level.

[0004] Secondly, traditional experimental optimization is costly and inefficient. Existing parameter selection relies heavily on time-consuming and laborious physical experiments, requiring researchers to repeatedly adjust the parameters of lenses or lasers of different specifications. This approach not only increases equipment wear and tear and experimental costs, but also, due to the lack of systematic theoretical guidance, makes it difficult to reveal the evolution of the time-frequency characteristics of laser ultrasound longitudinal waves under the synergistic effects of multiple variables, resulting in parameter selection often failing to reach the physical limits of detection resolution.

[0005] Therefore, how to avoid tedious experimental trial and error, establish an accurate and reliable numerical simulation model, equivalently transform the complex physical process and perform transient analysis, and then systematically explore the comprehensive influence of light source parameters on the time-frequency characteristics of laser ultrasonic longitudinal waves, achieve efficient synergistic optimization of excitation source parameters, and obtain longitudinal wave detection signals with high signal-to-noise ratio and high frequency resolution has become a key technical problem that urgently needs to be solved in the field of laser ultrasonic nondestructive testing. Summary of the Invention

[0006] To address the problems raised in the background art, a method for optimizing laser ultrasonic excitation source parameters based on finite element simulation is provided in the first aspect of this invention, comprising: Construct a finite element simulation model of the target material and configure the simulation environment based on the physical property parameters of the target material; Based on the physical mechanism of laser ablation, the phase transformation and vaporization process induced by the incident laser on the surface of the target material is equivalently transformed into the equivalent stress acting on the surface of the finite element simulation model, which serves as the boundary load. In the finite element simulation model, multiple sets of excitation source parameters are coordinated and adjusted to obtain the ultrasonic signal response excited by the equivalent stress under different combinations of excitation source parameters; The time-frequency characteristics of the target wave mode in the ultrasonic signal response are extracted, and the optimal combination of excitation source parameters is determined from the multiple sets of excitation source parameters with the goal of improving the signal-to-noise ratio and high-frequency components.

[0007] In some embodiments of the present invention, the equivalent conversion of the phase change and vaporization process induced by the incident laser on the surface of the target material into an equivalent stress acting on the surface of the finite element simulation model includes: when the surface temperature of the target material reaches the vaporization threshold, calculating the vertically downward reaction force generated by the plasma plume based on the latent heat of vaporization, specific heat capacity, and absorbed laser energy of the target material, and applying it as a solid mechanical equivalent stress to the stimulated boundary of the finite element simulation model; the value of the equivalent stress is determined by the following parameters: the square of the ratio of the laser energy absorbed by the material to the absorption coefficient of the material, the density of the target material, and the square of the thermodynamic comprehensive characteristic value; wherein, the thermodynamic comprehensive characteristic value is: the sum of the latent heat of vaporization and the reference heat parameter; the reference heat parameter is the product of the specific heat capacity of the target material and the difference between the vaporization temperature and the initial temperature.

[0008] In some embodiments of the present invention, the coordinated adjustment of multiple sets of excitation source parameters includes: selecting laser pulse energy, laser pulse width, and laser spot radius as core adjustment variables; and performing coordinated parameter scanning on the above three variables in the finite element simulation model to simulate the transient influence of laser power density fluctuations on the ultrasonic field distribution.

[0009] Furthermore, in the finite element simulation model, the spatiotemporal distribution of the incident laser is characterized by both a spatial distribution function and a temporal distribution function; wherein, the value of the spatial distribution function is equal to the exponent raised to the square of the ratio of the current radial position to the laser spot radius, which is base natural logarithm and negative; the value of the temporal distribution function is equal to the ratio of the current time to the laser pulse width, multiplied by the exponent raised to the exponent raised to the ratio of the current time to the laser pulse width, which is base natural logarithm and negative.

[0010] In some embodiments of the present invention, the step of extracting the time-frequency characteristics of the target wave mode in the ultrasonic signal response and determining the optimal parameter combination includes: extracting the ultrasonic longitudinal wave in the ultrasonic signal response as the target wave mode, and performing maximum value normalization processing and spectrum analysis on the extracted longitudinal wave signal; increasing the laser pulse energy and reducing the spot radius to improve the signal-to-noise ratio of the longitudinal wave signal, and widening the high-frequency band of the longitudinal wave signal by reducing the spot radius and shortening the laser pulse width.

[0011] In some embodiments of the present invention, the construction of the finite element simulation model of the target material further includes: performing mesh discretization processing on the surface of the finite element simulation model, setting the maximum element size of the mesh to be less than one-tenth of the highest frequency component of the target ultrasonic wave; and setting the transient solution time step of the finite element simulation model to satisfy the Courant-Friedrich-Lyuvi conditions to ensure the numerical stability of the transient wave propagation solution and the high frequency sampling accuracy of the wavefront.

[0012] In a second aspect, the present invention provides a laser ultrasonic excitation source parameter optimization system based on finite element simulation, comprising: a construction module for constructing a finite element simulation model of a target material and configuring a simulation environment based on the physical property parameters of the target material; a conversion module for converting the phase transition and vaporization process induced by the incident laser on the surface of the target material into equivalent stress acting on the surface of the finite element simulation model, based on the physical mechanism of laser ablation, as a boundary load; a solution module for coordinating and adjusting multiple sets of excitation source parameters in the finite element simulation model to obtain the ultrasonic signal response excited by the equivalent stress under different combinations of excitation source parameter parameters; and a determination module for extracting the time-frequency characteristics of the target wave mode in the ultrasonic signal response and determining the optimal combination of excitation source parameters from the multiple sets of excitation source parameters with the optimization objective of improving the signal-to-noise ratio and high-frequency components.

[0013] The beneficial effects of this invention are: Compared to the extremely high computational cost of traditional methods that completely simulate phase transitions, melting, and gasification processes, the core innovation of this invention lies in proposing an equivalent force conversion mechanism between latent heat of gasification and plasma reaction force. This equivalent reaction force model cleverly reduces the dimensionality of the complex ablation physics process, improving the computational efficiency of multiphysics simulation by at least one order of magnitude while ensuring the accuracy of high-frequency longitudinal wave time-domain characteristics. It fundamentally solves the problem of computational non-convergence and is extremely suitable for optimizing massive amounts of excitation source parameters in industrial applications.

[0014] In exploring the underlying physical mechanisms, this invention profoundly reveals the intrinsic influence of the synergistic effect of multiple excitation source parameters on the characteristics of ultrasonic signals, possessing significant theoretical guiding value. In actual physical processes, changes in laser pulse width, spot radius, and energy all cause complex fluctuations in laser power density. Traditional experimental methods often struggle to accurately isolate and quantify the cross-interference of these variables. To address this, this scheme uses a finite element model to sequentially and synergistically adjust the three core parameters mentioned above, and performs normalized extraction and spectral analysis of the ultrasonic longitudinal wave component. Simulation results intuitively and clearly indicate that increasing laser energy and reducing spot size effectively improves the signal-to-noise ratio; simultaneously, using a smaller spot size and shorter pulse width is more conducive to exciting high-frequency ultrasonic components. This quantitative revelation of the underlying principle provides a clear and reliable optimization direction for the design and parameter selection of optical path systems in practical measuring instruments.

[0015] Focusing on practical engineering applications, this invention significantly enhances the non-destructive testing capability for minute defects within materials, exhibiting excellent versatility and scalability. Thanks to the aforementioned optimized combination of high signal-to-noise ratio and high-frequency excitation parameters, this method directly and significantly improves detection resolution, playing a decisive role in promoting high-resolution imaging research on test samples containing microporous defects and actual workpieces. Furthermore, the core optimization framework of this invention breaks through the limitations of single-material applications. Researchers only need to replace the target material's density, Young's modulus, Poisson's ratio, coefficient of thermal expansion, and related latent heat of vaporization in the model to quickly transfer this synergistic optimization scheme to the non-destructive evaluation of various metal alloys, composite materials, or novel thin films, giving this technology extremely broad prospects for industrial application. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the basic process of the laser ultrasonic excitation source parameter optimization method based on finite element simulation in some embodiments of the present invention; Figure 2 This is a schematic diagram of a laser ultrasonic finite element simulation model in some embodiments of the present invention; Figure 3 This is a schematic diagram of laser ultrasonic signals received by multiple detection points in a simulation model in some embodiments of the present invention; Figure 4 These are frequency domain and time domain schematic diagrams of different pulses in some embodiments of the present invention; Figure 5 This is a schematic diagram of a two-dimensional surface scan of a defect in an aluminum alloy standard sample in some embodiments of the present invention; Figure 6 This is a schematic diagram of the laser ultrasonic excitation source parameter optimization system based on finite element simulation in some embodiments of the present invention; Figure 7 This is a schematic diagram of the structure of an electronic device in some embodiments of the present invention. Detailed Implementation

[0017] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0018] Example 1 refer to Figures 1 to 3 In a first aspect of the present invention, a method for optimizing the parameters of a laser ultrasonic excitation source based on finite element simulation is provided, comprising: S100. Construct a finite element simulation model of the target material and configure the simulation environment based on the physical property parameters of the target material; S200. Based on the physical mechanism of laser ablation, the phase transformation and vaporization process induced by the incident laser on the surface of the target material is equivalently converted into the equivalent stress acting on the surface of the finite element simulation model, as a boundary load. S300. In the finite element simulation model, multiple sets of excitation source parameters are coordinated and adjusted to obtain the ultrasonic signal response excited by the equivalent stress under different combinations of excitation source parameters; S400. Extract the time-frequency characteristics of the target wave mode in the ultrasonic signal response, and determine the optimal combination of excitation source parameters from the multiple sets of excitation source parameters with the goal of improving the signal-to-noise ratio and high-frequency components.

[0019] In step S100 of some embodiments of the present invention, a finite element simulation model of the target material is constructed, and the simulation environment is configured based on the physical property parameters of the target material; Specifically, a numerical model of the laser-ultrasonic propagation process was constructed. Based on the COMSOL Multiphysics simulation platform, a two-dimensional cuboid geometric model with dimensions of 30 mm × 10 mm was established. The model material was set as aluminum alloy 6061, with the following material parameters: density 2700 kg / m³. 3 The Young's modulus is 70.2 × 10⁻⁶. 9 Pa, Poisson's ratio is 0.34, and the coefficient of thermal expansion is 2.31 × 10⁻⁶. -61 / K. Laser excitation uses a point source approximation, set at the origin (0, 0). The bottom and side boundaries of the model are set as low-reflection boundaries to simulate infinite domain conditions. Ultrasonic signal detection points are arranged at two locations: directly below the excitation point (0, -10 mm) and on the model surface (10 mm, 0), to collect ultrasonic responses under different propagation paths. The model surface is discretized using a free triangular mesh, with a maximum element size of 0.1 mm. This size strictly satisfies the criterion that "the maximum element size is less than 1 / 10 of the target acoustic wavelength" to prevent severe numerical dispersion of high-frequency signals in the discrete mesh, ensuring effective sampling of high-frequency ultrasonic components. Transient analysis is used for time-domain solutions, with a time step of 5 ns. This step must satisfy the Courant-Friedrich-Lyuvy (CFL) condition to ensure that the time step is less than the time it takes for the acoustic wave to cross a single mesh element, thus ensuring numerical stability and steepness of the transient wavefront. The total simulation duration is 10 μs, fully covering the propagation process of various ultrasonic modes.

[0020] In aluminum materials, the theoretical formulas for the wave velocities of longitudinal waves, transverse waves, and surface waves excited by laser ultrasound are as follows: , , , In the formula, Here, represents the elastic modulus, and represents the density. It is Poisson's ratio. It is the shear modulus. Substituting the parameters of 6061 aluminum alloy, the wave velocities of the three types of sound waves can be calculated. , , At a detection point 10 mm from the excitation source, the theoretical arrival times of the three types of waves are respectively , , Simulation results show that the arrival times of longitudinal waves, transverse waves, surface waves, and longitudinal waves passing over the surface are respectively... , , and The results are in high agreement with the theoretical values, verifying the accuracy and reliability of this model in the simulation of laser ultrasonic propagation.

[0021] To further reveal the influence of key parameters on the time-frequency characteristics of longitudinal waves, this application sequentially and collaboratively adjusts the laser pulse energy, pulse width, and incident spot diameter in a constructed two-dimensional finite element simulation model. By performing maximum value normalization on the signal received at the detection point and accurately extracting the longitudinal wave components for spectral analysis, the system demonstrates the time-domain and frequency-domain response characteristics under different parameter combinations.

[0022] In some embodiments of the present invention, the construction of the finite element simulation model of the target material further includes: performing mesh discretization processing on the surface of the finite element simulation model, setting the maximum element size of the mesh to be less than one-tenth of the highest frequency component of the target ultrasonic wave; and setting the transient solution time step of the finite element simulation model to satisfy the Courant-Friedrich-Lyuvi conditions to ensure the numerical stability of the transient wave propagation solution and the high frequency sampling accuracy of the wavefront.

[0023] It is understandable that traditional simulations, when realistically simulating ablation mechanisms (including multiphase evolution such as vaporization, melting, and plasma plumes), are extremely difficult to converge and computationally expensive. The innovation of this invention lies in proposing a simplified equivalent stress conversion mechanism, which directly equates the latent heat of vaporization, specific heat capacity, and plasma reaction momentum to the boundary loads of the solid mechanics module.

[0024] In step S200 of some embodiments of the present invention, the equivalent conversion of the phase change and gasification process into equivalent stress acting on the model surface includes: S201. When the surface temperature of the target material reaches the vaporization threshold, the vertically downward reaction force generated by the plasma plume is calculated based on the latent heat of vaporization, specific heat capacity and absorbed laser energy of the target material, and is applied as a solid mechanical equivalent force to the stimulated boundary of the finite element simulation model. Specifically, in the physical model of laser-ultrasound under the ablation mechanism, the laser focal point can be considered as a point source. In the initial stage of ablation-mechanical laser-ultrasound generation, the sample surface temperature rises, thus accompanied by thermoelastic laser-ultrasound generation in the early stages of ablation. However, this ultrasound has a short duration and weak signal intensity, which can be ignored. When the material surface temperature exceeds the ablation threshold, the plasma plume acts on the sample surface, generating a stress perpendicular to the sample surface and directed downwards, expressed as: , In the formula, The equivalent stress generated on the sample surface. The absorption coefficient is... Laser energy absorbed by the material The specific heat capacity of the alloy sample. The latent heat of vaporization of the material, The vaporization temperature of the material. The initial temperature of the material is denoted as . Through this equivalent dimensionality reduction, this method avoids non-convergent multiphase flow calculations while accurately identifying the core thermodynamic parameters that determine the intensity of longitudinal waves, ensuring a balance between simulation efficiency and physical realism.

[0025] S202. The value of the equivalent stress is determined by the following parameters: the square of the ratio of the laser energy absorbed by the material to the absorption coefficient of the material, the square of the density of the target material and the thermodynamic comprehensive characteristic value; wherein, the thermodynamic comprehensive characteristic value is: the sum of the latent heat of vaporization and the reference heat parameter; the reference heat parameter is the product of the specific heat capacity of the target material and the difference between the vaporization temperature and the initial temperature.

[0026] Specifically, in the laser-ultrasonic physical model under the ablation mechanism, the optical path system is regarded as an ideal optical path system, that is, the laser energy is the energy received by the material surface, and the power density of the incident laser is... for: , In the formula, For laser single pulse energy, For pulse width, Let be the laser spot radius. Of the laser energy incident on the material surface, part is reflected or scattered into the air, and the other part is absorbed by the material. The absorption of laser energy is related to the absorption coefficient of the material, and its expression is: .

[0027] In the formula, n is the refractive index of the material. Let be the wavelength of the incident laser. According to the law of conservation of energy, the total energy of the incident laser is... It can be represented as: .

[0028] In the formula, For the absorption of energy by materials, This represents the energy reflected and scattered by the material. The spatiotemporal distribution of the incident laser is as follows: , , In the formula and These represent the spatial and temporal distributions of the incident laser, respectively. Let be the radius of the focal spot. The expression for the radius of the focal spot is: , In the formula, M These are the mode parameters for the laser. F The focal length of the lens. The wavelength of the laser. D The laser beam spot diameter is located at the lens position. K is the refractive index coefficient. In calculating the focal spot radius, the first term is very small and can be ignored; therefore, the above formula can be written as: , The incident laser energy is converted into heat energy after being absorbed. The amount of energy absorbed by the material surface is: , In the formula, denoted as the light absorption coefficient of the material.

[0029] The energy absorbed by a material is converted into heat. Assuming the metallic material is an isotropic ideal material whose thermodynamic properties do not change with temperature, the heat conduction equation in the material is: , In the formula, T(x,y,z,t) represents the temperature distribution of the material, and Q(x,y,z,t) represents the heat generated by the laser absorbed per unit volume per unit time. For thermal conductivity, K For thermal diffusion absorption, and These represent the material's density and specific heat capacity, respectively. , K , and The transformation relationship between them is as follows: , The classical thermodynamic conduction equation in cylindrical coordinates is: , In the formula For the heat conduction tensor, The heat source is the bulk. The process of the material absorbing laser energy occurs on the alloy surface, and the absorbed heat energy can be regarded as a boundary condition.

[0030] refer to Figure 3 and Figure 4 , Figure 3 The laser ultrasonic signals received by probe point 1 (a) and probe point 2 (b) in the simulation model are shown; Figure 4 The results show different pulse energies: (a) time domain results, (b) frequency domain results; different spot radii: (c) time domain results, (d) frequency domain results; different pulse widths: (e) time domain results, (f) frequency domain results.

[0031] In step S300 of some embodiments of the present invention, in the finite element simulation model, multiple sets of excitation source parameters are coordinated and adjusted to obtain the ultrasonic signal response excited by the equivalent stress under different combinations of excitation source parameters; The coordinated adjustment of multiple excitation source parameters includes selecting laser pulse energy, laser pulse width, and laser spot radius as core adjustment variables; in the finite element simulation model, coordinated parameter scanning is performed on the above three variables to simulate the transient effect of laser power density fluctuations on the ultrasonic field distribution.

[0032] Furthermore, in the finite element simulation model, the spatiotemporal distribution of the incident laser is characterized by both a spatial distribution function and a temporal distribution function; wherein, the value of the spatial distribution function is equal to the exponent raised to the square of the ratio of the current radial position to the laser spot radius, which is base natural logarithm and negative; the value of the temporal distribution function is equal to the ratio of the current time to the laser pulse width, multiplied by the exponent raised to the exponent raised to the ratio of the current time to the laser pulse width, which is base natural logarithm and negative.

[0033] Specifically, when the laser spot radius is greater than the heat propagation depth during the laser's action time, a one-dimensional approximation of the model can be performed, allowing the volumetric heat source to... The thermodynamic conduction equation can be expressed as: , Its boundary conditions are: , The initial conditions are: .

[0034] The excitation, propagation, and reception of laser ultrasound are influenced by numerous factors, making it a complex physical process. Its physical model involves various partial differential equations, including the heat conduction equation for the temperature field, the excitation equation for transient waves, and the propagation equation for ultrasonic waves, making analytical solutions nearly impossible. Therefore, numerical simulation methods are generally used to solve such problems. Common numerical simulation methods include the boundary element method, the multigrid method, and the finite element method. Currently, the finite element method dominates laser ultrasound simulation. Therefore, this invention selects the finite element method for laser ultrasound simulation based on the aforementioned theories.

[0035] In step S400 of some embodiments of the present invention, extracting the time-frequency characteristics of the target wave mode in the ultrasonic signal response and determining the optimal parameter combination includes: S401. Extract the ultrasonic longitudinal wave from the ultrasonic signal response as the target wave mode, and perform maximum value normalization and spectrum analysis on the extracted longitudinal wave signal; S402. The signal-to-noise ratio of the longitudinal wave signal is improved by increasing the laser pulse energy and reducing the spot radius, and the high-frequency band of the longitudinal wave signal is broadened by reducing the spot radius and shortening the laser pulse width.

[0036] refer to Figure 5 Simulation results clearly indicate that the key to optimizing P-wave quality lies in the scientific matching of parameters: on the one hand, increasing the laser pulse energy and reducing the spot size can effectively enhance the P-wave signal intensity and significantly improve the detection signal-to-noise ratio; on the other hand, using a smaller spot diameter and a shorter pulse width is more conducive to exciting abundant high-frequency ultrasonic components within the material. This targeted optimization of the high-frequency characteristics of the P-wave can directly shorten the ultrasonic wave length, thereby significantly improving the spatial resolution of the laser ultrasonic detection system for characteristic defects such as micropores and cracks within the material, providing core data support for achieving high-resolution visualization characterization. Guided by the finite element simulation results, to achieve better excitation performance, this invention employs a 3ns pulsed laser with a relatively narrow pulse width and a laser energy of 25mJ. A focusing optical path system was designed, using a double-beam-expanding optical path composed of plano-concave and plano-convex lenses with focal lengths of 50mm and 100mm respectively, and an aspherical focusing lens with a focal length of 50mm. This focuses the laser beam with a radius of approximately 4.5mm to approximately 20μm. This design not only enhances the signal-to-noise ratio and frequency components of the ultrasonic longitudinal wave, but also provides higher spatial resolution for subsequent surface scanning, achieving high-definition and precise visualization imaging of micropores of 0.1mm, 0.2mm, 0.3mm, and 0.4mm in aluminum alloy samples.

[0037] It is understandable that the equivalent physical model of the ablation mechanism in this invention is as follows: Traditional ablation mechanisms are extremely complex (including phase transitions, vaporization, plasma, etc.), and direct simulation computation is extremely intensive and difficult to converge. The key point of this invention is to establish a simplified physical model that directly and equivalently transforms the complex process after the material absorbs laser energy into a vertically downward stress acting on the sample surface.

[0038] A "cooperative" optimization mechanism for excitation source parameters: This mechanism overcomes the limitations of single-variable testing and clearly identifies the coupled influence of pulse energy, pulse width, and spot radius on laser power density. By cooperatively adjusting these three parameters in a finite element model, the system systematically explores their combined effect on the longitudinal waves of the ultrasonic field.

[0039] Example 2 refer to Figure 6 In a second aspect, the present invention provides a laser ultrasonic excitation source parameter optimization system 1 based on finite element simulation, comprising: Module 11 is used to construct a finite element simulation model of the target material and configure the simulation environment based on the physical property parameters of the target material. The conversion module 12 is used to convert the phase change and vaporization process induced by the incident laser on the surface of the target material into equivalent stress acting on the surface of the finite element simulation model, based on the physical mechanism of laser ablation, as a boundary load. Solver module 13 is used to coordinately adjust multiple sets of excitation source parameters in the finite element simulation model and solve for the ultrasonic signal response excited by the equivalent stress under different combinations of excitation source parameters. The determination module 14 is used to extract the time-frequency characteristics of the target wave mode in the ultrasonic signal response, and to determine the optimal combination of excitation source parameters from the multiple sets of excitation source parameters with the optimization goal of improving the signal-to-noise ratio and high-frequency components.

[0040] Furthermore, the determining module 14 includes an extraction unit, used to extract the ultrasonic longitudinal wave in the ultrasonic signal response as the target wave mode, and to perform maximum value normalization processing and spectrum analysis on the extracted longitudinal wave signal.

[0041] Furthermore, the determining module 14 also includes an optimization unit, used to improve the signal-to-noise ratio of the longitudinal wave signal by increasing the laser pulse energy and reducing the spot radius, and to broaden the high-frequency band of the longitudinal wave signal by reducing the spot radius and shortening the laser pulse width.

[0042] Example 3 refer to Figure 7 In a third aspect, the present invention provides an electronic device comprising: one or more processors; and a storage device for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors implement the laser ultrasonic excitation source parameter optimization method based on finite element simulation of the first aspect of the present invention.

[0043] Electronic device 500 may include a processing unit (e.g., a central processing unit, a graphics processing unit, etc.) 501, which can perform various appropriate actions and processes according to a program stored in read-only memory (ROM) 502 or a program loaded from storage device 508 into random access memory (RAM) 503. The RAM 503 also stores various programs and data required for the operation of electronic device 500. The processing unit 501, ROM 502, and RAM 503 are interconnected via bus 504. An input / output (I / O) interface 505 is also connected to bus 504.

[0044] Typically, the following devices can be connected to I / O interface 505: input devices 506 including, for example, touchscreens, touchpads, keyboards, mice, cameras, microphones, accelerometers, gyroscopes, etc.; output devices 507 including, for example, liquid crystal displays (LCDs), speakers, vibrators, etc.; storage devices 508 including, for example, hard disks; and communication devices 509. Communication device 509 allows electronic device 500 to communicate wirelessly or wiredly with other devices to exchange data. Although Figure 7An electronic device 500 with various devices is shown; however, it should be understood that it is not required to implement or possess all of the devices shown. More or fewer devices may be implemented or possessed alternatively. Figure 7 Each box shown can represent a device or multiple devices as needed.

[0045] Specifically, according to embodiments of this disclosure, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, embodiments of this disclosure include a computer program product comprising a computer program carried on a computer-readable medium, the computer program containing program code for performing the methods shown in the flowcharts. In such embodiments, the computer program can be downloaded and installed from a network via a communication device 509, or installed from a storage device 508, or installed from a ROM 502. When the computer program is executed by a processing device 501, it performs the functions defined in the methods of embodiments of this disclosure. It should be noted that the computer-readable medium described in embodiments of this disclosure can be a computer-readable signal medium or a computer-readable storage medium, or any combination of the two. A computer-readable storage medium can be, for example—but not limited to—an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples of computer-readable storage media may include, but are not limited to: electrical connections having one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination thereof. In embodiments of this disclosure, a computer-readable storage medium may be any tangible medium containing or storing a program that can be used by or in connection with an instruction execution system, apparatus, or device. In embodiments of this disclosure, a computer-readable signal medium may include a data signal propagated in baseband or as part of a carrier wave, carrying computer-readable program code. Such propagated data signals may take various forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof. A computer-readable signal medium may also be any computer-readable medium other than a computer-readable storage medium, which can send, propagate, or transmit a program for use by or in connection with an instruction execution system, apparatus, or device. Program code contained on a computer-readable medium may be transmitted using any suitable medium, including but not limited to: wires, optical fibers, RF (radio frequency), etc., or any suitable combination thereof.

[0046] The aforementioned computer-readable medium may be included in the aforementioned electronic device; or it may exist independently and not assembled into the electronic device. The aforementioned computer-readable medium carries one or more computer programs, which, when executed by the electronic device, cause the electronic device to: Computer program code for performing the operations of embodiments of this disclosure can be written in one or more programming languages ​​or a combination thereof. Programming languages ​​include object-oriented programming languages—such as Java, Smalltalk, C++, and Python—and conventional procedural programming languages—such as the "C" language or similar programming languages. The program code can be executed entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving remote computers, the remote computer can be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or can be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0047] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of this disclosure. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for optimizing the parameters of a laser ultrasonic excitation source based on finite element simulation, characterized in that, include: Construct a finite element simulation model of the target material and configure the simulation environment based on the physical property parameters of the target material; Based on the physical mechanism of laser ablation, the phase transformation and vaporization process induced by the incident laser on the surface of the target material is equivalently transformed into the equivalent stress acting on the surface of the finite element simulation model, which serves as the boundary load. In the finite element simulation model, multiple sets of excitation source parameters are coordinated and adjusted to obtain the ultrasonic signal response excited by the equivalent stress under different combinations of excitation source parameters; The time-frequency characteristics of the target wave mode in the ultrasonic signal response are extracted, and the optimal combination of excitation source parameters is determined from the multiple sets of excitation source parameters with the goal of improving the signal-to-noise ratio and high-frequency components.

2. The method for optimizing laser ultrasonic excitation source parameters based on finite element simulation according to claim 1, characterized in that, The process of converting the phase transition and vaporization process induced by the incident laser on the surface of the target material into equivalent stress acting on the surface of the finite element simulation model includes: When the surface temperature of the target material reaches the vaporization threshold, the vertically downward reaction force generated by the plasma plume is calculated based on the latent heat of vaporization, specific heat capacity and absorbed laser energy of the target material, and is applied as a solid mechanical equivalent force to the stimulated boundary of the finite element simulation model. The value of the equivalent stress is determined by the following parameters: The square of the ratio of the laser energy absorbed by the material to the absorption coefficient of the material, the square of the density of the target material, and the square of the comprehensive thermodynamic characteristic value; The thermodynamic comprehensive characteristic value is: the sum of the latent heat of vaporization and the reference heat parameter; the reference heat parameter is the specific heat capacity of the target material multiplied by the difference between the vaporization temperature and the initial temperature.

3. The laser ultrasonic excitation source parameter optimization method based on finite element simulation according to claim 1, characterized in that, The coordinated adjustment of multiple sets of excitation source parameters includes: Laser pulse energy, laser pulse width, and laser spot radius were selected as the core adjustment variables. In the finite element simulation model, a synergistic parameter scan is performed on the three variables to simulate the transient effect of laser power density fluctuations on the ultrasonic field distribution.

4. The laser ultrasonic excitation source parameter optimization method based on finite element simulation according to claim 3, characterized in that, In the finite element simulation model, the spatiotemporal distribution of the incident laser is characterized by both the spatial distribution function and the temporal distribution function. Wherein, the value of the spatial distribution function is equal to the exponent raised to the square of the ratio of the current radial position to the laser spot radius, which is base natural logarithm and is negative; The value of the time distribution function is equal to the ratio of the current time to the laser pulse width, multiplied by an exponent that is a negative power of the ratio of the current time to the laser pulse width, with the natural logarithm as the base.

5. The method for optimizing laser ultrasonic excitation source parameters based on finite element simulation according to claim 1, characterized in that, The step of extracting the time-frequency characteristics of the target wave mode in the ultrasonic signal response and determining the optimal parameter combination includes: The ultrasonic longitudinal wave in the ultrasonic signal response is extracted as the target wave mode, and the extracted longitudinal wave signal is subjected to maximum value normalization and spectrum analysis. The signal-to-noise ratio of the longitudinal wave signal is improved by increasing the laser pulse energy and reducing the spot radius, and the high-frequency band of the longitudinal wave signal is broadened by reducing the spot radius and shortening the laser pulse width.

6. The method for optimizing laser ultrasonic excitation source parameters based on finite element simulation according to claim 1, characterized in that, The finite element simulation model of the target material also includes: The surface of the finite element simulation model is discretized into a mesh, and the maximum element size of the mesh is set to be less than one-tenth of the highest frequency component of the target ultrasonic wave. The transient solution time step of the finite element simulation model is set to satisfy the Courant-Friedrich-Lyuvi conditions to ensure the numerical stability of the transient wave propagation solution and the high-frequency sampling accuracy of the wavefront.

7. The method for optimizing laser ultrasonic excitation source parameters based on finite element simulation according to claim 1, characterized in that, The laser ultrasonic excitation source parameter optimization system used in this method includes: The construction module is used to build a finite element simulation model of the target material and configure the simulation environment based on the physical property parameters of the target material; The conversion module is used to convert the phase transition and vaporization process induced by the incident laser on the surface of the target material into equivalent stress acting on the surface of the finite element simulation model, based on the physical mechanism of laser ablation, as a boundary load. The solver module is used to coordinate and adjust multiple sets of excitation source parameters in the finite element simulation model to solve for the ultrasonic signal response excited by the equivalent stress under different combinations of excitation source parameters. The determination module is used to extract the time-frequency characteristics of the target wave mode in the ultrasonic signal response, and to determine the optimal combination of excitation source parameters from the multiple sets of excitation source parameters with the optimization goal of improving the signal-to-noise ratio and high-frequency components.

8. The laser ultrasonic excitation source parameter optimization method based on finite element simulation according to claim 7, characterized in that, The determining module includes: The extraction unit is used to extract the ultrasonic longitudinal wave in the ultrasonic signal response as the target wave mode, and to perform maximum value normalization and spectrum analysis on the extracted longitudinal wave signal.

9. The method for optimizing laser ultrasonic excitation source parameters based on finite element simulation according to claim 8, characterized in that, The determining module further includes: The optimization unit is used to improve the signal-to-noise ratio of the longitudinal wave signal by increasing the laser pulse energy and reducing the spot radius, and to broaden the high-frequency band of the longitudinal wave signal by reducing the spot radius and shortening the laser pulse width.

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