Method for measuring key parameters of sound pressure calculation model of laser piston sounder

Abstract

The invention discloses a method for measuring key parameters of a sound pressure calculation model of a laser piston sounder, and belongs to the technical field of laser piston sounders. Sequentially collecting response voltages of the infrasound sensor at different piston cavity lengths, calculating a ratio of the response voltages of the infrasound sensor at different piston cavity lengths, and obtaining experimental data of the calculated sound pressure ratio of the piston sounder at different piston cavity lengths; and according to the experimental data, fitting the to-be-measured parameters in the sound pressure calculation model of the piston sounder by adopting a genetic algorithm to obtain to-be-measured key parameters in the sound pressure calculation model of the piston sounder. According to the method, the problem of accurate measurement of piston cavity volume change and additional acoustic impedance introduced by acoustic coupling of the infrasound sensor and the piston sounder can be solved, and the calculation accuracy of a sound pressure calculation model of the laser piston sounder is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of laser piston sounders, and in particular relates to a method for measuring key parameters of a sound pressure calculation model of a laser piston sounder. Background Art

[0002] Infrasound usually refers to sound waves with a frequency below 20Hz, which are commonly found in nature, industrial production, and transportation. Examples include natural phenomena such as earthquakes and volcanic eruptions, the operation of large machinery, transportation, rocket and missile launches, and supersonic aircraft flights.

[0003] Due to the strong penetrating power and long propagation distance of infrasound waves, monitoring technology using infrasound sensor arrays for infrasound source location and identification is widely used in fields such as national defense security, geological disaster prevention and control, and geophysics research. These technologies include nuclear explosion detection, prediction of natural disasters such as earthquakes, volcanoes, and mudslides, rocket and missile trajectory monitoring, and natural gas pipeline leak detection. Infrasound sensors are the data source for monitoring systems. The accuracy of their sound pressure measurements and the quality of the target sound source radiation signal determine the accuracy of nuclear explosion yield estimation, target sound source location, and feature identification. These factors directly impact the validity and reliability of infrasound monitoring data and reconnaissance results, necessitating metrological assurance.

[0004] Taking into account the signal characteristics of infrasound waves in different application scenarios, the calibration frequency range of infrasound sensors should cover at least 0.01Hz to 20Hz. The laser piston generator is a standard infrasound source for primary calibration of infrasound sensors and the main standard for the infrasound air sound pressure benchmark. It consists of a piston generator and a laser interferometer. The piston generator is a sound-generating device that generates standard infrasound waves for infrasound sensor calibration. The laser interferometer is a value-assigning device that measures the displacement of the reciprocating piston and, in combination with theoretical formulas, can assign a value to the sound pressure (unit: Pa) of the infrasound wave radiated within the piston generator. This allows calibration testing of the sound pressure sensitivity (unit: mV / Pa) based on the response voltage (unit: V) of the infrasound sensor.

[0005] The basic principle of a pistonphone is to excite a plane wave in a closed cavity much smaller than the wavelength of the sound wave in the medium (at least 1 / 20 of the wavelength) through the reciprocating motion of a piston. The radiated sound pressure within a laser pistonphone is calculated. The accuracy of the calculated result is closely related to the parameter values ​​in the calculation formula and the sound pressure error correction model. In other words, the accuracy of the key parameters in the calculated sound pressure model directly affects the accuracy of the sound pressure assigned within the pistonphone.

[0006] Currently, the structural parameters of the piston cavity are primarily determined by design drawings, failing to account for changes in the piston cavity volume introduced by the actual assembly process and the acoustic coupling interface adapter. While the acoustic impedance of the infrasound sensor being measured is generally assumed to be infinite, the additional acoustic impedance introduced by the internal cavity and its gas connection to the piston cavity is non-negligible. Because these unknown structural parameters make it impossible to accurately calculate the additional acoustic impedance of the infrasound sensor being measured, the laser pistonphone can only be used to calibrate infrasound sensors and acoustic coupling methods that do not significantly change the piston cavity volume, limiting the applicability of the laser pistonphone calibration technique. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for measuring key parameters of a laser piston generator sound pressure calculation model, solve the problem of accurately measuring the piston cavity volume change and additional acoustic impedance introduced by the acoustic coupling between the infrasound sensor and the piston generator, improve the calculation accuracy of the laser piston generator sound pressure calculation model, directly improve the uncertainty level of the sound pressure sensitivity calibration of the laser piston generator method infrasound sensor, and expand the scope of application of the laser piston generator method calibration technology to infrasound sensors of different types and with different interfaces.

[0008] The technical solution adopted in the present invention is as follows:

[0009] A method for determining key parameters of a laser piston sounder sound pressure calculation model comprises the following steps:

[0010] (1) Based on the connection structure between the laser piston sounder and the infrasound sensor to be measured, a laser piston sounder sound pressure calculation model is constructed, wherein the connection structure between the laser piston sounder and the infrasound sensor to be measured includes a piston cavity, one end of the piston cavity is equipped with a piston, and the other end of the piston cavity is connected to the infrasound sensor to be measured through an air path;

[0011] (2) Based on the internal cavity of the infrasound sensor to be measured and the additional acoustic impedance introduced by the acoustic coupling of the infrasound sensor to be measured, a sound pressure error correction term is constructed to determine the key parameters to be measured in the sound pressure calculation model of the laser piston generator. The key parameters include the equivalent length of the piston cavity, the internal cavity of the infrasound sensor to be measured and the additional acoustic impedance introduced by the acoustic coupling of the infrasound sensor to be measured;

[0012] (3) Three piston cavities with different cavity lengths were processed. Except for the cavity length, other structural parameters of the piston sounder remained unchanged;

[0013] (4) acoustically coupling the same infrasound sensor to be tested with three piston cavities of different lengths of the piston sounder, sequentially collecting the response voltages of the infrasound sensor at different piston cavity lengths, calculating the ratio of the infrasound sensor response voltages at different piston cavity lengths, and obtaining experimental data on the calculated sound pressure ratios of the piston sounder at different piston cavity lengths;

[0014] (5) Based on the experimental data of the sound pressure ratio calculated by the piston sounder at different piston cavity lengths, a genetic algorithm is used to fit the parameters to be measured in the piston sounder sound pressure calculation model, and the optimal solution for the key parameters to be measured in the piston sounder sound pressure calculation model is obtained.

[0015] Furthermore, in step (1), the calculation formula of the laser piston sounder sound pressure calculation model is:

[0016]

[0017] Where p is the acoustic pressure amplitude in the piston cavity, γ is the specific heat ratio of air, p0 is the static pressure, r c is the piston radius, x is the piston displacement, V0 is the volume of the piston cavity when the piston is in equilibrium position, and Δp(H, L, W) is the error correction related to heat conduction, cavity leakage, and acoustic pressure fluctuation.

[0018] Furthermore, the sound pressure error correction term in step (2) can be expressed as:

[0019] Δp(H, L, W) = p WC ×p LHC (2);

[0020] Where: p WC is the sound pressure fluctuation correction, p LHC Correction for coupling of heat conduction and cavity leakage;

[0021] The correction formula for sound pressure fluctuation is:

[0022]

[0023] in, is the mth zero of the first-order Bessel function, that is, L is the length of the piston cavity, the piston center point when the piston is in equilibrium position is the origin, z is the distance from the piston cavity to the origin along the axial direction, r is the distance from the origin along the radial direction, a is the radius of the piston cavity, r c is the piston radius, ω = 2πf is the angular frequency of the sound wave, f is the sound wave frequency, and c0 is the air sound speed;

[0024] The coupled correction formula for heat conduction and cavity leakage is:

[0025]

[0026] Where j is the imaginary unit, T L is the leakage time constant of the pistonphone, Y r is the equivalent admittance introduced by the internal cavity of the infrasound sensor to be measured and the gas path connection between it and the piston sounder, ρ0 is the air density in the cavity when the piston is in the equilibrium position, c0 is the air sound speed, α t is the thermal diffusion coefficient of the enclosed gas, x m is the mth zero point of the 0th order Bessel function, that is, J0(x m )=0.

[0027] Furthermore, the step (3) is specifically as follows: processing three piston cavities, except for the cavity length, the other structural parameters of the piston sounder are the same, and the equivalent lengths of the piston cavities are marked as L, L+ΔL1, and L+ΔL2, respectively, where ΔL1 and ΔL2 are the changes in the physical length of the piston cavity, which are set during processing.

[0028] Furthermore, the specific steps of step (4) are:

[0029] (4.1) Acoustically couple the same infrasound sensor to the three piston chambers of the piston generator in sequence, and collect and analyze the electrical signal output, recording the response voltage.

[0030] For a piston cavity with an equivalent length of L, the response voltage series of the infrasound sensor at the calibration frequency point is recorded as U0;

[0031] For a piston cavity with an equivalent length of L+ΔL1, the response voltage series of the infrasound sensor at the calibration frequency point is recorded as U1;

[0032] For a piston cavity with an equivalent length of L+ΔL2, the response voltage series of the infrasound sensor at the calibration frequency point is recorded as U2;

[0033] (4.2) Let the sensitivity series of the infrasound sensor used at the calibration frequency be recorded as S. Then the measurement results of the sound pressure generated in the piston cavity with equivalent lengths of L, L + ΔL1, and L + ΔL2 are expressed as follows:

[0034]

[0035] Combining formulas (9) to (11) in pairs can eliminate the sensitivity of the infrasound sensor and obtain:

[0036]

[0037] Among them, the sound pressure p generated in the piston cavity with equivalent lengths of L, L+ΔL1, and L+ΔL2 is a0、p a1 、p a2 The theoretical model is given by formula (1) and formula (2), where the parameters to be measured are the equivalent length L of the piston cavity and the equivalent acoustic impedance (a+jb) of the infrasound sensor to be measured, that is, the equivalent admittance Y r The reciprocal of , a, j and b are the real part, imaginary unit and imaginary part of the equivalent acoustic impedance respectively.

[0038] Furthermore, the specific steps of step (6) are:

[0039] The range of the equivalent length L is obtained based on the physical length of the piston cavity. ΔL1 and ΔL2 are the changes in the physical length of the piston cavity.

[0040] According to the structural parameters of the infrasound sensor to be measured and the gas path connection between the infrasound sensor to be measured and the piston sounder, the value range of the corresponding equivalent acoustic impedance is obtained;

[0041] Combined with the determined value range and based on the experimental data of the sound pressure ratio calculated by the piston sounder at different piston cavity lengths, a genetic algorithm is used to fit the key parameters to be measured in the sound pressure calculation model of the laser piston sounder, and the optimal solution of the equivalent length L and the equivalent acoustic impedance of the infrasound sensor to be measured is obtained.

[0042] Furthermore, the specific steps of using the genetic algorithm to fit the equivalent length L of the piston cavity in the laser piston sounder sound pressure calculation model and the equivalent acoustic impedance of the infrasound sensor to be measured are as follows:

[0043] According to the response voltages U0, U1, and U2 of the infrasound sensor at different piston cavity lengths, the experimental data for calculating the sound pressure ratio of the piston sounder are obtained. Substitute the experimental environment parameters into the empirical formulas of air density, thermal diffusion coefficient, sound speed, specific heat ratio and other parameters to provide input parameters for the sound pressure calculation model of formula (1) and formula (2), and substitute the known parameters in the model to obtain the model data for calculating the sound pressure ratio of the piston sounder

[0044] Define a fitness function, quantify the error between the model data and experimental data for calculating the sound pressure ratio of the pistonphone, determine the optimization target, and ensure the global optimality of parameter fitting through the joint constraints of the three sets of data;

[0045] Begin the genetic algorithm configuration and evolution execution. Encode the real and imaginary parts of the equivalent cavity length and the equivalent acoustic impedance of the infrasound sensor according to the specified value range. Configure the genetic operators for crossover, mutation, and selection. Hybrid crossover maintains diversity, Gaussian perturbation avoids local optima, and tournament selection retains high-quality individuals. Then, execute the evolution. Initialize the number of individuals and the number of generations to balance global search and convergence speed.

[0046] The genetic algorithm extracts the optimal individual and obtains the optimal solution for the equivalent length L of the piston cavity in the piston sound pressure calculation model and the equivalent acoustic impedance of the infrasound sensor to be measured.

[0047] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0048] 1. The present invention extracts parameters to be measured in the pistonphone sound pressure calculation model, including the equivalent length of the piston cavity, the internal cavity of the infrasound sensor, and the additional acoustic impedance introduced by its acoustic coupling with the pistonphone. During the actual calibration process, the additional acoustic impedance introduced by the acoustic coupling of different types of infrasound sensors and the change in the pistonphone cavity volume can be quantitatively measured through experimental methods. This improves the accuracy of the pistonphone sound pressure calculation results, thereby reducing the measurement uncertainty of the laser pistonphone infrasound sensor calibration results. This expands the scope of application of the laser pistonphone calibration technology, no longer limiting it to infrasound sensors without a significant internal cavity and whose acoustic coupling method does not significantly change the pistonphone cavity volume, such as standard-sized laboratory standard microphones and working standard microphones, thus meeting the primary calibration requirements of different types of infrasound sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be considered as limiting the scope. A person of ordinary skill in the art can also derive other relevant drawings based on these drawings without inventive effort, among which:

[0050] Figure 1 This is a schematic diagram of the connection structure between the laser piston sounder of the present invention and the infrasound sensor to be measured;

[0051] Figure 2 Schematic diagram of key parameter determination of the present invention. DETAILED DESCRIPTION

[0052] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0053] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are intended to fall within the scope of protection of the present invention.

[0054] In conjunction with the instructions Figure 1-2 ;

[0055] Among them, the typical structure of the laser piston sounder and its connection relationship with the infrasound sensor are as follows: Figure 1 As shown in Figure 2, the calculation formula for the radiated sound pressure of the piston sounder is:

[0056]

[0057] Where p is the acoustic pressure amplitude in the piston cavity, γ is the specific heat ratio of air, p0 is the static pressure, r c is the piston radius, x is the piston displacement, V0 is the volume of the piston cavity when the piston is in equilibrium position, and Δp(H, L, W) is the error correction related to heat conduction, cavity leakage, and acoustic pressure fluctuation.

[0058] The sound pressure error correction effects of a pistonphone include heat conduction, cavity leakage, and sound pressure fluctuations. At higher frequencies, sound pressure fluctuation correction dominates; at lower frequencies, heat conduction and cavity leakage correction dominate. Heat conduction and cavity leakage are highly coupled and require coupled correction, while they are less coupled with sound pressure fluctuations and can be corrected separately. The sound pressure error correction term in formula (1) can be expressed as:

[0059] Δp(H, L, W) = p WC ×p LHC (2)

[0060] Where: p WC is the sound pressure fluctuation correction, p LHC Correction for coupling of heat conduction and cavity leakage.

[0061] The correction formula for sound pressure fluctuation is:

[0062]

[0063]

[0064] in: is the mth zero of the first-order Bessel function, that is, L is the length of the piston cavity, the piston center point when the piston is in equilibrium position is the origin, z is the distance from the piston cavity to the origin along the axial direction, r is the distance from the origin along the radial direction, a is the radius of the piston cavity, r cis the piston radius, ω=2πf is the angular frequency of the sound wave, f is the sound wave frequency, and c0 is the air sound speed.

[0065] The coupled correction formula for heat conduction and cavity leakage is:

[0066]

[0067] Where: j is the imaginary unit, T L is the leakage time constant of the pistonphone, Y r is the equivalent admittance introduced by the internal cavity of the infrasound sensor to be measured and the gas path connection between it and the piston sounder, ρ0 is the air density in the cavity when the piston is in the equilibrium position, α t is the thermal diffusion coefficient of the enclosed gas, x m is the mth zero point of the 0th order Bessel function, that is, J0(x m )=0.

[0068] In the calculation formulas for the radiated sound pressure of the piston sounder described in formulas (1) and (2), the static pressure, piston radius and piston motion displacement can be accurately measured, and the specific heat ratio of air can be calculated according to the empirical formula; ideally, the cavity volume of the piston sounder can be calculated according to a standard cylindrical cavity, and the calculation parameters include the radius and length of the piston cavity. Among them, the radius of the piston cavity can be accurately measured, and its length is related to the sealing structure of the piston and the cavity, such as film sealing, gap sealing, etc., which makes the calculation of its cavity volume more complicated. If the cavity volume is still calculated using a cylindrical cavity, it is more appropriate to express its cavity length in terms of equivalent length to characterize the correction of the cavity volume by the irregular structure of the piston cavity; in addition, the internal cavity of the infrasound sensor to be measured and the additional cavity volume introduced by the gas path interface with the piston sounder are not easy to measure directly. In the calculation process of formula (2), the internal cavity of the infrasound sensor to be measured and the additional acoustic impedance introduced by acoustic coupling are described in terms of equivalent acoustic impedance. Therefore, in the calculation formula of the radiated sound pressure of the piston generator, the key parameters that are difficult to measure accurately are summarized as the equivalent length of the piston cavity and the equivalent acoustic impedance of the infrasound sensor to be measured.

[0069] like Figure 2 As shown, the key parameters of the laser piston sound pressure calculation model are determined:

[0070] Three piston cavities were machined. Except for the cavity length, all other structural parameters of the piston sounder were the same. The equivalent lengths of the piston cavities were marked as L, L+ΔL1, and L+ΔL2, respectively. ΔL1 and ΔL2 are the changes in the physical length of the piston cavity, which are set during machining and are known quantities.

[0071] The same infrasound sensor to be tested is acoustically coupled with the three cavities of the pistonphone in sequence, and the electrical signal output is analyzed and recorded through data acquisition.

[0072] For a piston cavity with an equivalent length of L, the response voltage series of the infrasound sensor at the calibration frequency point is recorded as U0;

[0073] For a piston cavity with an equivalent length of L+ΔL1, the response voltage series of the infrasound sensor at the calibration frequency point is recorded as U1;

[0074] For a piston cavity with an equivalent length of L+ΔL2, the response voltage series of the infrasound sensor at the calibration frequency point is recorded as U2;

[0075] Assuming that the sensitivity series of the infrasound sensor used at the calibration frequency is recorded as S, the measurement results of the sound pressure generated in the piston cavity with equivalent lengths of L, L+ΔL1, and L+ΔL2 are expressed as follows:

[0076]

[0077] Combining formulas (9) to (11) in pairs can eliminate the sensitivity of the infrasound sensor and obtain:

[0078]

[0079] Among them, the sound pressure p generated in the piston cavity with equivalent lengths of L, L+ΔL1, and L+ΔL2 is a0 、p a1 、p a2 The theoretical model is given by formula (1) and formula (2), where the parameters to be measured are the equivalent length L of the piston cavity and the equivalent acoustic impedance (a+jb) of the infrasound sensor to be measured, that is, the equivalent admittance Y r The reciprocal of , a, j and b are the real part, imaginary unit and imaginary part of the equivalent acoustic impedance respectively. According to the test data of formula (12) to formula (14), the three unknown parameters in the laser piston sounder calculation sound pressure model are fitted by genetic algorithm.

[0080] The range of the equivalent length L is given according to the physical length of the piston cavity. ΔL1 and ΔL2 are the changes in the physical length of the piston cavity and are known quantities.

[0081] According to the structural parameters of the infrasound sensor to be measured and its gas path connection with the pistonphone, the value range of the equivalent acoustic impedance of the two is estimated, and the value range can be appropriately expanded;

[0082] Combined with the above-determined value range, according to the experimental data of the sound pressure ratio calculated by the piston sounder at different piston cavity lengths, a genetic algorithm is used to fit the key parameters to be measured in the sound pressure calculation model of the laser piston sounder.

[0083] Specifically, the steps for fitting the key parameters of the laser piston sound pressure calculation model using the genetic algorithm are as follows:

[0084] According to the response voltages U0, U1, and U2 of the infrasound sensor at different piston cavity lengths, the experimental data for calculating the sound pressure ratio of the piston sounder are obtained.

[0085] Substitute the experimental environment parameters (temperature, air pressure, humidity) into the empirical formulas of air density, thermal diffusivity, sound velocity, specific heat ratio and other parameters to provide input parameters for the sound pressure calculation model of formula (1) and formula (2), and substitute the known parameters in the model to obtain the model data for calculating the sound pressure ratio of the piston sounder.

[0086] Define a fitness function, quantify the error between the model data and experimental data for calculating the sound pressure ratio of the pistonphone, determine the optimization target, and ensure the global optimality of parameter fitting through the joint constraints of the three sets of data;

[0087] Begin the genetic algorithm configuration and evolution execution. Encode individuals (equivalent cavity length, real and imaginary parts of the infrasound sensor's additional acoustic impedance) according to the previously determined value ranges. Configure the genetic operators for crossover, mutation, and selection. Hybrid crossover maintains diversity, Gaussian perturbation avoids local optima, and tournament selection retains high-quality individuals. Then, execute the evolution. The initial number of individuals and the number of generations to evolve must balance global search and convergence speed.

[0088] The genetic algorithm extracts the optimal individual and obtains the optimal solution for the equivalent length L of the piston cavity in the piston sound pressure calculation model and the equivalent acoustic impedance of the infrasound sensor to be measured.

[0089] In addition, when measuring the key parameters of the sound pressure calculation model of the laser piston sounder, the number of piston cavities used is not limited to three, but is at least two. The number of piston cavities only affects the available data and fitting accuracy of the fitting algorithm; the parameter fitting method based on experimental data is not limited to the genetic algorithm, and other algorithms and models that can achieve the same function are available; the sound pressure calculation model of the piston sounder is not limited to the formula given in this patent, especially the coupling correction of heat conduction and cavity leakage, and the sound pressure fluctuation correction model.

[0090] The above are the embodiments of the present invention. The foregoing are the preferred embodiments of the present invention. If the preferred implementation methods in each preferred embodiment are not obviously self-contradictory or based on a certain preferred implementation method, each preferred implementation method can be arbitrarily superimposed and used in combination. The embodiments and the specific parameters in the embodiments are only for the purpose of clearly describing the verification process of the invention, and are not intended to limit the scope of patent protection of the present invention. The scope of patent protection of the present invention is still subject to its claims. Any equivalent structural changes made by using the contents of the description and drawings of the present invention should also be included in the scope of protection of the present invention.

Claims

1. A method for determining key parameters of a laser piston sound pressure calculation model, characterized in that: The following steps are involved: (1) Based on the connection structure between the laser piston sounder and the infrasound sensor to be measured, a laser piston sounder sound pressure calculation model is constructed, wherein the connection structure between the laser piston sounder and the infrasound sensor to be measured includes a piston cavity, one end of the piston cavity is equipped with a piston, and the other end of the piston cavity is connected to the infrasound sensor to be measured through an air path; (2) Based on the internal cavity of the infrasound sensor to be measured and the additional acoustic impedance introduced by the acoustic coupling of the infrasound sensor to be measured, a sound pressure error correction term is constructed to determine the key parameters to be measured in the sound pressure calculation model of the laser piston generator. The key parameters include the equivalent length of the piston cavity, the internal cavity of the infrasound sensor to be measured and the additional acoustic impedance introduced by the acoustic coupling of the infrasound sensor to be measured; (3) Three piston cavities with different cavity lengths were processed. Except for the cavity length, other structural parameters of the piston sounder remained unchanged; (4) acoustically coupling the same infrasound sensor to be tested with three piston cavities of different lengths of the piston sounder, sequentially collecting the response voltages of the infrasound sensor at different piston cavity lengths, calculating the ratio of the infrasound sensor response voltages at different piston cavity lengths, and obtaining experimental data on the calculated sound pressure ratios of the piston sounder at different piston cavity lengths; (5) Based on the experimental data of the sound pressure ratio calculated by the piston sounder at different piston cavity lengths, a genetic algorithm is used to fit the parameters to be measured in the piston sounder sound pressure calculation model, and the optimal solution for the key parameters to be measured in the piston sounder sound pressure calculation model is obtained.

2. A method for determining key parameters of a laser piston sound pressure calculation model according to claim 1, characterized in that: In step (1), the calculation formula of the laser piston sounder sound pressure calculation model is: Where p is the acoustic pressure amplitude in the piston cavity, γ is the specific heat ratio of air, p0 is the static pressure, r c is the piston radius, x is the piston displacement, V0 is the volume of the piston cavity when the piston is in equilibrium position, and Δp(H, L, W) is the error correction related to heat conduction, cavity leakage, and acoustic pressure fluctuation.

3. A method for determining key parameters of a laser piston sound pressure calculation model according to claim 2, characterized in that: The sound pressure error correction term in step (2) can be expressed as: Δp(H,L,W)=p WC ×p LHC (2); Where: p WC is the sound pressure fluctuation correction, p LHC Correction for coupling of heat conduction and cavity leakage; The correction formula for sound pressure fluctuation is: in, is the mth zero of the first-order Bessel function, that is, L is the length of the piston cavity, the piston center point when the piston is in equilibrium position is the origin, z is the distance from the piston cavity to the origin along the axial direction, r is the distance from the origin along the radial direction, a is the radius of the piston cavity, r c is the piston radius, ω = 2πf is the angular frequency of the sound wave, f is the sound wave frequency, and c0 is the air sound speed; The coupled correction formula for heat conduction and cavity leakage is: Where j is the imaginary unit, T L is the leakage time constant of the pistonphone, Y r is the equivalent admittance introduced by the internal cavity of the infrasound sensor to be measured and the gas path connection between it and the piston sounder, ρ0 is the air density in the cavity when the piston is in the equilibrium position, c0 is the air sound speed, α t is the thermal diffusion coefficient of the enclosed gas, x m is the mth zero point of the 0th order Bessel function, that is, J0(x m )=0.

4. The method for determining key parameters of a laser piston sound pressure calculation model according to claim 1, characterized in that: The step (3) is specifically as follows: processing three piston cavities, wherein, except for the cavity length, the other structural parameters of the piston sounder are the same, and the equivalent lengths of the piston cavities are marked as L, L+ΔL1, and L+ΔL2, respectively, where ΔL1 and ΔL2 are the changes in the physical length of the piston cavity, which have been set during processing.

5. A method for determining key parameters of a laser piston sound pressure calculation model according to claim 4, characterized in that: The specific steps of step (4) are: (4.1) Acoustically couple the same infrasound sensor to the three piston chambers of the piston generator in sequence, and collect and analyze the electrical signal output, recording the response voltage. For a piston cavity with an equivalent length of L, the response voltage series of the infrasound sensor at the calibration frequency point is recorded as U0; For a piston cavity with an equivalent length of L+ΔL1, the response voltage series of the infrasound sensor at the calibration frequency point is recorded as U1; For a piston cavity with an equivalent length of L+ΔL2, the response voltage series of the infrasound sensor at the calibration frequency point is recorded as U2; (4.2) Let the sensitivity series of the infrasound sensor used at the calibration frequency be recorded as S. Then the measurement results of the sound pressure generated in the piston cavity with equivalent lengths of L, L + ΔL1, and L + ΔL2 are expressed as follows: Combining formulas (9) to (11) in pairs can eliminate the sensitivity of the infrasound sensor and obtain: Among them, the sound pressure p generated in the piston cavity with equivalent lengths of L, L+ΔL1, and L+ΔL2 is a0 、p a1 、p a2 The theoretical model is given by formula (1) and formula (2), where the parameters to be measured are the equivalent length L of the piston cavity and the equivalent acoustic impedance of the infrasound sensor to be measured, that is, the equivalent admittance Y r The reciprocal of .

6. A method for determining key parameters of a laser piston acoustic pressure calculation model according to claim 5, characterized in that: The specific steps of step (6) are: The range of the equivalent length L is obtained based on the physical length of the piston cavity. ΔL1 and ΔL2 are the changes in the physical length of the piston cavity. According to the structural parameters of the infrasound sensor to be measured and the gas path connection between the infrasound sensor to be measured and the piston sounder, the value range of the corresponding equivalent acoustic impedance is obtained; Combined with the determined value range and based on the experimental data of the sound pressure ratio calculated by the piston sounder at different piston cavity lengths, a genetic algorithm is used to fit the key parameters to be measured in the sound pressure calculation model of the laser piston sounder, and the optimal solution of the equivalent length L and the equivalent acoustic impedance of the infrasound sensor to be measured is obtained.

7. A method for determining key parameters of a laser piston sound pressure calculation model according to claim 6, characterized in that: The specific steps of using genetic algorithm to fit the equivalent length L of the piston cavity in the sound pressure calculation model of the laser piston sounder and the equivalent acoustic impedance of the infrasound sensor to be measured are as follows: According to the response voltages U0, U1, and U2 of the infrasound sensor at different piston cavity lengths, the experimental data for calculating the sound pressure ratio of the piston sounder are obtained. Substitute the experimental environment parameters into the empirical formulas of air density, thermal diffusion coefficient, sound speed, specific heat ratio and other parameters to provide input parameters for the sound pressure calculation model of formula (1) and formula (2), and substitute the known parameters in the model to obtain the model data for calculating the sound pressure ratio of the piston sounder Define a fitness function, quantify the error between the model data and experimental data for calculating the sound pressure ratio of the pistonphone, determine the optimization target, and ensure the global optimality of parameter fitting through the joint constraints of the three sets of data; Begin the genetic algorithm configuration and evolution execution. Encode the real and imaginary parts of the equivalent cavity length and the additional acoustic impedance of the infrasound sensor according to the specified value range. Configure the genetic operators for crossover, mutation, and selection. Hybrid crossover maintains diversity, Gaussian perturbation avoids local optima, and tournament selection retains high-quality individuals. Then, execute the evolution. Initialize the number of individuals and the number of generations to balance global search and convergence speed. The genetic algorithm extracts the optimal individual and obtains the optimal solution for the equivalent length L of the piston cavity in the piston sound pressure calculation model and the equivalent acoustic impedance of the infrasound sensor to be measured.

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