Microperforated plate structure parameter calculation method based on genetic algorithm and microperforated plate

Abstract

The invention belongs to the technical field of micro-perforated plate resonance sound absorption structures, and discloses a micro-perforated plate structure parameter calculation method based on a genetic algorithm and a micro-perforated plate, and the calculation method comprises the following steps: S1, calculating a transfer matrix of micropores; s2, calculating a transfer matrix of the cavity; s3, determining output sound pressure, output sound velocity and a total transfer matrix; s4, determining an acoustic absorption coefficient; s5, establishing an optimization model according to a genetic algorithm by taking the fullest sound absorption coefficient curve as a target function according to the sound absorption coefficient obtained in the S4; s6, the optimization model obtained in the S5 is used for making an iteration curve, structural parameters of the micro-perforated plate are obtained according to the iteration curve, and the structural parameters are the perforation rate, the plate thickness, the cavity depth and the hole diameter; the invention aims to provide the micro-perforated plate structure parameter calculation method based on the genetic algorithm and the micro-perforated plate so as to obtain the micro-perforated plate with high absorption and wide frequency band.

Description

Technical Field

[0001] The invention relates to the technical field of micro-perforated plate resonance sound absorption structures, in particular to a method for calculating structural parameters of a micro-perforated plate based on a genetic algorithm and the micro-perforated plate. Background Art

[0002] In recent years, due to the increasing severity of environmental noise pollution, noise pollution control has become an urgent social problem to be solved in the development of green ecology in today's society. Traditional sound-absorbing materials, such as polyester, polyurethane, mineral fiber, etc., have a series of defects in human life and social production, such as poor durability, poor fire resistance, and secondary pollution, so their use is largely restricted. However, micro-perforated plate can solve the above problems. It is a resonant sound-absorbing structure composed of a perforated plate with a perforation diameter as small as a micrometer and a cavity behind the plate. It is not limited by materials and environment, and can also be used under high temperature, high humidity, air flow impact and corrosion conditions. Its theoretical system has not only been perfected after more than 40 years of research and development. Therefore, the resonant sound-absorbing structure of micro-perforated plate has a good application prospect in the field of noise control, and the research on its sound absorption performance has attracted much attention. At present, the acoustic-electric analogy method is used to theoretically calculate the double-layer micro-perforated plate sound absorption structure. Due to the influence of the cavity sound quality, when the cavity distance is greater than 30mm or the frequency is higher than 3000HZ, a large error is generated, and the sound absorption effect is relatively poor. Summary of the invention

[0003] The present invention intends to provide a method for calculating structural parameters of a micro-perforated plate based on a genetic algorithm and a micro-perforated plate, so as to obtain a micro-perforated plate with high absorption and broadband.

[0004] In order to achieve the above object, the present invention provides the following technical solutions:

[0005] A method for calculating structural parameters of a micro-perforated plate based on a genetic algorithm comprises the following steps:

[0006] S1: According to the transfer matrix principle of micropores, the transfer matrix of micropores is calculated;

[0007] S2: Calculate the transfer matrix of the cavity based on the sound pressure and particle velocity;

[0008] S3: Based on the transfer matrix of the micropore obtained in S1, the transfer matrix of the cavity obtained in S2, and the input sound pressure and input sound velocity, determine the output sound pressure, output sound velocity and the total transfer matrix;

[0009] S4: Determine the sound absorption coefficient according to the output sound pressure, output sound velocity and total transfer matrix obtained in S3;

[0010] S5: Based on the sound absorption coefficient obtained in S4, ensure that the sound absorption coefficient of the micro-perforated plate reaches above 0.6 within the sound absorption frequency range of 0-5000 Hz, take the fullest sound absorption coefficient curve as the objective function, and establish an optimization model based on the genetic algorithm;

[0011] S6: Using the optimization model obtained in S5 to make an iterative curve, the structural parameters of the micro-perforated plate are obtained according to the iterative curve. The structural parameters are the perforation rate, plate thickness, cavity depth and hole diameter.

[0012] Furthermore, in S1, the expression for calculating the micropore transfer matrix is:

[0013]

[0014] Among them, Z s is the acoustic impedance ratio, Z s The expression is:

[0015]

[0016] In the above expression, ρ is the air density, μ is the kinematic viscosity, d is the aperture, t is the tube length, w is the angular frequency, j is the Bessel function,

[0017] Furthermore, in S2, the expression for calculating the transfer matrix of the cavity is:

[0018]

[0019] In the above expression, ρ 0 、c 0 , k are the density of air, sound wave, and wave number respectively, D is the depth of the cavity, and j is the Bessel function.

[0020] Furthermore, in S3, the expressions for determining the output sound pressure and the output sound velocity are:

[0021]

[0022] In the above expression, p 2 、u 2 Represent the input sound pressure and input sound velocity respectively, p 1 、u 1 Represent the output sound pressure and output sound velocity respectively.

[0023] Furthermore, in S3, the expression for determining the total transfer matrix is:

[0024]

[0025] Further, in S4, the expression for determining the sound absorption coefficient is:

[0026]

[0027] In the above expression, ρ 0 、c 0 They are the density of air, sound waves, and Z s is the acoustic impedance ratio, Re and Im represent the real part and imaginary part respectively.

[0028] Furthermore, in S5, the expression of the optimization model established according to the genetic algorithm is:

[0029]

[0030] In the above expression, max(A) is the sum of the sound absorption coefficients, f is the frequency, and a(f) is the sound absorption coefficient function within the set frequency range.

[0031] Furthermore, in S6, the optimization model obtained in S5 is used to make an iterative curve, and the calculation parameters are: population size: POPSIZE=100, maximum genetic generation: MAXGEN=500, crossover rate: PC=0.9, mutation rate: PM=0.1; the value range of four structural parameters: perforation rate: 0.1≤P≤1, plate thickness: 0.1≤t≤1, cavity depth: 1≤D≤100.

[0032] The microperforated plate obtained according to the calculation method of the microperforated plate structural parameters based on the genetic algorithm described above includes a single-layer microperforated plate and a double-layer microperforated plate, and the four structural parameters of the single-layer microperforated plate are: perforation rate: 0.050%, plate thickness: 0.388mm, hole diameter: 0.101mm, and cavity depth: 21.878mm; the four structural parameters of the double-layer microperforated plate are: the perforation rates of the first layer and the second layer are respectively 0.025% and 0.025%, the plate thicknesses of the first layer and the second layer are respectively 0.2mm and 0.1mm, the hole diameters of the first layer and the second layer are respectively 0.1mm and 0.1mm, the depth of the cavity between the first layer and the second layer is 17mm, and the distance between the second layer and the rear end tube cavity is 40mm.

[0033] The beneficial effects of the technical solution are:

[0034] 1. The present invention uses genetic algorithms to optimize and simulate the structural parameters of micro-perforated plates, which makes up for the error caused by the approximate calculation of the cavity acoustic impedance when the cavity distance is large or the frequency is high when the traditional acoustic-electric analogy method is used to calculate the double-layer micro-perforated plate sound absorption structure;

[0035] 2. The structural parameters of the single-layer microporous plate of the present invention are optimized by genetic algorithm, and the sound absorption effect of the double-layer microporous plate in the range of 0-4000HZ is better than that of the acoustic-electric analogy method. The structural parameters of the double-layer microporous plate are optimized by genetic algorithm, and the sound absorption effect of the double-layer microporous plate in the range of 0-5000HZ is better than that of the acoustic-electric analogy method.

[0036] 3. The structural parameters of the single-layer microporous plate optimized by genetic algorithm were used to make microporous plates for experiments. The calculation results of the two methods for the single-layer microporous plate are generally consistent with the experimental data. However, when the cavity depth in the double-layer plate is greater than 30mm and the frequency reaches above 3000HZ, the acoustic-electric analogy method ignores the influence of the acoustic mass of the cavity on the sound absorption coefficient. Therefore, there is an obvious error between the theoretical calculation of the acoustic-electric analogy method and the experimental measurement method. The transfer matrix method is more consistent with the experimental measurement method. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The micro-perforated plate acoustic unit of the present invention and its equivalent circuit diagram;

[0038] Figure 2 It is an iterative curve diagram optimized by the genetic algorithm of the present invention;

[0039] Figure 3 The sound absorption curves of the single-layer micro-perforated plate obtained by the transfer matrix method and the acoustic-electric analogy method after the genetic algorithm optimization of the present invention are shown;

[0040] Figure 4 The sound absorption curves of the double-layer micro-perforated plate obtained by the transfer matrix method and the acoustic-electric analogy method after the genetic algorithm optimization of the present invention are shown;

[0041] Figure 5 It is a comparison curve diagram of two theoretical analysis methods and impedance tube experimental measurement method of a single-layer micro-perforated plate obtained after genetic algorithm optimization of the present invention;

[0042] Figure 6 It is a comparison curve diagram of two theoretical analysis methods of the double-layer micro-perforated plate obtained after the genetic algorithm optimization of the present invention and the impedance tube experimental measurement method. DETAILED DESCRIPTION

[0043] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments:

[0044] A method for calculating structural parameters of a micro-perforated plate based on a genetic algorithm comprises the following steps:

[0045] S1: According to the transfer matrix formula of micropores, the transfer matrix of micropores is calculated. The expression for calculating the transfer matrix of microperforation is:

[0046]

[0047] Among them, Z sis the acoustic impedance ratio, Z s The expression is:

[0048]

[0049] In the above expression, ρ is the air density, μ is the kinematic viscosity, d is the aperture, t is the tube length, w is the angular frequency, j is the Bessel function,

[0050] S2: Based on the sound pressure and particle velocity, the transfer matrix of the cavity is calculated. In S2, the expression for calculating the transfer matrix of the cavity is:

[0051]

[0052] In the above expression, ρ 0 、c 0 , k are the density of air, sound wave, and wave number, respectively, D is the depth of the cavity, and j is the Bessel function;

[0053] S3: Based on the transfer matrix of the micropore obtained in S1, the transfer matrix of the cavity obtained in S2, and the input sound pressure and input sound velocity, the output sound pressure, output sound velocity and the total transfer matrix are determined, such as Figure 1 As shown in the figure, according to the equivalent circuit analysis, the input end is the acoustic quantity of the unit, and the output end is the acoustic quantity of the rear part of the system. A transfer function based on the transfer matrix is ​​constructed, that is, the expression for determining the output sound pressure and output sound velocity is:

[0054]

[0055] In the above expression, p 2 、u 2 Represent the input sound pressure and input sound velocity respectively, p 1 、u 1 Represent the output sound pressure and output sound velocity respectively; the expression for determining the total transfer matrix is:

[0056]

[0057] S4: Determine the sound absorption coefficient based on the output sound pressure, output sound velocity and total transfer matrix obtained in S3, combined with the sound absorption characteristics of the material. When the incident light is perpendicular, the acoustic impedance ratio Z s The relationship with the sound pressure reflection coefficient γ is:

[0058]

[0059] where u 1 ,p 1 Represent the output sound velocity and output sound pressure respectively;

[0060] The sound pressure reflection coefficient γ is expressed as:

[0061]

[0062] Combining equations (1) and (2) yields:

[0063]

[0064] According to the definition formula of sound absorption coefficient: α = 1-γ 2 , Substituting equations (2) and (3) into the equation, we can get the expression of sound absorption coefficient:

[0065]

[0066] In the above expression, ρ 0 、c 0 They are the density of air, sound waves, and Z s is the acoustic impedance ratio, Re and Im represent the real part and imaginary part respectively;

[0067] S5: According to the sound absorption coefficient obtained in S4, the sound absorption coefficient of the micro-perforated plate is guaranteed to be above 0.6 within the sound absorption frequency range of 0-5000Hz. The fullest sound absorption coefficient curve is taken as the objective function, and an optimization model is established according to the genetic algorithm. The expression of the optimization model established according to the genetic algorithm is:

[0068]

[0069] In the above expression, max(A) is the sum of the sound absorption coefficients, f is the frequency, and a(f) is the sound absorption coefficient function within the set frequency range;

[0070] S6: Using the optimization model obtained in S5 to make an iterative curve, the structural parameters of the micro-perforated plate are obtained according to the iterative curve. The structural parameters are perforation rate, plate thickness, cavity depth and hole diameter. Using the optimization model obtained in S5 to make an iterative curve, the operation parameters are: population number: POPSIZE=100, maximum genetic generation: MAXGEN=500, crossover rate: PC=0.9, mutation rate: PM=0.1; the value range of the four structural parameters: perforation rate: 0.1≤P≤1, plate thickness: 0.1≤t≤1, cavity depth: 1≤D≤100, hole diameter: 0.005≤d≤0.05, the iterative curve after genetic algorithm optimization is as follows Figure 2 As shown, from Figure 2 It can be concluded that when the number of iterations reaches 300, the optimization results of the four structural parameters have reached an ideal state, the total sound absorption coefficient of the entire frequency range 0-5000Hz has reached 73.23, and the effective sound absorption coefficient area accounts for a = A max / A=73.12 / (1×100)=73.12%, effective sound absorption can be obtained, and the frequency band is longer. The four parameters of the single-layer micro-perforated plate are as follows:

[0071] Plate thickness t = 0.388 mm, hole diameter d = 0.101 mm, perforation rate P = 0.050%, cavity depth D = 21.878 mm;

[0072] The four parameters of double-layer micro-perforated panels are as follows:

[0073] The thickness of the first plate and the second plate are t1 = 0.2 mm and t2 = 0.1 mm respectively; the diameters of the holes of the first plate and the second plate are d1 = 0.1 mm and d2 = 0.1 mm respectively; the perforation rates of the first plate and the second plate are P1 = 0.025% and P2 = 0.025% respectively; the depth of the cavity between the first plate and the second plate is 17 mm, and the distance between the second plate and the rear end tube cavity is 40 mm;

[0074] Single-layer boards are frequently used in experimental basic analysis and have sufficient theoretical basis. The sound absorption coefficient and frequency curves of the transfer matrix method and the acoustic-electric analogy method in the range of 0-5000Hz are plotted as follows Figure 3 As shown by Figure 3 It can be seen that the sound absorption coefficients of the two methods both reach an effective sound absorption coefficient of 0.6 at 1600HZ, and the sound absorption effect of the transfer matrix method in the low frequency band is significantly higher than that of the acoustic-electric analogy method. The transfer matrix method reaches a peak value at around 2550HZ, close to 1; the acoustic-electric analogy method reaches a peak value at around 3050HZ, close to 0.95. The sound absorption frequency bands of both methods are relatively long, and the sound absorption effect of the transfer matrix method is better. In summary, the structural parameters of the single-layer board have a relatively good sound absorption effect in the range of 0-4000HZ after the genetic algorithm is optimized.

[0075] Considering that the double-layer board sound-absorbing material has a wider range of uses, the sound absorption coefficient and frequency curves of the transfer matrix method and the acoustic-electric analogy method in the range of 0-5000Hz are plotted as follows Figure 4 As shown by Figure 4 It can be seen that the sound absorption coefficients of the two methods both reach an effective sound absorption coefficient of 0.6 at 1500HZ. The sound absorption effect of the acoustic-electric analogy method in the low frequency band is significantly higher than that of the transfer matrix method, and the sound absorption effect in the medium and high frequency bands is far worse than that of the transfer matrix method. The acoustic-electric analogy method reaches a peak value at a frequency of about 2000HZ, close to 1; the transfer matrix method reaches a peak value at a frequency of about 2750HZ, close to 0.95. The sound absorption frequency band is longer than that of the acoustic-electric analogy method, and the sound absorption effect of the transfer matrix method is better.

[0076] To sum up, the structural parameters of the single-layer board have a better sound absorption effect in the range of 0-4000HZ after being optimized by the genetic algorithm, and the structural parameters of the double-layer board have a better sound absorption effect in the range of 0-5000HZ after being optimized by the genetic algorithm.

[0077] There are many processing methods for micro-perforation. According to the actual social production situation, the traditional method has certain limitations. CNC machine tool processing, laser processing, EDM, and electron beam processing are more commonly used. Laser drilling has significant advantages such as good effect, strong versatility, high cross precision and high economic benefits.

[0078] According to the optimization parameter results of the genetic algorithm, single-layer and double-layer micro-perforated plates are prepared, as shown in the following table:

[0079] Table 1 shows the four structural parameters of single-layer and double-layer micro-perforated plates after optimization by genetic algorithm

[0080]

[0081] The prepared micro-perforated plate was installed at the end of the impedance tube, and the impedance tube with an inner diameter of 100 mm was used to measure the sound absorption coefficient of the acoustic single-layer sample in the frequency range of 400 Hz to 5000 Hz. A computer was used to record the relevant data. The experiment was measured many times and the average value of the measurement results was calculated, as shown in Table 2.

[0082] Table 2 is the experimental measurement data of the single-layer plate impedance tube method

[0083]

[0084]

[0085] The comparison curves of the two theoretical analysis methods and the impedance tube experimental measurement method for the single-layer micro-perforated plate obtained after genetic algorithm optimization are shown in the figure. Figure 5 As shown;

[0086] Considering that the double-layer micro-perforated plate cannot be directly installed on the experimental measurement equipment, a cylindrical aluminum thin sleeve was designed in the experiment. The first and second layers of micro-perforated plates were sealed and bonded at both ends of it. An impedance tube with an inner diameter of 100 mm was used to measure the sound absorption coefficient of the acoustic double-layer sound absorption sample in the frequency range of 400 Hz to 5000 Hz. The experiment was measured many times and the average value of the measurement results was calculated, as shown in Table 3.

[0087] Table 3 Experimental measurement data of double-layer plate impedance tube method

[0088]

[0089]

[0090]

[0091] The comparison curves of the two theoretical analysis methods and the impedance tube experimental measurement method for the single-layer micro-perforated plate obtained after genetic algorithm optimization are shown in the figure. Figure 6 As shown, from Figure 5 and Figure 6 It can be observed that the simulation curves of the two methods optimized by genetic algorithms are too smooth, achieving the expected ideal effect. Under the two theoretical methods, both single and double-layer boards have faster sound absorption bands, which are longer than the acoustic-electric analogy method, and the bandwidth of the effective sound absorption coefficient of 0.6 is also wider. The sound absorption effect of the transfer matrix method is better. The calculation results of the two methods for single-layer boards are consistent with the experimental data as a whole. However, when the cavity depth in the double-layer board is greater than 30mm and the frequency reaches above 3000HZ, the acoustic-electric analogy method ignores the influence of the acoustic mass of the cavity on the sound absorption coefficient. Therefore, there is an obvious error between the theoretical calculation of the acoustic-electric analogy method and the experimental measurement method.

[0092] The microperforated plate obtained according to the calculation method of the microperforated plate structural parameters based on the genetic algorithm described above includes a single-layer microperforated plate and a double-layer microperforated plate, and the four structural parameters of the single-layer microperforated plate are: perforation rate: 0.050%, plate thickness: 0.388mm, hole diameter: 0.101mm, and cavity depth: 21.878mm; the four structural parameters of the double-layer microperforated plate are: the perforation rates of the first layer and the second layer are respectively 0.025% and 0.025%, the plate thicknesses of the first layer and the second layer are respectively 0.2mm and 0.1mm, the hole diameters of the first layer and the second layer are respectively 0.1mm and 0.1mm, the depth of the cavity between the first layer and the second layer is 17mm, and the distance between the second layer and the rear end tube cavity is 40mm.

[0093] In summary, the present invention adopts genetic algorithm to optimize and simulate the structural parameters of micro-perforated plates, which makes up for the error caused by the approximate calculation of cavity acoustic impedance when the cavity distance is large or the frequency is high when the traditional acoustic-electric analogy method is used to calculate the sound absorption structure of the double-layer micro-perforated plate; the structural parameters of the single-layer microporous plate of the present invention are better than the acoustic-electric analogy method in the sound absorption effect of 0-4000HZ after genetic algorithm optimization, and the structural parameters of the double-layer microporous plate are better than the acoustic-electric analogy method in the sound absorption effect of 0-5000HZ after genetic algorithm optimization; microporous plates are made by using the structural parameters of the single-layer microporous plate optimized by the genetic algorithm for experiments, and the calculation results of the two methods of the single-layer microporous plate are consistent with the experimental data as a whole, while in the double-layer plate, when the cavity depth is greater than 30mm and the frequency reaches above 3000HZ, the acoustic-electric analogy method ignores the influence of the acoustic mass of the cavity on the sound absorption coefficient, so there is an obvious error between the theoretical calculation of the acoustic-electric analogy method and the experimental measurement method, and the transfer matrix method is more consistent with the experimental measurement method.

[0094] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the technical solution of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for calculating structural parameters of a micro-perforated plate based on a genetic algorithm, characterized in that: The following steps are involved: S1: According to the transfer matrix principle of micropores, the transfer matrix of micropores is calculated; S2: Calculate the transfer matrix of the cavity based on the sound pressure and particle velocity; S3: Based on the transfer matrix of the micropore obtained in S1, the transfer matrix of the cavity obtained in S2, and the input sound pressure and input sound velocity, determine the output sound pressure, output sound velocity and the total transfer matrix; S4: Determine the sound absorption coefficient according to the output sound pressure, output sound velocity and total transfer matrix obtained in S3; S5: Based on the sound absorption coefficient obtained in S4, ensure that the sound absorption coefficient of the micro-perforated plate reaches above 0.6 within the sound absorption frequency range of 0-5000 Hz, take the fullest sound absorption coefficient curve as the objective function, and establish an optimization model based on the genetic algorithm; S6: Using the optimization model obtained in S5 to make an iterative curve, the structural parameters of the micro-perforated plate are obtained according to the iterative curve. The structural parameters are the perforation rate, plate thickness, cavity depth and hole diameter.

2. The method for calculating the structural parameters of a micro-perforated plate based on a genetic algorithm according to claim 1, characterized in that: In S1, the expression for calculating the micropore transfer matrix is: Among them, Z s is the acoustic impedance ratio, Z s The expression is: In the above expression, ρ is the air density, μ is the kinematic viscosity, d is the aperture, t is the tube length, w is the angular frequency, j is the Bessel function, 3. The method for calculating the structural parameters of a micro-perforated plate based on a genetic algorithm according to claim 1, characterized in that: In S2, the expression for calculating the transfer matrix of the cavity is: In the above expressions, ρ0, c0, k are the density of air, sound wave, and wave number, respectively, D is the depth of the cavity, and j is the Bessel function.

4. The method for calculating the structural parameters of a micro-perforated plate based on a genetic algorithm according to claim 1, characterized in that: In S3, the expressions for determining the output sound pressure and output sound velocity are: In the above expressions, p2 and u2 represent the input sound pressure and input sound velocity, respectively, and p1 and u1 represent the output sound pressure and output sound velocity, respectively.

5. The method for calculating the structural parameters of a micro-perforated plate based on a genetic algorithm according to claim 1, characterized in that: In S3, the expression for determining the total transfer matrix is:

6. The method for calculating the structural parameters of a micro-perforated plate based on a genetic algorithm according to claim 1, characterized in that: In S4, the expression for determining the sound absorption coefficient is: In the above expression, ρ0 and c0 are the density of air and sound wave, respectively. s is the acoustic impedance ratio, Re and Im represent the real part and imaginary part respectively.

7. The method for calculating the structural parameters of a micro-perforated plate based on a genetic algorithm according to claim 1, characterized in that: In S5, the expression of the optimization model established according to the genetic algorithm is: In the above expression, max(A) is the sum of the sound absorption coefficients, f is the frequency, and a(f) is the sound absorption coefficient function within the set frequency range.

8. The method for calculating the structural parameters of a micro-perforated plate based on a genetic algorithm according to claim 1, characterized in that: In S6, the optimization model obtained in S5 is used to make an iterative curve, and the calculation parameters are: population size: POPSIZE=100, maximum genetic generation: MAXGEN=500, crossover rate: PC=0.9, mutation rate: PM=0.1; the value range of four structural parameters: perforation rate: 0.1≤P≤1, plate thickness: 0.1≤t≤1, cavity depth: 1≤D≤100.

9. The micro-perforated plate obtained by the method for calculating the structural parameters of a micro-perforated plate based on a genetic algorithm according to any one of claims 1 to 8, characterized in that: The micro-perforated plate includes a single-layer micro-perforated plate and a double-layer micro-perforated plate. The four structural parameters of the single-layer micro-perforated plate are: perforation rate: 0.050%, plate thickness: 0.388mm, hole diameter: 0.101mm, and cavity depth: 21.878mm; the four structural parameters of the double-layer micro-perforated plate are: the perforation rates of the first layer and the second layer are respectively 0.025% and 0.025%, the plate thicknesses of the first layer and the second layer are respectively 0.2mm and 0.1mm, the hole diameters of the first layer and the second layer are respectively 0.1mm and 0.1mm, the depth of the cavity between the first layer and the second layer is 17mm, and the distance between the second layer and the rear end tube cavity is 40mm.

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