1. The multilayer film type acoustic metamaterial structure is characterized by comprising a plurality of stacked film type acoustic metamaterial units with different structural parameters, wherein each metamaterial unit is divided by a hard frame to form a wide-band low-frequency sound insulation structure with a plurality of sound insulation peaks.

2. A multilayer thin film type acoustic metamaterial structure as claimed in claim 1, wherein the metamaterial unit includes a layer of elastic thin film and an additional mass disposed at the center of the elastic thin film.

3. A multilayer thin film type acoustic metamaterial structure as claimed in claim 1, wherein the natural frequencies f of the additional mass and the elastic thin film are:

wherein a and c are the radii of the elastic membrane and the additional mass block respectively; the unit of the film tension T is N/m, which is the product of the film prestress sigma and the film thickness h; m is the mass of the additional mass block; when the acoustic excitation frequency is close to f, the metamaterial unit generates an anti-resonance phenomenon, and the frequency is the sound insulation peak frequency of the metamaterial unit.

4. The multilayer thin film type acoustic metamaterial structure according to claim 1, wherein the structure formed by stacking each metamaterial unit generates a plurality of sound insulation peaks, and the acoustic metamaterial structure is constructed in a mode of equal spacing, peak valley value complementation or customization according to a noise source according to the sound insulation peak frequency, and specifically comprises the following steps:

the sound insulation peaks of the acoustic metamaterial structure constructed in an equidistant mode are distributed at equal intervals;

in the acoustic metamaterial structure constructed in a peak-valley complementary mode, the sound insulation peak frequency of a first metamaterial unit is located at the middle position of a frequency band needing sound insulation, the sound insulation peak values of a second metamaterial unit and a third metamaterial unit cover two sound insulation valleys of the first metamaterial unit, and by analogy, the sound insulation peaks and the sound insulation valleys of the metamaterial units are mutually offset to cover the whole frequency band needing sound insulation;

and each sound insulation peak of the acoustic metamaterial structure constructed in a form customized according to the noise source is arranged according to a plurality of frequency points with the highest noise amplitude of the noise source.

5. The structure of claim 1, wherein the elastic membrane is fixed to the upper and lower surfaces of the two adjacent rigid frames by glue after being tensioned.

6. The method for designing the multilayer thin film type acoustic metamaterial structure based on claim 1, comprising the following steps:

s1, calculating the sound insulation peak frequency of the metamaterial unit;

and S2, constructing the acoustic metamaterial structure in one form of equal spacing, peak value valley value complementation and noise source customization according to the sound insulation peak frequency.

7. The method for designing a multilayer thin film type acoustic metamaterial structure as claimed in claim 6, wherein the step S1 includes the steps of:

s1.1, establishing a spring-mass model of the film type acoustic metamaterial unit, wherein the spring-mass model is subjected to incident sound wavesThe elastic membrane and the additional mass block generate displacement under the action of excitation, and an elastic action is generated between the elastic membrane and the additional mass block; the elastic properties of the elastic film are expressed as the equivalent stiffness k₁The vibration differential equation is established as follows:

wherein m is₁、m₂Masses, u, of the elastic membrane and of the additional mass, respectively₁、u₂The displacements of the elastic membrane and the additional mass block respectively are expressed in a simple harmonic form; solving to obtain:

wherein ω is₀Is the excitation frequency of the incident sound wave,natural circular frequency acting for additional mass and elastic membrane;

s1.2, calculating equivalent stiffness k of elastic film₁The unit force method is adopted, a normal force F is supposed to be applied to the additional mass block at the center of the elastic film, the amplitude of the elastic film under the excitation of incident sound waves is very small, the small deformation condition is met, and the normal displacement eta of the additional mass block is solved by a film vibration equation:

wherein a and c are the radii of the elastic membrane and the additional mass block respectively; the unit of the film tension T is N/m, which is the product of the film prestress sigma and the film thickness h; the ratio of the normal force F to the normal displacement eta is the equivalent stiffness k of the elastic film₁：

S1.3, calculating the natural circular frequency of the action of the additional mass block and the elastic film, and calculating the equivalent rigidity k of the elastic film₁And an additional massMass m of₂Substitution formulaAnd converting the natural circular frequency omega into a frequency f by using omega-2 pi f, so as to obtain the natural frequency of the additional mass block and the elastic membrane:

when the sound wave excitation frequency is close to the natural frequency f, the metamaterial generates an anti-resonance phenomenon, and the sound insulation effect is most obvious at the moment, so the natural frequency f is the sound insulation peak frequency of the metamaterial.

8. The design method of the multilayer thin film type acoustic metamaterial structure as claimed in claim 6, wherein in the step S2, the acoustic metamaterial structure is constructed in the form of equidistant isolation peak frequencies, and the method comprises the following steps:

a1, selecting a frequency band needing sound insulation and the number of sound insulation peaks, and determining the frequency of each sound insulation peak according to the principle of equal spacing;

a2, preliminarily determining the radius a of the elastic film according to the actual installation condition; preliminarily determining the tension T of the elastic film according to the maximum tensile stress of the selected film material;

a3, determining the structural parameters of each metamaterial unit according to the selected sound insulation peak frequency and a sound insulation peak frequency calculation formula, firstly adjusting the mass m or the film tension T of the additional mass block, and then adjusting the radius a of the elastic film and the radius c of the additional mass block when the effect cannot be achieved by adjusting the mass m or the film tension T.

9. The method for designing a multilayer thin film type acoustic metamaterial structure as claimed in claim 6, wherein in step S2, the acoustic metamaterial structure is constructed in a complementary form of peak value and valley value, and the method comprises the following steps:

b1, selecting a frequency range needing sound insulation, and constructing structural parameters of the first metamaterial unit based on a sound insulation peak frequency calculation formula to enable the sound insulation peak frequency to be located in the middle of a frequency band needing sound insulation;

b2, taking the first sound insulation valley frequency and the second sound insulation valley frequency of the first metamaterial unit in the step B1 as sound insulation peak frequencies, and respectively constructing a second metamaterial unit and a third metamaterial unit so that the sound insulation peaks of the second metamaterial unit and the third metamaterial unit cover two sound insulation valleys of the first metamaterial unit;

b3, similarly, the first sound insulation valley frequency of the second metamaterial unit and the second sound insulation valley frequency of the third metamaterial unit are used as sound insulation peak frequencies, the rest metamaterial units are respectively constructed, and the rest metamaterial units are analogized until the whole frequency band needing sound insulation is covered.

10. The method for designing a multilayer thin film type acoustic metamaterial structure as claimed in claim 6, wherein the step S2, constructing the acoustic metamaterial structure in a form customized according to the noise source, comprises the steps of:

c1, observing the frequency spectrum of the noise source, and selecting a plurality of frequency points with the highest noise amplitude;

c2, preliminarily determining the radius a of the elastic film according to the actual installation condition; preliminarily determining the tension T of the elastic film according to the maximum tensile stress of the selected film material;

and C3, determining the structural parameters of each metamaterial unit by a sound insulation peak frequency calculation formula according to the selected frequency point, firstly adjusting the mass m or the film tension T of the additional mass block, and when the effect cannot be achieved by adjusting the mass m or the film tension T, adjusting the radius a of the elastic film and the radius C of the additional mass block.

Background

In many places in life, serious noise problems exist, and noise is more and more serious in the traffic fields of automobiles, subways, aviation and the like and the life fields of architectural decoration and the like. The sound insulation walls on two sides of the expressway and the subway rail, the sound insulation material of the KTV box, the front wall of the automobile, the carpet sound insulation pad and the like can attenuate the transmission of noise to a certain extent, but can not effectively isolate the noise of a low frequency band. The problem of solving low frequency noise has always been a very difficult challenge, and low frequency noise's wavelength is long, the penetrability is strong, and the sound insulation performance of traditional sound insulation structure obeys the change law of quality law, and is better at high frequency section sound insulation effect, but at low frequency section sound insulation performance very poor. This severely restricts the design of the sound insulation parts of the vehicle and the sound insulation structure of the hall, and provides technical challenges for low-frequency sound insulation. The acoustic metamaterial developed in recent years provides a new solution for low-frequency sound absorption, sound insulation, vibration reduction and the like, and particularly, a thin-film structure can realize low-frequency sound insulation through an ultra-thin and ultra-light structure.

The acoustic metamaterial is a hot spot in the field of current mechanical and noise control. The local resonance units are artificially and periodically arranged, so that the super-normal characteristics, such as negative mass density and negative elastic modulus, are achieved. The characteristics make it different from the traditional homogeneous sound insulation material, and sound insulation performance breaking through the mass law can be achieved in a low frequency range. The film type acoustic metamaterial comprises partial units which are formed by a tensioned film fixed on a hard frame and a mass block attached to the center of the film, and sound insulation is carried out through partial resonance of each unit.

The film type acoustic metamaterial can form a sound insulation peak at a low frequency band, the sound insulation effect of the metamaterial near the frequency is far superior to that of a traditional sound insulation material with equal mass, but simultaneously, a sound insulation valley can be formed on the left side and the right side of the sound insulation peak frequency respectively, the sound insulation amount is almost zero, and practical application of the metamaterial is limited.

In 2018, invented patent by billows et al: a film type acoustic metamaterial design method (application number 201811228253.9) for inhibiting multi-frequency harmonic noise provides a multi-layer film type metamaterial structure, a plurality of sound insulation peak frequencies are formed by changing the number of neodymium iron boron magnets placed in the center of each layer of metamaterial in a mode of changing the center mass, the sound insulation peak frequencies cannot be calculated, the sound insulation peak frequencies of each layer of metamaterial cannot be flexibly regulated and controlled and combined, and efficient and accurate low-frequency sound insulation is achieved.

Disclosure of Invention

The invention provides a design method of a multilayer film type acoustic metamaterial structure based on sound insulation peak frequency calculation, aiming at improving the defects of metamaterials, wherein each layer of film and each mass block are respectively an acoustic metamaterial unit, structural parameters of each metamaterial are designed based on the calculation of the sound insulation peak frequency of the metamaterial so as to accurately regulate and control the sound insulation peak frequency of the metamaterial, the designed metamaterial units are overlapped together to form a wide-band low-frequency sound insulation structure with a plurality of sound insulation peaks, the sound insulation peaks can be designed to be at equal intervals, peak valley values are complementary, and the sound insulation peak frequency band is customized based on a noise source, so that the defects that the sound insulation quantity of a single metamaterial at a sound insulation valley is low and the sound insulation frequency band is narrow are overcome, and the design method has a good application prospect.

The purpose of the invention is realized by at least one of the following technical solutions.

The utility model provides a multilayer film type acoustics metamaterial structure, includes the different film type acoustics metamaterial unit of a plurality of superimposed structural parameters, cuts apart through the stereoplasm frame between every metamaterial unit, guarantees that the vibration between each acoustics metamaterial unit does not influence each other, constitutes the wide band section low frequency sound-insulating structure that has a plurality of sound-insulating peaks.

Further, the metamaterial unit includes an elastic membrane and an additional mass, and the additional mass is placed in the center of the elastic membrane.

Further, the natural frequency f of the additional mass and the elastic membrane is:

wherein a and c are the radii of the elastic membrane and the additional mass block respectively; the unit of the film tension T is N/m, which is the product of the film prestress sigma and the film thickness h; m is the mass of the additional mass block; when the acoustic wave excitation frequency is close to f, the metamaterial unit generates an anti-resonance phenomenon, and the sound insulation effect is most obvious at the moment, so that the frequency is the sound insulation peak frequency of the metamaterial unit.

Further, a structure formed by overlapping each metamaterial unit generates a plurality of sound insulation peaks, and the acoustic metamaterial structure is constructed in a mode of equal spacing and peak valley complementation or customization according to a noise source according to the sound insulation peak frequency, and specifically comprises the following steps:

the sound insulation peaks of the acoustic metamaterial structure constructed in an equidistant mode are distributed at equal intervals;

in the acoustic metamaterial structure constructed in a peak-valley complementary mode, the sound insulation peak frequency of a first metamaterial unit is located at the middle position of a frequency band needing sound insulation, the sound insulation peak values of a second metamaterial unit and a third metamaterial unit cover two sound insulation valleys of the first metamaterial unit, and by analogy, the sound insulation peaks and the sound insulation valleys of the metamaterial units are mutually offset to cover the whole frequency band needing sound insulation;

and each sound insulation peak of the acoustic metamaterial structure constructed in a form customized according to the noise source is arranged according to a plurality of frequency points with the highest noise amplitude of the noise source.

Further, the elastic films are respectively fixed on the upper surface and the lower surface of the two adjacent hard frames by glue after being tensioned.

A design method of a multilayer thin film type acoustic metamaterial structure comprises the following steps:

s1, calculating the sound insulation peak frequency of the metamaterial unit;

and S2, constructing the acoustic metamaterial structure in one form of equal spacing, peak value valley value complementation and noise source customization according to the sound insulation peak frequency.

Further, step S1 includes the steps of:

s1.1, establishing a spring-mass model of the film type acoustic metamaterial unit, wherein the spring-mass model is subjected to incident sound wavesThe elastic membrane and the additional mass block generate displacement under the action of excitation, and an elastic action is generated between the elastic membrane and the additional mass block; the elastic properties of the elastic film are expressed as the equivalent stiffness k₁The vibration differential equation is established as follows:

wherein m is₁、m₂Masses, u, of the elastic membrane and of the additional mass, respectively₁、u₂The displacements of the elastic membrane and the additional mass block respectively are expressed in a simple harmonic form; solving to obtain:

wherein ω is₀Is the excitation frequency of the incident sound wave,natural circular frequency acting for additional mass and elastic membrane;

s1.2, calculating equivalent stiffness k of elastic film₁The unit force method is adopted, a normal force F is supposed to be applied to the additional mass block at the center of the elastic film, the amplitude of the elastic film under the excitation of incident sound waves is very small, the small deformation condition is met, and the normal displacement eta of the additional mass block is solved by a film vibration equation:

wherein a and c are the radii of the elastic membrane and the additional mass block respectively; the unit of the film tension T is N/m, which is the product of the film prestress sigma and the film thickness h; the ratio of the normal force F to the normal displacement eta is the equivalent stiffness k of the elastic film₁：

S1.3, calculating the natural circular frequency of the action of the additional mass block and the elastic film, and calculating the equivalent rigidity k of the elastic film₁And mass m of the additional mass₂Substitution formulaUsing a combination of omega-2 pif, converting the natural circular frequency omega (unit rad) into frequency f (unit Hz), and obtaining the natural frequency of the mass block and the elastic membrane:

when the sound wave excitation frequency is close to the natural frequency f, the metamaterial generates an anti-resonance phenomenon, and the sound insulation effect is most obvious at the moment, so the natural frequency f is the sound insulation peak frequency of the metamaterial.

Further, in step S2, constructing an acoustic metamaterial structure in the form of equidistant isolation peak frequencies, including the following steps:

a1, selecting a frequency band needing sound insulation and the number of sound insulation peaks, and determining the frequency of each sound insulation peak according to the principle of equal spacing;

a2, preliminarily determining the radius a of the elastic film according to the actual installation condition; preliminarily determining the tension T of the elastic film according to the maximum tensile stress of the selected film material;

a3, determining the structural parameters of each metamaterial unit according to the selected sound insulation peak frequency and a sound insulation peak frequency calculation formula, firstly adjusting the mass m or the film tension T of the additional mass block, and then adjusting the radius a of the elastic film and the radius c of the additional mass block when the effect cannot be achieved by adjusting the mass m or the film tension T.

Further, in step S2, the method for constructing the acoustic metamaterial structure in a complementary form of peak and valley includes the following steps:

b1, selecting a frequency range needing sound insulation, and constructing structural parameters of the first metamaterial unit based on a sound insulation peak frequency calculation formula to enable the sound insulation peak frequency to be located in the middle of a frequency band needing sound insulation;

b2, taking the first sound insulation valley frequency and the second sound insulation valley frequency of the first metamaterial unit in the step B1 as sound insulation peak frequencies, and respectively constructing a second metamaterial unit and a third metamaterial unit so that the sound insulation peaks of the second metamaterial unit and the third metamaterial unit cover two sound insulation valleys of the first metamaterial unit;

b3, similarly, the first sound insulation valley frequency of the second metamaterial unit and the second sound insulation valley frequency of the third metamaterial unit are used as sound insulation peak frequencies, the rest metamaterial units are respectively constructed, and the rest metamaterial units are analogized until the whole frequency band needing sound insulation is covered.

Further, in step S2, the method for constructing the acoustic metamaterial structure in a form customized according to the noise source includes the following steps:

c1, observing the frequency spectrum of the noise source, and selecting a plurality of frequency points with the highest noise amplitude;

c2, preliminarily determining the radius a of the elastic film according to the actual installation condition; preliminarily determining the tension T of the elastic film according to the maximum tensile stress of the selected film material;

and C3, determining the structural parameters of each metamaterial unit by a sound insulation peak frequency calculation formula according to the selected frequency point, firstly adjusting the mass m or the film tension T of the additional mass block, and when the effect cannot be achieved by adjusting the mass m or the film tension T, adjusting the radius a of the elastic film and the radius C of the additional mass block.

The invention has the following beneficial technical effects:

(1) the structure after the metamaterial of a plurality of different sound insulation peak frequencies is overlapped can produce a plurality of sound insulation peaks, broaden the sound insulation frequency band and solve the problems that the original single metamaterial has narrow sound insulation range and is difficult to apply

(2) Modeling is carried out on the film mass block structure of the metamaterial, the sound insulation peak frequency of the metamaterial is calculated by solving the anti-resonance frequency, the sound insulation peak frequency of each metamaterial in the multilayer metamaterial structure can be accurately regulated and controlled, and a better superposition effect is obtained

(3) In the structure designed by the invention, the amplitude of the valley is greatly improved in addition to realizing a plurality of sound insulation peaks

Drawings

FIG. 1 is a schematic diagram of a metamaterial unit spring-mass model.

FIG. 2 is a schematic diagram of a structure combination of a multilayer thin film type metamaterial.

FIG. 3 is a schematic diagram of the structure separation of a multilayer thin film type metamaterial.

FIG. 4 is a graphical representation of the results of the metamaterial A sound insulation test.

FIG. 5 is a graphical representation of the results of a metamaterial B sound insulation test.

FIG. 6 is a graphical representation of metamaterial C sound insulation test results.

FIG. 7 is a graphical representation of the results of a sound insulation test for a multilayer metamaterial structure.

Detailed Description

The present invention will be described in further detail with reference to the following examples.

Example (b):

in this embodiment, as shown in fig. 2 and 3, a multilayer thin film type acoustic metamaterial structure includes 3 stacked thin film type acoustic metamaterial units with different structural parameters, including a first frame 1, a second frame 2, a third frame 3, and a fourth frame 4 for supporting and separating each metamaterial unit as a substrate, a first elastic film 6, a second elastic film 8, and a third elastic film 10 fixed between the frames after being tensioned, and a first additional mass 5, a second additional mass 7, and a third additional mass 9 respectively attached to each layer of elastic film; the vibration among all the acoustic metamaterial units is not influenced mutually, and a wide-frequency-band low-frequency sound insulation structure with a plurality of sound insulation peaks is formed.

In this embodiment, the first frame 1, the second frame 2, the third frame 3, and the fourth frame 4 are all made of ABS resin, and the thickness of each layer is 3mm, so the overall structure can be controlled to be very light and thin, and meet certain strength requirements, and be convenient for use in various different situations, and the inner and outer diameters of the four frames are equal, 40mm and 100mm respectively.

In this embodiment, the first elastic film 6, the second elastic film 8 and the third elastic film 10 are made of polyethylene films with a thickness of 0.1mm, the polyethylene films are tightly adhered to the frames on the two sides by using 3M glue after the films are tensioned, the polyethylene films are cheap and easy to process and can meet the requirement of odor, the odor is an important assessment index in the sound insulation product of the automotive interior, and the extra risk of the product can be reduced by using the polyethylene films.

In this embodiment, the first additional mass 5, the second additional mass 7 and the third additional mass 9 are made of aluminum material, and are glued to the centers of the corresponding elastic membranes.

In the multilayer film type acoustic metamaterial structure of the embodiment, a first metamaterial unit a is composed of a first additional mass block 5 and a first elastic film 6, a second metamaterial unit B is composed of a second additional mass block 7 and a second elastic film 8, a third metamaterial unit C is composed of a third additional mass block 9 and a third elastic film 10, the first metamaterial unit a and the second metamaterial unit B are different in structural parameters, different sound insulation effects are achieved, a good superposition effect can be obtained through design, the superposition form comprises sound insulation peak equidistant intervals, sound insulation peak and sound insulation valley complementary and customized according to a noise source.

In the embodiment, only the case where the sound insulation peaks are equally spaced is implemented, and the specific steps are as follows.

According to the actual engineering requirements, the sound insulation performance of a certain product in the range of 400Hz-1200Hz is expected to be improved, the number of sound insulation peaks is selected to be 3, and the sound insulation peak frequencies of three metamaterial units are determined to be 600Hz, 800Hz and 1000Hz respectively according to the principle of equal spacing.

The method for calculating the sound insulation peak frequency of the metamaterial unit comprises the following steps:

s1.1, as shown in figure 1, establishing a spring-mass model of the thin film type acoustic metamaterial unit, wherein the spring-mass model is subjected to incident sound wavesThe elastic membrane and the additional mass block generate displacement under the action of excitation, and an elastic action is generated between the elastic membrane and the additional mass block; the elastic properties of the elastic film are expressed as the equivalent stiffness k₁The vibration differential equation is established as follows:

wherein m is₁、m₂Respectively of elastic membrane and additional massAmount u₁、u₂The displacements of the elastic membrane and the additional mass block respectively are expressed in a simple harmonic form; solving to obtain:

wherein ω is₀Is the excitation frequency of the incident sound wave,natural circular frequency acting for additional mass and elastic membrane;

s1.2, calculating equivalent stiffness k of elastic film₁The unit force method is adopted, the additional mass block at the center of the elastic film is supposed to apply a normal force F, the amplitude of the elastic film under the excitation of incident sound waves is very small, the small deformation condition is met, and the normal displacement eta of the additional mass block can be solved by a film vibration equation:

wherein a and c are the radii of the elastic membrane and the additional mass block respectively; the unit of the film tension T is N/m, which is the product of the film prestress sigma and the film thickness h; the ratio of the normal force F to the normal displacement eta is the equivalent stiffness k of the elastic film₁：

S1.3, calculating the natural circular frequency of the action of the additional mass and the elastic membrane, and calculating the equivalent rigidity k1 of the membrane and the mass m of the additional mass₂Substitution formulaAnd the natural circular frequency omega (unit rad) is converted into the frequency f (unit Hz) by using omega-2 pi f, and the natural frequency of the additional mass block and the elastic membrane is obtained:

when the sound wave excitation frequency is close to the natural frequency f, the metamaterial generates an anti-resonance phenomenon, and the sound insulation effect is most obvious at the moment, so the natural frequency f is the sound insulation peak frequency of the metamaterial.

According to the sound insulation peak frequency calculation formula, the structural parameters related to the sound insulation peak frequency comprise the membrane tension T, the mass m of the additional mass block, the elastic membrane and the radiuses a and c of the additional mass block. The radius of the elastic membrane is determined by the inner diameter of the frame, the adjustment is difficult, and the influence of the radius of the mass block on the sound insulation peak frequency is less obvious, so the sound insulation peak of the metamaterial unit is adjusted mainly by changing the tension of the membrane and the mass of the additional mass block in the embodiment.

Firstly, an appropriate additional mass block size is preliminarily selected, in the embodiment, the radius of the first additional mass block 5 is selected to be 3mm, the height of the first additional mass block is selected to be 3mm, and the density of aluminum is selected to be 2700kg/m³The mass of the first additional mass 5 is therefore 0.23 g. The radius of the elastic membrane is 20mm of the inner radius of the frame, and in order to enable the sound insulation peak frequency of the metamaterial unit to appear at 600Hz, the tension of the first elastic membrane 6 is as follows:

T＝2πmf²log(a/c)＝428.6N/m；

the first metamaterial unit A is manufactured according to the parameters, and the impedance tube test result is shown in fig. 4, wherein the transmission loss curve has a peak value at 560Hz, an amplitude value of about 70dB and a valley value at 380Hz and 1780Hz, the amplitude value is almost 0, the sound insulation peak is reduced very fast, and the sound insulation frequency band is very narrow. And then, on the basis of the structural parameters of the first metamaterial unit A, keeping the tension of the film unchanged, and adjusting the mass of the additional mass block to enable the sound insulation peak frequency to appear at 800 Hz. The mass of the second additional mass 7 is calculated:

similarly, when a sample B of the second metamaterial unit is manufactured and impedance tube sound insulation test is carried out, as shown in FIG. 5, the sound insulation peak of the transmission loss curve appears at 780Hz, which is not much different from the expected sound insulation peak.

Then, in the same way, determining the structural parameters of the third metamaterial unit C, keeping the other parameters unchanged on the basis of the structural parameters of the second metamaterial unit B, and adjusting the film tension to enable the sound insulation peak of the metamaterial unit to appear at 1000Hz, wherein the tension of the third elastic film 10 is as follows:

T＝2πmf²log(a/c)＝673N/m；

and (3) manufacturing a third metamaterial unit C sample piece to carry out impedance tube sound insulation test, wherein as shown in fig. 6, the sound insulation peak of the transmission loss curve appears at 960Hz, and has small difference with the expected value.

The multilayer film type acoustic metamaterial is a combination of a first metamaterial unit A, a second metamaterial unit B and a third metamaterial unit C, wherein the two metamaterial units of a middle frame are shared to reduce the overall thickness, corresponding multilayer metamaterial sample pieces are manufactured, the structural parameters are shown in table 1, impedance tubes are used for testing the sound insulation performance of the metamaterial sample pieces and are shown in figure 7, three sound insulation peaks appear in the superposed structure and are respectively located at 540Hz, 760Hz and 960Hz and basically keep the same with the single metamaterial unit, so that the sound insulation performance of the whole structure in a frequency band of 400Hz-1200Hz is obviously improved, the metamaterial sample piece has a wider sound insulation frequency band, and the low-frequency sound insulation effect is prominent

TABLE 1 double-layer film type acoustic metamaterial structural parameters

Compared with homogeneous sound insulation materials with equal weight, the multilayer film type acoustic metamaterial structure has a good sound insulation effect at low frequency, breaks through the limitation of the quality law of the traditional sound insulation materials, meets the requirements of light-weight low-frequency sound insulation on the premise of not increasing the thickness and the mass, can enable sound insulation peaks to be distributed according to a desired form after being designed, obtains a wider low-frequency sound insulation frequency band, improves the defect that sound insulation valleys originally exist in the metamaterial, obtains a better low-frequency sound insulation effect, and is more beneficial to application in practical engineering.