Use of asymmetric microporous membranes in thin film acoustic metamaterials, An asymmetric microporous membrane type acoustic metamaterial

Abstract

The application belongs to the technical field of noise control, and particularly relates to application of an asymmetric microporous film in a film type acoustic metamaterial and an asymmetric microporous film type acoustic metamaterial. The asymmetric microporous film type acoustic metamaterial is made of an asymmetric microporous film. The asymmetric microporous film has an asymmetric microporous structure. The porosity of one side of the film is low, and the aperture is small. The smooth and dense structure is more conducive to improving the sound insulation performance of the material. The other side is a porous loose layer, the porosity is high, and the aperture is large. The loose porous structure is more conducive to improving the sound absorption performance of the material. Therefore, the asymmetric microporous film has sound absorption and sound insulation synergistic effect. The two sides of the asymmetric microporous film are interconnected, the pressure on the two sides of the film is consistent, and the low-frequency noise reduction performance of the asymmetric microporous film type acoustic metamaterial is significantly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of noise control, and particularly relates to application of an asymmetric microporous film in a thin film type acoustic metamaterial and the asymmetric microporous film type acoustic metamaterial. BACKGROUND

[0002] The thin film type acoustic metamaterial is generally composed of a film, a frame and a mass, wherein the frame serves as a base to provide support and fixing, the film serves as a sound propagation medium and has a certain elasticity, and the mass serves as a control object to change the vibration mode of the unit structure and thus affect the propagation of sound waves. Under the excitation of sound waves, the film-mass system has a special vibration mode to produce sound insulation effect. By designing the structure and layout of the unit cell in the thin film type acoustic metamaterial, the mass density law can be broken, the sound insulation frequency band can be expanded, and good sound absorption or sound insulation characteristics can be exhibited in the low frequency range.

[0003] The film is the most important part of the entire thin film type acoustic metamaterial structure, and its physical properties, thickness, area and tension significantly affect the performance of the thin film type acoustic metamaterial. The existing thin film type acoustic metamaterial noise reduction structure usually adopts a dense film and a sealed cavity, but the gas pressure in the sealed cavity is prone to change due to the influence of environmental temperature and humidity, which changes the tension of the film and causes the working frequency of the acoustic metamaterial to drift, resulting in a significant decrease in noise reduction performance or even failure. SUMMARY

[0004] Therefore, the application provides the application of the asymmetric microporous film in the thin film type acoustic metamaterial and the asymmetric microporous film type acoustic metamaterial. The asymmetric microporous film type acoustic metamaterial made of the asymmetric microporous film can synergistically absorb and insulate sound and has excellent low frequency noise reduction performance.

[0005] To achieve the above purpose, the application provides the following technical solutions.

[0006] The application provides the application of the asymmetric microporous film in the thin film type acoustic metamaterial.

[0007] Preferably, the thickness of the asymmetric microporous film is 50-500 microns, the density is 204.61-416.31 kg / m 3 , and the elastic modulus is 8.91x10 7 -4.01x10 8 Pa.

[0008] Preferably, the porosity of one side of the asymmetric microporous film is 10-30%, the pore size is 0.01-0.5 microns, the porosity of the other side is 60-90%, and the pore size is 1-5 microns.

[0009] The application further provides an asymmetric microporous film type acoustic metamaterial, comprising a film and a frame 2, wherein the film is an asymmetric microporous film 1, and further comprising a back plate 4 arranged in parallel with the asymmetric microporous film 1 and a support 3 connecting the frame 2 and the back plate 4.

[0010] The asymmetric microporous film 1 is the asymmetric microporous film used in the application of the above technical solution.

[0011] Preferably, the diameter of the asymmetric microporous film 1 is 10 cm; and the effective diameter of the asymmetric microporous film 1 in the frame 2 is 7-9 cm.

[0012] Preferably, the frame 2 is a ring-shaped frame; the material of the frame 2 is stainless steel; the outer diameter of the ring-shaped frame is 10 cm, the inner diameter is 7-9 cm, and the thickness is 0.5-1 cm.

[0013] Preferably, the diameter of the back plate 4 is 10 cm, and the thickness is 0.5-1 cm; the material of the back plate 4 is stainless steel.

[0014] Preferably, the support 3 is a circular tube-shaped frame; the thickness of the tube wall of the circular tube-shaped frame is 0.5-1 cm, and the length is 10-30 cm; the material of the support 3 is stainless steel.

[0015] Preferably, the preparation method of the asymmetric microporous film comprises the following steps:

[0016] The polyetherimide powder is dissolved in an organic solvent and defoamed to obtain a casting solution;

[0017] The casting solution is formed into a film, and the obtained wet film is placed in a coagulation bath for solidification to obtain a solidified film;

[0018] The solidified film is sequentially immersed in isopropyl alcohol and n-hexane for drying to obtain an asymmetric microporous film.

[0019] Preferably, the organic solvent comprises one or more of N,N-dimethylacetamide, N,N-dimethylformamide and N-methylpyrrolidone; and the mass ratio of the polyetherimide powder and the organic solvent is 12-25:75-88.

[0020] The application provides application of an asymmetric microporous film in a thin film type acoustic metamaterial. The asymmetric microporous film in the application has an asymmetric microporous structure, the porosity of one side of the film is low, the aperture is small, and the smooth and dense structure is more conducive to improving the sound insulation performance of the material, and the other side is a porous loose layer, the porosity is high, the aperture is large, and the loose porous structure is more conducive to improving the sound absorption performance of the material, so that the asymmetric microporous film has sound absorption and sound insulation synergistic effect, and the two sides of the asymmetric microporous film are interconnected, ensuring that the pressures on the two sides of the film are consistent, and the asymmetric microporous film type acoustic metamaterial made of the asymmetric microporous film can significantly improve the low-frequency noise reduction performance. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 A structure schematic diagram of the asymmetric microporous film type acoustic metamaterial provided for the embodiment of the application is shown in the figure.

[0022] Figure 2 A structure top view schematic diagram of the asymmetric microporous film type acoustic metamaterial provided for the embodiment of the application is shown in the figure.

[0023] Figure 3 A structure side view schematic diagram of the asymmetric microporous film type acoustic metamaterial provided for the embodiment of the application is shown in the figure.

[0024] Figure 4 A relationship diagram of the polyetherimide concentration and the thickness of the asymmetric microporous film in the application is shown in the figure.

[0025] Figure 5 A relationship diagram of the polyetherimide concentration and the density of the asymmetric microporous film in the application is shown in the figure.

[0026] Figure 6 A relationship diagram of the polyetherimide concentration and the porosity and average aperture of the asymmetric microporous film in the application is shown in the figure.

[0027] Figure 7 A relationship diagram of the polyetherimide concentration and the elastic modulus of the asymmetric microporous film in the application is shown in the figure.

[0028] Figure 8 A relationship diagram of the coating thickness and the thickness of the asymmetric microporous film in the application is shown in the figure.

[0029] Figure 9 A relationship diagram of the coating thickness and the density of the asymmetric microporous film in the application is shown in the figure.

[0030] Figure 10 A relationship diagram of the coating thickness and the porosity and average aperture of the asymmetric microporous film in the application is shown in the figure.

[0031] Figure 11 A relationship diagram of the coating thickness and the elastic modulus of the asymmetric microporous film in the application is shown in the figure.

[0032] Figure 12 Figure 1 is a schematic diagram of a double microphone method sound absorption testing device in the present application;

[0033] Figure 13 Figure 2 is a schematic diagram of a four sensor method sound insulation testing device in the present application;

[0034] Figure 14 Figure 3 is a sound absorption testing result diagram of an experimental assembly of an asymmetric microporous membrane type acoustic metamaterial unit in the present application;

[0035] Figure 15 Figure 4 is a sound insulation testing result diagram of an experimental assembly of an asymmetric microporous membrane type acoustic metamaterial unit in the present application. DETAILED DESCRIPTION

[0036] The present application provides an application of an asymmetric microporous membrane in a membrane type acoustic metamaterial.

[0037] In the present application, the thickness of the asymmetric microporous membrane is preferably 50-500 μm, more preferably 400 μm; the density is preferably 204.61-416.31 kg / m 3 , more preferably 241.62-393.18 kg / m 3 ; the elastic modulus is preferably 8.91×10 7 -4.01×10 8 Pa, more preferably 1.58-3.43×10 8 Pa.

[0038] In the present application, the porosity of one side of the asymmetric microporous membrane is preferably 10-30%, more preferably 16.7-18.0%, the pore size is preferably 0.01-0.5 μm, more preferably 0.047-0.229 μm, the porosity of the other side is preferably 60-90%, more preferably 64.32-77.54%, and the pore size is preferably 1-5 μm, more preferably 1.242-3.830 μm.

[0039] In the present application, the material of the asymmetric microporous membrane is preferably polyetherimide.

[0040] The asymmetric microporous membrane in the present application has an asymmetric microporous structure, the porosity of one side of the membrane is low and the pore size is small, and the smooth and dense structure is more conducive to improving the sound insulation performance of the material, while the other side is a porous loose layer with high porosity and large pore size, and the loose porous structure is more conducive to improving the sound absorption performance of the material, so that the asymmetric microporous membrane has a sound absorption and sound insulation synergistic effect, and the two sides of the asymmetric microporous membrane are connected to each other, ensuring that the pressures on both sides of the membrane are consistent, and the use of the asymmetric microporous membrane in a membrane type acoustic metamaterial can significantly improve the low frequency noise reduction performance thereof.

[0041] The application further provides an asymmetric microporous film type acoustic metamaterial, comprising a film and a frame 2, wherein the film is an asymmetric microporous film 1, and further comprising a back plate 4 arranged in parallel with the asymmetric microporous film 1 and a support 3 connecting the frame 2 and the back plate 4.

[0042] The asymmetric microporous film 1 is the asymmetric microporous film used in the application.

[0043] The asymmetric microporous film type acoustic metamaterial provided by the application comprises an asymmetric microporous film 1.

[0044] In the application, the diameter of the asymmetric microporous film 1 is preferably 10 cm; and the effective diameter of the asymmetric microporous film 1 in the frame 2 is preferably 7-9 cm, more preferably 9 cm.

[0045] In the application, the preparation method of the asymmetric microporous film 1 preferably comprises the following steps:

[0046] The polyetherimide powder is dissolved in an organic solvent and defoamed to obtain a casting solution;

[0047] The casting solution is formed into a film, and the obtained wet film is placed in a coagulation bath for solidification to obtain a solidified film;

[0048] The solidified film is sequentially immersed in isopropyl alcohol and n-hexane for drying to obtain an asymmetric microporous film.

[0049] Unless otherwise specified, the application does not have special requirements for the source of the raw materials used for preparation, and commercially available goods known to those skilled in the art can be used.

[0050] The application preferably dissolves polyetherimide powder in an organic solvent to obtain a polyetherimide organic solution.

[0051] Before the polyetherimide powder is dissolved in an organic solvent, the application preferably dries the polyetherimide powder. In the application, the drying is preferably vacuum drying; the temperature of the vacuum drying is preferably room temperature-80℃, more preferably 80℃, the time is preferably 5-12 h, more preferably 8 h, and the vacuum degree is preferably -0.1 MPa; and the equipment for the vacuum drying is preferably a vacuum oven.

[0052] In the embodiment of the application, the polyetherimide powder is specifically a light yellow powdery solid, and the model is Ultem-1000 of American Innovative.

[0053] In the present application, the organic solvent preferably comprises one or more of N,N-dimethylacetamide, N,N-dimethylformamide and N-methylpyrrolidone, more preferably N,N-dimethylacetamide, N,N-dimethylformamide or N-methylpyrrolidone; when the organic solvent is one of the above, the present application does not have a special limitation on the ratio of different kinds of organic solvents, and any ratio is acceptable.

[0054] In the embodiments of the present application, the N,N-dimethylacetamide (DMAc) is specifically AR, 99.5%, CAS: 127-19-5, colorless viscous liquid, Aladdin Reagent (Shanghai) Co., Ltd.; the N,N-dimethylformamide (DMF) is specifically AR, 99.5%, CAS: 68-12-2, colorless viscous liquid, Aladdin Reagent (Shanghai) Co., Ltd.; and the N-methylpyrrolidone (NMP) is specifically AR, 99.5%, CAS: 872-50-4, colorless viscous liquid, Aladdin Reagent (Shanghai) Co., Ltd.

[0055] In the present application, the mass ratio of the polyetherimide powder and the organic solvent is preferably 12-25:75-88, more preferably 15-23:78-85. In the embodiments of the present application, the mass ratio of the polyetherimide powder and the organic solvent is specifically 12:88, 18:82, 20:80, 23:77 or 25:75.

[0056] In the present application, the temperature for the dissolving is preferably 50-80℃, more preferably 60-70℃, and the time is preferably 5-10h, more preferably 6-8h; the dissolving is preferably carried out under stirring; the stirring rate is preferably 50-300r / min, more preferably 100-200r / min; and the dissolving is preferably carried out under water bath.

[0057] After obtaining the polyetherimide organic solution, the present application preferably deaerates the polyetherimide organic solution to obtain a casting solution.

[0058] In the present application, the deaeration is room temperature vacuum deaeration; the vacuum degree for the vacuum deaeration is preferably -0.1MPa; and the time for the deaeration is preferably 1-4h, more preferably 2h.

[0059] After obtaining the casting solution, the present application preferably forms a film from the casting solution to obtain a wet film.

[0060] In the present application, the film forming is preferably doctor blade film forming; the thickness of the doctor blade is preferably 100-1000 μm, more preferably 200-900 μm. In the embodiments of the present application, the thickness of the doctor blade is specifically 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm or 1000 μm; the equipment used for the doctor blade film forming is preferably a film coater.

[0061] After obtaining the wet film, the present application preferably places the wet film in a coagulation bath for solidification to obtain a solidified film.

[0062] In the present application, the coagulation bath is preferably water; the solidification time is preferably 1-30 min, more preferably 5-10 min.

[0063] In the embodiments of the present application, the process for preparing the solidified film is specifically as follows: the glass plate of the film coater is cleaned with distilled water and ethanol, then wiped; the thickness of the doctor blade of the film coater is set; the casting solution is poured on the glass plate; the film coater is started to complete the doctoring; the glass plate of the film coater is taken out and soaked in the coagulation bath; until the film is solidified and spontaneously separated from the glass plate; the glass plate is taken out and cleaned with ethanol.

[0064] After the solidification, the present application preferably stores the solidified film obtained by the solidification in water.

[0065] In the present application, the storage mode is preferably soaking in water and standing; the standing time is preferably 12-24 h, more preferably 12-15 h.

[0066] After obtaining the solidified film, the present application preferably immerses the solidified film in isopropyl alcohol and n-hexane in sequence to obtain a solidified film filled with n-hexane.

[0067] In the present application, the immersion in isopropyl alcohol is preferably soaking in isopropyl alcohol and standing; the standing time is preferably 30-60 min, more preferably 30-40 min; the process of immersing the solidified film in isopropyl alcohol is preferably repeated for 2 times.

[0068] In the present application, the immersion in n-hexane is preferably soaking in n-hexane and standing; the standing time is preferably 30-60 min, more preferably 30-40 min.

[0069] After obtaining the solidified film filled with n-hexane, the present application preferably dries the solidified film filled with n-hexane to obtain an asymmetric microporous film.

[0070] In the present application, the drying temperature is preferably 30-40℃, more preferably 30-35℃; the drying time is preferably 0.5-3h, more preferably 1-2h; and the drying equipment is preferably a blast drying oven.

[0071] In the present application, the specific drying process is as follows: the solidified film is taken out of the n-hexane, fixed on a 15x20cm square acrylonitrile-butadiene-styrene copolymer (ABS) frame, the four edges and four corners of the solidified film are fixed with iron clips, the solidified film is tightly fixed on the frame, and then drying is performed.

[0072] The present application removes n-hexane in the solidified film by drying to obtain an asymmetric microporous membrane.

[0073] In the present application, if the PEI film after standing is directly dried, the pores in the film will collapse during the drying process due to the large surface tension of water, resulting in the destruction of the pore structure. The solvent exchange of isopropanol-n-hexane can reduce the damage to the pore structure of the film during the drying process of the PEI film: isopropanol is miscible with water, n-hexane is miscible with isopropanol, the film is first soaked in isopropanol, so that the residual water in the film is replaced by isopropanol, and the water in the film is removed; then the film is soaked in isopropanol, so that the isopropanol in the film is replaced by n-hexane, and n-hexane has low surface tension and is easy to volatilize, so that the pores in the film can be avoided from collapsing after direct drying.

[0074] The present application uses a phase inversion method to prepare an asymmetric microporous membrane, and by controlling the initial stage of phase inversion, the film morphology can be controlled to form an asymmetric microporous structure film material with a dense skin layer (low porosity and small pore size) and a porous support layer (porous and loose, high porosity, and large pore size).

[0075] The thin films with different thickness, density, pore structure and elastic modulus, and the sound absorption and sound insulation performances of the thin film type acoustic metamaterials prepared based on the thin films are also different. Specifically, with the increase of the thin film thickness, the maximum sound absorption coefficient value decreases, the sound absorption peak bandwidth increases, and the sound absorption frequency point corresponding to the peak value of the sound absorption curve moves to the high frequency; the thin film thickness has a greater impact on the unit sound insulation, and with the increase of the thin film thickness, the sound insulation curve has a tendency to move to the high frequency, and the first sound insulation peak value increases. With the increase of the thin film density, the first sound insulation valley frequency and the sound insulation peak frequency of the whole material change little, the second sound insulation valley frequency moves to the low frequency, the maximum sound insulation amount is basically unchanged, the frequency bandwidth greater than a certain sound amount decreases slightly, and the decreasing amplitude is not large. With the increase of the elastic modulus of the thin film material, the sound insulation amount curve of the acoustic metamaterial moves to the high frequency, and the bandwidth at the sound insulation peak becomes wider. The thin film with larger porosity and pore size has better sound absorption performance, and the thin film with larger density and thickness has better sound insulation performance. Therefore, the appropriate thin film material can be selected according to the requirements of the sound absorption and sound insulation performance of the acoustic metamaterial in specific application scenarios. The asymmetric microporous film material with different parameter performances (such as thickness, density, pore structure and elastic modulus) can be obtained by changing the preparation conditions of the asymmetric microporous film in the application, and then the sound absorption and sound insulation performance of the asymmetric microporous film type acoustic metamaterial can be changed. The sound absorption and sound insulation peak positions and the corresponding peak values of the thin film type acoustic metamaterials constructed by the asymmetric microporous film materials with different thickness, density, pore structure and elastic modulus are quite different. If sound absorption or sound insulation is required for a specific frequency band in the specific application process, the thin film type acoustic metamaterial with strong sound absorption or sound insulation performance in the corresponding frequency band can be selected, that is, the component frame structure of the acoustic metamaterial does not need to be replaced, only the different asymmetric microporous films need to be replaced, and the effective control of the specific noise can be realized.

[0076] The asymmetric microporous film material is prepared by using the phase inversion method in the application, the technology is mature, the production of the film material can be batched, and the production cost of the film material is reduced.

[0077] The asymmetric microporous film type acoustic metamaterial provided in the application comprises a frame 2 for fixing the asymmetric microporous film 1. In the application, the frame 2 is preferably a ring-shaped frame; the material of the frame 2 is preferably stainless steel; the outer diameter of the ring-shaped frame is preferably 10 cm, the inner diameter is preferably 7-9 cm, more preferably 9 cm, and the thickness is preferably 0.5-1 cm, more preferably 0.5 cm.

[0078] The asymmetric microporous film type acoustic metamaterial provided in the application comprises a back plate 4 arranged in parallel with the asymmetric microporous film 1. In the application, the diameter of the back plate 4 is preferably 10 cm, and the thickness is preferably 0.5-1 cm, more preferably 0.5 cm; the material of the back plate 4 is preferably stainless steel.

[0079] The asymmetric microporous thin-film acoustic metamaterial provided by this invention includes a support 3 connecting a frame 2 and a backplate 4. In this invention, the support 3 is preferably a cylindrical frame; the wall thickness of the cylindrical frame is preferably 0.5-1 cm, more preferably 0.5 cm, and the length is preferably 10-30 cm, more preferably 25 cm; the material of the support 3 is preferably stainless steel.

[0080] In this invention, the preferred assembly method for the asymmetric microporous thin-film acoustic metamaterial is as follows:

[0081] (1) Tensile the asymmetric microporous membrane 1 using a membrane stretching machine, and control the tension to be 20 N / m;

[0082] (2) Apply adhesive to one side of frame 2 and then stick it to the tensioned asymmetric microporous membrane 1. Let it stand for a period of time to allow the adhesive to cure. Cut off frame 2 with asymmetric microporous membrane 1 attached with a blade.

[0083] (3) Apply adhesive to both ends of the support 3, attach the back plate 4 to one end, and attach the frame 2 with the asymmetric microporous membrane 1 to the other end, so that the components are aligned with each other. Let it stand for a period of time to cure the adhesive and obtain the asymmetric microporous membrane type acoustic metamaterial.

[0084] Figure 1 This is a schematic diagram of the structure of the asymmetric microporous thin-film acoustic metamaterial provided in an embodiment of the present invention; Figure 2 A top view of its structure; Figure 3 The diagram shows a side view of its structure, where 1 represents the asymmetric microporous membrane, 2 the frame, 3 the support, and 4 the backplate. Figures 1 to 3 As shown, the asymmetric microporous film acoustic metamaterial provided by the present invention has an asymmetric microporous film, a frame for fixing the asymmetric microporous film, a back plate arranged parallel to and opposite to the asymmetric microporous film, and a support connecting the frame and the back plate.

[0085] In this invention, because the two sides of the asymmetric microporous membrane are interconnected, the pressure balance on both sides of the membrane can be maintained after assembly into an acoustic metamaterial component. This makes it less susceptible to changes in external environmental temperature and humidity, thus improving the stability of the acoustic metamaterial. The asymmetric microporous membrane-type acoustic metamaterial component of this invention has a simple structure and is easy to assemble. It exhibits good sound absorption and sound insulation performance in the low to medium range and can be used as noise reduction material for vehicles and buildings, as well as in vibration damping devices for large machinery.

[0086] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments thereof, but they should not be construed as limiting the scope of protection of the present invention.

[0087] Example 1

[0088] Polyetherimide (PEI) powder was placed in a vacuum oven, vacuum dried at 80°C, -0.1 MPa for 8 h, then the heating was turned off and the vacuum was maintained overnight to cool to room temperature;

[0089] PEI powder and N,N-dimethylacetamide were added to a round-bottom flask to obtain a PEI mass concentration of 12%, 15%, 18%, 20%, 23%, and 25%, the round-bottom flask was fixed on an iron stand, the rotation speed of the mechanical stirrer was adjusted to 100 r / min, and stirring was performed at 60°C in a water bath for 6 h until the solid was completely dissolved, then the round-bottom flask was removed, the water on the outer wall of the flask was wiped off, and the flask was placed in a vacuum oven at room temperature and vacuum degassed at -0.1 MPa for 2 h to obtain a PEI casting solution;

[0090] The glass plate of the film applicator accessory was washed with distilled water and ethanol, then wiped, the film applicator knife thickness was set to 400 μm, 10 mL of the casting solution was poured onto the glass plate, the film applicator was started to complete the scraping, then the glass plate was removed and immersed in a coagulation bath, until the film was solidified and spontaneously separated from the glass plate, the glass plate was washed with ethanol and wiped, after the scraping was completed, the PEI film immersed in the coagulation bath was transferred to a container containing distilled water, and after 24 h, the PEI film was immersed in isopropanol for 30 min, and the above process was repeated twice to replace the water remaining in the film holes with isopropanol; then the PEI film was immersed in n-hexane for 30 min to replace the residual isopropanol in the film holes with n-hexane; finally, the PEI film was removed, fixed on a 15 x 20 cm square ABS frame, the four edges and corners of the film were fixed with iron clips to make the film taut on the frame, and the asymmetric microporous film was dried in a forced air drying oven at 30°C for 1 h, then removed and stored in a sealed bag.

[0091] Example 2

[0092] The difference from Example 1 is that the mass concentration of polyetherimide is 12%, 15%, 18%, 20%, 23%, and 25%, the film applicator knife thickness is set to 100, 200, 300, 400, 500, 600, 700, 800, 900, and 1000 μm, respectively, and the remaining contents are the same as those of Example 1.

[0093] Example 3

[0094] The asymmetric microporous films prepared with polyetherimide mass concentrations of 15%, 18%, and 23% in Example 1, with a diameter of 10 cm and a thickness of 50–500 μm, are assembled with a stainless steel annular frame (thickness of 0.5 cm) with an outer diameter of 10 cm and an inner diameter of 9 cm, a cylindrical frame (wall thickness of 0.5 cm and length of 25 cm), and a stainless steel backplate with a diameter of 10 cm and a thickness of 0.5 cm to form an asymmetric microporous film-type acoustic metamaterial. The effective diameter of the film in the unit structure of the asymmetric microporous film-type acoustic metamaterial is 9 cm.

[0095] The material parameters of each part of the asymmetric microporous thin-film acoustic metamaterial are shown in Table 1:

[0096] Table 1 Parameters of asymmetric microporous thin-film acoustic metamaterials

[0097]

[0098] The specific assembly method is as follows:

[0099] (1) Tensile the asymmetric microporous membrane using a membrane stretching machine, and control the tension to be 20 N / m.

[0100] (2) Apply adhesive to one side of the stainless steel ring frame and then stick it to the tensioned asymmetric microporous membrane. Let it stand for a period of time to allow the adhesive to cure. Use a blade to cut off the stainless steel ring frame with the asymmetric microporous membrane attached.

[0101] (3) Apply adhesive to both ends of the stainless steel tubular frame, attach a stainless steel back plate to one end, and attach a stainless steel ring frame with an asymmetric microporous membrane to the other end, align the components with each other, and let stand for a period of time for the adhesive to cure, thus obtaining the asymmetric microporous membrane type acoustic metamaterial unit experimental component.

[0102] Performance testing

[0103] (1) The thickness of asymmetric microporous films with different polyetherimide concentrations prepared in Example 1 was measured, and the results are as follows: Figure 4 As shown.

[0104] Depend on Figure 4 It can be seen that the change in polyetherimide concentration during the preparation of asymmetric microporous films has no significant effect on the thickness of the asymmetric microporous films. When other preparation conditions remain unchanged, the film thickness is basically maintained at around 200 μm.

[0105] (2) The density of asymmetric microporous films with different polyetherimide concentrations prepared in Example 1 was measured, and the results are as follows: Figure 5 As shown.

[0106] Depend on Figure 5It can be seen that the density of the asymmetric microporous film gradually increases with the increase of polyetherimide concentration. This is mainly because the increased polyetherimide concentration during the preparation process increases the viscosity of the casting solution, and the asymmetric microporous film obtained after phase transformation is more compact overall, thus increasing the film density.

[0107] (3) The porosity and average pore size of the asymmetric microporous films with different polyetherimide concentrations prepared in Example 1 were measured, and the results are as follows: Figure 6 As shown.

[0108] Depend on Figure 6 It can be seen that with the increase of polyetherimide concentration, both the porosity and average pore size of the asymmetric microporous film decrease. The decrease in porosity is basically linear, while the decrease in average pore size gradually slows down. This is mainly because the increase in polyetherimide concentration during the preparation process increases the viscosity of the casting solution, making the asymmetric microporous film obtained after phase transformation more compact overall, and the average pore size gradually decreases. The increase in polyetherimide concentration also hinders the formation of macroporous structures in the film and promotes the formation of microporous structures, leading to a decrease in average pore size and a gradual approach to the pore size value corresponding to the microporous structures.

[0109] (4) The elastic modulus of the asymmetric microporous films with different polyetherimide concentrations prepared in Example 1 was measured, and the results are as follows: Figure 7 As shown.

[0110] Depend on Figure 7 It can be seen that with the increase of polyetherimide concentration, the elastic modulus of the asymmetric microporous film gradually increases, and the trend of change is similar to the effect of polyetherimide concentration on film density. Figure 5 The values ​​are close. This indicates that the elastic modulus of the asymmetric microporous film mainly depends on the density of the film material; the higher the polyetherimide concentration, the higher the film density and the greater the elastic modulus.

[0111] In summary, as the concentration of polyetherimide increases during the preparation process, the viscosity of the casting solution increases, leading to a decrease in the exchange rate between solvent and non-solvent during the phase inversion and film formation process. This slows down the phase separation / curing rate of polyetherimide, resulting in a decrease in film porosity, a reduction in macropore size, an increase in micropore size, and a decrease in average pore size. Simultaneously, the density of the asymmetric microporous film increases, and the elastic modulus increases accordingly. When other preparation parameters remain unchanged, changes in polyetherimide concentration have no significant effect on the thickness of the asymmetric microporous film.

[0112] (5) The thickness of the asymmetric microporous films with different coating thicknesses prepared in Example 2 was measured, and the results are as follows: Figure 8 As shown.

[0113] Depend on Figure 8 It can be seen that the thickness of the asymmetric microporous film increases with increasing coating thickness, and the two show a linear relationship. This indicates that coating thickness is the most important factor determining the thickness of the polyetherimide asymmetric microporous film.

[0114] (6) The density of asymmetric microporous films with different coating thicknesses prepared in Example 2 was measured, and the results are as follows: Figure 9 As shown.

[0115] Depend on Figure 9 It can be seen that changes in coating thickness have no significant effect on the density of the asymmetric film. Figure 5 It can be seen that the film density mainly depends on the viscosity of the casting solution, which in turn depends on the concentration of polyetherimide added during the preparation of the casting solution. Changing the coating thickness during the phase inversion film preparation process does not affect the composition of the casting solution.

[0116] (7) The porosity and average pore size of the asymmetric microporous films with different coating thicknesses prepared in Example 2 were measured, and the results are as follows: Figure 10 As shown.

[0117] Depend on Figure 10 It can be seen that when the coating thickness is 100 μm, both the porosity and average pore size of the asymmetric microporous membrane reach their maximum values; when the coating thickness is 200 μm, both the porosity and average pore size of the film reach their minimum values; as the coating thickness increases to 600 μm, the porosity and average pore size of the film gradually increase; when the coating thickness is 600–900 μm, the porosity and average pore size remain basically unchanged; when the coating thickness reaches 1000 μm, the porosity and average pore size show a decreasing trend again. This indicates that the effect of coating thickness on the pore structure of the asymmetric microporous film is not linear.

[0118] (8) The elastic modulus of the asymmetric microporous films with different coating thicknesses prepared in Example 2 was measured, and the results are as follows: Figure 11 As shown.

[0119] Depend on Figure 11 It can be seen that the coating thickness has a significant effect on the elastic modulus of asymmetric microporous films. Figure 10 The effects of coating thickness on pore size and porosity show essentially opposite trends: the elastic modulus reaches its minimum at a coating thickness of 100 μm, its maximum at 200 μm, and then gradually decreases with increasing coating thickness, stabilizing around 600–900 μm. At 1000 μm, the elastic modulus shows an increasing trend. This indicates that coating thickness affects the pore structure (pore size and porosity) of the film, further influencing the trend of elastic modulus change. The trends of pore size and porosity are exactly opposite to those of elastic modulus.

[0120] In summary, the polyetherimide concentration mainly affects the casting solution preparation process, and by changing the casting solution viscosity, the film density, porosity, average pore size and elastic modulus change accordingly. The coating thickness mainly affects the phase inversion process, and is the main factor determining the film thickness. By changing the pore structure of the film, the elastic modulus changes accordingly. In the material parameters of the asymmetric microporous film, the density is mainly controlled by the casting solution preparation process, the thickness is mainly controlled by the phase inversion process, and the pore structure (porosity, average pore size) and elastic modulus are jointly affected by the two preparation processes.

[0121] The present application can prepare films with different thickness, density, pore structure and elastic modulus by changing the polyetherimide concentration and coating thickness in the preparation process of the asymmetric microporous film, and determining the appropriate film preparation method according to the specific needs of the subsequent acoustic metamaterial application.

[0122] (9) Acoustic performance test

[0123] Three kinds of asymmetric microporous film materials were prepared by using different polyetherimide concentrations and coating thicknesses, and were denoted as film 1 to film 3. The preparation and basic performance parameters of the materials are shown in Table 2:

[0124] Table 2. Preparation and basic performance parameters of asymmetric microporous film materials

[0125]

[0126] The film 1 to film 3 were assembled into asymmetric microporous film type acoustic metamaterial unit experimental assemblies according to the above steps, and were denoted as assembly 1 to assembly 3. The impedance tube was used to test the sound absorption and sound insulation performance, and the test frequency range was 100-1600 Hz.

[0127] The specific test method is as follows:

[0128] 1. Sound absorption test: The double microphone method based on the impedance tube was used to test the sound absorption performance of the asymmetric microporous film type acoustic metamaterial, and the test device is shown in Figure 12 .

[0129] When sound waves are incident from one medium to another medium with different acoustic characteristics, reflection will occur at the interface between the two media, and part of the incident sound energy will return to the first medium. When the incident angle is oblique, the reflection angle is equal to the incident angle.

[0130] When sound encounters a large obstacle in its propagation, it will be divided into several parts. One part of the sound energy is absorbed by the obstacle, another part may be reflected, and the remaining part of the sound energy is transmitted through the obstacle. Let the total sound energy incident on the obstacle be W i, the part that can be transmitted is W t , the part that can be reflected is W r , the part of energy that can be absorbed by material consumption is W a The relationship between them can be expressed as:

[0131] W i = W t + W r + W a

[0132] Sound absorption is to reduce sound reflection by relying on the sound absorption of materials, and the sound absorption performance of sound absorption materials is usually represented by the sound absorption coefficient α:

[0133]

[0134] 2, sound insulation test: the sound insulation performance of the asymmetric microporous film type acoustic metamaterial in example 3 is tested by four microphone method based on impedance tube, the test principle is as shown in Figure 13 , the specific steps are as follows: first, make test samples and record the thickness of the samples; Then the connection of the equipment and the installation of the test piece, when installing the test piece with the positioner, it needs to be placed flat, preferably without protrusions or depressions due to excessive extrusion, and the test piece should be perpendicular to the pipe wall to ensure coaxiality; Then smear a circle of vaseline around the hard frame for sealing to prevent sound leakage; Finally, set the parameters in the analysis software and test. A complete test is divided into a and b twice, a test impedance tube end open, a test ends, b test, b test impedance tube end closed, through the software calculation can get the sound insulation performance of the material.

[0135] The evaluation index of sound insulation performance is sound insulation quantity, or called sound transmission loss (STL), unit is dB, defined as the decibel ratio of the sound energy incident on the structure and the sound energy transmitted through the structure, the calculation formula is:

[0136]

[0137] Among them, is the sound transmission coefficient, defined as the ratio of the sound energy transmitted through the sound insulation structure and the total sound energy incident on the structure, that is:

[0138]

[0139] Among them, Wt is the transmitted sound power, Wi is the incident sound power. The above formula can also be written as:

[0140]

[0141] Among them, I t and I ip represents the transmitted sound intensity and the incident sound intensity. t and p i τ represents the transmitted sound pressure and the incident sound pressure. A larger transmission coefficient τ indicates poorer sound insulation performance, while a smaller transmission coefficient τ indicates better sound insulation performance.

[0142] Test results are as follows Figures 14 to 15 As shown.

[0143] from Figure 14 As can be seen, the sound absorption performance of the asymmetric microporous thin-film acoustic metamaterial unit experimental components assembled with different thin-film materials varies significantly. Component 1 exhibits strong sound absorption peaks near 490Hz, 530Hz, 900Hz, 980Hz, 1350Hz, 1420Hz, 1440Hz, and 1540Hz, with peak sound absorption coefficients of 0.68, 0.74, 0.84, 0.53, 0.62, 0.58, 0.99, and 0.87, respectively; Component 2 exhibits strong sound absorption peaks near 880Hz, 970Hz, 1100Hz, 1360Hz, 1420Hz, and 1540Hz, with peak sound absorption coefficients of 0.99, 0.95, 0.60, 0.60, 0.97, and 0.98, respectively; and Component 3 exhibits strong sound absorption peaks near 590-600Hz, 1000Hz, 1020Hz, and 1210Hz, with peak sound absorption coefficients of 0.86, 0.97, 0.99, and 0.75, respectively. Of the three components, component 1 has the best sound absorption effect.

[0144] from Figure 15It can be seen that the sound insulation performance of the experimental assembly of the asymmetric microporous film type acoustic metamaterial unit assembled by different film materials is obviously different. Among them, the assembly 1 has relatively strong sound absorption peaks near 530Hz, 570Hz, 970Hz, 1040Hz, 1460Hz, 1480Hz and 1580Hz, and the sound insulation amounts are 21.56dB, 23.53dB, 23.16dB, 18.15dB, 20.32dB, 22.32dB and 29.44dB respectively; the assembly 2 has relatively strong sound insulation peaks near 340Hz, 360Hz and 670Hz, and the peak values of the sound insulation amounts are 12.18dB, 14.65dB and 20.22dB respectively, and there is a relatively wide sound insulation peak at 750-1180Hz, and the maximum sound insulation amount is 9.62dB; the assembly 3 has relatively strong sound absorption peaks near 518Hz, 616Hz, 820Hz, 900Hz, 950Hz, 1000Hz, 1070Hz, 1120Hz, 1460Hz and 1580Hz, and the sound absorption coefficients are 26.40dB, 28.44dB, 15.91dB, 22.95dB, 13.85dB, 22.10dB, 11.69dB, 16.88dB, 16.43dB and 27.04dB respectively. The sound insulation effect of the assembly 3 is the best among the three assemblies.

[0145] In summary, the asymmetric microporous film material is prepared by the phase inversion method in the application, the technology is mature, and the production cost of the film material is reduced.

[0146] By changing the preparation conditions of the asymmetric microporous film, the asymmetric microporous film material with different parameter performance can be obtained, and the sound absorption and sound insulation performance of the asymmetric microporous film type acoustic metamaterial can be changed, so that the effective control of specific noise can be realized by replacing different asymmetric microporous films without changing the overall structure of the acoustic metamaterial.

[0147] The asymmetric microporous film type acoustic metamaterial assembly in the application has simple structure and low assembly difficulty, has good sound absorption and sound insulation performance in the medium and low range, can be used as a noise reduction material for vehicles and buildings, and can be used in a vibration reduction device of a large machine.

[0148] In the application, the two sides of the asymmetric microporous film are in communication with each other, the pressure balance of the two sides of the film can be maintained after being assembled into an acoustic metamaterial assembly, the asymmetric microporous film is not easily affected by changes in external environmental temperature and humidity, and the use stability of the acoustic metamaterial is improved.

[0149] Although the above embodiments have been described in detail, it should be understood that these are only some embodiments of the present application but not all the embodiments. Other embodiments can be obtained according to the above embodiments without creativity, and these embodiments all belong to the protection scope of the present application.

Claims

1. An asymmetric microporous thin-film acoustic metamaterial, comprising a thin film and a framework (2), characterized in that, The film is an asymmetric microporous film (1), and also includes a back plate (4) arranged parallel to the asymmetric microporous film (1) and a support (3) connecting the frame (2) and the back plate (4); The asymmetric microporous film has a thickness of 50–500 μm and a density of 204.61–416.31 kg / m³. 3 The elastic modulus is 8.91 × 10⁻⁶. 7 ~4.01×10 8 Pa; The asymmetric microporous film has a porosity of 10-30% and a pore size of 0.01-0.5 μm on one side, and a porosity of 60-90% and a pore size of 1-5 μm on the other side.

2. The asymmetric microporous thin-film acoustic metamaterial according to claim 1, characterized in that, The diameter of the asymmetric microporous membrane (1) is 10 cm; the effective diameter of the asymmetric microporous membrane (1) within the frame (2) is 7-9 cm.

3. The asymmetric microporous thin-film acoustic metamaterial according to claim 1, characterized in that, The frame (2) is a ring frame; the frame (2) is made of stainless steel; the outer diameter of the ring frame is 10cm, the inner diameter is 7-9cm, and the thickness is 0.5-1cm.

4. The asymmetric microporous thin-film acoustic metamaterial according to claim 1, characterized in that, The back plate (4) has a diameter of 10cm and a thickness of 0.5-1cm; the back plate (4) is made of stainless steel.

5. The asymmetric microporous thin-film acoustic metamaterial according to claim 1, characterized in that, The bracket (3) is a cylindrical frame; the wall thickness of the cylindrical frame is 0.5-1cm and the length is 10-30cm; the material of the bracket (3) is stainless steel.

6. The asymmetric microporous thin-film acoustic metamaterial according to claim 1, characterized in that, The method for preparing the asymmetric microporous thin film includes the following steps: Polyetherimide powder was dissolved in an organic solvent and then degassed to obtain a casting solution; The casting solution is used to form a film, and the resulting wet film is placed in a coagulation bath for curing to obtain a cured film. The cured film was sequentially immersed in isopropanol and n-hexane and then dried to obtain an asymmetric microporous film.

7. The asymmetric microporous thin-film acoustic metamaterial according to claim 6, characterized in that, The organic solvent includes one or more of N,N-dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone; the mass ratio of the polyetherimide powder to the organic solvent is 12-25:75-88.

Images