Passively tunable double-layer thin-film acoustic metamaterial

Abstract

The application discloses a passive adjustable double-layer thin film type acoustic metamaterial and belongs to the technical field of acoustic metamaterials. The acoustic metamaterial comprises a hard frame, a thin film, a sheet mass, an adjusting rod and a bending sheet. The thin film comprises an upper thin film and a lower thin film, and the sheet mass comprises an upper sheet mass and a lower sheet mass. The adjusting rod comprises a fixed rod and a telescopic rod, and the bending sheet is fixed on both sides of the lower thin film. By cooperation of the adjusting rod and the bending sheet, the additional stiffness of the lower thin film is changed, the intrinsic modal of the upper and lower layer system is separated, and the passive adjustment of the sound insulation peak frequency is realized. The application has a simple structure, can realize wide-frequency, light-weight and adjustable sound insulation performance in a 50-1500 Hz frequency band, and effectively suppresses the medium-frequency noise of power equipment such as a hydraulic pump.

Description

Technical Field

[0001] This invention relates to the field of acoustic metamaterials technology, and more particularly to a passively tunable double-layer thin-film acoustic metamaterial. Background Technology

[0002] Traditional sound insulation materials, limited by their inherent properties, fall short in dealing with complex sound waves. In contrast, acoustic metamaterials, as an emerging technology, stand out with their unique sound wave modulation capabilities, demonstrating noise reduction potential unmatched by traditional materials. Acoustic metamaterials, represented by plate-like, honeycomb-like, and thin-film structures, have all shown great promise in sound insulation applications.

[0003] In modern industrial plants or construction machinery, the noise generated by power equipment such as hydraulic pumps has become a significant problem affecting the operating environment and surrounding areas. Particularly during gear meshing and hydraulic pulsation, significant noise frequencies are generated: around 500Hz mainly comes from gear meshing impact and pump body structural radiation, while around 1000Hz originates from hydraulic pulsation and gear radial vibration. This mid-frequency noise not only deteriorates the working environment but may also interfere with nearby sensitive areas.

[0004] Therefore, there is an urgent need for a lightweight, wide-band adjustable thin-film acoustic metamaterial in the 50Hz-1500Hz frequency range. This material can be applied to the design of sound insulation devices for industrial equipment, such as covering the housing of hydraulic pumps, installing at pipeline connections, or laying on equipment bases, to effectively suppress gear meshing noise generated during operation, further improve the auditory comfort of operators, and reduce the impact on the environment. Summary of the Invention

[0005] The purpose of this invention is to provide a passively adjustable double-layer thin-film acoustic metamaterial to solve the problems existing in the prior art.

[0006] To achieve the above objectives, the present invention provides a passively adjustable double-layer thin-film acoustic metamaterial, comprising a rigid frame, a thin film, sheet-like masses, an adjustment rod, and a bending plate; the thin film comprises an upper thin film and a lower thin film disposed on the rigid frame; the sheet-like masses comprise an upper sheet-like mass disposed on the upper thin film and a lower sheet-like mass disposed on the lower thin film; the adjustment rod comprises a fixed rod and a telescopic rod, the fixed rod being disposed inside the rigid frame, the telescopic rod being slidably connected to the fixed rod, and the end of the telescopic rod being connected to the bending plate; the bending plate comprises a left bending plate and a right bending plate, the left bending plate and the right bending plate being fixed to both sides of the lower thin film respectively; by adjusting the length of the telescopic rod, the bending state of the bending plate is changed, thereby adjusting the peak frequency of sound insulation.

[0007] Preferably, the rigid frame is made of a rigid material, including metal or synthetic resin.

[0008] Preferably, the film has a pre-tension force and is made of high-density polyethylene; the film is adhered to the inner ring of the rigid frame.

[0009] Preferably, the sheet-like mass is in the form of a thin sheet, and the material is metal or other rigid material; the upper sheet-like mass and the lower sheet-like mass are respectively disposed at the center of the upper film and the lower film by means of adhesion.

[0010] Preferably, the adjusting rod is made of a rigid material, including metal or synthetic resin.

[0011] Preferably, the curved sheet is thin and made of metal.

[0012] Preferably, the fixing rod and the rigid frame are rigidly connected, including by gluing or welding.

[0013] Preferably, the upper sheet-like mass and the lower sheet-like mass are square or circular in shape.

[0014] Preferably, the length of the telescopic rod is adjustable, and by changing the length of the adjusting rod, the bending plate can switch between an inward bending state and an outward bending state.

[0015] Preferably, the rigid frame has an inner frame side length of 26mm, an outer frame side length of 30mm, and a height of 20mm.

[0016] Compared with the prior art, the present invention has the following advantages and technical effects: The passively adjustable double-layer thin-film acoustic metamaterial provided by this invention structurally alters the acoustic characteristics of the double-layer thin-film acoustic metamaterial through the cooperation of an adjustment rod and a bending plate, thereby improving the overall sound insulation. Furthermore, the desired acoustic characteristics can be obtained by adjusting different parameters, achieving passive adjustment of the sound insulation peak frequency. It exhibits lightweight, wide-bandwidth adjustable sound insulation performance within the 50-1500Hz frequency range, making it suitable for the design of sound insulation devices for industrial equipment. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention.

[0018] Figure 1 This is a schematic diagram of the overall structure of the bending sheet in an embodiment of the present invention.

[0019] Figure 2 This is a schematic diagram of the overall structure of the bending sheet in an embodiment of the present invention when it is bent outward.

[0020] Figure 3 This is a schematic diagram of the finite element simulation model of an embodiment of the present invention.

[0021] Figure 4 This is a comparison chart of the STL calculation result curve and the mass law in an embodiment of the present invention.

[0022] In the figure: 1. Rigid frame; 2. Thin film; 21. Upper thin film; 22. Lower thin film; 3. Sheet mass; 31. Upper sheet mass; 32. Lower sheet mass; 4. Adjusting rod; 41. Fixing rod; 42. Telescopic rod; 5. Bending plate; 51. Left bending plate; 52. Right bending plate; 61. Incident acoustic cavity; 62. Transmitted acoustic cavity; 63. First plane wave radiation surface; 64. Second plane wave radiation surface. Detailed Implementation

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other. The described embodiments are merely some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0024] like Figures 1 to 4 As shown, this invention provides a passively adjustable double-layer thin-film acoustic metamaterial, comprising a rigid frame 1, a thin film 2, sheet-like masses 3, an adjusting rod 4, and a bending plate 5; the thin film 2 includes an upper thin film 21 and a lower thin film 22 disposed on the rigid frame 1; the sheet-like masses 3 include an upper sheet-like mass 31 disposed on the upper thin film 21 and a lower sheet-like mass 32 disposed on the lower thin film 22; the adjusting rod 4 includes a fixed rod 41 and a telescopic rod 42, the fixed rod 41 being disposed inside the rigid frame 1, the telescopic rod 42 being slidably connected to the fixed rod 41, and the end of the telescopic rod 42 being connected to the bending plate 5; the bending plate 5 includes a left bending plate 51 and a right bending plate 52, the left bending plate 51 and the right bending plate 52 being fixed on both sides of the lower thin film 22 respectively; by adjusting the length of the telescopic rod 42, the bending state of the bending plate 5 is changed, thereby adjusting the peak frequency of sound insulation.

[0025] This invention provides overall support through a rigid frame 1, with the thin film 2 and sheet-like mass 3 forming a vibration system. An adjusting rod 4, in conjunction with a bending plate 5, introduces additional stiffness, altering the system's equivalent stiffness and thus achieving passive adjustment of the sound insulation peak frequency, thereby improving sound insulation performance. By setting a sliding connection structure between the fixed rod 41 and the telescopic rod 42, the extension length of the telescopic rod 42 can be easily changed, thereby adjusting the bending state of the bending plate 5 and achieving continuous adjustment of the additional stiffness, ultimately achieving passive adjustment of the sound insulation peak frequency. By symmetrically arranging the left bending plate 51 and the right bending plate 52 on both sides, the lower thin film 22 is subjected to uniform additional stiffness, avoiding eccentric vibration and ensuring the stability and consistency of the acoustic metamaterial's sound insulation performance.

[0026] Further optimization of the scheme: the rigid frame 1 is made of rigid material, including metal or synthetic resin.

[0027] The rigid frame 1 is made of rigid material, which can provide stable support for the upper membrane 21 and the lower membrane 22, maintain the shape stability of the membrane, and ensure that the frame does not deform during the vibration of the acoustic metamaterial, thereby ensuring the reliability of the sound insulation performance, as well as the stability and durability of the structure, and avoiding deformation during use that affects the acoustic performance.

[0028] The scheme is further optimized so that the film 2 has pre-tension and is made of high-density polyethylene; the film 2 is pasted on the inner ring of the rigid frame 1.

[0029] By giving the upper film 21 and the lower film 22 pretension and using high-density polyethylene material, the film can be given appropriate stiffness and elasticity, enabling it to generate effective vibration modes under acoustic excitation. At the same time, the pretension helps to improve the stability of the film's resonant frequency, thereby obtaining good sound insulation characteristics.

[0030] Further optimization of the scheme: the sheet mass 3 is in the form of a thin sheet, and the material is metal or other rigid material; the upper sheet mass 31 and the lower sheet mass 32 are respectively set at the center of the upper film 21 and the lower film 22 by an adhesive method.

[0031] The upper sheet mass 31 and the lower sheet mass 32 are made of thin sheet brass material, which can increase the local mass density and make the film generate a negative dynamic mass density effect at a specific frequency, thereby forming a sound insulation peak; the high density characteristics of brass help to reduce the resonant frequency and broaden the sound insulation frequency band.

[0032] Further optimization of the design: the material of the adjusting rod 4 is a rigid material, including metal or synthetic resin.

[0033] The selection of material for the adjusting rod 4 ensures stability and accuracy during the adjustment process, preventing deformation that could lead to adjustment failure.

[0034] Further optimization of the design: the curved sheet 5 is a thin sheet made of metal.

[0035] The bending plate 5 is made of aluminum, which has good elastic deformation ability and can produce stable bending deformation under the action of the adjusting rod 4, introducing controllable additional stiffness.

[0036] The design is further optimized so that the fixing rod 41 and the rigid frame 1 are rigidly connected, including by gluing or welding.

[0037] By using rigid connection methods such as adhesive bonding or welding to fix the fixing rod 41 to the rigid frame 1, it can be ensured that the adjusting rod 4 does not undergo relative displacement during vibration, thus ensuring the accurate transmission of additional stiffness and improving the accuracy and repeatability of sound insulation peak frequency adjustment.

[0038] Further optimization of the scheme: the upper sheet-like mass 31 and the lower sheet-like mass 32 are square or circular in shape.

[0039] By setting the upper sheet mass 31 and the lower sheet mass 32 to square or circular, the appropriate shape can be selected according to the actual processing conditions and sound insulation requirements. Square sheet masses are easy to cut and position, while circular sheet masses are isotropic, which helps to simplify design and simulation analysis, and are easy to process and install.

[0040] The design was further optimized so that the length of the telescopic rod 42 is adjustable. By changing the length of the adjusting rod 4, the bending piece 5 can switch between the inward bending state and the outward bending state.

[0041] By changing the length of the adjusting rod 4, the bending direction (inward or outward) and degree of bending of the bending piece 5 can be controlled, thereby changing the additional stiffness of the lower film 22, causing the intrinsic modes of the upper and lower systems to separate, realizing the shift of the sound insulation peak frequency to high or low frequencies, and meeting the sound insulation requirements of different noise sources.

[0042] Further optimization of the design: the inner frame of rigid frame 1 has a side length of 26mm, the outer frame has a side length of 30mm, and the height is 20mm.

[0043] The specific dimensions of the rigid frame 1 ensure a compact structure, facilitating integration into the sound insulation devices of industrial equipment while meeting the sound insulation requirements of specific frequency bands.

[0044] The scheme is further optimized so that the thickness of the upper film 21 and the lower film 22 is 0.1 mm, the thickness of the upper sheet mass 31 and the lower sheet mass 32 is 0.2 mm, and the side length is 15 mm.

[0045] By setting the thickness of the upper film 21 and the lower film 22 to 0.1 mm, and the thickness of the upper sheet mass 31 and the lower sheet mass 32 to 0.2 mm and the side length to 15 mm, optimized sound insulation performance can be obtained in the 50-1500 Hz frequency band, while ensuring lightweight structure, which is convenient for installation and use in actual engineering.

[0046] The passively adjustable double-layer thin-film acoustic metamaterial provided by this invention is implemented as follows: First, prepare a rigid frame 1. This frame is made of ABS resin material with a density ρ = 1160 kg / m³. 3 The elastic modulus E = 2.3 × 10⁻⁶ 9 Pa, Poisson's ratio ν = 0.38, inner frame side length 26mm, outer frame side length 30mm, height 20mm, internally equipped with two crossbeams connecting and fixing rods 41, crossbeam width 2mm, height 1mm. The upper film 21 and lower film 22 are respectively fixed to the inner ring of the rigid frame 1 by adhesive bonding. The film material is HDPE (high-density polyethylene), density ρ = 1200kg / m³. 3 The elastic modulus E = 0.36 × 10 9 Pa, Poisson's ratio ν = 0.32, film side length 26 mm, thickness 0.1 mm, and pre-tension applied. Then, the upper sheet mass 31 is fixed to the center of the upper film 21 by adhesive bonding, and the lower sheet mass 32 is fixed to the center of the lower film 22 by adhesive bonding. The sheet mass material is brass with a density ρ = 8960 kg / m³. 3 Elastic modulus E = 11 × 10 9 Pa, Poisson's ratio ν = 0.35, side length 15mm, thickness 0.2mm. Next, the fixing rod 41 is fixed to the crossbeam inside the rigid frame 1 by adhesive bonding. The fixing rod 41 is made of aluminum and has a radius of 0.5mm. The telescopic rod 42 is slidably connected to the fixing rod 41. The telescopic rod 42 is also made of aluminum and has a radius of 0.5mm. The material parameters of the adjusting rod 4 are: density ρ = 2700kg / m³. 3 Elastic modulus E = 70 × 10 9 Pa; Poisson's ratio ν = 0.33. The left curved sheet 51 and the right curved sheet 52 are fixed to both sides of the lower film 22 by adhesive bonding. The curved sheet material is aluminum with a density ρ = 2700 kg / m³. 3 Elastic modulus E = 70 × 10 9 Pa; Poisson's ratio ν = 0.33, thickness 0.2 mm, outer ring radius 15.94 mm, inner ring radius 15.74 mm; finally, connect the lower end of the telescopic rod 42 to the bending piece 5.

[0047] During use, the bending state (inward or outward) of the bending piece 5 is changed by adjusting the length of the telescopic rod 42 according to the target noise frequency. When the length of the telescopic rod 42 is small, the bending piece 5 is in an inward bending state. At this time, the additional stiffness of the lower film 22 is small, the system resonance frequency is low, and the sound insulation peak is located in the lower frequency band. When the length of the telescopic rod 42 is increased, the bending piece 5 gradually becomes an outward bending state, the additional stiffness increases, the resonance frequency of the lower system shifts upward, causing the intrinsic modes of the upper and lower systems to separate, and the sound insulation peak frequency shifts to a higher frequency.

[0048] To analyze the sound insulation characteristics of this thin-film acoustic metamaterial, the acoustic-solid coupling and piezoelectric effect frequency domain analysis module of the large-scale commercial finite element software COMSOL Multiphysics 6.2 was used. The entire finite element simulation model consists of three parts: the incident acoustic cavity 61, the double-layer thin-film acoustic metamaterial, and the transmission acoustic cavity 62. When a plane sound wave is incident from the first plane wave radiation surface 63, passes through the thin-film acoustic metamaterial, and exits from the second plane wave radiation surface 64, the incident acoustic cavity 61 contains the incident sound pressure Pi and the reflected sound pressure Pr, and the transmission acoustic cavity 62 contains the transmitted sound pressure Pt. Therefore, the normal incident sound transmission loss STL can be calculated.

[0049] in, For incident sound energy; For transmitting sound energy, p i and p t These are the incident sound pressure and the transmitted sound pressure, respectively. ρ 0 represents the density of air. c 0 represents the speed of sound in air. The incident sound pressure is defined as 1 Pa, the frequency sweep range is 50 Hz to 1500 Hz, and the step size is 10 Hz.

[0050] Thin-film acoustic metamaterials possess a negative dynamic mass density, resulting in a sound insulation peak. However, this peak is only generated at specific frequencies and has a narrow sound insulation bandwidth. This invention utilizes a double-layer thin-film acoustic metamaterial, replacing the traditional mass block with a sheet mass 3. An adjustment rod 4 is added to fix the center position of the lower sheet mass 32, causing the upper sheet mass 31 and the lower sheet mass 32 to exhibit different intrinsic modes, thus broadening the sound insulation bandwidth of the metamaterial.

[0051] In the double-layer thin-film structure of the present invention, the upper and lower thin films are respectively attached with sheet-like masses, and the lower thin film has curved plates on both sides, which are connected to a rigid frame via adjusting rods. This structure can be equivalent to a two-degree-of-freedom vibration system, and its equation of motion can be expressed as: in,m 1 , m 2 The equivalent mass of the upper and lower sheet-like layers. k 1 、k 2 Equivalent stiffness of the upper and lower thin films k c This is the additional stiffness introduced by the adjusting rod through the bending plate; x 1 、x 2 The displacement of the upper and lower sheet-like masses; F 1 , F 2 The excitation force is the sound pressure.

[0052] By solving this system of equations, the resonant frequency of the system can be obtained as follows: in, .

[0053] Because the adjusting rod introduces additional stiffness through the bending plate, the equivalent stiffness of the lower system increases, and its resonant frequency shifts upward, causing the intrinsic modes of the upper and lower systems to separate. By adjusting the length of the telescopic rod and changing the bending state of the bending plate, the additional stiffness can be altered, thereby adjusting the sound insulation peak frequency and obtaining the desired acoustic characteristics.

[0054] For a direct comparison, finite element simulations were performed on the sound insulation of the thin-film acoustic metamaterial in this example. The sound insulation without a metal substrate and that of a homogeneous plate with the same surface density were also calculated. Simulation results show that the average sound insulation in the inward-bending state is 25.20 dB, an increase of 1.93 dB compared to the homogeneous plate with the same surface density. When the length of the telescopic rod 42 increases, the bending plate 5 changes from an inward-bending state to an outward-bending state. While the sound insulation peak frequency shifts to higher frequencies, the average sound insulation increases to 29.08 dB, an increase of 5.81 dB compared to the homogeneous plate with the same surface density. This demonstrates that the double-layer thin-film acoustic metamaterial provided by this invention exhibits excellent sound insulation performance in the 50-1500 Hz frequency range, and the sound insulation peak frequency can be adjusted passively, effectively suppressing mid-frequency noise around 500 Hz and 1000 Hz generated by power equipment such as hydraulic pumps.

[0055] In summary, this invention utilizes a double-layer thin-film structure in conjunction with an adjusting rod 4 and a bending plate 5 to achieve intrinsic mode separation by altering the additional stiffness, thereby obtaining wideband adjustable sound insulation characteristics. This structure is simple, lightweight, and easy to implement, and can be widely applied in industrial equipment soundproof enclosures, pipeline soundproof coverings, equipment base soundproof pads, and other applications, significantly improving the auditory comfort of the operating environment.

[0056] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A passively adjustable double-layer thin-film acoustic metamaterial, characterized in that, The system includes a rigid frame (1), a thin film (2), sheet mass (3), an adjusting rod (4), and a bending sheet (5); the thin film (2) includes an upper thin film (21) and a lower thin film (22) disposed on the rigid frame (1); the sheet mass (3) includes an upper sheet mass (31) disposed on the upper thin film (21) and a lower sheet mass (32) disposed on the lower thin film (22); the adjusting rod (4) includes a fixing rod (41) and a telescopic rod (42), the fixing rod (41) The telescopic rod (42) is slidably connected to the fixed rod (41) inside the rigid frame (1), and the end of the telescopic rod (42) is connected to the bending piece (5). The bending piece (5) includes a left bending piece (51) and a right bending piece (52), which are respectively fixed on both sides of the lower film (22). The bending state of the bending piece (5) is changed by adjusting the length of the telescopic rod (42), thereby adjusting the peak frequency of the sound insulation.

2. The passively adjustable double-layer thin-film acoustic metamaterial according to claim 1, characterized in that, The rigid frame (1) is made of a rigid material, including metal or synthetic resin.

3. The passively adjustable double-layer thin-film acoustic metamaterial according to claim 1, characterized in that, The film (2) has a pre-tension force and is made of high-density polyethylene; the film (2) is attached to the inner ring of the rigid frame (1).

4. The passively adjustable double-layer thin-film acoustic metamaterial according to claim 1, characterized in that, The sheet mass (3) is in the form of a thin sheet and is made of metal or other rigid materials; the upper sheet mass (31) and the lower sheet mass (32) are respectively disposed at the center of the upper film (21) and the lower film (22) by means of adhesion.

5. The passively adjustable double-layer thin-film acoustic metamaterial according to claim 1, characterized in that, The adjusting rod (4) is made of a rigid material, including metal or synthetic resin.

6. The passively adjustable double-layer thin-film acoustic metamaterial according to claim 1, characterized in that, The curved sheet (5) is thin and made of metal.

7. The passively adjustable double-layer thin-film acoustic metamaterial according to claim 1, characterized in that, The fixing rod (41) is rigidly connected to the rigid frame (1), including by gluing or welding.

8. The passively adjustable double-layer thin-film acoustic metamaterial according to claim 1, characterized in that, The upper sheet mass (31) and the lower sheet mass (32) are square or circular in shape.

9. The passively adjustable double-layer thin-film acoustic metamaterial according to claim 1, characterized in that, The length of the telescopic rod (42) is adjustable. By changing the length of the adjusting rod (4), the bending piece (5) can switch between an inward bending state and an outward bending state.

10. The passively tunable bilayer thin-film acoustic metamaterial according to claim 1, characterized in that, The rigid frame (1) has an inner frame side length of 26mm, an outer frame side length of 30mm, and a height of 20mm.

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