Dynamic adjustable acoustic filter based on acoustic metamaterial
By filling the Helmholtz resonator cavity with liquid medium to regulate the equivalent acoustic metamaterial, the problem that existing acoustic metamaterial filters cannot be dynamically adjusted is solved, and fast and convenient acoustic performance regulation is achieved, which is suitable for a variety of application scenarios.
Patent Information
- Application Number
- CN202510618194.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-14
- Publication Date
- 2025-07-11
AI Technical Summary
The existing acoustic metamaterial acoustic filter design based on Helmholtz resonators cannot be dynamically adjusted, resulting in the filtering range of the acoustic band gap curing, making it difficult to adapt to the needs of complex and variable acoustic scenes. The mechanical adjustment scheme has structural complexity, reliability problems and high energy consumption.
By filling the cavity of the Helmholtz resonator with different liquid media, such as water, petroleum, ethanol, etc., the equivalent acoustic impedance of the acoustic metamaterial is regulated, and fast and convenient acoustic performance regulation is achieved to avoid mechanical structural changes.
It realizes dynamic adjustment with rapid response, broadens the scope of regulation, reduces manufacturing costs, improves the flexibility and practicality of acoustic devices, and is suitable for mechanical equipment, aerospace and other fields.
Smart Images
Figure CN120299440A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of acoustic metamaterials, and particularly relates to a dynamically tunable acoustic filter based on acoustic metamaterials. Background Art
[0002] The existing acoustic metamaterial acoustic filter designs based on Helmholtz resonators mainly rely on static structures with fixed geometric parameters. The core method is to reverse design or optimize parameters such as the neck diameter and cavity volume of the resonator through simulation calculations to pre-determine the distribution range of the acoustic bandgap. However, such methods have the following limitations:
[0003] Non-adjustability: Helmholtz resonators are usually made of rigid materials (such as metals, polymers), and their geometric parameters are fixed after processing. Once formed, it is impossible to dynamically adjust the neck or cavity size by physical means, resulting in the filtering range of the acoustic bandgap being completely solidified and difficult to adapt to the requirements of complex and changing acoustic scenarios.
[0004] Technical barriers to dynamic regulation: Although theoretically, the parameters of the resonator can be adjusted by mechanical drive devices (such as micro motors, piezoelectric ceramics), in practical applications, there are extremely high technical thresholds: (a) Structural complexity: It is necessary to integrate precision mechanical components (such as telescopic mechanisms, transmission devices), which greatly increases the design complexity and manufacturing cost; (b) Reliability issues: Long-term mechanical adjustment is likely to cause component wear or failure, affecting the regulation accuracy; (c) Response speed and energy consumption: The response time of mechanical adjustment is usually long (in the order of seconds), and continuous external energy supply is required, making it difficult to meet real-time dynamic requirements.
[0005] In summary, current acoustic metamaterials based on Helmholtz resonators generally lack the ability of dynamic regulation without structural modification, and their acoustic bandgap characteristics are solidified after manufacturing, severely limiting their application potential in fields such as noise control and adaptive filtering. Therefore, there is an urgent need for an acoustic metamaterial design method with simple process, low cost, and support for dynamic adjustment. Summary of the Invention
[0006] Object of the Invention: The object of the present invention is to provide a dynamically tunable acoustic filter based on acoustic metamaterials. By selecting different liquid media to fill the metamaterial cavity, the equivalent acoustic impedance of the acoustic metamaterial is directly regulated, thereby changing the position and width of the bandgap, and realizing fast, convenient, and reversible regulation of acoustic performance without changing the geometric structure of the metamaterial.
[0007] Technical solution: A dynamically tunable acoustic filter based on acoustic metamaterials of the present invention includes N unit arrays arranged periodically and made of rigid materials; each unit array includes a waveguide section and a Helmholtz resonator connected thereto; the Helmholtz resonator includes a neck and a cavity, and the cavity is filled with a medium. Avoid mechanical structure modification and improve the flexibility and practicability of acoustic devices.
[0008] Further, the medium filled in the cavity is a liquid with a density ρ = 500 - 1500 kg / m 3 and a sound velocity c = 300 - 1500 m / s, including water, petroleum, and ethanol.
[0009] Further, the lattice size L of the unit array is 4 - 8 mm; the diameter l of the waveguide section is 1 - 6 mm.
[0010] Further, the diameter 2a1 of the neck is 1 - 3 mm, and the height d1 of the neck is 0.3 - 3 mm.
[0011] Further, the diameter 2a2 of the cavity is 3 - 6 mm, the height d2 of the cavity is 2 - 8 mm, and the volume V = πa2 2 d2.
[0012] Further, the range of N is 50 - 100.
[0013] Further, the rigid material is a metal steel plate.
[0014] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages:
[0015] 1. Avoid mechanical structure modification and simplify the process: Replace structural parameters with material parameters, break through the physical limitations of mechanical regulation, and there is no risk of loss of moving parts, especially suitable for applications such as mechanical equipment, aerospace, and noise reduction in metal processing;
[0016] 2. Fast dynamic response and wide regulation range: Conventional mechanical adjustment schemes require a long response time. The present invention can achieve a fast response through liquid medium replacement, support multi-medium mixing to realize continuous offset of the center frequency of the bandgap within a certain range, and adapt to complex acoustic scenarios.
[0017] 3. High compatibility and potential for intelligent expansion: Once the geometric structure of the existing design is manufactured, it is difficult to adjust. The present invention can be compatible with the upgrade of the existing Helmholtz resonator (only need to add a medium filling port), and can achieve full-automatic regulation through a microfluidic chip or an electronically controlled medium, and is suitable for noise reduction in metal processing, adaptive filtering equipment, etc.
[0018] 4. Convenient manufacturing: Adopt a simple structure of connecting a waveguide to a Helmholtz resonator and can be mass-produced.
[0019] Energy-free: Different from active noise cancellation systems, this metamaterial achieves noise reduction through its physical structure without the need for additional energy input, ensuring long-term stability and reliability.
[0020] 5. Dynamic regulation of material parameters: The filtering range can be adjusted in real time without physical modification to meet complex and changing acoustic requirements;
[0021] 6. Process simplification and universality: Without complex driving devices, it has low manufacturing costs, is compatible with the upgrade of existing Helmholtz structures, and can be extended to intelligent acoustic systems (such as microfluidic control, medical ultrasound);
[0022] 7. Multi-parameter collaborative optimization: Based on the non-linear coupling effect, the position and bandwidth of the stopband can be controlled, breaking through the discretization limitations of traditional fixed-structure designs. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Figure 1 : Schematic diagram of the geometric parameter annotation structure of the basic unit of the dynamically tunable acoustic filter;
[0024] Figure 2 : Schematic cross-sectional view of the finite element model for numerical calculation of the dynamically tunable acoustic filter;
[0025] Figure 3 : (a) Band structure (b) Frequency response curve of sound waves in the metamaterial acoustic filter when the medium is water;
[0026] Figure 4 : (a) Band structure (b) Frequency response curve of sound waves in the metamaterial acoustic filter when the medium is oil;
[0027] Figure 5 : (a) Band structure (b) Frequency response curve of sound waves in the metamaterial acoustic filter when the medium is ethanol. DETAILED DESCRIPTION OF THE INVENTION
[0028] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings.
[0029] The present invention proposes a design of an acoustic filter for an acoustic metamaterial that dynamically regulates the sound wave stopband through a liquid medium. The metamaterial is composed of periodically arranged units, and each unit contains a waveguide section and a Helmholtz resonator connected thereto. Each Helmholtz resonator unit has fixed geometric parameters (neck diameter, cavity volume), and a replaceable liquid medium filling port is preset in the cavity. The main technical features of this metamaterial are as follows:
[0030] Structural Design: The acoustic metamaterial filter consists of an array of N periodically arranged units made of rigid materials and a replaceable liquid medium inside the cavity. Among them, the lattice size of the periodic unit is L, the diameter of the waveguide is l, and the resonator includes a neck (diameter 2a1, height d1) and a cavity (cavity height d2, diameter 2a2, volume V = πa2 2 d2). The medium filled in the cavity is a liquid (such as water, petroleum, ethanol) with a density ρ = 500 - 1500 kg / m 3 and a sound speed c = 300 - 1500 m / s.
[0031] Bandgap Regulation: By changing the material parameters of the filled medium, the equivalent acoustic impedance of the acoustic metamaterial is regulated, thereby adjusting the frequency range of the transmitted acoustic bandgap.
[0032] Working Principle:
[0033] (1) Bandgap Formation Mechanism: When Helmholtz resonators are arranged in a periodic structure, the interaction between their resonance characteristics and the structural periodicity forms a locally resonant bandgap. Near the resonance frequency of the Helmholtz resonator, the acoustic wave energy is strongly absorbed or reflected, forming a stopband. At this time, the metamaterial exhibits an equivalent negative density or negative bulk modulus, preventing the propagation of acoustic waves.
[0034] (2) Coupling Effect and Parameter Influence:
[0035] Lattice Constant L: A smaller L enhances the coupling between units and broadens the local resonance bandgap; a larger L may introduce a Bragg bandgap. The focus of this invention is on the low-frequency bandgap dominated by local resonance. By adjusting L, the Bragg effect is suppressed, highlighting the role of local resonance.
[0036] Number of Units N: Increasing the number of units makes the bandgap more significant (such as a lower transmission coefficient) and reduces the fluctuation effect.
[0037] Numerical simulation results show that when N ≥ 50, this gain effect will not be significant.
[0038] This acoustic metamaterial is composed of one-dimensional periodically arranged units, and each unit contains a waveguide section and a Helmholtz resonator. The resonator consists of a short neck (acoustic mass) and a cavity (acoustic capacitance), forming a resonant system similar to an LC circuit. The cross-sectional area of the resonator neck should be small enough, and it can be assumed that the resonator is connected along the waveguide point. The unit is made of metal (steel plate), and it can be assumed that the boundary is a rigid wall. The sound wave propagates along the direction of the periodic structure arrangement, and all components are independent of other directions. When the wavelength is large enough compared to the transverse dimension of the pipe, the sound wave transmitted inside the combined waveguide can be approximated as one-dimensional and propagating along the periodic extension direction. When the frequency of the incident wave is lower than the cut-off frequency of the waveguide, it can be assumed to be a plane wave. In this case, the sound wave propagating in the waveguide is very similar to the electromagnetic wave propagating in a transmission line. The voltage difference across the circuit part corresponds to the pressure difference across the acoustic element, and the current at each point in the circuit corresponds to the volume velocity of the fluid in the acoustic element.
[0039] The resonant frequency f of the resonator h is determined by the neck mass M ha and the cavity acoustic capacitance C ha and thus the resonant frequency can be expressed as:
[0040]
[0041] When the frequency of the incident sound wave approaches f h , the resonator undergoes strong resonance, resulting in the exchange of kinetic energy (fluid vibration in the neck) and potential energy (cavity compression) of the sound wave, generating localized energy absorption. Therefore, the center frequency of the bandgap is mainly determined by the geometric parameters of the resonator (neck length, cavity volume), independent of the wavelength, and is applicable to sub-wavelength scale control. Each periodic unit is divided into two parts, namely the waveguide and the LC equivalent circuit. Due to the short neck, the part acting as an inductor can be expressed as M ha =ρd1 / S1, and the capacitance of the resonant cavity corresponds to the capacitance C ha =S2d2 / ρc 2 to represent, where ρ is the density of the fluid, c is the speed of sound in the liquid medium, a1 and d1 are the radius and length of the short neck, a2 and d2 are the radius and length of the resonator cavity, and are the cross-sectional areas of the short neck and the cavity respectively. When the resonator is coupled with the waveguide, the subsequent radiation effect should be included. Due to acoustic radiation, the short neck may become "longer", and the equivalent additional mass is the radiation mass. So the effective length of the short neck must be modified to d effect =d1 + 1.7a1, and thus the resonant frequency can be expressed as
[0042]
[0043] It can be seen that the physical properties (density ρ and sound velocity c) of the fluid medium filled in the acoustic metamaterial can affect the equivalent acoustic parameters, and further regulate the frequency-domain distribution of the bandgap and the width of the forbidden band, where:
[0044] Effect of density ρ: When ρ increases, M ha increases, while C ha decreases, resulting in an increase in the resonance frequency and a shift of the bandgap towards the high-frequency direction (blue shift);
[0045] Effect of sound velocity c: When c increases, C ha significantly decreases, thereby increasing the resonance frequency and also causing a blue shift of the bandgap.
[0046] The following specifically illustrates the bandgap regulation method and effect of the present invention through specific embodiments:
[0047] Material selection: A periodic structural unit is composed of a rigid material (1 mm thick steel), and the cavity is filled with a liquid medium.
[0048] Structural design: The acoustic metamaterial is constructed by periodically arranging N basic units along the x-axis direction. Each periodic unit is a waveguide connected to a Helmholtz resonator, and the cross-section is as shown in Figure 1 . Among them, the lattice size L is 4 mm, the waveguide diameter l is 4 mm, the neck diameter 2a1 of the Helmholtz resonator is 2 mm, the neck height d1 is 1 mm, the cavity diameter 2a2 is 3.14 mm, and the cavity height d2 is 5 mm. The fluid in the waveguide part and the fluid medium material in the Helmholtz resonator can be replaced with different liquid media. The cross-section of the finite element model for the numerical calculation of the acoustic wave transmission simulation in the dynamically tunable acoustic filter of the acoustic metamaterial based on this is as shown in Figure 2 .
[0049] Example 1:
[0050] Filling medium: Water (density ρ w = 998 kg / m 3 , c w = 1483 m / s);
[0051] Structural parameters: Fix the geometric parameters of the metamaterial structure, lattice size L = 4 mm, waveguide diameter l = 4 mm, neck diameter 2a1 of the Helmholtz resonator = 2 mm, neck height d1 = 1 mm, cavity diameter 2a2 = 3.14 mm, cavity height d2 = 5 mm;
[0052] Test environment: The acoustic metamaterial acoustic filter is composed of 55 periodic units, and the boundary is a rigid wall.
[0053] Experimental results:
[0054] Inject water into the resonator cavity and the waveguide to ensure that the medium is completely filled. Calculate the eigenvibrations of the acoustic metamaterial lattice through a finite element model, solve for the eigenvalues, and obtain the acoustic wave band structure diagram as shown in Figure 3 (a). In the frequency band under investigation, it can be observed that there is a relatively obvious band gap (the gray-marked part in the figure), with its upper frequency being 64.85 kHz, its lower frequency being 45.395 kHz, and the band gap width d wW being 19.455 kHz, and the center frequency f 0W being 55.123 kHz.
[0055] For a better suppression effect, considering the process and cost at the same time, select the number of periods N to be 55. Use finite element software to construct a metamaterial acoustic filter with rigid walls at the boundaries, calculate the sound pressure change of the model, and the frequency response curve is as shown in the gray area of Figure 3 (b). A relatively obvious band gap appears at the same position, and the transmitted signal decays efficiently in the periodic extension direction.
[0056] Example 2:
[0057] Filling medium: Petroleum (density ρ O = 580 kg / m 3 , c O = 347 m / s);
[0058] Structural parameters: The same as in Example 1;
[0059] Test environment: The same as in Example 1.
[0060] Experimental results:
[0061] After draining the water medium, inject petroleum to ensure that there are no air bubbles in the cavity and the medium is completely filled. Calculate the eigenvibrations of the acoustic metamaterial lattice through a finite element model, solve for the eigenvalues, and obtain the acoustic wave band structure diagram as shown in Figure 4 (a). In the frequency band under investigation, it can be observed that there is a relatively obvious band gap (the gray-marked part in the figure), with its upper frequency being 60.41 kHz, its lower frequency being 42.29 kHz, and the band gap width d wO being 18.13 kHz, and the center frequency f 0O being 51.35 kHz.
[0062] For a better suppression effect, considering the process and cost at the same time, select the number of periods N to be 55. Use finite element software to construct a metamaterial acoustic filter with rigid walls at the boundaries, calculate the sound pressure change of the model, and the frequency response curve is as shown in the gray area of Figure 4 (b). A relatively obvious band gap appears at the same position, and the transmitted signal decays efficiently in the periodic extension direction.
[0063] Example 3:
[0064] Filling medium: ethanol (density ρ E = 789 kg / m 3 , c E = 1168 m / s);
[0065] Structural parameters: the same as those in Example 1;
[0066] Test environment: the same as those in Example 1.
[0067] Experimental results:
[0068] After draining the water medium, inject petroleum to ensure that there are no air bubbles in the cavity and the medium is completely filled. Calculate the eigenvibration of the acoustic metamaterial lattice through the finite element model, solve the eigenvalue, and obtain the acoustic wave energy band structure diagram as shown in Figure 5 (a). In the frequency band under investigation, it can be observed that there is a relatively obvious band gap (the gray marked part in the figure), the upper frequency of which is 51.09 kHz, the lower frequency is 35.79 kHz, and the band gap width d wE is 15.3 kHz, and the central frequency f 0E is 43.44 kHz.
[0069] For better suppression effect, considering the process and cost at the same time, the number of periods N is selected as 55. Use finite element software to construct a metamaterial acoustic filter with a rigid wall boundary, calculate the sound pressure change of the model, and the frequency response curve is as shown in the gray area of Figure 5 (b). A relatively obvious band gap appears at the same position, and the transmitted signal decays efficiently in the periodic extension direction.
[0070] Example 4:
[0071] Filling medium: glycerol (density ρ G = 1260 kg / m 3 , c G = 1920 m / s);
[0072] Structural parameters: the same as those in Example 1;
[0073] Test environment: the same as those in Example 1.
[0074] Experimental results:
[0075] After draining the water medium, inject glycerol to ensure that there are no air bubbles in the cavity and the medium is completely filled. Calculate the eigenvibration of the acoustic metamaterial lattice through the finite element model, solve the eigenvalue, and obtain the acoustic wave energy band structure diagram as shown in Figure 6 (a). In the frequency band under investigation, it can be observed that there is a relatively obvious band gap (the gray marked part in the figure), the upper frequency of which is 84.16 kHz, the lower frequency is 58.92 kHz, and the band gap width d wGis 25.24 kHz, and the center frequency f 0G is 71.54 kHz.
[0076] For better suppression effect, considering the process and cost at the same time, the number of periods N is selected to be 55. Use finite element software to construct a metamaterial acoustic filter with rigid walls at the boundaries, calculate the sound pressure change of the calculation model, and the frequency response curve is as shown in the gray area in Figure 6 (b), and a relatively obvious band gap appears at the same position, and the transmitted signal is efficiently attenuated in the periodic extension direction.
Claims
1. A dynamically tunable acoustic filter based on acoustic metamaterials, characterized in that, It includes an array of N periodically arranged units made of a rigid material; each unit array includes a waveguide section and a Helmholtz resonator connected thereto; the Helmholtz resonator includes a neck and a cavity, and the cavity is filled with a medium.
2. The dynamic tunable acoustic filter based on acoustic metamaterials according to claim 1, characterized in that, The cavity is filled with a medium which is a liquid with a density ρ = 500 - 1500 kg / m 3 and a sound velocity c = 300 - 1500 m / s, including water, petroleum, and ethanol.
3. The dynamic tunable acoustic filter based on acoustic metamaterials according to claim 1, characterized in that, The diameter 2a1 of the neck is 1 - 3 mm, and the height d1 of the neck is 0.3 - 3 mm.
4. An acoustically tunable acoustic filter based on acoustic metamaterials according to claim 1, characterized in that, The diameter 2a2 of the cavity is 3 - 6 mm, the height d2 of the cavity is 2 - 8 mm, and the volume V = πa2 2 d2.
5. The dynamic tunable acoustic filter based on acoustic metamaterials according to claim 1, characterized in that, The lattice size L of the unit array is 4 - 8 mm; the diameter l of the waveguide section is 1 - 6 mm.
6. The dynamic tunable acoustic filter based on acoustic metamaterials according to claim 1, characterized in that The range of N is 50 - 100.
7. The dynamic tunable acoustic filter based on acoustic metamaterials according to claim 1, characterized in that, The rigid material is a metal steel plate.