Low frequency acoustic metamaterials based on multi-order helmholtz cavity

Abstract

This invention provides a low-frequency acoustic metamaterial based on a multi-order Helmholtz cavity, belonging to the field of acoustic noise reduction technology. By setting a cylindrical inner cavity within the outer shell, and using multiple radial partitions to divide the inner cavity into circumferentially arranged fan-shaped resonant cavities corresponding one-to-one with the target low-frequency frequencies, and in conjunction with corresponding connected neck openings and an embedded structure composed of longitudinally staggered nested plates, a multi-layered, sequentially connected damping cavity is formed. This solves the problems of traditional noise reduction structures being unable to simultaneously match multiple discrete low-frequency noise points, the tendency of multi-unit stacking to generate harmful acoustic coupling, and the difficulty in balancing low-frequency noise reduction efficiency and structural compactness. It achieves the technical effects of realizing precise, coupling-free control of multi-frequency low-frequency noise within a single compact structure, improving sound energy dissipation efficiency, and maintaining structural miniaturization and high stability.

Description

Technical Field

[0001] This invention belongs to the field of acoustic noise reduction technology, and more specifically, it relates to a low-frequency acoustic metamaterial based on a multi-order Helmholtz cavity. Background Technology

[0002] The noise generated by substation operation has typical discrete spectrum characteristics, with its energy highly concentrated in the power frequency harmonic bands such as 100Hz, 200Hz, and 400Hz. This type of low-frequency noise is difficult to attenuate effectively due to its long wavelength and strong penetrating power, and is a major source of pollution affecting the surrounding acoustic environment quality.

[0003] Traditional resonant structures such as Helmholtz resonators can only be designed for a single frequency and cannot cover multiple discrete harmonic frequency bands at the same time. If the frequency response range is broadened by simply stacking resonant units of different sizes, it will not only cause structural redundancy, but also cause strong near-field acoustic coupling between units, resulting in resonant peak frequency shift and deterioration of noise reduction performance. It is impossible to achieve precise and coordinated noise control at target frequencies such as 100Hz, 200Hz and 400Hz. Summary of the Invention

[0004] The purpose of this invention is to provide a low-frequency acoustic metamaterial based on a multi-order Helmholtz cavity, which aims to achieve precise noise reduction of different low-frequency noises without coupling.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: to provide a low-frequency acoustic metamaterial based on a multi-order Helmholtz cavity, comprising: The outer shell body has a cylindrical inner cavity; Multiple radial partitions are arranged at an angle in the cylindrical inner cavity, dividing the cylindrical inner cavity into multiple sector-shaped resonant cavities that correspond one-to-one with the target frequency; the multiple sector-shaped resonant cavities are arranged circumferentially around the axis of the outer shell body; Multiple neck openings are spaced apart on the outer shell body, and each of the multiple neck openings corresponds to a multiple of the fan-shaped resonant cavities, and is used to connect the fan-shaped resonant cavities and the external sound field; The embedded structure includes at least two nested plates spaced apart within the fan-shaped resonant cavity, with adjacent nested plates staggered longitudinally, and the embedded structure divides the fan-shaped resonant cavity into multiple layers of sequentially connected damping cavities.

[0006] In another embodiment of this application, the nesting plate is fixedly connected to the top plate or bottom plate of the outer shell body.

[0007] In another embodiment of this application, the nesting plate includes: The upper nesting plate is connected to the top plate of the outer shell body, and the lower end of the upper nesting plate is spaced apart from the bottom plate of the outer shell body. The upper nesting plate and the bottom plate form a first channel connecting two adjacent shock-absorbing cavities. The lower nesting plate is connected to the bottom plate of the outer shell body. The upper end of the lower nesting plate is spaced apart from the top plate of the outer shell body. A second channel connecting two adjacent shock-absorbing cavities is formed between the lower nesting plate and the top plate. The first channel and the second channel are alternately set.

[0008] In another embodiment of this application, the outer casing body includes: The upper shell includes an upper circumference plate, which is arranged around the outer periphery of the top plate and extends downward; the neck opening is formed on the top plate; The lower housing includes a lower enclosure plate, which is arranged around the outer periphery of the bottom plate and extends upward. The lower enclosure plate is connected to the upper enclosure plate and forms the cylindrical inner cavity with the help of the bottom plate and the top plate. The upper nesting plate is fixed to the lower end of the top plate, and the lower nesting plate is fixed to the upper end of the bottom plate; and the heights of the upper and lower nesting plates are the same and less than the height of the cylindrical inner cavity.

[0009] As another embodiment of this application, the upper housing and the lower housing can be connected by welding or hot-melt.

[0010] In another embodiment of this application, the cavity volume of the plurality of sector resonant cavities is inversely proportional to the square of the corresponding plurality of target frequencies.

[0011] As another embodiment of this application, for the three types of core low-frequency noise of 100Hz, 200Hz and 400Hz, the cylindrical inner cavity is divided into three fan-shaped resonant cavities, and the volume ratio of the three fan-shaped resonant cavities is 1:1 / 4:1 / 16.

[0012] In another embodiment of this application, the neck opening is a circular hole.

[0013] As another embodiment of this application, it also includes: The neck tube is fixedly connected to the top plate of the outer shell body, and the inner cavity of the neck tube forms the neck opening.

[0014] In another embodiment of this application, the radial partition extends radially along the outer shell body, with one end of the radial partition extending to the central axis of the outer shell body and the other end fixed to the inner sidewall of the outer shell body.

[0015] The beneficial effects of the low-frequency acoustic metamaterial based on a multi-order Helmholtz cavity provided by this invention are as follows: Compared with the prior art, the low-frequency acoustic metamaterial based on a multi-order Helmholtz cavity of this invention forms a cylindrical inner cavity inside its outer shell. A radial partition located in the cylindrical inner cavity connects the axis of the outer shell to the inner wall of the outer shell, and its upper end extends to the top plate of the outer shell and its lower end extends to the bottom plate of the outer shell, dividing the cylindrical inner cavity into multiple sector-shaped resonant cavities. Each sector-shaped resonant cavity corresponds to a frequency for which noise reduction is required. Each sector-shaped resonant cavity is connected to a neck, which is used to connect to the external sound field. Sound waves enter the sector-shaped resonant cavity through the neck and are attenuated and dissipated within the sector-shaped resonant cavity.

[0016] Each sector resonant cavity can be tuned independently without interference, allowing for precise alignment with the target frequency. Structurally, this blocks the acoustic energy transmission path between different sector resonant cavities, preventing near-field acoustic coupling. Dividing the cylindrical inner cavity of the outer shell into independent sector resonant cavities, multiple sector resonant cavities are integrated within the same shell. This sector-shaped partitioning and nesting structure design achieves efficient space utilization, eliminating the need for externally stacked independent modules. This allows the entire noise reduction structure to maintain a minimum total volume while possessing multi-frequency control capabilities, with the overall size remaining at the subwavelength scale. This perfectly resolves the contradiction between low-frequency noise reduction and device miniaturization.

[0017] The nested plates of the embedded structure are arranged longitudinally in an alternating pattern, creating multiple layers of continuous and interconnected damping cavities inside the fan-shaped resonant cavity. After the sound waves enter the fan-shaped resonant cavity through the neck opening, they will propagate along the meandering path formed by the staggered nested plates, and be transmitted back and forth between the multiple layers of damping cavities, extending the propagation distance of the sound waves in the cavity, while increasing the contact area between the sound waves and the inner wall of the structure, so that the sound energy is continuously dissipated through the viscosity effect and the thermal conduction effect during the propagation process.

[0018] This invention utilizes multiple independent fan-shaped resonant cavities to correspond to different target low frequencies, achieving precise noise reduction at multiple frequency points. The physical separation effect of the radial partition completely eliminates harmful acoustic coupling between multiple resonant units, avoiding resonance peak frequency shift and noise reduction performance degradation, ensuring stable and reliable noise reduction effects at each frequency point, and solving the problem that traditional noise reduction structures cannot simultaneously match multiple discrete low-frequency noise points. The multi-layer damping cavity formed by the embedded structure extends the sound wave propagation path and increases the sound energy dissipation area, improving broadband sound energy dissipation capability on the basis of low-frequency resonance noise reduction, and enhancing the overall noise reduction effect. The circumferentially arranged fan-shaped resonant cavities make full use of the cylindrical internal cavity space, eliminating the need to stack multiple independent modules, achieving structural compactness and miniaturization, adapting to space-limited application scenarios such as substations, balancing low-frequency noise reduction efficiency and structural compactness, while meeting the requirements of multi-frequency collaborative control, no coupling interference, and lightweight structure, significantly improving the applicability and reliability of low-frequency acoustic noise reduction. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the noise reduction structure provided in an embodiment of the present invention; Figure 2 A schematic cross-sectional view of the noise reduction structure provided in an embodiment of the present invention along the horizontal direction; Figure 3 For along Figure 2 Sectional view of line AA in the middle; Figure 4 The sound insulation curve provided for the embodiments of the present invention; Figure 5 The streamline diagram of the sound pressure level at 100Hz provided in the embodiment of the present invention; Figure 6 The streamline diagram of the sound pressure level at 200Hz provided in the embodiment of the present invention; Figure 7 The streamline diagram of the sound pressure level at 400Hz is provided for an embodiment of the present invention.

[0021] In the diagram: 1. Upper shell; 2. Lower shell; 3. Neck; 4. Upper partition; 5. Lower partition; 6. Lower nesting plate; 7. Upper nesting plate. Detailed Implementation

[0022] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0023] Please see Figures 1 to 7The low-frequency acoustic metamaterial based on a multi-order Helmholtz cavity provided by this invention will now be described. The low-frequency acoustic metamaterial based on a multi-order Helmholtz cavity includes a shell body, multiple radial partitions, multiple neck openings 3, and multiple sets of embedding structures. The shell body has a cylindrical inner cavity; the radial partitions are angled within the cylindrical inner cavity, dividing it into multiple sector-shaped resonant cavities corresponding to target frequencies; the multiple sector-shaped resonant cavities are arranged circumferentially around the axis of the shell body; the neck openings 3 are spaced apart on the shell body, each corresponding to a sector-shaped resonant cavity, and are used to connect the sector-shaped resonant cavities to the external sound field; the embedding structure includes at least two nested plates spaced apart within the sector-shaped resonant cavities, with adjacent nested plates staggered longitudinally, dividing the sector-shaped resonant cavities into multiple layers of sequentially connected damping cavities.

[0024] Traditional resonant structures such as the Helmholtz resonator can be designed for a single frequency and cannot cover multiple discrete harmonics at the same time.

[0025] To address this problem, this application proposes a noise reduction structure. The interior of the outer shell forms a cylindrical cavity. A radial partition within this cavity connects the axis of the outer shell to its inner wall, extending from its upper end to the top plate and its lower end to the bottom plate. This divides the cylindrical cavity into multiple sector-shaped resonant cavities, each corresponding to a desired noise reduction frequency. Each sector-shaped resonant cavity is connected to a neck opening 3, which connects to an external sound field. Sound waves enter the sector-shaped resonant cavity through the neck opening 3 and are attenuated and dissipated within the cavity.

[0026] Each sector resonant cavity can be tuned independently without interference, allowing for precise alignment with the target frequency. Structurally, this blocks the acoustic energy transmission path between different sector resonant cavities, preventing near-field acoustic coupling. Dividing the cylindrical inner cavity of the outer shell into independent sector resonant cavities, multiple sector resonant cavities are integrated within the same shell. This sector-shaped partitioning and nesting structure design achieves efficient space utilization, eliminating the need for externally stacked independent modules. This allows the entire noise reduction structure to maintain a minimum total volume while possessing multi-frequency control capabilities, with the overall size remaining at the subwavelength scale. This perfectly resolves the contradiction between low-frequency noise reduction and device miniaturization.

[0027] An embedded structure is provided within each sector-shaped resonant cavity. The embedded structure includes at least two nested plates, which are nested in layers and spaced apart. The shape of the nested plates is similar to that of the sector-shaped resonant cavity, dividing the sector-shaped resonant cavity into at least two layers of damping cavities. Due to the longitudinal staggered arrangement of the nested plates, adjacent damping cavities are sequentially connected. The arrangement of the nested plates within the sector-shaped resonant cavity forms a tortuous transmission channel.

[0028] The nested plates of the embedded structure are arranged longitudinally in an alternating manner, forming a multi-layered continuous damping cavity inside the fan-shaped resonant cavity. After the sound wave enters the fan-shaped resonant cavity through the neck 3, it will propagate along the meandering path formed by the staggered nested plates, and be transmitted back and forth between the multi-layer damping cavities, extending the propagation distance of the sound wave in the cavity, while increasing the contact area between the sound wave and the inner wall of the structure, so that the sound energy is continuously dissipated through the viscosity effect and the thermal conduction effect during the propagation process.

[0029] Each sector-shaped resonant cavity, relying on its independent space and dedicated neck 3, generates Helmholtz resonance effect for the corresponding target frequency. When resonance occurs, the sound energy is highly localized in the cavity and converted into heat energy. Sound waves of non-target frequencies are reflected due to acoustic impedance mismatch. The multi-layer embedded structure and independent resonant cavities work together to achieve synchronous processing of noise at multiple frequencies.

[0030] The low-frequency acoustic metamaterial based on a multi-order Helmholtz cavity provided by this invention, compared with the prior art, can correspond to different target low frequencies through multiple independent fan-shaped resonant cavities, achieving precise noise reduction at multiple frequency points; the physical separation effect of the radial partition completely eliminates harmful acoustic coupling between multiple resonant units, avoids resonance peak frequency shift and noise reduction performance degradation, and ensures stable and reliable noise reduction effect at each frequency point, solving the problem that traditional noise reduction structures cannot simultaneously match multiple discrete low-frequency noise frequency points; the multi-layer damping cavity formed by the embedded structure extends the sound wave propagation path and increases the sound energy dissipation area, improving the broadband sound energy dissipation capability on the basis of low-frequency resonance noise reduction, and enhancing the overall noise reduction effect; the circumferentially arranged fan-shaped resonant cavities make full use of the cylindrical inner cavity space, eliminating the need to stack multiple independent modules, achieving structural compactness and miniaturization, adapting to space-limited application scenarios such as substations, balancing low-frequency noise reduction efficiency and structural compactness, while meeting the usage requirements of multi-frequency collaborative control, no coupling interference, and lightweight structure, significantly improving the applicability and reliability of low-frequency acoustic noise reduction.

[0031] The outer casing can be made of a standing wave tube with a wall thickness of 2mm.

[0032] The radial baffle extends radially along the outer shell body, with one end extending to the central axis of the outer shell body and the other end fixed to the inner sidewall of the outer shell body.

[0033] In some possible embodiments, please refer to Figures 1 to 3 The nesting plate is fixedly connected to the top or bottom plate of the outer shell.

[0034] Radial baffles divide the cylindrical inner cavity into independent sector-shaped resonant cavities. Nested plates fixed to the top or bottom plate form stable partitions inside the resonant cavities. Their positions and orientations are not affected by sound wave excitation or external vibrations, and they always maintain a longitudinally staggered arrangement, ensuring that the spatial shape and connection path of the multi-layer damping cavity remain constant.

[0035] The fixedly connected nested plate and the outer shell form an integral rigid boundary, which will not generate additional structural vibration under the action of low frequency sound waves, avoid secondary noise caused by component vibration, and at the same time ensure that there is no gap between the nested plate and the outer shell to prevent sound energy from leaking from the connection gap, thus ensuring the acoustic sealing of the resonant cavity and the damping cavity.

[0036] By fixing the nesting plates to the top or bottom plate and adjusting the height of the nesting plates to achieve longitudinal staggering, and forming a channel between the free end of the nesting plates and the inner wall of the outer shell body, the shock-absorbing cavities on both sides are connected.

[0037] The nested plate includes an upper nested plate 7 and a lower nested plate 6. The upper nested plate 7 is connected to the top plate of the outer shell body, and the lower end of the upper nested plate 7 is spaced apart from the bottom plate of the outer shell body, forming a first channel connecting two adjacent damping cavities between the upper nested plate 7 and the bottom plate; the lower nested plate 6 is connected to the bottom plate of the outer shell body, and the upper end of the lower nested plate 6 is spaced apart from the top plate of the outer shell body, forming a second channel connecting two adjacent damping cavities between the lower nested plate 6 and the top plate; the first channel and the second channel are alternately arranged.

[0038] The first channel below the upper nested plate 7 and the second channel above the lower nested plate 6 are arranged alternately, so that the multi-layer shock-absorbing cavities form a series connected structure.

[0039] The outer shell provides a closed inner cavity, and the radial partition separates independent fan-shaped resonant cavities. The neck 3 guides external sound waves into the resonant cavity. After entering, the sound waves first contact the first layer of nested plates, and then enter the next layer of damping cavity through the first or second channel. They are transmitted layer by layer along the alternating channels, forming a meandering propagation trajectory in the cavity.

[0040] As the sound waves propagate within the channel and damping cavity, they continuously contact the nested plates and the inner wall of the resonant cavity, and the sound energy is continuously dissipated through viscous resistance and heat conduction. At the same time, the fan-shaped resonant cavity generates Helmholtz resonance at the target frequency. The resonance effect and the channel dissipation effect work together to achieve dual processing of the target low-frequency noise.

[0041] Nested plates enclose multiple layers of damping cavities, which resemble the shape of a fan-shaped resonant cavity. Depending on the position of the neck 3, the volume of each damping cavity is consistent or increases proportionally from the inside out.

[0042] Optionally, the nested plate encloses a sub-cavity with a similar outline to the fan-shaped cavity, centered on the neck opening 3. The size of the nested plate increases radially from the inside to the outside along the cylindrical cavity of the noise reduction structure. This arrangement around the neck opening 3 allows sound waves to quickly enter the sound energy dissipation structure after entering the fan-shaped resonant cavity, improving energy utilization efficiency. The sub-cavities enclosed by the nested plate have the same outline as the fan-shaped cavity, maximizing the use of internal space and avoiding gaps that conflict with the structure. The gradual increase in size from the inside to the outside allows sound waves to travel radially layer by layer, gradually extending the propagation distance and enhancing the dissipation effect, achieving continuous and progressive energy consumption. This structure is highly compatible with the fan-shaped resonant cavity and does not interfere with the uniform distribution and stable excitation of the dual resonant modes.

[0043] The nested plates increase the propagation distance and spatial complexity of sound waves within the fan-shaped resonant cavity. Sound waves must repeatedly pass through the propagation channels enclosed by the upper and lower nested plates, during which time they continuously lose energy due to viscosity and thermal conduction.

[0044] In some possible embodiments, please refer to Figures 1 to 3 The outer shell body includes an upper shell 1 and a lower shell 2. The upper shell 1 includes an upper circumferential plate, which is arranged around the outer periphery of the top plate and extends downward; a neck opening 3 is opened on the top plate; the lower shell 2 includes a lower circumferential plate, which is arranged around the outer periphery of the bottom plate and extends upward, the lower circumferential plate is connected to the upper circumferential plate and forms a cylindrical inner cavity with the help of the bottom plate and the top plate; an upper nested plate 7 is fixed to the lower end of the top plate, and a lower nested plate 6 is fixed to the upper end of the bottom plate; and the heights of the upper nested plate 7 and the lower nested plate 6 are the same and less than the height of the cylindrical inner cavity.

[0045] The outer shell adopts a split design of upper shell 1 and lower shell 2. The upper and lower enclosures are connected to each other, forming a closed and regular cylindrical inner cavity with the top and bottom plates, providing precise installation space for radial partitions and nested plates.

[0046] The neck opening 3 is located on the top plate and corresponds one-to-one with the fan-shaped resonant cavities, precisely guiding external sound waves into the corresponding resonant cavities and ensuring the stability of the incident direction and position of the sound waves. The upper nested plate 7 is fixed to the lower end of the top plate and the lower nested plate 6 is fixed to the upper end of the bottom plate. They are of the same height and less than the height of the inner cavity, forming a multi-layered damping cavity with uniform height and sequential connection.

[0047] The combination of the split shell and the fixed nesting plate makes the internal acoustic structure and the outer shell form a rigid whole. The fan-shaped resonant cavity separated by the radial partition and the damping cavity separated by the nesting plate maintain independent acoustic function in the closed inner cavity. After the sound wave enters through the neck 3, it propagates in a detour along the preset channel, and the sound energy is continuously dissipated. At the same time, each resonant cavity generates Helmholtz resonance for the target frequency, and the dual effect achieves efficient noise reduction.

[0048] The connection between the upper and lower enclosures ensures the airtightness of the inner cavity, preventing sound energy from leaking out of the shell gaps. The height of the nested plates is adapted to the inner cavity size, maximizing the use of space and improving acoustic performance without increasing the overall volume.

[0049] Optionally, the upper shell 1 and the lower shell 2 can be connected by welding or hot-melt, that is, the upper and lower enclosures are fixed by welding or hot-melt connection.

[0050] The noise reduction structure can use polylactic acid (PLA) as the core structural material. PLA possesses excellent 3D printing suitability, moderate density and stiffness, and can form a near-rigid boundary with high acoustic impedance in the target low-frequency range, ensuring that acoustic energy is mainly dissipated through intracavity resonance. The environmentally friendly and low-cost characteristics of PLA also facilitate large-scale applications. The noise reduction structure can be fabricated using 3D printing technology.

[0051] Based on the properties of polylactic acid (PLA) material and standard testing conditions, the parameters of the noise reduction structure can be determined as follows: The noise reduction structure can be evaluated by placing it in a standing wave tube with a radius of 50 mm; the radial partition has a wall thickness of 2 mm and an axial height of 50 mm; the top plate, bottom plate, and upper and lower surrounding plates of the noise reduction structure have a thickness of 10 mm; each neck opening 3 is a circular hole with a neck opening radius of 2 mm. The nested plate has a wall thickness of 2 mm and an axial height of 42 mm.

[0052] The radial partition includes an upper partition 4 and a lower partition 5. The upper partition 4 is located inside the upper housing 1, and the lower partition 5 is fixed inside the lower housing 2. During installation, the upper partition 4 and the lower partition 5 are connected to divide the cylindrical cavity into multiple sector-shaped resonant cavities.

[0053] In some possible embodiments, please refer to Figure 2 The volume of multiple sector-shaped resonant cavities is inversely proportional to the square of the corresponding multiple target frequencies.

[0054] Based on the rule that volume is inversely proportional to the square of frequency, radial partitions divide the cylindrical cavity into sector-shaped resonant cavities corresponding to different target frequencies. The Helmholtz resonance frequency is inversely proportional to the square root of the cavity volume; therefore, the volume of each sector-shaped resonant cavity must be precisely matched to the corresponding target frequency to ensure that the resonant cavity produces the strongest resonance effect at the target frequency.

[0055] For the three core low-frequency noises of 100Hz, 200Hz and 400Hz, the cylindrical inner cavity is divided into three sector-shaped resonant cavities, and the volume ratio of the three sector-shaped resonant cavities is 1:1 / 4:1 / 16.

[0056] The frequency ratios of 100Hz, 200Hz, and 400Hz are 1:2:4, the frequency square ratio is 1:4:16, and the corresponding cavity volume ratio is 1:1 / 4:1 / 16. The radial partition divides the cylindrical inner cavity into three independent sector-shaped resonant cavities according to this ratio. Each cavity corresponds to a core target frequency point, and the neck opening 3 corresponds one-to-one with the resonant cavity to guide the sound wave incidence.

[0057] The three resonant cavities are physically isolated and have no mutual acoustic coupling, generating efficient Helmholtz resonances at 100Hz, 200Hz, and 400Hz respectively. The multi-layer damping cavity with embedded structure assists in dissipating sound energy. The three work together to achieve precise and efficient noise reduction for the three types of core low-frequency noise in the substation.

[0058] The position of the radial baffle is set according to the cavity volume ratio, and the volume ratio is converted into a non-uniform central angle distribution of the cylindrical cavity. The occupancy of each sector resonant cavity by the 2mm thick baffle is strictly compensated through iterative calculation to confirm the final angle of the sector resonant cavity and ensure the accuracy of the tuning frequency of each sector resonant cavity.

[0059] The modeling and iteration process can use acoustic finite element simulation software, such as COMSOL Multiphysics and ANSYS. The total volume of the cylindrical cavity of the noise reduction structure, the thickness of the partition, and the theoretical volume ratio are used as initial input parameters to establish a fully parametric three-dimensional geometric model. The partition angle, the circumferential dimension of the fan-shaped resonant cavity, and the effective volume are defined as adjustable design variables, so that the model can be automatically updated with the variables.

[0060] The volume of the partition is extracted from the parametric model, and the volume occupied by each partition on the fan-shaped cavities on both sides is calculated. The theoretical effective volume is defined as the target output. Then, a variable-driven iterative method is used, with the ratio of the actual effective volume to the theoretical volume as the optimization objective and the circumferential angle of the partition as the iterative variable. The software's built-in optimization solver performs iterative calculations, gradually correcting the partition angle until the effective volume of each cavity meets the theoretical ratio requirement.

[0061] Finally, the iterative geometric model is substituted into the Helmholtz resonant frequency formula for acoustic calculation to verify whether the target frequency is accurately matched. If there is a deviation, the septum angle and neck parameters are adjusted until the resonant frequency is completely consistent with the target frequency.

[0062] During the modeling and iterative calculation, the thickness of multiple baffles in the cylindrical cavity of the noise reduction structure is calculated iteratively at the same time, and the cavity angle of all sector resonant cavities is adjusted synchronously.

[0063] For example, when modeling and iterating the three fan-shaped resonant cavities in the noise reduction structure for three types of core low-frequency noise (100Hz, 200Hz, and 400Hz), additional angle compensation is given to the cavity of the fan-shaped resonant cavity corresponding to 400Hz, and synchronous fine-tuning is performed on the cavity of the fan-shaped resonant cavity corresponding to 200Hz and the cavity of the fan-shaped resonant cavity corresponding to 100Hz. This effectively counteracts the influence of the partition volume and ensures the accuracy of the tuning frequency of each cavity.

[0064] Ultimately, each of the fan-shaped cavities distributed in this non-uniform proportion constitutes a Fabry-Perot resonator, while simultaneously connecting with the external sound field through its neck opening to form a Helmholtz resonator. The two are coupled to form a Helmholtz-Fabry-Perot composite resonator system, thereby generating extremely strong acoustic impedance at their respective target frequencies, achieving precise control of specific low-frequency noise.

[0065] In some possible embodiments, please refer to Figures 1 to 2 The neck opening 3 is a round hole.

[0066] The final frequency of each sector resonator is precisely tuned by the neck length. After optimization, the neck lengths corresponding to different target frequencies are determined as follows: 11.4 mm for the sector resonator at 100 Hz, 9.2 mm for the sector resonator at 200 Hz, and 3.81 mm for the sector resonator at 400 Hz.

[0067] To allow for adjustment of the neck opening length, a neck tube is provided at the neck opening 3. The neck tube is fixedly connected to the top plate of the outer shell body, and the inner cavity of the neck tube forms the neck opening 3.

[0068] The neck size directly determines the Helmholtz resonant frequency, acoustic impedance, and peak value, making it a core adjustable parameter of the dual-resonance system. Precise tuning of the neck size can compensate for manufacturing errors and equivalent parameter variations caused by the nested structure, ensuring the actual resonant frequency perfectly matches the target frequency. The tuned neck 3, combined with the fan-shaped resonant cavity and the nested path extension structure, achieves optimal harmony. The nested structure handles broadband dissipation, while the resonant system handles peak attenuation, forming a complete and coordinated noise reduction mechanism.

[0069] After completing the main cavity segmentation and path extension structure design based on volume ratio, the neck parameters of each sector resonant cavity need to be finally tuned. Based on the Helmholtz resonant frequency formula and considering the equivalent increase in neck length caused by the nested plate path, the geometric dimensions of the neck are finely adjusted using the finite element parametric scanning method. This allows for the systematic determination of the optimal parameter combination of the neck structure in the simulation environment, ensuring that the entire noise reduction structure produces a sharp and accurate sound insulation or sound absorption peak at the target frequency.

[0070] Neck size simulation and parameter optimization can be performed using acoustic finite element simulation software, including COMSOL Multiphysics, ANSYS, etc.

[0071] The neck opening width, length, and wall thickness are set as adjustable parameters and integrated with the fan-shaped resonant cavity and nested path extension structure to establish a fully parametric acoustic simulation model. Mesh refinement is performed on key areas such as the neck opening, nested plates, and resonant cavity to ensure calculation accuracy. A frequency domain solver is set up to calculate sound transmission loss or absorption coefficient curves. Using the neck opening geometry as a variable, multiple sets of parameter scans are performed within the design range to obtain acoustic response curves corresponding to different neck opening parameters. Sound insulation / absorption peak values ​​at 100Hz, 200Hz, and 400Hz are extracted to determine if the peak position and amplitude meet design requirements. If the peak value is offset or insufficient, the neck opening dimension parameters are adjusted, and the simulation calculation is repeated until the target frequency peak value is accurate and stable, thus determining the final neck opening dimension parameters.

[0072] The simulation effect of low-frequency noise reduction using the low-frequency acoustic materials in this application is as follows: Figures 4 to 7 As shown.

[0073] The noise reduction method and structure in this invention can be used in a variety of noise reduction scenarios, such as targeted management of discrete noise in substations and power facilities, performance improvement of low-frequency sound barriers for rail transit and urban elevated roads, characteristic noise control of industrial rotating machinery, low-frequency acoustic optimization of high-end audiovisual spaces, and lightweight sound insulation design for aerospace and ship cabins.

[0074] In targeted management of discrete noise from substations and power facilities, noise reduction structures are used as core units to directly construct compact sound barriers or transformer silencing kits that target power frequency harmonics such as 100Hz, 200Hz, and 400Hz, replacing traditional broadband and bulky structures with precise frequency matching.

[0075] To improve the performance of low-frequency sound barriers for rail transit and urban elevated roads, a noise reduction structure with a customized frequency can be embedded inside the sound barrier panel to specifically suppress the characteristic low-frequency line spectrum noise radiated by train wheel and rail and bridge vibrations, significantly improving the sound insulation of key frequency bands without increasing the thickness and weight of the barrier.

[0076] For the control of characteristic noise of industrial rotating machinery, the noise reduction structure can be manufactured as the inner lining module of the pipe silencer or equipment soundproof cover. By tuning, its resonance peak is aligned with the fundamental frequency and main harmonics of the equipment such as fans and pumps, and prominent discrete noise is directly attenuated from the propagation path.

[0077] For low-frequency acoustic optimization in high-end audiovisual spaces, the noise reduction structure can be used as a highly efficient, thin low-frequency trap in professional acoustic environments such as recording studios and audio-visual rooms. It can accurately absorb specific standing waves in the 63Hz-250Hz range and optimize low-frequency response without taking up too much space.

[0078] For lightweight sound insulation design of aerospace and ship cabins, noise reduction structures can be integrated into aircraft cabin walls and ship cabin sound insulation structures. Under strict weight and thickness constraints, they can specifically improve the isolation performance of low-frequency engine noise and improve cabin acoustic comfort.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-frequency acoustic metamaterial based on a multi-order Helmholtz cavity, characterized in that, include: The outer shell body has a cylindrical inner cavity; Multiple radial partitions are arranged at an angle in the cylindrical inner cavity, dividing the cylindrical inner cavity into multiple sector-shaped resonant cavities that correspond one-to-one with the target frequency; the multiple sector-shaped resonant cavities are arranged circumferentially around the axis of the outer shell body; Multiple neck openings are spaced apart on the outer shell body, and each of the multiple neck openings corresponds to a multiple of the fan-shaped resonant cavities, and is used to connect the fan-shaped resonant cavities and the external sound field; The embedded structure includes at least two nested plates spaced apart within the fan-shaped resonant cavity, with adjacent nested plates staggered longitudinally, and the embedded structure divides the fan-shaped resonant cavity into multiple layers of sequentially connected damping cavities.

2. The low-frequency acoustic metamaterial based on a multi-order Helmholtz cavity as described in claim 1, characterized in that, The nesting plate is fixedly connected to the top or bottom plate of the outer shell body.

3. The low-frequency acoustic metamaterial based on a multi-order Helmholtz cavity as described in claim 1, characterized in that, The nesting plate includes: The upper nesting plate is connected to the top plate of the outer shell body, and the lower end of the upper nesting plate is spaced apart from the bottom plate of the outer shell body. The upper nesting plate and the bottom plate form a first channel connecting two adjacent shock-absorbing cavities. The lower nesting plate is connected to the bottom plate of the outer shell body. The upper end of the lower nesting plate is spaced apart from the top plate of the outer shell body. A second channel connecting two adjacent shock-absorbing cavities is formed between the lower nesting plate and the top plate. The first channel and the second channel are alternately set.

4. The low-frequency acoustic metamaterial based on a multi-order Helmholtz cavity as described in claim 3, characterized in that, The outer shell body includes: The upper housing includes an upper circumference plate, which is arranged around the outer periphery of the top plate and extends downward; the neck opening is formed on the top plate; The lower housing includes a lower enclosure plate, which is arranged around the outer periphery of the bottom plate and extends upward. The lower enclosure plate is connected to the upper enclosure plate and forms the cylindrical inner cavity with the help of the bottom plate and the top plate. The upper nesting plate is fixed to the lower end of the top plate, and the lower nesting plate is fixed to the upper end of the bottom plate; and the heights of the upper and lower nesting plates are the same and less than the height of the cylindrical inner cavity.

5. The low-frequency acoustic metamaterial based on a multi-order Helmholtz cavity as described in claim 4, characterized in that, Therefore, the upper shell and the lower shell can be connected by welding or hot melting.

6. The low-frequency acoustic metamaterial based on a multi-order Helmholtz cavity as described in claim 1, characterized in that, The cavity volume of the plurality of sector resonant cavities is inversely proportional to the square of the corresponding plurality of target frequencies.

7. The low-frequency acoustic metamaterial based on a multi-order Helmholtz cavity as described in claim 6, characterized in that, For the three types of core low-frequency noise at 100Hz, 200Hz and 400Hz, the cylindrical inner cavity is divided into three fan-shaped resonant cavities, and the volume ratio of the three fan-shaped resonant cavities is 1:1 / 4:1 / 16.

8. The low-frequency acoustic metamaterial based on a multi-order Helmholtz cavity as described in claim 1, characterized in that, The neck opening is a round hole.

9. The low-frequency acoustic metamaterial based on a multi-order Helmholtz cavity as described in claim 1, characterized in that, Also includes: The neck tube is fixedly connected to the top plate of the outer shell body, and the inner cavity of the neck tube forms the neck opening.

10. The low-frequency acoustic metamaterial based on a multi-order Helmholtz cavity as described in claim 1, characterized in that, The radial partition extends radially along the outer shell body, with one end extending to the central axis of the outer shell body and the other end fixed to the inner sidewall of the outer shell body.

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