A multilayer composite acoustic modulation structure with a double-sided gradient metasurface and its design and manufacturing method.

Abstract

This invention discloses a multilayer composite acoustic control structure with a double-sided gradient metasurface and its design and manufacturing method, relating to the field of acoustic metamaterials and structural sound insulation technology. Specifically, the structure includes, along the sound wave propagation direction, a first metal plate layer, a first porous sound-absorbing material layer, a first air layer, a double-sided gradient metasurface layer, a second air layer, a second porous sound-absorbing material layer, and a second metal plate layer, arranged symmetrically. This invention effectively suppresses cavity standing wave resonance and significantly improves broadband sound insulation performance and oblique incidence sound insulation stability by utilizing the mass barrier of the metal plate layer, the energy dissipation of the porous material layer, and the phase modulation and mode conversion of the double-sided gradient metasurface layer, combined with the acoustic coupling buffering effect of the independent air layer. Compared with existing structures, this invention improves sound insulation by 20-40 dB, achieving synergistic optimization of sound absorption and sound insulation without increasing structural thickness and mass.

Description

Technical Field

[0001] This invention relates to the field of acoustic metamaterials and structural sound insulation technology, and in particular to a multilayer composite acoustic control structure with a double-sided gradient metasurface and its design and manufacturing method, for use in broadband noise control and high-performance sound insulation applications under complex sound field conditions. Background Technology

[0002] With the development of modern industry and transportation systems, noise problems generated by various equipment, vehicles and engineering structures during operation are becoming increasingly prominent. Especially in aerospace, rail transportation and building envelopes, it is necessary to meet the requirements of lightweight and compact structure, as well as broadband and high-efficiency sound insulation and noise control. The engineering requirements are becoming increasingly stringent.

[0003] In existing sound insulation structures, single-layer metal plates rely on the mass law for sound insulation, which is acceptable in the mid-to-high frequency range. However, their sound insulation is limited in the low-frequency and mid-low-frequency ranges, and they are easily affected by resonance and coincidence effects caused by the coupling of the plate's bending modes with airborne sound waves, leading to a significant decrease in sound insulation and making it difficult to meet broadband sound insulation requirements. To improve performance, multi-layer composite structures are often used, introducing air layers or porous sound-absorbing material layers between the metal plates, hoping to improve sound insulation through impedance mismatch and energy dissipation. However, traditional multi-layer plates often form significant cavity standing waves and coupled resonances, especially creating a sound insulation "trough" in the mid-frequency range. Increasing the cavity thickness can alleviate this to some extent, but it significantly increases the structural thickness and mass. While porous materials have good sound absorption effects in the mid-to-high frequency range, they are difficult to significantly improve the overall sound insulation performance in the low-frequency range, and fully filled porous materials often sacrifice structural compactness. Meanwhile, the acoustic metamaterials and acoustic metasurfaces developed in recent years have shown that by using subwavelength structures to control the phase and propagation modes of sound waves, anomalous reflection, refraction and surface wave excitation can be achieved under ultrathin conditions. However, related studies have mostly focused on sound absorption or beam manipulation, with insufficient attention paid to their system coupling and synergistic mechanism with traditional multilayer sound insulation structures.

[0004] There is still a lack of a structural form and design method in the current technology that can introduce a double-sided gradient metasurface into a multi-layer composite structure under the constraints of limited thickness and mass, while taking into account both sound absorption and sound insulation, suppressing cavity standing waves and improving the stability of oblique incidence sound insulation. Summary of the Invention

[0005] In view of the problems of insufficient sound insulation performance in the mid-to-low frequency range, easy generation of cavity standing wave resonance, and poor sound insulation stability under oblique incident sound field, the present invention proposes a multi-layer composite acoustic control structure with double-sided gradient metasurface and its design and manufacturing method.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] This invention provides a multilayer composite acoustic control structure with a double-sided gradient metasurface and its design and manufacturing method, comprising, in sequence along the sound wave propagation direction: a first metal plate layer, a first porous sound-absorbing material layer, a first air layer, a double-sided gradient metasurface layer, a second air layer, a second porous sound-absorbing material layer, and a second metal plate layer;

[0008] The dual-sided gradient metasurface layer is disposed at the center of the multi-layer composite acoustic control structure. The first air layer and the second air layer are respectively disposed on both sides of the dual-sided gradient metasurface layer. The first porous sound-absorbing material layer is disposed between the first metal plate layer and the first air layer. The second porous sound-absorbing material layer is disposed between the second metal plate layer and the second air layer, so that the overall structure is symmetrically arranged along the dual-sided gradient metasurface layer.

[0009] The first air layer and the second air layer are independent acoustic coupling buffers, used to prevent the porous sound-absorbing material layer from covering the acoustic channel entrance of the double-sided gradient metasurface layer, and to ensure that the incident sound wave is effectively coupled into the interior of the double-sided gradient metasurface layer.

[0010] The dual-sided gradient metasurface layer is a planar gradient metasurface structure used to introduce a spatial phase gradient to achieve acoustic wave mode conversion, perform phase modulation on the incident sound wave and achieve acoustic wave mode conversion. Combined with the mass barrier effect of the first metal plate layer and the second metal plate layer, and the energy dissipation effect of the first porous sound-absorbing material layer and the second porous sound-absorbing material layer, it achieves coordinated control of sound absorption and sound insulation of the incident sound wave.

[0011] Furthermore,

[0012] The dual-sided gradient metasurface layer includes an incident-side gradient metasurface and an exit-side gradient metasurface. The incident-side gradient metasurface is used to gradient-modulate the phase distribution, propagation direction, or equivalent acoustic impedance of the incident sound wave. The exit-side gradient metasurface is used to perform secondary modulation on the sound wave after propagation through the multi-layer composite acoustic modulation structure to suppress sound wave transmission. The dual-sided gradient metasurface and the multi-layer composite acoustic modulation structure work together to improve the overall sound insulation performance in the target frequency band.

[0013] Furthermore,

[0014] The double-sided gradient metasurface layer is composed of multiple acoustic sub-units of deep subwavelength scale arranged periodically along the transverse direction with a period length d. Each period contains M acoustic sub-units, where M≥2. The equivalent acoustic parameters of each acoustic sub-unit exhibit a monotonically increasing or decreasing gradient distribution along the arrangement direction. In an acoustically equivalent sense, the double-sided gradient metasurface layer is regarded as a non-uniform anisotropic equivalent medium. Its acoustic properties are jointly determined by the equivalent refractive index n_eff and the equivalent characteristic impedance Z_eff of the corresponding acoustic sub-unit. The equivalent refractive index and equivalent characteristic impedance are obtained by using a parameter inversion method after numerical simulation and / or experimental testing of the reflection coefficient and transmission coefficient of each acoustic sub-unit.

[0015] Furthermore,

[0016] The double-sided gradient metasurface layer introduces a spatial phase gradient along the transverse direction to non-uniformly modulate the incident sound wave, causing some of the incident propagating wave to be transformed into surface waves or higher-order diffraction modes propagating along the double-sided gradient metasurface layer after interacting with it, thereby weakening the propagation component of the sound wave in the direction perpendicular to the structure. The double-sided gradient metasurface layer divides the originally continuous air cavity into multiple discrete channels with deep subwavelength scales, disrupting the formation conditions of transverse and longitudinal standing waves inside the structure and suppressing sound insulation failure caused by cavity resonance. Under the action of obliquely incident sound waves, the double-sided gradient metasurface layer reduces the modal matching degree between the incident sound wave and the bending wave of the metal plate by reconstructing the tangential wave number of the sound wave, weakening the adverse effect of the coincidence effect on the sound insulation performance, and maintaining a high and relatively smooth sound insulation amount within a large incident angle range.

[0017] Furthermore,

[0018] The first and second porous sound-absorbing material layers are open-pore porous media with rigid skeletons. Their acoustic behavior is described by the Johnson-Champoux-Allard equivalent fluid model. Their effective density and effective bulk modulus are determined by macroscopic parameters such as porosity, flow resistance, tortuosity, viscous characteristic length and thermal characteristic length, which characterize the energy dissipation of sound waves in the porous material through viscous effect, thermal conduction effect and internal friction mechanism.

[0019] Furthermore,

[0020] The first and second metal plate layers are made of aluminum alloy plates and serve as the main mass sound insulation units. Their thickness and areal density are used to regulate the sound insulation performance of the structure in the low-frequency and mid-low-frequency ranges, and together with the double-sided gradient metasurface layers, they affect the critical matching frequency distribution of the structure. The thickness of the first and second metal plate layers is 0.5mm to 3mm, the thickness of the first and second porous sound-absorbing material layers is 5mm to 30mm, the thickness of the first and second air layers is 10mm to 40mm, and the thickness of the double-sided gradient metasurface layers is 2mm to 10mm.

[0021] Furthermore,

[0022] The acoustic subunits of the dual-sided gradient metasurface layer are coiled channels, labyrinth channels, or Helmholtz resonant cavity structures. Each acoustic subunit achieves gradient changes in the equivalent refractive index n_eff and the equivalent acoustic impedance Z_eff by changing the length of the internal acoustic channel, the cross-sectional size, or the cavity structure parameters. The metasurface period length d satisfies the subwavelength condition λ / d>2, where λ is the wavelength in air at the target frequency.

[0023] Furthermore,

[0024] When the surface waves excited by the dual-sided gradient metasurface layer propagate along the metasurface interface, they are coupled into the pore structure of the adjacent first and second porous sound-absorbing material layers through the acoustic coupling effect of the first and second air layers, thereby achieving efficient dissipation of sound energy and forming a synergistic sound absorption and insulation mechanism between the gradient metasurface and the porous sound-absorbing material.

[0025] A design method for a multilayer composite acoustic modulation structure containing a double-sided gradient metasurface includes the following steps:

[0026] The first step is to determine the design constraints, including the target sound insulation frequency band, total structural thickness, and total structural mass requirements. The material types and initial thicknesses of the first metal plate layer, the second metal plate layer, the first porous sound-absorbing material layer, and the second porous sound-absorbing material layer are initially selected. The period, number of acoustic sub-units, and phase gradient form of the double-sided gradient metasurface layer are selected, and the geometric parameters of the acoustic sub-units are initially given.

[0027] The second step is to perform full-wave simulation and / or experimental testing on the acoustic sub-units of the double-sided gradient metasurface layer to obtain the reflection coefficient and transmission coefficient of each acoustic sub-unit, and to extract the equivalent refractive index n_eff and equivalent characteristic impedance Z_eff of the acoustic sub-unit using the parameter inversion method.

[0028] The third step is to establish the transfer matrices of the first metal plate layer, the first porous sound-absorbing material layer, the first air layer, the second air layer, the second porous sound-absorbing material layer, and the second metal plate layer respectively based on the transfer matrix method, and then multiply them together according to the structural layer order to obtain the global transfer matrix of each uniform layer.

[0029] The fourth step is to establish an acoustic field coupling model at the interface where the double-gradient metasurface layer is located, based on the Floquet–Bloch theory and the Rayleigh–Bloch mixed mode matching method. The acoustic field is expanded into a superposition of plane waves / interface waves containing multiple diffraction orders. Combined with the equivalent parameters obtained in the second step, the coupling relationship between the double-gradient metasurface layer and each uniform layer is established.

[0030] The fifth step involves combining the global transfer matrix from the third step with the coupling model from the fourth step to calculate the transmission coefficient and sound insulation of the structure at different frequencies and incident angles, thereby obtaining the initial sound insulation performance curve.

[0031] The sixth step involves iteratively adjusting the thicknesses of the first metal plate layer, the second metal plate layer, the first porous sound-absorbing material layer, the second porous sound-absorbing material layer, the first air layer, the second air layer, and the phase gradient parameters of the double-sided gradient metasurface layer, with the average sound insulation in the target frequency band, the smoothness of the sound insulation curve, and the minimum sound insulation at oblique incidence as optimization targets.

[0032] Step 7: Determine whether the adjusted structural parameters meet the design constraints of Step 1 and whether the sound insulation performance meets the optimization target. If they do, output the optimal design scheme; otherwise, return to Step 6 to continue adjusting the parameters until the design requirements are met.

[0033] A method for manufacturing a multilayer composite acoustic modulation structure containing a double-sided gradient metasurface includes the following steps:

[0034] S1: Prepare the components of each layer of the structure. The first metal plate layer and the second metal plate layer are processed by CNC precision machining or mold forming. The melamine foam is cut according to the design size to obtain the first porous sound-absorbing material layer and the second porous sound-absorbing material layer. The double-sided gradient metasurface layer composed of deep subwavelength acoustic subunits is prepared by 3D printing technology or CNC precision machining.

[0035] S2: Construct a structural assembly base, fix the first metal plate layer on the assembly base, and bond the first porous sound-absorbing material layer to the designated position of the first metal plate layer with structural adhesive to ensure that the two are bonded together without gaps.

[0036] S3: Set up a first air layer. Install a spacer frame or support structure on the side of the first porous sound-absorbing material layer away from the first metal plate layer to form a first air layer that matches the design thickness. The spacer frame is made of rigid non-metallic material and does not affect the propagation of sound waves.

[0037] S4: Install the double-sided gradient metasurface layer and fix the double-sided gradient metasurface layer to the side of the first air layer away from the first porous sound-absorbing material layer with mechanical fasteners to ensure that the double-sided gradient metasurface layer is in the center of the structure and has a flat surface.

[0038] S5: Set a second air layer. Install a spacer frame or support structure with the same specifications as in step three on the side of the double-sided gradient metasurface layer away from the first air layer to form a second air layer that matches the design thickness. The second air layer and the first air layer are arranged symmetrically about the double-sided gradient metasurface layer.

[0039] S6: Symmetrically assemble the other side of the structural layer, and bond the second porous sound-absorbing material layer to the side of the second air layer away from the double-sided gradient metasurface layer with structural adhesive. Then, bond the second metal plate layer to the side of the second porous sound-absorbing material layer away from the second air layer with structural adhesive.

[0040] S7: Structural fixing and inspection. Mechanical fasteners are used to assist in fixing each layer. The positional accuracy of each layer, the thickness of the air layer, and the bonding strength are inspected to ensure they meet the design requirements, thus completing the manufacturing of the overall structure.

[0041] The beneficial effects of this invention are as follows:

[0042] First, this invention constructs a seven-layer symmetrical composite structure consisting of "metal plate - porous material - air layer - double-sided gradient metasurface - air layer - porous material - metal plate". This organically combines the mass sound insulation mechanism of the metal plate layer, the energy dissipation mechanism of the porous sound-absorbing material layer, and the phase modulation mechanism of the double-sided gradient metasurface to form a multi-level synergistic acoustic modulation system. Without significantly increasing the structural thickness and surface density, it achieves an integrated and synergistic improvement of sound absorption and sound insulation functions.

[0043] Secondly, this invention independently sets up a first air layer and a second air layer on both sides of the double-gradient metasurface as acoustic coupling buffers. On the one hand, this avoids the interface impedance abrupt change caused by the porous material directly covering the entrance of the metasurface acoustic channel, ensuring that the incident sound wave can be effectively coupled into the interior of the metasurface for phase modulation. On the other hand, by combining the air layer with the porous material layer and the metal plate layer, the cavity resonance characteristics inside the structure are adjusted. Combined with the discretization of the continuous air cavity by the double-gradient metasurface, the formation conditions of transverse and longitudinal standing waves in traditional multi-layer plate structures are effectively suppressed, and the sound insulation failure problem caused by mid-frequency cavity resonance is significantly weakened.

[0044] Third, this invention uses a double-sided gradient metasurface layer with a spatial phase gradient as the core control unit. Through the periodic arrangement and gradient design of deep subwavelength acoustic subunits, non-uniform phase modulation is applied to the incident sound wave, converting part of the incident propagation wave into surface waves or higher-order diffraction modes propagating along the interface. This weakens the propagation component of the sound wave in the normal direction. At the same time, the surface wave forms an efficient coupling with the porous sound-absorbing material layers on both sides during the propagation of the surface wave along the interface, so that the sound energy is fully dissipated through the viscosity effect and heat conduction mechanism, thereby greatly improving the sound absorption and insulation efficiency of the structure.

[0045] Fourth, by introducing a spatial phase gradient into the double-sided gradient metasurface layer, this invention reconstructs the tangential wavenumber of the sound wave, reduces the modal matching degree between the incident sound wave and the bending wave of the metal plate, effectively weakens the adverse effects of the coincidence effect on the sound insulation performance, and the excitation of surface waves or higher-order diffraction modes is not sensitive to the incident angle, so that the structure can still maintain a high and relatively smooth sound insulation in a large incident angle range (0° to 60° and above), significantly improving the sound insulation stability under oblique incident conditions.

[0046] Fifth, through simulation and experimental verification, the structure of this invention can completely eliminate mid-frequency resonance failure points and improve sound insulation by 20-40 dB compared with traditional air-sandwich structures in a wide frequency range of 0-5000 Hz. Compared with a fully filled porous material structure of the same thickness, it achieves an additional gain of 10-20 dB in the mid-to-high frequency band. Through synergistic optimization of structural parameters, it can achieve an average sound insulation of ≥50 dB in the core noise frequency band of 500-3000 Hz, and the sound insulation fluctuation is ≤5 dB in a wide incident angle range. At the same time, the surface density of the structure is reduced by more than 15% compared with traditional sound insulation structures, achieving lightweight, wide frequency range, and all-angle high-performance sound insulation. Attached Figure Description

[0047] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. 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.

[0048] Figure 1 This is an exploded view of the multi-layer composite sound insulation structure of the present invention;

[0049] Figure 2 This is a schematic diagram of the composite sound insulation structure configuration of the present invention;

[0050] Figure 3 This is a simplified diagram of sound wave transmission in an embodiment of the present invention;

[0051] Figure 4This is a schematic diagram illustrating the principle of the sound wave incident direction in an embodiment of the present invention;

[0052] Figure 5 This is an exploded structural diagram of the acoustic subunit of the double-sided gradient metasurface layer of the present invention;

[0053] Figure 6 This is a schematic diagram of the sound-absorbing metasurface layer and acoustic subunit structure of the periodic composite structure of the present invention;

[0054] Figure 7 The frequency domain sound insulation of the three structures of this invention at different incident angles;

[0055] Figure 8 This is a schematic diagram of the simple structural composite sound insulation board model and mesh division of the present invention;

[0056] Figure 9 This is a schematic diagram of the metasurface sandwich composite sound insulation board model and mesh division of the present invention;

[0057] Figure 10 This is a schematic diagram of the interface for extracting the phase and absorption coefficient of acoustic sub-units in COMSOL Multiphysics of this invention;

[0058] Figure 11 This is a schematic diagram of the metasurface and the sound absorption coefficient curves of each unit in this invention;

[0059] Figure 12 This is a graph showing the effect of the thickness of the porous material layer on the sound insulation under different incident angles and frequencies according to the present invention.

[0060] Figure 13 This is a flowchart illustrating the design process of the multilayer composite acoustic control structure of the present invention.

[0061] Figure 14 This is a flowchart illustrating the working principle of the multilayer composite acoustic control structure of the present invention.

[0062] Figure label:

[0063] 1-First metal plate layer, 2-First porous sound-absorbing material layer, 3-First air layer, 4-Double-sided gradient metasurface layer, 5-Second air layer, 6-Second porous sound-absorbing material layer, 7-Second metal plate layer. Detailed Implementation

[0064] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0065] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0066] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0067] Example 1

[0068] like Figure 1 and Figure 2 As shown, this embodiment provides a multi-layer composite sound insulation structure, wherein, Figure 1 This is a schematic diagram showing the overall disassembly of the multi-layered composite sound insulation structure, clearly illustrating the disassembly relationship and assembly sequence of the seven layers. Figure 2 This is a schematic diagram of the composite sound insulation structure, which visually presents the symmetrical layout of the overall structure.

[0069] like Figure 1 As shown, the multi-layer composite acoustic control structure of this embodiment consists of a first metal plate layer 1, a first porous sound-absorbing material layer 2, a first air layer 3, a double-sided gradient metasurface layer 4, a second air layer 5, a second porous sound-absorbing material layer 6, and a second metal plate layer 7 along the direction of sound wave propagation. The overall structure is arranged in a strictly symmetrical manner with the double-sided gradient metasurface layer 4 as the center.

[0070] Sound wave propagation path as follows Figure 3 As shown, Figure 3 The diagram shows a simplified representation of sound wave propagation. The arrows indicate the reflection, transmission, and energy dissipation processes of sound waves as they propagate from the incident side to the transmission side within the structure, passing through the interfaces of each layer.

[0071] The principle of sound wave incident direction is as follows Figure 4 As shown, Figure 4 The study macroscopically illustrates the state of sound waves incident on the structural surface at different angles. Specifically, the first metal plate layer 1 and the second metal plate layer 7 are made of aerospace-grade aluminum alloy plates, each with a thickness of 1 mm; the first porous sound-absorbing material layer 2 and the second porous sound-absorbing material layer 6 are made of melamine foam, each with a thickness of 10 mm; and the first air layer 3 and the second air layer 5 are filled with still air, each with a thickness of 30 mm.

[0072] like Figure 5As shown, the double-sided gradient metasurface layer 4 is composed of multiple acoustic subunits arranged periodically in the transverse direction at a deep subwavelength scale. The equivalent thickness is 5 mm and the period length is d = 20 mm. Each period contains 4 acoustic subunits. Each acoustic subunit changes its internal acoustic channel length and cross-sectional size to make its equivalent refractive index and equivalent characteristic impedance change monotonically and linearly in the transverse direction.

[0073] like Figure 6 As shown, Figure 6 The diagram shows a periodic composite sound-absorbing metasurface layer and an acoustic subunit structure. The three-dimensional structural details of the acoustic subunit illustrate the physical mechanism by which the metasurface layer forms a spatial phase gradient distribution at the interface, converting part of the incident propagating wave into surface waves or higher-order diffraction modes propagating along the interface.

[0074] Verified through COMSOL Multiphysics simulation and impedance tube experimental testing, such as Figure 7 As shown, Figure 7 Three structures were demonstrated: an air-sandwich structure, a porous material fully-filled structure, and the gradient metasurface sandwich structure of this invention. Frequency domain sound insulation curves were compared at incident angles of 0°, 30°, and 60°. Within the 0-5000 Hz analysis frequency band, compared to the traditional air-sandwich structure, this embodiment completely eliminated the periodic resonance failure point at the 1300 Hz isofrequency, achieving a sound insulation improvement of 20-40 dB. Compared to the porous material fully-filled structure of the same thickness, it achieved an additional gain of approximately 10-20 dB in the mid-to-high frequency band of 1000-5000 Hz. Under oblique incidence conditions (0°, 30°, 60°), the structure of this embodiment still maintained a high and smooth sound insulation, with significantly better sound insulation stability under oblique incidence than the traditional structure.

[0075] The finite element simulation model and mesh generation used in this embodiment are as follows: Figure 8 and Figure 9 As shown, where Figure 8 This is a schematic diagram of a simple composite sound insulation panel model and its mesh division. Figure 9 The two figures are a model and a schematic diagram of the mesh generation of the metasurface sandwich composite sound insulation board. The comparison of the two figures shows the mesh refinement method of the structure of the present invention during the modeling process, which ensures the accuracy and convergence of the simulation calculation.

[0076] Example 2

[0077] like Figure 12 As shown, this embodiment is based on embodiment 1, and optimizes the key structural parameters to meet the requirements of lightweight and compactness for building envelope and industrial noise control. Its structural sequence is the same as that of embodiment 1.

[0078] Figure 12This demonstrates the effect of porous material layer thickness on sound insulation under different incident angles and frequencies. Figure 12 a is the 0° angle of incidence. Figure 12 b is the 30° angle of incidence. Figure 12 The three sub-figures (c = 60° incident angle), the influence of air layer thickness on sound insulation under different incident angles and frequencies, and the influence of metal layer thickness on sound insulation under different incident angles and frequencies, respectively, present the influence of each layer thickness variation on the structural sound insulation performance in the form of three-dimensional surface plots, providing a quantitative basis for parameter optimization.

[0079] The thickness of the first metal plate layer 1 and the second metal plate layer 7 is optimized to 1.5 mm, such as... Figure 12 As shown in the thickness comparison curve of the intermediate metal layer, this thickness selection can improve low-frequency sound insulation while pushing the coincidence effect frequency to a higher frequency range; the thickness of the first porous sound-absorbing material layer 2 and the second porous sound-absorbing material layer 6 is optimized to 25 mm, as... Figure 12 As shown in the thickness comparison curve of the porous material layers, this thickness maximizes the mid-to-high frequency sound energy dissipation efficiency while ensuring structural compactness; the thickness of the first air layer 3 and the second air layer 5 is optimized to 15 mm, as... Figure 12 As shown in the comparison curve of the air layer thickness, this thickness further achieves structural lightweighting without significantly sacrificing sound insulation performance; the equivalent thickness of the double-sided gradient metasurface layer 4 is optimized to 2 mm, the period length is adjusted to 15 mm, and the equivalent acoustic parameters of the acoustic sub-unit exhibit a monotonically linearly decreasing gradient along the lateral direction to adapt to the characteristics of building noise being mainly in the mid-to-low frequency range.

[0080] Tests showed that the total thickness of the structure in this embodiment is 85 mm, the average sound insulation is ≥50 dB in the core noise frequency band of buildings from 500 to 3000 Hz, and the sound insulation fluctuates ≤5 dB in a wide incident angle range of -80° to 80°. The surface density of the structure is reduced by 15% compared with traditional sound insulation structures, achieving a synergistic improvement in lightweight and high sound insulation performance.

[0081] Example 3

[0082] like Figure 9 , Figure 10 and Figure 11 As shown, this embodiment discloses a manufacturing and assembly method applicable to the structure described in Embodiment 1 or Embodiment 2.

[0083] like Figure 9 As shown, Figure 9 The model and mesh division diagram of the metasurface sandwich composite sound insulation board are shown. The double-sided gradient metasurface layer 4 is prepared by using photopolymerization 3D printing technology with high rigidity photosensitive resin as raw material. After printing, post-curing treatment is performed to ensure that the internal sound channels are unobstructed and the surface is flat.

[0084] like Figure 10 As shown, Figure 10 The phase and absorption coefficient diagrams of the acoustic sub-units were extracted from COMSOL Multiphysics. The phase response and absorption coefficient curves of each acoustic sub-unit at the target frequency were extracted using the software's post-processing function to verify the effectiveness of the acoustic sub-unit design.

[0085] like Figure 11 As shown, Figure 11 The figure shows the sound absorption coefficient curves of the metasurface and each unit. The figure also shows the sound absorption coefficient curves of the entire metasurface and each acoustic subunit in the 200-4000 Hz frequency band. By comparison, the distribution pattern of the sound absorption peak of each acoustic subunit and the sound absorption performance of the entire metasurface in a wide frequency range can be seen.

[0086] During the assembly process, a steel assembly base is first erected to fix the first metal plate layer 1. Acoustic structural adhesive is evenly applied to its surface to precisely adhere the first porous sound-absorbing material layer 2. Then, a prefabricated spacer frame is bonded at a designated position of the first porous sound-absorbing material layer 2 to form a reserved space for the first air layer 3. Subsequently, the prepared double-sided gradient metasurface layer 4 is fixed to the spacer frame with mechanical fasteners and calibrated with a level to ensure that it is in the center of the structure and parallel to the metal plate layer. Then, a spacer frame of the same specification is bonded to the other side of the double-sided gradient metasurface layer 4 in the same way to form the second air layer 5.

[0087] Finally, the second porous sound-absorbing material layer 6 and the second metal plate layer 7 are bonded together in sequence using the same process to complete the symmetrical assembly of the overall structure.

[0088] This manufacturing method features high assembly precision and strong controllability of air layer thickness, effectively ensuring the phase modulation effect of the double-sided gradient metasurface layer 4 and the synergistic sound absorption and insulation performance between each layer, with a finished product qualification rate of ≥98%.

[0089] Example 4

[0090] like Figure 13 As shown, this embodiment discloses a multi-layer composite acoustic control structure design method, which can be applied to the customized design and parameter optimization of the structure described in Embodiment 1 or Embodiment 2.

[0091] Figure 13 The flowchart for the design of multi-layer composite acoustic control structures presents the entire process in block diagram form, from design constraint input, acoustic sub-unit parameter inversion, multi-layer transfer matrix modeling, metasurface hybrid mode matching, performance simulation calculation to parameter iterative optimization. The data flow and iterative relationship between each step are clearly expressed through logical connections.

[0092] like Figure 13As shown, the design constraints are first determined based on the target application scenario, including the target sound insulation frequency band, total structural thickness, total structural mass, and incident angle range. Then, acoustic sub-unit modeling and parameter inversion are performed. Full-wave simulation is conducted on the acoustic sub-units of the double-sided gradient metasurface layer 4 to extract the reflection and transmission coefficients of the sub-units. The equivalent refractive index n_eff and equivalent characteristic impedance Z_eff of each sub-unit are obtained using parameter inversion. Based on this, multi-layer coupling modeling is carried out. The transfer matrix of each uniform layer is established based on the transfer matrix method, and the global transfer matrix is ​​obtained by multiplying them according to the structural layer order.

[0093] Subsequently, hybrid mode matching of the metasurface layers was performed. Based on Floquet-Bloch theory and Rayleigh-Bloch hybrid mode matching method, an acoustic field coupling model was established at the interface of the double-gradient metasurface layer 4. The acoustic field was expanded into a superposition of plane waves and interface waves containing multiple diffraction orders, and the modal coupling relationship between different diffraction orders was established. Combining the global transfer matrix and the acoustic field coupling model, the sound insulation of the structure at different frequencies and incident angles was calculated. With the average sound insulation in the target frequency band, the smoothness of the sound insulation curve, and the minimum sound insulation at oblique incidence as optimization objectives, the thickness of each layer and the phase gradient parameters of the double-gradient metasurface layer 4 were iteratively adjusted until the optimal structural parameter scheme that satisfies all design constraints was obtained. This method can accurately predict the sound insulation performance under different structural parameters and different incident conditions, and the design efficiency is improved by more than 80% compared with the traditional trial and error method.

[0094] Example 5

[0095] like Figure 14 As shown in the figure, this embodiment, combined with the working principle flowchart, elaborates in detail the synergistic control mechanism of the multi-layer composite acoustic control structure of the present invention on sound waves.

[0096] Figure 14 This is a flowchart illustrating the working principle of a multi-layered composite acoustic control structure. It shows the entire control path of sound waves as they pass through the structure in a parallel and progressive manner, from "mass barrier - porous dissipation - air layer coupling - metasurface phase modulation - mode conversion - secondary dissipation - final sound insulation". The links between each link are connected by arrows, which intuitively presents the functional positioning and synergistic relationship of each layer of the structure.

[0097] like Figure 14As shown, when a sound wave is incident on the surface of the structure along the normal or oblique direction, it first enters the first metal plate layer 1, which forms a primary barrier to the incident sound energy according to the mass law. The transmitted sound wave then enters the first porous sound-absorbing material layer 2, where the sound wave is initially dissipated through the viscous friction and thermal conduction mechanisms in the pores. The sound wave, after initial dissipation, propagates through the first air layer 3 to the incident side of the double-gradient metasurface layer 4. The independent air layer here acts as an acoustic coupling buffer, ensuring that the sound wave can effectively couple into the interior of the metasurface. After the sound wave enters the double-gradient metasurface layer 4, the layer applies non-uniform phase modulation to the incident sound wave through the spatial phase gradient formed by the deep subwavelength acoustic subunits arranged periodically along the transverse direction. This converts part of the incident propagating wave into surface waves or higher-order diffraction modes propagating along the metasurface interface, significantly weakening the propagation component of the sound wave in the direction perpendicular to the structure. At the same time, the metasurface divides the originally continuous air cavity into multiple discrete channels with deep subwavelength scales, disrupting the formation conditions of transverse and longitudinal standing waves inside the structure. The acoustic energy, converted into surface waves or higher-order diffraction modes, propagates laterally along the metasurface interface. Through acoustic coupling in the second air layer 5, it is guided into the second porous sound-absorbing material layer 6. Since the acoustic energy of the surface waves is mainly concentrated near the interface, it can effectively couple into the pore structure of the porous material and be efficiently absorbed and dissipated through viscosity, thermal conduction, and internal friction mechanisms. The remaining minimal acoustic energy continues to propagate to the second metal plate layer 7, where it provides final sound insulation. Throughout the process, when the sound wave is incident at an oblique angle, the bilateral gradient metasurface layer 4 reduces the modal matching degree between the incident sound wave and the bending wave of the metal plate by reconstructing the tangential wave number of the sound wave, thus mitigating the adverse effects of the coincidence effect on the sound insulation performance and maintaining a high and relatively smooth sound insulation level over a wide range of incident angles. Through the synergistic effect of the above-mentioned three-level mechanism of "mass blocking - porous dissipation - metasurface control," this invention achieves full-chain control of the incident sound wave.

[0098] In the description of this invention, it should be noted that the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0099] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0100] In the several embodiments provided by this invention, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. The apparatus embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. Furthermore, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Additionally, the coupling or direct coupling or communication connection shown or discussed may be through some communication interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0101] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0102] In addition, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0103] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

[0104] Furthermore, although the operations of the method of the present invention are described in a specific order in the accompanying drawings, this does not require or imply that these operations must be performed in that specific order, or that all the operations shown must be performed to achieve the desired result. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step, and / or one step may be broken down into multiple steps.

Claims

1. A multilayer composite acoustic modulation structure containing a double-sided gradient metasurface, Its features are, Along the direction of sound wave propagation, it includes, in sequence: a first metal plate layer (1), a first porous sound-absorbing material layer (2), a first air layer (3), a double-sided gradient metasurface layer (4), a second air layer (5), a second porous sound-absorbing material layer (6), and a second metal plate layer (7). The double-sided gradient metasurface layer (4) is located at the center of the multi-layer composite acoustic control structure. The first air layer (3) and the second air layer (5) are respectively located on both sides of the double-sided gradient metasurface layer (4). The first porous sound-absorbing material layer (2) is located between the first metal plate layer (1) and the first air layer (3). The second porous sound-absorbing material layer (6) is located between the second metal plate layer (7) and the second air layer (5), so that the overall structure is symmetrically arranged along the double-sided gradient metasurface layer (4). The first air layer (3) and the second air layer (5) are independent acoustic coupling buffers, used to prevent the porous sound-absorbing material layer from covering the acoustic channel entrance of the double-sided gradient metasurface layer (4) and to ensure that the incident sound wave is effectively coupled into the interior of the double-sided gradient metasurface layer (4). The double-sided gradient metasurface layer (4) is a planar gradient metasurface structure used to introduce a spatial phase gradient to realize acoustic mode conversion, to perform phase modulation on the incident sound wave and realize acoustic mode conversion. Combined with the mass barrier effect of the first metal plate layer (1) and the second metal plate layer (7), and the energy dissipation effect of the first porous sound-absorbing material layer (2) and the second porous sound-absorbing material layer (6), it realizes the coordinated control of sound absorption and sound insulation of the incident sound wave.

2. The double-sided gradient metasurface multilayer composite acoustic modulation structure according to claim 1, Its features are, The dual-sided gradient metasurface layer (4) includes an incident-side gradient metasurface and an exit-side gradient metasurface. The incident-side gradient metasurface is used to gradient control the phase distribution, propagation direction, or equivalent acoustic impedance of the incident sound wave. The exit-side gradient metasurface is used to perform secondary control on the sound wave after propagation through the multi-layer composite acoustic control structure to suppress sound wave transmission. The dual-sided gradient metasurface and the multi-layer composite acoustic control structure work together to improve the overall sound insulation performance in the target frequency band.

3. The double-sided gradient metasurface multilayer composite acoustic modulation structure according to claim 1, Its features are, The double-sided gradient metasurface layer (4) is composed of multiple acoustic subunits of deep subwavelength scale arranged periodically along the transverse direction with a period length d. Each period contains M acoustic subunits and M≥2. The equivalent acoustic parameters of each acoustic subunit are distributed with a monotonically increasing or decreasing gradient along the arrangement direction. In an acoustically equivalent sense, the double-sided gradient metasurface layer (4) is regarded as a non-uniform anisotropic equivalent medium. Its acoustic properties are determined by the equivalent refractive index n_eff and equivalent characteristic impedance Z_eff of the corresponding acoustic subunit. The equivalent refractive index and equivalent characteristic impedance are obtained by using the parameter inversion method after numerical simulation and / or experimental testing of the reflection coefficient and transmission coefficient of each acoustic subunit.

4. The double-sided gradient metasurface multilayer composite acoustic modulation structure according to claim 2, Its features are, The double-sided gradient metasurface layer (4) introduces a spatial phase gradient along the transverse direction to perform non-uniform phase modulation on the incident sound wave, so that part of the incident propagation wave is transformed into surface wave or higher-order diffraction mode propagating along the double-sided gradient metasurface layer (4) after interacting with it, thereby weakening the propagation component of the sound wave in the direction perpendicular to the structure. The double-sided gradient metasurface layer (4) divides the originally continuous air cavity into multiple deep subwavelength scale discrete channels, destroys the formation conditions of transverse and longitudinal standing waves inside the structure, and suppresses the sound insulation failure caused by cavity resonance. Under the action of obliquely incident sound waves, the double-sided gradient metasurface layer (4) reduces the modal matching degree between the incident sound waves and the bending waves of the metal plate by reconstructing the tangential wave number of the sound waves, weakens the adverse effect of the coincidence effect on the sound insulation performance, and maintains a high and relatively smooth sound insulation amount within a large incident angle range.

5. The double-sided gradient metasurface multilayer composite acoustic modulation structure according to claim 1, Its features are, The first porous sound-absorbing material layer (2) and the second porous sound-absorbing material layer (6) are open-pore porous media with rigid skeletons. Their acoustic behavior is described by the Johnson-Champoux-Allard equivalent fluid model. Their effective density and effective bulk modulus are determined by macroscopic parameters such as porosity, flow resistance, tortuosity, viscous characteristic length and thermal characteristic length, which characterize the energy dissipation of sound waves in the porous material through viscous effect, thermal conduction effect and internal friction mechanism.

6. The double-sided gradient metasurface multilayer composite acoustic modulation structure according to claim 1, Its features are, The first metal plate layer (1) and the second metal plate layer (7) are made of aluminum alloy plates and serve as the main mass sound insulation unit. Their thickness and surface density are used to regulate the sound insulation performance of the structure in the low and mid-low frequency ranges, and together with the double-sided gradient metasurface layer (4), they affect the critical matching frequency distribution of the structure. The thickness of the first metal plate layer (1) and the second metal plate layer (7) is 0.5mm to 3mm, the thickness of the first porous sound-absorbing material layer (2) and the second porous sound-absorbing material layer (6) is 5mm to 30mm, the thickness of the first air layer (3) and the second air layer (5) is 10mm to 40mm, and the thickness of the double-sided gradient metasurface layer (4) is 2mm to 10mm.

7. The double-sided gradient metasurface multilayer composite acoustic modulation structure according to claim 3, Its features are, The acoustic subunits of the double-sided gradient metasurface layer (4) are coiled channels, labyrinth channels or Helmholtz resonant cavity structures. Each acoustic subunit achieves gradient changes in equivalent refractive index n_eff and equivalent acoustic impedance Z_eff by changing the length of the internal acoustic channel, cross-sectional size or cavity structure parameters. The metasurface period length d satisfies the subwavelength condition λ / d>2, where λ is the wavelength in air at the target frequency.

8. The double-sided gradient metasurface multilayer composite acoustic modulation structure according to claim 1, Its features are, When the surface wave excited by the double-sided gradient metasurface layer (4) propagates along the metasurface interface, it is coupled into the pore structure of the adjacent first porous sound-absorbing material layer (2) and second porous sound-absorbing material layer (6) through the acoustic coupling effect of the first air layer (3) and the second air layer (5), thereby achieving efficient dissipation of sound energy and forming a synergistic sound absorption and insulation mechanism between the gradient metasurface and the porous sound-absorbing material.

9. A design method for a multilayer composite acoustic modulation structure containing a double-sided gradient metasurface. The double-sided gradient metasurface multilayer composite acoustic modulation structure as described in any one of claims 1-8 is adopted. Its features are, Includes the following steps: The first step is to determine the design constraints, including the target sound insulation frequency band, total structural thickness, and total structural mass requirements. The material types and initial thicknesses of the first metal plate layer (1), the second metal plate layer (7), the first porous sound-absorbing material layer (2), and the second porous sound-absorbing material layer (6) are initially selected. The period, number of acoustic sub-units, and phase gradient form of the double-sided gradient metasurface layer (4) are selected, and the geometric parameters of the acoustic sub-units are initially given. The second step is to perform full-wave simulation and / or experimental testing on the acoustic sub-units of the double-sided gradient metasurface layer (4) to obtain the reflection coefficient and transmission coefficient of each acoustic sub-unit, and use the parameter inversion method to extract the equivalent refractive index n_eff and equivalent characteristic impedance Z_eff of the acoustic sub-units. The third step is to establish the transfer matrices of the first metal plate layer (1), the first porous sound-absorbing material layer (2), the first air layer (3), the second air layer (5), the second porous sound-absorbing material layer (6), and the second metal plate layer (7) respectively based on the transfer matrix method, and multiply them together according to the structural layer order to obtain the global transfer matrix of each uniform layer. The fourth step is to establish a sound field coupling model at the interface of the double-sided gradient metasurface layer (4) based on the Floquet–Bloch theory and the Rayleigh–Bloch mixed mode matching method. The sound field is expanded into a superposition of plane waves / interface waves containing multiple diffraction orders. Combined with the equivalent parameters obtained in the second step, the coupling relationship between the double-sided gradient metasurface layer (4) and each uniform layer is established. The fifth step involves combining the global transfer matrix from the third step with the coupling model from the fourth step to calculate the transmission coefficient and sound insulation of the structure at different frequencies and incident angles, thereby obtaining the initial sound insulation performance curve. The sixth step is to iteratively adjust the thickness of the first metal plate layer (1), the second metal plate layer (7), the first porous sound-absorbing material layer (2), the second porous sound-absorbing material layer (6), the first air layer (3), the second air layer (5) and the phase gradient parameters of the double-sided gradient metasurface layer (4) with the average sound insulation in the target frequency band, the smoothness of the sound insulation curve and the lowest sound insulation at oblique incidence as optimization targets. Step 7: Determine whether the adjusted structural parameters meet the design constraints of Step 1 and whether the sound insulation performance meets the optimization target. If they do, output the optimal design scheme; otherwise, return to Step 6 to continue adjusting the parameters until the design requirements are met.

10. A method for manufacturing a multilayer composite acoustic modulation structure containing a double-sided gradient metasurface. The multilayer composite acoustic modulation structure with a double-sided gradient metasurface as described in any one of claims 1-8 is adopted. Its features are, Includes the following steps: S1: Prepare the components of each layer of the structure, process the first metal plate layer (1) and the second metal plate layer (7) by CNC precision machining or mold forming, cut melamine foam according to the design size to obtain the first porous sound-absorbing material layer (2) and the second porous sound-absorbing material layer (6), and prepare the double-sided gradient metasurface layer (4) composed of deep subwavelength acoustic subunits by 3D printing technology or CNC precision machining. S2: Build a structural assembly base, fix the first metal plate layer (1) on the assembly base, and bond the first porous sound-absorbing material layer (2) with structural adhesive at the designated position of the first metal plate layer (1) to ensure that the two are in close contact without gaps. S3: Set up a first air layer (3), install a spacer frame or support structure on the side of the first porous sound-absorbing material layer (2) away from the first metal plate layer (1) to form a first air layer (3) that matches the design thickness. The spacer frame is made of rigid non-metallic material and does not affect the propagation of sound waves. S4: Install the double-sided gradient metasurface layer (4), fix the double-sided gradient metasurface layer (4) to the side of the first air layer (3) away from the first porous sound-absorbing material layer (2) by mechanical fasteners, and ensure that the double-sided gradient metasurface layer (4) is in the center of the structure and the surface is flat. S5: Set a second air layer (5), install a spacer frame or support structure with the same specifications as in the third step on the side of the double-sided gradient metasurface layer (4) away from the first air layer (3) to form a second air layer (5) that matches the design thickness, and the second air layer (5) and the first air layer (3) are arranged symmetrically about the double-sided gradient metasurface layer (4). S6: Symmetrically assemble the other side of the structural layer, and bond the second porous sound-absorbing material layer (6) to the side of the second air layer (5) away from the double-sided gradient metasurface layer (4) with structural adhesive, and then bond the second metal plate layer (7) to the side of the second porous sound-absorbing material layer (6) away from the second air layer (5) with structural adhesive. S7: Structural fixing and inspection. Mechanical fasteners are used to assist in fixing each layer. The positional accuracy of each layer, the thickness of the air layer, and the bonding strength are inspected to ensure they meet the design requirements, thus completing the manufacturing of the overall structure.

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