Tube bundle composite type low-frequency broadband sound absorption metamaterial unit cell with built-in porous lining layer, regulation and control method and sound absorption device

Abstract

The invention discloses a tube bundle composite type low-frequency broadband sound absorption metamaterial unit cell with a built-in porous lining layer, a regulation and control method and a sound absorption device. The unit cell specifically comprises an embedded tube bundle plate, a plurality of tube bundles, a back cavity and the porous lining layer. The back cavity forms a resonant cavity; the porous lining layer is laid on each wall surface of the inner side of the back cavity in a tight fit manner; the embedded tube bundle plate is laid at an opening in one end of the back cavity, and a plurality of through holes matched with the tube bundle in diameter are formed in the embedded tube bundle plate; a plurality of tube bundles vertically extend into the back cavity along the embedded tube bundle plate, and the ends, extending into the back cavity, of the tube bundles are separated from the inner side face of the back cavity where the porous lining is laid; through the innovative design of tube bundle local resonance-multi-scale dissipation in the cavity and system-level multi-unit parallel optimization, continuous and efficient broadband sound absorption is achieved.

Description

Technical Field

[0001] This invention relates to the field of low-frequency noise control technology in acoustic metamaterials, specifically to a tube bundle composite low-frequency broadband sound-absorbing metamaterial unit cell with an internal porous liner.

[0002] This invention also relates to a method for regulating the cell properties of a tube bundle composite low-frequency broadband sound-absorbing metamaterial with an embedded porous liner.

[0003] The present invention also relates to a broadband sound absorption method based on cooperative dissipation.

[0004] The present invention also relates to a broadband sound-absorbing device. Background Technology

[0005] Low-frequency noise typically refers to noise below 500Hz. Due to its long wavelength, strong penetration, and slow attenuation, it has become a major source of pollution in transportation, industrial production, and urban building environments, seriously endangering human health and quality of life. Traditional sound-absorbing materials, such as porous materials, follow the "quarter-wavelength" principle in the low-frequency range. To effectively absorb 500Hz noise, a thickness of up to 17 centimeters is theoretically required, which severely restricts its application in space-constrained lightweight and compact engineering scenarios.

[0006] The emergence of acoustic metamaterials has provided a new paradigm for thin-layer control of low-frequency noise. By manipulating sound waves through artificially designed subwavelength localized resonant units such as Helmholtz resonators and membrane structures, they achieve highly efficient low-frequency sound absorption even when the structural thickness is much smaller than the operating wavelength. However, these typical resonant metamaterials have an inherent drawback: an extremely narrow sound absorption bandwidth. Their efficient sound absorption performance is usually limited to the vicinity of a sharp resonance peak, and cannot effectively cover the broadband low-frequency noise with continuous spectrum characteristics commonly found in practical engineering.

[0007] To broaden the sound absorption bandwidth, current research is mainly exploring two technical paths: 1. Multi-resonance coupling path: Multiple units with different resonant frequencies are connected in parallel and combined to broaden the bandwidth by superimposing multiple resonant peaks. However, this method often leads to complex structures, increased size, and the formation of "absorption valleys" between peaks, making it difficult to achieve smooth and continuous broadband absorption.

[0008] 2. Material-Structure Composite Approach: This approach combines resonant elements, such as Helmholtz resonators, with porous materials that absorb sound over a wide frequency range. Theoretically, this approach can synergistically leverage the low-frequency localization enhancement of the resonant structure and the broadband dissipation advantages of porous materials, and is considered one of the most promising solutions for achieving low-frequency broadband sound absorption.

[0009] The existing technology is as follows: A composite sound-absorbing structure based on a Helmholtz resonator and porous material filling: The basic structure of this scheme is as follows Figure 1 As shown on the left, it is usually composed of a traditional Helmholtz resonator, whose back cavity is simply or partially filled with porous materials such as foam or fiber cotton. Its working principle is that the Helmholtz resonator generates resonance at a specific frequency through the vibration of the air column in the neck, which concentrates the sound energy in the cavity. The filling porous material utilizes its huge specific surface area and complex pore structure to efficiently dissipate the concentrated sound energy into heat energy through viscous loss and thermal conduction effects. Its advantage is that, compared with a pure resonant structure, the introduction of porous material increases the system damping, which can broaden the resonance peak width to a certain extent and improve the peak absorption coefficient.

[0010] Problems with existing technology: 1. Limited bandwidth expansion and the existence of "absorption valleys": Simple filling methods cannot achieve deep synergy between the resonance mechanism and the porous dissipation mechanism. Porous materials mainly provide "overdamped" background absorption, while the resonance peaks remain relatively independent. This results in "absorption valleys" where the absorption coefficient drops sharply in the frequency band between resonance peaks, making it impossible to achieve a truly continuous, smooth, and efficient broadband absorption curve, such as... Figure 1 The comparison on the right is shown.

[0011] 2. Structural-functional coupling, making performance control difficult: In this scheme, the adjustment of the resonant frequency is mainly achieved by changing the cavity volume and neck size, while the adjustment of the damping characteristics is strongly coupled by changing the filling amount and material properties of the porous material. When attempting to move the resonant peak position by adjusting the geometric parameters, the volume and distribution of the porous material in the cavity will inevitably change simultaneously, thus strongly coupling and altering the damping characteristics of the system, and vice versa. This coupling relationship makes it extremely difficult to independently and precisely control the absorption peak value and absorption bandwidth, limiting the design flexibility and the upper limit of performance optimization, and making it impossible to accurately match according to a specific noise spectrum.

[0012] 3. Limited energy dissipation area and suboptimal efficiency: In traditional filled structures, acoustic energy is mainly concentrated and dissipated in localized areas within the resonant cavity and near the neck. Porous materials fail to achieve maximum interaction with the resonant field, failing to fully utilize the entire structure's space for efficient and distributed energy dissipation, thus limiting further performance improvements. Figure 4 As shown in (c), its energy dissipation density distribution is concentrated, and the maximum utilization of the dissipation space is not achieved, making it extremely difficult to achieve a near-perfect sound absorption effect in a limited subwavelength space.

[0013] 4. Simple parallel connection easily leads to impedance mismatch and an uneven absorption curve. To broaden the bandwidth, existing technologies often simply connect multiple resonant units in parallel. However, if there is a lack of impedance matching design between the units, their absorption curves are often merely mechanically superimposed, resulting in drastic fluctuations and obvious "absorption valleys" in the overall curve, failing to form a continuous, smooth, stable, and efficient broadband absorption platform. This severely affects its application performance in practical scenarios requiring wideband uniform sound absorption.

[0014] In summary, although existing technical solutions recognize the advantages of composite technology, their "simple filling" paradigm fails to fundamentally solve the problem of the synergy between resonance and dissipation mechanisms, resulting in performance bottlenecks in pursuing the core goal of "low frequency, wide bandwidth, high efficiency, and thin layer". Summary of the Invention

[0015] The purpose of this invention is to address the aforementioned problems by providing a tube bundle composite low-frequency broadband sound-absorbing metamaterial unit cell with an internal porous liner. By introducing the porous liner, a synergistic mechanism of tube bundle local resonance and back cavity multi-scale visco-heat dissipation is constructed at the single unit scale, and the acoustic impedance and acoustic impedance are relatively independently adjustable.

[0016] The technical solution adopted in this invention is as follows: A tube bundle composite low-frequency broadband sound-absorbing metamaterial unit cell with built-in porous liner, wherein the unit cell specifically includes an embedded tube bundle plate and multiple tube bundles, a back cavity, and a porous liner; The porous liner is tightly and closely laid on each wall surface inside the back cavity; The embedded tube bundle plate is laid at the opening at one end of the back cavity, and the embedded tube bundle plate has multiple through holes that match the diameter of the tube bundle. Multiple tube bundles extend vertically into the back cavity along the embedded tube bundle plate, and one end of each tube bundle extending into the back cavity is separate from the inner side of the back cavity where the porous liner is laid. Furthermore, the embedded tube bundle plate, multiple tube bundles, back cavity, and porous liner are integrally formed.

[0017] Furthermore, the flow resistance of the porous liner is in the range of 5000 N·s / m. 4 ~200000N·s / m 4 .

[0018] This invention also employs a method for controlling the cell properties of a tube-bundle composite low-frequency broadband sound-absorbing metamaterial with an embedded porous liner, the method specifically comprising: Maintaining the permeability of the unit cell structure nS a / S A Constant, where, n For the number of tube bundles, Sa The cross-sectional area of ​​a single tube bundle. S A This represents the cross-sectional area of ​​the dorsal cavity; The normalized acoustic impedance Re(Zs / Z0) is controlled by adjusting the number and diameter of the tube bundles.

[0019] Furthermore, the modulation of the normalized acoustic impedance Re(Zs / Z0) specifically includes: The normalized acoustic impedance Re(Zs / Z0) is increased by increasing the number of tube bundles while decreasing the diameter of the tube bundles. By reducing the number of tube bundles while increasing the diameter of the tube bundles, the normalized acoustic impedance Re(Z) is reduced. s / Z0); Where, when Re(Z) s When / Z0)≈1, the unit cell structure is in a critically damped state, at the resonant frequency f Maximize the peak sound absorption coefficient at point 0; When Re(Z) s When / Z0)>1, the unit cell structure is in an overdamped state, at the resonant frequency f Under the premise that 0 remains unchanged, its half-absorption bandwidth Δ f The damping threshold is broadened compared to the critical damping state; When Re(Z) s When / Z0) < 1, the unit cell structure is in an underdamped state, and its half-absorption bandwidth Δ f Narrowing.

[0020] This invention also employs a broadband sound absorption method based on cooperative dissipation, using the aforementioned tubular double-pore low-frequency broadband sound-absorbing metamaterial unit cell, the method comprising: When the incident sound wave is introduced into the back cavity through the tube bundle, it excites resonance in the cavity. Specifically, the incident sound wave first enters the tube bundle inside the resonant cavity through the tube bundle opening. The tube bundle is the neck of the Helmholtz resonator. When the sound wave frequency matches the resonant frequency of the tube bundle structure, the air column inside the tube bundle vibrates violently, generating local resonance and efficiently accumulating sound energy at low frequencies. After resonance is triggered, the incident sound wave is then transmitted to the porous lining inside the cavity for dissipation.

[0021] The present invention also employs a broadband sound-absorbing device, comprising a plurality of tube bundle composite low-frequency broadband sound-absorbing metamaterial unit cells with built-in porous liner, wherein the plurality of unit cell structures are arrayed in parallel.

[0022] Furthermore, several of the said unit cell structures include at least two unit cells with different structural parameters, the structural parameters including at least one of bundle diameter, bundle length and bundle number.

[0023] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: This invention discloses a tubular, dual-pore, low-frequency broadband sound-absorbing metamaterial unit cell, specifically an embedded tubular plate porous liner ETBP-PL metamaterial. Its core advantage lies in its innovative design, which achieves continuous and efficient broadband sound absorption through intra-unit resonance-porous synergistic dissipation and system-level multi-unit parallel optimization. Specifically, the embedded tubular bundle acts as a highly efficient sound energy collector, precisely focusing sound energy at low frequencies through Helmholtz resonance; while the porous liner, which comprehensively encloses the back cavity, constitutes a distributed dissipation network, efficiently converting sound energy through viscosity and thermal effects. This deep synergy between resonant positioning and porous dissipation... This invention extends the dissipation region from the local boundary to the entire cavity space, significantly improving the performance of a single unit. Furthermore, by using impedance decoupling design to achieve parallel coupling of multiple units, each unit operates in an overdamped state, with their absorption peaks superimposed and smoothly connected. Ultimately, with a subwavelength thickness of 52mm, it achieves broadband sound absorption with an average coefficient as high as 0.941 (α≥0.9) in the 259~480Hz frequency band, and the thickness is only 1 / 25 of the wavelength at the lower limit frequency of 259Hz. This invention fundamentally solves the bottleneck problem of narrow bandwidth and insufficient sound absorption efficiency in the low-frequency range of traditional sound absorption structures. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the periodic structure and a schematic diagram of a representative unit cell structure of ETBP-PL in this invention; Figure 2 In the diagram, (a) is a schematic diagram of the equivalent process of ETBP-PL, in which the back cavity with the rectangular perforated porous liner can be regarded as a combination of two hypothetical materials; (b) is a schematic diagram and cross-sectional view of ETBP-PL; (c) is a schematic diagram of the propagation of a plane wave in a two-dimensional cross section, in which the back cavity can be regarded as an equivalent homogeneous medium. Figure 3 The sound absorption characteristics of ETBP-PL, ETBP and PL: (a) sound absorption coefficient; (b) normalized surface impedance; Figure 4 The acoustic quantity distribution of the sound wave propagation process in ETBP and ETBP-PL is as follows: (a) sound pressure distribution; (b) particle vibration velocity RMS; (c) energy dissipation density and acoustic energy flow (the direction and length of the red arrows represent the direction and magnitude of the acoustic energy flow, respectively, and the color code represents the energy dissipation density); (d) comparison of energy dissipation of each component in ETBP and ETBP-PL.

[0025] Figure 5 For different pipe diameters d a Energy dissipation ratio of each component in the ETBP-PL; Figure 6 Schematic diagrams of three types of ETBP-PL units; Figure 7 The acoustic characteristics of three ETBP-PL structures are: (a) sound absorption coefficient; (b) normalized surface acoustic resistance; (c) normalized surface acoustic impedance. Figure 8 The acoustic quantity distributions of ETBP-PL for three different porous materials are shown: (a) sound pressure distribution; (b) particle vibration RMS; and (c) energy dissipation density and acoustic energy flow.

[0026] Figure 9 In the diagram, (a) is the acoustic measurement experimental setup; (b) is the exploded view of absorber 1; (c) is the exploded view of absorber 2; (d) is the sound absorption coefficient of absorber 1 (analysis / simulation / experiment); and (e) is the sound absorption coefficient diagram of absorber 2 (analysis / simulation / experiment). Detailed Implementation

[0027] The present invention will now be described in detail with reference to the accompanying drawings.

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the 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 and not intended to limit the invention.

[0029] Example This embodiment provides a tubular, dual-pore, low-frequency broadband sound-absorbing metamaterial unit cell, such as... Figure 1 As shown, the unit cell is mounted on a rigid backplate to withstand plane acoustic waves incident normally.

[0030] The core of the unit cell structure in this embodiment lies in a multi-layered composite structure; such as Figure 2 As shown, the unit cell structure: The back cavity structure constitutes the resonant cavity; a porous liner is tightly fitted onto all inner walls of the back cavity structure, including the bottom and four sides, forming a continuous porous material layer; multiple embedded tube bundles, each tube bundle is vertically and fixedly embedded at one end into the opening of the embedded tube bundle plate, and extends into the back cavity, but its end maintains a certain distance from the bottom of the back cavity. In this embodiment, the tube bundle and the embedded tube bundle plate can be an integrally formed structure; the embedded tube bundle plate covers the opening of the back cavity and has multiple through openings on it. The construction of this embodiment successfully combines the Helmholtz resonant structure composed of tube bundles, back cavity and plate with the porous liner that fully surrounds the back cavity into an organic whole.

[0031] This embodiment introduces a dual-pore liner to construct a synergistic mechanism of localized tube resonance and multi-scale viscosity dissipation of the back cavity at the single-unit scale; the aim is to significantly broaden the half-absorption bandwidth of a single resonance peak, with a target increase of more than 160%, and to greatly improve the peak absorption coefficient to nearly 1.0, so that a single metamaterial unit has excellent broadband sound absorption potential.

[0032] like Figure 2 As shown in (a), the design evolution of the structure in this embodiment is illustrated, the key being the transformation of the traditional cavity into a functional composite cavity; as Figure 2 As shown in (b), all the key geometric parameters are clearly marked.

[0033] Among them, the embedded tube bundle plate and the tube bundle are acoustic modulators and resonant triggers: The incident sound wave first enters the embedded tube bundle through the opening on the tube bundle plate. The tube bundle is equivalent to the neck of the Helmholtz resonator. When the frequency of the sound wave matches the resonant frequency of the structure, the air column inside the tube bundle will vibrate violently and generate local resonance, thereby efficiently concentrating sound energy at low frequencies.

[0034] The introduction of multiple tube bundles is equivalent to creating multiple parallel resonant paths with specific acoustic qualities and acoustic impedances within a single cavity. This can be achieved by designing different tube bundle diameters (d...). a ), length (l) n The number (n) and the overall resonance and damping characteristics can be flexibly adjusted. Through specific design (such as adjusting the size and number of tube bundles while keeping the perforation rate constant), the acoustic impedance and acoustic impedance can be adjusted relatively independently. This allows engineers to precisely control the center frequency and bandwidth / peak value of the absorption peak, just like adjusting the frequency knob and the damping knob, greatly improving the freedom and specificity of the design.

[0035] Among them, the back cavity and porous liner are acoustic energy traps and dissipation enhancers: The back cavity, as a resonant cavity, has its internal space (after deducting the volume occupied by the tube bundle) and the tube bundle together determining the resonant frequency. The most critical feature of this embodiment is that all inner walls of the back cavity, not just the bottom, are covered with a porous liner of uniform thickness.

[0036] This embodiment's design creates a dual-pore system: the porous material matrix provides micron-sized micropores, while the internal space of the back cavity constitutes millimeter-sized mesopores; such as Figure 2 As shown in (c), this composite cavity can be considered equivalent to a homogeneous medium with special acoustic properties. Through its dual-pore structure, it excites multi-scale dissipation within the back cavity, extending the energy dissipation region from the local tube bundle to the entire back cavity space, as shown in [example]. Figure 4 As shown in (c). Meanwhile, as Figure 5As shown, as the tube diameter increases from 3mm to 5mm, the primary and secondary dissipation regions shift from tube bundle resonance to the back cavity, and the energy dissipation ratio of the back cavity increases from 51.7% to 77.2%. The two maintain stable total dissipation through a synergistic compensation mechanism, thereby achieving broadband high-efficiency sound absorption. The aim is to maximize the use of limited space and achieve near-theoretical high-efficiency sound energy conversion with a subwavelength thickness of λ / 30.

[0037] When sound waves are introduced into the back cavity through the tube bundle, they excite resonance within the cavity. On the other hand, the sound waves strongly penetrate into the porous lining around the perimeter and bottom. The huge specific surface area of ​​the porous material efficiently dissipates the sound energy into heat energy through viscosity and thermal conduction effects. This enveloping lining design greatly increases the contact area and interaction time between the sound waves and the porous material, achieving distributed energy dissipation throughout the entire space.

[0038] The ultimate integration goal of this embodiment is to optimize and combine multiple ETBP-PL units with different resonant frequencies based on the aforementioned adjustable single unit, through overdamped coupling and parallel design strategies; the aim is to eliminate absorption valleys between units, so that their absorption curves are superimposed and merged into a continuous, flat, and highly efficient absorption platform, such as... Figure 9 As shown in (e), α≥0.9 in the 259-480Hz range, thereby achieving truly engineering-ready low-frequency broadband noise control while maintaining an ultra-thin overall structure.

[0039] The collaborative working principle and action relationship in this embodiment are as follows: The working principle of this embodiment is the result of the synergistic effect of the above-mentioned components, and its sound wave propagation path and energy conversion process can be achieved through... Figure 2 (c) is shown as an acoustic-electric analog circuit for clear understanding: Sound wave propagation path: Sound waves (analogous to electric current) are incident from the outside and first encounter the acoustic impedance of the embedded tube bundle (region I). Subsequently, the sound waves propagate in two paths: one path enters the lower half of the back cavity (region II) downwards, and the other path reflects upwards back to the upper half of the back cavity (region III). The key innovation lies in the fact that the impedance of the back cavity is the equivalent impedance formed by the coupling of the air domain (central hole) surrounding the tube bundle and the porous liner (micropore) surrounding it through the dual-pore theory. Finally, after the upper and lower paths are connected in parallel, they are connected in series with the impedance of the tube bundle to form the total impedance.

[0040] Energy dissipation mechanisms (synergistic effect): Path extension and enhanced dissipation: The presence of the porous liner not only provides strong background dissipation, but its equivalent acoustic parameters (equivalent density, bulk modulus) also change the sound velocity and wavenumber in the cavity, which is equivalent to extending the effective propagation path of the sound wave in the cavity, thereby enhancing the low-frequency coupling effect.

[0041] Impedance decoupling and synergistic compensation: By precisely designing the geometric parameters of the tube bundle (such as diameter and quantity), relatively independent adjustment of the system's acoustic impedance (real part) and acoustic reactance (imaginary part) can be achieved. This is known as an impedance decoupling strategy. Figure 6 and Figure 7 As shown, while keeping the resonant frequency (determined by the acoustic impedance zero point) constant, the damping (acoustic impedance) can be adjusted by changing the tube bundle configuration, thereby independently optimizing the width and height of the absorption peak.

[0042] Multiscale dissipation: such as Figure 4 As shown in the energy dissipation cloud diagram in (c), in this embodiment, energy dissipation occurs simultaneously in the inner wall of the tube bundle (local resonance dissipation) and in the entire back cavity with the porous liner (distributed multi-scale broadband dissipation). These two mechanisms complement and synergize in frequency: the tube bundle resonance provides a higher dissipation peak at a specific low frequency, while the porous liner provides a stable dissipation background over a wider frequency band. The combination of the two achieves continuous broadband high-efficiency sound absorption.

[0043] Key parameters and design freedom of this embodiment: like Figure 2 As shown in (b), the performance of the unit cell structure in this embodiment can be precisely controlled through the following key geometric parameters, which provides great flexibility for its application: Overall dimensions: The width W and total height H of the unit cell determine the spatial footprint and fundamental resonant frequency range of the structure.

[0044] Tube bundle parameters: inner diameter da, length ln, wall thickness t2, and quantity n are used to precisely control the resonant frequency and acoustic impedance, and are the main operating variables for achieving impedance decoupling.

[0045] Liner parameters: The thickness lp of the porous liner and the JCA parameters of the porous material (such as porosity and flow resistance) determine the strength of the broadband dissipation capability.

[0046] Structural thickness: Thickness t1 of the panel and back cavity wall.

[0047] In summary, this embodiment creates a dual-pore system physically through an innovative composite structure of embedded tube bundles and an all-around encapsulated porous liner. In principle, it achieves deep synergy between local resonance and distributed multi-scale dissipation. Furthermore, through an impedance decoupling strategy, it endows the system with the significant advantage of independent and precise performance control, thereby successfully achieving high-performance low-frequency broadband sound absorption at the subwavelength scale.

[0048] Solve for the cavity impedance of the structure in this embodiment: Based on the dual-pore theory, the back cavity consists of a porous material matrix (micropores) and perforated pores (mesopores), and can be approximated as an equivalent homogeneous medium, such as... Figure 2As shown in (c), the effective density ρ_eff and effective bulk modulus K_eff of the back cavity are obtained by coupling the effective density and effective bulk modulus (ρ_p, K_p) of the mesopore domain with the effective density and effective bulk modulus (ρ_m, K_m) of the micropore domain, as shown in the following equation: (1) (2) In the formula, the total volume of the back cavity is V t = ( L -2 t 1) 2 ( H -2 t 1) The volume of the microporous domain is V m =[( L -2 t 1) 2 -( L -2 t 1-2 l p ) 2 ]( H -2 t 1- l p )+( L -2 t 1) 2 l p The volume of the mesoporous domain is V P = V t - V m -nπ( d a +2· t 2) 2 ( l n - t 1) / 4, where the space occupied by the embedded tube bundle has been excluded; ω is the angular frequency. P 0 = 101325 Pa represents atmospheric pressure. m Fd represents the porosity of the porous material matrix, and Fd represents the ratio of the average pressure in the porous material matrix to the pressure in the mesopore region; for low permeability difference (mesopore size / micropore size << 10³). F d ≈1.

[0049] For high permeability difference (mesopore size / micropore size >> 10³). Fd As it varies with frequency, its expression is: (3) In the formula, p m The average pressure in the micropore domain, p pi The average pressure in the mesopore region and the dynamic permeability. D ( ω This is used to characterize dynamic thermal permeability, and its expression is: (4) In the formula, ω d =(1- h ) P 0 / m σ m D (0) is the characteristic frequency of the pressure diffusion effect. Near this frequency, significant sound pressure diffusion occurs from the mesopore domain to the micropore domain. h = V p / V t Indicates the mesopore porosity. σ m This represents the static flow resistance of a porous material matrix. D (0)=( L -2 t 1) 2 [In(1 / h )-3 / 2+2 h - h 2 / 2] / 4π is the static thermal permeability, and the characteristic length of the micropores is... M d =8 D (0) / Λ d 2 (1- h ), where Λ d =2 V m / [( L -2 t 1-2 l p ) 2 +4(L -2 t 1-2 l p ()( H -2 t 1- l p )] represents twice the ratio of the micropore domain volume to the micropore-mesopore interface area.

[0050] The propagation of sound waves in a porous material matrix is ​​analyzed using the Johnson–Champoux–Allard (JCA) model, and its effective density ρm and effective bulk modulus Km are expressed as follows: (5) (6) In the formula, the JCA model includes five parameters: curvature. α∞ Porosity m Static flow resistance m The parameters are: viscous characteristic length Λ and thermal characteristic length Λ′; where the first four parameters describe viscous dissipation, while... m and Λ′ are used to characterize the heat conduction mechanism; j The imaginary unit is used to represent the physical properties of air, which are determined by its density. ρ0 Dynamic viscosity η Specific heat ratio γ Thermal conductivity κ and specific heat capacity Cp Definition, P r = ηC p / κ It is a Prandtl number.

[0051] Effective density of the mesoporous domain ρ p and effective bulk modulus K p The calculation method is as follows: (7) (8) In the formula, J n Indicates the first type n Bessel function of order 1, It is a dimensionless parameter; r p =( L -2 t 1-2 l p ) 2 / The effective perforation diameter radius.

[0052] Subsequently, the effective wavenumber of the back cavity k eff With effective speed of sound c eff It can be determined by the following formula: (9) (10) A schematic diagram of plane wave propagation in ETBP-PL is shown below. Figure 2 As shown in (c), it is assumed that the sound wave propagates only along the back cavity. z The plane wave radiates from the nozzle and propagates in two directions: one part towards the bottom of the back cavity and the other part towards the perforated panel; therefore, according to the direction of propagation of the plane wave, the back cavity can be divided into two regions: region II and region III.

[0053] The acoustic impedance of region II can be expressed as: (11) Since there are tube bundles within region III, the impact of the space occupied by the tube bundles on the acoustic impedance of region III must be considered; therefore, the acoustic impedance of region III can be expressed as: (12) In the formula, S c =( W-2t 1) 2 This represents the inner cross-sectional area of ​​the dorsal cavity. S e =π( d a + 2 t 2) 2 / 4 represents the cross-sectional area of ​​the tube bundle (including the tube wall thickness).

[0054] Therefore, the surface acoustic impedance of the back cavity can be expressed as: (13) Solve for the tube bundle impedance in this embodiment: The functions of the viscous and thermal fields in the tube bundle are as follows: (14) (15) The complex wave number can then be calculated. kc Complex speed c c and complex air density As shown below: (16) (17) (18) The acoustic impedance of the tube bundle can be expressed as: (19) In the formula, Z e The endpoint correction term, used to account for the discontinuity between the tube bundle end and the dorsal cavity, is expressed as follows: (20) Solve for the sound absorption coefficient of the entire structure in this embodiment: Considering the series relationship between the back cavity and the tube bundle, the total surface impedance of ETBP-PL can be obtained: (twenty one) Therefore, the sound absorption coefficient can be expressed as: (twenty two) In the formula, c 0=343 m / s Let be the speed of sound in air, and Re(·) and Im(·) represent the real and imaginary parts of the complex parameter, respectively.

[0055] Impedance decoupling model: To elucidate the intrinsic mechanism of impedance decoupling, the equivalent acoustic impedance of ETBP-PL can be expressed as: z = r s + j ( ωm s -1 / ωc s )(twenty three) In the formula, r s and ωm s -1 / ωc s These represent normalized acoustic impedance and acoustic impedance, respectively.

[0056] The porous liner back cavity introduces additional acoustic resistance, the relevant parameters of which can be approximated as follows: (24a) (24b) (24c) In the formula, = Indicates the perforation rate of the tube bundle. .

[0057] As shown in equation (24a), with the perforation rate remaining constant, the equivalent acoustic resistance increases as the tube diameter decreases, since the tube bundle length is much larger than its diameter (l). n d a The last term in equation (24b) is 0.85d. a / l n The contribution to the equivalent acoustic quality (ms) is negligible. Furthermore, since the cavity dimensions and porous liner configurations of the three structures are completely identical, according to equation (24c), their equivalent acoustic compliance is also essentially the same. Therefore, the equivalent acoustic quality and compliance remain approximately constant, thus maintaining a consistent acoustic impedance. Due to the resonant frequency... These two parameters together determine that all three structures exhibit the same resonant frequency.

[0058] In summary, the specific advantages of this invention are as follows: (1) Achieving a performance leap from narrowband to ultra-wideband, with a continuous and smooth sound absorption curve. This invention achieves ultrawideband and continuously smooth sound absorption performance through the deep synergy between local resonance induced by embedded tube bundles and multi-scale dissipation excited by omnidirectional porous liner.

[0059] Data Support: The performance advantages of this invention have been fully verified through theoretical simulation and experimental measurement: Simulation shows that the optimized single-unit ETBP-PL structure achieves near-perfect absorption (α=0.989) at 221Hz with a thickness of 52mm, its thickness being only 1 / 30 of the wavelength, and its absorption peak value is increased by 49.6% compared to the pure resonant structure, while its half-absorption bandwidth is broadened by 160%. Figure 3 As shown in (a); experiments further confirm that a multi-unit parallel absorber achieves continuous broadband absorption with an average coefficient of 0.941 in the 259–480 Hz frequency band, while maintaining a thickness of 52 mm (1 / 25 of the 259 Hz wavelength). The high degree of agreement between theory and experimental results fully demonstrates the successful transformation of this design from single-peak high performance to broadband absorption. Figure 9 (e).

[0060] Mechanism Analysis: The mechanism by which this invention achieves broadband high performance is a progressive process from intra-unit synergy to inter-unit coupling: First, by introducing a porous liner to construct a distributed multi-scale dissipation network within the cavity, the sound energy dissipation is extended from the local area ("point") of the embedded tube bundle to the entire back cavity space ("surface"). This single-unit synergy mechanism is the fundamental reason for improving the absorption peak and half-bandwidth. Then, through the impedance decoupling and overdamped coupling strategy of multi-unit parallel connection, each unit has a slightly broadened and staggered absorption peak, which is finally fused into a continuous and efficient (average α≥0.9) ultra-wideband sound absorption curve in the 259–480Hz frequency band.

[0061] (2) It breaks through the shackles of impedance coupling and realizes independent and flexible control of absorption performance. This invention innovatively proposes an impedance decoupling strategy. By adjusting the configuration of the embedded tube bundles, such as their diameter and number, the acoustic impedance of the system, which determines the absorption peak height and bandwidth, and the acoustic impedance, which determines the resonant frequency, can be adjusted relatively independently.

[0062] Data support: such as Figure 6 As shown, by changing the tube bundle configuration (ETBP-PLA, PLB, PLC). Figure 7 As shown, the shape of the sound absorption curve can be significantly changed while keeping the resonant frequency basically unchanged (about 127Hz): from underdamped (high peak but narrow bandwidth) to critical coupling (peak close to 1 and optimized bandwidth), and then to overdamped (peak slightly lower but widest bandwidth).

[0063] Mechanism analysis: This decoupling capability stems from the unique multi-path parallel acoustic circuit design of this invention, such as... Figure 2 As shown in (c), the tube bundle primarily contributes to acoustic quality (affecting frequency) and acoustic resistance (affecting bandwidth), while the porous liner provides adjustable, large damping and acoustic capacitance. This allows engineers to precisely customize the desired sound absorption curve for the target noise spectrum, much like adjusting a "knob," offering design flexibility far exceeding existing technologies.

[0064] (3) It breaks through the thickness limitation and achieves efficient low-frequency sound absorption at the subwavelength scale. This invention fully utilizes the "subwavelength" characteristics of local resonant metamaterials to excite strong low-frequency sound field concentration and dissipation at an extremely thin scale.

[0065] Data support: Theoretical simulation and experimental verification jointly confirm the superior performance of this invention: such as Figure 3 As shown in (a), the optimized single-unit ETBP-PL structure achieves near-perfect absorption at 221 Hz (α = 0.989) with a thickness of only 1 / 30 of the wavelength, demonstrating excellent deep subwavelength characteristics; furthermore, as Figure 9The experimental results shown in (d) indicate that the sound absorber 1, with each unit having the same structural dimensions and a parallel design, exhibits a low-frequency peak at 204Hz, with the peak value approaching 1.0, confirming the efficient low-frequency absorption of a single unit. Figure 9 The experimental results shown in (e) indicate that the sound absorber 2, which uses a parallel design and has different structural dimensions for each unit, achieves broadband sound absorption with an average coefficient of 0.941 (α≥0.9) in the 259~480Hz frequency band. While maintaining a thickness of 52mm, the thickness is only 1 / 25 of the wavelength of 259Hz, successfully converting theoretical performance into measurable broadband sound absorption effect.

[0066] Mechanism analysis: such as Figure 8 As shown in the sound pressure distribution in (a), the embedded tube bundle and the back cavity constitute a highly efficient Helmholtz resonator, which can concentrate and "capture" sound wave energy in the cavity at a scale much smaller than the wavelength; at the same time, the encapsulated porous liner ensures that the captured energy can be dissipated efficiently, thus solving the problem of low-frequency sound absorption without relying on huge thickness.

[0067] (4) Significantly improved space utilization and energy dissipation efficiency. The "wrap-in" porous liner design of this invention transforms the entire internal space of the back cavity into an effective sound energy dissipation zone, maximizing space utilization and energy dissipation efficiency.

[0068] Data support: such as Figure 4 (d) shows that the quantified energy dissipation indicates that in the ETBP-PL, the energy dissipation in the back cavity region (including the porous liner) accounts for as high as 67.6%, far exceeding the 13.9% of the traditional ETBP structure. Figure 8 The acoustic energy flow lines in (c) also show that the sound waves are effectively guided and dissipated throughout the porous liner.

[0069] Mechanism analysis: The enhanced sound absorption is mainly attributed to the introduction of a porous liner, which introduces additional damping and efficiently converts sound energy into heat energy through viscous heat dissipation, thereby improving impedance matching (e.g., Figure 3 (b) shows that the reduced reflection increases the absorption coefficient, while effectively broadening the absorption bandwidth and preventing excessively sharp resonance peaks. In addition, the porous liner not only increases the effective cavity compliance but also generates phase delay through viscous heat dissipation in the porous material, effectively extending the acoustic propagation path. The combined effect expands the effective compressible volume, thereby reducing the resonant frequency.

[0070] In summary, this invention is not a simple improvement on existing technologies, but a fundamental innovation. Through its unique "embedded tube bundle + omnidirectional liner" structure, it achieves deep synergy in mechanism, broadband high efficiency in performance, and independent controllability in design. Ultimately, it solves the long-standing technical challenge of low-frequency broadband sound absorption at the subwavelength scale, providing a leading solution for noise control in high-end equipment, building, and transportation industries.

[0071] This article uses specific embodiments to illustrate the principles and implementation methods of the present invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A tube-bundle composite low-frequency broadband sound-absorbing metamaterial unit cell with an internal porous liner, characterized in that, The unit cell specifically includes an embedded tube bundle plate and multiple tube bundles, a back cavity, and a porous liner; The porous liner is tightly and closely laid on each wall surface of the inner side of the back cavity; The embedded tube bundle plate is laid at the opening at one end of the back cavity, and the embedded tube bundle plate has multiple through holes that match the diameter of the tube bundle. Multiple tube bundles extend vertically into the back cavity along the embedded tube bundle plate, and one end of each tube bundle extending into the back cavity is separate from the inner side of the back cavity where the porous liner is laid.

2. The tube bundle composite low-frequency broadband sound-absorbing metamaterial unit cell with an internal porous liner as described in claim 1, characterized in that, The embedded tube bundle plate, multiple tube bundles, back cavity, and porous liner are integrally formed.

3. The tube bundle composite low-frequency broadband sound-absorbing metamaterial unit cell with an internal porous liner as described in claim 1, characterized in that, The porous liner has a flow resistance range of 5000 N·s / m. 4 ~200000N·s / m 4 .

4. A method for controlling the performance of a unit cell of a tube-bundle composite low-frequency broadband sound-absorbing metamaterial with an embedded porous liner, characterized in that, The method specifically includes: Maintaining the permeability of the unit cell structure nS a / S A Constant, where, n For the number of tube bundles, S a The cross-sectional area of ​​a single tube bundle. S A This represents the cross-sectional area of ​​the dorsal cavity; The normalized acoustic impedance Re(Zs / Z0) is controlled by adjusting the number and diameter of the tube bundles.

5. A method for controlling the performance of a unit cell of a tubular composite low-frequency broadband sound-absorbing metamaterial with an embedded porous liner, as described in claim 4, characterized in that... The adjustment of the normalized acoustic impedance Re(Zs / Z0) specifically includes: The normalized acoustic impedance Re(Zs / Z0) is increased by increasing the number of tube bundles while decreasing the diameter of the tube bundles. By reducing the number of tube bundles while increasing the diameter of the tube bundles, the normalized acoustic impedance Re(Z) is reduced. s / Z0); Where, when Re(Z) s When / Z0)≈1, the unit cell structure is in a critically damped state, at the resonant frequency f Maximize the peak sound absorption coefficient at point 0; When Re(Z) s When / Z0)>1, the unit cell structure is in an overdamped state, at the resonant frequency f Under the premise that 0 remains unchanged, its half-absorption bandwidth Δ f The damping threshold is broadened compared to the critical damping state; When Re(Z) s When / Z0) < 1, the unit cell structure is in an underdamped state, and its half-absorption bandwidth Δ f Narrowing.

6. A broadband sound absorption method based on cooperative dissipation, employing a tubular double-pore low-frequency broadband sound-absorbing metamaterial unit cell as described in claims 1-3, characterized in that, The method includes: When the incident sound wave is introduced into the back cavity through the tube bundle, it excites resonance in the cavity. Specifically, the incident sound wave first enters the tube bundle inside the resonant cavity through the tube bundle opening. The tube bundle is the neck of the Helmholtz resonator. When the sound wave frequency matches the resonant frequency of the tube bundle structure, the air column inside the tube bundle vibrates violently, generating local resonance and efficiently accumulating sound energy at low frequencies. After resonance is triggered, the incident sound wave is then transmitted to the porous lining inside the cavity for dissipation.

7. A broadband sound-absorbing device, comprising a plurality of tube bundle composite low-frequency broadband sound-absorbing metamaterial unit cells with an internal porous liner as described in any one of claims 1 to 3, characterized in that, Several of the aforementioned unit cell structures are arrayed in parallel.

8. A broadband sound-absorbing device according to claim 7, characterized in that, The plurality of said unit cell structures include at least two unit cells with different structural parameters, said structural parameters including at least one of bundle diameter, bundle length and bundle number.

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