Sound absorption metamaterial of circular truncated cone type foamed aluminum composite micro-perforated plate

Abstract

The invention belongs to the technical field of broadband sound absorption and noise reduction, and discloses a sound absorption metamaterial of a circular truncated cone type foamed aluminum composite micro-perforated panel, which comprises circular truncated cone type foamed aluminum, the outer wall of the circular truncated cone type foamed aluminum is fixedly sleeved with an annular first micro-perforated panel, and the central axis of the first micro-perforated panel is coaxial with the central axis of the circular truncated cone type foamed aluminum; the outer diameter of the first micro-perforated plate is not smaller than the diameter of the lower bottom of the circular truncated cone type foamed aluminum; a second micro-perforated plate is arranged on the lower bottom face of the circular truncated cone type foamed aluminum, a second micro-perforated plate rear cavity is formed below the second micro-perforated plate, and the diameter of the second micro-perforated plate is not smaller than that of the lower bottom face of the circular truncated cone type foamed aluminum. The technical problem that a traditional sound absorption material is narrow in applicable frequency range can be solved, and the limitation that the resonant frequency of traditional cylindrical foamed aluminum cannot be adjusted is hoped to be broken through.

Description

Technical Field

[0001] The present invention belongs to the technical field of broadband sound absorption and noise reduction, and particularly relates to a sound-absorbing metamaterial of a truncated-cone-shaped aluminum foam composite micro-perforated plate. Background Art

[0002] With the development of modern industry and society, the problem of noise pollution has become increasingly serious, having an adverse impact on people's life, work, physical and mental health. In many scenarios where noise needs to be controlled, such as in building environments, factory workshops, and the interiors of transportation vehicles (cars, airplanes, etc.), there is an urgent need for efficient sound-absorbing materials to reduce noise.

[0003] Traditional sound-absorbing materials have certain limitations in terms of sound absorption performance, applicable frequency range, structural strength, etc. For example, although some porous sound-absorbing materials have good sound absorption effects in the medium and high frequency bands, their low-frequency sound absorption ability is insufficient; some fibrous sound-absorbing materials have problems such as poor fire resistance and easy aging.

[0004] However, new types of acoustic metamaterials, such as the invention patent CN202010743135.3, have the disadvantages of complex structure, high manufacturing difficulty, and limited low-frequency sound absorption frequency range. Summary of the Invention

[0005] To solve the problems existing in the prior art, the purpose of the present invention is to provide a sound-absorbing metamaterial of a truncated-cone-shaped aluminum foam composite micro-perforated plate. The present invention can solve the technical problem of the narrow applicable frequency range of traditional sound-absorbing materials, and hopes to break through the limitation that the resonance frequency of traditional cylindrical aluminum foam cannot be adjusted.

[0006] To achieve the corresponding purpose by solving the above technical problems, the technical solution provided by the present invention is as follows:

[0007] A sound-absorbing metamaterial of a truncated-cone-shaped aluminum foam composite micro-perforated plate, comprising a truncated-cone-shaped aluminum foam, an annular first micro-perforated plate is fixedly sleeved on the outer wall of the truncated-cone-shaped aluminum foam, and the central axis of the first micro-perforated plate is coaxial with the central axis of the truncated-cone-shaped aluminum foam; the outer diameter of the first micro-perforated plate is not less than the lower bottom diameter of the truncated-cone-shaped aluminum foam;

[0008] The lower bottom surface of the truncated-cone-shaped aluminum foam is provided with a second micro-perforated plate, there is a second micro-perforated plate rear cavity below the second micro-perforated plate, and the diameter of the second micro-perforated plate is not less than the lower bottom diameter of the truncated-cone-shaped aluminum foam.

[0009] Preferably, at least one micro-perforated plate parallel to the second micro-perforated plate is provided at intervals below the second micro-perforated plate, and each micro-perforated plate has a micro-perforated plate rear cavity;

[0010] The diameters of all the micro-perforated plates provided below the second micro-perforated plate are not less than the lower bottom diameter of the truncated-cone-shaped aluminum foam.

[0011] Preferably, both the second micro-perforated plate and the micro-perforated plate arranged below are cylindrical micro-perforated plates.

[0012] Preferably, at least one micro-perforated plate is arranged at an interval below the second micro-perforated plate, and this micro-perforated plate serves as the third micro-perforated plate. There is a cavity behind the third micro-perforated plate below the third micro-perforated plate, and the cavity between the second micro-perforated plate and the third micro-perforated plate is the cavity behind the second micro-perforated plate.

[0013] Preferably, the upper bottom surface diameter of the frustum-shaped aluminum foam is 10 - 19 mm, the lower bottom surface diameter is 29 mm, the height of the frustum-shaped aluminum foam is 30 mm, the porosity of the frustum-shaped aluminum foam is 62.1% - 78.0%, and the flow resistance rate is 45992 - 145936 Pa·s / m 2 。

[0014] Preferably, the distance between the first micro-perforated plate and the lower bottom surface of the frustum-shaped aluminum foam is 12 - 24 mm.

[0015] Preferably, any two of the first micro-perforated plate, the second micro-perforated plate, and the third micro-perforated plate have different thicknesses, different perforation rates, and different perforation pore diameters, and the other parameters of the first micro-perforated plate, the second micro-perforated plate, and the third micro-perforated plate except for thickness, perforation rate, and perforation pore diameter are the same.

[0016] Preferably: the thickness of the first micro-perforated plate is 0.2 - 1.5 mm, the perforation pore diameter is 0.3 - 1 mm, and the perforation rate is 1.78% - 2.56%;

[0017] the thickness of the second micro-perforated plate is 0.2 - 0.6 mm, the perforation pore diameter is 0.2 - 0.5 mm, and the perforation rate is 0.36% - 0.68%;

[0018] the thickness of the third micro-perforated plate is 0.5 - 0.9 mm, the perforation pore diameter is 0.4 - 0.8 mm, and the perforation rate is 1.25% - 1.78%.

[0019] Preferably: the thickness of the cavity behind the second micro-perforated plate is 10 - 20 mm.

[0020] Preferably: the thickness of the cavity behind the third micro-perforated plate is 10 - 20 mm.

[0021] The present invention has the following beneficial effects:

[0022] In the acoustic metamaterial of the circular table-shaped aluminum foam composite micro-perforated plate of the present invention, the circular table-shaped aluminum foam, the annular first micro-perforated plate, and the annular cavity constitute the first acoustic absorption unit of the present invention. Among them, the annular cavity is the cavity formed between the area below the first micro-perforated plate and the circular table-shaped aluminum foam and the outer side wall of the circular table-shaped aluminum foam. The cross-section of the annular cavity is triangular. One side of the triangle is the outer side wall of the circular table-shaped aluminum foam, one side is on the lower surface of the first micro-perforated plate (the length of this side is the radius difference between the lower bottom of the circular table-shaped aluminum foam and the inner diameter of the first micro-perforated plate), and one side is virtual (it is the perpendicular line from the edge of the lower bottom of the circular table-shaped aluminum foam to the lower surface of the first micro-perforated plate (see Figure 1 the dotted line shown)); the second micro-perforated plate and the second micro-perforated plate rear cavity below it serve as the second acoustic absorption unit of the present invention; when in use, one side of the upper bottom of the circular table-shaped aluminum foam is the sound source incident side, that is, the sound wave is incident from one side of the upper bottom of the circular table-shaped aluminum foam and exits from one side of the lower bottom of the circular table-shaped aluminum foam. In the structure of the present invention, along the propagation direction of the sound source incident, the first acoustic absorption unit and the second acoustic absorption unit are arranged in series continuously. Therefore, the present invention has a composite characteristic, enabling the synergistic effect of the circular table-shaped structure, aluminum foam, and micro-perforated plate, effectively making up for the problem of insufficient low-frequency sound absorption of traditional sound absorption materials and significantly increasing the width of the sound absorption frequency band. Compared with a single sound absorption material or structure, the present invention greatly improves the average sound absorption coefficient. In addition, the present invention can obtain the above-mentioned annular cavities with different heights by sleeving the first micro-perforated plate at different height positions on the circular table-shaped aluminum foam, so that without increasing the thickness of the circular table-shaped aluminum foam, the sound absorption coefficient in the high-frequency band of the material can be adjusted and optimized. Generally speaking, this novel acoustic metamaterial of the circular table-shaped aluminum foam composite micro-perforated plate of the present invention has strong designability and can adjust the geometric parameters of the circular table, the performance parameters of the aluminum foam, and the parameters of the micro-perforated plate according to different sound absorption requirement scenarios. This high designability enables the acoustic metamaterial to flexibly adapt to the specific sound absorption requirements in various fields such as architecture, industry, and aerospace. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for description in the embodiments. Obviously, the following described drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0024] Figure 1 It is a schematic structural diagram of the acoustic metamaterial of the circular table-shaped aluminum foam composite micro-perforated plate in the embodiment of the present invention;

[0025] Figure 2 is Figure 1 a top view of the structure shown;

[0026] Figure 3(a) is a schematic structural diagram of the sound-absorbing metamaterial of the truncated-cone-shaped aluminum foam composite micro-perforated plate in Embodiment 1 of the present invention; Figure 3(b) is the sound absorption coefficient of the sound-absorbing metamaterial of the truncated-cone-shaped aluminum foam composite micro-perforated plate in Embodiment 1 of the present invention;

[0027] Figure 4(a) is a schematic structural diagram of the sound-absorbing metamaterial of the truncated-cone-shaped aluminum foam composite micro-perforated plate in Embodiment 2 of the present invention; Figure 4(b) is the sound absorption coefficient of the sound-absorbing metamaterial of the truncated-cone-shaped aluminum foam composite micro-perforated plate in Embodiment 2 of the present invention;

[0028] Figure 5(a) is a schematic structural diagram of the sound-absorbing metamaterial of the truncated-cone-shaped aluminum foam composite micro-perforated plate in Embodiment 3 of the present invention; Figure 5(b) is the sound absorption coefficient of the sound-absorbing metamaterial of the truncated-cone-shaped aluminum foam composite micro-perforated plate in Embodiment 3 of the present invention.

[0029] In the figure, 1 - truncated-cone-shaped aluminum foam, 2 - first micro-perforated plate, 3 - annular cavity, 4 - second micro-perforated plate, 5 - cavity behind the second micro-perforated plate, 6 - third micro-perforated plate, 7 - cavity behind the third micro-perforated plate. Detailed implementation manners

[0030] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components described and shown in the accompanying drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the protection scope of the present invention.

[0031] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by terms such as "upper", "lower", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the structure referred to must have a specific orientation, be constructed in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first", "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first", "second" may explicitly or implicitly include one or more of such features.

[0032] Various schematic structural diagrams according to the disclosed embodiments of the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and for the purpose of clear expression, some details may be omitted. The shapes of various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary, and in practice, there may be deviations due to manufacturing tolerances or technical limitations. Those skilled in the art can design regions with different shapes, sizes, and relative positions according to actual needs.

[0033] To overcome the deficiencies of existing sound-absorbing materials, the present invention combines a frustum-shaped structure, aluminum foam, and a micro-perforated plate, aiming to design a new type of sound-absorbing metamaterial that can comprehensively utilize the advantages of each component to achieve more excellent sound-absorbing performance, especially in a wide frequency band range, including low frequency, medium frequency, and high frequency, to efficiently absorb sound waves and meet the noise reduction requirements in complex environments. The present invention breaks the limitations of traditional flat plate designs by compounding the frustum-shaped aluminum foam 1 with the micro-perforated plate, changing the propagation path and reflection mode of sound waves, enabling sound waves to interact more fully within the material. The compounding of aluminum foam and the micro-perforated plate further enhances this interaction, and different materials play a synergistic sound-absorbing effect in different frequency bands, greatly broadening the sound-absorbing frequency band and effectively improving the sound-absorbing efficiency, especially showing a significant improvement in medium and high frequency sound absorption compared with traditional sound-absorbing materials.

[0034] Specifically, referring to Figure 1 and Figure 2 , the sound-absorbing metamaterial of the frustum-shaped aluminum foam compounded with the micro-perforated plate in this embodiment includes a frustum-shaped aluminum foam 1. An annular first micro-perforated plate 2 is fixedly sleeved on the outer wall of the frustum-shaped aluminum foam 1, and the central axis of the first micro-perforated plate 2 is coaxial with the central axis of the frustum-shaped aluminum foam 1; the outer diameter of the first micro-perforated plate 2 is not less than the lower bottom diameter of the frustum-shaped aluminum foam 1; a second micro-perforated plate 4 is provided on the lower bottom surface of the frustum-shaped aluminum foam 1, and there is a second micro-perforated plate rear cavity 5 below the second micro-perforated plate 4, and the diameter of the second micro-perforated plate 4 is not less than the lower bottom surface diameter of the frustum-shaped aluminum foam 1. In this embodiment, the upper bottom of the frustum-shaped aluminum foam 1 refers to the bottom surface with a smaller diameter, and the lower bottom refers to the bottom surface with a larger diameter. Referring to Figure 1 In the orientation shown, in the sound-absorbing metamaterial of the frustum-shaped aluminum foam compounded with the micro-perforated plate in this embodiment, the sound wave incident direction is from top to bottom.

[0035] As a preferred implementation of the present invention, on the basis of the above embodiment, in this embodiment, at least one micro-perforated plate parallel to the second micro-perforated plate 4 (see the third micro-perforated plate 6) is provided at intervals below the second micro-perforated plate 4, and each micro-perforated plate has a micro-perforated plate rear cavity; the diameters of all the micro-perforated plates provided below the second micro-perforated plate 4 are not less than the lower bottom surface diameter of the frustum-shaped aluminum foam 1.

[0036] As a preferred embodiment of the present invention, at least one micro-perforated plate is provided at an interval below the second micro-perforated plate 4. This micro-perforated plate serves as the third micro-perforated plate 6. There is a cavity behind the third micro-perforated plate 7 below the third micro-perforated plate 6, and the cavity between the second micro-perforated plate 4 and the third micro-perforated plate 6 is the cavity behind the second micro-perforated plate 5. The first micro-perforated plate 2, the second micro-perforated plate 4, and the third micro-perforated plate 6 are all cylindrical micro-perforated plates. The first micro-perforated plate 2, the second micro-perforated plate 4, the third micro-perforated plate 6, and the diameter of the lower bottom of the conical foam aluminum 1 are the same.

[0037] The sound-absorbing metamaterial of the conical foam aluminum composite micro-perforated plate in this embodiment includes a double-layer micro-perforated plate composed of the conical foam aluminum 1, the first micro-perforated plate 2, the second micro-perforated plate 4, the cavity behind the second micro-perforated plate 5, the third micro-perforated plate 6, and the cavity behind the third micro-perforated plate 7. The second micro-perforated plate 4 is arranged on the lower bottom surface of the conical foam aluminum 1. The shape of the first micro-perforated plate 2 is a ring and it is fixedly sleeved on the side wall of the conical foam aluminum 1. The first micro-perforated plate 2 is parallel to the bottom surface of the conical foam aluminum 1. The first micro-perforated plate 2, the second micro-perforated plate 4, and the third micro-perforated plate 6 are parallel, and the first micro-perforated plate 2, the second micro-perforated plate 4, the third micro-perforated plate 6, and the diameter of the lower bottom of the conical foam aluminum 1 are the same. An annular cavity 3 as shown in Figure 1 is formed between the lower part of the first micro-perforated plate 2 and the side wall of the conical foam aluminum 1. The interface shape of the annular cavity 3 is triangular.

[0038] The sound-absorbing metamaterial of the conical foam aluminum composite micro-perforated plate in this embodiment includes two sound-absorbing units arranged in series and continuously. The two sound-absorbing units are respectively denoted as the first sound-absorbing unit and the second sound-absorbing unit. The first sound-absorbing unit includes the conical foam aluminum 1, the first micro-perforated plate 2, and the annular cavity 3 sandwiched between the two (i.e., the conical foam aluminum 1 and the first micro-perforated plate 2). The second sound-absorbing unit includes the second micro-perforated plate 4 and the cavity behind the second micro-perforated plate 5, the third micro-perforated plate 6, and the cavity behind the third micro-perforated plate 7. The two sound-absorbing units are divided into upper and lower layers with different heights along the propagation direction of the sound wave incidence. The inside of both layers is air. The outer embedded height of the first micro-perforated plate 2 from the conical foam aluminum 1 is adjusted to be 12 - 24 mm to adjust the size of the annular cavity 3. It should be noted that when the first micro-perforated plate 2 is at different heights of the conical foam aluminum 1, the inner diameter of the first micro-perforated plate 2 is equal to the outer diameter of the conical foam aluminum 1 at the corresponding height, so that the first micro-perforated plate 2 can be installed on the conical foam aluminum 1.

[0039] In this embodiment, a finite element model of a truncated conical aluminum foam composite micro-perforated plate is established in the pressure acoustics module of COMSOL Multiphysics 6.1 according to preset parameters, and software simulation is used to explore whether the structural parameters have broadband sound absorption characteristics. Specifically, this embodiment optimizes the size and porosity of the truncated conical aluminum foam 1 to achieve an average sound absorption coefficient α≥0.95 within 2500~6300Hz, including the following steps:

[0040] Step 1: Calculate the characteristic impedance of the truncated conical aluminum foam 1 according to the empirical model of Delany and Bazley as:

[0041]

[0042] where Z c is the characteristic impedance of the porous material (i.e., the truncated conical aluminum foam 1) (Pa·s / m 3 ), ρ 0 and c 0 are the density of air (kg / m 3 ) and the speed of sound in air (m / s) respectively, f is the frequency (Hz), and σ is the flow resistivity in air (N·s / m 4 ).

[0043] Step 2: Correct the characteristic impedance of the truncated conical aluminum foam 1, and the correction coefficient is 1.26.

[0044] Step 3: Calculate the sound absorption coefficient of the truncated conical aluminum foam 1 according to the theoretical formula of the sound absorption coefficient as:

[0045] α=1-[(Z-Z 0 ) / (Z+Z 0 )] 2 (2)

[0046] where Z is the characteristic impedance of the truncated conical aluminum foam 1, and Z 0 is the characteristic impedance of air.

[0047] Optimize the size, spacing, and rear cavity size of the cylinder to improve the average sound absorption coefficient and the ability to target specific noise sources, including the following steps;

[0048] Step 1: Calculate the acoustic impedance Z s of the cavity (i.e., the rear cavity 5 of the second micro-perforated plate and the rear cavity 7 of the third micro-perforated plate) behind each micro-perforated plate (i.e., the second micro-perforated plate 4 and the third micro-perforated plate 6) as

[0049]

[0050] where L is the depth of the rear cavity;

[0051] Step 2: Correct the acoustic impedance of the irregular annular cavity 3, with the correction coefficient being 1.06;

[0052] Step 3: Calculate the sound absorption coefficient of each micro-perforated panel according to the Maa theory as

[0053]

[0054] where, w = 2πf is the angular frequency, d is the thickness of the micro-perforated panel, Z s is the acoustic impedance of the air layer behind, and m is the surface mass of the micro-perforated panel;

[0055] Step 4: In the pressure acoustics module of COMSOL Multiphysics 6.1, establish a finite element model in which three micro-perforated panels are connected in series from top to bottom according to the acoustic impedance inside each micro-perforated panel and each preset parameter, and set an inner perforated panel for each micro-perforated panel plane in the model.

[0056] Among them, the preset numbers are the perforation rates p 1 、p 2 、p 3 of the first micro-perforated panel 2, the second micro-perforated panel 4, and the third micro-perforated panel 6, the thicknesses t 1 、t 2 、t 3 , the perforation apertures d 1 、d 2 、d 3 ;

[0057] Step 5: Determine the noise reduction target frequencies designed for the first micro-perforated panel 2, the second micro-perforated panel 4, and the third micro-perforated panel 6 according to the structural vibration and the peak absorption frequency. Take the material and geometric parameters of the first micro-perforated panel 2, the second micro-perforated panel 4, and the third micro-perforated panel 6 as input parameters, and take the maximization of the average sound absorption coefficient within a certain frequency range as the optimization target;

[0058] Step 6: Carry out the optimization design by using the multi-objective optimization design method, as shown in formula (5)

[0059]

[0060] where f i is the discrete frequency point within the frequency range, and n is the number of frequency points.

[0061] Step 7: Divide the low-frequency band into (f l1 -f l2 ), the middle-frequency band (f m1 -f m2 ), and the high-frequency band (f h1 -f h2 ) and perform for the low-frequency band target The same applies to the middle frequency band and the high frequency band.

[0062] Step 8: Assign weights w l w m w h , and construct the objective function of the comprehensive sound absorption coefficient as:

[0063]

[0064] Step 9: Design the composite micro-perforated panel for a specific noise source, and optimize the sound absorption coefficient according to the spectral characteristics of the noise source. Let the noise spectrum function be N(f), then the optimization objective of the sound absorption coefficient based on noise spectrum weighting can be constructed as:

[0065]

[0066] Step 10: Read the final sound absorption and noise reduction effect, and determine whether to further optimize the micro-hole shapes of the first micro-perforated panel 2, the second micro-perforated panel 4, and the third micro-perforated panel 6 into spiral or stepped shapes by comparing and analyzing whether the sound absorption effects of the above frequency bands meet the required noise control requirements, mainly considering the noise reduction effect at the peak frequency. If optimization is required, return to Step 1 for secondary optimization of the components.

[0067] According to the above process, a set of optimized matching parameters for the components of the sound-absorbing metamaterial of the round table-shaped aluminum foam composite micro-perforated panel in this embodiment are as follows: the upper bottom diameter d 1 of the round table-shaped aluminum foam 1 is 10 - 19 mm, the lower bottom diameter d 2 is 29 mm, the thickness (i.e., height) D 1 is 30 mm, the porosity is 62.1% - 78.0%, and the flow resistivity is 45992 - 145936 Pa·s / m 2 ;

[0068] The thickness t 1 of the first micro-perforated panel 2 is 0.2 - 1.5 mm, the perforation aperture d 1 is 0.3 - 1 mm, and the perforation rate p 1 is 1.78% - 2.56%; the thickness t 2 of the second micro-perforated panel 4 is 0.2 - 0.6 mm, the perforation aperture d 2 is 0.2 - 0.5 mm, and the perforation rate p 2 is 0.36% - 0.68%; the thickness t 3 of the third micro-perforated panel 6 is 0.5 - 0.9 mm, the perforation aperture d 3 is 0.4 - 0.8 mm, and the perforation rate p 3is 1.25% to 1.78%; the micro-perforated panel absorbers (i.e., the first micro-perforated panel 2, the second micro-perforated panel 4, and the third micro-perforated panel 6) use micro-perforated panels with the same parameters except for thickness, perforation rate, perforation diameter, and perforation radius;

[0069] According to the solution provided by the above embodiments, the present invention provides the following specific embodiments to verify and illustrate the solution of the present invention.

[0070] Embodiment 1:

[0071] Referring to Fig. 3(a), the thickness t of the first micro-perforated panel 2 in this embodiment 1 = 1.5 mm, the perforation aperture d 1 = 1 mm, the perforation rate p 1 = 1%; the thickness t of the second micro-perforated panel 4 2 = 0.6 mm, the perforation aperture d 2 = 0.5 mm, the perforation rate p 2 = 1%; the thickness t of the third micro-perforated panel 6 3 = 0.8 mm, the perforation aperture d 3 = 0.6 mm, the perforation rate p 3 = 1.5%; the thickness of the annular cavity 3 (i.e., the height in the up and down direction) is 15 mm, and the correction coefficient is 1.06; the thickness of the cavity behind the second micro-perforated panel 5 is 20 mm, and the thickness of the cavity behind the third micro-perforated panel 7 is 20 mm. The upper surface radius of the frustum-shaped aluminum foam 1 is 7.5 mm, and the lower surface radius is 14.5 mm. The thickness of the frustum-shaped aluminum foam 1 is 30 mm, the flow resistivity is 114368 Pa·s / m 2 and the correction coefficient is 1.26.

[0072] As can be seen from Fig. 3(b), the sound-absorbing metamaterial of the frustum-shaped aluminum foam composite micro-perforated panel achieves an average sound absorption coefficient α≥0.95 in the medium and high frequency range of 3000 - 6300 Hz, and has two sound absorption peaks in the medium and low frequency range, significantly improving the low-frequency sound absorption coefficient. Among them, the simulation shows that the structural sound absorption coefficient reaches 100% at 493 Hz, achieving perfect sound absorption.

[0073] Embodiment 2:

[0074] Referring to Fig. 4(a), the thickness t of the first micro-perforated panel 2 1 = 1.2 mm, the perforation aperture d 1 = 0.5 mm, the perforation rate p 1 = 1%; the thickness t of the second micro-perforated panel 4 2 = 0.6 mm, the perforation aperture d 2 = 0.5 mm, the perforation rate p 2 = 0.77%; the thickness t of the third micro-perforated panel 6 3= 0.5 mm, perforation aperture d 3 = 0.5 mm, perforation rate p 3 = 0.8%; the thickness of the annular cavity 3 is 15 mm and the correction factor is 1.06; the thickness of the cavity 5 behind the second micro-perforated plate is 15 mm, and the thickness of the cavity 7 behind the third micro-perforated plate is 15 mm. The upper surface radius of the frustum-shaped aluminum foam is 7.5 mm and the lower surface radius is 14.5 mm. The thickness of the frustum-shaped aluminum foam 1 is 20 mm and the flow resistivity is 45992 Pa·s / m 2 and the correction factor is 1.26.

[0075] It can be seen from Fig. 4(b) that a perfect absorption coefficient appears at f1 = 846 Hz. Since the frustum-shaped aluminum foam 1 with a flow resistivity smaller than that of Example 1 is used, the absorption peak moves 353 Hz towards the high frequency. An average absorption coefficient α≥0.95 is also achieved within 3000 Hz - 6300 Hz. The total frequency band absorption coefficient of the composite absorption structure can reach more than 85%. The measurement results of the absorption coefficient show that by regulating the above geometric parameters, multi-band perfect absorption and the effect for specific noise sources can be achieved, effectively utilizing the coordinated effect of the frustum-shaped aluminum foam and the micro-perforated plate.

[0076] Example 3:

[0077] Referring to Fig. 5(b), the thickness t of the first micro-perforated plate 2 1 = 1.2 mm, perforation aperture d 1 = 0.5 mm, perforation rate p 1 = 1%; the thickness t of the second micro-perforated plate 4 2 = 0.6 mm, perforation aperture d 2 = 0.5 mm, perforation rate p 2 = 0.77%; the thickness t of the third micro-perforated plate 6 3 = 0.5 mm, perforation aperture d 3 = 0.5 mm, perforation rate p 3 = 0.8%; the thickness of the annular cavity 3 is 20 mm and the correction factor is 1.06; the thickness of the cavity 5 behind the second micro-perforated plate is 10 mm, and the thickness of the cavity 7 behind the third micro-perforated plate is 10 mm; the upper surface radius of the frustum-shaped aluminum foam 1 is 7.5 mm and the lower surface radius is 14.5 mm. The thickness of the frustum-shaped aluminum foam 1 is 20 mm and the flow resistivity is 145936 Pa·s / m 2 and the correction factor is 1.26.

[0078] As can be seen from Figure 5(b), in the frequency range of 3000 Hz to 6300 Hz, the sound absorption coefficient of this composite sound absorption structure decreases significantly compared with the above two embodiments, and the average sound absorption coefficient decreases by 8%. However, the first sound absorption peak moves 50 Hz towards the low frequency. The sound absorption coefficient measurement results show that the existence of the externally embedded inner perforated plate greatly improves the low-frequency sound absorption performance and the adjustment ability of the high-frequency sound absorption performance. The height of the externally embedded inner perforated plate can be reasonably adjusted according to the actual situation to meet the engineering requirements.

[0079] In the above embodiments of the present invention, two serially arranged sound absorption units are provided. The first sound absorption unit includes a truncated-cone-shaped aluminum foam, an externally embedded micro-perforated plate, and an annular cavity formed between the two. The second sound absorption unit includes a micro-perforated plate and a back cavity. The front end of the back cavity is open and a micro-perforated plate is provided, and the back end is closed to form a cavity. The micro-perforated plates of all sound absorption units are parallel to each other. In this structure, the parameters such as the shape and density of the truncated-cone-shaped aluminum foam have been carefully optimized, endowing the truncated-cone-shaped aluminum foam with special physical properties, and forming a continuous sound absorption broadband with an average sound absorption coefficient α≥0.9 in the medium and high frequency ranges. At the same time, by adjusting the externally embedded height of the externally embedded micro-perforated plate, the size of the quasi-circular ring cavity can be affected, so as to optimize the medium and high frequency sound absorption coefficient of the material without increasing the thickness of the truncated-cone-shaped aluminum foam. The second sound absorption unit can output two sound absorption peaks at different frequencies in the low frequency range by adjusting the perforation rate, perforation diameter, plate thickness and cavity thickness of the micro-perforated plate. Through the synergistic effect of the two, the sound absorption metamaterial of the truncated-cone-shaped aluminum foam composite micro-perforated plate can exhibit extremely excellent sound absorption performance in a quite wide frequency range. Whether in the low frequency, medium frequency or high frequency region, it can effectively absorb sound waves, greatly overcoming the problem of narrow sound absorption frequency bands of traditional sound absorption materials.

[0080] In summary, compared with a single sound absorption material or structure, this novel sound absorption metamaterial of the truncated-cone-shaped aluminum foam composite micro-perforated plate of the present invention greatly improves the average sound absorption coefficient. The composite characteristics enable the synergistic effect of the truncated-cone-shaped structure, aluminum foam and micro-perforated plate, effectively making up for the problem of insufficient low-frequency sound absorption of traditional sound absorption materials and significantly increasing the width of the sound absorption frequency band. By adjusting the externally embedded height of the externally embedded micro-perforated plate to affect the size of the concave cavity, the medium and high frequency sound absorption coefficient of the material can be adjusted and optimized without increasing the thickness of the truncated-cone-shaped aluminum foam. Generally speaking, this novel sound absorption metamaterial of the truncated-cone-shaped aluminum foam composite micro-perforated plate has strong designability, and the geometric parameters of the truncated-cone shape, the performance parameters of the aluminum foam and the parameters of the micro-perforated plate can be adjusted according to different sound absorption requirement scenarios. This high degree of designability enables the sound absorption metamaterial to flexibly meet the specific sound absorption requirements in various fields such as architecture, industry, aerospace, etc.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: it is still possible to modify the specific implementation manners of the present invention or make equivalent replacements, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A frustum-shaped aluminum foam composite micro-perforated plate sound-absorbing metamaterial, characterized in that: It comprises a frustum-shaped foam aluminum (1), wherein an annular first micro-perforated plate (2) is fixedly sleeved on the outer wall of the frustum-shaped foam aluminum (1), and the central axis of the first micro-perforated plate (2) is coaxial with the central axis of the frustum-shaped foam aluminum (1); the outer diameter of the first micro-perforated plate (2) is not less than the bottom diameter of the frustum-shaped foam aluminum (1); A second micro-perforated plate (4) is provided on the lower bottom surface of the truncated cone-shaped foam aluminum (1), a second micro-perforated plate rear cavity (5) is provided below the second micro-perforated plate (4), and the diameter of the second micro-perforated plate (4) is not less than the diameter of the lower bottom surface of the truncated cone-shaped foam aluminum (1).

2. The frustum-shaped aluminum foam composite micro-perforated plate sound-absorbing metamaterial according to claim 1, characterized in that: At least one micro-perforated plate parallel to the second micro-perforated plate (4) is arranged below the second micro-perforated plate (4), and each micro-perforated plate has a micro-perforated plate rear cavity; The diameters of all micro-perforated plates arranged below the second micro-perforated plate (4) are not less than the diameter of the lower bottom surface of the frustum-shaped foamed aluminum (1).

3. The frustum-shaped aluminum foam composite micro-perforated plate sound-absorbing metamaterial according to claim 2, characterized in that: The second micro-perforated plate (4) and the micro-perforated plate arranged below are both cylindrical micro-perforated plates.

4. The frustum-shaped aluminum foam composite micro-perforated plate sound-absorbing metamaterial according to claim 2, characterized in that: At least one microperforated plate is arranged below the second microperforated plate (4), the microperforated plate serving as a third microperforated plate (6), a third microperforated plate rear cavity (7) is provided below the third microperforated plate (6), and the cavity between the second microperforated plate (4) and the third microperforated plate (6) is the second microperforated plate rear cavity (5).

5. The frustum-shaped aluminum foam composite micro-perforated plate sound-absorbing metamaterial according to claim 4, characterized in that: The upper bottom diameter of the truncated cone type foam aluminum (1) is 10 to 19 mm, the lower bottom diameter is 29 mm, the height of the truncated cone type foam aluminum (1) is 30 mm, the porosity of the truncated cone type foam aluminum (1) is 62.1% to 78.0%, and the flow resistance is 45992 to 145936 Pa·s / m 2 .

6. The frustum-shaped aluminum foam composite micro-perforated plate sound-absorbing metamaterial according to claim 5, characterized in that: The distance between the first micro-perforated plate (2) and the bottom surface of the truncated cone-shaped foam aluminum (1) is 12 to 24 mm.

7. The frustum-shaped aluminum foam composite micro-perforated plate sound-absorbing metamaterial according to claim 5, characterized in that: Any two of the first micro-perforated plate (2), the second micro-perforated plate (4) and the third micro-perforated plate (6) have different thicknesses, different perforation rates and different perforation apertures; except for the thickness, perforation rate and perforation aperture, the first micro-perforated plate (2), the second micro-perforated plate (4) and the third micro-perforated plate (6) have the same parameters.

8. The frustum-shaped aluminum foam composite micro-perforated plate sound-absorbing metamaterial according to claim 7, characterized in that: The first micro-perforated plate (2) has a thickness of 0.2 to 1.5 mm, a perforation diameter of 0.3 to 1 mm, and a perforation rate of 1.78% to 2.56%; The second micro-perforated plate (4) has a thickness of 0.2 to 0.6 mm, a perforation diameter of 0.2 to 0.5 mm, and a perforation rate of 0.36% to 0.68%; The third micro-perforated plate (6) has a thickness of 0.5-0.9 mm, a perforation diameter of 0.4-0.8 mm, and a perforation rate of 1.25%-1.78%.

9. The frustum-shaped aluminum foam composite micro-perforated plate sound-absorbing metamaterial according to claim 5, characterized in that: The thickness of the second micro-perforated plate rear cavity (5) is 10-20 mm.

10. The frustum-shaped aluminum foam composite micro-perforated plate sound-absorbing metamaterial according to claim 5, characterized in that: The thickness of the third micro-perforated plate rear cavity (7) is 10-20 mm.

Images