Sound absorption metamaterial based on foamed aluminum and similar to Helmholtz resonance effect

Abstract

The invention belongs to the technical field of noise control, and discloses a foamed aluminum-based sound absorption metamaterial with a Helmholtz resonance-like effect, which comprises a plurality of Helmholtz resonance-like units, each Helmholtz resonance-like unit has different resonance frequencies, the resonance frequencies are arranged on different frequency bands, and all the frequency bands form a preset broadband range; each Helmholtz resonance-like unit comprises a perforated foamed aluminum plate and a cavity corresponding to the perforated foamed aluminum plate, the perforated foamed aluminum plate is provided with a circular through hole, the through hole penetrates through the perforated foamed aluminum plate, and a foamed aluminum cylinder with a preset length is inserted into the through hole; the porosity of the perforated foamed aluminum plate is smaller than that of the foamed aluminum cylinder, and the flow resistance rate of the perforated foamed aluminum plate is larger than that of the foamed aluminum cylinder. According to the invention, the sound absorption bandwidth can be greatly improved, the structure is simple, and the production cost and the technical difficulty are obviously reduced, so that the structure has wide application potential in multiple fields.

Description

Technical Field

[0001] The invention belongs to the technical field of noise control, and in particular relates to a sound-absorbing metamaterial based on a Helmholtz-like resonance effect of foamed aluminum. Background Art

[0002] At present, various sound-absorbing materials and technologies are widely used in the field of noise control, including foam materials, fiber materials, porous plates, and resonant sound-absorbing structures. These materials and technologies have good sound absorption performance within a specific frequency range, but often have poor effects within a wide frequency range. For example: Invention patent CN201910770054.9 proposes a multi-unit coupled micro-perforated plate low-frequency broadband sound absorption structure and its design method, but the structure is complex, puts higher requirements on the preparation process, and only has excellent sound absorption performance at 400~2400Hz.

[0003] The Helmholtz cavity is a commonly used acoustic resonance structure that consists of a neck and a cavity, which can produce a sound absorption effect for a specific frequency. This structure achieves energy absorption at a specific frequency by interacting the air column vibration in the neck with the air vibration in the cavity.

[0004] Aluminum foam is a lightweight porous metal material with good mechanical properties and certain sound absorption performance. Its porosity and flow resistivity are the key factors affecting the sound absorption effect. Aluminum foam with small porosity has a higher flow resistivity and is acoustically analogous to a rigid material.

[0005] Although existing sound absorbing materials and structures are effective in specific applications, they have the following limitations: (1) Frequency band limitation: Many sound-absorbing materials and technologies are only effective within a narrow frequency band and cannot cover the wide frequency range of 0~5000Hz.

[0006] (2) Uneven sound absorption coefficient: In a wide frequency band, the average sound absorption coefficient of existing sound absorption structures is often low, and it is difficult to reach the ideal level of above 0.7.

[0007] (3) Complex structure: In order to achieve broadband sound absorption, it may be necessary to combine multiple materials and structures, resulting in complex design and construction and increased costs. Summary of the invention

[0008] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a sound-absorbing metamaterial based on the Helmholtz resonance effect of foamed aluminum. The present invention couples the excellent sound absorption performance of the foamed aluminum material in medium and high frequencies with the Helmholtz resonance structure to achieve excellent sound absorption performance in a wider frequency band. It has the advantages of simple structure and high sound absorption efficiency, and has a high sound absorption coefficient while having a wide-band sound absorption effect.

[0009] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A sound-absorbing metamaterial based on the Helmholtz-like resonance effect of foamed aluminum, comprising a plurality of Helmholtz-like resonance units, each of which has a different resonance frequency, and the resonance frequency of each Helmholtz-like resonance unit is set in a different frequency band, and all the frequency bands constitute a preset wide frequency range; Each Helmholtz-like resonance unit includes a perforated foam aluminum plate and a cavity corresponding to the perforated foam aluminum plate, wherein the perforated foam aluminum plate is provided with a circular perforation, the perforation passes through the perforated foam aluminum plate, and a foam aluminum cylinder of a preset length is inserted into the perforation; The porosity of the perforated foam aluminum plate is less than the porosity of the foam aluminum cylinder, and the flow resistivity of the perforated foam aluminum plate is greater than the flow resistivity of the foam aluminum cylinder.

[0010] Preferably, the perforated aluminum foam plate has a thickness of 10-20 mm, a porosity of 10%-25%, and a flow resistance of 114368. ~180156 .

[0011] Preferably, the porosity of the foamed aluminum cylinder is 80% to 95%, and the flow resistance is 14820 to 41881. , the diameter is 5~10mm, and the foam aluminum cylinder and the perforation are fixedly connected by friction.

[0012] Preferably, the depth of the cavity is 40-80 mm.

[0013] Preferably, one end of the foam aluminum cylinder is flush with the surface of the perforated foam aluminum plate, and the other end extends into the cavity.

[0014] Preferably, all the Helmholtz-like resonance units share a perforated foam aluminum plate, the perforated foam aluminum plate is provided with the perforations at positions corresponding to each Helmholtz-like resonance unit, the perforated foam aluminum plate has a rear cavity, a partition is provided at the rear cavity, and the rear cavity is separated into cavities corresponding to the perforated foam aluminum plate in each Helmholtz-like resonance unit by the partition.

[0015] Preferably, the diameters of the holes on the perforated foam aluminum plates of all the Helmholtz-like resonance units are the same.

[0016] Preferably, the number of the Helmholtz-like resonance units is four, and the four Helmholtz-like resonance units are respectively recorded as a low-frequency band Helmholtz-like resonance unit, a medium-low frequency band Helmholtz-like resonance unit, a medium-high frequency band Helmholtz-like resonance unit and a high-frequency band Helmholtz-like resonance unit, wherein the sound absorption frequency band of the low-frequency band Helmholtz-like resonance unit is 0~1250Hz, the sound absorption frequency band of the medium-low frequency band Helmholtz-like resonance unit is 1250~2500Hz, the sound absorption frequency band of the medium-high frequency band Helmholtz-like resonance unit is 2500~3750Hz, and the sound absorption frequency band of the high-frequency band Helmholtz-like resonance unit is 3750~5000Hz.

[0017] Preferably: in the low-frequency band Helmholtz-like resonance unit, the length of the foam aluminum cylinder extending into the cavity of the low-frequency band Helmholtz-like resonance unit is 1 / 4 to 1 / 3 of the depth of the cavity; In the low- to medium-frequency band Helmholtz-like resonance unit, the length of the foamed aluminum cylinder extending into the cavity of the low-frequency band Helmholtz-like resonance unit is 1 / 3 to 1 / 2 of the depth of the cavity; In the mid-high frequency band Helmholtz resonance unit, the length of the foam aluminum cylinder extending into the cavity of the low frequency band Helmholtz resonance unit is 1 / 2 to 2 / 3 of the cavity depth; In the high-frequency band Helmholtz-like resonance unit, the length of the foam aluminum cylinder extending into the cavity of the low-frequency band Helmholtz-like resonance unit is 2 / 3 to 3 / 4 of the depth of the cavity.

[0018] Preferably, in the low-frequency band Helmholtz-like resonance unit, the length of the foam aluminum cylinder extending into the cavity of the low-frequency band Helmholtz-like resonance unit is 15-20 mm; In the low- and medium-frequency band Helmholtz resonance unit, the length of the foam aluminum cylinder extending into the cavity of the low-frequency band Helmholtz resonance unit is 20-25 mm; In the mid- and high-frequency band Helmholtz resonance unit, the length of the foam aluminum cylinder extending into the cavity of the low-frequency band Helmholtz resonance unit is 25 to 30 mm; In the high-frequency band Helmholtz resonance unit, the length of the foam aluminum cylinder extending into the cavity of the low-frequency band Helmholtz resonance unit is 30-35 mm.

[0019] The present invention has the following beneficial effects: The sound-absorbing metamaterial based on the Helmholtz-like resonance effect of foam aluminum of the present invention includes four independent Helmholtz-like resonance units, and each Helmholtz-like resonance unit adopts a foam aluminum plate with small porosity and large flow resistivity as a quasi-rigid plate. A perforation is arranged on each quasi-rigid plate, and a foam aluminum material with large porosity (i.e., a foam aluminum cylinder) is filled in the hole to form the neck of the Helmholtz-like resonance cavity. A cavity is arranged below the quasi-rigid plate of each Helmholtz-like resonance unit, which together with the filling material (i.e., the foam aluminum cylinder) constitutes a complete Helmholtz-like resonance cavity. By controlling the filling height of the foam aluminum cylinder, the resonance frequency of each Helmholtz-like resonance unit can be adjusted, and a broadband sound absorption effect can be achieved through coupling. In the present invention, the resonance frequency of each Helmholtz-like resonance unit can be accurately controlled by adjusting the length of the foam aluminum material (i.e., the foam aluminum cylinder) filled in the perforation extending into the lower cavity. Foam aluminum cylinders of different lengths will lead to different resonance frequencies, thereby achieving a broadband sound absorption effect. The present invention connects a plurality of Helmholtz-like resonance units in parallel, sets the resonance frequency of each Helmholtz-like resonance unit in a different frequency band, and through this parallel coupling mode, enables the entire structure to provide efficient sound absorption performance within a preset wide frequency range. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0021] FIG. 1( a ) is a schematic structural diagram of a sound-absorbing metamaterial based on the Helmholtz resonance effect of foamed aluminum in an embodiment of the present invention; FIG. 1( b ) is a front view of the structure shown in FIG. 1( a ); Figure 2 This is a finite element model diagram of a sound-absorbing metamaterial based on the Helmholtz-like resonance effect of foamed aluminum in an embodiment of the present invention; FIG3( a ) is a schematic diagram of a sound-absorbing metamaterial based on the Helmholtz resonance effect of foamed aluminum according to Example 1 of the present invention, and FIG3( b ) is a sound absorption coefficient of the sound-absorbing metamaterial based on the Helmholtz resonance effect of foamed aluminum according to Example 1; FIG4( a ) is a schematic diagram of a sound-absorbing metamaterial based on the Helmholtz resonance effect of foamed aluminum according to Example 2 of the present invention, and FIG4( b ) is a sound absorption coefficient of the sound-absorbing metamaterial based on the Helmholtz resonance effect of foamed aluminum according to Example 2; FIG5( a ) is a schematic diagram of a sound-absorbing metamaterial based on the Helmholtz resonance-like effect of foamed aluminum according to Example 3 of the present invention, and FIG5( b ) is a diagram of the sound absorption coefficient of the sound-absorbing metamaterial based on the Helmholtz resonance-like effect of foamed aluminum according to Example 3 of the present invention.

[0022] In the figure, 1-foam aluminum plate, 1-1-first perforation, 1-2-second perforation, 1-3-third perforation, 1-4-fourth perforation, 2-rear cavity, 3-first foam aluminum cylinder, 4-second foam aluminum cylinder, 5-third foam aluminum cylinder, 6-fourth foam aluminum cylinder, 7-first partition, 8-second partition. DETAILED DESCRIPTION

[0023] In order to make the purpose, 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 in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention described and shown in the drawings here can usually be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0024] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper" and "lower" and the like 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 or be constructed in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0025] Various structural schematic diagrams according to the embodiments disclosed in the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions with different shapes, sizes, and relative positions according to actual needs.

[0026] See Figure 1(a), Figure 1(b) and Figure 2The present embodiment is a sound-absorbing metamaterial based on the Helmholtz-like resonance effect of foam aluminum, comprising a plurality of Helmholtz-like resonance units, each of which has a different resonance frequency, and the resonance frequency of each Helmholtz-like resonance unit is set at a different frequency band, and all frequency bands constitute a preset wide frequency range; each Helmholtz-like resonance unit comprises a perforated foam aluminum plate and a cavity corresponding to the perforated foam aluminum plate, the perforated foam aluminum plate is provided with a circular perforation, the perforation passes through the perforated foam aluminum plate, and a foam aluminum cylinder of a preset length is inserted into the perforation; the porosity of the perforated foam aluminum plate is less than the porosity of the foam aluminum cylinder, and the flow resistivity of the perforated foam aluminum plate is greater than the flow resistivity of the foam aluminum cylinder.

[0027] As a preferred embodiment of the present invention, all Helmholtz-like resonance units share a perforated foam aluminum plate, the perforated foam aluminum plate is provided with the perforations at positions corresponding to each Helmholtz-like resonance unit, the perforated foam aluminum plate has a rear cavity 2, a partition is provided at the rear cavity 2, and the rear cavity 2 is separated by the partition into cavities corresponding to the perforated foam aluminum plate in each Helmholtz-like resonance unit.

[0028] The following embodiment of the present invention uses a multi-unit parallel broadband sound absorption structure as an example to verify the technical solution of the present invention. Specifically, the structure of the sound absorption metamaterial based on the Helmholtz-like resonance effect of foam aluminum includes four independent Helmholtz-like resonance units, and each Helmholtz-like resonance unit uses a foam aluminum plate with a small porosity and a large flow resistivity as a quasi-rigid plate. A circular perforation is provided on each quasi-rigid plate, and a foam aluminum cylinder made of a foam aluminum material with a large porosity is filled in the perforation to form the neck of the Helmholtz-like resonance cavity. A cavity is provided under the quasi-rigid plate of each Helmholtz-like resonance unit, which together with the filling material (i.e., the foam aluminum cylinder) constitutes a complete Helmholtz-like resonance cavity. By controlling the filling height of the foam aluminum cylinder, the resonant frequency of each Helmholtz-like resonance unit can be adjusted, and a broadband sound absorption effect can be achieved through coupling.

[0029] The resonance frequency control method of the present invention is as follows: by adjusting the length of the foam aluminum cylinder filled in the hole extending into the cavity below, the resonance frequency of each Helmholtz-like resonance unit can be accurately controlled. Foam aluminum cylinders of different lengths will lead to different resonance frequencies, thereby achieving a broadband sound absorption effect.

[0030] The parallel coupling method in the present invention is as follows: four Helmholtz-like resonance units are connected in parallel, and the resonance frequency of each unit is set at a different frequency band. Through this parallel coupling method, the entire structure can provide efficient sound absorption performance in a wide frequency range of 0 to 5000 Hz. The sound absorption structure of the following embodiment of the present invention (i.e., the sound absorption metamaterial based on the Helmholtz-like resonance effect of foamed aluminum) has an average sound absorption coefficient of more than 0.7 in a wide frequency range of 0 to 5000 Hz, which is significantly better than the prior art; the structure is simple and the cost is reduced.

[0031] In order to achieve excellent sound absorption performance in the range of 0-5000 Hz, parameters of four Helmholtz-like resonance unit structures are preset, including: the foam aluminum rigid plate (i.e., foam aluminum plate 1) is a cube with a thickness of 10-20 mm, a porosity of 10%-25%, and a flow resistance of 114368. ~180156 The diameter of the perforation is 5-10 mm; the foam aluminum filling material is a cylinder (i.e., foam aluminum cylinder), with a porosity of 80%-95% and a flow resistance of 14820-41881 , the cavity depth is 40~80mm; at the same time, some basic formulas are also modified by parameters. Since the rigid plate part of the Helmholtz resonator is replaced by a rigid plate with a small porosity, and the inner neck part is embedded with a cylindrical foam aluminum with a large porosity, the parameters of the foam aluminum have a great influence on the entire structure, especially the porosity and flow resistivity of the foam aluminum. For example: when the foam aluminum is used as a quasi-rigid plate, the porosity will affect its structural strength and the trajectory and dissipation of the sound wave incident into the resonance cavity; when it is embedded in the perforation as an inner diameter, its porosity and flow resistivity will affect the effective volume of the internal cavity and the sound wave incident mode. In addition, the Helmholtz-like cavity and neck impedance proposed by the present invention will also be affected to a certain extent. Therefore, the present invention introduces a correction coefficient on the basic formula. The correction principle is to introduce a correction coefficient on the basis of the basic formula. The correction coefficient is determined by the size parameters and structural characteristics of the material.

[0032] The sound-absorbing metamaterial based on the Helmholtz-like resonance effect of foam aluminum in the following embodiment of the present invention is composed of four Helmholtz-like resonance units, specifically including: a foam aluminum plate 1 with a rear cavity 2; the foam aluminum plate 1 has four evenly distributed perforations, the four perforations are respectively recorded as a first perforation 1-1, a second perforation 1-2, a third perforation 1-3, and a fourth perforation 1-4, and a first foam aluminum cylinder 3, a second foam aluminum cylinder 4, a third foam aluminum cylinder 5, and a fourth foam aluminum cylinder 6 are respectively embedded in the four perforations to form an inner neck; the rear cavity 2 has a first baffle 7 and a second baffle 8, which divides the rear cavity 2 into four chambers, and each Helmholtz-like resonance unit corresponds to a cavity; The foam aluminum plate 1 has a large flow resistivity and a small porosity, and can be used as a rigid panel of a Helmholtz-like resonator; the flow resistivity of the foam aluminum plate 1 ranges from 114 to 368. ~180156 , the porosity is 10%~25%; the foam aluminum cylinder has a small flow resistivity and a large porosity; the flow resistivity of the first foam aluminum cylinder 3, the second foam aluminum cylinder 4, the third foam aluminum cylinder 5, and the fourth foam aluminum cylinder 6 is 14820 ~41881 , the porosity is 80%~95%; the diameters of the first foam aluminum cylinder 3, the second foam aluminum cylinder 4, the third foam aluminum cylinder 5, and the fourth foam aluminum cylinder 6 are the same, the inner diameters of the first perforation 1-1, the second perforation 1-2, the third perforation 1-3, and the fourth perforation 1-4 are the same, and the diameters of the first foam aluminum cylinder 3, the second foam aluminum cylinder 4, the third foam aluminum cylinder 5, and the fourth foam aluminum cylinder 6 are the same as the diameters of the first perforation 1-1, the second perforation 1-2, the third perforation 1-3, and the fourth perforation 1-4. The friction between the non-smooth surfaces of the foam aluminum cylinders can make the first foam aluminum cylinder 3 firmly nested in the first perforation 1-1, the second foam aluminum cylinder 4 firmly nested in the second perforation 1-2, the third foam aluminum cylinder 5 firmly nested in the third perforation 1-3, and the fourth foam aluminum cylinder 6 firmly nested in the fourth perforation 1-1. Since the first foam aluminum cylinder 3, the second foam aluminum cylinder 4, the third foam aluminum cylinder 5, and the fourth foam aluminum cylinder 6 have a large porosity, they can be analogized to the neck of the Helmholtz resonator; The preset structure of the sound-absorbing metamaterial based on the Helmholtz resonance effect of foamed aluminum in the following embodiment of the present invention includes the following parameters: The thickness t of the quasi-rigid plate of the foam aluminum plate 1 of each quasi-Helmholtz resonance unit; the porosity and flow resistivity of the foam aluminum plate 1; the diameters of the four perforations (i.e., the first perforation 1-1, the second perforation 1-2, the third perforation 1-3, and the fourth perforation 1-4) are respectively , , , ; Depth of rear cavity 2 h ; The thickness of the two partitions (i.e. the first partition 7 and the second partition 8) inside the rear cavity 2 ; The height of the partition is consistent with the depth of the thickness cavity 2; the porosity of the perforated internally nested foam aluminum cylinders (i.e., the first foam aluminum cylinder 3, the second foam aluminum cylinder 4, the third foam aluminum cylinder 5, and the fourth foam aluminum cylinder 6) and flow resistance And the filling height of the foam aluminum cylinder ; Each Helmholtz-like resonance unit is composed of a perforated foam aluminum plate 1 (quasi-rigid plate) and a corresponding cavity to form a Helmholtz-like resonance structure; a cylindrical foam aluminum is embedded in the perforation of the foam aluminum plate 1; by controlling the height of the foam aluminum filled inside the perforation, the four Helmholtz-like resonance units respectively dominate the sound absorption performance in different frequency bands; the resonance structure is optimized to achieve broadband sound absorption performance (average sound absorption coefficient α≥0.7) from 0 to 5000 Hz, and the optimization design specifically includes the following steps: Step 1: Determine the frequency band division and divide the frequency range of 0~5000Hz into four frequency bands, namely 0~1250Hz, 1250~2500Hz, 2500~3750Hz, and 3750~5000Hz.

[0033] Step 2: Calculate the resonant frequencies of the four Helmholtz-like resonant units: (1) Calculation of effective volume: Considering the porosity of aluminum foam, the effective volume will be smaller than the actual volume. It is expressed as: (1) in, V : volume of the resonance cavity; : Effective porosity of foamed aluminum; (2) Calculation of effective flow resistivity: The flow resistance of aluminum foam will affect the acoustic resistance of the Helmholtz-like resonator. It can be expressed as: (2) in, :Flow resistance of aluminum foam.

[0034] (3) Corrected resonant frequency: Considering the characteristics of foamed aluminum and the influence of inner diameter length on it, the resonant frequency is corrected to: (3) in, For the i The cross-sectional area of ​​a perforation is: For the i The diameter of the perforation.

[0035] Step 3: Adjust the filling length of the foam aluminum cylinder so that the resonant frequencies of the four Helmholtz-like resonance units are in different frequency bands: For each quasi-Helmholtz resonance unit, the target resonance frequency is achieved by adjusting the length of the filled foam aluminum cylinder extending into the cavity. In the low frequency band (0-1250 Hz), the filling length of the first foam aluminum cylinder 3 is at least 1 / 4 to 1 / 3 of the cavity depth; in the medium-low frequency band (1250-2500 Hz), the filling length of the second foam aluminum cylinder 4 is 1 / 3 to 1 / 2 of the cavity depth; in the medium-high frequency band (2500-3750 Hz), the filling length of the third foam aluminum cylinder 5 is 1 / 2 to 2 / 3 of the cavity length; in the high frequency unit (3750-5000 Hz), the filling length of the fourth foam aluminum cylinder 6 is 2 / 3 to 3 / 4 of the cavity length; According to the preset parameters of the Helmholtz-like resonance structure corresponding to the aluminum foam matrix, the corresponding acoustic impedance is calculated to ensure that the impedance of the neck and cavity matches the air impedance as much as possible to achieve efficient sound absorption. The preset parameters include: (1) Pipeline impedance: The neck can be regarded as a pipeline. Its impedance is expressed as: (4) (2) Foam aluminum impedance: The resistivity of foam aluminum will affect the propagation of sound waves in the neck, thereby affecting the neck impedance. A correction factor can be introduced to consider the influence of foam aluminum resistivity and porosity: (5) Where j is the imaginary unit; is the angular frequency; is the density of aluminum foam; is the speed of sound in aluminum foam; is the flow resistivity correction factor.

[0036] (6) in, is the porosity of aluminum foam, L is the height of the cylinder, D is the diameter of the cylindrical aluminum foam, n is an empirical index; (3) Neck impedance: The neck impedance Z can be regarded as the series connection of the pipeline impedance and the foam aluminum impedance: (7) (4) Cavity impedance: The cavity of the Helmholtz-like resonant cavity can be regarded as a physical and chemical acoustic spring. Foamed aluminum will affect the equivalent volume of the cavity, thereby affecting the cavity impedance. A correction factor is introduced to consider the influence of the porosity of foamed aluminum. Its impedance can be calculated using the following formula: (8) in, V : cavity volume; S : Cross-sectional area of ​​the perforation.

[0037] From the above, the total impedance of the Helmholtz-like resonator based on the foam aluminum matrix is: (9) According to the above process, the heights of the foam aluminum cylinders are determined as follows: In the low frequency band (0~1250Hz), the filling height of the first foam aluminum cylinder 3 is 15~20mm, and the filling height of the second foam aluminum cylinder 4 is 20~25mm; in the medium and high frequency bands (2500~3750Hz), the filling height of the third foam aluminum cylinder 5 is 25~30mm; in the high frequency unit (3750~5000Hz), the filling height of the fourth foam aluminum cylinder 6 is 30~35mm.

[0038] Comparative Example 1 Since the structure described in the present invention is a sound-absorbing structure based on the Helmholtz resonance effect, the embodiment needs to be compared with a Helmholtz resonance cavity structure without nested foam aluminum. See Figure 3 (a), the thickness of the upper aluminum rigid plate is t=5mm, the depth of the rear cavity is h=40mm, and the diameter of the four perforations on the rigid plate, i.e., the neck-like, is d=5mm. (The cylindrical perforations on the foam aluminum rigid plate of this structure do not have foam aluminum nested inside) Example 1 As shown in Figure 3 (a), the porosity of the upper layer of foam aluminum is 80%, and the flow resistance is 14820 , thickness is 5mm, the depth of the rear cavity is 40mm, the diameter of the four perforations on the rigid plate, i.e. the neck, is d=5mm; the heights of the four foam aluminum cylinders are 15mm, 20mm, 25mm, and 30mm respectively. The porosity of the internally nested foam aluminum cylinder is 10%, and the flow resistance is 114368 .

[0039] Example 2 As shown in Figure 4 (a), the porosity of the upper layer of foam aluminum is 85%, and the flow resistance is 30246 , thickness is 10mm, the depth of the back cavity is 60mm, the diameter of the four perforations on the rigid plate, i.e. the neck, is d=7mm; the heights of the four foam aluminum cylinders are 20mm, 25mm, 30mm, and 35mm respectively. The porosity of the internally nested foam aluminum cylinder is 15%, and the flow resistance is 145936 .

[0040] Example 3 As shown in Figure 5 (a), the porosity of the upper layer of foam aluminum is 95%, and the flow resistance is 41881 , thickness is 20mm, the depth of the back cavity is 80mm, the diameter of the four perforations on the rigid plate, i.e. the neck, is d=10mm; the heights of the four foam aluminum cylinders are 20mm, 25mm, 30mm, and 35mm respectively. The porosity of the internally nested foam aluminum cylinder is 25%, and the flow resistance is 180156 .

[0041] Referring to Figures 3 (b), 4 (b) and 5 (b), it can be seen from the three sound absorption curves of the embodiments that the Helmholtz resonator-like sound absorption metamaterial based on the foam aluminum matrix has a wider sound absorption band and better sound absorption effect than the ordinary Helmholtz resonance cavity. In Examples 2 and 3, four obvious sound absorption peaks appeared in the range of 0~5000Hz, and the sound absorption peaks were distributed in 0~1250Hz, 1250~2500Hz, 2500~3750Hz, and 3750~5000Hz, respectively. This shows that due to the changes in the filling height and porosity of the different foam aluminum, the four units have corresponding sound absorption peaks in different frequency bands, and at the same time, the four units are connected in parallel to produce a coupling effect, so that there are good sound absorption peaks and wider bandwidths in the entire frequency band (0~5000Hz). As the filling height of foam aluminum increases, the cavity volume of the Helmholtz-like resonance structure becomes larger, and the sound absorption ability of the sound absorber for low frequencies becomes stronger, ultimately achieving a relatively excellent sound absorption peak over the entire frequency band.

[0042] Specifically, the average sound absorption coefficient of Example 1 is 0.55, and there are obvious sound absorption peaks only at 400-500Hz and 2000-3000Hz, with a maximum value of no more than 0.7. After the design of the present invention is introduced, referring to FIG4 (b), four peaks appear, at 980Hz, 2150Hz, 2970Hz and 4250Hz, respectively, and the peak value reaches 0.96 at the highest. The average sound absorption coefficient is also improved, which significantly improves the problems of narrow sound absorption band and low peak value. The increase in the thickness of the upper layer of foam aluminum also directly leads to an increase in the sound absorption coefficient. This is because the greater the thickness of the foam aluminum, the more sound waves it absorbs, the greater the sound absorption, and the better the sound absorption effect, especially when dealing with high-frequency sound waves. For the quasi-rigid board, keep its porosity at a low level to ensure structural strength and flow resistivity. For the filling material foam aluminum, keep its porosity at a high level to optimize the sound absorption effect when it is matched with the quasi-rigid board.

[0043] In summary, the present invention can greatly improve the sound absorption bandwidth, has the advantages of simple structure, and significantly reduces production costs and technical difficulties, making the structure have broad application potential in multiple fields.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A sound-absorbing metamaterial based on the Helmholtz resonance effect of foamed aluminum, characterized in that: It includes a plurality of Helmholtz-like resonance units, each of which has a different resonance frequency, and the resonance frequency of each Helmholtz-like resonance unit is set in a different frequency band, and all the frequency bands constitute a preset wide frequency range; Each Helmholtz-like resonance unit includes a perforated foam aluminum plate and a cavity corresponding to the perforated foam aluminum plate, wherein the perforated foam aluminum plate is provided with a circular perforation, the perforation passes through the perforated foam aluminum plate, and a foam aluminum cylinder of a preset length is inserted into the perforation; The porosity of the perforated foam aluminum plate is less than the porosity of the foam aluminum cylinder, and the flow resistivity of the perforated foam aluminum plate is greater than the flow resistivity of the foam aluminum cylinder.

2. The sound-absorbing metamaterial based on the Helmholtz resonance effect of foamed aluminum according to claim 1, characterized in that: The perforated foam aluminum plate has a thickness of 10-20 mm, a porosity of 10%-25%, and a flow resistance of 114368. ~180156 .

3. The sound-absorbing metamaterial based on the Helmholtz resonance effect of foamed aluminum according to claim 1, characterized in that: The porosity of the foam aluminum cylinder is 80% to 95%, and the flow resistance is 14820 to 41881 , the diameter is 5~10mm, and the foam aluminum cylinder and the perforation are fixedly connected by friction.

4. The sound-absorbing metamaterial based on the Helmholtz resonance effect of foamed aluminum according to claim 1, characterized in that: The depth of the cavity is 40-80 mm.

5. The sound-absorbing metamaterial based on the Helmholtz resonance effect of foamed aluminum according to claim 1, characterized in that: One end of the foam aluminum cylinder is flush with the surface of the perforated foam aluminum plate, and the other end extends into the cavity.

6. The sound-absorbing metamaterial based on the Helmholtz resonance effect of foamed aluminum according to claim 1, characterized in that: All the Helmholtz-like resonance units share a perforated foam aluminum plate, the perforated foam aluminum plate is provided with the perforations at positions corresponding to each Helmholtz-like resonance unit, the perforated foam aluminum plate has a rear cavity (2), a partition is provided at the rear cavity (2), and the rear cavity (2) is separated into cavities corresponding to the perforated foam aluminum plate in each Helmholtz-like resonance unit by the partition.

7. The sound-absorbing metamaterial based on the Helmholtz resonance effect of foamed aluminum according to claim 1, characterized in that: The diameter of the holes in the perforated aluminum foam plates of all Helmholtz-like resonance units is the same.

8. A sound-absorbing metamaterial based on the Helmholtz resonance effect of foamed aluminum according to any one of claims 1 to 7, characterized in that: The number of the Helmholtz-like resonance units is four, and the four Helmholtz-like resonance units are respectively recorded as a low-frequency band Helmholtz-like resonance unit, a medium-low frequency band Helmholtz-like resonance unit, a medium-high frequency band Helmholtz-like resonance unit and a high-frequency band Helmholtz-like resonance unit, wherein the sound absorption frequency band of the low-frequency band Helmholtz-like resonance unit is 0-1250 Hz, the sound absorption frequency band of the medium-low frequency band Helmholtz-like resonance unit is 1250-2500 Hz, the sound absorption frequency band of the medium-high frequency band Helmholtz-like resonance unit is 2500-3750 Hz, and the sound absorption frequency band of the high-frequency band Helmholtz-like resonance unit is 3750-5000 Hz.

9. The sound-absorbing metamaterial based on the Helmholtz resonance effect of foamed aluminum according to claim 8, characterized in that: In the low-frequency band Helmholtz-like resonance unit, the length of the foam aluminum cylinder extending into the cavity of the low-frequency band Helmholtz-like resonance unit is 1 / 4 to 1 / 3 of the depth of the cavity; In the low- to medium-frequency band Helmholtz-like resonance unit, the length of the foamed aluminum cylinder extending into the cavity of the low-frequency band Helmholtz-like resonance unit is 1 / 3 to 1 / 2 of the depth of the cavity; In the mid-high frequency band Helmholtz resonance unit, the length of the foam aluminum cylinder extending into the cavity of the low frequency band Helmholtz resonance unit is 1 / 2 to 2 / 3 of the cavity depth; In the high-frequency band Helmholtz-like resonance unit, the length of the foam aluminum cylinder extending into the cavity of the low-frequency band Helmholtz-like resonance unit is 2 / 3 to 3 / 4 of the depth of the cavity.

10. The sound-absorbing metamaterial based on the Helmholtz resonance effect of foamed aluminum according to claim 9, characterized in that: In the low-frequency band Helmholtz-like resonance unit, the length of the foam aluminum cylinder extending into the cavity of the low-frequency band Helmholtz-like resonance unit is 15-20 mm; In the low- and medium-frequency band Helmholtz resonance unit, the length of the foam aluminum cylinder extending into the cavity of the low-frequency band Helmholtz resonance unit is 20-25 mm; In the mid- and high-frequency band Helmholtz resonance unit, the length of the foam aluminum cylinder extending into the cavity of the low-frequency band Helmholtz resonance unit is 25 to 30 mm; In the high-frequency band Helmholtz resonance unit, the length of the foam aluminum cylinder extending into the cavity of the low-frequency band Helmholtz resonance unit is 30-35 mm.

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