A composite sound-absorbing structure based on acoustic black holes

Abstract

This invention discloses a composite sound-absorbing structure based on acoustic black holes, comprising multiple coplanar acoustic black hole units containing nested Helmholtz resonators. Each unit includes multiple perforated plates connected in series and a Helmholtz resonator with a nested cavity connected to its end. This composite structure increases the equivalent acoustic cavity length through the nested cavity, significantly enhancing low-frequency sound absorption performance below 200Hz, achieving excellent subwavelength sound absorption characteristics while maintaining a compact thickness. Through parameter optimization of the unit coplanarity and target frequency band, the total thickness at the 86Hz sound absorption peak is approximately λ / 50, and an average sound absorption coefficient of 0.8604 within the 226–1000Hz range can be achieved with a total thickness of less than 70 mm. The nested cavity design improves acoustic control flexibility, enabling precise control of complex low-frequency broadband noise. It possesses advantages such as small size, wide bandwidth, and strong low-frequency absorption, making it suitable for high-end noise control fields such as aerospace and shipbuilding, with broad application prospects.

Description

Technical Field

[0001] This invention relates to a composite sound-absorbing structure based on an acoustic black hole for low-frequency broadband sound absorption, comprising a nested cavity Helmholtz resonator, belonging to the field of noise control technology. Background Technology

[0002] An acoustic black hole (SBH) is a sound-absorbing structure with broadband sound absorption performance in the mid-to-high frequency range. It consists of multiple gradually changing rings and cavities, achieving broadband sound absorption through resonant coupling of multiple cavities using the slow-wave effect. It is widely used for noise control in applications such as pipelines. However, traditional SBHs are highly dependent on structural thickness, and their sound energy loss mainly stems from the absorption of sound energy by air impedance. Furthermore, because the terminal radius of an SBH is not zero during actual manufacturing, it cannot absorb all incident sound waves, especially resulting in poor low-frequency performance. Therefore, in recent years, a series of studies have been conducted to compensate for the structure's low-frequency performance and improve its subwavelength performance. Perforated panels (PP) and Helmholtz resonators (HR) are both effective low-frequency sound absorption devices. They both utilize the compressibility of air within the micro-perforations and neck of the cavity to convert sound energy into heat energy when exposed to sound waves. They can effectively reduce low-frequency sound energy with subwavelength structural thickness, thus enhancing the low-frequency performance of SBH (Sound Absorber). In the research of Zhang Jianrun et al. (Chen Y, Yu K, Fu Q, Zhang J, Lu X, Du X, et al. A broadband and low-frequency sound absorber of sonicblack holes with multi-layered micro-perforated panels. Applied Acoustics 2024;217:109817), by incorporating multiple layers of PP, the sound energy loss is transformed into a combined effect of the PP and the cavity, achieving good broadband performance from 225 Hz to 3000 Hz. However, its performance below 200 Hz still has shortcomings, and its structural thickness is relatively large, requiring further improvement in subwavelength performance. In the research of Mao et al. (Peng L, Mao Q. Helmholtz Resonator with Sonic Black Hole Neck. The International Journal of Acoustics and Vibration 2023;28:460–8), a low-frequency performance improvement was achieved by connecting an HR after the SBH. However, this increases the structural thickness, increases dependence on the ring, and compromises broadband performance.In addition to adding relevant low-frequency sound loss structures, low-frequency broadband performance can also be achieved by using the coplanarity of multiple target frequency band sound absorption units (Xian Y, Cheng B, Liu Y, Zhang Y, Zhang Z, Rugwizangoga BK. A hybrid sonic black hole for enhancing low-frequency sound absorption. PhysScr 2025;100:055003).

[0003] Existing research on Subwavelength Helicopter (SBH) often focuses on improving its mid-to-high frequency (above 1000 Hz) performance, with limited research on extending its low-frequency and subwavelength performance limits. Furthermore, in large structures such as ships, or in scenarios with multiple low-speed rotating structures, the focus is often not on single-frequency low-frequency noise control, but rather on controlling complex low-frequency broadband noise. Therefore, there is an urgent need to develop technologies to enhance the subwavelength and low-frequency (especially below 200 Hz) performance of SBHs. Summary of the Invention

[0004] Purpose of the invention: To address the shortcomings of existing technologies, this invention constructs an acoustic black hole unit (NHR-SBH) with nested Helmholtz resonators (NHR) in an SBH, thereby improving the deficiency of traditional SBHs requiring large structural thickness at low frequencies (below 200 Hz). Furthermore, through the coupled resonance of multiple units, the low-frequency broadband sound absorption performance is enhanced, meeting the requirements for regulation and absorption in complex low-frequency noise environments.

[0005] Technical solution: The present invention discloses a composite sound-absorbing structure based on acoustic black holes, comprising multiple coplanar acoustic black hole units (NHR-SBH) containing nested Helmholtz resonators. Each NHR-SBH includes multiple perforated plates (PP) connected in series and a Helmholtz resonator (NHR) containing a nested cavity connected at the end.

[0006] Furthermore, the number of NHR-SBH units is two or more, preferably four or more. Each NHR-SBH unit contains three or more PPs, preferably three to five. There is one or more nested cavities. The PPs have multiple perforations, the diameter of which is less than 5 mm, preferably 1 to 3 mm. The thickness of the PPs is 1 to 2 mm, and the distance between adjacent PPs is 1 to 10 mm.

[0007] Furthermore, when there are multiple nested cavities, the width of the cross-section of each nested cavity increases progressively outward from the last PP. The outermost nested cavity has only one neck facing inward, while the other nested cavities each have two necks facing inward. The sum of the neck lengths within each nested cavity does not exceed the height of that nested cavity.

[0008] Furthermore, the cross-section of the nested cavity is square. When there is one nested cavity, the height of the nested cavity is 8-30 mm; when there are multiple nested cavities, the height of the nested cavity is 7-41 mm, and the cross-sectional width of the nested cavity is 6-48 mm.

[0009] Furthermore, the radius of the perforated region area on the PP in each NHR-SBH unit satisfies the following formula (1):

[0010] (1)

[0011] Where R is the maximum radius of the perforated region, L is the structural thickness of the NHR-SBH unit (distance from top to bottom), and d c It is the distance between two PPs, r end σ is the radius of the perforated area on the last PP block in the NHR-SBH unit, σ is the perforation rate of the PP in the NHR-SBH unit, where N1 is the number of PP layers in the NHR-SBH unit, and N2 is the number of nested cavities in the NHR.

[0012] This invention proposes a composite acoustic black hole structure (NHR-SBH) that simultaneously incorporates NHR and PP. The NHR-SBH unit is square, and each NHR-SBH unit is composed of multiple cascaded PP NHRs with gradually varying perforated areas and circular shapes.

[0013] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0014] (1) This invention optimizes the structure according to different operating frequency bands (50-1000 Hz, 100-1000 Hz, 150-1000 Hz, and 200-1000 Hz), achieving average sound absorption coefficients of 0.6972, 0.6984, 0.868, and 0.7931, respectively. The structural thicknesses are 78.70 mm, 75.79 mm, 80.86 mm, and 90.40 mm, respectively, with low-frequency peak frequencies of 86 Hz, 116 Hz, 161 Hz, and 226 Hz, respectively. The total structural thickness is equivalent to λ / 50, λ / 39, λ / 26, and λ / 17, respectively (λ is the wavelength of the low-frequency peak frequency). In this invention patent, the performance of the structure is verified using three methods: theoretical modeling, finite element calculation, and experimental verification. The relative errors between the experimental and finite element results for the above four frequency bands are 7.96%, 6.76%, 6.47%, and 5.67%, respectively.

[0015] (2) The composite structure of this invention enhances the equivalent acoustic length by utilizing nested cavities, significantly improving low-frequency sound absorption performance below 200 Hz. While maintaining a compact thickness, it achieves excellent subwavelength sound absorption characteristics, with total structural thicknesses of only 78.70 mm, 75.79 mm, and 80.86 mm (equivalent to λ / 50, λ / 39, and λ / 26) at peak sound absorption at 86 Hz, 116 Hz, and 161 Hz, respectively. After optimization of unit coplanarity and parameters, the structure exhibits good sound absorption performance over a wide frequency range of 50–1000 Hz, with an average sound absorption coefficient of 0.8604 over 226–1000 Hz. The nested cavity design improves acoustic control flexibility, enabling precise control of complex low-frequency broadband noise. It possesses advantages such as small size, wide bandwidth, and strong low-frequency absorption, making it suitable for high-end noise control fields such as aerospace and shipbuilding, with broad application prospects.

[0016] (3) By using nested structures, the low-frequency performance of HR can be enhanced by varying the area in the direction perpendicular to the thickness, especially for applications with strict requirements on structural thickness but fewer restrictions in the direction perpendicular to the thickness. In NHR-SBH, the energy-gathering effect of the SBH structure can be effectively utilized by gradually varying the area of ​​the perforated region or the neck area, especially at the neck position of the NHR (the neck position where energy gathers will change accordingly with the change of operating frequency).

[0017] (4) Compared with existing cases of achieving low-frequency broadband using SBH, this invention innovatively proposes to achieve low-frequency broadband synergistic sound absorption through the joint design of coplanar square units. In the optimized design of the coplanar structure (CoNSBHs) containing 4 NHR-SBH units, the frequency of the low-frequency resonant peak of each unit is optimized and adjusted. A genetic algorithm is used to optimize the structure, and the average sound absorption coefficient of different frequency bands is used as the optimization target to design a structure that meets different application scenarios. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the composite sound-absorbing structure in Example 1, wherein (a) is a top view of Example 1, (b) is a side view of Example 1, and (c) is a finite element model diagram of Example 1.

[0019] Figure 2 This is an internal schematic diagram of the composite sound-absorbing structure in Example 1;

[0020] Figure 3 This is a schematic diagram of the parameter settings of the composite sound absorption structure in Example 1; wherein, (a) is a schematic diagram of the width and height parameters of the nested cavity interface in the composite sound absorption structure, and (b) is a schematic diagram of the overall parameters of the composite sound absorption structure.

[0021] Figure 4 This is a schematic diagram of the modeling and results of the simulation test of the composite sound-absorbing structure in Example 1, where (a) is the finite element model establishment diagram and (b) is the result diagram;

[0022] Figure 5 This is a schematic diagram of the modeling and results of the simulation test of the composite sound-absorbing structure in Example 2, where (a) is a top view of CoNSBHs in the range of 100-1000 Hz, (b) is a side view of CoNSBHs in the range of 100-1000 Hz, (c) is a finite element model establishment diagram, and (d) is a result diagram.

[0023] Figure 6 This is a schematic diagram of the modeling and results of the simulation test of the composite sound-absorbing structure in Example 3, where (a) is a top view of CoNSBHs in the range of 150-1000 Hz, (b) is a side view of CoNSBHs in the range of 150-1000 Hz, (c) is a finite element model establishment diagram, and (d) is a result diagram.

[0024] Figure 7 This is a schematic diagram of the modeling and results of the simulation test of the composite sound-absorbing structure in Example 4, where (a) is a top view of CoNSBHs in the range of 200-1000 Hz, (b) is a side view of CoNSBHs in the range of 100-1000 Hz, (c) is a finite element model establishment diagram, and (d) is a result diagram.

[0025] Figure 8 This is a schematic diagram of the internal structure of the composite sound absorber in Example 5;

[0026] Figure 9 This is a schematic diagram of the internal structure of the PP sound-absorbing structure in Comparative Example 1;

[0027] Figure 10 This is a schematic diagram of the internal structure of the NHR sound-absorbing structure in Comparative Example 2;

[0028] Figure 11 These are simulation results of the sound-absorbing structures in Example 5, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0029] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0030] Example 1 (for 50-1000 Hz)

[0031] like Figure 1 As shown, the present invention discloses a composite sound-absorbing structure CoNSBHs based on an acoustic black hole. The CoNSBHs is divided into four NHR-SBH units: a first NHR-SBH unit 1, a second NHR-SBH unit 2, a third NHR-SBH unit 3, and a fourth NHR-SBH unit 4. The first NHR-SBH unit 1, the second NHR-SBH unit 2, the third NHR-SBH unit 3, and the fourth NHR-SBH unit 4 are coplanar along the hole direction to form an integral CoNSBHs.

[0032] Among them, such as Figure 2-3 As shown, the first NHR-SBH unit 1 includes three equally spaced (spacing = 10 mm) PPs: first PP101, second PP102, and third PP103. The bottom of the third PP103 is connected to an NHR with four nested cavities (first nested cavity 104, second nested cavity 105, third nested cavity 106, and fourth nested cavity 107). The first PP101, second PP102, and third PP103 form three cavities with the NHR with four nested cavities: first cavity 110, second cavity 109, and third cavity 108. In each nested cavity of the NHR with four nested cavities, except for the fourth nested cavity 107 which has only one neck facing inwards, the other nested cavities have two necks facing inwards. The neck lengths are denoted as L. neck11 L neck12 L neck21 L neck22 L neck31 L neck32 L neck4 The sum of the neck lengths within each nested cavity cannot exceed the height of that nested cavity: in the first nested cavity 104, the height H4 > L.neck11 +L neck12 In the second nested cavity 105, the height H3 > L neck21 +L neck22 In the third nested cavity 106, the height H2 > L neck31 +L neck32 The fourth nested cavity 107 H1>L neck4 The cross-sections of the four nested cavities are all square, with their cross-sectional widths W increasing sequentially (W1 < W2 < W3 < W4). The perforation diameter on the three PP cavities is d = 1 mm, the PP thickness is t = 2 mm, and the perforation rate is σ = 0.11.

[0033] The specific geometric parameters of the first NHR-SBH element 1 are shown in Table 1.

[0034] The second NHR-SBH unit 2, the third NHR-SBH unit 3, and the fourth NHR-SBH unit 4 are all designed according to the parameter design method in the first NHR-SBH unit 1, and have the same structure. The specific geometric parameters are shown in Table 1. The data listed in Table 1 are the unit parameters of the first NHR-SBH unit 1, the second NHR-SBH unit 2, the third NHR-SBH unit 3, and the fourth NHR-SBH unit 4, which are coplanar along the hole direction and form a whole CoNSBHs.

[0035] The radii of the PP and perforated area in the first NHR-SBH unit 1, the second NHR-SBH unit 2, the third NHR-SBH unit 3, and the fourth NHR-SBH unit 4 all satisfy the following formula (1):

[0036] (1)

[0037] Where R is the maximum radius of the perforated region area, L is the structural thickness of the NHR-SBH unit (distance from top to bottom), and d c It is the distance between two adjacent PP, r end σ is the radius of the perforated area on the last PP block in the NHR-SBH unit, σ is the perforation rate of the PP in the NHR-SBH unit, where N1 is the number of PP layers in the NHR-SBH unit, and N2 is the number of nested cavities in the NHR.

[0038] Table 1. Structural parameters of CoNSBHs in Example 1

[0039] Unit 1 Unit 2 Unit 3 Unit 4 <![CDATA[Number of PP layers N1]]> 3 3 3 3 <![CDATA[Number of NHR layers N2]]> 4 4 4 4 Perforation rate σ in the perforated area 0.11 0.02 0.04 0.14 The diameter d (mm) of the perforation. 1.00 2.36 2.04 1.00 Maximum perforation area radius R (mm) 23.00 23.00 23.00 23.00 <![CDATA[Adjacent PP spacing d c > 10 10 10 10 PP thickness t (mm) 2.00 2.00 2.00 2.00 Lneck (mm) <![CDATA[L neck11 1.29 L neck12 1.05 L neck21 1.47 L neck22 1.15L neck31 1.01 L neck32 4.14 L neck4 3.32]]> 3.50 2.90 2.69 2.172.67 3.42 1.40 1.06 1.02 1.12 2.213.13 1.78 5.00 2.67 1.69 1.01 2.161.00 1.00 1.07 H(mm) <![CDATA[H410.52H321.93H233.92H138.34]]> 16.40 26.75 36.7840.70 8.20 16.53 27.3535.59 11.32 22.68 34.6639.50 W(mm) <![CDATA[W414.05W329.00W230.00W148.00]]> 8.41 21.09 30.0048.00 13.07 23.21 30.0048.00 18.81 20.00 30.0048.00 <![CDATA[d c (mm)]]> 10 10 10 1 Wall thickness b (mm) 1 1 1 1 L (mm) 75.34 77.70 72.59 76.50

[0040] Simulation tests were conducted on the composite sound-absorbing structure described above. During the tests, the pressure acoustics module in COMSOL Multiphysics 6.2 software was used to establish the finite element model. Internal impedance was used for the PP, and narrow-region acoustics was used to model the neck and nested cavity of the NHR. The modeling and results are illustrated below. Figure 4 As shown. By Figure 4 As can be seen, the composite sound-absorbing structure in this embodiment achieves an average coefficient of 0.6972 within the range of 50-1000 Hz, with its first absorption peak frequency of 86 Hz, a structural thickness of 77.70 mm (approximately λ / 50), and an experimental and finite element structural error of 7.96%.

[0041] Example 2 (for 100-1000 Hz)

[0042] This embodiment is designed for 100-1000 Hz plane wave noise. Its structure is the same as that of Embodiment 1, consisting of a first NHR-SBH unit 1, a second NHR-SBH unit 2, a third NHR-SBH unit 3, and a fourth NHR-SBH unit 4. However, the parameters of each NHR-SBH unit are different from those in Embodiment 1, as shown in Table 2.

[0043] Table 2 Structural parameters of CoNSBHs in Example 2

[0044] Unit 1 Unit 2 Unit 3 Unit 4 <![CDATA[Number of PP layers N1]]> 3 3 3 2 <![CDATA[Number of NHR layers N2]]> 4 4 4 4 Perforation rate σ in the perforated area 0.17 0.06 0.04 0.03 Perforation diameter d (mm) 1.00 3.00 3.00 3.00 Maximum perforation area radius R (mm) 23.00 23.00 23.00 23.00 PP thickness t (mm) 2.00 2.00 2.00 2.00 Lneck (mm) <![CDATA[L neck11 2.57L neck12 1.98L neck21 3.24L nec22 3.72L neck31 1.01L neck32 4.39 L neck4 1.10]]> 1.81 4.97 1.00 1.941.00 5.00 2.02 1.56 4.23 4.03 3.705.00 3.80 1.74 1.50 4.17 4.13 2.162.74 1.02 4.68 H(mm) <![CDATA[H49.55 H319.37 H228.76 H130.96]]> 11.78 19.72 27.7130.90 10.01 22.24 35.0437.00 8.30 15.88 20.6926.59 W(mm) <![CDATA[W416.80 W329.00 W235.13 W148.00]]> 12.24 29.00 30.0048.00 10.13 28.00 30.5648.00 19.00 24.01 31.8348.00 <![CDATA[d c (mm)]]> 10 10 10 1 Wall thickness b (mm) 1 1 1 1 L (mm) 67.90 67.96 74.00 53.59

[0045] The simulation test process is the same as in Example 1, and the results are as follows: Figure 5 As shown. By Figure 5 As can be seen, this embodiment achieves an average coefficient of 0.6984 in the range of 100–1000 Hz, with a first absorption peak frequency of 116 Hz, a structural thickness of 74.00 mm (λ / 40), and an experimental and finite element structural error of 6.76%.

[0046] Example 3 (for 150-1000 Hz)

[0047] This embodiment is designed for plane wave noise in the 150-1000 Hz range. Its structure is the same as that of Embodiment 1, consisting of first NHR-SBH unit 1, first NHR-SBH unit 2, first NHR-SBH unit 3, and first NHR-SBH unit 4. However, in this embodiment, the number of PP layers in each NHR-SBH unit differs from that in Embodiment 1. Therefore, the structural parameters of each NHR-SBH unit in this embodiment differ from those in Embodiment 1. Nevertheless, the structure of each NHR-SBH unit in this embodiment is similar to that of Embodiment 1, differing only in the number of PP or NHR layers. Specific parameters for this embodiment are shown in Table 3.

[0048] Table 3 Structural parameters of CoNSBHs in Example 3

[0049] Unit 1 Unit 2 Unit 3 Unit 4 <![CDATA[Number of PP layers N1]]> 5 5 5 5 <![CDATA[Number of NHR layers N2]]> 1 1 2 2 Perforation rate σ in the perforated area 0.06 0.09 0.21 0.09 Perforation diameter d (mm) 2.50 3.00 1.00 1.20 Maximum perforation area radius R (mm) 23.00 23.00 23.00 23.00 PP thickness t (mm) 1.20 1.10 2.00 1.00 Lneck (mm) <![CDATA[L neck1 15.00]]> <![CDATA[L neck1 11.91]]> <![CDATA[L neck11 2.57L neck12 4.55L neck2 4.77]]> <![CDATA[L neck11 1.49L neck12 1.09L neck2 5.00]]> H(mm) <![CDATA[H120]]> 12.98 <![CDATA[H210.09H118.80]]> 7.5717.13 W(mm) <![CDATA[W148.00]]> 48.00 <![CDATA[W214.23W148.00]]> 10.1848.00 <![CDATA[d c (mm)]]> 10 10 10 1 Wall thickness b (mm) 1 1 1 1 L (mm) 77.00 69.48 79.80 28.13

[0050] The simulation test process is the same as in Example 1, and the results are as follows: Figure 6 As shown. By Figure 6 As can be seen, this embodiment achieves an average coefficient of 0.7931 for 150–1000 Hz, with a first absorption peak frequency of 161 Hz, a structural thickness of 79.80 mm (λ / 26), and an experimental and finite element structural error of 6.47%.

[0051] Example 4 (for 200-1000 Hz)

[0052] This embodiment is designed for 200-1000 Hz plane wave noise. Its structure is the same as that of Embodiment 1, consisting of a first NHR-SBH unit 1, a second NHR-SBH unit 2, a third NHR-SBH unit 3, and a fourth NHR-SBH unit 4. However, in this embodiment, the number of PP layers and the number of NHR layers in each NHR-SBH unit are different from those in Embodiment 1. The specific parameters of this embodiment are shown in Table 4.

[0053] Table 4 Structural parameters of CoNSBHs in Example 4

[0054] Unit 1 Unit 2 Unit 3 Unit 4 <![CDATA[Number of PP layers N1]]> 5 5 5 5 <![CDATA[Number of NHR layers N2]]> 1 1 2 2 Perforation rate σ in the perforated area 0.19 0.20 0.16 0.13 Perforation diameter d (mm) 1.9 1 1.00 1.30 Maximum perforation area radius R (mm) 23.00 23.00 23.00 23.00 PP thickness t (mm) 2.00 2.00 2.00 2.00 Lneck (mm) <![CDATA[L neck1 21.72]]> <![CDATA[L neck1 6.67]]> <![CDATA[L neck11 3.61L neck12 10L neck2 7.57]]> <![CDATA[L neck11 3.61 L neck12 10.00 L neck2 7.57]]> H(mm) <![CDATA[H128.40]]> 8.97 <![CDATA[H214.85H123.54]]> 14.85 23.54 W(mm) <![CDATA[W148.00]]> 48.00 <![CDATA[W219.21W148.00]]> 42.72 48.00 <![CDATA[d c (mm)]]> 10 10 10 1 Wall thickness b (mm) 1 1 1 1 L (mm) 89.40 69.98 84.54 38.54

[0055] The simulation test process is the same as in Example 1, and the results are as follows: Figure 7 As shown. By Figure 7 As can be seen, this embodiment achieves an average coefficient of 0.8680 for 200–1000 Hz, with a first absorption peak frequency of 226 Hz, a structural thickness of 89.40 mm (λ / 17 of the corresponding acoustic wave length), and an experimental and finite element structural error of 5.67%.

[0056] Example 5

[0057] This embodiment also consists of CoNSBHs composed of four NHR-SBH units, but each NHR-SBH unit has the same structure, as shown in the schematic diagram below. Figure 8 As shown, it consists of 5 layers of PP and a Helmholtz resonator with 2 nested cavities, denoted as SBH-NHR, and its structural parameters are shown in Table 5.

[0058] Table 5 Structural parameters of the sound-absorbing structure in Example 5

[0059] NHR-SBH Unit 1 <![CDATA[Number of PP layers N1]]> 5 <![CDATA[Number of NHR layers N2]]> 2 Perforation rate σ in the perforated area 0.06 Perforation diameter d (mm) 2.50 Maximum perforation area radius R (mm) 23.00 PP thickness t (mm) 1.20 Lneck (mm) 2 H (mm) <![CDATA[H210H120]]> W (mm) <![CDATA[W224.00W148.00]]> <![CDATA[d c (mm)]]> 10 Wall thickness b (mm) 1 L (mm) 78

[0060] The simulation test process is the same as in Example 1, and the simulation results are as follows: Figure 11 As shown. By Figure 11 It can be seen that the sound absorption performance is best within 1000 Hz, and there is an absorption peak with an absorption coefficient of 0.98 at 171 Hz, with a structural thickness of about λ / 25.

[0061] Comparative Example 1

[0062] This comparative example consists of four identical PP sound-absorbing units, one of which has the following structure: Figure 9 As shown, the sound-absorbing structure is composed of 7 layers of PP, denoted as PPs, and the structural parameters are shown in Table 6.

[0063] Table 6 Structural parameters of the sound-absorbing structure in Comparative Example 1

[0064] Unit 1 <![CDATA[Number of PP layers N1]]> 7 Perforation rate σ in the perforated area 0.06 Perforation diameter d (mm) 2.50 Maximum perforation area radius R (mm) 23.00 PP thickness t (mm) 1.20 W(mm) 48.00 <![CDATA[d c (mm)]]> 10 Wall thickness b (mm) 1 L (mm) 79.4

[0065] For PP S The model is based on internal impedance. The simulation results are as follows: Figure 11 As shown. By Figure 11 It is evident that it has no obvious absorption peak below 1000 Hz and its sound absorption performance is poor. Its superior performance is mainly in the mid-to-high frequencies after 800 Hz.

[0066] Comparative Example 2

[0067] This comparative example consists of four identical absorption structures containing nested cavities, one of which is as follows: Figure 10 As shown, the sound-absorbing structure, consisting of 7 nested cavities, is denoted by NHRs. The structural parameters are shown in Table 7.

[0068] Table 7 Structural parameters of the sound-absorbing structure in Comparative Example 2

[0069] Unit 1 <![CDATA[Number of NHR layers N2]]> 7 H(mm) <![CDATA[H710H621H532H443H354H265H176]]> W(mm) <![CDATA[W76.86W613.71W520.57W427.43W334.29W241.14W148.00]]> Lneck (mm) 2 Wall thickness b (mm) 1 L (mm) 77

[0070] The neck and nested cavity of the NHR are modeled using narrow-region acoustics. Simulation results are as follows: Figure 11 As shown. By Figure 11 It can be seen that NHRs also have an absorption peak at 171 Hz, but their absorption coefficient is 0.79 and their structural thickness is about λ / 26. However, their broadband performance decreases after 500 Hz.

[0071] The performance results of the three structures in Example 5, Comparative Example 1, and Comparative Example 2 are as follows: Figure 11 As shown, the low-frequency performance and broadband performance of Example 5 are better than the coplanar performance of the other two structures. Therefore, it is evident that the CoNSBHs structure of the present invention has significant advantages.

Claims

1. A composite sound-absorbing structure based on an acoustic black hole, characterized in that, The acoustic black hole unit comprises multiple coplanar acoustic black hole units with nested Helmholtz resonators. Each acoustic black hole unit includes multiple perforated plates connected in series and a Helmholtz resonator with a nested cavity connected at the end.

2. The composite sound-absorbing structure based on an acoustic black hole according to claim 1, characterized in that, The number of acoustic black hole units containing nested Helmholtz resonators is more than two.

3. The composite sound-absorbing structure based on an acoustic black hole according to claim 1, characterized in that, Each acoustic black hole unit containing nested Helmholtz resonators has more than three perforated plates and more than one nested cavity.

4. The composite sound-absorbing structure based on an acoustic black hole according to claim 3, characterized in that, The perforated plate has multiple perforations with a diameter of less than 5 mm, a thickness of 1-2 mm, and a distance of 1-10 mm between adjacent PP plates.

5. The composite sound-absorbing structure based on an acoustic black hole according to claim 3, characterized in that, When there are multiple nested cavities, the width of the cross-section of the nested cavity increases sequentially from the last perforated plate outwards.

6. The composite sound-absorbing structure based on an acoustic black hole according to claim 5, characterized in that, The outermost nested cavity has only one neck facing inwards, while the other nested cavities have two necks facing inwards.

7. The composite sound-absorbing structure based on an acoustic black hole according to claim 6, characterized in that, The sum of the lengths of the necks within each nested cavity is no greater than the height of that nested cavity.

8. The composite sound-absorbing structure based on an acoustic black hole according to claim 7, characterized in that, The cross-section of the nested cavity is square.

9. The composite sound-absorbing structure based on an acoustic black hole according to claim 3, characterized in that, When the number of nested cavities is 1, the height of the nested cavity is 8-30 mm. When the number of nested cavities is multiple, the height of the nested cavity is 7-41 mm, and the cross-sectional width of the nested cavity is 6-48 mm.

10. The composite sound-absorbing structure based on an acoustic black hole according to claim 1, characterized in that, The radius of the perforated area on the perforated plate in each acoustic black hole unit containing nested Helmholtz resonators satisfies the following formula (1): （1） Where R is the maximum radius of the perforated region, L is the structural thickness of the acoustic black hole unit containing the nested Helmholtz resonator, and d c It is the distance between the two perforated plates, r end σ is the radius of the perforated area on the last perforated plate in the acoustic black hole structure, σ is the perforation rate of the perforated plate in the acoustic black hole structure, where N1 is the number of layers of the perforated plate and N2 is the number of layers of the nested cavity of the Helmholtz resonator.

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