Cross Reference to Related Application(s)

The present disclosure claims the benefit of Singapore Patent Application No. 10202002691 U filed on 24 March 2020, which is incorporated in its entirety by reference herein.

Technical Field

The present disclosure generally relates to an acoustic attenuation panel. More particularly, the present disclosure describes various embodiments of an acoustic attenuation panel as well as acoustic attenuation structure comprising a plurality of acoustic attenuation panels.

Background

Noise is produced almost everywhere and long exposure to excessive levels of noise can lead to several adverse human health issues. Many solutions have been developed to reduce the levels of noise exposure and several guidelines have been recommended for safe levels of noise exposure originating from various sources. A variety of traditional materials have been used to reduce noise, such as natural fibres (e.g. cotton and wool), granular materials (e.g. concrete and clay), synthetic cellular materials (e.g. glass wool, melamine foam, and polyurethane), and mass loaded vinyl. These materials are efficient for absorbing sound in the high frequency range, but often fail to reduce low frequency noise (less than 200 Hz) effectively, unless material thickness is significantly increased. Instead of using thicker traditional materials, artificial materials with superior sound absorption properties have been developed to address low frequency noise reduction.

These materials have been used to produce structures, such as panels and claddings, to reduce levels of noise exposure. For example, such claddings can be used on interior walls to create a soundproof room, but this would result in natural ventilation problems because the claddings seal the room from the ambient environment. Windows are commonly used in residential households for natural ventilation but unfortunately also allow noise to enter the households, even if such noise-reduction materials are used in parts of the windows.

Therefore, in order to address or alleviate at least one of the aforementioned problems and/or disadvantages, there is a need to provide an improved acoustic attenuation panel.

Summary

According to an aspect of the present disclosure, there is an acoustic attenuation panel comprising a panel body comprising a set of panel units. Each panel unit comprises: a set of ventilation holes for communication of air through the panel body; an array of attenuation sections formed in the panel body; and each attenuation section comprising a maze channel having a proximal open end arranged to receive acoustic waves carried by the air, wherein the maze channels are configured to confine propagation of the acoustic waves and increase their wave propagation distances, thereby attenuating the acoustic waves.

An acoustic attenuation panel according to the present disclosure are thus disclosed herein. Various features, aspects, and advantages of the present disclosure will become more apparent from the following detailed description of the embodiments of the present disclosure, by way of non-limiting examples only, along with the accompanying drawings.

Brief Description of the Drawings

Figures 1A and 1 B are illustrations of an acoustic attenuation panel according to embodiments of the present disclosure.

Figures 2A and 2B are illustrations of cross sections of the acoustic attenuation panel. Figures 3A and 3B are further illustrations of the acoustic attenuation panel according to some other embodiments of the present disclosure.

Figures 4A to 4C are illustrations related to investigations performed on the acoustic attenuation panel to evaluate its acoustic absorption performance.

Figures 5A to 5I are illustrations related to investigations performed on the acoustic attenuation panel to evaluate how different parameters affect its acoustic absorption performance.

Figures 6A and 6B are illustrations related to investigations performed on the acoustic attenuation panel to evaluate its air ventilation performance.

Figures 7A to 7C are illustrations of assemblies of the acoustic attenuation panel for various applications.

Detailed Description

For purposes of brevity and clarity, descriptions of embodiments of the present disclosure are directed to an acoustic attenuation panel, in accordance with the drawings. While aspects of the present disclosure will be described in conjunction with the embodiments provided herein, it will be understood that they are not intended to limit the present disclosure to these embodiments. On the contrary, the present disclosure is intended to cover alternatives, modifications and equivalents to the embodiments described herein, which are included within the scope of the present disclosure as defined by the appended claims. Furthermore, in the following detailed description, specific details are set forth in order to provide a thorough understanding of the present disclosure. Flowever, it will be recognized by an individual having ordinary skill in the art, i.e. a skilled person, that the present disclosure may be practiced without specific details, and/or with multiple details arising from combinations of aspects of particular embodiments. In a number of instances, well-known systems, methods, procedures, and components have not been described in detail so as to not unnecessarily obscure aspects of the embodiments of the present disclosure. In embodiments of the present disclosure, depiction of a given element or consideration or use of a particular element number in a particular figure or a reference thereto in corresponding descriptive material can encompass the same, an equivalent, or an analogous element or element number identified in another figure or descriptive material associated therewith.

References to “an embodiment / example”, “another embodiment / example”, “some embodiments / examples”, “some other embodiments / examples”, and so on, indicate that the embodiment(s) / example(s) so described may include a particular feature, structure, characteristic, property, element, or limitation, but that not every embodiment / example necessarily includes that particular feature, structure, characteristic, property, element or limitation. Furthermore, repeated use of the phrase “in an embodiment / example” or “in another embodiment / example” does not necessarily refer to the same embodiment / example.

The terms “comprising”, “including”, “having”, and the like do not exclude the presence of other features / elements / steps than those listed in an embodiment. Recitation of certain features / elements / steps in mutually different embodiments does not indicate that a combination of these features / elements / steps cannot be used in an embodiment.

As used herein, the terms “a” and “an” are defined as one or more than one. The use of 7” in a figure or associated text is understood to mean “and/or” unless otherwise indicated. The term “set” is defined as a non-empty finite organization of elements that mathematically exhibits a cardinality of at least one (e.g. a set as defined herein can correspond to a unit, singlet, or single-element set, or a multiple-element set), in accordance with known mathematical definitions. The recitation of a particular numerical value or value range herein is understood to include or be a recitation of an approximate numerical value or value range.

In representative or exemplary embodiments of the present disclosure, there is an acoustic attenuation panel 100 as shown in Figures 1A and 1 B. The panel 100 includes a panel body 110 having a set of one or more panel units 120. Each panel unit 120 includes a set of one or more ventilation holes 130 for communication of air through the panel body 110. More specifically, the ventilation holes 130 remain open or exposed for communication of air through the panel body 110 when the cover part 114 is joined to the main part 112. Each panel unit 120 further includes an array of attenuation sections 140 formed in the panel body 110, wherein the attenuation sections 140 are configured for attenuation of acoustic waves. Acoustic waves commonly include audible sound in the form of sound waves traveling through air.

Each attenuation section 140 includes a maze channel 142 having a proximal open end 144 arranged to receive acoustic waves carried by the air. For example, ambient noise generates sound waves that are carried by the air to the acoustic attenuation panel 100. The maze channel 142 is a continuous pathway that folds and bends to increase the channel length like a zigzag pathway. The maze channels 142 are configured to confine propagation of the acoustic waves and increase their wave propagation distances, thereby attenuating the acoustic waves.

In many embodiments as shown in Figures 1A and 1 B, the panel body 110 includes a main part 112 and a cover part 114, wherein the panel units 120 are disposed in the main part 112 and the cover part 114 is joined to the main part 112 to cover the panel units 120. In one embodiment, the main part 112 and cover part 114 are separately formed and joined together, such as by agglutinating them together using a silicone adhesive. A compressive load is applied to the main part 112 and cover part 114 to seal the joint and ensure the joint is leakage-proof. In another embodiment, the main part 112 and cover part 114 are integrally formed as a single unit.

The ventilation holes 130 may include a central ventilation hole 132 through the panel body 110, wherein the array of attenuation sections 140 is arranged to surround the central ventilation hole 132. The maze channel 142 of each attenuation section 140 is arranged to receive, via the proximal open end 144, the acoustic waves diverging from the central ventilation hole 132. The ventilation holes 130 may further include a number of peripheral ventilation holes 134 surrounding the central ventilation hole 132 and optionally interposing the attenuation sections 140. For example, a peripheral ventilation hole 134 is disposed between each pair of adjacent attenuation sections 140.

As shown in Figure 1 B, some of the acoustic waves incident on the panel units 120 are reflected while some of the acoustic waves are transmitted through the ventilation holes 130. In addition, some of the acoustic waves are transmitted into the attenuation sections 140 and absorbed by the maze channels 142, thereby attenuating the acoustic waves and reducing the sound level. Figure 2A illustrates the divergence of the acoustic waves from the central ventilation hole 132 to the maze channels 142 via their proximal open ends 144. Figure 2B illustrates the propagation of the acoustic waves through a maze channel 142.

As shown in Figure 2B, each attenuation section 140 has an overall length represented by A and an overall width represented by B. The overall height or depth of the panel unit 120 is represented by H. Preferably, the overall height FI is below 3 cm. Each maze channel 142 has a number of folds or bends and this is represented by the parameter N. As shown in Figure 2B, the maze channel 142 has four folds and thus N = 4. The folds are created by forming a number of partitions 146 in the maze channel 142. Each partition 146 has a length I and a thickness t. The air gap of the maze channel 142 or the space between the partitions 146 is represented by g. The air gap g and length I are represented by Equations 1 and 2, respectively.

Both the air gap and the proximal open end 144 have rectangular cross sections with the same width g and height FI, although it will be appreciated that other shapes are possible as well, such as circular cross sections. As shown in Figure 2B, the dashed line inside the maze channel 142 outlines the propagation path of the acoustic waves. As the acoustic waves travel along a zigzag path, the wave propagation distances are increased, resulting in attenuation of the acoustic waves.

The attenuation sections 140 are preferably arranged in a polygonal array. For example as shown in Figure 2A, the panel unit 120 has six attenuation sections 140 arranged in a hexagonal array. More preferably, the attenuation sections 140 are arranged at regular intervals in the polygonal array. In some other embodiments, such as shown in Figure 3A, the panel unit 120 has four attenuation sections 140 arranged in a square array. It will be appreciated that the number of attenuation sections 140 need not correspond to the number of sides of the polygonal array. For example, in a rectangular array, there may be more attenuation sections 140 arranged along the longer side than along the shorter side. It will also be appreciated that the attenuation sections 140 can be arranged in other ways, such as circular or elliptical arrays.

In some embodiments as shown in Figures 2A and 3A, the maze channels 142 are closed other than the proximal open ends 144. In other words, for a maze channel 142, the acoustic waves can enter the maze channel 142 via the proximal open end 144 but would not be able to exit the maze channel 142. In some embodiments as shown in Figure 3B, a maze channel 142 has at least one distal open end 148 for the propagating acoustic waves to exit from the maze channel 142. The distal open ends 148 provide exit points that may lead to the peripheral ventilation holes 134 and/or other attenuation sections 140. For example, the acoustic waves may exit from a distal open end 148 of a maze channel 142 to a peripheral ventilation hole 134, and may possibly enter a distal open end 148 of another maze channel 142. The opening of the maze channels 142 by the distal open ends 148 fluidically interconnects the maze channels 142, thereby increasing the effective path length for the acoustic waves and their wave propagation distances, which would result in improved attenuation of the acoustic waves.

Moreover, the maze channels 142 need not be arranged in the same way. The maze channels 142 may have different parameters, such as different number of folds (parameter N) or different air gap sizes. For example as shown in Figure 3B, the maze channels 142 have different number of folds, i.e. N = 4,6,8,10,12,14. It will be appreciated that the attenuation sections 140 in a panel unit 120 can be identical to each other or configured differently from each other by varying other parameters.

Various investigations were performed to evaluate the functionality of an acoustic attenuation panel unit 120 in regard to acoustic absorption and ventilation. The acoustic absorption performance can be evaluated based on the acoustic absorption coefficient a of the panel unit 120 which can be represented by Equation 3. The term R represents the reflection coefficient and can be represented by Equation 4. The term z represents the acoustic impedance of the surface of the panel unit 120 relative to the background medium, i.e. air. The coupled-mode theory (CMT) was used in estimating the acoustic impedance z and can be represented by Equation 5. Notably, acoustic impedance is a measure of the ease with which an acoustic wave propagates through a particular medium.

The term k _c represents the complex acoustic wave number inside the maze channel 142 and can be represented by Equations 6 and 7. The term i represents a mathematics imaginary function or a complex number. The term b represents the acoustic loss factor. A perfect acoustic absorption through the panel unit 120 can be realized when two conditions - frequency f = f _m and β = β _m - are achieved simultaneously. The term f _m represents the resonant frequency and can be represented by Equation 8. The term c represents the speed of sound in the background medium, which is about 333 m/s in air. The term β _m represents the critical loss factor and can be represented by Equation 9.

In Equations 8 and 9, m = 1 ,2,3, ... and represents the number of modes. The term L _eff represents the total effective path length of the maze channel 142 and can be represented by Equation 10. The term Q represents the angle of incidence of the acoustic waves entering the maze channel 142. The corresponding relative acoustic absorption bandwidth is represented by Equation 11 , where Δf represents the full width at half maximum (FWHM) for the m ^th order peak acoustic absorption. In addition, the acoustic attenuation effect of the maze channels 142 can be evaluated based on the effective relative refractive index n _r of the panel unit 120 according to Equation 12.

Both computer or numerical simulations and physical experiments were performed in the investigations. The finite element method (FEM)-based COMSOL Multiphysics® version 5.4 software was used for performing full-wave numerical simulations of acoustic wave propagation in the panel unit 120. A standard inbuilt pressure acoustic- structure interaction module was selected for evaluating the acoustic absorption performance of the panel unit 120 in the frequency domain. For obtaining the acoustic absorption and transmission characteristics of the panel unit 120, the standard impedance tube setup was replicated in the COMSOL Multiphysics® software. More specifically, a backed rigid material (steel) was placed at the end of the panel unit 120, and the acoustic absorption coefficient was calculated. Due to the high density (p = 7800 kg/m ³ ) and Young’s modulus (E = 210 GPa) of steel relative to the air (air density p = 1.12 kg/m ³ ), acoustic waves can hardly penetrate the steel material, and thus the backed steel plate can be treated as a rigid body. A plane wave radiation boundary condition was used to simulate the incident acoustic waves. The acoustic waves were simulated in the frequency range from about 80 Hz to about 1600 Hz, corresponding to the wavelength range of about 4.3 m to about 0.215 m. In addition, perfectly matched layers were added on the outer sidewalls to enclose the computational domain, thereby preventing the subsequent reflections from the boundaries. The mesh element size was set to be smaller than 1/5 of the shortest simulated wavelength, i.e. the mesh element size was smaller than 43 mm.

Investigations were performed on samples of the acoustic attenuation panel unit 120 to evaluate its acoustic absorption performance. The samples were fabricated by 3D printing with fused deposition modelling technology and the material is polylactide. Polylactide or PLA has material properties of Young's modulus E = 1.28 GPa, density p = 1210 kg/m ³ , and Poisson's ratio v = 0.36. Photographs of a sample are shown in Figure 4A. The panel unit 120 has parameters of N = 4, A = 27 mm, B = 20 mm, t = 0.75 mm, and H = 15 mm. The sample of the panel unit 120 may be referred to as sample S1 (N = 4). A numerical simulation was performed on a computer model of the sample S1 (N = 4) with the same parameters as the fabricated one. With reference to Figure 4B, the chart 200 shows the simulation results 202 on acoustic absorption spectra based on the computer model. It was observed that a distinguished peak acoustic absorption had ensued at the resonant frequency of about 884 Hz. Given that the speed of sound in air is about 333 m/s, the corresponding wavelength l at the resonant frequency is about 377 mm in the propagating wave direction. The wavelength is about 25 times the height of the sample S1 (N = 4), i.e. H ≈ 0.04λ. The simulated resonant frequency agrees well with the theoretical calculations obtained by using Equation 8, whereby f _m = 865 Hz. Such a high peak acoustic absorption had resulted from the decaying of incoming acoustic waves. The dissipation of the acoustic waves inside the maze channels 142 occurs due to frictional resistance at the interface between air and walls of the maze channels 142. For a better demonstration of the resonant behaviour, the simulated acoustic pressure field distribution 204 for the sample S1 (N = 4) at the resonant frequency of about 884 Hz is shown in Figure 4B. The acoustic pressure field distribution 204 clearly shows the incident acoustic pressure had been directed towards the maze channels 142 and had resulted in a multiplied acoustic pressure field at the end of the maze channels 142 in each of the attenuation sections 140.

A physical experiment was performed on the fabricated sample S1 (N = 4) for comparison against the numerical simulation. With reference to Figure 4B, the chart 200 shows the corresponding experimental results 206 on the acoustic absorption spectra. In the experiment, the acoustic absorption coefficient a was measured using a standard impedance tube by BSWA® and following the ASTM E1050-12 Standard. The experimentally measured peak acoustic absorption in the experimental results 206 agrees well with the simulation results 202. This investigation showed that the sample S1 (N = 4) exhibited excellent absorption at about 884 Hz with a high relative acoustic absorption bandwidth.

Simulations were also performed to simulate the sound pressure level (SPL) distributions for the sample S1 (N = 4) and a reference sample S1 (N = 0). The reference sample S1 (N = 0) has the same parameters as the sample S1 (N = 4), except the reference sample S1 (N = 0) does not have maze channels 142 in the attenuation sections 140. Notably, each attenuation section 140 is a simple cavity. With reference to Figure 4C, the chart 210 shows the simulated SPL distributions 212,214 for the sample S1 (N = 4) and the reference sample S1 (N = 0), respectively. The SPL values were extracted at the end of the maze channels 142 / attenuation sections 140, as indicated by the dot 211 in the inset diagram 213. As shown in the simulated SPL distribution 212, for the sample S1 (N = 4), a pressure level gain of around 20 dB was observed at the peak resonant frequency of about 884 Hz, as indicated by the reference line 215. Such a high SPL amplification was realized due to the occurrence of acoustic wave phase delay inside the labyrinthine structure of the maze channels 142 in the attenuation sections 140. The effective relative refractive index for the sample S1 (N = 4) was calculated using Equation 12 to be about 3.67 times higher than that for the reference sample S1 (N = 0). At this resonant frequency, the labyrinthine attenuation sections 140 behaved like a resonator for transmission of photons across two opposite flat mirrors, and consequent formation of the standing wave inside the attenuation sections 140 resulted in the high gains. Figure 4C also shows the spatial distribution 216,218 of the sound pressure field at the resonant frequency for the sample S1 (N = 4) and the reference sample S1 (N = 0), respectively.

Investigations were performed on samples of the panel unit 120 to evaluate the how different parameters affect the acoustic absorption performance. In one experiment to evaluate the influence of the parameter N, the samples of the panel units 120 have common parameters of A = 27 mm, B = 20 mm, t = 0.75 mm, and H = 15 mm. The experiment was performed on samples S1 (N = 3), S1 (N = 4), S1 (N = 5), and S1 (N = 8). As shown in Figure 5A, the sample S1 (N = 5) has the same parameters as the sample S1 (N = 4) described above, except the sample S1 (N = 5) has 5 folds or bends in each maze channel 142.

With reference to Figure 5B, the chart 220 shows the experimental results 222,224,226,228 on acoustic absorption spectra for the samples S1 (N = 3), S1 (N = 4), S1 (N = 5), and S1 (N = 8), respectively. It was observed for the sample S1 (N = 3) (result 222) that the resonant frequency was about 1180 Hz with a near-perfect peak acoustic absorption coefficient of about 0.994. It was also observed that resonant frequency at the peak acoustic absorption decreased with increasing parameter N, which is in line with the theoretical predictions. However, a slight reduction in the peak acoustic absorption was observed for the samples S1 (N = 5) (result 226) and S1 (N = 8) (result 228). An adjustable resonant frequency band can thus be achieved by adjusting the parameter N, i.e. changing the number of folds or bends in the maze channels 142.

The effect of the parameter H, i.e. height of the panel units 120, was investigated for evaluating possible improvement in absorption of low frequency acoustic waves. In one experiment, the samples of the panel units 120 have common parameters of A = 27 mm, B = 20 mm, and t = 0.75 mm. The experiment was performed on samples S1 (N = 3; H = 10 mm), S1 (N = 3; H = 15 mm), S1 (N = 5; H = 10 mm), S1 (N = 5; H = 15 mm), S1 (N = 8; H = 15 mm), and S1 (N = 8; H = 25 mm).

With reference to Figure 5C, the chart 230 shows the experimental results 231 ,232,233,234,235,236 on acoustic absorption spectra for the samples S1 (N = 3; H = 10 mm), S1 (N = 3; H = 15 mm), S1 (N = 5; H = 10 mm), S1 (N = 5; H = 15 mm), S1 (N = 8; H = 15 mm), and S1 (N = 8; H = 25 mm), respectively. It was observed that, for each sample, the average acoustic absorption was collectively enhanced with increasing height H. The near-perfect peak acoustic absorption appears at the resonant frequency of about1180 Hz for the sample S1 (N = 3; H = 15 mm) (result 232). Moderate peak acoustic absorption coefficients of about 0.74 and 0.64 were observed for the samples S1 (N = 5; H = 15 mm) (result 234) S1 (N = 8, H = 25 mm) (result 236), respectively. It was also observed that, for the sample S1 (N = 8, H = 15 mm) (result 235), the peak acoustic absorption coefficient was about 0.52. This means that increasing the height H from 15 mm to 25 mm, which is about 66%, would only result in a small increase in the peak acoustic absorption coefficients (from 0.52 to 0.64), despite the panel units 120 being bulkier. Other options for enhancing the absorption of low frequency acoustic waves were explored consequently.

The use of traditional absorptive materials was explored. A sample S2 of the panel unit 120 was fabricated to include a porous filler material, such as foam or cotton, in the maze channels 142. As shown in Figure 5D, a thin foam material 150 was disposed at a distal end of each maze channel 142. Other than the inclusion of the foam material 150, the sample S2 (N = 5, H = 15 mm) has the same parameters as the sample S1 (N = 5, H = 15 mm) described above. Fluidic interconnection between the labyrinthine attenuation sections 140 was also explored. Samples S3 of the panel unit 120 were fabricated with each maze channel 142 having the proximal open ends 144 and distal open ends 148. The distal open ends 148 open the maze channels 142 and fluidically interconnects them. In one experiment, the samples S1 ,S2,S3 of the panel units 120 have common parameters of A = 27 mm, B = 20 mm, and t = 0.75 mm. The experiment was performed on samples S1 (N = 5; H = 15 mm), S2 (N = 5; H = 15 mm), S3 (N = 5; H = 15 mm), S1 (N = 8; H = 25 mm), S3 (N = 8; H = 25 mm), and S3 (N = 14; H = 25 mm) (as shown in Figure 5E).

With reference to Figure 5F, the chart 240 shows the experimental results 241 ,242,243,244,245,246 on acoustic absorption spectra for the samples S1 (N = 5; H = 15 mm), S2 (N = 5; H = 15 mm), S3 (N = 5; H = 15 mm), S1 (N = 8; H = 25 mm), S3 (N = 8; FI = 25 mm), and S3 (N = 14; FI = 25 mm), respectively. It was observed that, for the samples S1 (N = 5, FI = 15 mm) (result 241 ) and S2 (N = 5, FI = 15 mm) (result 242), the peak acoustic absorption coefficients were about 0.7 and 0.8, respectively. This means that adding the foam material 150 resulted in a minor improvement in the peak acoustic absorption at a relatively higher frequency. The minor improvement was due to the cumulative effect space coiling in the maze channels 142 and filling the ends of the maze channels 142 with the foam material 150 or other porous materials, even though porous materials are normally efficient for absorption of medium to high frequency acoustic waves.

Moreover, it was observed that, for the samples S3 (N = 8; FI = 25 mm) (result 245) and S3 (N = 14; FI = 25 mm) (result 246), the resonant frequency at the peak acoustic absorption decreased with increasing parameter N. It was also observed that, for the samples S1 (N = 5; H = 15 mm) (result 241 ), S3 (N = 5; H = 15 mm) (result 243), S1 (N = 8; FI = 25 mm) (result 244), and S3 (N = 8; FI = 25 mm) (result 245), higher acoustic absorption was achieved by the samples S3 than the samples S1. This was due to the fluidic interconnection between the maze channels 142 in the labyrinthine attenuation sections 140, which increased the effective path length and wave propagation distances, resulting in significant improvement in acoustic absorption. Higher acoustic absorption can thus be achieved by opening the maze channels 142 with the distal open ends 148 as opposed to closed maze channels 142.

Investigations were performed on the sample S1 (N = 4) to evaluate the how the angle of incidence of the acoustic waves on the panel unit 120 affects the acoustic absorption performance. In the simulation, the angle of incidence varied between 0°, 30°, and 60°. With reference to Figure 5G, the chart 250 shows the simulated results 252,254,256 on acoustic absorption spectra for the respective angles of incidence φ . The chart 250 also shows an inset diagram 258 illustrating the angle of incidence f which is the intersection angle between the incident acoustic waves and the normal direction of the sample S1 (N = 4) boundary. It was observed that there was no significant change in the acoustic absorption performance regardless of whether the acoustic waves were incident directly or obliquely on the sample S1 (N = 4). It should be noted that there was a minor decrease in the peak acoustic absorption coefficients with increasing angle of incidence, i.e. as the acoustic waves become more oblique. As the angle of incidence has minimal impact on the acoustic absorption performance, the acoustic attenuation panel 100 can potentially be used for applications in free space.

Investigations were performed on samples S3 of the panel unit 120 to evaluate its broadband acoustic absorption performance over a range of frequencies. Notably, the samples S3 have the distal open ends 148. The broadband acoustic absorption was achieved by configuring the attenuation sections 140 the unit cells with different number of folds or bends in the respective maze channels 142. Figure 5H shows two fabricated samples S3. The first sample S3 has six attenuation sections 140 and the maze channels 142 have 4, 6, 8, 10, 12, and 14 folds, respectively. The first sample S3 may thus be referred to sample S3 (N = 4,6,8,10,12,14). The second sample S3 has 6 attenuation sections 140 and the maze channels 142 have 3, 4, 5, 6, 7, and 8 folds, respectively. The second sample S3 may thus be referred to sample S3 (N = 3, 4, 5, 6, 7, 8).

With reference to Figure 5I, an experiment was performed and the chart 260 shows the experimental results 262,264 on acoustic absorption spectra for the samples S3 (N = 4,6,8,10,12,14) and S3 (N = 3, 4, 5, 6, 7, 8). It was observed that the sample S3 (N = 4,6,8,10,12,14) exhibited acoustic absorption of more than 50%, i.e. α > 0.5, over a wide frequency range from about 530 Hz to about 1230 Hz (which is more than one octave). The corresponding relative acoustic absorption bandwidth at this frequency range was calculated to be as high as 82.1 %. The peak acoustic absorption coefficient a of about 0.99 occurred at a frequency of about 852 Hz. The corresponding wavelength λ at this frequency is about 391 mm, i.e. H ≈ 0.077λ given that H = 30 mm. The sample S3 (N = 3, 4, 5, 6, 7, 8) similarly exhibited broadband acoustic absorption (α > 0.5) over a wide frequency range from about 834 Hz to about 1354 Hz. The corresponding relative acoustic absorption bandwidth at this frequency range was calculated to be 42.5%. These results show that the attenuation sections 140 and maze channels 142 can be configured with different number of folds or bends based on the target applications of the acoustic attenuation panel 100, while still achieving the desired acoustic absorption performance.

Investigations were performed to evaluate the air ventilation performance of the panel unit 120. Numerical simulations were performed on computer models of the sample S1 (N = 4) using a finite element-based computational fluid dynamics (CFD) analysis module in ABAQUS software. Figure 6A shows a finite element model 270 of the sample S1 (N = 4) placed between an upstream or inlet air domain 272 and a downstream or outlet air domain 274. A first sample S1 (N = 4) has an overall ventilation opening of about 43%, and a second sample S1 (N = 4) has an overall ventilation of about 30%. The overall ventilation opening percentage was calculated by the dividing the cross-sectional area of the sample S1 (N = 4) to the cross-sectional area of the ventilation holes 130. The difference in the overall ventilation opening can be achieved by adjusting the size of the ventilation holes 130. In the simulations, air was configured to flow from the inlet air domain 272 to the outlet air domain 274 across the samples S1 (N = 4) at different inlet air velocities (0.10, 0.15, 0.20, 0.25, and 0.30 m/s). The pressure differential across the samples S1 (N = 4) was measured for the respective inlet air velocities.

With reference to Figure 6B, the chart 280 shows the simulation results 282,284 on the ventilation performance for the first and second samples S1 (N = 4), respectively. It was observed that the pressure differential increased with increasing inlet air velocities. Moreover, the second sample S1 (N = 4) with a smaller overall ventilation opening yielded a larger pressure differential. The larger pressure differential was likely established by wind and buoyancy forces due to higher airflow resistance at the smaller overall ventilation opening. Nevertheless, the average pressure differential across the samples S1 (N = 4) was negligible and these results show that the acoustic attention panel 100 can be used for sound mitigation with simultaneous natural ventilation.

The results from the various investigations showed that the acoustic attenuation panel 100 is an effective way for broadband acoustic absorption to mitigate noise exposure. The panel unit 120 exhibited configurable acoustic properties over a wide frequency range from about 500 Hz to about 1300 Hz, which corresponds to the low-to-mid frequency range and is more than one octave, wherein there was high-efficiency absorption at a frequency of about 1000 Hz. The high broadband acoustic absorption is achieved by array of attenuation sections 140 each having a maze channel 142 of subwavelength dimensions. For example, the overall height H is less than 3 cm and just a fraction of the acoustic wavelengths. The incident acoustic waves are confined in the comparatively thin maze channels 142 which increase the effective path length and wave propagation distances for the acoustic waves. The propagating acoustic waves dissipate and slow down over the longer effective path length because of visco- thermal effects and frictional resistance at the interface between air and walls of the maze channels 142. This results in excellent acoustic attenuation properties such as high effective relative refractive index and effective acoustic impedance. Moreover, by configuring the panel unit 120 with particular dimensions, such as the overall length A and overall width B, the panel unit 120 can induce a complete phase shift across it and achieve superior acoustic absorption properties. A thin panel 100 with a desired acoustic sound absorption profile can be designed by adjusting the parameters of the panel units 120 accordingly.

Moreover, the panel unit 120 has ventilation holes 130 for partial fluid passage or air communication across the panel unit 120. The acoustic attenuation panel 100 can thus be used in environments where natural ventilation is desired. For example, in recent years, natural ventilation in high-rise buildings has provided an effective and economical solution for fresh air circulation while reducing the overall use of electricity. However, naturally ventilated window panels also allow noise to enter the households, adversely affecting public health and quality of life. The acoustic attenuation panel 100 can be used such situations to achieve natural ventilation and acoustic attenuation simultaneously.

The acoustic attenuation panel 100 can be used in various target applications that desire both natural ventilation and air circulation, as well as acoustic attenuation for reducing levels of noise exposure. The acoustic attenuation panel 100 is highly scalable by configuring the arrangement and number of panel units 120, as well as the attenuation sections 140 and maze channels 142 in each panel 120, thereby tuning the acoustic / ventilation performances can be tuned for the target applications. Some non-limiting examples of target applications include traffic noise insulation with proper natural ventilation at residential buildings, machinery noise insulation in factories and plants, aircraft engine noise insulation at airports, and various architectural applications where simultaneous noise shielding and natural ventilation are required.

The acoustic attenuation panel 100 can be assembled to form various other structures for acoustic absorption and ventilation performances. In one embodiment with reference to Figure 7A, one or more acoustic attenuation panels 100 may be assembled to form a window panel that can be used in residential buildings that desire noise mitigation and natural ventilation. One or more acoustic attenuation panels 100 may also be used as internal or peripheral partitions, such as in balconies, void decks, or open spaces, for noise mitigation while maintaining some level of natural ventilation and sunlight.

In some embodiments with reference to Figure 7B, one or more acoustic attenuation panel 100 may be assembled to form a ventilation louver. The ventilation louver includes the panel body 110 having a set of panel units 120 and a set of ventilation holes 130 for communication of air through the panel body 110. Each panel unit 120 has an array of attenuation sections 140 each having a maze channel 142. The panel units 120 are arranged such that the proximal open ends 144 of the maze channels 142 face the same direction as the ventilation holes 130. More specifically, the panel units 120 are arranged perpendicularly to the spine of the panel body 110 as shown in Figure 7B. It will be appreciated that the panel units 120 may be arranged obliquely while keeping the ventilation holes 130 open. The ventilation louver can be used for noise insulation and natural ventilation, as well as for sheltering against sunlight and rain. Ventilation louvers are generally installed on the periphery of buildings. Existing ventilation louvers may be modified, such as by incorporating the panel units 120 into the narrow gaps between blades of the louver. The blades can be tilted, and the louver can be in the form of V-shaped louver.

In some embodiments with reference to Figure 7C, there is an acoustic attenuation structure 300 including a plurality of acoustic attenuation panels 100. More specifically, the acoustic attenuation panels 100 are joined to form an enclosure 300 for housing a machine 310, such as a generator or motor drive. The acoustic attenuation structure or enclosure 300 may be in the form of a cube, cuboid, or polyhedron. The enclosure 300 may be modified from an existing enclosure by replacing some or all sides of the enclosure 300 with the panels 100. The enclosure 300 may be referred to as a sonic cage for the machine 310 as the panels 100 are able to mitigate the noise generated from the machine 310. The sonic cage can be used on board ships for mitigation of machine or generator noise, in buildings for mitigation of compressor noise, or any other applications that require both noise insulation and air ventilation.

As described herein, the acoustic attenuation panel 100 has been described and experimentally validated to exhibit strong broadband acoustic absorption particularly in the low-to-mid frequency range. The investigation results showed almost perfect acoustic absorption with high relative acoustic absorption bandwidth. The investigation results also showed that the acoustic absorption performance can be tailored within a wide frequency range by adjusting the various parameters. The acoustic attenuation panel 100 can thus serve as an effective solution for low-to-mid frequency noise control in confined spaces that require efficient ventilation.

The acoustic attenuation panel 100 can be fabricated by various manufacturing methods. In some embodiments, the panel 100 or a product comprising it may be formed by a manufacturing process that includes an additive manufacturing process. A common example of additive manufacturing is three-dimensional (3D) printing; however, other methods of additive manufacturing are available. Rapid prototyping or rapid manufacturing are also terms which may be used to describe additive manufacturing processes.

As used herein, “additive manufacturing” refers generally to manufacturing processes wherein successive layers of material(s) are provided on each other to “build-up” layer- by-layer or “additively fabricate”, a 3D component. This is compared to some subtractive manufacturing methods (such as milling or drilling), wherein material is successively removed to fabricate the part. The successive layers generally fuse together to form a monolithic component which may have a variety of integral sub components. In particular, the manufacturing process may allow an example of the disclosure to be integrally formed and include a variety of features not possible when using prior manufacturing methods.

Additive manufacturing methods described herein enable manufacture to any suitable size and shape with various features which may not have been possible using prior manufacturing methods. Additive manufacturing can create complex geometries without the use of any sort of tools, moulds, or fixtures, and with little or no waste material. Instead of machining components from solid billets of plastic or metal, much of which is cut away and discarded, the only material used in additive manufacturing is what is required to shape the part.

Suitable additive manufacturing techniques in accordance with the present disclosure include, for example, Fused Deposition Modelling (FDM), Selective Laser Sintering (SLS), 3D printing such as by inkjets and laserjets, Stereolithography (SLA), Direct Selective Laser Sintering (DSLS), Electron Beam Sintering (EBS), Electron Beam Melting (EBM), Laser Engineered Net Shaping (LENS), Electron Beam Additive Manufacturing (EBAM), Laser Net Shape Manufacturing (LNS), Direct Metal Deposition (DMD), Digital Light Processing (DLP), Continuous Digital Light Processing (CDLP), Direct Selective Laser Melting (DSLM), Selective Laser Melting (SLM), Direct Metal Laser Melting (DMLM), Direct Metal Laser Sintering (DMLS), Material Jetting (MJ), NanoParticle Jetting (NPJ), Drop On Demand (DOD), Binder Jetting (BJ), Multi Jet Fusion (MJF), Laminated Object Manufacturing (LOM), and other known processes.

The additive manufacturing processes described herein may be used for forming components using any suitable material. For example, the material may be metal, plastic, polymer, composite, or any other suitable material that may be in solid, liquid, powder, sheet material, wire, or any other suitable form or combinations thereof. More specifically, according to exemplary embodiments of the present disclosure, the additively manufactured components described herein may be formed in part, in whole, or in some combination of materials suitable for use in additive manufacturing processes and which may be suitable for the fabrication of examples described herein.

As noted above, the additive manufacturing process disclosed herein allows a single component to be formed from multiple materials. Thus, the examples described herein may be formed from any suitable mixtures of the above materials. For example, a component may include multiple layers, segments, or parts that are formed using different materials, processes, and/or on different additive manufacturing machines. In this manner, components may be constructed which have different materials and material properties for meeting the demands of any particular application. In addition, although the components described herein are constructed entirely by additive manufacturing processes, it should be appreciated that in alternate embodiments, all or a portion of these components may be formed via casting, machining, and/or any other suitable manufacturing process. Indeed, any suitable combination of materials and manufacturing methods may be used to form these components.

Additive manufacturing processes typically fabricate components based on 3D information, for example a 3D computer model (or design file), of the component. Accordingly, examples described herein not only include products or components as described herein, but also methods of manufacturing such products or components via additive manufacturing and computer software, firmware or hardware for controlling the manufacture of such products via additive manufacturing. The structure of the product may be represented digitally in the form of a design file. A design file, or computer aided design (CAD) file, is a configuration file that encodes one or more of the surface or volumetric configuration of the shape of the product. That is, a design file represents the geometrical arrangement or shape of the product.

Design files can take any now known or later developed file format. For example, design files may be in the Stereolithography or “Standard Tessellation Language” (.stl) format which was created for Stereolithography CAD programs of 3D Systems, or the Additive Manufacturing File (.amf) format, which is an American Society of Mechanical Engineers (ASME) standard that is an extensible markup-language (XML) based format designed to allow any CAD software to describe the shape and composition of any 3D object to be fabricated on any additive manufacturing printer. Further examples of design file formats include AutoCAD (.dwg) files, Blender (.blend) files, Parasolid ( x_t) files, 3D Manufacturing Format ( 3mf) files, Autodesk (3ds) files, Collada (.dae) files and Wavefront (.obj) files, although many other file formats exist.

Design files can be produced using modelling (e.g. CAD modelling) software and/or through scanning the surface of a product to measure the surface configuration of the product. Once obtained, a design file may be converted into a set of computer executable instructions that, once executed by a processer, cause the processor to control an additive manufacturing apparatus to produce a product according to the geometrical arrangement specified in the design file. The conversion may convert the design file into slices or layers that are to be formed sequentially by the additive manufacturing apparatus. The instructions (otherwise known as geometric code or “G- code”) may be calibrated to the specific additive manufacturing apparatus and may specify the precise location and amount of material that is to be formed at each stage in the manufacturing process. As discussed above, the formation may be through deposition, through sintering, or through any other form of additive manufacturing method.

The code or instructions may be translated between different formats, converted into a set of data signals and transmitted, received as a set of data signals and converted to code, stored, etc., as necessary. The instructions may be an input to the additive manufacturing system and may come from a part designer, an intellectual property (IP) provider, a design company, the operator or owner of the additive manufacturing system, or from other sources. An additive manufacturing system may execute the instructions to fabricate the product using any of the technologies or methods disclosed herein.

Design files or computer executable instructions may be stored in a (transitory or non- transitory) computer readable storage medium (e.g., memory, storage system, etc.) storing code, or computer readable instructions, representative of the product to be produced. As noted, the code or computer readable instructions defining the product that can be used to physically generate the object, upon execution of the code or instructions by an additive manufacturing system. For example, the instructions may include a precisely defined 3D model of the product and can be generated from any of a large variety of well-known CAD software systems such as AutoCAD®, TurboCAD®, DesignCAD 3D Max, etc. Alternatively, a model or prototype of the product may be scanned to determine the 3D information of the product. Accordingly, by controlling an additive manufacturing apparatus according to the computer executable instructions, the additive manufacturing apparatus can be instructed to print out the product.

In light of the above, embodiments include methods of manufacture via additive manufacturing. This includes the steps of obtaining a design file representing the product and instructing an additive manufacturing apparatus to manufacture the product according to the design file. The additive manufacturing apparatus may include a processor that is configured to automatically convert the design file into computer executable instructions for controlling the manufacture of the product. In these embodiments, the design file itself can automatically cause the production of the product once input into the additive manufacturing apparatus. Accordingly, in this embodiment, the design file itself may be considered computer executable instructions that cause the additive manufacturing apparatus to manufacture the product. Alternatively, the design file may be converted into instructions by an external computing system, with the resulting computer executable instructions being provided to the additive manufacturing apparatus. Given the above, the design and manufacture of implementations of the subject matter and the operations described in this specification can be realized using digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. For instance, hardware may include processors, microprocessors, electronic circuitry, electronic components, integrated circuits, etc. Implementations of the subject matter described in this specification can be realized using one or more computer programs, i.e. , one or more modules of computer program instructions, encoded on computer storage medium for execution by, or to control the operation of, data processing apparatus. Alternatively or in addition, the program instructions can be encoded on an artificially generated propagated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal that is generated to encode information for transmission to suitable receiver apparatus for execution by a data processing apparatus. A computer storage medium can be, or be included in, a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination of one or more of them. Moreover, while a computer storage medium is not a propagated signal, a computer storage medium can be a source or destination of computer program instructions encoded in an artificially generated propagated signal. The computer storage medium can also be, or be included in, one or more separate physical components or media (e.g., multiple CDs, disks, or other storage devices).

Although additive manufacturing technology is described herein as enabling fabrication of complex objects by building objects point-by-point, layer-by-layer, typically in a vertical direction, other methods of fabrication are possible and within the scope of the present subject matter. For example, although the discussion herein refers to the addition of material to form successive layers, one skilled in the art will appreciate that the methods and structures disclosed herein may be practiced with any additive manufacturing technique or other manufacturing technology.

In the foregoing detailed description, embodiments of the present disclosure in relation to the acoustic attenuation panel are described with reference to the provided figures. The description of the various embodiments herein is not intended to call out or be limited only to specific or particular representations of the present disclosure, but merely to illustrate non-limiting examples of the present disclosure. The present disclosure serves to address at least one of the mentioned problems and issues associated with the prior art. Although only some embodiments of the present disclosure are disclosed herein, it will be apparent to a person having ordinary skill in the art in view of this disclosure that a variety of changes and/or modifications can be made to the disclosed embodiments without departing from the scope of the present disclosure. Therefore, the scope of the disclosure as well as the scope of the following claims is not limited to embodiments described herein.