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12 pages, 6509 KiB

Open AccessArticle

Development of a Metasilencer Considering Flow in HVAC Systems

by Hyunsu Kim, Yoonjung Kwon, Sangwoo Lee, Juin Kim and Dongchul Park

Appl. Sci. 2022, 12(22), 11322; https://doi.org/10.3390/app122211322 - 8 Nov 2022

Cited by 2 | Viewed by 1331

Although the driving noise of electric vehicles has been reduced compared with that of internal combustion engine vehicles, a new interior noise problem is emerging. It is crucial to reduce the noise of the heating, ventilation, and air conditioning (HVAC) system, which is [...] Read more.

Although the driving noise of electric vehicles has been reduced compared with that of internal combustion engine vehicles, a new interior noise problem is emerging. It is crucial to reduce the noise of the heating, ventilation, and air conditioning (HVAC) system, which is one of the main causes of interior noise. Therefore, in this study, a metasilencer with an acoustic metasurface structure is presented. The metasilencer was designed to restrain the travel direction of the sound wave of the target frequency into a U-shaped configuration using an acoustic metasurface while considering the flow noise effect of the HVAC system. Acoustic analysis confirmed the noise reduction frequency range and refraction effect of the metasurface. The speaker test confirmed the noise reduction effect of the silencer. The same was also confirmed via HVAC tests, even in the presence of a flow. Full article

(This article belongs to the Special Issue Recent Advance in Acoustic Metamaterials)

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11 pages, 2375 KiB

Open AccessArticle

Bidirectional Acoustic Negative Refraction Based on a Pair of Identical Purely Imaginary Metamaterials Slabs

by Ling-Ling Zhang, Yang Ji, Peng Chen, Qian Dai and Xiao-Jun Liu

Appl. Sci. 2022, 12(19), 9914; https://doi.org/10.3390/app12199914 - 1 Oct 2022

Viewed by 1234

Abstract

Acoustic purely imaginary metamaterials (PIMs) slabs can support the coexistence of coherent perfect absorption and laser modes and are used to achieve negative refraction. Previous works have focused on a pair of different PIM slabs, one operating in CPA mode and the other [...] Read more.

Acoustic purely imaginary metamaterials (PIMs) slabs can support the coexistence of coherent perfect absorption and laser modes and are used to achieve negative refraction. Previous works have focused on a pair of different PIM slabs, one operating in CPA mode and the other in laser mode. However, this structure has restrictions on the incident wave direction, specifically the wave can only be incident from the CPA side. In this paper, we derive the analytical expressions for the parameters required for the coexistence of CPA and laser modes in acoustic PIM slabs. Numerical simulation results show that such PIM slab can freely switch states between the coherent complete absorber and the laser depending on the incidence direction. On this basis, by using a pair of identical PIM slabs, bidirectional negative refraction and planar focusing can be achieved. In addition, the parameters in the appropriate range can be found by adjusting the mode order, which facilitates the experimental verification. So far, the required acoustic purely imaginary metamaterials (PIMs) have not been experimentally demonstrated, and the results presented in the manuscript are theoretical speculations on their existence, so practical applications may require more sophisticated design and engineering. Full article

(This article belongs to the Special Issue Recent Advance in Acoustic Metamaterials)

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13 pages, 4642 KiB

Open AccessArticle

Theoretical Zero-Thickness Broadband Holograms Based on Acoustic Sieve Metasurfaces

by Ye Tian, Shuyu Zuo, Qian Lv, Guanjun Yin and Jianzhong Guo

Appl. Sci. 2022, 12(13), 6453; https://doi.org/10.3390/app12136453 - 25 Jun 2022

Cited by 1 | Viewed by 1244

Abstract

Acoustic holography is an essential tool for controlling sound waves, generating highly complex and customizable sound fields, and enabling the visualization of sound fields. Based on acoustic sieve metasurfaces (ASMs), this paper proposes a theoretical design approach for zero-thickness broadband holograms. The ASM [...] Read more.

Acoustic holography is an essential tool for controlling sound waves, generating highly complex and customizable sound fields, and enabling the visualization of sound fields. Based on acoustic sieve metasurfaces (ASMs), this paper proposes a theoretical design approach for zero-thickness broadband holograms. The ASM is a zero-thickness rigid screen with a large number of small holes that allow sound waves to pass through and produce the desired real image in the target plane. The hole arrangement rules are determined using a genetic algorithm and the Rayleigh–Sommerfeld theory. Because the wave from a hole has no extra phase or amplitude modulation, the intractable modulation dispersion can be physically avoided, allowing the proposed ASM-based hologram to potentially function in any frequency band as long as the condition of paraxial approximation is satisfied. Using a numerical simulation based on the combination of the finite element method (FEM) and the boundary element method (BEM), this research achieves broadband holographic imaging with a good effect. The proposed theoretical zero-thickness broadband hologram may provide new possibilities for acoustic holography applications. Full article

(This article belongs to the Special Issue Recent Advance in Acoustic Metamaterials)

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10 pages, 3635 KiB

Open AccessArticle

Acoustic Negative Refraction and Planar Focusing Based on Purely Imaginary Metamaterials

by Ling-Ling Zhang and Xiao-Jun Liu

Appl. Sci. 2022, 12(12), 5962; https://doi.org/10.3390/app12125962 - 11 Jun 2022

Cited by 2 | Viewed by 1238

Abstract

Acoustic purely imaginary metamaterials (PIMs) contain loss and gain uniformly distributed in space, but in different parameters. Therefore, the PIMs contain the elements of gain and loss simultaneously. As a result, some extraordinary wave modes may appear depending on whether gain or loss [...] Read more.

Acoustic purely imaginary metamaterials (PIMs) contain loss and gain uniformly distributed in space, but in different parameters. Therefore, the PIMs contain the elements of gain and loss simultaneously. As a result, some extraordinary wave modes may appear depending on whether gain or loss elements dominate. In this work, we theoretically and numerically investigate the general excitation conditions for acoustic lasing, coherent perfect absorption (CPA) and for their co-existence in the framework of acoustic PIMs. All-angle negative refraction and planar focusing are achieved by pairing two PIM slabs with conjugating parameters. The proposed structure provides an alternative basis for possible applications of acoustic perfect imaging. Full article

(This article belongs to the Special Issue Recent Advance in Acoustic Metamaterials)

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12 pages, 4068 KiB

Open AccessArticle

Tunable Beam Splitter Based on Acoustic Binary Metagrating

by Zhengang Liu, Fangfang Ju, Shengyou Qian and Xiaojun Liu

Appl. Sci. 2022, 12(8), 3758; https://doi.org/10.3390/app12083758 - 8 Apr 2022

Cited by 2 | Viewed by 1253

Abstract

As an inversely designed artificial surface, acoustic metasurfaces usually consist of subwavelength unit cells in an array configuration, exhibiting exceptional abilities in acoustic wave manipulation. In contrast to metasurfaces with subwavelength units and complex configurations, we propose here a comprehensive concept of a [...] Read more.

As an inversely designed artificial surface, acoustic metasurfaces usually consist of subwavelength unit cells in an array configuration, exhibiting exceptional abilities in acoustic wave manipulation. In contrast to metasurfaces with subwavelength units and complex configurations, we propose here a comprehensive concept of a beam splitter based on an acoustic binary metagrating (ABM), capable of splitting a given acoustic wave into two predesigned directions. The ABM is composed of only two kinds of elements, corresponding to the elements “0” and “1”, respectively. The diffraction orders in the ABM take a value of n = −1 (split beam 1) and n = 1 (split beam 2), and hence, the beam splitting occurs. We exemplify the ABM by etching only one straight-walled groove per period on a planar hard surface. In our design, the reflected angles of these two split beams can be readily controlled by setting a proper incident angle. Theoretical analysis and numerical simulations were undertaken to provide the proof of concept for the proposed acoustic beam splitter. Full article

(This article belongs to the Special Issue Recent Advance in Acoustic Metamaterials)

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10 pages, 2726 KiB

Open AccessArticle

Low-Frequency Low-Reflection Bidirectional Sound Insulation Tunnel with Ultrathin Lossy Metasurfaces

by Yi-Jun Guan, Yu-Wei Xu, Yong Ge, Hong-Xiang Sun, Shou-Qi Yuan and Xiao-Jun Liu

Appl. Sci. 2022, 12(7), 3470; https://doi.org/10.3390/app12073470 - 29 Mar 2022

Cited by 1 | Viewed by 1634

Abstract

We report both numerical and experimental constructions of a tunnel structure with low-frequency low-reflection bidirectional sound insulation (BSI). The designed tunnel was constructed from a pair of lossy acoustic metasurfaces (AMs), which consists of six ultrathin coiled unit cells, attached on both sides. [...] Read more.

We report both numerical and experimental constructions of a tunnel structure with low-frequency low-reflection bidirectional sound insulation (BSI). The designed tunnel was constructed from a pair of lossy acoustic metasurfaces (AMs), which consists of six ultrathin coiled unit cells, attached on both sides. Based on the generalized Snell′s law and phase modulations for both AMs, the tunnel with the low-frequency BSI was constructed based on sound reflections and acoustic blind areas created by the AMs. The obtained transmittances were almost the same for sound incidences from both sides and were lower than −10 dB in the range 337–356 Hz. The simulated and measured results agreed well with each other. Additionally, we show that the low-reflection characteristic of the tunnel can be obtained simultaneously by thermoviscous energy loss in coiled channels of the unit cells. Finally, an interesting application of the designed tunnel in an open-window structure with low-frequency low-reflection BSI is further simulated in detail. The proposed tunnel based on the ultrathin lossy AMs has the advantages of ultrathin thickness (about λ/35), low-frequency low-reflection BSI, and high-performance ventilation, which may have potential applications in architectural acoustics and noise control. Full article

(This article belongs to the Special Issue Recent Advance in Acoustic Metamaterials)

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8 pages, 6364 KiB

Open AccessArticle

Ultra-Broadband Bending Beam and Bottle Beam Based on Acoustic Metamaterials

by Xudong Fan, Xiaolong Huang, Yang Kang, Can Li, Ning Li and Chunsheng Weng

Appl. Sci. 2022, 12(6), 3025; https://doi.org/10.3390/app12063025 - 16 Mar 2022

Cited by 4 | Viewed by 1767

Abstract

We report the realization of an ultra-broadband bending beam based on acoustic metamaterials by the theoretical prediction and the numerical validation. The proposed structure is composed of a series of straight tubes with spatially modulated depths. We analytically derive the depth profile required [...] Read more.

We report the realization of an ultra-broadband bending beam based on acoustic metamaterials by the theoretical prediction and the numerical validation. The proposed structure is composed of a series of straight tubes with spatially modulated depths. We analytically derive the depth profile required for the generation of an ultra-broadband bending beam, and examine the performance of the metastructure numerically. The design is then extended for the generation of a three-dimensional bottle beam. The transverse trapping behaviours on small rigid objects by the bottle beam are investigated based on the force potential. Our work will help the further study of broadband acoustic meta-structures, and may also find applications in a variety of fields such as ultrasound imaging, health monitoring and particle manipulations. Full article

(This article belongs to the Special Issue Recent Advance in Acoustic Metamaterials)

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14 pages, 3627 KiB

Open AccessArticle

Acoustic Equivalent Lasing and Coherent Perfect Absorption Based on a Conjugate Metamaterial Sphere

by Xing-Xing Ma, Qi Wei, Xing-Feng Zhu, Jie Yao and Da-Jian Wu

Appl. Sci. 2022, 12(4), 1777; https://doi.org/10.3390/app12041777 - 9 Feb 2022

Cited by 2 | Viewed by 1535

Abstract

Acoustic conjugate metamaterials (ACMs), in which the imaginary parts of the effective complex mass density and bulk compressibility are cancelled out in the refractive index, possess the elements of loss and gain simultaneously. Previous works have focused on panel ACMs for plane wave [...] Read more.

Acoustic conjugate metamaterials (ACMs), in which the imaginary parts of the effective complex mass density and bulk compressibility are cancelled out in the refractive index, possess the elements of loss and gain simultaneously. Previous works have focused on panel ACMs for plane wave incidence. In this paper, we explore the extraordinary scattering properties, including the acoustic equivalent lasing (AEL) and coherent perfect absorption (CPA) modes, of a three-dimensional ACM sphere, where incident spherical waves with specific topological orders could be extremely scattered and totally absorbed, respectively. Theoretical analysis and numerical simulations show that the AEL or CPA mode with a single order can be realized with a small monolayer ACM sphere with appropriate parameters. A huge (relative to incident wavelength) ACM sphere with pure imaginary parameters could support the even- (or odd-) order AEL and odd- (or even-) order CPA modes simultaneously. In addition, the AEL and/or CPA with multiple orders could be realized based on a small multilayered ACM sphere. The proposed ACM sphere may provide an alternative method to design acoustic functional devices, such as amplifiers and absorbers. Full article

(This article belongs to the Special Issue Recent Advance in Acoustic Metamaterials)

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