scholarly journals Ultra-Thin Metasurface-Based Absorber of Low-Frequency Sound With Bandwidth Optimization

2021 ◽  
Vol 8 ◽  
Author(s):  
Yi-jun Guan ◽  
Yong Ge ◽  
Hong-xiang Sun ◽  
Shou-qi Yuan ◽  
Yun Lai ◽  
...  
Keyword(s):  
Circular Hole ◽  
Low Frequency ◽  
Frequency Noise ◽  
Fractional Bandwidth ◽  
Practical Applications ◽  
Frequency Sound ◽  
Bandwidth Optimization ◽  
Viscous Loss ◽  
Cavity Structure ◽  
Different Diameters

We report, both theoretically and experimentally, a type of ultra-thin metasurface-based low-frequency sound absorber with bandwidth optimization. Such a metasurface unit consists of an ultrathin resonator (thickness∼1/90 wavelength) with a circular hole on the upper panel and four narrow slits inside a multiple-cavity structure. Eigenmode simulations of the unit show rich artificial Mie resonances, in which a type of monopolar Mie resonance mode can be obtained at 238.4 Hz. Based on the excitation of the monopolar mode, we can realize the near-perfect low-frequency sound absorption with the maximum absorption coefficient and fractional bandwidth of 0.97 and 12.9%, respectively, which mainly arises from the high thermal-viscous loss around the circular hole and four narrow slits of the unit. More interestingly, by combining 4 units with different diameters of the circular hole, we further enhance the fractional bandwidth of the compound unit to 18.7%. Our work provides a route to design ultra-thin broadband sound absorbers by artificial Mie resonances, showing great potential in practical applications of low-frequency noise control and architectural acoustics.

scholarly journals Low-Frequency, Open, Sound-Insulation Barrier by Two Oppositely Oriented Helmholtz Resonators

Micromachines ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1544
Author(s):  
Yi-Jun Guan ◽  
Yong Ge ◽  
Hong-Xiang Sun ◽  
Shou-Qi Yuan ◽  
Xiao-Jun Liu
Keyword(s):  
High Performance ◽  
Low Frequency ◽  
Single Layer ◽  
Sound Insulation ◽  
Architectural Acoustics ◽  
Frequency Sound ◽  
Helmholtz Resonators ◽  
Viscous Loss ◽  
Insulation Effect ◽  
Broadband Sound

In this work, a low-frequency, open, sound-insulation barrier, composed of a single layer of periodic subwavelength units (with a thickness of λ/28), is demonstrated both numerically and experimentally. Each unit was constructed using two identical, oppositely oriented Helmholtz resonators, which were composed of a central square cavity surrounded by a coiled channel. In the design of the open barrier, the distance between two adjacent units was twice the width of the unit, showing high-performance ventilation, and low-frequency sound insulation. A minimum transmittance of 0.06 could be observed around 121.5 Hz, which arose from both sound reflections and absorptions, created by the coupling of symmetric and asymmetric eigenmodes of the unit, and the absorbed sound energy propagating into the central cavity was greatly reduced by the viscous loss in the channel. Additionally, by introducing a multilayer open barrier, a broadband sound insulation was obtained, and the fractional bandwidth could reach approximately 0.19 with four layers. Finally, the application of the multilayer open barrier in designing a ventilated room was further discussed, and the results presented an omnidirectional, broadband, sound-insulation effect. The proposed open, sound-insulation barrier with the advantages of ultrathin thickness; omnidirectional, low-frequency sound insulation; broad bandwidth; and high-performance ventilation has great potential in architectural acoustics and noise control.

Design of Transformer Substation Low Frequency Sound Absorber and Test Study on Sound Absorption Property

2013 ◽  
Vol 468 ◽  
pp. 134-140 ◽  
Author(s):  
Xia Zhang ◽  
Shu Ning Duan ◽  
Mei Gen Cao ◽  
Juan Mo ◽  
Yu Han Sun ◽  
...  
Keyword(s):  
Sound Absorption ◽  
Low Frequency ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Frequency Sound ◽  
Sound Absorber ◽  
Test Study ◽  
Transformer Substation ◽  
Cavity Thickness ◽  
Standing Wave Tube

In allusion to the characteristic that transformer noise is mainly low-frequency noise, firstly the sound absorber is studied and analyzed on aspect of materials, sound absorption structure cavity thickness and punching rate etc in standing wave tube laboratory, secondly transformer substation low-frequency sound absorber is presented, and finally sound absorption properties of absorber is verified through random incidence Test. The analyses and study indicates that: compared with thin plate resonance absorber and micropunching sound absorber, the sound absorption band width of transformer substation low-frequency sound absorber has been improved under unchanged sound absorption effect and transformer low-frequency noise may be effectively absorbed.

scholarly journals Effect of Cavity Structure on Acoustic Characteristics of Phononic Crystals Based on Double-Layer Plates

Crystals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 995
Author(s):  
Chuanmin Chen ◽  
Zhaofeng Guo ◽  
Songtao Liu ◽  
Hongda Feng ◽  
Chuanxi Qiao
Keyword(s):  
Noise Reduction ◽  
Band Gap ◽  
Double Layer ◽  
Transmission Loss ◽  
Low Frequency ◽  
Phononic Crystals ◽  
Frequency Noise ◽  
Structural Factors ◽  
Low Frequency Noise ◽  
Cavity Structure

Localized resonance phononic crystals (LRPCs) are increasingly attracting scientists’ attention in the field of low-frequency noise reduction because of the excellent subwavelength band gap characteristics in the low-frequency band. However, the LRPCs have always had the disadvantage that the noise reduction band is too narrow. In this paper, in order to solve this problem, LRPCs based on double-layer plates with cavity structures are designed. First, the energy bands of phononic crystals plate with different thicknesses were calculated by the finite element method (FEM). At the same time, the mechanism of band gap generation was analyzed in combination with the modalities. Additionally, the influence of structure on the sound transmission loss (STL) of the phononic crystals plate and the phononic crystals cavity plates were analyzed, which indicates that the phononic crystals cavity plates have notable characteristics and advantages. Moreover, this study reveals a unique ”cavity cave” pattern in the STL diagram for the phononic crystals cavity plates, and it was analyzed. Finally, the influence of structural factors on the band structure and STL of phononic crystals cavity plates are summarized, and the theoretical basis and method guidance for the study of phononic crystals cavity plates are provided. New ideas are also provided for the future design and research of phononic crystals plate along with potential applications in low-frequency noise reduction.

Research of HRTF Character of Head-Mounted Microphone Array

2015 ◽  
Vol 743 ◽  
pp. 479-483
Author(s):  
Yi Zhang ◽  
B.B. Shen ◽  
S.J. Meng
Keyword(s):  
Frequency Band ◽  
High Frequency ◽  
Microphone Array ◽  
Low Frequency ◽  
Diffraction Effect ◽  
Localization Algorithm ◽  
Attenuation Effect ◽  
Practical Applications ◽  
Acoustic Localization ◽  
Frequency Sound

Head-mounted microphone array has practical applications in robot acoustic localization system and wearable anti-sniper positioning system. Usually, sound source localization methods are based on linear or nonlinear unblocked microphone arrays. But head-mounted microphone array is a kind of blocked arrays, with which it needs information of Head Related Transfer Function (HRTF) for precise localization. In this paper, we research the HRTF character of head-mounted microphone array for localization in high frequency band and low frequency band respectively, and design a localization algorithm for low frequency sound based on head-mounted microphone array to analysis the threshold between high and low frequency. Experimental results show that the Head-mounted Microphone Array causes diffraction effect for low frequency sound, and amplitude attenuation effect for high frequency sound, and when the low frequency band is limited into 1 KHz, the localization algorithm for low frequency realizes the best performance.

scholarly journals Research on Low Frequency Sound Insulation Properties of Membrane-Type Acoustic Metamaterials

2021 ◽  
Vol 1210 (1) ◽  
pp. 012001
Author(s):  
Xiaokai Yin ◽  
Yongchao Xu ◽  
Hongyu Cui
Keyword(s):  
Noise Control ◽  
Low Frequency ◽  
Sound Insulation ◽  
Frequency Noise ◽  
Acoustic Metamaterials ◽  
Frequency Sound ◽  
Field Coupling ◽  
Cabin Noise ◽  
Sound Structure ◽  
Membrane Type

Abstract To solve the problem of low-frequency noise control in ship cabins, a new membrane-type acoustic metamaterial (MAM) with bulges on the surface of thin films is designed based on the characteristics of lightweight and low-frequency sound insulation of membrane-type acoustic metamaterials. The sound structure coupling module of COMSOL multiphysical field coupling software is used to analyse the sound insulation performance of MAMs. The sound insulation properties of the additional mass film and self-similar fractal convex structure are further discussed. The metamaterial structure studied in this paper has a better sound insulation effect than ordinary film, which provides strong technical support for ship cabin noise control.

Low Frequency Noise Considerations for Combustion Turbine Projects

1997 ◽  
Author(s):  
Lisa A. Beeson ◽  
George A. Schott
Keyword(s):  
Noise Control ◽  
Low Frequency ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Pressure Pulsations ◽  
Relative Difficulty ◽  
Low Frequencies ◽  
Sound Energy ◽  
Frequency Sound ◽  
Human Ear

Combustion turbine projects have become a popular choice for providing a clean and efficient source of electricity. However, since combustion turbines generally produce low frequency sound energy, special siting considerations should be evaluated to minimize the potential for impacts on sensitive receptors, such as residences, churches, hospitals, and schools. For successful siting of combustion turbine projects near sensitive receptors, it is necessary to incorporate noise control features into plant designs to reduce not only audible noise but also noise at frequencies which are even lower than the human ear can perceive. These extremely low frequencies can rattle walls and windows, causing pressure pulsations which may be perceived by some people, or vibration of small objects inside houses and other structures. Even “quiet” plants which include extensive noise control features may still result in perceptible low frequency noise due to the relative difficulty of attenuating low frequency sound energy. Noise attenuation options are discussed, including active, passive, and reactive technologies, along with the impacts associated with each type of design. Guidelines for siting combustion turbine power generation facilities near sensitive receptors are presented, to enable development of projects which not only meet applicable noise requirements, but also reduce the potential for community complaints.

Linear and nonlinear mechanisms of sound radiation by instability waves in subsonic jets

2010 ◽  
Vol 658 ◽  
pp. 509-538 ◽  
Author(s):  
VICTORIA SUPONITSKY ◽  
NEIL D. SANDHAM ◽  
CHRISTOPHER L. MORFEY
Keyword(s):  
Nonlinear Interaction ◽  
Stokes Equations ◽  
Low Frequency ◽  
Current Approach ◽  
Frequency Noise ◽  
Instability Waves ◽  
Frequency Sound ◽  
Highly Nonlinear ◽  
Linear And Nonlinear ◽  
Low Frequency Waves

Linear and nonlinear mechanisms of sound generation in subsonic jets are investigated by numerical simulations of the compressible Navier–Stokes equations. The main goal is to demonstrate that low-frequency waves resulting from nonlinear interaction between primary, highly amplified, instability waves can be efficient sound radiators in subsonic jets. The current approach allows linear, weakly nonlinear and highly nonlinear mechanisms to be distinguished. It is demonstrated that low-frequency waves resulting from nonlinear interaction are more efficient in radiating sound when compared to linear instability waves radiating directly at the same frequencies. The results show that low-frequency sound radiated predominantly in the downstream direction and characterized by a broadband spectral peak near St = 0.2 can be observed in the simulations and described in terms of the nonlinear interaction model. It is also shown that coherent low-frequency sound radiated at higher angles to the jet axis (θ = 60°–707°) is likely to come from the interaction between two helical modes with azimuthal wavenumbers n = ±1. High-frequency noise in both downstream and side-line directions seems to originate from the breakdown of the jet into smaller structures.

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