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Other absorbers and diffusers
Published in Trevor J. Cox, Peter D'Antonio, Acoustic Absorbers and Diffusers, 2016
Trevor J. Cox, Peter D'Antonio
These sonic crystals need large lattice spacing for audio frequencies, and this makes them impractical devices in many situations. By replacing the cylinders with resonators, say by using hollow cylinders with slits to form a set of Helmholtz resonators, it is possible to get band gaps at lower frequencies.28 This is an example of a locally resonant acoustic metamaterial.29 Metamaterials are structures made up of arrays of subwavelength components, which allow the global acoustic properties of a material to be altered by changing the components. By appropriate choice of components, these materials can appear to defy the laws of nature, producing negative densities and other strange properties. For example, negative effective bulk modulus implies that the applied pressure and resultant volume change are out of phase: increased pressure results in a bigger volume!
Genetic Optimization Techniques in Reduction of Noise Hazards
Published in Dariusz Pleban, Occupational Noise and Workplace Acoustics, 2020
An example of new trends in noise reduction which enjoy increasing popularity in recent years are acoustic metamaterials [Zangeneh-Nejad and Fleury 2019]. Due to their complex internal structure, these materials are characterized by sound-insulating properties better than those predicted based on the grounds of the mass law or the individual properties of component materials used to construct them. The process of developing such materials is typically a process of multi-parameter optimization in which genetic algorithms may be successfully employed. Examples of application of genetic algorithms in development of new acoustic metamaterials are presented in Blevins [2016] and Lagarrigue et al. [2016].
Manufacturing of membrane acoustical metamaterials for low frequency noise reduction and control: A review
Published in Mechanics of Advanced Materials and Structures, 2023
Chao Wang, Lin Cai, Mingchen Gao, Lei Jin, Lucheng Sun, Xiaoyun Tang, Guangyu Shi, Xin Zheng, Chunyu Guo
Currently, there are three methods for achieving "acoustic stealth": acoustic stealth based on transformation acoustics theory, acoustic stealth based on scattering cancelation theory, and acoustic stealth based on sound absorption mechanism[28, 30–33]. Acoustic metamaterials belong to the latter category. The sound absorption mechanism is realized through the use of acoustic cladding, with the acoustic cladding made of acoustic metamaterials [34, 35]. Acoustic metamaterials can be divided into three categories according to their mechanisms: scattering sound absorption mechanism[36–39], cavity resonance[40–44] mechanism, and local resonance[45–48] mechanism. This review focuses on membrane acoustic metamaterials (MAMs) based on the local resonance mechanism, which are expected to become the dominant structure in the field of low frequency noise reduction and even be applied in the water environment. The second section provides a brief introduction to MAMs, followed by a summary of their manufacture in the third section. The fourth section concludes with a summary and outlook.
Exact strain gradient modelling of prestressed nonlocal diatomic lattice metamaterials
Published in Mechanics of Advanced Materials and Structures, 2023
Binying Wang, Jinxing Liu, Ai Kah Soh, Naigang Liang
In recent decades, efforts have been devoted to researches of metamaterials to promote both lattice metamaterial theory and technology development. Metamaterials refer to a new kind of artificially synthetic materials, which possess some novel properties not found in conventional materials [1, 2]. In such a context, acoustic metamaterials can exhibit unique physical characteristics, such as effective negative bulk modulus, effective negative mass density, etc. These extraordinary properties also make acoustic metamaterials achieve great progress in practical application including noise control, vibration suppression, waveguides, invisible cloaks and so on [3, 4]. Particularly, many researches have been carried out to analyze the wave propagation, dispersion characteristics and effective negative parameters in elastic metamaterials [5–12].
Homogenization and free-vibration analysis of elastic metamaterial plates by Carrera Unified Formulation finite elements
Published in Mechanics of Advanced Materials and Structures, 2021
Maria Cinefra, Alberto Garcia de Miguel, Matteo Filippi, Caroline Houriet, Alfonso Pagani, Erasmo Carrera
According to the same principles of wave propagation in periodic structures [13–15], acoustic metamaterials are tuned to the acoustic wavelength and consist of a periodic arrangement of inclusions or cylindrical pores embedded within a material matrix, that are typically spaced less than a wavelength apart. These materials disrupt the propagation of waves by scattering and refraction effects. In acoustics, low frequencies are especially difficult to absorb with conventional materials, as the order of magnitude of the wavelength is 1 m, which is much greater than the reasonable thickness of damping materials [16]. Acoustic metamaterial are able to perform better than conventional materials because their structure is such that they do not respect physical properties like positive density or bulk modulus on a global scale at resonance—although they obviously respect physical laws at any time locally.