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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].
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.
Modeling and optimizing an acoustic metamaterial to minimize low-frequency structure-borne sound
Published in Mechanics Based Design of Structures and Machines, 2020
Daniel John Jagodzinski, Matthias Miksch, Quirin Aumann, Gerhard Müller
Researchers have given considerable effort to develop novel lightweight materials capable of reducing low-frequency structure-borne sound (Sui et al. 2015; Claeys et al. 2016; Miksch, Ramirez, and Müller 2019). These materials are often termed metamaterials because the macroscopic material behavior is greatly influenced by its microscopic structure, resulting in interesting properties, such as seemingly negative effective density or negative Poisson’s ratio (Liu et al. 2000; Patiballa and Krishnan 2020). Acoustic metamaterials have a great potential to improve the vibrational behavior of structures as well as sound radiation and sound insulation (Yan et al. 2010; Sugino et al. 2017; Van Belle et al. 2019). Especially at lower frequencies, periodic resonance-based acoustic metamaterials can achieve optimal noise and vibration suppression properties (Claeys et al. 2013; Sun, Du, and Pai 2010).
Localization of waves in double-negative acoustic metamaterial multilayers with thickness disorder
Published in Waves in Random and Complex Media, 2023
Acoustic metamaterials are acoustic analogs of electromagnetic metamaterials. The effective mass density and effective bulk modulus play an important role in acoustic metamaterials. If either of these properties is negative, the acoustic metamaterial is called single negative (SN). The acoustic properties of these materials have been investigated through theoretical analysis of the lattice model [1–5]. Vibrational properties of acoustic metamaterial multilayers, which are composed of a periodic cluster arrangement of mass and mass-in-mass microstructures, have been numerically studied [4]. SN acoustic metamaterials strongly absorb vibrational excitations near its resonant frequency. Such materials are useful for vibrational damping, whereas their other industrial applications may be limited. If both the effective mass density and effective bulk modulus of the material are negative, it is then called double-negative (DN) acoustic metamaterial. Li and Chan have theoretically discussed the concept of double-negative acoustic media [6]. From this perspective, it is interesting to employ DN systems to study acoustic metamaterial composites for investigating the propagation of elastic waves. Huang and Sun proposed a mechanical model based on an acoustic metamaterial, in which the effective mass density and effective modulus simultaneously became negative within a certain frequency regime [7]. Zhai, Chen, Ding, and Zhao have proposed a meta-molecule model representing an acoustic metamaterial [8]. Li, Wang, and Wang proposed a different elastic model based on translational resonance to simultaneously obtain the negative mass and negative modulus within specific frequency ranges [9].