Spider web-structured labyrinthine acoustic metamaterials for low-frequency sound control (original) (raw)
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Labyrinthine Acoustic Metamaterials with Space-Coiling Channels for Low-Frequency Sound Control
Acta Acustica united with Acustica, 2018
We numerically analyze the performance of labyrinthine acoustic metamaterials with internal channels folded along a Wunderlich space-filling curve to control low-frequency sound in air. In contrast to previous studies, we perform direct modeling of wave propagation through folded channels, not introducing effective theory assumptions. As a result, we reveal that metastructures with channels, which allow wave propagation in the opposite direction to incident waves, have different dynamics as compared to those for straight slits of equivalent length. The differences are attributed to activated tortuosity effects and result in 100% wave reflection at band gap frequencies. This total reflection phenomenon is found to be insensitive to thermo-viscous dissipation in air. For labyrinthine channels generated by iteration levels, one can achieve broadband total sound reflection by using a metamaterial monolayer and efficiently control the amount of absorbed wave energy by tuning the channel width. Thus, the work contributes to a better understanding of labyrinthine metamaterials with potential applications for reflection and filtering of low-frequency airborne sound.
Acoustic Properties of a Metamaterial Acoustic Barrier
2020
In the last years, many papers have reported the results of researchers on acoustic metamaterials. The study of acoustic metamaterials represents a new research field in noise control. Metamaterials are artificial structures with periodical elements, made by the arrangement of scatterers in a square or triangular lattice configuration. The reason for such sound attenuation is due to the destructive interference of waves in the band of frequencies and the propagating wave has a decaying amplitude, which causes the sound attenuation to take place in the "bandgap" region. Metamaterials are structures designed and built to control the propagation of the waves. So the metamaterials are new materials obtained by the interaction of artificial objects and geometric structures of regular shape. The term metamaterials was coined nearly a decade, the word metamaterial is made of two words: meta and material. The word meta, from "metamorfosi" means a change in conditions, in this context it means later. The prefix "meta" originates from the Greek word for "after" or "beyond". The latest applications are in the room acoustics, noise barriers. This paper describes the state of art of the applications of the metamaterials in the acoustics field and the applications of metamaterials for the sound attenuation of an acoustic barrier are reported. The acoustic measurements were done in a scale model (1:10). The sound attenuation is shown in particular frequencies range, in the function of the distance of the barrier elements.
Spider web-inspired labyrinthine acoustic metamaterials
arXiv: Materials Science, 2017
The field of acoustic metamaterials has attracted much attention in recent years due to the possibilities they provide for wave manipulation and for the generation of exotic properties such as negative refraction, super-resolution imaging or cloaking. In particular, recently introduced labyrinthine metamaterials can generate extremely high effective refractive index values and simultaneously effective negative mass density and bulk modulus, due to their characteristic topological architecture. In this paper, we design a novel labyrinthine metamaterial structure, exploiting a spider web geometry for a bioinspired design. The resulting deviations from a regular circular lattice geometry provide additional tunability of the frequencies at which band gaps or negative group velocity modes occur, thus enabling versatility in the functionalities of the resulting structures. Time transient simulations demonstrate the effectiveness of the proposed metamaterials in manipulating wave fields in...
Porous labyrinthine acoustic metamaterials with high transmission loss property
Journal of Applied Physics, 2019
This study systemically investigates a porous labyrinthine type of acoustic metamaterials (LAMs), a sort of acoustic metasurface, analytically, numerically, and in laboratory tests. The LAMs are composed of a series of porous elements, where stainless steel plates with various lengths are inserted into the melamine foam. At the frequency of interest 2000 Hz, porous elements with a thickness smaller than oneeighth of the target wavelength are designed to generate a linearly varied phase gradient on the refracting surface and slightly varied phase responses on the reflecting surface; the elements play key roles in refracted and reflected wave manipulations, respectively. Two porous LAMs with different periodical lengths are designed based on the generalized Snell's law to study the effect of the periodical length on refraction and reflection phenomena in the scattered sound pressure fields. By reducing the length to smaller than one-half of the target wavelength, the high-order wave modes will disappear in the refracted and reflected sound pressure fields at omnidirectional incidence, resulting in enhancements of transmission loss and also sound absorption coefficient in a wide range of incidence angles compared with the uniform melamine foam with the same thickness. The thin porous LAMs provide a method to improve sound transmission loss and sound absorption properties of an uniform porous material and show potentials to be used in cabins of high-speed trains and aircraft.
Acoustic metamaterials for sound focusing and confinement
New Journal of Physics, 2007
We give a theoretical design for a locally resonant two-dimensional cylindrical structure involving a pair of C-shaped voids in an elastic medium which we term as double 'C' resonators (DCRs) and imbedded thin stiff bars, that displays the negative refraction effect in the low frequency regime. DCRs are responsible for a low frequency band gap which hybridizes with a tiny gap associated with the presence of the thin bars. Using an asymptotic analysis, typical working frequencies are given in closed form: DCRs behave as Helmholtz resonators modeled by masses connected to clamped walls by springs on either side, while thin bars behave as a periodic bi-atomic chain of masses connected by springs. The discrete models give an accurate description of the location and width of the stop band in the case of the DCR and the first two dispersion bands for the periodic thin bars. We then combine our asymptotic formulae for arrays of DCR and thin-bars to design a composite structure that displays a negative refraction effect and has a negative phase velocity in a frequency band, and thus behaves in many ways as a negative refractive acoustic medium (NRAM). Finite element computations show that at this frequency, a slab of such NRAM works as a phononic flat superlens whereas two corners of such NRAM sharing a vertex act as an open resonator and can be used to confine sound to a certain extent.
Sound Attenuation of an Acoustic Barrier Made with Metamaterials
Canadian Acoustics, 2019
Metamaterials represent a new approach in applied acoustics and noise control fields, although the first studies of them date back to a half century ago to Viselago, and later to Pendry. In this paper, after a brief introduction to the state of art of metamaterials for acoustic applications, the sound attenuation of an acoustic barrier made following metamaterial rules is investigated. A 1:10 scale model was built using cylindrical wooden bars, 30 cm high and 1.5 cm in diameter. The total length of the barrier model was 100 cm. The barrier was investigated for four alternating rows of cylindrical bars, spacing each bar with an empty space to create different regular geometries. The insertion losses of each configuration are reported.
2019
The purpose of this research is to develop alternative 3D labyrinthine-type acoustical metamaterials by utilizing ‘space-coiling’ for sound control in architectural applications. Acoustical metamaterials have a great potential on their application for building and room acoustics due to their extreme properties in sound absorption and transmission. They can be used as an interior partition, an interior surface layer, and also as a design element. They are advantageous in comparison to the traditional acoustical materials such that by tuning their physical properties more hygienic, lighter or thinner alternatives can be produced. In this research, the design ideas of acoustic metamaterials (AMMs) originate from golden ratio (GR) and web labyrinth (WL). In data collection and analysis, both experimental and theoretical methods are used. As a first step, all design alternatives are modelled in 3D, then are printed out by a CNC 3D printer, finally, the AMMs are tested in impedance tube t...
2021
In this work, we demonstrate in a proof of concept experiment the efficient noise absorption of a 3-D printed panel designed with appropriately arranged space-coiled labyrinthine acoustic elementary cells. The labyrinthine units are numerically simulated to determine their dispersion characteristics and then experimentally tested in a Kundt Tube to verify the dependence of absorption characteristics on cell thickness and lateral size. The resonance frequency is found to scale linearly with respect to both thickness and lateral size in the considered range, enabling tunability of the working frequency. Using these data, a flat panel is designed and fabricated by arranging cells of different dimensions in a quasi-periodic lattice, exploiting the acoustic “rainbow” effect, i.e. superimposing the frequency response of the different cells to generate a wider absorption spectrum, covering the required frequency range between 800 and 1200 Hz. The panel is thinner and more lightweight compa...