Acoustic barriers based on periodic arrays of scatterers (original) (raw)
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Applied Sciences
Theory regarding metamaterials was developed in the 1960s, aiming to control the propagation of electromagnetic waves. Under this scope, research has been focused on the realization of materials having specific characteristics to be invisible to the electromagnetic and optics fields. These principles have been expanded only recently to the acoustic sector, with metamaterials capable of controlling the sound propagation due to the interference effect between the soundwaves and the periodic structural elements composing the system. This paper deals with sound attenuation and analyzes a metamaterial acoustic barrier characterized by multiple rows in different configurations. The variety of configurations depends on different diameters of the wooden scatterers (i.e., 9 mm and 15 mm) and the distance between the sound source and the closest edge of the barrier (i.e., 400 mm and 800 mm). Despite having the same height (i.e., 300 mm) of a scaled model, the combination of different diameter...
Effect of periodic structure on sound propagation Gupta 2010 SPIE
In this study, propagation of acoustic wave through a periodic structure has been analyzed. Such a periodic structure has been found to attenuate sound significantly in certain frequency bands, and therefore it can be used as a frequency filter and sound barrier. Experiments were performed to measure the sound attenuation by the periodic structure made of acrylic cylinders. The experimental results were compared with a simulation study using the finite element method, and they are in good agreement. The benefit of such structure is that it is light weight compared to the solid barriers, and it can be tailored according to the frequency of the sound source to be attenuated.
Numerical Evaluation of Sound Attenuation Provided by Periodic Structures
The use of periodic structures as noise abatement devices has already been the object of considerable research seeking to understand its efficiency and see to what extent they can provide a functional solution in mitigating noise from different sources. The specific case of sonic crystals consisting of different materials has received special attention in studying the influence of different variables on its acoustic performance. The present work seeks to contribute to a better understanding of the behavior of these structures by implementing an approach based on the numerical method of fundamental solutions (MFS) to model the acoustic behavior of two-dimensional sonic crystals. The MFS formulation proposed here is used to evaluate the performance of crystals composed of circular elements, studying the effect of varying dimensions and spacing of the crystal elements as well as their acoustic absorption in the sound attenuation provided by the global structure, in what concerns typical traffic noise sources, and establishing some broad indications for the use of those structures.
In this work we present the design and the manufacturing processes, as well as the acoustics standardization tests, of an acoustic barrier formed by a set of multi-phenomena cylindrical scatterers. Periodic arrangements of acoustic scatterers embedded in a fluid medium with different physical properties are usually called Sonic Crystals. The multiple scattering of waves inside these structures leads to attenuation bands related to the periodicity of the structure by means of Bragg scattering. In order to design the acoustic barrier, two strategies have been used: First, the arrangement of scatterers is based on fractal geometries to maximize the Bragg scattering; second, multi-phenomena scatterers with several noise control mechanisms, as resonances or absorption, are designed and used to construct the periodic array. The acoustic barrier reported in this work provides a high technological solution in the field of noise control.
Performance of sonic crystal acoustic barrier with resonant scatterers
2017
Sonic crystals have been regarded with interest for the attenuation of sound waves in a specific frequency range, since it is possible to define their geometry to match a given range of dominant noise frequencies. Besides the attenuation due to the geometric configuration (multiple internal scattering), the sound attenuation can be extended to a broader range of frequencies, making use of complementary resonance phenomena. In the present article, a numerical formulation based on the Method of Fundamental Solutions is presented, with the objective of describing both phenomena and allowing the evaluation of different configurations for sonic crystal barriers
Relative performance of different strategies for wave attenuation by periodic structures
2017
For a periodic structure of symmetric scatterers, such as a ribbed plate or cylinder, Bloch-Floquet waves (BFW) are well-known periodic structure waves (PSW). Conventional wisdom is to attenuate BFW propagation by reflections, energy absorption or stopping bands. Recent theoretical results show that periodic structures with asymmetric scatterers do not lead to BFW, revealing more possibilities for noise reduction through these different PSW. This paper compares the performance of reciprocal and nonreciprocal wave propagation as methods for PSW attenuation. It is found that nonreciprocal wave propagation, such as could be realized with asymmetric metamaterial scatterers, could achieve significantly better attenuation with relatively small deviations from symmetric scatterer properties.
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.
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.
Journal of Physics D: Applied Physics, 2013
The tunable and the engineering possibilities of waveguides in periodic arrays made of rigid square-rod scatterers are theoretically and experimentally reported in this work. Due to the square shape of the scatterers, the control of their orientation with respect to the direction of the incident wave can be used for moulding the propagating acoustic waves inside the periodic structure. On the one hand, the plane wave expansion with supercell approximation is used to obtain the band structure of the periodic system. On the other hand, the scattering of waves in finite periodic arrays is analysed using the finite elements method. Experimentally, a prototype made of rigid square-rod scatterers is used to validate the theoretical predictions. A spatial-frequency filter and some applications in waveguiding for audible sound are discussed in this work. Good agreement between theory and experiments and the high tunability of the system are demonstrated.