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1

Fluid-fluid phononic crystal with elastic coat working in audible frequencies

Klimek Aleksandra

Vibrations in Physical Systems

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2019

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Vol. 30, nr 1

art. no. 2019145

EN

Phononic Crystals are receiving rising attention in the field of modern acoustic materials. PCs are artificial structures of periodically arranged scatterers. Such a structure enables creating a band gap in which, due to the Bragg diffraction phenomenon, vibrations are restrained or even forbidden. In this paperwork, the fluid-fluid PC is tested and simulated - the scatterers are constructed of water cylinders with an ethylene propylene diene monomer coat (EPDM - a hyperelastic rubber) and are embedded in air. The band gap is calculated to emerge in the audible range of frequency. Every simulation is performed with the use of the finite element method.

2

Effect of point defects in a two-dimensional phononic crystal on the reemission of acoustic wave

Gruszka K., Garus S., Garus J., Błoch K., Nabiałek M.

Inżynieria Materiałowa

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2014

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Vol. 35, nr 2

132--135

EN

The article presents the results of the study on impact of the distribution, number and type of conglomeration of point defects on the parameters of the acoustic wave passing through the phononic crystal. For the simulation, the method of finite differences in time domain (FDTD) was used. In the paper several types of point defects distribution topology both inside and on the surface of the two-dimensional phononic crystal was examined. In order to suppress waves reflected from the edge of medium PML (Perfectly Matched Layers) algorithm was applied. In the simulation a lossless medium was considered. The study revealed that a small amount of point defects inside the body of phononic crystal has weak effect on the acoustic wave remission, while relatively small number of defects placed on the crystal's surface significantly affected the characteristics of the acoustic wave.

PL

W artykule przedstawiono wyniki badań wpływu rozmieszczenia, liczby oraz typu konglomeracji defektów punktowych na parametry fali akustycznej przechodzącej przez kryształ fononiczny. Do przeprowadzenia symulacji wykorzystano metodę różnic skończonych w domenie czasu (FDTD). W pracy zbadano kilkanaście rodzajów topologii rozmieszczenia defektów punktowych zarówno wewnątrz, jak i na powierzchni dwuwymiarowego kryształu fononicznego. W celu wytłumienia fal odbitych od krawędzi ośrodka zastosowano algorytm PML (Perfectly Matched Layers). W symulacji rozważano ośrodek bezstratny. Badania ujawniły, że niewielka liczba defektów punktowych znajdujących się wewnątrz kryształu fononicznego ma mały wpływ na reemisję fali akustycznej, natomiast relatywnie mała liczba defektów umieszczonych na powierzchni kryształu wpływa istotnie na parametry przechodzącej fali akustycznej.

3

The influence of fill factor on the phononic crystal eigenfrequencies

Gruszka K., Nabiałek M., Szota M.

Archives of Materials Science and Engineering

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2014

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Vol. 66, nr 2

74--80

EN

Purpose: The aim of this article is to determine the effect of basic cell fill factor change on the eigenfrequencies observed in two-dimensional phononic crystal. Design/methodology/approach: To perform simulation, the FDFD (finite difference frequency domain) algorithm was used. On this basis, the search for eigenfrequencies was carried out starting from lowest possible acoustic frequency range (~20 Hz) and limited to first nine search results found (up to nearly 2.2 kHz) for increasing fill factor while maintaining the shape of a rod inside cell. Findings: The fill factor has a significant influence on the eigenfrequencies of the studied system when the frequency is above 1 kHz. With the increase of this factor at relatively low frequencies (less than 1 kHz in this case) there were no major changes observed. Research limitations/implications: The results were found only for specific system consisting of materials with similar sound velocity. Therefore, more research should be carried out for other cases i.e. taking into account the different topology of primary cells and various materials with other propagation velocity of acoustic waves in these mediums. Practical implications: Simulation of two-dimensional phononic crystal systems allows for designing new specialized multi-component materials with various acoustic properties. These systems can be adapted in a variety of applications, including acoustic filters, slow-wave devices, acoustic autocollimators and many other. Originality/value: Basic research allow to improve the quality of knowledge on more advanced problems. For this reason, it is important to know in detail how simple systems work and to determine the basic properties of these systems.

4

Design, Manufacture and Characterization of an Acoustic Barrier Made of Multi-Phenomena Cylindrical Scatterers Arranged in a Fractal-Based Geometry

Casteneira-Ibanez S., Rubio C., Romero-Garcia V., Sanchez-Perez J. V., Garcia-Raffi L. M.

Archives of Acoustics

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2012

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Vol. 37, No. 4

455-462

EN

In this work we present the design and the manufacturing processes, as well as the acoustics standard- ization 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 con- trol 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.

5

Phononic Band Gaps in One-dimensional Phononic Crystals with Nanoscale Periodic Corrugations at Interfaces. FDTD and PWM Simulations

Nowak P., Krawczyk M.

Computational Methods in Science and Technology

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2010

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Vol. 16, No. 1

85-95

EN

We present and apply two complementary calculation methods used in phononic crystal studies: the finite difference time domain (FDTD) method and the plain wave method (PWM). The FDTD technique allows to simulate the time dependence of a wave packet of vibrational modes propagating through a composite and to determine the transmission coefficient. The PWM method is used for the determination of the phononic dispersion relation in systems with discrete translational symmetry. We use both methods for investigating the effect of periodic interface perturbations on the spectrum of longitudinal vibrational modes in 1D phononic crystals composed of semiconducting materials. The material parameters in the composites under consideration are modulated in the nanoscale.