Abstract
The emergence of acoustic metamaterials generated a lot of attention in the study of low-frequency vibration, noise control and reduction in engineering applications. As a result, the elastic wave bandgap characteristics of a two-dimensional microcavity local resonator structure for two soft rubber materials was investigated using finite element methods (FEM). The transmission spectrum of the displacement eigenmodes of the bandgap edges relating to the lowest bandgap was calculated. The results showed that the phononic crystal structure without a microcavity local resonator plate has bandgap characteristics of elastic wave propagation in the high-frequency range between 2200~2400Hz. However, with the introduction of microcavity resonator plates in the phononic crystal structure low-frequency bandgaps are obtained in the region of 0~198Hz and 0~200Hz respectively. The low-frequency bandgaps appeared as a result of the microcavity local resonator plate which increased the path length through which the wave is transmitted. The phononic crystal microcavity local resonator plate structure has varying transmission loss characteristics of -65dB, -85dB, -100dB and -150dB in the low-frequency range depending on the number of local resonator plates introduced into the cell structure and density of the cell structure. The study provided a good demonstration of wave propagation in artificially engineered materials with critical emphasis on the effects of local resonators in a microcavity structure.
Highlights
In recent years, huge attention has been focused on the study of artificially engineered materials known as phononic crystal acoustic metamaterials
The bandgap structure is expressed as the dispersion of the elastic waves in the infinite periodic phononic crystal, which can be clearly defined by the band structure analysis
The formation of bandgap characteristics of the unit cell structure occurs as a result of elastic wave propagation effects in the periodic structure under Blotch Floquet periodicity boundary conditions
Summary
Huge attention has been focused on the study of artificially engineered materials known as phononic crystal acoustic metamaterials. Phononic Crystal structures composed of two or more materials with different mechanical properties such as density and modulus of elasticity which leads to bandgaps (BGs) generation during the transmission of elastic or acoustic waves [3, 4]. Phononic crystal materials have rich physical properties and an enormous potential application in the design of acoustic devices for the control and reduction of the effects on lowfrequency vibration and noise [5, 6]. To control and reduce the effects of vibration and noise in engineering structures and components, it is of great importance to obtain bandgaps with large bandwidth in low-frequency ranges [7, 8]. Researchers have developed structures which yield large bandgaps with good wave propagation characteristics in the low-frequency range. Jia., et al, [12] carried out a study on a phononic crystal structure which composed of a
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