Document Type : Research Article
Mechanical Engineering Department, Iran University of Science and Technology, Tehran, Iran
Associate Professor, School of Mechanical Engineering, Iran University of Science & Technology, Tehran, IRAN.
Metamaterials are manmade materials used due to their different properties originating from their geometry. Sound attenuation is a property, which depends on structure geometry; the small structures could reduce sound propagation within a mid-high frequency. To change the range of sound propagated in metamaterial from high-frequency to low-frequency, however, internal resonators could be used due to their rotational vibration having highly effect on sound attenuation. In this paper, an acoustical analysis is done on a hexachiral lattice structure with an internal resonator showing the ability to decrease sound wave propagation among the structure in the low-frequency range and causes corresponding bandgaps in this frequency range (1-4500 Hz). Geometry parameters that can affect the width and range of bandgaps are studied including the radius of the resonator, the thickness of the ligament, and the distance between each node. However, the radius of the resonator has a positive impact on the ability of attenuation, but the distance between each node has a more negative impact on the bandgap. Optimization is done on the geometric parameters considering the weight of the structure, which leads us to the construction of light structures capable of reducing sound propagation.