A thin-walled cavity structure with double-layer tapered scatterer locally resonant metamaterial plates for extreme low-frequency attenuation

• Published in: International journal of solids and structures Vol. 293; p. 112742
• Main Authors: Ravanbod, Mohammad, Ebrahimi-Nejad, Salman, Mollajafari, Morteza
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.05.2024
• Subjects: Absorptive-reflective metamaterial; Acoustic metamaterials; Cavity structure; Local resonance; Tunable stopbands; Cavity structure; Local resonance; Tunable stopbands; Absorptive-reflective metamaterial; Acoustic metamaterials
• ISSN: 0020-7683; 1879-2146
• DOI: 10.1016/j.ijsolstr.2024.112742

•A novel thin-walled structure with dual-function reflection and absorption is designed for wide sound filtration in the low-frequency range.•The proposed structure coupled the local resonant, cavity, and convex mechanisms to open a broad stopband of 64.9805.6Hz.•The tapered scatterer generates a wide stopband, low stopband opening frequency, and outstanding dispersion features.•64.9-805.6Hz286%, 35.42dB0-1KHz). The cavity mechanism boosts the STL levels while maintaining the dispersion characteristics given by the convex structure.•The results indicated a broad stopband with a total SCF of, allowing the structure to block incoming acoustic waves with 35.42dB RMSNA. Locally resonant acoustic metamaterials (LRAMs) are effective spatial frequency filters due to their local resonance system. However, they own narrow stopbands, charge additional weight on the primary system, and operate only at the adjusted frequency range. In this paper, a novel dual-target LRAM is proposed based on coupling the cavity and convex mechanisms, utilizing the benefits of both sound-barrier and sound-absorbing types of acoustic metamaterials. A combination of the cavity and convex structures is presented and investigated for the first time, which exploits both the reflection and absorption theories simultaneously to improve the sound attenuation performance of acoustic metamaterials. By arranging two-layer finite periodic of 5×5 proposed convex unit cells along x and y directions and separating them by an air cavity, a supercell named hybrid locally resonant acoustic metamaterials (HLRAM) baffle is designed. The band structures, transmission spectrum, and displacement vector fields are calculated employing the finite element method (FEM). In addition, vibration modes at the edges of stopbands are computed and carefully analyzed to determine the formation mechanism, mechanics/dynamic response, and dispersion features of stopbands. Meanwhile, sensitivity analyses have been conducted on the model to investigate the influence of material and geometry parameters on dispersion characteristics. Equivalent spring-mass analytic models are used to direct the modifications of structure and the adjustment of structural and material parameters in order to achieve a wide stopband with a low opening frequency. Thereby, the effective stiffness and mass values influencing the starting and cutoff frequencies are adjusted in a desirable manner. The results show that the structure can generate a wide stopband that covers the frequency range of 64.9-805.6Hz, allowing the structure to block incoming acoustic waves with 35.42dB root mean square of noise attenuation (RMSNA) the given frequency range (0-1kHz). This study indicates that the HLRAM has a preponderance among conventional techniques as we can manipulate dispersion characteristics and the sound transmission loss (STL) based on the desired sound reduction level and shift stopbands to the intended frequency range. This can be achieved by altering cavity size, material, or geometry parameters.