A tunable conical helical spring acoustic metamaterial for complex and harsh environments

Abstract Traditional local resonance (LR) structures can control low-frequency elastic waves, but they still face significant challenges in complex and harsh engineering applications. Due to the complexity of boundary conditions and vibration modes in harsh environments, a high degree of flexibility in vibration isolation structures is required. Fortunately, helical acoustic metamaterials offer such advantages. This paper proposes a tunable conical helical spring (TCHS: a combination of multiple unequal pitches and radii) acoustic metamaterial, which can effectively control elastic waves and vibrations in complex and harsh environments. The mechanisms underlying the generation of bending vibration band gaps were analyzed using the finite element method (FEM). This analysis included examining the transmission spectra, eigenmodes, and displacement vector fields of the LR structure. By adjusting geometric parameters such as the pitch and radius of the conical helical spring, low-frequency band gaps between 34–43 Hz and 45–122 Hz were successfully achieved. Most importantly, the vibration characteristics of the phononic crystal plate were studied under various boundary conditions (bilateral fixed, unilateral fixed, and free constraints) as well as loading conditions (point load and edge load). The results demonstrate that the decay positions observed in the transmission spectra under different conditions were highly consistent with the energy band positions. Therefore, the structure offers potential applications in the field of vibration and noise control in complex and harsh environments.