New mechanism of tunable broadband in local resonance structures

Conventional local resonance (LR) structures can effectively obtain broadband, but it is still challenging in engineering for designing a small-scale and lightweight acoustic metamaterials with broadband by breaking the dependence of broadband on mass or structure size. In this work, a new LR plate with a tunable stiffness ratio, has two negative stiffness regions, is analyzed as a tunable elastic metamaterial, in which some interesting results obtained show that the two negative stiffness regions not only are greatly enlarged but also the distance between them can be better adjusted only by adjusting the stiffness ratio within the LR plate. Because the negative stiffness can effectively restrain the propagation of elastic waves, two band-gaps within the LR plate are obtained by finite element method (FEM). Most importantly, the two broadband are not only wider and wider, but also the distance between them is better adjusted only by adjusting the stiffness ratio other than increasing quality or structures size in traditional methods, and finally a ultra-wide band is obtained by the new method, which is effectively enlarged even more 2 times than that of conventional LR plates. Meanwhile, it also means that the lightweight and small-scale acoustical metamaterials with adjustable stiffness can completely to obtain broadband by eliminating the dependence of broadband on structure size and greatly reducing the production cost. Therefore, this new method of realizing broadband could provide an important theoretical basis for the development of small-scale acoustical metamaterials and eliminating the dependence of broadband on structure size, could have potential applications for vibration and noise attenuation.