Tuning bandgaps in metastructured beams: numerical and experimental study

Tunable metastructures (including phononic crystals and metamaterials) have the unique advantage that one can change the operating frequency and acoustic wave characteristics as needed. In this paper, the bandgap characteristics and their controllability of a metastructured beam with mass-spring oscillators and under an axial force are investigated in depth both by the finite element method and by experiment. The experimental and numerical results indicate that there is one local resonance (LR) bandgap and multiple Bragg scattering (BS) bandgaps. The width and position of each bandgap can be tuned effectively by adjusting the axial force, lattice constant, and spring stiffness, and a super wide pseudo-gap can be obtained under suitable conditions. By integrating different mass-spring oscillators into one metastructured beam, the bandgap width can be broadened and pseudogap- like characteristics can be achieved. By changing the number of different oscillators, the propagating distance of elastic waves in the beam can also be controlled. It is further revealed that point defects have a large influence on the BS bandgaps but little effect on the LR bandgap. The present work provides an important reference for the optimal design of adjustable high-performance metastructures.