Tuning bandgaps in metastructured beams: numerical and experimental study

Abstract

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.

概要

目的:1. 研究晶格常数、预应力和弹簧刚度对超结构梁 带隙的影响,优化结构并形成伪禁带或低频且宽 的禁带;2. 通过实验验证伪禁带的存在性、排列 对带隙的影响以及缺陷对带隙的影响等。

创新点:1. 通过预应力调节超结构梁的带隙特征,并可以 形成伪禁带;2. 通过排列不同弹簧振子构成宽频 禁带和宽频伪禁带。

方法:1. 通过有限元软件模拟预应力、弹簧刚度和晶格 常数等参数对该超结构梁带隙的影响情况;2. 设 计合适的参数并进行结构优化,使得该结构的带 隙宽,频率低,且易于实验实现;3. 在实验中通 过替换弹簧、改变弹簧间距和施加轴向拉力分别 研究弹簧刚度、晶格常数和预应力的影响,并通 过移除部分弹簧和同时布置不同弹簧的方式研 究缺陷和排列对带隙的影响。

结论:1. 该结构存在一条局域共振禁带和多条布拉格散 射禁带;通过调节预应力、弹簧刚度和晶格常数 等可以有效地控制带隙特征。2. 在特定条件下可 以形成宽频伪禁带;通过排列不同弹簧振子可以 达到拓宽禁带、形成宽频伪禁带的效果。3. 缺陷 对布拉格散射禁带的影响较大,对局域共振禁带 的影响较小。