多類型複合地震超結構之寬頻帶設計與分析

Metamaterial is a new type of composites made of artificially structured constituents, in which it exploits local resonances to attenuate or to block propagating waves well above the characteristic size of the material structure. The concept of metamaterials was first originated in the context of optics, and applied later to thermal conduction, to acoustic waves, and more recently to seismic wave. The underlying concept relies on the design of material structure, with suitable material constituents and geometric configuration, so that the coupling interference at frequencies near local resonances will result in attenuation of the propagating waves in ways not behaved normally. Seismic metamaterial, corresponding to long-wavelength and low frequency range, is challenging in that the band width needs to be sufficiently broad. In this work, following the concept of Krodel et al. [51], we propose to use a hexagonal array of composite cylinders, made of a stiff steel core surrounded with soft rubber. To obtain broadband attenuation characteristics, the volume fraction of each composite cylinder is suitably devised so that each individual layer of composite cylinders will correspond to a different bandgap. The array, constituted by multiple layers of metamaterial, will effectively behave as a medium with wave mitigation in the infrasound regime (2-9.6 Hz). Numerical simulations based on discrete model as well as full-scale continuum model will be studied. Our finite element simulations show that within the bandgap the wave energy can be attenuated substantially. Lastly we propose a few issues that could be further explored in the future. This will add to the feasibility of practical field test in the future.