新型態外部隔減震技術 - 地震超材料之設計與分析

Seismic metamaterials are known as a new class of artificially structured media in which, within a certain designed frequency range, seismic waves can be attenuated or controlled in ways not seen in nature. The concept of metamaterials was originated from electromagnetic and acoustic waves about 10 years ago. This artificially engineered material utilizes coupling interference effect between propagating waves and local resonances to prevent the propagation of waves at frequencies near resonances. Seismic metamaterial, corresponding to long-wavelength and low frequency range, is a new research domain with some distinct features compared to those of other physical phenomena. In this work, we propose a simple two-dimensional configuration of seismic metamaterial, made of three different materials, aiming to mitigate the destructive effects of earthquakes. The simple model consists of concentric square cylinders, constituted by steel, rubber and soil, targeting at wave mitigation in the infrasound regime (1-10 Hz). Numerical simulations based on simplified discrete model as well as full-scale continuum layout will be studied. Our finite element simulations show that within the attenuation zone the displacement amplitude can be reduced significantly. These numerical studies demonstrate that the simple design of seismic metamaterial can be served as a promising tool towards seismic cloaking where a full threedimensional simulation of body as well as surface waves, together with the geological information, can be properly accommodated.