Wave Motions in an Effective Chiral Composite: Dispersion Equations and Elastic Moduli

概要

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In this study, we investigate elastic wave propagation in an effective chiral (isotropic, noncentrosymmetric) composite. This composite is constructed by embedding the structural chiral microstructures or springs in a host medium. To ensure that the chiral effect can be found in the samples, a hypothesis about the material constants to characterize the effective chiral composites is proposed herein. Such a material is mirror asymmetric or chiral; therefore, six independent wave numbers can be found. Two of the wave numbers represent nondispersive longitudinal fields, the remaining four are dispersive circularity polarized transverse fields. According to the dispersion equations, two transition frequencies (90 Hz and 12 kHz) divide the frequency response of the transverse wave numbers into three different groups and the four transverse modes can only be distinguished in a specified frequency range. The above observation may account for why the microstructural size of the chiral composite should be sufficiently larger than the transverse wavelength so that an incident elastic shear wave can sense its chirality while the microstructural size should be adequately small that the composite is effectively chiral.
社団法人応用物理学会の論文
1997-10-15