Chiral composites as underwater acoustic attenuators

A plane-wave propagation in an elastic matrix containing the structural chiral microstructures is employed to model the dynamic response of a particles-mixture composite. Two nondispersive longitudinal wavenumbers and four dispersive circularly polarized transverse wavenumbers result from the dispersion equation of the so-called effective chiral (isotropic, noncentrosymmetric) composite. Our previous research indicated both that two transition frequencies divide the frequency spectrum of the transverse wavenumbers into three varying groups and that the four transverse modes can be distinguished only in a specified frequency range. This study illustrates the reflected and transmitted characteristics at a fluid-chiral interface at certain frequencies. The reflected and transmitted fields at the fluid-isotropic interface are solved to depict the effects of the chirality. The chiral material should instigate a reducible reflected plane wave and may be used as an anechoic coating to "absorb" sound underwater, due to the mode conversion of the chirality in the chiral medium.