Point defect states in 2D acoustic band gap materials consisting of solid cylinders in viscous liquid

We investigated point defect states in two-dimensional acoustic band gap materials consisting of steel cylinders in liquid with viscous damping. Numerical results show that when the viscous penetration depth is comparable to the structural length scale, point defect states fall in large complete acoustic band gaps. It is also found that the magnitude of the viscosity in the liquid has an influence on the gap and defect state properties at the same time and that large viscous damping can enlarge the band gap but assemble the defect states. An expected gap frequency and a defect state frequency can be obtained by choosing a proper viscous damping parameter θ