Elastic metamaterial

Summary

An elastic metamaterial is an engineered composite whose small built-in structures make it respond to waves in ways that its ingredient materials do not. In certain frequency bands its effective mass density or its effective elastic modulus can be negative, so that waves cannot travel through it. The usual cause is a local resonance of the inner structures, at wavelengths much longer than the structures. Such materials are used to block vibration and to steer elastic and acoustic waves.