Alternatively: a metamaterial is a compound material, and is usually designed to provide specific properties needed in cases when a suitable natural material is unavailable. Acoustic metamaterials are those designed to provide acoustic properties; is is useful to compare these with electromagnetic metamaterials which provide electromagnetic properties.

One common way of constructing metamaterials is to embed an array of one type of material inside another: e.g. perhaps an array of hard spheres (or voids) inside an elastic background material.

The properties designed for are dynamic ones (i.e. regarding a controlled response to vibration), and are typically specified in terms of the dispersive response of the material; although creating bandgaps or frequency dependent absorption are also important.

Further, by designing a s structure with specific and different metamaterial properties at different points, you can use those properties to control wave propagation within the whole structure, creating devices such as waveguides, illusion generators, or cloaks.