1. Principles and fundamentals

1.1 Definition

In Greek, the prefix "meta" means "beyond". Metamaterials therefore refer to a class of materials whose properties go beyond those of common materials. More precisely, they are composite media whose internal structure, designed and realized by human beings, interacts with an incident wave (electromagnetic, acoustic, seismic) in such a way as to create macroscopic properties known as "effective" that are unusual, or even unobserved, in natural materials. First of all, we need to go back to phononic crystals, artificial structures formed by a periodic distribution of at least two materials. These structures can exhibit frequency bands in which the propagation of acoustic or elastic waves is evanescent.