Introduction

Metasurfaces are subwavelenghtly thick electromagnetic structures that may be used to control the scattering of electromagnetic waves. This chapter presents a general description of metasurfaces and metamaterials and the types of electromagnetic transformations that they can realize. It provides a historical perspective on the origin and concept of metamaterials, and discusses the emergence of metasurfaces along with their applications and synthesis strategies. Although the interest in metamaterials was at its peak in the first decade of the twenty‐first century, it is their two‐dimensional counterparts – the metasurfaces – that progressively became the dominant source of attention. Metasurfaces have also been commonly used to control the amplitude of the incident wave and, for instance, been used as perfect absorbers by altering the amplitude of the fields so that no reflection or transmission can occur.