A metamaterial is a 3D structure comprised of at least two different materials, with a response or function that impossible to achieve with any individual constituent material.
A metasurface is a 2D version of a metamaterial where the structural elements are confined to a 2D plane.
The response/function of a metamaterial results from the ensemble effects of designed and engineered meta-atom elements. These can take many forms. The response or function may be electromagnetic (photonic, RF & microwave, THz etc), acoustic (audio, ultrasonic, vibrational), magnetic, mechanical/structural, thermal, or chemical.
The ‘Metamaterials’ topic is inherently interdisciplinary, spanning advanced materials (plasmonics, active materials, RF, high index contrast, 2D materials, phase change materials, transparent conductive oxides, soft materials), theoretical physics, quantum physics, chemistry, biology, engineering (mechanical and electrical), acoustics, computer sciences (e.g. artificial intelligence, high performance computing), and robotics.
In terms of applications, metamaterials have phenomenal potential, in important areas, from energy to ICT, defence & security, aerospace, and healthcare. Numerous market research studies predict very significant growth over the next decade, for example, by 2030 the metamaterial device market is expected to reach a value of over $10bn (Lux Research 2019).