Broadband Metamaterial Absorbers

The recent rise of metamaterials opens new opportunities for absorbers due to their designed electrodynamic properties and effects, allowing the creation of materials with effective values of permittivity and permeability that are not available in naturally occurring materials. Since their first experimental demonstration in 2008, recent literature has offered great advances in metamaterial perfect absorbers (MMPAs) operating at frequencies from radio to optical. Broadband absorbers are indispensable in thermophotovoltaics, photodetection, bolometry, and manipulation of mechanical resonances. Although it is easy to obtain MMPAs with single band or multiband, achieving broadband MMPA (BMMPA) remains a challenge due to the intrinsically narrow bandwidth of surface plasmon polaritons, localized surface plasmon resonances generated on metallic surfaces at nanoscale or high Q-factor in GHz region. To guide future development of BMMPA, recent progress is reviewed here: the methods to create broadband absorption and their potential applications. The four mainstream methods to achieve BMMPAs are introduced, including planar and vertical element arrangements, their welding with lumped elements and the use of plasmonic nanocomposites, accompanied by the description of other, less common approaches. Following this, applications of BMMPA in solar photovoltaics, photodetection, bolometry, and manipulation of mechanical resonances are reviewed. Finally, challenges and prospects are discussed.