The Development of Nonlinear Metasurface Absorbers: From Passive to Active

The rapid development of metasurface accelerates the planarization of microwave absorbers, and their tunabilities are further enhanced by the lumped circuit integrations. With the help of nonlinear components, such as diodes, varactors, transistors, and detectors, the absorbers were endowed with potentials to sense incoming waves and exhibit power-or waveform-dependent performances, which are defined as nonlinear absorption. Several typical nonlinear absorbers are reviewed in this paper, and their working mechanisms are briefly presented. It can be found that the circuits were developed from passive to active, along which more flexibilities of tuning were achieved. These works may pave a way for intelligent metasurface designs in the future.