2. School of Engineering, South China Agricultural University, Guangzhou, Guangdong 510642, China
Overview: Infrared photodetectors have been widely used in the fields of military and national economy including aeronautics and astronautics, optical communication, industrial control and so on. The high infrared absorption rate is extremely important for the signal response of the photodetectors. However, the sensitive element of the infrared photodetector does not have good infrared absorption characteristics, so it needs a material that can improve the infrared absorption rate. Among them, metamaterials are widely concerned by researchers because of their novel and non-traditional properties. Metamaterials are typically engineered by arranging a set of small scatterers in a regular array throughout a region of space, thus obtaining some desirable bulk electromagnetic behaviors. The desired property is often the one that is not normally found in nature (negative refractive index, near-zero index, and so on). With the deepening of research, researchers began to expand in the application of metamaterials, and proposed different models, such as metasurfaces, metadevices.
For many applications, metasurfaces can be used take place of metamaterials. Compared to three-dimensional metamaterial structures, metasurfaces have the advantage of taking up less physical space. Consequently, metasurfaces offer the possibility of realizing less-lossy structures.
In this review, we describe the research progress of several common absorption metasurfaces in recent years. The first one is the perfect metasurfaces absorber, which has the ability to absorb all incident waves at a single frequency. By optimizing the structural model, the perfect metasurface absorbers achieve impedance matching with free space, and use the dielectric loss and ohmic loss of the structural unit to achieve strong absorption of electromagnetic waves. However, as the result of relying on resonance absorption, the absorption spectrum of perfect metasurface absorbers is very narrow. Then, the metasurfaces of broadband absorption in the infrared, terahertz and visible light bands are reviewed in detail. And the most common way to achieve broadband absorption of metasurfaces is to use a vertically cascaded structure. In addition, metasurfaces can also achieve broadband absorption by combining graphene or catenary optics. Finally, tunability of the PCM metasurface absorber has also been investigated.