Abstract
Switchable metamaterial absorbers/reflectors (MAs/MRs) are important bifunctional electromagnetic devices and have been the subject of numerous scientific studies. However, there is a lack of bifunctional devices that operate in the terahertz band. Here, we theoretically propose a broadband switchable MA with many excellent properties, such as good thermal stability, high insensitivity to inferior film quality of the graphene, excitation polarization and wide incident angles, and outstanding structural parameter tolerance. The bandwidth of the proposed broadband MA is 3.4 THz with an absorptivity over 90% in the frequency band of 1.6-5 THz. The proposed absorber can switch to a reflector with a reflectivity over 93% by tuning the chemical potential of the graphene and reducing the temperature. Therefore, the switching intensity of the proposed MA exceeds 83%. The physical mechanisms of the broadband absorption of the proposed structure are investigated using the impedance matching theory and the multiple reflection interference theory. The reflection mechanism of the proposed broadband reflector is discussed by analyzing the effective parameters. The absorption and switching mechanism are theoretically investigated by performing detailed numerical calculations to analyze the surface loss intensity, electric field, and magnetic field. These findings can accelerate the development of terahertz broadband switchable devices.
Highlights
N ARROWBAND and broadband metamaterial absorbers (MAs) have been widely investigated due to their unique application requirements, such as carrier-wave modulation [1], imaging [2], sensing [3], and so forth
The unit cell of the designed metamaterial structure is shown in Fig. 1, which consists of three layers
The incident plane wave propagates along two paths, i.e., one part is reflected into the air with the reflection coefficient R12 = r12eiφ12 and the other part is transmitted into the spacer with the transmission coefficient T12 = t12eiθ12
Summary
N ARROWBAND and broadband metamaterial absorbers (MAs) have been widely investigated due to their unique application requirements, such as carrier-wave modulation [1], imaging [2], sensing [3], and so forth. Various methods have been adopted to achieve broadband absorption, including stacking multi-layer resonators of different sizes [7],[8], embedding graphene sheets in a conventional MA structure [9],[10], combining multiple resonators of different sizes into one unit [11],[12], and using discrete patterns of graphene sheets [13]-[16] The latter method is preferred due to the ultrathin structure and convenient tunability. Various electro-optical materials have been appealed extensively in THz switchable devices as switching components, such as liquid crystals [19], semiconductors [20],[21], and graphene [1],[22],[23]-[25]. The proposed broadband MA exhibits several advantages, including high thermal stability, excellent performance inertia to film quality of graphene, structural parameter insensitivity, polarization independence, and constant results at large incident angles
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