Thermal controlled multi-functional metasurface for freely switching of absorption, reflection, and transmission.

Metasurfaces have garnered significant attention in recent years due to their substantial electromagnetic (EM) wave manipulation capabilities. However, most previously documented metasurfaces have been limited to controlling just a single EM wave mode, encompassing transmission, reflection, or absorption. Such limitations have impeded the broader applications of metasurfaces. To address this issue, this study introduces a multi-functional metasurface (MFM) in the utilization of Ge2Sb2Te5 (GST), vanadium dioxide (VO2), and graphene. This novel design enables real-time control over the transmission, absorption, and reflection of EM waves as necessitated through thermal control, allowing for seamless transitions from complete transmission to complete reflection. Furthermore, this configuration achieves extensive broadband perfect absorption, spanning up to 1.83 THz. The optical response mechanism of this MFM across distinct operational modes is meticulously analyzed through electric field distribution. Remarkably, this proposed MFM exhibits polarization insensitivity and maintains good optical performance even under conditions of wide-angle incidence. With the ability to switch to different operating modes according to the needs of different environments, the proposed MFM has the potential to be used in a wide range of scenarios, including radar stealth, wireless communications, and military search.

An electrical/thermal dual-controlled quad-functional terahertz metasurface absorber.

Although the design of graphene-based tunable broadband terahertz (THz) absorbers has attracted much attention, improving the functionality of the absorbers to adapt to different scenarios is still worth studying. This paper presents an innovative design of a quad-functional metasurface absorber (QMA) in the THz region, which can switch the absorption frequency/band by means of dual voltage/thermal manipulation. By electrically manipulating the chemical potential of graphene, the QMA can switch freely between the narrowband absorption mode ("NAM") and the broadband absorption mode ("BAM"), while thermally manipulating the phase transition of VO2 allows switching between the low-frequency absorption mode ("LAM") and the high-frequency absorption mode ("HAM"). Detailed mechanistic analysis shows that the "NAM" and "BAM" are due to the switching of the fundamental and second order graphene surface plasmon polariton (SPP) resonances, respectively, and the switching between "LAM" and "HAM" is due to the phase transformation of VO2. Furthermore, the QMA is polarization insensitive in all absorption modes and maintains excellent absorption performance at large angular incidence of TE- and TM-polarized waves. All the results indicate that the proposed QMA has great potential for stealth, sensing, switching, and filtering applications.

Metasurface inverse designed by deep learning for quasi-entire terahertz wave absorption.

Ultra-broadband and efficient terahertz (THz) absorption is of paramount importance for the development of high-performance detectors. These detectors find applications in next-generation wireless communications, military radar systems, security detection, medical imaging, and various other domains. In this study, we present an ultra-wideband THz wave metasurface absorber (UTWMA) featuring a composite surface microstructure and a multilayer absorbing material (graphene). This UTWMA demonstrates remarkable capabilities by achieving highly efficient absorption levels, reaching 96.33%, within the 0.5-10 THz frequency range. To enhance the efficiency and precision of the design process, we have incorporated artificial neural networks, which enable rapid and accurate parameter selection. Moreover, we have conducted a comprehensive analysis of the absorption mechanism exhibited by the UTWMA at different frequencies. This analysis combines insights from the electric field distribution and effective medium theory. The findings presented in this paper are expected to catalyze further research in the domain of broadband THz technology, particularly in the context of metasurfaces and related fields. Additionally, this work paves the way for the development of compact, supercontinuous THz photovoltaic or photothermal electrical devices.