Abstract
In this paper, a new type of terahertz (THz) metamaterial (MM) modulator has been presented with bifunctional properties based on vanadium dioxide (VO2). The design consists of a VO2 resonator, polyimide substrate, frequency selective surface (FSS) layer, and VO2 film. Based on the metal-insulator transition (MIT) of VO2, this structure integrated with VO2 material can achieve the dynamic modulation on both transmission and reflection waves at 2.5 THz by varying the electrical conductivity value of VO2. Meanwhile, it also exhibits adjustable absorption performance across the whole band from 0.5–7 THz. At the lower conductivity (σ = 25 S/m), this structure can act as a bandpass FSS, and, at the high conductivity (σ = 2 × 105 S/m), it behaves like a wideband absorber covering 2.52–6.06 THz with absorption A > 0.9, which realizes asymmetric transmission. The surface electric field distributions are illustrated to provide some insight into the physical mechanism of dynamic modulation. From the simulated results, it can be observed that this design has the capability of controlling tunable manipulation on both transmission/reflection responses at a wide frequency band. This proposed design may pave a novel pathway towards thermal imaging, terahertz detection, active modulators, etc.
Highlights
Waves [1,2,3,4,5], which enables them to be extensively studied; plentiful applications have been proposed in different regions including the polarization converter [6,7,8], the antenna [9,10,11,12,13], absorber [14,15,16], etc., which has greatly promoted the development of functional devices
To control and manipulate the transmission/reflection response [17,18,19], a variety of active structures based on metamaterials, such as the tunable frequency selective surface (FSS) [20,21], switchable absorber [22,23,24], and coding metasurface [25,26], have been designed to implement the dynamic modulation performance
In the case of insulating state, this structure can be used as a bandpass FSS, while when σVO2 = 2 × 105 S/m, it acts as a wideband absorber over the frequency band of 2.52–6.06 THz, covering 82.5% fractional bandwidth with absorptivity of more than 0.9
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. There is a dramatic variation in the electrical and optical performance during the phase transition (4–5 order of magnitude change on the electrical conductivity σVO2 ), so VO2 is a promising candidate in tunable MM devices at THz frequencies to achieve excellent modulation characteristics. When σVO2 gradually changes from 25 to 2 × 105 S/m with the external temperature increasing, the transmittance would slowly decrease from 0.89 to approximately 0 around 2.5 THz, and absorption behavior performs dynamic modulation across 0.5–7 THz. In the case of insulating state (σVO2 = 25 S/m), this structure can be used as a bandpass FSS, while when σVO2 = 2 × 105 S/m, it acts as a wideband absorber over the frequency band of 2.52–6.06 THz, covering 82.5% fractional bandwidth with absorptivity of more than 0.9.
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