Coding metasurface has attracted much attention due to its flexible design of coding sequences and powerful control ability of light beams. However, the traditional coding metasurfaces with pin-diode switches between two metallic patches are usually used in the microwave band. Few studies have been carried out in the terahertz (THz) region with tunable metastructures. In order to realize the dynamic modulation of terahertz metasurface, in this paper we use the phase change material vanadium dioxide (VO2) to activate modulation coding metasurface in the terahertz band. We designed a VO2 embedded hybrid structure with metallic patches as the metasurface unit, which can produce a 180- degree phase change near 0.69 THz during the phase transition of VO2 from an insulating state to the metallic state. Meanwhile, we have constructed a metasurface array with the above designed tunable VO2 components and non-tunable metallic units to realize the dynamic switching of the far-field beam at that frequency. Our simulated results indicate that when the VO2 conductivity increases from 200 to 200000 S/m, the far-field reflected beams of the metasurface array can change from the separation of about 41° apart to close together. Notably, this coding metasurface will remain the reflectivity higher than 0.76 at the working frequency and exhibit polarization insensitive feature to the incident light. The active coding metasurface we designed provides a new idea for flexible beam control and has broad application prospects in terahertz functional devices.
We demonstrate the active control of resonant frequency in terahertz (THz) metamaterial comprised of split ring resonator arrays (SRRs). It is found that the introduction of different substrates can greatly modify the sensing capabilities of the SRRs structure, i.e., the SRRs designed on PET (polyethylene terephthalate) is more sensitive to THz wave accompanied with higher resonance frequency as well as wider non-resonant region. Furthermore, our simulated findings indicate that THz response sensitivity can be distinctly tuned by changing the gap of SRRs on PET. The mechanism of inductance-capacitance (LC) resonance and dipole resonance is exploited to explain the varied THz transmission responses. Our work infers that the SRRs structure based on PET with low dielectric constant is a significantly better option for biological and chemical sensing applications.
The study of terahertz band has been widely concerned, and the combination of metamaterials and various reconstruction mechanisms has made great progress in recent years. In this paper, we simulate the effect of splitting the gallium arsenide(GaAs) layer with different conductivity in the twisted split-ring resonator(SRR) pairs structure on the inductive coupling strength. We find that with the increase of the conductivity of the doped GaAs layer, the transmittance of the nonresonant region decreases, the resonance intensity decreases, and the frequency shows a blue-shift. When the conductivity increases to more than 64 S/m, the two resonant dips merge into one, and the inductive coupling gradually weakens until disappears. At the same time, we simulate the current and electric field diagram to confirm our results. Our findings are helpful to adjust the resonant intensity of metamaterials by optical pumping or DC bias in the following experiments, which improves the basic understanding of metamaterials and reconfiguration mechanisms.
Nowadays, the combination of metamaterials and molybdenum disulfide (MoS2) plays more and more important roles, due to its broad applications in many areas. Here, we propose a novel hybrid structure for terahertz (THz) wave manipulation with the integration of MoS2 layer and metamaterials consisting of split ring resonators (SRRs) arrays on Si substrate. Compared with the simulation results of single ring resonator and double ring resonators, it is found that the original dual-mode resonance transforms four mode resonance after inserting the inner ring. When the inner ring is rotated, the multi-mode resonance does not change. The resonance intensity decreases and the frequency moves to the low frequency with the red-shift effect, when MoS2 is added. The hybrid MoS2-SRRs structure THz modulator has multi-mode resonance, and the interaction between SRRs and MoS2 is revealed through the analysis of multi-mode resonance.
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