Citation: | Yuzhu Tang, Wenying Ma, Yaohua Wei, et al. A tunable terahertz metamaterial and its sensing performance[J]. Opto-Electronic Engineering, 2017, 44(4): 453-457. doi: 10.3969/j.issn.1003-501X.2017.04.010 |
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Abstract: A novel electromagnetically induced transparency (EIT)-like metamaterial in terahertz domain is proposed. The metamaterial is composed by a single metal wire and a couple metal wires above it. A plane wave propagates along the perpendicular direction to the structure with its electronic field direction paralleled to the double metal wires. The structure’s transmission spectra are simulated by CST Microwave Studio. In the simulation, the solver is chosen to be frequency domain solver while the boundary conditions are set as unit cell in x-y plane, and open (add space) in z-direction. The metal strips are set to be copper with its conductivity of 5.88×109 S/m and its thickness Δh=0.3 μm. The substrate material is quartz with its permittivity of 3.75 and thickness h=50 μm.
Numerical simulations demonstrate that by rotating the single metal wire around its center, EIT phenomenon is created. The single metal wire is regarded as quasi-bright mode element while the couple metal wires are considered as one bright mode element. The EIT phenomenon is produced by the interference between these two elements. The amplitude of the transparent peak grows as the rotation angle increases. When the rotation angle is 60°, the EIT window appears at 0.844 THz while the amplitude of the transparent peak exceeds 0.5 and reaches its maximum. It is remarkable that the width of the transparent window is only 1.57 GHz and the Q-factor is as high as 538, which makes the structure suitable for ultranarrow terahertz frequency selection. As the rotation angle keeps increasing, the amplitude of the transparent peak gets smaller and finally vanishes as the rotation angle equals 90°. Hence, we can tune the transparent window by rotating the single metal wire. The influence of the substrate’s dielectric loss is also simulated. The result indicates that the transparent peak is sensitive to the dielectric loss, and the amplitude of the transparent peak becomes quite small when the dielectric loss is 0.01. At last, we have analyzed the sensing performance of the metamaterial with the rotation angle of 60°. The structure’s refractive sensitivity is 228.9 GHz/RIU while its FOM value is 145.8. Therefore, the metamaterial can be used for refractive sensing. In conclusion, the proposed structure is simple and adjustable, with high Q-factor value and good sensing performance.
Schematic of the unit cell.
Simulated transmittance spectra with different values of rotation angle θ.
Influence of dielectric loss of the substrate.
Surface current distribution and the transmittance spectrum of structure 1.
Transmittance spectrum of the structure 2.
Current distributions on the structure 2 at (a) 0.831 THz, (b) 0.8444 THz and (c) 0.8464 THz.
Influence of refractive index on transmittance spectra of structures 1 and 2.
Transmission frequency shift under different refractive indices of the surrounding material.
Influence of refractive index on transmittance spectra of structure 3.