Mechanically tunable terahertz multi-band bandstop filter based on near field coupling of metamaterials

We experimentally present a mechanically tunable multiband terahertz (THz) bandstop filter based on near field coupling of metamaterials. The unit cell of the device consists of an outside aluminum hexagon ring and an inner aluminum circle on high resistance silicon substrate. Two rings are asymmetrically split at the same position deviating from the center of the unit cell. Initially, the device has four resonance absorption peaks at 0.46 THz, 0.57 THz, 0.66 THz and 0.90 THz, respectively. When the azimuth increases from 0° to 90°, the transmission amplitude at these four absorption peaks can be simultaneously modulated. While, the absorption peak at 0.90 THz shows evident blue shift. The effects of geometric parameters on the tunability of bandstop filter are investigated using the finite-difference time-domain (FDTD) method. The sample is fabricated using a surface micromachining process and characterized using a THz time domain spectroscopy (TDS) system. The experiment is in good agreement with the simulation, and the measured amplitude modulation depth exceeds 12 dB at every resonance frequency. The proposed tunable THz filter can be applied in many fields, such as THz communications, sensing and multi-frequency switching. (paper)