26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

MEMS-Reconfigurable Bilayer Metasurface Bandpass Filter for Tunable Terahertz Transmission

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Poster COMMAD - Optoelectronic and Microelectronic Materials and Devices Afternoon Tea and Poster Session 2

Description

Actively reconfigurable terahertz (THz) spectral components are required for adaptive spectroscopy, imaging, and wireless systems. However, achieving transmission filtering with substantial tunability in a compact planar architecture remains challenging. This work presents a microelectromechanical system (MEMS) reconfigurable bilayer THz metasurface bandpass filter based on the controlled displacement of a suspended gold membrane relative to a fixed metasurface. The upper membrane is patterned with cross apertures, while the lower metasurface comprises encapsulated gold square patches in alignment with the overlying cross apertures. The two patterned layers are separated by a micrometre-scale air gap and suspended over a backside-etched silicon transmission window. Their complementary high-pass-like and low-pass-like responses form a coupled, gap-dependent transmission passband.
AC voltage actuation generates electrostatic attraction between the layers, reducing the intermembrane separation and modifying the hybridised near-field coupling of the bilayer resonators. Laser scanning confocal microscopy was used to quantify membrane displacement, and THz time-domain spectroscopy was used to measure the corresponding signal-transmission spectra. Confocal metrology showed that the air gap decreased from approximately 1.6 μm at 0.5 VRMS to 0.6 μm at 8 VRMS. This mechanical reconfiguration continuously red-shifted the transmission resonance from approximately 3.1 to 2.5 THz, giving a tuning range of 0.6 THz. Simultaneously, the full width at half maximum decreased from 0.8 to 0.6 THz.
Full-wave electromagnetic simulations were evaluated at the experimentally determined intermembrane air-gap values. The measured resonance positions and gap-dependent red-shift trend closely followed the simulated response, supporting a coupling-mediated tuning mechanism. The demonstrated MEMS-integrated device provides a compact route to dynamically reconfigurable THz bandpass filters for spectral selection, sensing, and imaging applications.