We experimentally demonstrate a switchable metamaterial absorber for infrared spectral region using MEMS technology. In order to achieve active tunability; air gap is introduced as the part of dielectric spacer layer and is electrostatically actuated. As the air gap is decreased, the peak absorption wavelength will blue shift accordingly. The tuning range is approximately 700 nm for 300 nm air gap change. Complementary cross is used as the metamaterial unit cell pattern. Owing to the π/2 rotational symmetry of the metamaterial unit cell geometry and out of plane actuation direction of the metamaterial layer, the resultant absorption retains the polarization insensitive characteristics at different actuation states. Additionally high temperature stable materials such as, molybdenum and silicon-di-oxide are used as structural materials for potential use in rugged applications.
The tunable terahertz metamaterial (TTM) has attracted intense research interest, since the electromagnetic response of the metamaterial can be actively controlled through external stimulus, which is of great significance in real time applications. The active control of metamaterial characteristics is crucial in order to provide a flexible and versatile platform for mimicking fundamental physical effects. To realize the electromagnetic tunability, various approaches have been demonstrated to increase the flexibility in applications, such as changing the effective electromagnetic properties. Alternatively, MEMS-based techniques are well developed. The structural reconfiguration is a straightforward way to control the electromagnetic properties. The metamaterial properties can be directly modified by reconfiguring the unit cell which is the fundamental building block of metamaterials. Currently, our research works are focusing on MEMS-based TTM adopting stress-induced curved actuators (SICA) to adjust the resonant frequency of devices. Herein, the proposed TTM designs are double split-ring resonator (DSRR), electric split-ring resonator (eSRR), Omega-ring metamaterial (ORM), symmetric and asymmetric T-shape metamaterial (STM and ATM), respectively. We demonstrated these TTM can be active, continuous, and recoverable control the resonant frequency by using electrostatic or electrothermal actuation mechanism. Therefore, the TTM devices can be effectively used for sensors, optical switches, and filters applications.
We present the design and the characterization of a polycrystalline silicon (Si)-based photonic crystal (PhC)-suspended membrane, working in the mid-infrared wavelengths. In order to facilitate transmission measurement, the PhC membrane is released by removing the underneath Si substrate. Around 97% reflection and 3% transmission at 3.58-μm wavelength are measured at room temperature. Characterization is also done at 450°C and it reveals that the peak reflection of the PhC membrane shifts by 75 nm to higher wavelengths. This corresponds to a linear wavelength shift of 0.174 nm/°C and the thermo-optic coefficient is calculated to be +1.70×10−4 K−1. By altering the dimension of the PhC air holes, it is also shown that such a thermo-optic effect is compensated.