Tunable multiband terahertz metamaterials using a reconfigurable electric split-ring resonator array

Abstract

We demonstrate micromachined reconfigurable metamaterials working at multiple frequencies simultaneously in the terahertz range. The proposed metamaterial structures can be structurally reconfigured by employing flexible microelectromechanical system-based cantilevers in the resonators, which are designed to deform out of plane under an external stimulus. The proposed metamaterial structures provide not only multiband resonance frequency operation but also polarization-dependent tunability. Three kinds of metamaterials are investigated as electric split-ring resonator (eSRR) arrays with different positions of the split. By moving the position of the split away from the resonator's center, the eSRR exhibits anisotropy, with the dipole resonance splitting into two resonances. The dipole-dipole coupling strength can be continuously adjusted, which enables the electromagnetic response to be tailored by adjusting the direct current (DC) voltage between the released cantilevers and the silicon substrate. The observed tunability of the eSRRs is found to be dependent on the polarization of the incident terahertz wave. This polarization-dependent tunability is demonstrated by both experimental measurements and electromagnetic simulations. Keywords: MEMS; reconfigurable metamaterials; split-ring resonator; terahertz; tunability INTRODUCTION Electromagnetic waves in the terahertz (THz) frequency range have received tremendous attention due to their various advantages. Much research has been carried out to characterize the interactions of these waves with matter, for which potential applications include medical imaging, security screening and non-destructive evaluation. However, there are still several restrictions that limit the full exploitation of fruitful applications covering the THz region due to the lack of an appropriate response at these frequencies for many naturally existing materials. [1][2][3][4] As artificially structured electromagnetic materials, metamaterials have been extensively investigated for the possibility of creating novel electromagnetic properties that are not available in natural materials, such as a negative refractive index, superlensing and cloaking.1-4 The electric permittivity and magnetic permeability of metamaterials can be designed for desired specifications and can be scaled to operate over nearly the entire electromagnetic spectrum. These artificial materials could find potential applications in the development of novel THz devices, which is traditionally difficult to achieve due to the absence of suitable functional sources and detectors. [5][6][7][8][9] Due to the limitations of fabrication and characterization technology, 10-12 investigations of metamaterial-based devices were initially implemented in the microwave frequency range. Metamaterials that operate in the THz range have attracted intense interest along with the advancement of fabrication technologies. 7,[13][14][15] Inspired by the realization of tunability, the research on metamaterials has been extended from the structura...

Active Control of Electromagnetically Induced Transparency Analog in Terahertz MEMS Metamaterial

“…When the voltage was brought back to 0 V, the cantilevers came back to the original OFF state. [23][24][25]28,31 ] The transmission spectra were then measured for the MEMS metamaterial in both ON and OFF states. The transmission spectra were normalized with respect to transmission of pure silicon substrate of the same thickness as the samples.…”

“…The versatility of MEMS design has enabled active manipulation of numerous THz properties such as magnetic resonance, [19][20][21][22] electrical resonance, [23][24][25] anisotropy, [ 26 ] broadband response, [ 27 ] isotropic resonance switching [ 28 ] multiresonance switching, [29][30][31] and coupling strength between resonators. [ 32 ] The enhanced controllability and direct integration of MEMS actuators into metamaterial unit cell geometry is an ideal fi t for the realization of selective control of coupled mode resonators.…”

“…[ 21,24 ] The bare Si wafer is cleaned and 100 nm thick thermal silicon-di-oxide (SiO 2 ) layer is deposited. This SiO 2 layer acts as the sacrifi cial layer used to release the microcantilevers.…”

Voltage-tunable dual-layer terahertz metamaterials

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All-integrated terahertz modulators

“…As these resonances are fundamentally based on the structural dimensions of the metamaterial pattern, physically changing the shape of the resonant components in these arrays has a strong effect on the resonance conditions. MEMS have been used to physically alter the resonant components of individual unit cells in metamaterials, leading to the realization of active, electronically tunable THz devices [58][59][60][61][62]. MEMS are advantageous, as unit cells can be individually addressed electronically, increasing the range of tuning parameters.…”