We present a computational and experimental study of a novel terahertz (THz) device resulting from hybridization of metamaterials with pseudomorphic high electron mobility transistors (HEMTs), fabricated in a commercial gallium arsenide (GaAs) process. Monolithic integration of transistors into each unit cell permits modulation at the metamaterial resonant frequency of 0.46 THz. Characterization is performed using a THz time-domain spectrometer (THz-TDS) and we demonstrate switching values over 30%, and THz modulation at frequencies up to 10 megahertz (MHz). Our results demonstrate the viability of incorporating metamaterials into mature semiconductor technologies and establish a new path toward achieving electrically tunable THz devices.

/pdf/high-speed-terahertz-modulation-from-metamaterials-with-3wvqv13cui.pdf

High speed terahertz modulation from metamaterials with embedded high electron mobility transistors

Metamaterials are being applied to the development and construction of many new devices throughout the electromagnetic spectrum. Limitations posed by the metamaterial operational bandwidth and losses can be effectively mitigated through the incorporation of tunable elements into the metamaterial devices. There are a wide range of approaches that have been advanced in the literature for adding reconfiguration to metamaterial devices all the way from the RF through the optical regimes, but some techniques are useful only for certain wavelength bands. A range of tuning techniques span from active circuit elements introduced into the resonant conductive metamaterial geometries to constituent materials that change electromagnetic properties under specific environmental stimuli. This paper presents a survey of the development of reconfigurable and tunable metamaterial technology as well as of the applications where such capabilities are valuable.

/pdf/reconfigurable-and-tunable-metamaterials-a-review-of-the-4b3l1y2auq.pdf

Reconfigurable and Tunable Metamaterials: A Review of the Theory and Applications

In this letter, the properties of split-ring resonators (SRRs) loaded with high-Q capacitors and nonlinear varactors are theoretically analyzed and experimentally measured. We demonstrate that the resonance frequency fm of the nonlinear SRRs can be tuned by increasing the incident power. fm moves to lower and higher frequencies for the SRR loaded with one varactor and two back-to-back varactors, respectively. For high incident powers, we observe bistable tunable metamaterials and hysteresis effects. Moreover, the coupling between two nonlinear SRRs is also discussed.

/pdf/nonlinear-properties-of-split-ring-resonators-326arf0d81.pdf

Nonlinear properties of split-ring resonators.

This paper presents the results of a feasibility study for the design of multi-band tunable metamaterials based on the use of micro-split SRR (MSSRR) structures. In this study, we have designed and constructed a conventional split-ring resonator (SRR) unit cell (type A) and two modified SRR unit cells having the same design parameters except that they contain two (type B) or four (type C) additional micro-splits on the outer square ring, along the arm having the main split. Transmission characteristics of the resulting MSSRR cells are obtained both numerically and experimentally and compared to those of the ordinary SRR unit cell. It is observed that the presence of the additional micro-splits leads to the increase of resonance frequency by substantial amounts due to the series capacitance effect. Next, we have designed and constructed 2×2 homogeneous arrays of magnetic resonators which consist of the same type of cells (either A, or B, or C). Such MSSRR blocks are found to provide only a single frequency band of operation around the magnetic resonance frequency of the related unit cell structure. Finally, we have designed and constructed 2×2 and 3×2 inhomogeneous arrays which contain columns of different types of metamaterial unit cells. We have shown that these inhomogeneous arrays provide two or three different frequency bands of operations due to the use of different magnetic resonators together. The number of additional micro-splits in a given MSSRR cell can be interactively controlled by various switching technologies to modify the overall metamaterial topology for the purpose of activating different sets of multiple resonance frequencies. In this context, use of electrostatically actuated RF MEMS switches is discussed, and their implementation is suggested as a future work, to control the states of micro-splits in large MSSRR arrays to realize tunable multi-band metamaterials.

A tunable multi-band metamaterial design using micro-split SRR structures

A planar lens made of gradient index metamaterials can transform cylindrical waves to plane waves, and the beam direction of plane waves is controlled by adjusting the refractive-index distributions of the lens. Based on such properties, we present high-performance beam-scanning antennas experimentally using the gradient-index planar lens and horn antenna. The lens is carefully designed with metamaterials to achieve different refractive indices and good matching of impedance. The near-field distributions of antennas are measured using a two-dimensional near-field microwave scanning apparatus, and the radiation patterns are presented to show the high directivity and low sidelobe.

Experiments on high-performance beam-scanning antennas made of gradient-index metamaterials

A one-dimensional metamaterial structure is realized by printing subwavelength paired S-shaped metallic strips only on one side of a dielectric substrate. The simultaneously negative effective permittivity and permeability of such metamaterial are retrieved from the scattering parameters yielded in the numerical simulation. Experiments aimed to verify the transmission and refraction properties of the metamaterial are conducted, and the results show the existence of the negative refraction within the same frequency band, as indicated in the simulation. The proposed structure design makes it easy to fabricate and provides feasibilities for making controllable metamaterial by incorporating itself with lumped active elements.

Experimental validation of negative refraction of metamaterial composed of single side paired S-ring resonators

In the present letter, a design for active left-handed material collaborated with microwave varactors is proposed and experimentally realized. Both the results of simulation and experiment verify the tunable left-handed properties of the structure in microwave band. A controllable beam steering is then observed experimentally by a prism fabricated by such metamaterial. The simplicity of the active design and its tunable negative refraction indices make it useful for various applications.

Mingkai Mu

Papers

Experimental validation of negative refraction of metamaterial composed of single side paired S-ring resonators

Active left-handed material collaborated with microwave varactors