We present experimental measurements of three-and four-wave mixing phenomena in an artificially structured nonlinear magnetic metacrystal at microwave frequencies. The sum frequency generation signal for the varactor-loaded split-ring resonator (VLSRR) metamaterial agrees quantitatively with that predicted using an analytical effective medium model describing the VLSRR medium. A resonant enhancement of the nonlinear response is observed near the metamaterial resonance. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3592574]
"While one can utilize an array of microplasmas for a variety of applications, we exploit the high nonlinearity of plasmas to realize a non-linear metamaterial. Nonlinear metamaterials are an emerging class of artificial materials with exciting applications in frequency generation444546 and parametric amplification4748; they are realized today using varactor loaded split ring resonators which are difficult to scale up due to electrical routing requirements. The electromagnetic properties of the metamaterial medium can be altered by changing the capacitance of the varactor in the gap of each unit cell45 and in our case by the nonlinearity of the microplasma in the gap of each split ring resonators. "
[Show abstract][Hide abstract] ABSTRACT: Since the initial demonstration of negative refraction and cloaking using metamaterials, there has been enormous interest and progress in making practical devices based on metamaterials such as electrically small antennas, absorbers, modulators, detectors etc that span over a wide range of electromagnetic spectrum covering microwave, terahertz, infrared (IR) and optical wavelengths. We present metamaterial as an active substrate where each unit cell serves as an element for generation of plasma, the fourth state of matter. Sub-wavelength localization of incident electromagnetic wave energy, one of the most interesting properties of metamaterials is employed here for generating high electric field to ignite and sustain microscale plasmas. Frequency selective nature of the metamaterial unit cells make it possible to generate spatially localized microplasma in a large array using multiple resonators. A dual resonator topology is shown for the demonstration. Since microwave energy couples to the metamaterial through free space, the proposed approach is naturally wireless. Such spatially controllable microplasma arrays provide a fundamentally new material system for future investigations in novel applications, e.g. nonlinear metamaterials.
"Pendry et al.  theoretically predicted that high nonlinearities could be realized in resonant metamaterials such as SRRs by placing nonlinear elements at locations where electric (or magnetic) field is concentrated due to the resonance effect. Nonlinear metamaterials have been applied to applications such as property-tunable metamaterials   , frequency mixing , imaging beyond the diffraction limit , and bistable media   . In this section, we review some papers on SHG in nonlinear metamaterials with a single resonant structures in a unit cell      . "
[Show abstract][Hide abstract] ABSTRACT: In this review, we describe recent developments in func-tional metamaterials based on coupled resonators. We first consider coupled resonator metamaterials that mimic electromagnetically in-duced transparency (EIT). We present a circuit model for EIT-like metamaterials and introduce a new coupled resonator in which the coupling is provided by a field gradient so that the group velocity can be varied by varying the incident angle. We then describe the principles for enhancing second harmonic generation (SHG) in nonlinear resonant metamaterials. Optical and microwave experiments of SHG in singly resonant metamaterials are presented. A method for further enhancing SHG using a doubly resonant metamaterial is also described.
[Show abstract][Hide abstract] ABSTRACT: We present the design and experimental implementation of an RF limiter metamaterial using a sheet of nonlinear metamaterials. We demonstrate that complementary electric inductive-capacitive resonators loaded with nonlinear p-i-n diodes can act as RF limiter unit cells. We design and fabricate limiter metamaterials and compare them to traditional circuit limiters. Our limiter metamaterial exhibits a minimum insertion loss under 3 dB, a maximum decrease in transmission of 6.95 dB and broadband performance, with a minimum decrease in transmission of 3 dB over 18% bandwidth. The limiter metamaterial is suitable for a wide variety of practical applications requiring protection of sensitive devices from high power.
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