279 research outputs found
Experimental demonstration of the enhanced transmission through circular and rectangular sub-wavelength apertures using omega-like split-ring resonators
Cataloged from PDF version of article.Enhanced transmission through circular and rectangular sub-wavelength apertures using omega-shaped split-ring resonator is
numerically and experimentally demonstrated at microwave frequencies. We report a more than 150,000-fold enhancement through
a deep sub-wavelength aperture drilled in a metallic screen. To the authors’ best knowledge, this is the highest experimentally
obtained enhancement factor reported in the literature. In the paper, we address also the origins and the physical reasons behind the
enhancement results. Moreover, we report on the differences occurring when using circular, rectangular apertures as well as doublesided
and single-sided omega-like split ring resonator structures.
(C) 2012 Elsevier B.V. All rights reserve
FSS-based approach for the power transmission enhancement through electrically small apertures
Cataloged from PDF version of article.In this paper, a novel approach, based on the employment of frequency selective surfaces, to enhance the power transmission through sub-wavelength apertures at the microwave frequencies is presented. A heuristic interpretation of the phenomenon is given, as well as an analytical model, based on the transmission line network representation. Finally, the performance of the proposed structure is validated through a set of full-wave numerical simulations. © 2011 Springer-Verlag
Optimization and tunability of deep subwavelength resonators for metamaterial applications: complete enhanced transmission through a subwavelength aperture
Cataloged from PDF version of article.In the present work, we studied particle candidates for metamaterial applications, especially in terms of their electrical size and resonance strength. The analyzed particles can be easily produced via planar fabrication techniques. The electrical size of multi-split ring resonators, spiral resonators, and multi-spiral resonators are reported as a function of the particle side length and substrate permittivity. The study is continued by demonstrating the scalability of the particles to higher frequencies and the proposition of the optimized particle for antenna, absorber, and superlens applications: a multi-spiral resonator with lambda/30 electrical size operating at 0.810 GHz. We explain a method for tuning the resonance frequency of the multi-split structures. Finally, we demonstrate that by inserting deep subwavelength resonators into periodically arranged subwavelength apertures, complete transmission enhancement can be obtained at the magnetic resonance frequency. (C) 2009 Optical Society of Americ
Miniaturized negative permeability materials
Cataloged from PDF version of article.Experimental and numerical studies of mu-negative (MNG) materials such as multisplit ring resonators (MSRRs) and spiral resonators (SRs) are presented. The resonance frequency of the structures is determined by the transmission measurements and minimum electrical size of lambda(0)/17 for the MSRRs and of lambda(0)/82 for the SRs observed. These MNG materials can be easily produced by the well developed printed circuit board and optical lithography techniques. They are promising elements for the development of high resolution metamaterial lenses and electrically small antennas. (c) 2007 American Institute of Physics
Improved dispersibility of nanofibrillated cellulose via simple microwave-assisted esterification
Nanofibrillated cellulose (NFC) has been successfully esterified by lactic acid (LA) in the presence of HCl catalyst in an aqueous medium using a simple microwave heating process. The degree of substitution (DS) of ester groups on modified NFC (mNFC) was quantified through a systematic characterization consisting of titration, NMR, and XPS, revealing a consistent trend in the levels of DS in mNFC. The reaction parameters of the microwave heating process including the ratio between NFC and LA (1:10), amount of catalyst (5 wt%), energy input and time, have been optimized, achieving a DS of 0.66 in mNFC with a typical power of 800 Watts in 1 min only. The TEM and XRD results confirmed that the structure and characteristics of the nanofibrillated fibers were preserved following the process. Finally, the improved dispersibility of mNFC with high DS in low polarity solvents and polylactic acid (PLA) matrix was validated
Design of Miniaturized Narrowband Absorbers Based on Resonant-Magnetic Inclusions
Cataloged from PDF version of article.In this paper, we present the design of miniaturized narrowband-microwave absorbers based on different kinds of magnetic inclusions. The operation of the proposed components originates from the resonance of a planar array of inclusions excited by an incoming wave with a given polarization. As in common absorber layouts, a 377 Omega resistive sheet is also used to absorb the electromagnetic energy of the impinging field. Since the planar array of magnetic inclusions behaves at its resonance as a perfect magnetic conductor, the resistive sheet is placed in close proximity of the resonating inclusions, without perturbing their resonance condition. In contrast to other typical absorber configurations presented in the literature, the absorber proposed in this paper is not backed by a metallic plate. This feature may be useful for stealth applications, as discussed thoroughly in the paper. The other interesting characteristic of the proposed absorbers is the subwavelength thickness, which has shown to depend only on the geometry of the basic resonant inclusions employed. At first, regular split-ring resonators (SSRs) disposed in an array configuration are considered and some application examples are presented. Absorbers based on SRRs are shown to reach thickness of the order of lambda(0)/20. In order to further squeeze the electrical thickness of the absorbers, multiple SRRs and spiral resonators are also used. The employment of such inclusions leads to the design of extremely thin microwave absorbers, whose thickness may even be close to lambda(0)/100. Finally, some examples of miniaturized absorbers suitable for a practical realization are proposed
Equivalent-Circuit Models for the Design of Metamaterials Based on Artificial Magnetic Inclusions
Cataloged from PDF version of article.In this paper, we derive quasi-static equivalent-circuit models for the analysis and design of different types of artificial magnetic resonators-i.e., the multiple split-ring resonator, spiral resonator, and labyrinth resonator-which represent popular inclusions to synthesize artificial materials and metamaterials with anomalous values of the permeability in the microwave and millimeter-wave frequency ranges. The proposed models, derived in terms of RLC equivalent circuits, represent an extension of the models presented in a recent publication. In particular, the extended models take into account the presence of a dielectric substrate hosting the metallic inclusions and the losses due to the finite conductivity of the conductors and the finite resistivity of the dielectrics. Exploiting these circuit models, it is possible to accurately predict not only the resonant frequency of the individual inclusions, but also their quality factor and the relative permeability of metamaterial samples made by given arrangements of such inclusions. Finally, the three models have been tested against full-wave simulations and measurements, showing a good accuracy. This result opens the door to a quick and accurate design of the artificial magnetic inclusions to fabricate real-life metamaterial samples with anomalous values of the permeability
Analytical Model of Connected Bi-Omega: Robust Particle for the Selective Power Transmission Through Sub-Wavelength Apertures
Cataloged from PDF version of article.In this paper, we present a new analytical model of
the connected bi-omega structure consisting of two bi-omega particles
connected together through their arms. A single bi-omega
particle consists of a pair of regular equal omegas with mirror
symmetry. Assuming the individual bi-omega particle electrically
small, the equivalent circuit is derived, in order to predict its
resonant frequency. Then, two bi-omega particles are connected
together, obtaining a symmetric structure that supports two
fundamental modes, with even and odd symmetries, respectively.
The proposed analytical model, then, is used to develop a procedure
allowing the design of the particle for a desired resonant
frequency. The effectiveness of the proposed analytical model and
design guidelines is confirmed by proper comparisons to full-wave
numerical and experimental results. We also demonstrate through
a proper set of experiments that the resonant frequencies of the
connected bi-omega particle depend only on the geometrical and
electrical parameters of the omegas and are rather insensitive to
the practical scenario where the particle itself is actually used, e.g.
in free-space, rectangular waveguide or across an aperture in a
metallic screen
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