Characterization Of Metamaterials Research Articles

Thue-Morse nanostructures for tunable light extraction in the visible region

Controlling light propagation at the nanoscale is a fascinating opportunity offered by modern photonics, more than a challenge to face off. This study is aimed at investigating a particular kind of nanocomposite and reconfigurable optical metamaterials that can be exploited for the realization of a new class of switchable photonic devices, representing a breakthrough with respect to the state of the art. Existing photonic devices exhibit, in general, a drawback in the absence of tunability; this work aims to the design and characterization of metamaterials exploiting reconfigurable media, like LCs, which enable realization of a tunable, high quality, photonic quasi-crystal based switchable mode selector. It turned out that, starting from an unpolarized white light source, through a light extraction mechanism based on the diffraction of light, the high quality structure, combined with a uniformly aligned Photo-responsive Liquid Crystal (PLC), is able to give rise to an extremely narrow (FWHM ≈5 nm) and linearly polarized single mode peak of the extracted light intensity. Moreover, we have shown that the spectral properties (switching) of the samples can be finely controlled by using both an external applied voltage and a suitable pump light source with a maximum increase of 45% of the extracted light. Finally, both Scanning Electron Microscopy (SEM) and Far Field Diffraction (FFD) analysis have shown the high quality morphology of the realized structure.

Correction of numerical aperture effect on reflection phase measurement using a thick-gap Fabry-Perot etalon.

We propose a method for the measurement of the reflection phase using a thick-gap Fabry-Perot (FP) etalon interferometry technique with correction for the numerical aperture effect of the optical setup. The setup is first calibrated using a known sample by comparing the reflectance from a two-beam interference model for the FP etalon with experimental data. We then apply the correction to a sample of interest and obtain the reflection phase of the sample. Our method can be used to measure the reflection phase of a small sample and could lead to practical applications in optical characterization of metamaterials. Moreover, the principle of our approach could be generalized to other systems in the correction of numerical aperture effect due to microscopic objectives.

Metamaterial characterization by applying different boundary conditions on triangular split ring resonator type metamaterials

AbstractThis study aims to demonstrate the effects of the different boundary conditions on triangular split ring resonator (TSRR)‐shaped metamaterials in X band frequency regime. Three different TSSR‐shaped metamaterials are designed and simulated in a certain frequency range. TSSR‐shaped metamaterials are utilized to show that the use of different boundary conditions may result in completely different electromagnetic responses. Characterization is explained by applying 5 different boundary conditions. To verify simulation results, an experimental study is realized for the unit cell boundary condition. Both experimental and simulation results are complying with each other. For further investigation, electrical energy density and surface current distributions are simulated and discussed.

Making Meta Better: The Synthesis of New-Shaped Periodic Artificial Structures Suitable for Metamaterial Behavior Characterization

Extensive research in the electromagnetics area has been conducted recently with the goal of developing novel artificial metamaterials-or left-handed (LH) materials-at microwave frequencies. The idea of negative magnetic permeability and negative electric permittivity as electromagnetic properties for LH materials was initially theorized by Veselago in 1968 [1]. LH materials are not found in nature, so engineers must modify a structure's geometry to achieve LH behavior.

Resonance control of mid-infrared metamaterials using arrays of split-ring resonator pairs

We present our design, fabrication and characterization of resonance-controllable metamaterials operating at mid-infrared wavelengths. The metamaterials are composed of pairs of back-to-back or face-to-face U-shape split-ring resonators (SRRs). Transmission spectra of the metamaterials are measured using Fourier-transform infrared spectroscopy. The results show that the transmission resonance is dependent on the distance between the two SRRs in each SRR pair. The dips in the transmission spectrum shift to shorter wavelengths with increasing distance between the two SRRs for both the back-to-back and face-to-face SRR pairs. The position of the resonance dips in the spectrum can hence be controlled by the relative position of the SRRs. This mechanism of resonance control offers a promising way of developing metamaterials with tunability for optical filters and bio/chemical sensing devices in integrated nano-optics.

Cramér-Rao bounds for determination of electric and magnetic susceptibilities in metasurfaces.

Accurate and robust characterization of metasurfaces and metamaterials in terms of effective parameters is critical to the design of novel metadevices. We compute the Cramér-Rao lower bounds on the variance of any estimator for both the electric and magnetic surface susceptibilities of metasurfaces. We show that retrieval of such effective properties is inherently difficult around resonances, most notably for low-loss metasurfaces. We also put forth a least-squares estimator to mitigate this difficulty for the normal components of susceptibility tensors, which are observed to be the most ill-behaved. The present work is relevant to the development of loss-compensated metasurfaces for which noise has to be closely considered for accurate and robust device characterization.

Chiral retrieval method based on right circularly polarized and left circularly polarized waves

The free-wave characterization of metamaterials is usually carried out by illuminating a sample with a linearly polarized plane electromagnetic wave. At points before and after the sample, sensors are introduced to measure the transverse components of the field, in order to compute the reflection and transmission coefficients related with the co- and cross-polar field components. Based on this information, retrieval algorithms allow parameters like rotation angle, effective chirality and refraction index to be calculated. Here we propose to use the transmission signals under illumination with plane circularly polarized waves, without sensing the reflection signal, to calculate the chirality parameter and the rotation angle due to the electromagnetic activity of the material. This new method, which allows a simpler characterization of a chiral slab, is applied to the study of metamaterials composed of both periodic and random distributions of metallic structures with chiral symmetry. The experimental results are contrasted with simulations and alternative measurements obtained using linearly polarized waves.

Electromagnetic characterization of metamaterials in the centimetric frequency band using an original adjustable height stripline

We propose a broadband measurement method for measuring the electromagnetic (EM) properties of metamaterials in the 1–6 GHz frequency range. For this experimental technique, an original adjustable height strip transmission-line was developed that makes it possible to characterize metamaterials with different volumes and different numbers of unit cells. Therefore, it was possible to assess the influence of the number of unit cells in a sample on the measured constitutive parameters (complex permittivity and permeability). This study enabled us to define the criterion of the representative elementary number of cells. This criterion must be satisfied in practice in order to determine the microwave behavior for the sample under test in as close as possible to an infinite medium, whose EM properties can only be determined from simulations. Experimental and theoretical results for split ring resonator-type metamaterials are presented, compared, and discussed.

Broadband electromagnetic metamaterials with reconfigurable fluid channels

We present the design, characterization, and experimental verification of broadband and tunable metamaterials based on reconfigurable fluid channels. We demonstrate through simulation that a finite-height cylinder of water in a background medium behaves as a nonresonant metamaterial. By changing liquid type or adjusting liquid level, we tune the effective material parameters of the metamaterial through altering the composition and amount of water used. We verify the efficacy of the metamaterial through experiment, demonstrating a design procedure for a metamaterial with broadband and tunable properties.

Importance of Mueller matrix characterization of bianisotropic metamaterials

We present a study on the optical properties of metamaterial layers containing U-shaped resonators. Using Finite Element Methods, we show that the description of the optical properties on one isolated resonator requires taking into account permittivity, permeability and magneto-electric tensors. The effect of weak spatial dispersion in arrays of resonators can be reproduced by adding two elements in the permittivity and magneto-electric coupling tensors. We show how the symmetries of the Mueller matrix of the sample can be used to discriminate the contributions of the different tensor elements. Generalized ellipsometry measurements made on a sample realized by e-beam lithography confirm the qualitative findings of the theoretical study. A quantitative determination of the different elements of permittivity, permeability and magneto-electric coupling is obtained by using oscillators with Lorentzian lineshape, to fit to the measurements.

Introduction to the special issue on acoustics of porous media.

The acoustical properties of porous media have been a subject of extensive research since the late 19th century. This theory has been adopted widely by various research communities to explain the acoustical behavior of porous absorbers used in noise control applications, porous sediments in ocean acoustics, porous rocks in geophysics, porous ground in outdoor sound propagation, and porous bones in medical ultrasound. In the last 20 years, this subject continued to attract considerable interest that has resulted in a very large number of publications in acoustics related journals. Special journal issues have appeared starting with the 1993 Journal of Applied Acoustics special issue on Sound Absorbing Materials that was organized by Professor Keith Attenborough. Subsequently, two more special issues have been published in the Journal of Applied Acoustics on innovative applications of acoustic [porous] materials in 2003 and in the Journal of Acustica United with Acta Acustica in 2010 on acoustics of porous materials organized by Professor Kirill Horoshenkov, Dr. Francois-Xavier Becot, and Dr. Luc Jaouen. The idea of this special issue of the Journal of the Acoustical Society of America (JASA) was conceived at the Symposium on the Acoustics of Poro-Elastic Materials in Ferrara (Italy) in December 2011 that was also attended by the JASA editor in chief, Professor Allan Pierce. This has been an attempt to promote research on acoustics of porous media and bridge the barriers between research communities who make use of the related theory, numerical models, and experimental methods for the benefit of various other science and engineering disciplines. Therefore the main objectives for this issue are (a) to present the most up-to-date developments in the research related to acoustics of porous media, (b) to illustrate those areas of science to which this research subject is directly relevant, and (c) to illustrate challenges to this subject area that are yet to be addressed. This issue is a compilation of 22 papers; this makes it the largest special issue on acoustics of porous media published so far. These papers contribute to new theoretical and numerical models and present new experimental evidence on sound propagation phenomenon in porous media, new experimental methods, and instruments for porous material characterization in the laboratory and in situ. The issue presents work on new relations between the non-acoustical and acoustical properties, effects of inhomogeneities, pore stratification, and mechanical properties of the elastic frame on sound propagation in a porous medium. More specifically, the presented papers cover a wide range of aspects related to modeling and experimental characterization of metamaterials with internal resonators, naturally occurring porous media with rather complex pore structure, porous media exposed to very high levels of acoustic excitation, porous media with a dissipative elastic frame, materials with partially connected pores, external roughness, and microperforations. This issue also presents new numerical modeling tools that enable us to predict sound propagation more efficiently in time and frequency domains and for more complex porous medium arrangements and to link these results more directly to the porous medium micro-structure. We are grateful to all the contributors to this issue. We would also like to thank the editorial staff at JASA and associate editors who have helped us to handle a large number of submissions. These are: Ms. Mary Guillemette, Ms. Kelly Quigley, Professor Nicholas Chotiros, Professor Guillaume Haiat, Professor Andrew Norris, Dr. Vladimir Ostashev, Professor Allan Pierce, Dr. Franck Sgard, Professor Roel Snieder, and Dr. D. Keith Wilson.

Near- and far-field spectroscopic imaging investigation of resonant square-loop infrared metasurfaces

Optical metamaterials have unique properties which result from geometric confinement of the optical conductivity. We developed a series of infrared metasurfaces based on an array of metallic square loop antennas. The far-field absorption spectrum can be designed with resonances across the infrared by scaling the geometric dimensions. We measure the amplitude and phase of the resonant mode as standing wave patterns within the square loops using scattering-scanning near-field optical microscopy (s-SNOM). Further, using a broad-band synchrotron-based FTIR microscope and s-SNOM at the Advanced Light Source, we are able to correlate far-field spectra to near-field modes of the metasurface as the resonance is tuned between samples. The results highlight the importance of multi-modal imaging for the design and characterization of optical metamaterials.

Macroscopic Self-Assembly and Optical Characterization of Nanoparticle-Ligand Metamaterials

A self-assembled metamaterial exhibiting a positive near-zero index of refraction at visible wavelengths is demonstrated. The metamaterial consists of thiolene-functionalized gold nanospheres self-assembled into macroscopic, crosslinked, monolayers. By measuring the real and imaginary parts of the phase shift of light transmitted through the self-assembled films the effective index of refraction is determined as a function of wavelength. These findings may pave a way to simply and efficiently self-assemble and optically characterize multifunctional, multilayer nanoparticle–ligand metamaterials.

Characterization of active metamaterials based on negative impedance converters

Negative impedance converters (NICs) are used to create impedance loads that can effectively cancel the inductive properties of magnetic dipoles, resulting in active metamaterials with increased bandwidth and reduced loss for μ-near-zero (MNZ) and negative-Re(μ) (MNG) media. We demonstrate techniques for analyzing the stability and characterizing the magnetic properties of effective media loaded with NICs. Specifically, we apply the Nyquist criterion to validate the stability of sample active metamaterials. It is shown that the practical NIC-loaded metamaterial may maintain stability and reduce dispersion, albeit with reduced performance as compared to the ideal NIC load.

Oblique incidence ellipsometric characterization and the substrate dependence of visible frequency fishnet metamaterials

We use spectroscopic ellipsometry to investigate the angular-dependent optical modes of fishnet metamaterials fabricated by nanoimprint lithography. Spectroscopic ellipsometry is demonstrated as a fast and efficient method for metamaterial characterization and the measured polarization ratios significantly simplify the calibration procedures compared to reflectance and transmittance measurements. We show that the modes can be well identified by a combination of comparing different substrates and considering the angular dependence of the Wood's anomalies. The lack of angular dispersion of the anti-symmetric gap-modes does not agree with the model and requires further theoretical investigation.

Three-dimensional magnetic terahertz metamaterials using a multilayer electroplating technique

In the last decade, the development of metamaterials has led to exotic phenomena not shown in nature, including negative refractive index, invisibility cloaking and perfect absorption. To achieve these effects requires creating magnetically resonant subwavelength structures, since naturally occurring magnetism typically occurs at relatively low frequencies. In the far-infrared, or terahertz (THz), region of the electromagnetic spectrum, it is difficult to obtain a strong magnetic response from planar metamaterials at normal incidence. In this paper, multilayer electroplating is used to fabricate three-dimensional (3D) split-ring resonators that stand up out of plane. This enables the maximum coupling to the magnetic response at normal incidence. Characterization using THz time-domain spectroscopy indicates a strong magnetic resonance, and parameter extraction reveals a negative permeability from 1 to 1.3 THz with the minimal value of −2. The successful design, fabrication and characterization of 3D metamaterials provide opportunities to achieve different electromagnetic properties and novel devices in the THz range.

Erratum: Electromagnetic characterization of planar and bulk metamaterials: A theoretical study [Phys. Rev. B82, 165114 (2010)

Received 22 December 2011DOI:https://doi.org/10.1103/PhysRevB.85.039901©2012 American Physical Society

Design and experimental characterization of nonlinear metamaterials

We apply an analytic theory [New J. Phys.12, 093010 (2010)] toward the design of varactor-loaded split-ring resonator metacrystals, having nonlinear electromagnetic properties on demand. The design methodology here is shown to be efficient and is validated by the excellent agreement between the analytically predicted and experimentally measured harmonic generation. The analytic formulas enable a path toward optimization of nonlinear properties, which we demonstrate by varying the spacing of the metamaterial elements to maximize the second-order nonlinear susceptibility of the system.

Design, fabrication and characterization of indefinite metamaterials of nanowires

Indefinite optical properties, which are typically characterized by hyperbolic dispersion relations, have not been observed in naturally occurring materials, but can be realized through a metamaterial approach. We present here the design, fabrication and characterization of nanowire metamaterials with indefinite permittivity, in which all-angle negative refraction of light is observed. The bottom-up fabrication technique, which applies electrochemical plating of nanowires in porous alumina template, is developed and demonstrated in achieving uniform hyperbolic optical properties at a large scale. We developed techniques to improve the uniformity and to reduce the defect density in the sample. The non-magnetic design and the off-resonance operation of the nanowire metamaterials significantly reduce the energy loss of electromagnetic waves and make the broad-band negative refraction of light possible.

Characterization of Metamaterials Using a Strip Line Fixture

A method is introduced to measure the effective constitutive parameters of metamaterials having negative permittivity, negative permeability, or negative permeability and negative permittivity simultaneously. The method is based on the strip line topology, thus offering low cost and low setup complexity in comparison to other methods. The method proposed here is validated by numerically simulating the measurement setup while using different types of metamaterials. To validate the method experimentally, a metamaterial having negative permeability over a band of frequencies is characterized. Good agreement is obtained between the experimental and numerical results.