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As the development of high power microwaves (HPM) continues, the potential threat to electronic systems increases. The use of metamaterials' (MM) unique characteristics has the capability to be a countermeasure against HPM weapons as shielding for electronic systems. This thesis continues to explore the use of MMs as a countermeasure by studying the integration of field effect transistors (FET) with metal/dielectric/metal MM as a method of detection. The effects on the MM absorption profile were examined with the integration of FETs. The behavior of the FETs was also examined at the MM resonant frequency. Finite element simulations and experiments, which introduced electromagnetic (E&M) fields onto the MM board, were used to conduct the analysis. Simulations demonstrated that FETs have the potential to shift the resonant frequency to the left and generate an electric potential at the resonant frequency. The experimental board resonant frequency did not shift due to the limited number of FETs on the board. We conclude that further work for MM board detection of HPM weapons, with exposure of MM boards to megawatt radiation of higher frequency, is required.

Second harmonic generation and optical parametric amplification in negative-index metamaterials (NIMs) are studied. The opposite directions of the wave vector and the Poynting vector in NIMs results in a "backward" phase-matching condition, causing significant changes in the Manley-Rowe relations and spatial distributions of the coupled field intensities. It is shown that absorption in NIMs can be compensated by backward optical parametric amplification. The possibility of distributed-feedback parametric oscillation with no cavity has been demonstrated. The feasibility of the generation of entangled pairs of left- and right-handed counter-propagating photons is discussed.

We demonstrate gain in a three-dimensional metal/semiconductor metamaterial by the integration of optically active semiconductor quantum structures. The rolling-up of a metallic structure on top of strained semiconductor layers containing a quantum well allows us to achieve a three-dimensional superlattice consisting of alternating layers of lossy metallic and amplifying gain material. We show that the transmission through the superlattice can be enhanced by exciting the quantum well optically under both pulsed or continuous wave excitation. This points out that our structures can be used as a starting point for arbitrary three-dimensional metamaterials including gain.

We propose and verify experimentally a new concept for achieving strong nonlinear coupling between the electromagnetic and elastic properties in metamaterials. This coupling is provided through a novel degree of freedom in metamaterial design: internal rotation within structural elements. Our meta-atoms have high sensitivity to electromagnetic wave power, and the elastic and electromagnetic properties can be independently designed to optimise the response. We demonstrate a rich range of nonlinear phenomena including self-tuning and bistability, and provide a comprehensive experimental demonstration of the predicted effects.

This article is from Scientific Reports , volume 4 . Abstract Recently metamaterials have inspired worldwide researches due to their exotic properties in transmitting, reflecting, absorbing or refracting specific electromagnetic waves. Most metamaterials are known to have anisotropic properties, but existing anisotropy models are applicable only to a single meta-atom and its properties. Here we propose an anisotropy model for asymmetrical meta-atom clusters and their polarization dependency. The proposed anisotropic meta-atom clusters show a unique resonance property in which their frequencies can be altered for parallel polarization, but fixed to a single resonance frequency for perpendicular polarization. The proposed anisotropic metamaterials are expected to pave the way for novel optical systems.

Epsilon-Near-Zero materials exhibit a transition in the real part of the dielectric permittivity from positive to negative value as a function of wavelength. Here we study metal-dielectric layered metamaterials in the homogenised regime (each layer has strongly subwavelength thickness) with zero real part of the permittivity in the near-infrared region. By optically pumping the metamaterial we experimentally show that close to the Epsilon-Equal-to-Zero (EEZ) wavelength the permittivity exhibits a marked transition from metallic (negative permittivity) to dielectric (positive permittivity) as a function of the optical power. Remarkably, this transition is linear as a function of pump power and occurs on time scales of the order of the 100 fs pump pulse that need not be tuned to a specific wavelength. The linearity of the permittivity increase allows us to express the response of the metamaterial in terms of a standard third order optical nonlinearity: this shows a clear inversion of the roles of the real and imaginary parts in crossing the EEZ wavelength, further supporting an optically induced change in the physical behaviour of the metamaterial.

This article is from Scientific Reports , volume 3 . Abstract Various infra-red and planar chiral metamaterials were fabricated using the modified Nanospherical-Lens Lithography. By replacing the light source with a hand-held ultraviolet lamp, its asymmetric light emission pattern produces the elliptical-shaped photoresist holes after passing through the spheres. The long axis of the ellipse is parallel to the lamp direction. The fabricated ellipse arrays exhibit localized surface plasmon resonance in mid-infra-red and are ideal platforms for surface enhanced infra-red absorption (SEIRA). We also demonstrate a way to design and fabricate complicated patterns by tuning parameters in each exposure step. This method is both high-throughput and low-cost, which is a powerful tool for future infra-red metamaterials applications.

Materials scientists are getting creative in the quest to quiet our increasingly noisy world. Using metamaterials - man made materials with special properties not found in nature - researchers could soon reduce or eliminate unwanted industrial sounds.

Materials scientists are getting creative in the quest to quiet our increasingly noisy world. Using metamaterials - man made materials with special properties not found in nature - researchers could soon reduce or eliminate unwanted industrial sounds.

Recent progress in advanced additive manufacturing techniques has stimulated the growth of the field of mechanical metamaterials. One area particular interest in this subject is the creation of auxetic material properties through elastic instability. This paper focuses on a novel methodology in the analysis of auxetic metamaterials through analogy with rigid link lattice systems. Our analytic methodology gives extremely good agreement with finite element simulations for both the onset of elastic instability and post-buckling behaviour including Poisson's ratio. The insight into the relationships between mechanisms within lattices and their mechanical behaviour has the potential to guide the rational design of lattice based metamaterials.

This article is from Scientific Reports , volume 4 . Abstract We propose a kind of anisotropic gradient-index (GRIN) metamaterials, which can be used to control differently-polarized waves independently. We show that two three- dimensional (3D) planar lenses made of such anisotropic GRIN metamaterials are able to make arbitrary beam deflections for the vertical (or horizontal) polarization but have no response to the horizontal (or vertical) polarization. Then the vertically- and horizontally-polarized waves are separated and controlled independently to deflect to arbitrarily different directions by designing the anisotropic GRIN planar lenses. We make experimental verifications of the lenses using such a special metamaterial, which has both electric and magnetic responses simultaneously to reach approximately equal permittivity and permeability. Hence excellent impedance matching is obtained between the GRIN planar lenses and the air. The measurement results demonstrate good performance on the independent controls of differently-polarized waves, as observed in the numerical simulations.

This article is from Nanoscale Research Letters , volume 8 . Abstract A blueshift tunable metamaterial (MM) exhibiting a double-negative refractive index based on a topological insulator (bismuth selenide, Bi2Se3) has been demonstrated in the near-infrared (NIR) spectral region. The potential of Bi2Se3 as a dielectric interlayer of the multilayer MM is explored. The optical response of elliptical nanohole arrays penetrating through Au/Bi2Se3/Au films is numerically investigated using the finite difference time domain (FDTD) method. The blueshift tuning range of the MM is as high as 370 nm (from 2,140 to 1,770 nm) after switching the Bi2Se3 between its trigonal and orthorhombic states.

Metamaterials are constructed such that, for a narrow range of frequencies, the momentum density depends on the local displacement gradient, and the stress depends on the local velocity. In these models the momentum density generally depends not only on the strain, but also on the local rotation, and the stress is generally not symmetric. A variant is constructed for which, at a fixed frequency, the momentum density is independent of the local rotation (but still depends on the strain) and the stress is symmetric (but still depends on the velocity). Generalizations of these metamaterials may be useful in the design of elastic cloaking devices.

There is some very interesting [research at the Hasso Plattner Institute 3D-printing metamaterials](https://hpi.de//en/baudisch/projects/metamaterial-mechanisms.html). Normally, complex mechanical properties arise from assembling components made of various materials; in contrast, a metamaterial object obtains its properties within a single part using a single material without assembly. Their work centers on using a deformable cell pattern, which they said would work with ABS and PLA, but all their demos are made with NinjaFlex... which deforms easily, but lacks the rigidity needed for many kinds of devices. To test the feasibility of combining rigidity and deformability, I created a simple design for metamaterial longnose pliers. The black pliers printed in ABS copy the metamaterial cell design they used, but the ABS proved too rigid; the nose barely moved before the ABS began to crack. For my second attempt, I reinforced the stress points, thinned the walls of the deformable cell structure, and printed using blue T-Glase. This more flexible material works better, but still the nose only closes about half way before the pivot points start to crush and tear. As one last test, I tried printing one out of NinjaFlex... and the thin nose simply flops around; the material is never truly rigid ([here's a video of PLA HingePliers picking-up the NinjaFlex cell-based metamaterial version](https://www.youtube.com/watch?v=xe1O9QEkFCQ)). Update: As of February 7, 2017, HassoPlattnerInstitute_HCI has posted [their design on Thingiverse](http://www.thingiverse.com/thing:2082621). One potential fix is to use different materials for the deformable and rigid parts; that approach was used in [Thing 1388783](http://www.thingiverse.com/thing:1388783). However, that requires assembly or dual extrusion... and the resulting tool clearly isn't a metamaterial. Our trick is to use a single, fairly stiff, material and to design the deformable and rigid regions so that operation does not develop damaging stress between them. The result is my HingePliers design, published here. This mechanism is not merely "printed assembled" without supports -- it is **literally one piece of material and doesn't even have any structural spans!** (Technically, the University of Kentucky logo embossed in the bottom side has tiny spans in it, but that shouldn't really count.) The central hinge uses 45-degree angles to avoid spans and the spring, which deforms harmlessly into free space (rather than against a rigid part), connects the two handles so that the entire device is literally one object made of a homogeneous material: blue PLA. On that basis, I would argue that my HingePliers thing is actually a metamaterial object, extracting very different behaviors from the same material by controlling structure. The pliers operate very smoothly, with good tension to restore them to their open position, yet can exert a reasonable amount of force through the rigid nose.

Source : FERMAT, Volume 41, Article 1, Aug.-Sep., 2020   The development of new artificial materials is a key issue of the modern world moving toward the 5G communication standard and Industry 4.0. Therefore, the characterization of these materials (determination of their key parameters) plays an important role. The dielectric and magnetic constants and their anisotropy can be measured in the microwave range; as integral characteristics, they give useful information for the whole sample and we have shown how they can depend on the sample composition, structure, inclusion orientation, fabrication technology, conditions for the sample growth and forming, etc. We present in this paper a summary of our concepts, models, measurement methodologies and measurement methods for extraction of the dielectric and magnetic parameters of different artificial materials, as a result of our experience in the material characterization in the Microwave Laboratory of the Faculty of Physics in Sofia University, Bulgaria. A set of useful examples is presented for the determination of the dielectric and magnetic parameters of big groups of artificial materials: reinforced substrates, 3D printed dielectrics, ceramics, multilayer radomes, foams, absorbers, gradient dielectrics and magneto-dielectrics, textile fabrics, meta-materials, carbon-containing materials, fresh plant tissues, plasmas, etc. A special circumstance in this research is the anisotropy of the considered materials (different permittivity and/or permeability in different directions), which is a very informative parameter and gives valuable additional information for the samples. We discuss in this paper the origin of the anisotropy of variety of materials, how to measure this parameter, how to use the anisotropy data in the design and simulations of microwave devices and antennas and how the anisotropy influences their main characteristics.

This article is from Scientific Reports , volume 3 . Abstract Recent developments in the field of metamaterials have revealed unparalleled opportunities for “engineering” space for light propagation; opening a new paradigm in spin- and quantum-related phenomena in optical physics. Here we show that unique optical properties of metamaterials (MMs) open unlimited prospects to “engineer” light itself. We propose and demonstrate for the first time a novel way of complex light manipulation in few-mode optical fibers using optical MMs. Most importantly, these studies highlight how unique properties of MMs, namely the ability to manipulate both electric and magnetic field components of electromagnetic (EM) waves, open new degrees of freedom in engineering complex polarization states of light at will, while preserving its orbital angular momentum (OAM) state. These results lay the first steps in manipulating complex light in optical fibers, likely providing new opportunities for high capacity communication systems, quantum information, and on-chip signal processing.

This article is from Scientific Reports , volume 3 . Abstract Recent developments in the field of metamaterials have revealed unparalleled opportunities for “engineering” space for light propagation; opening a new paradigm in spin- and quantum-related phenomena in optical physics. Here we show that unique optical properties of metamaterials (MMs) open unlimited prospects to “engineer” light itself. We propose and demonstrate for the first time a novel way of complex light manipulation in few-mode optical fibers using optical MMs. Most importantly, these studies highlight how unique properties of MMs, namely the ability to manipulate both electric and magnetic field components of electromagnetic (EM) waves, open new degrees of freedom in engineering complex polarization states of light at will, while preserving its orbital angular momentum (OAM) state. These results lay the first steps in manipulating complex light in optical fibers, likely providing new opportunities for high capacity communication systems, quantum information, and on-chip signal processing.

The Floquet-Bloch theorem allows waves in infinite, lossless periodic media to be expressed as a sum of discrete Floquet-Bloch modes, but its validity is challenged under the realistic constraints of loss and finite extent. In this work, we mathematically reveal the existence of Floquet-Bloch modes in the electromagnetic fields sustained by lossy, finite periodic layered media using Maxwell's equations alone without invoking the Floquet-Bloch theorem. Starting with a transfer-matrix representation of the electromagnetic field in a generic layered medium, we apply Fourier transformation and a series of mathematical manipulations to isolate a term explicitly dependent on Floquet-Bloch modes. Fourier-domain representation of the electromagnetic field can be reduced into a product of the Floquet-Bloch term and two other matrix factors: one governed by reflections from the medium boundaries and another dependent on layer composition. Electromagnetic fields in any finite, lossy, layered structure can now be interpreted in the Fourier-domain by separable factors dependent on distinct physical features of the structure. The developed theory enables new methods for analyzing and communicating the electromagnetic properties of layered metamaterials.

Results are presented of an experimental polarimetric technique to measure strain in opaque objects. Experiments were conducted utilizing metamaterials on polydimethylsiloxane (PDMS) sheets to produce strain-induced birefringence at terahertz frequencies. Preliminary measurements are encouraging and show a qualitative agreement with theoretical predictions.

Optical activity and circular dichroism are fascinating physical phenomena originating from the interaction of light with chiral molecules or other nano objects lacking mirror symmetries in three-dimensional (3D) space. While chiral optical properties are weak in most of naturally occurring materials, they can be engineered and significantly enhanced in synthetic optical media known as chiral metamaterials, where the spatial symmetry of their building blocks is broken on a nanoscale. Although originally discovered in 3D structures, circular dichroism can also emerge in a two-dimensional (2D) metasurface. The origin of the resulting circular dichroism is rather subtle, and is related to non-radiative (Ohmic) dissipation of the constituent metamolecules. Because such dissipation occurs on a nanoscale, this effect has never been experimentally probed and visualized. Using a suite of recently developed nanoscale-measurement tools, we establish that the circular dichroism in a nanostructured metasurface occurs due to handedness-dependent Ohmic heating.

We introduce and theoretically demonstrate a quantum metamaterial made of dense ultracold neutral atoms loaded into an inherently defect-free artificial crystal of light, immune to well-known critical chal- lenges inevitable in conventional solid-state platforms. We demonstrate an all-optical control on ultrafast time scales over the photonic topological transition of the isofrequency contour from an open to close topology at the same frequency. This atomic lattice quantum metamaterial enables a dynamic manipula- tion of the decay rate of a probe quantum emitter by more than an order of magnitude. This proposal may lead to practically lossless, tunable and topologically-reconfigurable quantum metamaterials, for single- or few-photon-level applications as varied as quantum sensing, quantum information processing, and quantum simulations using metamaterials.

This article is from Sensors (Basel, Switzerland) , volume 12 . Abstract Metamaterials are artificial media structured on a size scale smaller than wavelength of external stimuli, and they can exhibit a strong localization and enhancement of fields, which may provide novel tools to significantly enhance the sensitivity and resolution of sensors, and open new degrees of freedom in sensing design aspect. This paper mainly presents the recent progress concerning metamaterials-based sensing, and detailedly reviews the principle, detecting process and sensitivity of three distinct types of sensors based on metamaterials, as well as their challenges and prospects. Moreover, the design guidelines for each sensor and its performance are compared and summarized.

This article is from Sensors (Basel, Switzerland) , volume 12 . Abstract Metamaterials are artificial media structured on a size scale smaller than wavelength of external stimuli, and they can exhibit a strong localization and enhancement of fields, which may provide novel tools to significantly enhance the sensitivity and resolution of sensors, and open new degrees of freedom in sensing design aspect. This paper mainly presents the recent progress concerning metamaterials-based sensing, and detailedly reviews the principle, detecting process and sensitivity of three distinct types of sensors based on metamaterials, as well as their challenges and prospects. Moreover, the design guidelines for each sensor and its performance are compared and summarized.

This article is from Beilstein Journal of Nanotechnology , volume 5 . Abstract Many nano-optical applications require a suitable nanofabrication technology. Hole-mask colloidal nanolithography has proven to be a low-cost and large-area alternative for the fabrication of complex plasmonic nanostructures as well as metamaterials. In this paper, we describe the fabrication process step by step. We manufacture a variety of different plasmonic structures ranging from simple nano-antennas over complex chiral structures to stacked composite materials for applications such as sensing. Additionally, we give details on the control of the nanostructure lateral density which allows for the multilayer-fabrication of complex nanostructures. In two accompanying movies, the fabrication strategy is explained and details are being demonstrated in the lab. The movies can be found at the website of Beilstein TV.

We consider a sub-wavelength periodic layered medium whose slabs are filled by arbitrary linear metamaterials and standard nonlinear Kerr media and we show that the homogenized medium behaves as a Kerr medium whose parameters can assume values not available in standard materials. Exploiting such a parameter availability, we focus on the situation where the linear relative dielectric permittivity is very small thus allowing the observation of the extreme nonlinear regime where the nonlinear polarization is comparable with or even greater than the linear part of the overall dielectric response. The behavior of the electromagnetic field in the extreme nonlinear regime is very peculiar and characterized by novel features as, for example, the transverse power flow reversing. In order to probe the novel regime, we consider a class of fields (transverse magnetic nonlinear guided waves) admitting full analytical description and we show that these waves are allowed to propagate even in media with $\epsilon 0$ since the nonlinear polarization produces a positive overall effective permittivity. The considered nonlinear waves exhibit, in addition to the mentioned features, a number of interesting properties like hyper-focusing induced by the phase difference between the field components.

We study dispersion properties of layered metal-dielectric media having different layers thicknesses ratios. Plotting dispersion diagrams and isofrequency contours, we find that strong nonlocality is inherent property of such periodic structures. We introduce different level of losses and analyze complex modes of the metamaterial demonstrating that it operates in a regime with infinite numbers of eigenmodes, with nonlocality slightly affected by losses.

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Personal research and overview of acoustic metamaterials and their applications in various contemporary contexts.

Personal research and overview of acoustic metamaterials and their applications in various contemporary contexts.

This paper presents an all-electronic approach for loss compensation in metamaterials. This is achieved by embedding active-transistors based negative differential resistance (NDR) circuits in each unit cell of the metamaterial lattice. NDR circuits provide tunable loss compensation over a broad frequency range limited only by the maximum operating frequency of transistors that is reaching terahertz values in newer semiconductor processes. Design, simulation and experimental results of metamaterials composed of split ring resonators (SRR) with and without loss compensation circuits are presented.

A one dimensional, parity-time (${\cal PT}$)-symmetric magnetic metamaterial comprising split-ring resonators having both gain and loss is investigated. In the linear regime, the transition from the exact to the broken ${\cal PT}$-phase is determined through the calculation of the eigenfrequency spectrum for two different configurations; the one with equidistant split-rings and the other with the split-rings forming a binary pattern (${\cal PT}$ dimer chain). The latter system features a two-band, gapped spectrum with its shape determined by the gain/loss coefficient as well as the inter-element coupling. In the presense of nonlinearity, the ${\cal PT}$ dimer chain with balanced gain and loss supports nonlinear localized modes in the form of novel discrete breathers below the lower branch of the linear spectrum. These breathers, that can be excited from a weak applied magnetic field by frequency chirping, can be subsequently driven solely by the gain for very long times. The effect of a small imbalance between gain and loss is also considered. Fundamendal gain-driven breathers occupy both sites of a dimer, while their energy is almost equally partitioned between the two split-rings, the one with gain and the other with loss. We also introduce a model equation for the investigation of classical ${\cal PT}$ symmetry in zero dimensions, realized by a simple harmonic oscillator with matched time-dependent gain and loss that exhibits a transition from oscillatory to diverging motion. This behaviour is similar to a transition from the exact to the broken ${\cal PT}$ phase in higher-dimensional ${\cal PT}-$ symmetric systems. A stability condition relating the parameters of the problem is obtained in the case of piecewise constant gain/loss function that allows for the construction of a phase diagram with alternating stable and unstable regions.

We report on a Digital Image Correlation-based technique for the detection of in-plane elastic waves propagating in structural lattices. The experimental characterization of wave motion in lattice structures is currently of great interest due its relevance to the design of novel mechanical metamaterials with unique/unusual properties such as strongly directional behavior, negative refractive indexes and topologically protected wave motion. Assessment of these functionalities often requires the detection of highly spatially resolved in-plane wavefields, which for reticulated or porous structural assemblies is an open challenge. A Digital Image Correlation approach is implemented that tracks small displacements of the lattice nodes by centering image subsets about the lattice intersections. A high speed camera records the motion of the points by properly interleaving subsequent frames thus artificially enhancing the available sampling rate. This, along with an imaging stitching procedure, enables the capturing of a field of view that is sufficiently large for subsequent processing. The transient response is recorded in the form of the full wavefields, which are processed to unveil features of wave motion in a hexagonal lattice. Time snapshots and frequency contours in the spatial Fourier domain are compared with numerical predictions to illustrate the accuracy of the recorded wavefields and demonstrate the suitability of this technique for the experimental characterization of wave properties.

We suggest that all-photodesigned metamaterials, sub-wavelength custom patterns of photo-excited carriers on a semiconductor, can display an exotic extrinsic electromagnetic chirality in terahertz (THz) frequency range. We consider a photo-induced pattern exhibiting 1D geometrical chirality, i.e. its mirror image can not be superposed onto itself by translations without rotations and, in the long wavelength limit, we evaluate its bianisotropic response. The photo-induced extrinsic chirality turns out to be fully reconfigurable by recasting the optical illumination which supports the photo-excited carriers. The all-photodesigning technique represents a feasible, easy and powerful method for achieving effective matter functionalization and, combined with the chiral asymmetry, it could be the platform for a new generation of reconfigurable devices for THz wave polarization manipulation.

We propose and investigate a family of nonlinear metamaterials in which light rays propagate just in one direction -- one-way propagation. Furthermore, we argue how such nonlinear media could provide an analog model for investigating the Born-Infeld Lagrangian in the realm of fields larger than its scale field.

All-optical active plasmonic devices are of fundamental importance for designing efficient nanophotonic circuits. We theoretically propose and numerically investigate an active plasmonic device made up of a nonlinear epsilon-near-zero metamaterial slab of thickness smaller than 100 nanometers lying on a linear epsilon-near-zero metamaterial substrate. We predict that, in free-space coupling configuration, the device, operating at low-intensity, would display plasmon mediated hysteresis behavior since the phase difference between the reflected and the incident optical waves turns out to be multi-valued and dependent on the history of the excitation process. Such an hysteresis behavior would allow to regard the proposed device as a compact memory unit whose state is accessible by measuring either the mentioned phase difference or the power, which is multi-valued as well, carried by the nonlinear plasmon wave. Since multiple plasmon powers comprise both positive and negative values, the device would also operate as a switch of the plasmon power direction at each jump along an hysteresis loop.

Inspired by the parity-time symmetry concept, we show that a judicious spatial modulation of gain and loss in epsilon-near-zero metamaterials can induce the propagation of exponentially-bound interface modes characterized by zero attenuation. With specific reference to a bi-layer configuration, via analytical studies and parameterization of the dispersion equation, we show that this waveguiding mechanism can be sustained in the presence of moderate gain/loss levels, and it becomes leaky (i.e., radiative) below a gain/loss threshold. Moreover, we explore a possible rod-based metamaterial implementation, based on realistic material constituents, which captures the essential features of the waveguiding mechanism, in good agreement with our theoretical predictions. Our results may open up new possibilities for the design of optical devices and reconfigurable nanophotonics platforms.

The dispersive wave propagation in a periodic metamaterial with tetrachiral topology and inertial local resonators is investigated. The Floquet-Bloch spectrum of the metamaterial is compared with that of the tetrachiral beam lattice material without resonators. The resonators can be designed to open and shift frequency band gaps, that is, spectrum intervals in which harmonic waves do not propagate. Therefore, an optimal passive control of the frequency band structure can be pursued in the metamaterial. To this aim, a suitable constrained nonlinear optimization problem on a compact set of admissible geometrical and mechanical parameters is stated. According to functional requirements, the particular set of parameters which determines the largest low-frequency band gap between a pair of consecutive branches of the Floquet-Bloch spectrum is obtained. The optimization problem is successfully solved by means of a version of the method of moving asymptotes, combined with a quasi-Monte Carlo multi-start technique.

We consider reflection of electromagnetic waves from layered structures with various dielectric and magnetic properties, including metamaterials. Assuming periodic variations in the permittivity, we find that the reflection is in general anomalous. In particular, we note that the specular reflection vanishes and that the incident energy is totally reflected in the backward direction, when the conditions for resonant excitation of leaking surface waves are fulfilled.

We describe novel physics of nonlinear magnetoinductive waves in left-handed composite metamaterials. We derive the coupled equations for describing the propagation of magnetoinductive waves, and show that in the nonlinear regime the magnetic response of a metamaterial may become bistable. We analyze modulational instability of different nonlinear states, and also demonstrate that nonlinear metamaterials may support the propagation of domain walls (kinks) connecting the regions with the positive and negative magnetization.

The complex permittivity (?) and permeability (?) of a material determines the response of the material to electromagnetic radiation. In many cases, the real part of ? and ? are both positive for materials that can be found in nature. Metamaterials (MTMs) are engineered media that are designed to have either a negative permittivity or a negative permeability or both. Negative permittivity and permeability cause electromagnetic waves travelling through this medium to exhibit unusual characteristics.The zero specular reflection layers using double negative (DNG) materials were examined in the first part of this thesis. The equations related to specular absorbers are analyzed based on the transmission line approach and numerical solutions are used in order to generate universal design charts for zero specular reflection absorbers. A MATLAB program is developed in order to generate the universal curves for double-positive (DPS) and DNG materials.Several methods to extract the effective permittivity and permeability of both normal materials and MTMs from measured or simulated scattering parameters were examined in the second part of this thesis. Microwave Studio (MWS) by Computer Simulation Technology (CST) was used to model the materials in a free space environment in order to calculate the S-parameters (S11 and S21) from which the constitutive parameters ? and ? can be extracted. The results were compared to published data.

The complex permittivity (?) and permeability (?) of a material determines the response of the material to electromagnetic radiation. In many cases, the real part of ? and ? are both positive for materials that can be found in nature. Metamaterials (MTMs) are engineered media that are designed to have either a negative permittivity or a negative permeability or both. Negative permittivity and permeability cause electromagnetic waves travelling through this medium to exhibit unusual characteristics.The zero specular reflection layers using double negative (DNG) materials were examined in the first part of this thesis. The equations related to specular absorbers are analyzed based on the transmission line approach and numerical solutions are used in order to generate universal design charts for zero specular reflection absorbers. A MATLAB program is developed in order to generate the universal curves for double-positive (DPS) and DNG materials.Several methods to extract the effective permittivity and permeability of both normal materials and MTMs from measured or simulated scattering parameters were examined in the second part of this thesis. Microwave Studio (MWS) by Computer Simulation Technology (CST) was used to model the materials in a free space environment in order to calculate the S-parameters (S11 and S21) from which the constitutive parameters ? and ? can be extracted. The results were compared to published data.

A nanophononic metamaterial is a new type of nanostructured material that features an array, or a forest, of intrinsically distributed resonating substructures. Each substructure exhibits numerous local resonances, each of which may hybridize with the phonon dispersion of the underlying host material causing significant reductions in the group velocities and consequently a reduction in the lattice thermal conductivity. In this paper, molecular dynamics simulations are utilized to investigate both the dynamics and the thermal transport properties of a nanophononic metamaterial configuration consisting of a freely suspended silicon membrane with an array of silicon nanopillars standing on the surface. The simulations yield results consistent with earlier lattice-dynamics based predictions which showed a reduction in the thermal conductivity due to the presence of the local resonators. Using a spectral energy density approach, in which only simulation data is utilized and no a priori information on the nanostructure resonant phonon modes is provided, we show direct evidence of the existence of resonance hybridizations as an inherent mechanism contributing to the slowing down of thermal transport in this system.

We theoretically and experimentally investigate visco-thermal effects on the acoustic propagation through metamaterials consisting of rigid slabs with subwavelength slits embedded in air. We demonstrate that this unavoidable loss mechanism is not merely a refinement, but it plays a dominant role in the actual acoustic response of the structure. Specifically, in the case of very narrow slits, the visco-thermal losses avoid completely the excitation of Fabry-Perot resonances, leading to 100% reflection. This is exactly opposite to the perfect transmission predicted in the idealised lossless case. Moreover, for a wide range of geometrical parameters, there exists an optimum slit width at which the energy dissipated in the structure can be as high as 50%. This work provides a clear evidence that visco-thermal effects are necessary to describe realistically the acoustic response of locally resonant metamaterials.

We have fabricated a quarter-wave plate from a single layer birefringent metamaterial. For comparison, an appropriately scaled double layer meanderline structure was fabricated. At the design frequency of 639 GHz, the metamaterial structure achieves 99.9% circular polarization while the meanderline achieves 99.6%. The meanderline displays a larger bandwidth of operation, attaining over 99% circular polarization from 615 - 743 GHz, while the metamaterial achieves 99% from 626 - 660 GHz. However, both are broad enough for use with CW sources making metamaterials a more attractive choice due to the ease of fabrication. Both samples are free standing with a total thickness of 70um for the meanderline structure and a mere 20um for the metamaterial highlighting the large degree of birefringence exhibited with metamaterial structures.

We predict that optical Bloch oscillations can be observed in layered structures with left-handed metamaterials and zero average refractive index where the layer thickness varies linearly across the structure. We demonstrate a new type of the Bloch oscillations associated with coupled surface waves excited at the interfaces between the layers with left-handed material and conventional dielectric.

We introduce and model a three-dimensional (3D) atomic-scale phononic metamaterial producing two-path phonon interference antiresonances to control the heat flux spectrum. We show that a crystal plane partially embedded with defect-atom arrays can completely reflect phonons at the frequency prescribed by masses and interaction forces. We emphasize the predominant role of the second phonon path and destructive interference in the origin of the total phonon reflection and thermal conductance reduction in comparison with the Fano-resonance concept. The random defect distribution in the plane and the anharmonicity of atom bonds do not deteriorate the antiresonance. The width of the antiresonance dip can provide a measure of the coherence length of the phonon wave packet. All our conclusions are confirmed both by analytical studies of the equivalent quasi-1D lattice models and by numerical molecular dynamics simulations of realistic 3D lattices.

We study the properties of a tunable nonlinear metamaterial operating at microwave frequencies. We fabricate the nonlinear metamaterial composed of double split-ring resonators and wires where a varactor diode is introduced into each resonator so that the magnetic resonance can be tuned dynamically by varying the input power. We show that at higher powers the transmission of the metamaterial becomes power dependent, and we demonstrate experimentally power-dependent transmission properties and selective generation of higher harmonics.

We study the propagation of electromagnetic waves in one-dimensional chirped periodic structures composed of alternating layers of negative-index (or left-handed) metamaterial and conventional dielectric, under the condition of the zero average refractive index. We consider the case when the periodic structure has a linear chirp, and the chirp is introduced by varying linearly the thickness of the layers across the structure. We apply an asymptotic analytical method for the analysis of the Bloch oscillations and find that, in a sharp contrast to ordinary periodic dielectric structures, the energy flow in multi-layered stacks with metamaterials may have the opposite direction at the band edges, thus providing novel possibilities for the beam steering in the transmission band.

In this paper, we derive a model from Maxwell equations for the magnetic resonance of split-ring resonators. Using this model we revisit the scaling of split-ring resonators. Inspired by our model, we propose a new type of split-hybrid metal-dielectric ring resonator, of which the ring is made composed of moderately high index dielectric material (e.g. SiC, TiO2, ZnS) (for the major portion), while and metal (e.g. Ag) fills the gap. Such a new magnetic metamaterial is able to overcome the saturation problem of split-ring resonatorssaturation-free and therefore is able to operate at short wavelength down to ultraviolet range.

The paper extends and enhances in several ways the recently proposed homogenization theory of metamaterials [J. Opt. Soc. Am. B 28, 577 (2011)]. The theory is based on a direct analysis of fields in the lattice cells rather than on an indirect retrieval of material parameters from transmission / reflection data. The theory is minimalistic, with only two fundamental premises at its core: (i) the coarse-grained fields satisfy Maxwell's equations and boundary conditions exactly; and (ii) the material tensor is a linear relationship between the pairs of coarse-grained fields. There are no heuristic assumptions and no artificial averaging rules. Nontrivial magnetic behavior, if present, is a logical consequence of the theory. The method yields not only all 36 standard material parameters, but also additional ones quantifying spatial dispersion rigorously. The approximations involved are clearly identified. A tutorial example and an application to a resonant structure with high-permittivity inclusions are given.