The work presented in this thesis concerns the application of concepts that are widely used in metamaterial research to the control of fluid flow. In particular surface structuring and resonance were investigated. The initial work focussed on Stokes flow over structured surfaces. The effective boundary conditions that the structuring creates, analogous to the impedance boundary condition encountered in electromagnetism and acoustics, were examined. Exact solutions for the flow and slip length along the grooves of a family of surfaces were derived. These were compared to Finite Element Method (FEM) models and previous work valid for arbitrary structured surfaces, which was based on a perturbation expansion. Good agreement was found for all available surfaces. The previously presented solution was then also compared to results for a sinusoidal surface, finding good agreement for low aspect ratios but diverging at intermediate aspect ratios. Extending the perturbation theory beyond first order was found to improve the agreement. To explore the concept of resonance in fluid dynamics laminar flow around a circular bluff body with an attached flexible tail was considered, investigating how the resonant behaviour of the elastic tail modified the drag and vortex shedding frequency of the body. The results were compared against the no tail case as well as a rigid tail. For short tail lengths the average drag was reduced compared to both reference cases, whilst the vortex shedding could be either enhanced or reduced. When one of the resonant frequencies of the tail matched the vortex shedding frequency of the body, the resonance motion of the tail resulted in in sharp changes to both the drag and vortex shedding frequency. In the finally section of the thesis I describe the Particle Image Velocimetry experiments that were set up to verify the resonant flexible tail behaviour. The process by which the initial set up was upgraded is given. Results are shown for a circular bluff body being towed through the fluid. This is then extended to a circular bluff body with an attached rigid tail. Preliminary results for the flexible tail case are then presented.

This thesis presents an investigation of fabrication technologies and electromagnetic characterisation of textile metamaterials in the microwave frequency range. Interdisciplinary in nature, the work bridges textile design practice and electromagnetic engineering. The particular ambition was to explore a number of surface techniques prevalent in the textile design field, and map their suitability for the construction of metatextiles for microwave operation. Two different classes of metatextiles, all-dielectric and dielectric with electrically conductive patterns, were examined. First, five structures of all-dielectric textiles and papers are reported; three textiles with graded embroidered and screen printed patterns, and two papers embellished with regular and irregular laser cut patterns. Permittivities for these materials were measured in a purpose-built test chamber and shown to be similar to permittivity ranges exhibited by solid discrete metamaterial cells previously reported in the scientific literature. Importantly these metatextiles were realised within one textile surface and one fabrication process, bypassing the need to assemble large numbers of isotropic material cells. This reveals the potential for rapid and low-cost manufacture of graded textile materials to produce anisotropic ground plane cloaks. Secondly, three studies are presented that examine the use of electrically conductive patterned textile materials in the design of metatextiles which exhibit negative refractive index over a narrow frequency band. A range of e-textile (electronic textile) fabrication technologies were explored to assess their suitability for prototyping splitring and wire arrays, resonating in a narrow region between 3 - 10 GHz. Designs utilised a repeated unit cell pattern on a two-dimensional textile surface and were subsequently pleated into the required three-dimensional structure. A small negative refractive index was achieved for an embroidered prototype at 4.9 GHz, and two 'printed and plated' prototypes at, 7.5 GHz and 9.5 GHz respectively. In summary the thesis demonstrates a set of guidelines for the fabrication of textile metamaterials for microwave frequencies, derived through a practice-led and interdisciplinary method based on material experimentation.

In this thesis we investigate acoustic metamaterials and how they can influence incident sound waves. Specifically we are interested in the mathematical technique of transformation acoustics and how several simple examples of metamaterials, devised via transformation acoustics, can be realised physically. We present a simple methodology for optimising microstructure consisting of rods with elliptical cross sections arranged on a rectangular array in order to best fit the material properties required by a desired transformation. We present in detail three such examples: a one dimensional scaling, the beam shifter, and a right angle bend. We apply the one dimensional scaling to a quarter wavelength resonator, theoretically predicting that we are able to lower the active frequency of the resonator without increasing its physical length. This result is then confirmed experimentally. We provide further experimental evidence of the broad band nature of the microstructure and suggest how it could be applied as a one dimensional acoustic cloak. Finally we present numerical simulations of acoustic propagation through microstructure chosen to realise a beam shifter and right angle bend. These are devices associated with more complicated two dimensional transformations that may prove useful in the field of noise control and redirection.

Recientes descubrimientos han hecho posible la creación de un nuevo tipo de materiales: los metamateriales. En sólo algunos años, el desarrollo de esta nueva rama científica ha dado lugar a numerosos descubrimientos y avances tecnológicos basados en las nuevas propiedades que exhiben estos nuevos materiales. Esta tesis recoge parte del trabajo desarrollado durante los últimos años por el grupo GEMMA y CIMITEC en la aplicación de líneas de transmisión de tipo resonante en el desarrollo de dispositivos de microondas. Su pequeño tamaño y la controlabilidad de sus propiedades eléctricas son las principales propiedades de las líneas metamaterial basadas en resonadores concentrados que posibilitan su empleo en el diseño de dispositivos de microondas de pequeñas dimensiones. Estos dispositivos son de interés especialmente en aquellas aplicaciones en las que un reducido tamaño es un requerimiento importante. No obstante, además de su reducido tamaño, dichos dispositivos pueden ofrecer mejoras en su respuesta y e incluso nuevas funcionalidades. El documento ha sido escrito como compendio de 13 artículos. Dichos artículos contienen gran parte de los resultados desarrollados durante la realización de esta tesis y se detallan en una lista más adelante. El documento se ha dividido en varias secciones dedicadas a diferentes aspectos: -En el segundo capítulo se presenta una breve introducción sobre metamaterials y materiales zurdos, incluyendo sus propiedades y sus elementos constitutivos. Se dedica una especial atención a la aplicación de dichos conceptos a estructuras planares y la síntesis de líneas de transmisión metamaterial. -El tercer capítulo trata sobre la implementación de líneas de transmission metamaterial mediante el modelo resonante, que es el empleado en este trabajo. Se presentan y estudian diferentes tipos de líneas de transmission metamaterial, con especial énfasis en las estructuras empleadas en las aplicaciones presentadas en el capítulo 4. -El cuarto capítulo se dedica a las aplicaciones de las estructuras ya presentadas al diseño de components concretos, incluyendo diferentes tipos de divisors de potencia, filtros de banda ancha y estrecha y estructuras reconfigurables basadas en materiales ferroeléctricos. -Por ultimo, el quinto capítulo incluye las conclusions y posibles futuros objetivos. ARTÍCULOS: Debido a la normative, los artículos marcados con un asterisco (*) no pueden ser considerados como parte fundamental de esta tesis, bien por ser artículos presentados a conferencias especializadas en lugar de revistas de investigación, o pore star pendientes de publicación en el momento del depósito de esta tesis. -Article A: M. Gil, J. Bonache, I. Gil, J. García-García and F. Martín, "On the transmission properties of left handed microstrip lines implemented by complementary split rings resonators", Int. Journal Numerical Modelling: Electronic Networks, Devices and Fields, vol. 19, pp 87-103, 2006. -Article B: M. Gil, J. Bonache, I. Gil, J. García-García and F. Martín, "Miniaturization of planar microwave circuits by using resonant-type left handed transmission lines", IET Microwave Antennas and Propagation, Vol.1, pp. 73-79, 2007. -Article C: M. Gil, I. Gil, J. Bonache, J. García-García and F. Martín, "Metamaterial transmission lines with extreme impedance values", Microwave and Optical Technology Letters, vol. 48, pp. 2499-2505, 2006. -Article D*: M. Gil, J. Bonache, I. Gil, J. García-García and F. Martín, "Artificial Left¬handed Transmission Lines for Small Size Microwave Components: Application to Power Dividers", presented at 36th European Microwave Conference (EuMC), Manchester (UK), pp. 1135-1138, 2006. -Article E: M. Gil, J. Bonache, J. Selga, J. García-García, F. Martín, "Broadband resonant type metamaterial transmission lines ", IEEE Microwave and Wireless Components Letters, vol. 17, pp. 97-99, 2007. -Article F: M. Gil, J. Bonache, J. García-García, J. Martel and F. Martín, "Composite Right/Left-Handed Metamaterial Transmission Lines Based on Complementary Split-Rings Resonators and Their Applications to Very Wideband and Compact Filter Design", IEEE Transactions on Microwave Theory and Techniques, Vol. 55, No. 6, pp. 1296-1304, 2007. -Article G: M. Gil, J. Bonache, F. Martín, "Metamaterial Filters with Attenuation Poles in the Pass Band for Ultra Wide Band Applications", Microwave and Optical Technology Letters, Vol. 49, Issue 12, pp 2909-2913, 2007. -Article H : M. Gil, J. Bonache, J. García-García and F. Martín, "New Left Handed Microstrip Lines With Complementary Split Rings Resonators (CSRRs) Etched in the Signal Strip", IEEE MTT-S Int'l Microwave Symposium Digest, Honolulu (HA), USA, pp. 1419-1422, 2007. -Article I: M. Gil, J. Bonache and F. Martín, "Synthesis and applications of new left handed microstrip lines with complementary split-ring resonators etched on the signal strip", IET Microwaves, Antennas & Propagation, Vol. 2, Issue 4, pp. 324-330, 2008. -Article J: J. Bonache, M. Gil, O. García-Abad and F. Martín, "Parametric analysis of microstrip lines loaded with complementary split ring resonators", Microwave and Optical Technology Letters, Vol. 50 , Issue 8, pp. 2093-2096, 2008. -Article K*: M. Gil, J. Bonache, F. Martín. "Ultra Compact Band Pass Filters Implemented Through Complementary Spiral Resonators (CSRs)", IEEE MTT-S Int'l Microwave Symposium Digest, Atlanta, USA, pp.323-326, 2008. -Article L: M. Gil, J. Bonache, and F. Martín, "Metamaterial filters: A review", Metamaterials, vol. 2, pp. 186-197, 2008. -Article M*: M. Gil, C. Damm, A. Giere, M. Sazegar, J. Bonache, R. Jakoby, F. Martín. "Electrically Tunable SRRs at Microwave frequencies based on BST thick films". Electronic Letters (submitted). / Recent advances have made possible the emergence of a new kind of materials: Metamaterials. In just some years, the development of this new scientific branch has given rise to numerous discoveries and technological advances based on the new properties shown by these novel materials. The present Thesis gathers a part of the work developed during the last years in the Group GEMMA and CIMITEC in the application of resonant-type metamaterial transmission lines to the development of microwave devices. The small size and the controllability of the electrical characteristics of metamaterial transmission lines based on sub-wavelength resonators are the main properties that make possible their use in the synthesis of microwave devices with compact dimensions and exceptional features. Microwave components based on metamaterial transmission lines are, therefore, of special interest in those applications in which compactness is a critical aspect. However, besides their small size, such devices can also offer a performance improvement or even new functionalities. This document has been written as a compendium of 13 articles. The articles contain most of the results of the work developed during the realisation of this Thesis and are included in a complete list given below. The document has been divided in several sections devoted to different aspects: -The second chapter presents a brief introduction about Metamaterials and left-handed materials, including their properties and constituent elements. Special attention is paid to the application of such concepts to planar structures and the synthesis of metamaterial transmission lines. -The third chapter delves into the implementation of metamaterial transmission lines by means of the resonant approach, which is applied in this work. Different kinds of resonant-type metamaterial transmission lines are presented and studied, with special emphasis on those structures which have been employed in the devices presented in chapter 4. -The fourth chapter is devoted to the applications of the previously studied structures to the design of specific components, including different kinds of power dividers, narrow- and broad-band filters and reconfigurable structures based on ferroelectric materials. -Finally, the fifth chapter includes some conclusions and possible next goals are exposed. ARTICLES: Due to regulation reasons, the articles marked with * cannot be considered as a basic part of this Thesis, either for being Conference, but not Journal Articles, or for being pending acceptance by the time of the Thesis submission. -Article A: M. Gil, J. Bonache, I. Gil, J. García-García and F. Martín, "On the transmission properties of left handed microstrip lines implemented by complementary split rings resonators", Int. Journal Numerical Modelling: Electronic Networks, Devices and Fields, vol. 19, pp 87-103, 2006. -Article B: M. Gil, J. Bonache, I. Gil, J. García-García and F. Martín, "Miniaturization of planar microwave circuits by using resonant-type left handed transmission lines", IET Microwave Antennas and Propagation, Vol.1, pp. 73-79, 2007. -Article C: M. Gil, I. Gil, J. Bonache, J. García-García and F. Martín, "Metamaterial transmission lines with extreme impedance values", Microwave and Optical Technology Letters, vol. 48, pp. 2499-2505, 2006. -Article D*: M. Gil, J. Bonache, I. Gil, J. García-García and F. Martín, "Artificial Left¬handed Transmission Lines for Small Size Microwave Components: Application to Power Dividers", presented at 36th European Microwave Conference (EuMC), Manchester (UK), pp. 1135-1138, 2006. -Article E: M. Gil, J. Bonache, J. Selga, J. García-García, F. Martín, "Broadband resonant type metamaterial transmission lines ", IEEE Microwave and Wireless Components Letters, vol. 17, pp. 97-99, 2007. -Article F: M. Gil, J. Bonache, J. García-García, J. Martel and F. Martín, "Composite Right/Left-Handed Metamaterial Transmission Lines Based on Complementary Split-Rings Resonators and Their Applications to Very Wideband and Compact Filter Design", IEEE Transactions on Microwave Theory and Techniques, Vol. 55, No. 6, pp. 1296-1304, 2007. -Article G: M. Gil, J. Bonache, F. Martín, "Metamaterial Filters with Attenuation Poles in the Pass Band for Ultra Wide Band Applications", Microwave and Optical Technology Letters, Vol. 49, Issue 12, pp 2909-2913, 2007. -Article H : M. Gil, J. Bonache, J. García-García and F. Martín, "New Left Handed Microstrip Lines With Complementary Split Rings Resonators (CSRRs) Etched in the Signal Strip", IEEE MTT-S Int'l Microwave Symposium Digest, Honolulu (HA), USA, pp. 1419-1422, 2007. -Article I: M. Gil, J. Bonache and F. Martín, "Synthesis and applications of new left handed microstrip lines with complementary split-ring resonators etched on the signal strip", IET Microwaves, Antennas & Propagation, Vol. 2, Issue 4, pp. 324-330, 2008. -Article J: J. Bonache, M. Gil, O. García-Abad and F. Martín, "Parametric analysis of microstrip lines loaded with complementary split ring resonators", Microwave and Optical Technology Letters, Vol. 50 , Issue 8, pp. 2093-2096, 2008. -Article K*: M. Gil, J. Bonache, F. Martín. "Ultra Compact Band Pass Filters Implemented Through Complementary Spiral Resonators (CSRs)", IEEE MTT-S Int'l Microwave Symposium Digest, Atlanta, USA, pp.323-326, 2008. -Article L: M. Gil, J. Bonache, and F. Martín, "Metamaterial filters: A review", Metamaterials, vol. 2, pp. 186-197, 2008. -Article M*: M. Gil, C. Damm, A. Giere, M. Sazegar, J. Bonache, R. Jakoby, F. Martín. "Electrically Tunable SRRs at Microwave frequencies based on BST thick films". Electronic Letters (submitted).

<p>The field of metamaterials has gained much attention within the scientific community over the past decade. With continuing advances and discoveries leading the way to practical applications, metamaterials have earned the attention of technology based corporations and defense agencies interested in their use for next generation devices. With the fundamental physics developed and well understood, current research efforts are driven by the demand for practical applications, with a famous example being the well-known microwave "invisibility cloak." Gaining exotic electromagnetic properties from their structure as opposed to their</p><p>intrinsic material composition, metamaterials can be engineered to</p><p>achieve tailored responses not available using natural materials. With typical designs incorporating resonant and dispersive elements much smaller than the operating wavelength, a homogenization scheme is possible, which leads to the meaningful interpretation of effective refractive index, and hence electric permittivity and magnetic permeability. The typical metamaterial is composed of arrays of scattering elements embedded in a host matrix. The scattering elements are typically identical, and the electromagnetic properties of the medium can be inferred from the properties of the unit cell. This convenience allows the designer to engineer the effective electromagnetic parameters of the medium by modifying the size, shape, and composition of the unit cell.</p><p>This dissertation summarizes several key projects related to my research efforts in metamaterials. The main focus of this dissertation is to develop practical approaches to frequency tunable and reconfigurable metamaterials. Chapter one serves as a background and introduction to the field of metamaterials. The purpose of chapters two, three and four is to develop different methods to realize tunable metamaterials - a broad class of controllable artificially engineered metamaterials. The second chapter develops an approach to characterizing metamaterials loaded with RF MEMS switches. The third chapter examines the effects of loading</p><p>metamaterial elements with varactor diodes and tunable ferroelectric</p><p>thin film capacitors (BST) for external tuning of the effective medium parameters, and chapter four develops a more advanced method to control the response of metamaterials using a digitally addressable control network. The content of these chapters leads up to an interesting application featured in chapter five - a reconfigurable frequency selective surface utilizing tunable and digitally addressable tunable metamaterials. The sixth and final chapter summarizes the dissertation and offers suggestions for future work in tunable and reconfigurable metamaterials. It is my hope that this dissertation will provide the foundation and motivation for new researchers in the field of metamaterials. I am confident that the reader will gain encouragement from this work with the understanding that very interesting and novel practical devices can be created using metamaterials. May this work be of aid and motivation to their research pursuits.</p> / Dissertation

<p>Complex artificial materials (metamaterials) strongly interact with light and can be used to fabricate structures which mimic a material response that has no natural equivalent. Classical tools for the design of optical or radio frequency devices are often ill-suited to utilize such media or have shortcomings in their ability to capture important physics in the device behavior. Recently it has been demonstrated that the structure of Maxwell's equations can be used to exploit this newly available freedom. By leveraging the `form-invariance' of Maxwell's equations under coordinate transforms, it is possible to develop material distributions in which light will behave as though flowing through warped coordinates. This design process is termed `transformation optics' and has inspired the creation of many novel electromagnetic structures such as the invisibility cloak.</p><p>In this dissertation the tools used in the field of transformation optics will be explored and expanded. Several new designs are discussed, each of which expands upon the ideas that have previously been employed in the field. To begin, I show that the explicit use of a transformation which extends throughout all space may be used to reduce the overall size of an optical device without changing its optical properties. A lens is chosen as a canonical device to demonstrate this behavior. For this work I provided the original idea for a compressing transformation as well as its dielectric-only implementation. I then mentored Dan Roberts as he confirmed the device properties through simulation. I further demonstrate that currents may be succesfully employed within the framework of transformation optics-resulting in novel antenna designs. For this work I suggested handling the sheet currents as the limit of a volumetric current density. I also demonstrated how an intermediate coordinate system could be used to easily handle the types of transformatios which were being explored.</p><p>For a particular functionality the choice of transformation is, in general, not unique. It is natural, then, to seek optimized transformations which reduce the complexity of the final structure. It was recently demonstrated that for some transformations a numerical scheme could be employed to find quasi-conformal transformations for which the requisite complex material distribution could be well approximated by an isotropic, inhomogeneous media. This process was previously used to demonstrate a carpet cloak-a device which masks a bump in a mirror surface. Unlike the more common transformation optical media, which exhibit strong losses at high frequencies, isotropic designs can be readily made to function at infrared or even optical frequencies.</p><p>The prospect of leveraging transformation optics in devices which operate at high frequencies, into the infrared and visible, motivates the use of quasi-conformal transformations in lens design. I demonstrate how transformation optics can be used to take a classical lens design based on spherical symmetry, such as a Luneburg lens, and warp it to suit the requirements of a planar imaging array. I report on the experimental demonstration of this lens at microwave frequencies. In the final design a lens is demonstrated in a two-dimensional field mapping waveguide to have a field of view of ~140 degrees and a bandwidth exceeding a full decade. In this work I proposed the idea of using the inverse of the quasi-conformal transform to arrive at the lens index profile. I performed all necessary simulations and wrote ray tracing code to confirm the properties of the lens. I proposed the metamaterial realization of the lens and performed the necessary retrievals for material design. I wrote code which would create the layout for an arbitrary gradient index structure in a standard computer aided drafting format. I fabricated three lenses-two of which are described in this thesis-and took all of the data shown in the thesis.</p><p>The most well known example of a transformation optical device is the invisibility cloak. Despite the great deal of attention paid to the cloak in the literature, the most natural way in which to quantify the efficacy of the cloak-its cross-section-has never been experimentally determined. This measurement is of practical interest because the cloak provides a useful canonical example of a medium which relies on the unique properties of metamaterials-strong anisotropy, inhomogeneity and both magnetic and electric response. Thus, a cloaking cross-section measurement provides a useful way to quantify advancements in the effective medium theories which form the basis for metamaterials. I report on the first such measurements, performed on the original microwave cloaking design. The experiments were carried out in a two-dimensional TE waveguide. Explicit field maps are used to determine the Bessel decomposition of the scattered wave. It is found that the cloak indeed reduces the scattering cross-section of a concealed metal cylinder in a frequency band from 9.91 to 10.14 GHz. The maximum cross-section reduction was determined to be 24%. The total cross-section and the Bessel decomposition of the scattered wave are compared to an analytical model for the cloaking design which assumes a discrete number of loss-less, homogenized cylinders. While the qualitative features of the cloak-a reduced cross-section at the cloaking frequency-are realized, there is significant deviation from the homogenized calculation. These deviations are associated with loss and inaccuracies of the effective-medium-model for metamaterials. In this work I proposed of direct integration of the fields to perform cross-section measurements. I worked out the necessary formulas to determine the coefficients in the Bessel expansion and the resulting scattering cross-section. I mentored an undergraduate student, Dan Gaultney, who scripted the application of the cross-section analysis and took the necessary data. All of the data in this thesis, however, is based on my own implementation of the data analysis.</p> / Dissertation

Thesis (M.Phil.)--City University of Hong Kong, 2009. / "Submitted to Department of Electronic Engineering in partial fulfillment of the requirements for the degree of Master of Philosophy." Includes bibliographical references.

The control and manipulation of infrared (IR) radiation beyond the capabilities of natural materials using silicon carbide (SiC), metamaterials, or a combination thereof, is presented. Control is first demonstrated using SiC, a polar crystal that exhibits a dielectric permittivity less than zero in the mid-IR range, through the excitation of tightly confined surface phonon-polaritons (SPPs), thus enabling a multitude of applications not possible with conventional dielectrics. Optimal, or critical coupling to SPPs is explored in SiC films through Otto-configuration attenuated total reflection. One practical application based on Otto-coupled SPPs is presented: IR refractive index sensing is shown for three pL-scale fluid analytes. It is then demonstrated that when two SiC films are brought to a few-micron separation, IR radiation can excite surface modes that possess phase velocities near the speed of light, a property required for efficient table-top particle accelerators. Metamaterials are engineered with subwavelength structure and possess optical properties not found in nature. Two such metamaterials will be introduced: metal films perforated with arrays of rectangular holes display the ability to control IR light polarization through spoof surface plasmon excitation, and metal/dielectric multilayers patterned with subwavelength-pitch corrugations display frequency-tunable, wide-angle, perfect IR absorption. Two experiments, which have implications in polarization control and thermal emission, combine the benefits of SiC with those of metamaterials: extraordinary optical transmission and absorption are observed in SiC hole arrays, and the design of individual SiC antennas permits the control of the bulk metamaterial responses of impedance and absorption/emission. Finally, a new optical beamline based on Fourier transform IR spectroscopy was designed, built, characterized, and implemented, serving as the major experimental objective of this dissertation. The novel beamline, which confines radiation to a 200-micron diameter and enables angle-dependent IR spectroscopy, was verified using multiple metamaterial structures. / text

Metals interact very differently with light than with radio waves and finite conductivities and losses often limit the way that RF concepts can be directly transferred to higher frequencies. Plasmonic materials are investigated here for various optical applications, since they can interact, confine and focus light at the nanoscale; however, regular plasmonic devices are severely limited by frequency dispersion and absorption, and confined signals cannot travel along plasmonic lines over few wavelengths. For these reasons, novel concepts and materials should be introduced to successfully manipulate and radiate light in the same flexible way we operate at lower frequencies. In line with these efforts, optical metamaterials exploit the resonant wave interaction of collections of plasmonic nanoparticles to produce anomalous light effects, beyond what naturally available in optical materials and in their basic constituents. Still, these concepts are currently limited by a variety of factors, such as: (a) technological challenges in realizing 3-D bulk composites with specific nano-structured patterns; (b) inherent sensitivity to disorder and losses in their realization; (c) not straightforward modeling of their interaction with nearby optical sources. In this study, we develop a novel paradigm to use single-element nanoantennas, and composite nanoantenna arrays forming two-dimensional metasurfaces and three-dimensional metamaterials, to control and manipulate light and its polarization at the nanoscale, which can possibly bypass the abovementioned limitations in terms of design procedure and experimental realization. The final design of some of the metamaterial concepts proposed in this work was inspired by biological species, whose complex structure can exhibit superior functionalities to detect, control and manipulate the polarization state of light for their orientation, signaling and defense. Inspired by these concepts, we theoretically investigate and design metasurfaces and metamaterial models with the help of fully vectorial numerical simulation tools, and we are able to outline the limitations and ultimate conditions under which the average optical surface impedance concept may accurately describe the complex wave interaction with planar plasmonic metasurfaces. We also experimentally explore various technological approaches compatible with these goals, such as the realization of lithographic single-element nanoantenna and nanoantenna arrays with complex circuit loads, periodic arrays of plasmonic nanoparticles or nanoapertures, and stacks of rotated plasmonic metasurfaces. At the conclusion of this effort, we have theoretically analyzed, designed and experimentally realized and characterized the feasibility of using discrete metasurfaces to realize phenomena and performance that are not available in natural materials, oftentimes inspired by the biological world. / text

The potential of terahertz time domain spectroscopy has until recently been neglected in the field of the ultrafast magnetism. At the same time this technique can serve as a useful complementary tool with respect with conventional methods to investigate ultrafast magnetization dynamics. This thesis aims to implement time domain terahertz spectroscopy to observe high frequency spin waves excited optically in different magnetic systems. This work covers several distinct phenomena related to the study of spin waves (magnonics) at terahertz frequencies. The generation of transient broadband nonlinear magnetization via inverse Faraday effect in terbium gallium garnet is described in chapter 4. We demonstrate a remarkable discrepancy of at least two orders of magnitude between the strengths of the direct and inverse Faraday effects, thereby challenging the commonly accepted understanding of their relationship. Additionally, a striking nonlocality of the optical response is found. In chapter 5 the results of THz absorption spectroscopy of the terbium gallium garnet are reported. The garnet exhibits an intricate paramagnetic state with several magnetic sub-lattices at cryogenic temperatures under the application of strong magnetic fields. Some precessional modes of these sub-lattices were measured. The components of the g-tensor of terbium ions were extracted from the data. In chapter 6 the ultrafast magnetization dynamics of thulium orthoferrite, studied my means of terahertz spectroscopy, is described. It is demonstrated that terahertz response of the orthoferrite provides crucial additional information with respect to the optical pump-probe signal. A novel exchange driven mechanism of optical manipulation of the magnetic state is demonstrated. Finally, chapter 7 is a theoretical discussion of so called planar magnonic metamaterials. It is shown that the arrays of ferromagnetic films may exhibit negative refraction index at sub-terahertz frequencies, provided the mechanism of spin wave quantization is introduced. The thesis ends with a brief conclusions chapter where a short summary of the results is given. Some possible future extensions of the conducted research are drawn as well.