Anisotropic Artificial Substrates for Microwave Applications

RÉSUMÉ Les matériaux anisotropes possèdent des propriétés électromagnétiques qui sont différentes dans différentes directions, ce qui résulte en des degrés de liberté supplémentaires pour la conception de dispositifs électromagnétique et mène à des applications. Certains matériaux anisotropes peuvent être trouvés dans la nature, comme les matériaux ferrimagnétiques, alors que d'autres peuvent être conçus artificiellement pour des applications spécifiques. Ces matériaux artificiels sont des structures composites qui sont faites d'implants métalliques insérés dans un médium hôte. Ces structures peuvent être considérées comme des matériaux effectifs nouveaux et peuvent posséder des propriétés que l'on ne retrouve pas dans la nature comme un indice de réfraction négatif, une chiralité ou une bi-anisotropie; ils sont donc appelés métamatériaux. Dû à la grande diversité d'implants qu'il est possible de concevoir, ces matériaux sont prometteurs pour la conception de dispositifs uniques et novateurs comme de nouvelles antennes, des antennes miniaturisées, des dispositifs non-réciproques, des analyseurs de signaux analogiques et des dispositifs de génie biomédical. Puisque dans les matériaux artificiels l'effet des implants dans le médium hôte n'est pas le même dans toutes les directions, ces matériaux ont la plupart du temps des caractéristiques anisotropes qui peuvent être contrôlées par les propriétés des implants. Cette propriété amène des degrés de liberté supplémentaires dans la conception de dispositifs nouveaux. L'effet d'anisotropie dans les structures artificielles est plus évident dans la plupart des substrats artificiels anisotropes à cause de leur structure planaire 2D. Une analyse électromagnétique rigoureuse des substrats artificiels anisotropes est requise afin de mieux comprendre leurs propriétés, ce qui est essentiel pour proposer des applications. L'insuffisance de l'analyse disponible dans la littérature a servi de motivation pour cette thèse dont l'objectif est d'effectuer l'analyse électromagnétique rigoureuse de substrats artificiels anisotropes dans le but d'explorer des applications. Afin de mieux comprendre les propriétés de l'anisotropie des substrats artificiels, leur méthode d'analyse et leurs applications, il peut être utile de d'abord mieux comprendre l'anisotropie de substrats naturels existant comme les matériaux ferrimagnétiques. Cette approche peut aussi mener à de nouvelles applications de ces matériaux anisotropes naturels. De plus, afin d'étudier certaines propriétés et applications des substrats anisotropes, certains aspects mal compris des matériaux isotropes doivent tout d'abord être éclaircis. Basée sur les objectifs et la méthodologie décrits ci-haut, la présente thèse contribue les réalisations et avancements suivants au domaine du génie micro-ondes. Le conducteur électromagnétique parfait (PEMC) comme condition frontière est un concept électromagnétique nouveau et fondamental. C'est une description généralisée des conditions aux frontières électromagnétiques incluant le conducteur électrique parfait (PEC) et le conducteur magnétique parfait (PMC). De par ses propriétés fondamentales, le PEMC a le potentiel de rendre possible plusieurs applications électromagnétiques. Cependant, jusqu'à maintenant le concept de condition frontière PEMC était demeuré un concept théorique et n'avait jamais été réalisé en pratique.----------ABSTRACT Anisotropic materials exhibit different electromagnetic properties in different directions and therefore they provide some degrees of freedom in the design of electromagnetic devices and enable many applications. Some kinds of anisotropic materials are available in the nature such as ferrimagnetic materials, while many others can be artificially designed for specific applications. The artificial materials are composite structures made of sub-wavelength metallic implants in a host medium, which constitute novel effective materials. These materials may exhibit properties not readily available in the nature, such as negative refractive index, chirality or bi-anisotropy, and therefore are called metamaterials. Due to the diversity of their possible implants, they have a great potential in unique and novel components, such as specific antennas, miniaturized antennas, non-reciprocal devices, analog signal processors, and biomedical engineering devices. Since in most of the artificial materials, the effect of the implants in the host medium is not the same in all the directions, these materials exhibit anisotropic characteristics which can be controlled by the properties of the implant. This characteristic provides some additional degrees of freedom in the design of novel devices. The anisotropy effect in the artificial structures is more evident in most of the anisotropic artificial substrates due to their 2D planar structure. Rigorous electromagnetic analysis of the anisotropic artificial substrates is required for gaining a better understanding of their properties which is essential for proposing novel applications. Insufficient available analysis in the literature has motivated this thesis whose objective is to perform rigorous electromagnetic analysis of the anisotropic artificial substrates towards exploring their applications. To acquire more insight into the anisotropic properties of artificial substrates, their analysis method, and their applications, it is useful to first better understand anisotropy of existing natural substrates such as ferrimagnetic materials. This approach may also lead to novel applications of the natural anisotropic materials. In addition, to investigating some of properties and applications of the anisotropic substrates, foremost we may need to clarify some unclear aspects regarding the isotropic materials. Based on the objectives and methodology of the thesis which were explained above, this thesis contributes to the following achievements and advances in microwave engineering. The perfect electromagnetic conductor (PEMC) boundary is a novel fundamental electromagnetic concept. It is a generalized description of the electromagnetic boundary conditions including the perfect electric conductor (PEC) and the perfect magnetic conductor (PMC) and due to its fundamental properties, it has the potential of enabling several electromagnetic applications. However, the PEMC boundaries concept had remained at the theoretical level and has not been practically realized. Therefore, motivated by the importance of this electromagnetic fundamental concept and its potential applications, the first contribution of this thesis is focused on the practical implementation of the PEMC boundaries by exploiting Faraday rotation principle and ground reflection in the ferrite materials which are intrinsically anisotropic. As a result, this thesis reports the first practical approach for the realization of PEMC boundaries

Asymmetrical Stripline Based Method for the Electromagnetic Characterization of Metamaterials

International audienceAn experimental method for obtaining the effective electromagnetic parameters of metamaterials is presented. The measurement cell consists in an asymmetric stripline which satisfies certain conditions required for the characterization of this type of materials. The advantages of this cell, its electromagnetic analysis and preliminary experimental and simulated results are shown

Disentangled ultra-high molecular weight polyethylene and its nanocomposites: relaxation dynamics, entanglement formation and anisotropic properties due to orientation

In the present doctoral research, the chain relaxations and dynamics present in linear disentangled ultra-high molecular weight polyethylene (both pure and as a composite) were investigated and presented. Considering its disentangled character, the relaxation dynamics and the formation of entanglements were primarily analysed. Additionally, the presence of fillers and the effect of uniaxial orientation were also studied. With respect to the chain relaxation analysis, torsional rheology and broadband dielectric spectroscopy were employed to identify the disentangled amorphous phase in comparison with fully entangled samples. The rheological results gave significantly different relaxation behaviour for the disentangled sample, affecting all the mechanical processes namely αc-, β- and -relaxations, with the latter exhibiting a non-Arrhenius temperature dependence, indicative of the dynamic glass-to-rubber transition. This indication would support previous studies that would locate the glass transition temperature of linear polyethylene around -100oC. The dielectric analysis was only possible in the presence of Al2O3 catalytic ashes and expanded further the relaxation investigation by showing two types of interfacial polarization attributed to the disentangled and entangled amorphous phases. [Continues.

Numerical Analysis of a Roadway Piezoelectric Harvesting System

Highways, streets, bridges, and sidewalks with heavy traffic dissipate a considerable amount of waste mechanical energy every day. Piezoelectric energy harvesting devices are a very promising technology that can convert the waste mechanical energy to clean and renewable energy to enhance the sustainability of infrastructures. Research efforts in large-scale energy harvesting have led to the advancement of piezoelectric devices to the point that large-scale implementation is starting to become more feasible. The energy harvested by these devices can be used in many ways such as providing heating or cooling, melting ice, monitoring structural conditions in bridges and tunnels, and powering wireless sensors. Additionally, these devices contain an off-grid power system meaning that it has a standalone battery connected to it. This is highly beneficial in areas where city power sources are not readily available. The objective of this thesis is to study the energy harvesting potential of a dual-mode piezoelectric generator to develop a roadway piezoelectric harvesting system with ultra-high-power density and efficiency. The dual-mode harvester is made up of APC 855 with two different modes, 33-mode and 15-mode. In order to structurally optimize the design, finite element analysis was performed using ANSYS Mechanical and APDL. Static and transient simulations for each model with detailed input conditions were evaluated to determine the optimal configuration. Two different vehicle sizes were evaluated to assess the load effect on the harvested power. In addition, open circuit and closed-circuit models with different resistance values were compared to determine the resistance that produces the highest energy. Furthermore, a comparison between the different polarization directions for the 15-mode harvester was investigated to determine the optimal polarization direction

Electromagnetic Wave Theory and Applications

Contains table of contents for Section 3, research summary and reports on six research projects.Joint Services Electronics Program (Contract DAAL 03-86-K-0002)Joint Services Electronics Program (Contract DAAL 03-89-C-0001)U.S. Navy - Office of Naval Research (Contract N00014-86-K-0533)National Science Foundation (Contract ECS 86-20029)U.S. Army Research Office (Contract DAAL03 88-K-0057)International Business Machine CorporationSchlumberger-Doll ResearchNational Aeronautics and Space Administration (Contract NAG 5-270)U.S. Navy - Office of Naval Research (Contract N00014-83-K-0258)National Aeronautics and Space Administration (Contract NAG 5-769)U.S. Army Corps of Engineers - Waterways Experimental Station (Contract DACA39-87-K-0022)Simulation TechnologiesU.S. Air Force - Rome Air Development Center (Contract F19628-88-K-0013)U.S. Navy - Office of Naval Research (Contract N00014-89-J-1107)Digital Equipment Corporatio

Size reduction of microstrip antennas using left-handed materials realized by complementary split-ring resonators

Recently, metamaterials (MTMs) engineered to have negative values of permittivity and permeability, resulting in a left-handed system, have provided a new frontier for microwave circuits and antennas with possibilities to overcome limitations of the right-handed system. Microwave circuit components such as waveguides, couplers, power dividers and filters, constructed on left-handed materials, have demonstrated properties of backward coupling, phase compensation, reduced sizes, and propagation of evanescent modes. However, there is very limited work to date, on the microstrip antennas with metamaterials. Microstrip antenna is widely used for its low-profile, simplicity of feed and compatibility with planar microstrip circuitry. As the trend towards miniaturization of electronic circuitry continues, antennas remain as the bulkiest part of wireless devices. There are three primary objectives to the present work: 1. Explore the possibility of miniaturizing microstrip patch antennas using left-handed materials through phase-compensation 2. Achieve negative permittivity using Complementary Split-Ring Resonators (CSRR) 3. Implement CSRR in the ground plane of a rectangular patch antenna, and validate through simulation and measurement A rectangular patch antenna with a combined DPS-DNG substrate has been analyzed with the cavity model, from which the condition for mode propagation has been derived. Criteria for ‘electrically small’ patch, using phase-compensation have been developed and propagating modes that satisfy these criteria have been obtained. With an objective to design practically realizable antennas, amongst several available LHM structures, the Complementary Split Ring Resonators (CSRR) has been chosen, primarily for the ease of implementation in the ground plane. CSRRs are periodic structures which alter the bulk effective permittivity of a host medium in which they are embedded. The effective permittivity becomes negative in a certain frequency band defined as a ‘stop-band’. In the present work the frequency response of the CSRR and the ‘stop-band’ has been determined using a full wave solver, from which, effective permittivity of the composite with CSRRs has been obtained by parameter extraction. Finally, several combinations of patch and CSRR in the ground plane have been designed and constructed in the X-band frequency range. Measurements of input characteristics and directivity have been validated through simulation by Ansoft Designer and HFSS. It has been observed that the best designs are achieved when the ‘stop-band’ of the CSRR corresponds to the desired resonant frequency of the antenna. Under these conditions, a size reduction of up to fifty percent has been achieved and it is noted that the back lobe is negligible and the directivity is comparable to that of a right-handed microstrip antenna

Green's Functions for Vertical Current Sources Embedded in Uniform Waveguides or Cavities Filled with Multilayered Media

A modal series representation of spatial-domain electric field Green's functions for arbitrarily oriented electric current sources embedded in shielded multilayer media is presented. The Green's func- tions associated with planar excitations are briefly recalled, and the method to compute them is generalized to vertical current sources, yielding new components of the Green's function necessary for the anal- ysis of vertical metallizations embedded in waveguides or cavities.Universidad Politécnica Federal de Lausanne (EPFL

Heterogeneous mixtures for synthetic antenna substrates

Heterogeneous mixtures have the potential to be used as synthetic substrates for antenna applications giving the antenna designer new degrees of freedom to control the permittivity and/or permeability in three dimensions such as by a smooth variation of the density of the inclusions, the height of the substrate and the manufacture the whole antenna system in one process. Electromagnetic, fabrication, environmental, time and cost advantages are potential especially when combined with nano-fabrication techniques. Readily available and cheap materials such as Polyethylene and Copper can be used in creating these heterogeneous materials. These advantages have been further explained in this thesis. In this thesis, the research presented is on canonical, numerical and measurement analysis on heterogeneous mixtures that can be used as substrates for microwave applications. It is hypothesised that heterogeneous mixtures can be used to design bespoke artificial dielectric substrates for say, patch antennas. The canonical equations from published literature describing the effective permittivity, ε_eff and effective permeability, μ_eff of heterogeneous mixtures have been extensively examined and compared with each other. Several simulations of homogenous and heterogeneous media have been carried out and an extraction/inversion algorithm applied to find their ε_eff and μ_eff. Parametric studies have been presented to show how the different variables of the equations and the simulations affect the accuracy of the results. The extracted results from the inversion process showed very good agreement with the known values of the homogenous media. Numerically and canonically computed values of ε_eff and μ_eff of various heterogeneous media were shown to have good agreement. The fabrication techniques used in creating the samples used in this research were examined, along with the different measurement methods used in characterising their electromagnetic properties via simulations and measurements. The challenges faced with these measurement methods were explained including the possible sources of error. Patch antennas were used to investigate how the performance of an antenna may be affected by heterogeneous media with metallic inclusions. The performance of the patch antenna was not inhibited by the presence of the metallic inclusions in close proximity. The patch measurement was also used as a measurement technique in determining the ε_eff of the samples

Optical Response in Planar Heterostructures: From Artificial Magnetism to Angstrom-Scale Metamaterials

The idea of expanding the range of properties of natural substances with artificial matter was introduced by V. G. Veselago in 1967. Since then, the field of metamaterials has dramatically advanced. Man-made structures can now exhibit a plethora of extraordinary electromagnetic properties, such as negative refraction, optical magnetism, and super-resolution imaging. Typical metamaterial motifs include split ring resonators, dielectric and plasmonic particles, fishnet and wire arrays. The principle of operation of these elements is now well-understood, and they are being exploited for practical applications on a global scale, ranging from telecommunications to sensing and biomedicine, in the radio frequency and terahertz domains. Accessing and controlling optical and near-infrared phenomena requires scaling down the dimensions of meta- materials to the nanometer regime, pushing the limits of state-of-the-art nano- lithography and requiring structurally less complex geometries. Hence, within the last decade, research in metamaterials has revisited a simpler, lithography- free structure, particularly planar arrangements of alternating metal and dielectric layers, termed hyperbolic metamaterials. Such media are readily realizable with well-established thin-film deposition techniques. They support a rich canvas of properties ranging from surface plasmonic propagation to negative refraction, and they can enhance the photoluminescence properties of quantum emitters at any frequency range. Here, we introduce a computational approach that allows tailoring the dielectric and magnetic effective properties of planar metamaterials. Previously, planar hyperbolic metamaterials have been considered non-magnetic. In contrast, we show theoretically and experimentally that planar arrangements com- posed of non-magnetic constituents can be engineered to exhibit a non-trivial magnetic response. This realization simplifies the structural requirements for tailoring optical magnetism up to very high frequencies. It also provides access to previously unexplored phenomena, for example artificially magnetic plasmons, for which we perform an analysis on the basis of available materials for achieving polarization-insensitive surface wave propagation. By combining the concept of metamaterials’ homogenization with previous transfer matrix approaches, we develop a general computational method for surface waves calculations that is free of previous assumptions, for example infinite or purely periodic media. Furthermore, we theoretically demonstrate that hyperbolic metamaterials can be dynamically tunable via carrier injection through external bias, using transparent conductive oxides and graphene, at visible and infrared frequencies, respectively. Lastly, we demonstrate that planar graphene-based van der Waals heterostructures behave effectively as supermetals, exhibiting reflective properties that surpass the reflectivity of gold and silver that are currently considered the state-of-the-art materials for mirroring applications in space applications. The (meta)materials we introduce exhibit an order-of-magnitude lower mass density, making them suitable candidates for future light-sail technologies intended for space exploration.</p