Compact electric-LC resonators for metamaterials

Alternative designs to an electric-LC (ELC) resonator, which is a type of metamaterial inclusion, are presented in this article. Fitting the resonator with an interdigital capacitor (IDC) helps to increase the total capacitance of the structure. In effect, its resonance frequency is shifted downwards. This implies a decreased overall resonator size with respect to its operating wavelength. As a result, the metamaterial, composed of an array of IDC-loaded ELC resonators with their collective electromagnetic response, possesses improved homogeneity and hence is less influenced by diffraction effects of individual cells. The impact of incorporating an IDC into ELC resonators in terms of the electrical size at resonance and other relevant properties are investigated through both simulation and experiment.Comment: 5 pages, 5 figure

Electromagnetic field energy density in artificial microwave materials with negative parameters

General relations for the stored reactive field energy density in passive linear artificial microwave materials are established. These relations account for dispersion and absorption effects in these materials, and they are valid also in the regions where the real parts of the material parameters are negative. These relations always give physically sound positive values for the energy density in passive metamaterials. The energy density and field solutions in active metamaterials with non-dispersive negative parameters are also considered. Basic physical limitations on the frequency dispersion of material parameters of artificial passive materials with negative real parts of the effective parameters are discussed. It is shown that field solutions in hypothetical materials with negative and non-dispersive parameters are unstable

AMM loaded Y-Shaped UWB Antenna for Health Monitoring Systems

The Ultra-wideband antennas are suitable for low power and high data rate applications for short-range communication. WBAN utilizes human body as the transmission channel. In this paper, a transmission line based artificial magnetic material is deployed into the UWB antenna in order to prevent interference problem with other wireless system in the vicinity. The complementary geometry of proposed AMM is etched into the Y-shaped UWB antenna. The antenna performance is measured for Y-shaped patch with and without inclusion. The results are presented in terms of Return Loss, VSWR, Radiation Pattern, E-Field Distribution and Radiated power. The designed antenna has application in Body Area Networks(BAN) and Personal Area Network (PAN) for heath monitoring systems and security purpose

Metamaterial

In-depth analysis of the theory, properties and description of the most potential technological applications of metamaterials for the realization of novel devices such as subwavelength lenses, invisibility cloaks, dipole and reflector antennas, high frequency telecommunications, new designs of bandpass filters, absorbers and concentrators of EM waves etc. In order to create a new devices it is necessary to know the main electrodynamical characteristics of metamaterial structures on the basis of which the device is supposed to be created. The electromagnetic wave scattering surfaces built with metamaterials are primarily based on the ability of metamaterials to control the surrounded electromagnetic fields by varying their permeability and permittivity characteristics. The book covers some solutions for microwave wavelength scales as well as exploitation of nanoscale EM wavelength such as visible specter using recent advances of nanotechnology, for instance in the field of nanowires, nanopolymers, carbon nanotubes and graphene. Metamaterial is suitable for scholars from extremely large scientific domain and therefore given to engineers, scientists, graduates and other interested professionals from photonics to nanoscience and from material science to antenna engineering as a comprehensive reference on this artificial materials of tomorrow

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

Tunable antenna design by metamaterial structures operating at S band

Un “metamaterial” por su definición ampliamente aceptada es una estructura construida artificialmente que obtiene sus propiedades materiales de su estructura en lugar de la composición de su material intrínseco. El ámbito de los materiales ha ganado mucha atención dentro de la comunidad científica en la última década. Con los continuos avances y descubrimientos conducen al camino de las aplicaciones prácticas; los metamateriales han ganado la atención de las empresas de base tecnológica y los organismos de defensa interesados en el uso de dispositivos de próxima generación. Las superficies selectivas en frecuencia (FSS) son una variedad potente de metamateriales que, dependiendo de la geometría de la superficie, se pueden utilizar para diseñar propiedades de radiación específicas tales como la emisión direccional, emisión polarizada circular y lineal, y la selectividad espectral. Los elementos de la FSS pueden ser tanto elementos metálicos sólidos como elementos metálicos con aberturas, y en los diseños tradicionales, la superficie selectiva en frecuencia (FSS) normalmente opera en torno a la resonancia de media longitud de onda de los elementos. En este proyecto se va a utilizar una superficie selectiva de frecuencia (FSS) con el fin de realizar metamateriales sintonizables -una amplia clase de metamateriales controlables diseñados artificialmente, y desarrollar una antena sintonizable que trabaje a 2.4 GHz. La FSS consiste en una serie de elementos rectángulos cargados con varactores y capacitores con una película delgada de material ferroeléctrico sintonizable (BST) para el ajuste externo de los parámetros de medio efectivo. Por lo tanto se diseñan unos varactores BST que son colocados entre los elementos metálicos que conforman la FSS. El efecto de la superficie selectiva en frecuencia es estudiado en dos antenas diferentes – antena ELPOSD (End-Loaded Planar Open-Sleeve Dipole) y una antena de parche microstrip. La antena ELPOSD consiste en un dipolo plano convencional con dos elementos parásitos muy juntos, y una carga en cada extremo del dipolo. Los beneficios principales de este tipo de antenas es que, además del rendimiento similar de la antena POSD (Planar Open-Sleeve Dipole) convencional, las antenas ELPOSD pueden ser miniaturizadas. La antena parche utilizada en este trabajo es un elemento metálico cuadrado plano alimentado a través de una línea microstrip. El material ferroeléctrico Barium Strontium Titanate (BST) es un material muy bien conocido hasta el momento. Para diseñar los varactores se utiliza una película delgada de BST, junto con los capacitores interdigitales (IDCs) que se utilizan en la capa del metal. La antena general consiste en un sustrato de múltiples capas donde en una capa se encuentra la Superficie selectiva en frecuencia (FSS) sintonizable y en otra la antena dipolo o antena de parche. La capacidad de la FSS completa varía introduciendo el material ferroeléctrico BST en el varactor. Como puede verse en los resultados, variando la permitividad del material BST de 200 a 300 se consigue una variación en frecuencia de 4.15 GHz a 3.5 GHz con una distancia alrededor de 100 MHz entre frecuencias resonantes. Esto equivale a una variación de la frecuencia alrededor del 8% entre los valores de permitividad adyacentes.A “metamaterial” by its widely accepted definition is an artificially engineered structure that gains its material properties from its structure as opposed to its intrinsic material composition. 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. Frequency Selective Surfaces (FSS) are a potent variety of metamaterials that, depending on the surface geometry, can be used to engineer specific radiation properties such as directional emission, linear and circular polarized emission, and spectral selectivity. The elements of the FSS can either be patches or apertures, and in traditional designs, the FSS usually operates around the half-wavelength resonance of the elements. In this project a Frequency Selective Surface (FSS) is used in order to realize tunable metamaterials –a broad class of controllable artificially engineered metamaterials, and develop a tunable antenna operating at 2.4 GHz. The FSS consist of an array of square patches loaded with varactors and tunable ferroelectric thin film capacitors (BST) for external tuning of the effective medium parameters. Therefore a BST varactor is designed and located between the patches of the FSS. The effect of the Frequency Selective Surface is studied in two different antennas –an End-Loaded Planar Open-Sleeve Dipole (ELPOSD) and a Square Patch. An End-Loaded Planar Open-Sleeve Dipole consist of a conventional planar dipole with two closely spaced parasitic elements, or sleeves, and loaded stubs at the end of the dipole. The main benefits of this type of antennas is that in addition to retaining similar performance to that of conventional planar open-sleeve dipole, end-loaded planar opensleeve dipole (ELPOSD) antennas can be miniaturized. The Square Patch antenna used in this work is a conventional planar square patch feed with a microstrip line. Barium Strontium Titanate (BST) is a well-known ferroelectric material and up to now. A BST thin film is used to design the varactors, along with the Interdigital Capacitors (IDCs) geometry used in the metal layer. The overall antenna consists of a multilayer substrate with tunable FSS layer and dipole or patch antenna. The capacitance of the whole FSS changes introducing the BST ferroelectric material into the varactor. As can be seen in the results, by varying the BST permittivity from 200 to 300, a variation in frequency is achieved from 1.98 GHz to 1.717 GHz with a distance around 100 MHz between resonance frequencies, which equals a variation of the frequency about 8% in the adjacent permittivity values.Ingeniería de TelecomunicaciónTelekomunikazio Ingeniaritz

Artificial Magnetic Materials: Limitations, Synthesis and Possibilities

Artificial magnetic materials (AMMs) are a type of metamaterials which are engineered to exhibit desirable magnetic properties not found in nature. AMMs are realized by embedding electrically small metallic resonators aligned in parallel planes in a host dielectric medium. In the presence of a magnetic field, an electric current is induced on the inclusions leading to the emergence of an enhanced magnetic response inside the medium at the resonance frequency of the inclusions. AMMs with negative permeability are used to develop single negative, or double negative metamaterials. AMMs with enhanced positive permeability are used to provide magneto-dielectric materials at microwave or optical frequencies where the natural magnetic materials fail to work efficiently. Artificial magnetic materials have proliferating applications in microwave and optical frequency region. Such applications include inversely refracting the light beam, invisibility cloaking, ultra miniaturizing and frequency bandwidth enhancing low profile antennas, planar superlensing, super-sensitive sensing, decoupling proximal high profile antennas, and enhancing solar cells efficiency, among others. AMMs have unique enabling features that allow for these important applications. Fundamental limitations on the performance of artificial magnetic materials have been derived. The first limitation which depends on the generic model of permeability functions expresses that the frequency dispersion in an AMM is limited by the desired operational bandwidth. The other constraints are derived based on the geometrical limitations of inclusions. These limitations are calculated based on a circuit model. Therefore, a formulation for permeability and magnetic susceptibility of the media based on a circuit model is developed. The formulation is in terms of a geometrical parameter that represents the geometrical characteristics of the inclusions such as area, perimeter and curvature, and a physical parameter that represents the physical, structural and fabrication characteristics of the medium. The effect of the newly introduced parameters on the effective permeability of the medium and the magnetic loss tangent are studied. In addition, the constraints and relations are used to methodically design artificial magnetic material meeting specific operational requirements. A novel design methodology based on an introduced analytical formulation for artificial magnetic material with desired properties is implemented. The synthesis methodology is performed in an iterative four-step algorithm. In the first step, the feasibility of the design is tested to meet the fundamental constraints. In consecutive steps, the geometrical and physical factors which are attributed to the area and perimeter of the inclusion are synthesized and calculated. An updated range of the inclusion's area and perimeter is obtained through consecutive iterations. Finally, the outcome of the iterative procedure is checked for geometrical realizability. The strategy behind the design methodology is generic and can be applied to any adopted circuit based model for AMMs. Several generic geometries are introduced to realize any combination of geometrically realizable area and perimeter (s,l) pairs. A realizable geometry is referred to a contour that satisfies Dido's inequality. The generic geometries introduced here can be used to fabricate feasible AMMs. The novel generic geometries not only can be used to enhance magnetic properties, but also they can be configured to provide specific permeability with desired dispersion function over a certain frequency bandwidth with a maximum magnetic loss tangent. The proposed generic geometries are parametric contours with uncorrelated perimeter and area function. Geometries are configured by tuning parameters in order to possess specified perimeter and surface area. The produced contour is considered as the inclusion's shape. The inclusions are accordingly termed Rose curve resonators (RCRs), Corrugated rectangular resonators (CRRs) and Sine oval resonators (SORs). Moreover, the detailed characteristics of the RCR are studied. The RCRs are used as complementary resonators in design of the ground plane in a microstrip stop-band filter, and as the substrate in design of a miniaturized patch antenna. The performance of new designs is compared with the counterpart devices, and the advantages are discussed

Decoupled and Descattered Monopole MIMO Antenna Array with Orthogonal Radiation Patterns

This chapter introduces a novel design concept to reduce mutual coupling among closely-spaced antenna elements of a MIMO array. This design concept significantly reduces the complexity of traditional/existing design approaches such as metamaterials, defected ground plane structures, soft electromagnetic surfaces, parasitic elements, matching and decoupling networks using a simple, yet a novel design alternative. The approach is based on a planar single decoupling element, consisting of a rectangular metallic ring resonator printed on one face of an ungrounded substrate. The decoupling structure surrounds a two-element vertical monopole antenna array fed by a coplanar waveguide structure. The design is shown both by simulations and measurements to reduce the mutual coupling by at least 20 dB, maintain the impedance bandwidth over which S11, is less than −10 dB, and reduce the envelope correlation coefficient to below 0.001. The boresight of the far-field radiation patterns of the two vertical monopole wire antennas operating at 2.4 GHz and separated by 8 mm (λo/16), where λo is the free-space wavelength at 2.45 GHz, is shown to be orthogonal and inclined by 45° with respect to the horizontal (azimuthal) plane while maintaining the shape of the isolated single antenna element

New frontiers in microwave metamaterials : magnetic-free non-reciprocal devices based on angular-momentum-biasing and negative-index metawaveguides

In this work, metamaterial concepts are applied to improve the design and realization of microwave components of a new generation. Conventional radiation sources, despite the mature and efficient development over the past century, maintain fundamental limitations. Slow-wave structures, such as backward-wave oscillators and traveling-wave tubes, function on the order of several operational wavelengths, leading to bulky architectures. Cherenkov radiation-based detectors are constrained to forward propagation, where the detection or diagnostic scheme may be damaged by energetic particles. Metamaterial concepts, specifically negative-index structures, provide new opportunities for these applications. In this context, we developed a detailed design of a negative-index metamaterial conducive to microwave generation. We experimentally validated a negative-index waveguide based on patterned plates of complementary split ring resonators. The design is conducive to interaction between particles and waves; it maintains a scalable negative-index band along with a longitudinal electric field component for particle interaction. The sub-wavelength resonant nature of the metamaterial allows for a compact design. In a different field of research, there is also significant need to squeeze the dimensions of microwave components. We have developed magnet-less, non-reciprocal, microwave circulators based on angular-momentum-biasing, which allow the realization of non-reciprocal devices that do not require magnets, and therefore lead to cheaper, lighter and significantly smaller devices. Angular-momentum-biasing, theoretically proposed recently in our research group, effectively mimics the collective alignment of electron spins seen in a ferromagnetic medium under a magnetic bias. Through spatiotemporal modulation, one can generate electrical rotation, leading to strong nonreciprocal response without magnetism. We have experimentally proven the theory on lumped element circulators and proposed transmission-line variations, providing over 50 dB of isolation in a range of frequency bands. This method provides efficient, easily tunable, fully integrable, compact devices that may revolutionize the future of integrated components. We have developed rigorous design principles that not only provide guidance for designs based on desired performance metrics, but also proves the passive nature of the concept. Furthermore, we have crafted mechanisms to enhance the bandwidth performance and improve linearity.Electrical and Computer Engineerin