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Millimeter wave (mmWave) radar systems are a leading technology in autonomous vehicle object sensing. The radar’s ability to detect surrounding objects is critical to its performance. One method of increasing object detection performance is to enhance object visibility. Frequency selective reflectors can increase object visibility. This work examines the performance of a mmWave 77 GHz radar system developed by Texas Instruments in conjunction with frequency selective surfaces. Two bandpass frequency selective surfaces are designed and fabricated using a loaded cross aperture configuration to analyze their application to object detection. The chosen design frequencies are 8 GHz and 79 GHz. The frequency selective surfaces are designed and simulated in 3-D electromagnetic simulation software, High Frequency Structure Simulator (HFSS). The frequency selective surfaces are fabricated on 127μm thick FR4 dielectric. The 8 GHz frequency selective surface demonstrates bandpass center frequency at 8.12 GHz. The 8 GHz and 79 GHz frequency selective surface reflection characteristics are compared to a copper sheets with the same physical cross section as each respective design. Although different testing methodology is used for each design, both frequency selective surfaces demonstrate bandpass characteristics at their respective design frequencies.

This thesis reports the methods, the deployment strategies and the resulting system performance improvement of in-building environmental modification. With the increasing use of mobile computing devices such as PDAs, laptops, and the expansion of wireless local area networks (WLANs), there is growing interest in increasing productivity and efficiency through enhancing received signal power. This thesis proposes the deployment of waveguides consisting of frequency selective surfaces (FSSs) in indoor wireless environments and investigates their effect on radio wave propagation. The received power of the obstructed (OBS) path is attenuated significantly as compared with that of the line of sight (LOS) path, thereby requiring an additional link budget margin as well as increased battery power drain. In this thesis, the use of an innovative model is also presented to selectively enhance radio propagation in indoor areas under OBS conditions by reflecting the channel radio signals into areas of interest in order to avoid significant propagation loss. An FSS is a surface which exhibits reflection and/or transmission properties as a function of frequency. An FSS with a pass band frequency response was applied to an ordinary or modified wall as a wallpaper to transform the wall into a frequency selective (FS) wall (FS-WALL) or frequency selective modified wall (FS-MWALL). Measurements have shown that the innovative model prototype can enhance 2.4GHz (IEEE 802.11b/g/n) transmissions in addition to the unmodified wall, whereas other radio services, such as cellular telephony at 1.8GHz, have other routes to penetrate or escape. The FSS performance has been examined intensely by both equivalent circuit modelling, simulation, and practical measurements. Factors that influence FSS performance such as the FSS element dimensions, element conductivities, dielectric substrates adjacent to the FSS, and signal incident angles, were investigated. By keeping the elements small and densely packed, a largely angle-insensitive FSS was developed as a promising prototype for FSS wallpaper. Accordingly, the resultant can be modelled by cascading the effects of the FSS wallpaper and the ordinary wall (FSWALL) or modified wall (FS-MWALL). Good agreement between the modelled, simulated, and the measured results was observed. Finally, a small-scale indoor environment has been constructed and measured in a half-wave chamber and free space measurements in order to practically verify this approach and through the usage of the deterministic ray tracing technique. An initial investigation showing that the use of an innovative model can increase capacity in MIMO systems. This can be explained by the presence of strong multipath components which give rise to a low correlated Rayleigh Channel. This research work has linked the fields of antenna design, communication systems, and building architecture.

Thesis (Ph. D.)--University of Texas at Dallas, 2006. / Includes vita. Includes bibliographical references (leaves 253-256).

<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

This thesis presents both theoretical and experimental investigations of the performance and capabilities of frequency selective surfaces (FSS) applied at THz frequencies. The aim is to explore and extend the use of FSS, traditionally limited to microwave frequencies, towards the THz regime of the spectrum, where interesting applications such as imaging, sensing and communications exist. The contribution of this work lies in three main areas within the scope of THz FSS, namely, performance, prototyping and applications. Unlike microwave FSS where extensive research has been performed to evaluate the performance of different FSS designs, particular problems arise at THz frequencies, significantly, the ohmic losses. While a few notable studies can be found on the issue of ohmic losses, part of this thesis investigates, for the first time, the power dissipation due to the presence of both ohmic and dielectric losses, in relation to the power stored in the vicinity of the FSS, the currents induced in the elements of the array and the array’s terminal impedance. By doing so, a better understanding of the performance of THz FSS has been given in terms of their quality factor, allowing for design guidelines previously unavailable. In order to demonstrate multiband operation experimentally, a novel fabrication process has been designed and developed to manufacture capacitive or dipole-based THz FSS on a dielectric layer. Dry deep-reactive ion etching has been employed in order to avoid the use of wet etching to provide better control of etch characteristics. Various FSS operating around 15THz have been demonstrated experimentally. In addition, THz FSS have been investigated theoretically in the realm of three different applications, namely, multiband operation, sensing capability and reconfigurability. Multiband characteristics using single-screen FSS have been achieved by perturbed dipole FSS exhibiting up to four resonances due to the excitation of even and odd current modes. After studying the near-fields in perturbed FSS, it has been found that this type of FSS represent a very attractive candidate for sensing applications due to the revealed near-field enhancement phenomena related to the excitation of the odd mode, where currents flow in opposite directions. Finally, a novel tunability approach to reach frequency reconfigurability by varying the near-field coupling between two closely spaced layers in a dual-layer configuration has been proposed. A MEMS movable four-arm membrane has been suggested to vary the distance between the two layers mechanically, leading to the frequency tuning effect. This approach has been shown to be particularly suitable for THz frequencies, and has been applied to demonstrate theoretically tunable FSS and other periodic structures, such as artificial magnetic conductors and dielectric gratings.

Thesis (Ph. D.)--Drexel University, 2005. / Includes abstract and vita. Includes bibliographical references (leaves 72-80).

Frequency selective surfaces (FSS) were originally developed for electromagnetic filtering applications at microwave frequencies. Electron-beam lithography has enabled the extension of FSS to infrared frequencies; however, these techniques create sample sizes that are seldom appropriate for real world applications due to the size and rigidity of the substrate. A new method of fabricating large area conformal infrared FSS is introduced, which involves releasing miniature FSS arrays from a substrate for implementation in a coating. A selective etching process is proposed and executed to create FSS particles from crossed-dipole and square-loop FSS arrays. When the fill-factor of the particles in the measurement area is accounted for, the spectral properties of the FSS flakes are similar to the full array from which they were created. As a step toward scalability of the process, a square-patch design is presented and formed into FSS flakes with geometry within the capability of ultraviolet optical lithography. Square-loop infrared FSS designs are investigated both in quasi-infinite arrays and in truncated sub-arrays. First, scattering-scanning near-field optical microscopy (s-SNOM) is introduced as a characterization method for square-loop arrays, and the near-field amplitude and phase results are discussed in terms of the resonant behavior observed in far-field measurements. Since the creation of FSS particles toward a large area coating inherently truncates the arrays, array truncation effects are investigated for square-loop arrays both in the near- and far-field. As an extension of the truncation study, small geometric changes in the design of square-loop arrays are introduced as a method to tune the resonant far-field wavelength back to that of the quasi-infinite arrays.

Orientador: Luiz Carlos Kretly / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-24T13:36:57Z (GMT). No. of bitstreams: 1 Silva_MauricioWeberBenjoda_D.pdf: 10953654 bytes, checksum: 6b4d1b6000f187a807b5cec8ba653713 (MD5) Previous issue date: 2014 / Resumo: Neste trabalho, as diferentes propriedades de superfícies seletivas em frequência, FSS - Frequency Selective Surfaces, são analisadas. As FSS são estruturas planares com células periódicas e podem ser classificadas como uma classe de metamateriais. Para tanto, o mecanismo de trabalho dessas estruturas foi extensivamente estudado, e um método próprio, baseado no modelo de circuito equivalente em conjunto com simulações de onda completa foi proposto. A ferramenta desenvolvida é útil para uma análise preliminar rápida de FSS, a qual foi utilizada para criar uma base de dados de elementos conhecidos na literatura. Diferente dos modelos de análise clássicos, a modelagem analítica proposta, que é uma das principais contribuições do trabalho, usa um simples algoritmo para aproximar a resposta de superfícies seletivas em frequência com geometrias arbitrárias, para incidências normal e oblíqua e para substratos com quaisquer espessuras. Nesse sentido, após a simulação eletromagnética da estrutura, é possível computar a resposta de uma FSS com diferentes parâmetros sem o consumo de tempo das simulações de onda completa. O modelo usa as características peculiares de superfícies de alta impedância, HIS - High Impedance Surface, que dentro de determina faixa comporta-se como condutor magnético perfeito, PMC - Perfect Magnetic Conductor, enquanto no restante da banda tem comportamento de um condutor elétrico perfeito, PEC - Perfect Electric Conductor, para sintetizar absorvedores finos e planares de micro-ondas. As estruturas, compostas de superfície seletiva em frequência resistivas sobre um substrato dielétrico aterrado, são projetadas visando aplicação em diferentes faixas de frequência de absorção e diferentes larguras de banda. Na faixa de 5,5 GHz, objetivou-se satisfazer as especificações dos sistemas WIMAX, WLAN, com os padrões IEEE 802.11a, bem como sistemas de radar, enquanto sinais de outras faixas podem trafegar com atenuação mínima ou nula. Para a faixa mais elevada, projetou-se uma estrutura que oferece absorção sobre a faixa de frequências de 10 GHz a 18 GHz, que pode ser empregada visando aplicações na banda-X e banda-Ku. O método de modelagem para a FSS e para os absorvedores propostos foi validado fisicamente através de montagens experimentais e instrumentação, especialmente desenvolvidas para estas estruturas. Os protótipos dos absorvedores fabricados são extremamente finos e foram medidos por meio de setups de medida em campo aberto e em câmara anecóica. As estruturas projetadas mostraram excelente desempenho para as faixas medidas, mantendo refletividade tipicamente abaixo de -10 dB ao longo de toda a banda. A metodologia desenvolvida nesta pesquisa pode ser ampliada para diferentes faixas de frequências, larguras de banda e aplicações / Abstract: In this work, the different properties of frequency selective surfaces - FSS are analyzed. Frequency selective surfaces are planar structures with periodic cells and can be classified as a kind of metamaterials. To this end, the working mechanism of these structures has been extensively studied, and a proper method based on the equivalent circuit model in conjunction with full-wave simulations was proposed. The developed tool is useful for a fast preliminary analysis of FSS, which was used to create a database of known elements presented in the literature. Unlike of classical analysis model, the proposed analytical modeling, which is one of the main thesis contributions, uses a simple algorithm for approximate the response of frequency selective surfaces with arbitrary shape, for normal and oblique incidence and for substrates with all thicknesses. In this sense, after the electromagnetic simulation of the structure, it is possible to compute the response of an FSS with different parameters without the time consuming full-wave simulations. The model uses the unique characteristics of High-Impedance Surfaces - HIS, which for certain frequency range, behaves as Perfect Magnetic Conductor - PMC, while outside this band behaves as a Perfect Electric Conductor - PEC, for synthesizing thin planar microwave absorbers. The structures, comprising resistive frequency selective surfaces over a grounded dielectric substrate, are designed aiming different absorption frequency bands and different bandwidths. In the 5.5 GHz frequency range, the aim was to satisfy the specifications of WiMAX, WLAN systems, in view of the IEEE 802.11a standards, as well as radar systems, while signals from other bands can travel across with zero or minimal attenuation. To the highest range, the designed structure provides absorption over 10 GHz to 18 GHz frequency range, and can be applied to the X- and Ku- band. The modeling method for the FSS and the proposed absorbers was physically validated through experimental setups and instrumentation, especially developed for these structures. The prototype of the fabricated absorbers are extremely thin and were characterized by using free space and anechoic chamber measurement setups. The designed structures showed excellent performance for measurements ranges, with reflectivity typically below -10 dB over the entire band. The methodology developed in this research can be extended to different frequency bands, bandwidth and applications / Doutorado / Eletrônica, Microeletrônica e Optoeletrônica / Doutor em Engenharia Elétrica

Bolometers are the most sensitive detectors for measuring millimeter and submillimeter wavelength astrophysical signals. Cameras comprised of arrays of bolometers have already made significant contributions to the field of astronomy. A challenge for bolometer cameras is obtaining observations at multiple wavelengths. Traditionally, observing in multiple bands requires a partial disassembly of the instrument to replace bandpass filters, a task which prevents immediate spectral interrogation of a source. More complex cameras have been constructed to observe in several bands using beam splitters and dichroic filters, but the added complexity leads to physically larger instruments with reduced efficiencies. The SPEctral Energy Distribution camera (SPEED) is a new type of bolometer camera designed to efficiently observe in multiple wavebands without the need for excess bandpass filters and beam splitters. SPEED is a ground-based millimeter-wave bolometer camera designed to observe at 2.1, 1.3, 1.1, and 0.85 mm simultaneously. SPEED makes use of a new type of bolometer, the frequency selective bolometer (FSB), to observe all of the wavebands within each of the camera's four pixels. FSBs incorporate frequency selective dipole surfaces as absorbing elements allowing each detector to absorb a single, narrow band of radiation and pass all other radiation with low loss. Each FSB also contains a superconducting transition-edge sensor (TES) that acts as a sensitive thermistor for measuring the temperature of the FSB. This thesis describes the development of the SPEED camera and FSB detectors. The design of the detectors used in the instrument is described as well as the the general optical performance of frequency selective dipole surfaces. Laboratory results of both the optical and thermal properties of millimeter-wave FSBs are also presented. The SPEED instrument and its components are highlighted and the optical design of the optics which couple SPEED to the Heinrich Hertz Telescope is given. This thesis concludes with an introduction to the jiggle mapping data analysis of bolometer instruments like SPEED.