This thesis describes an electrically thin surface used for electromagnetic applications in the microwave regime. The surface is free-standing and its primary purpose is to modify the phase distribution, or the phase and amplitude distribution of electromagnetic fields propagating through it: it is called phase shifting surface (PSS) in the first case, and phase and amplitude shifting surface (PASS) in the second case. For practical applications, the surface typically comprises three or four layers of metallic patterns spaced by dielectric layers. The patterns of the metallic layers are designed to locally alter the phase (and amplitude in the case of the PASS) of an incoming wave to a prescribed set of desired values for the outgoing wave. The PSS/PASS takes advantage of the reactive coupling by closely spacing of the metallic layers, which results in a larger phase shift range while keeping the structure significantly thin. The PSS concept is used to design components such as gratings and lens antennas which are presented in this document. The components are designed for an operating frequency of 30 GHz. The PSS phase grating gives high diffraction efficiency, even higher than a dielectric phase grating. Several types of lens antennas are also presented, which show comparable performance to that of a conventional dielectric plano-hyperbolic lens antenna with similar parameters. The PASS concept is used in a beam shaping application in which a flat-topped beam antenna is designed. This work demonstrates the potential for realising thin, lightweight and low-cost antennas at Ka band, in particular for substituting higher-gain antenna technologies such as conventional dielectric shaped lens antennas.

CNPq, Capes e FINEP / Este trabalho descreve a produção e caracterização de guias de onda óticos em cristal de fluoreto de lítio (LiF) produzidos expondo o cristal a um feixe focalizado de um laser de femtosegundo, com o deslocamento do cristal na direção perpendicular ao eixo de propagação do feixe. A medida da emissão, sob iluminação específica, demonstra a presença de centros de cor dos tipos F2 e F3+ nas regiões do cristal expostas ao feixe focalizado do laser. As estruturas produzidas possuem incremento do índice de refração em relação ao índice de refração do cristal. Tais estruturas são caracterizadas em termos da sua morfologia usando microscopia convencional e confocal. A capacidade de guiamento de luz é investigada acoplando fontes laser com diferentes comprimentos de ondas. Os modos suportados são também analisados, bem como as perdas na propagação. A produção de guias de ondas de Bragg é testada acoplando uma fonte de luz branca e comparando seu espectro com o espectro que passa somente pelo cristal. A capacidade de guiamento das estruturas produzidas é confirmada pela análise dos perfis de campo próximo. Os guias suportam poucos modos e os incrementos de índices obtidos são da ordem de 10^-4. / This work describes the production and characterization of optical waveguides in lithium fluoride crystal (LiF) produced by exposing the crystal to a focused femtosecond laser beam, with the crystal displacement perpendicular to the beam. The measured emissions, with specific illumination, demonstrate the presence of color centers of types F2 and F+3 at the crystal regions exposed to the focused laser beam. The produced structures have increased refractive index relative to the crystal refraction index. Such structures are characterized in terms of their morphology using conventional and confocal microscopy. Their ability to guide light is investigated through coupling different laser light. The propagation modes supported by the guides are also estimated, as well as the propagation losses. The production of a Bragg grating waveguide is locked for by coupling a white light in the guides and comparing its spectrum with that passing only through the crystal. The guiding capacity of the structural changes produced is confirmed by the near-field profile analysis. The guides support few propagation modes and the obtained changes in the refractive index are in the order of 10^-4.

Efficient and accurate sensing of various parameters is needed for numerous applications. In this regard, different categories of sensors play a significant role and different applications require diverse sensing mechanisms owing to the operating conditions and field constraints. Among the several sensor methodologies available, optical fiber sensors have found significant attention, because of their advantages such as negligible foot print, small mass, immunity to Electromagnetic Interference, etc. In the category of optical fiber sensors, Fiber Bragg Grating (FBG) sensors have found importance in many fields such as health monitoring of civil structures, environmental monitoring involving gas & humidity sensing, monitoring parameters like pressure, tilt, displacement, etc. In the recent times, FBGs have found applications in biomedical, biomechanical and biosensing fields. A FBG is a periodic change of the refractive index of the core of a single mode optical fiber along its longitudinal axis. The periodic modulation in the index of refraction is obtained by exposing a photosensitive germanium-doped silica fiber to an intense UV laser beam. FBGs, in the basic form, can sense strain and temperature. However, in recent years, several newer sensing applications of FBGs have been demonstrated. Some of the main features of the FBG sensor which qualify them for diverse sensing applications are high sensitivity, large operational bandwidth, multiplexing & multi modal sensing capability, etc. In this thesis work, FBG sensor based devices have been developed for newer applications in bio-medical fields for the measurement of force, flow and temperature. Particularly, novel transduction methodologies have been proposed, in order to convert the measurand parameter into a secondary parameter that can be sensed by the FBG sensor. The evaluation of the force required for a spinal needle to penetrate various tissue layers from skin to the epidural space is vital. In this work, a novel technique for dynamic monitoring of force experienced by a spinal needle during lumbar puncture using Fiber Bragg Grating (FBG) sensor has been developed. The Fiber Bragg Grating Force Device (FBGFD) developed, measures the force on the spinal needle due to varied resistance offered by different tissue layers during its traversal. The effect of gauge of the spinal needle used for the lumbar puncture procedure affects the force required for its insertion into the tissue. The FBGFD developed, has been further utilized for a comparative study of the force required for lumbar puncture of various tissue layers with spinal needle of different gauges. The results obtained may serve as a guideline for selection of suitable gauge spinal needle during lumbar puncture minimizing post puncture side effects on patients. The pulmonary function test carried out using a spirometer, provides vital information about the functional status of the respiratory system of the subject. A Fiber Bragg Grating Spirometer (FBGS) has been developed which has the ability to convert the rate of air flow into a shift in wavelength that can be acquired by the FBG sensor. The FBGS can dynamically acquire the complete breathing sequence comprising of the inhalation phase, pause phase and exhalation phase in terms of the air flow rate along with the time duration of each phase. Methods are adopted to analyse and determine important pulmonary parameters using FBGS and compare these parameters with those obtained with a commercially available hospital grade pneumotachograph spirometer. Thermal imaging is one of the emerging non-invasive neuro-imaging techniques which can potentially indicate the boundaries of a brain tumor. The variation in tissue surface temperature is indicative of a tumor existence. In this work a FBG temperature sensor (FBGTS) has been developed for thermography of a simulated tissue using Agar material. The temperature of the embedded heater which mimics a brain tumor along with the surface temperature of the tissue model, is acquired using FBGTSs simultaneously. Further, the surface temperatures are studied for varying heater temperatures as well as varying positions of the heater in the simulated tissue model. To conclude, FBG based devices have been developed in this work, for applications in biomedical domain, with appropriate transduction methodologies for sensing different parameters such as force, flow and temperature.

The electrostatic layer-by-layer (LbL) self-assembly of polyelectrolyte’s has shown applications in thin film coatings, micro patterning, nano-bioreactors and capsules for drug delivery. The film architecture can be precisely designed and controlled to nanometer scale precision with a range from 5 nm to a few microns. Both in vitro and in vivo studies indicate potential applications in biology, pharmaceutics, medicine, and other biomedical areas. This thesis work focused on the design and development of protocols to fabricate polyelectrolyte multi-layer patterns on a variety of substrates such as glass, metals and plastics such as acrylic and polycarbonate. The micro-scale polyelectrolyte patterns have applications in the creation of DNA, protein or cell based microarrays. This work also demonstrated the use of polyelectrolyte multi-layers in the enhancement of fluorescence signals from fluorophore-tagged molecules captured within the multi-layers. In-situ measurements using Fiber Bragg Gratings were carried out to study the kinetics of adsorption and desorption of polyelectrolytes participating in the layer buildup process under different process environmental conditions.

No description available.

Spectrally-based fiber optic sensors are a rapidly maturing technology capable of sensing several environmental parameters in environments that are unfitting to electrical sensors. However, the sensor interrogation systems for this type of sensors are not yet fit to replace conventional sensor systems. They lack the speed, compact size, and usability necessary to move into mainstream test and measurement. The Fiber Sensor Integrated Monitor (FSIM) technology leverages rapid optical components and parallel hardware architecture to move these sensors across the research threshold into greater mainstream use. By dramatically increasing speed, shrinking size, and targeting an interface that can be used in large-scale industrial interrogation systems, spectrally-based fiber optic sensors can now find more widespread use in both research labs and industrial applications. The technology developed in this thesis was demonstrated by producing two advanced interrogators: one that was one half the size of commercially available systems, and one that accelerated live spectral capture by one thousand times – both of which were operated by non-developers with little training.

This thesis describes an electrically thin surface used for electromagnetic applications in the microwave regime. The surface is free-standing and its primary purpose is to modify the phase distribution, or the phase and amplitude distribution of electromagnetic fields propagating through it: it is called phase shifting surface (PSS) in the first case, and phase and amplitude shifting surface (PASS) in the second case. For practical applications, the surface typically comprises three or four layers of metallic patterns spaced by dielectric layers. The patterns of the metallic layers are designed to locally alter the phase (and amplitude in the case of the PASS) of an incoming wave to a prescribed set of desired values for the outgoing wave. The PSS/PASS takes advantage of the reactive coupling by closely spacing of the metallic layers, which results in a larger phase shift range while keeping the structure significantly thin. The PSS concept is used to design components such as gratings and lens antennas which are presented in this document. The components are designed for an operating frequency of 30 GHz. The PSS phase grating gives high diffraction efficiency, even higher than a dielectric phase grating. Several types of lens antennas are also presented, which show comparable performance to that of a conventional dielectric plano-hyperbolic lens antenna with similar parameters. The PASS concept is used in a beam shaping application in which a flat-topped beam antenna is designed. This work demonstrates the potential for realising thin, lightweight and low-cost antennas at Ka band, in particular for substituting higher-gain antenna technologies such as conventional dielectric shaped lens antennas.

Hintergrund: Die Entwicklung von Nanotechnologien und insbesondere integrierten Schaltkreisen beruht auf dem Verständnis von Struktur und Funktion auf der Nanoskala, wofür exakte Messungen erforderlich sind. Kleinwinkel-Röntgenstreuung unter streifendem Einfall (GISAXS) ist eine Methode zur schnellen, berührungs- und zerstörungsfreien dimensionellen Messung von nanostrukturierten Oberflächen. Ziele: Es soll die Möglichkeit untersucht werden, die zunehmend komplexeren Proben aus Wissenschaft und Industrie mit Hilfe von GISAXS präzise zu vermessen. Ein weiteres Ziel ist es, Messtargets aus der Halbleiter-Qualitätskontrolle mit einer Größe von ca. 40x40 µm² zu messen, deren Signal typischerweise nicht zugänglich ist, weil ein Bereich von ca. 1x20 mm² auf einmal beleuchtet wird. Methoden: Synchrotron-basierte GISAXS-Messungen verschiedener Proben werden mit Hilfe einer Fourier-Konstruktion, der "distorted wave Born approximation" und einem Maxwell-Gleichungs-Löser basierend auf finiten Elementen analysiert. Ergebnisse: Aus GISAXS-Messungen kann die Linienform von Gittern mit einer Periode von 32 nm rekonstruiert werden und sie weicht weniger als 2 nm von Referenzmessungen ab. Eine sorgfältige Bayes'sche Unsicherheitsanalyse zeigt jedoch, dass wichtige dimensionelle Parameter innerhalb der Unsicherheiten nicht übereinstimmen. Für die Messung von kleinen Gittertargets entwerfe ich ein neuartiges Probendesign, bei dem das Target in Bezug auf die umgebenden Strukturen gedreht wird, und stelle fest, dass dadurch parasitäre Streuung effizient unterdrückt wird. Fazit: GISAXS-Messungen von komplexen Nanostrukturen und kleinen Targets sind möglich, jedoch würde GISAXS enorm von effizienteren Simulationsmethoden profitieren, die alle relevanten Effekte wie Rauhigkeit und Randeffekte einbeziehen. Hier gibt es vielversprechende theoretische Ansätze, so dass GISAXS eine zusätzliche Methode für die Halbleiter-Qualitätskontrolle werden könnte. / Background. The development of nanotechnology such as integrated circuits relies on an understanding of structure and function at the nanoscale, for which reliable and exact measurements are needed. Grazing-incidence small angle X-ray scattering (GISAXS) is a versatile method for the fast, contactless and destruction-free measurement of sizes and shapes of nanostructures on surfaces. Aims. A goal of this work is to investigate the possibility of precisely measuring the increasingly complex samples produced in science and industry using GISAXS. A second objective is to measure targets used in semiconductor quality control with a size of approx. 40x40 µm², whose signal is typically not accessible because an area of approx. 1x20 mm² is illuminated at once. Methods. I take synchrotron-based GISAXS measurements and analyze them using reciprocal space construction, the distorted wave born approximation, and a solver for Maxwell's equations based on finite elements. Results. I find that the line shape of gratings with a period of 32 nm can be reconstructed from GISAXS measurements and the results deviate less than 2 nm from reference measurements; however, a careful Bayesian uncertainty analysis shows that key dimensional parameters do not agree within the uncertainties. For the measurement of small grating targets, I create a novel sample design where the target is rotated with respect to the surrounding structures and find that this efficiently suppresses parasitic scattering. Conclusions. I show that GISAXS measurements of complex nanostructures and small targets are possible, and I highlight that further development of GISAXS would benefit tremendously from efficient simulation methods which describe all relevant effects such as roughness and edge effects. Promising theoretical approaches exist, so that GISAXS has the potential to become an additional method in the toolkit of semiconductor quality control.

No description available.

In this thesis work, a systematic quantitative study has been undertaken, on the performance of etched fiber Bragg Grating (FBG) sensors in the investigation of surface molecular adsorption in real-time; it is shown that the limit of detection (LOD) of FBGs etched below 2 microns diameter, is better compared to prominent optical label-free molecular sensing techniques such as Surface Plasmon Resonance (SPR). Novel fiber optic sensors based on FBG and etched FBG with various nano materials (polyelectrolytes, carbon nanotubes, hydrogel, metals and chalcogenides) coated on the surface of the core or cladding, have been proposed for sensing multi parameters such as pH, protein, humidity, gas, strain, temperature, and light etc. Besides being reproducible and repeatable, the proposed methods are fast, compact, and highly sensitive. A novel optical instrument has also been developed to measure angular deviation, binocular deviation and refractive index of glass slabs, and liquids, based on a shadow casting technique. This method uses the deviation in the geometrical shadow cast by a periodic dot pattern trans-illuminated by a distorted light beam from the transparent test specimen relative to a reference pattern.