This master´s thesis is focused on the ways of possible realisation of the directive horn antenna with suppressed side lobes in the frequency bands 71-76 GHz and 81-86 GHz. In this thesis a detailed research of the feasible options including parameters comparison and assessment of pros and cons of the particular solutions has been performed. Among the specified technical requirements, the emphasis has been placed on the manufacturing options and low cost availability of the materials applicable for the given antenna. The main part of the thesis deals with the conical horn antenna loaded with a hyperbolic dielectric lens, further the antenna with flat dielectric lens based on a transmitarray and also the integrated elliptical lens antenna. The following part of the thesis deals with the possibilities of characterizing the properties of the dielectric material of the lens.

No description available.

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.

In the sub-THz frequency range, the geodesic lens can realize low losses and beam scanning capability with high gain and high aperture efficiency due to its fully metallic property and rotational symmetry. Therefore, in high-frequency applications, a geodesic lens is considered a more promising solution in comparison to phased arrays or other beamforming techniques. To realize dual polarization for geodesic lenses, a polarization rotator using fully metallic screens can be placed at the lens aperture to increase the channel capacity. In this thesis, we propose a dual-polarized fully metallic geodesic lens antenna with the operation frequency centered at 120 GHz. The proposed design contains two layers of geodesic lenses and two polarization rotators placed in their respective apertures with ±45° polarization. By using a twist waveguide for the feeding, we eliminate the leakage caused by the air gap between the metal plates. The simulation results show that the dual-polarized lens can achieve an angular scanning range of ±60° and its scanning loss is 0.6 dB, with an aperture efficiency of 90%. Finally, we propose a prototype design with mechanical considerations to ensure robustness in future manufacturing, assembly, and testing. / Geodetiska linser kan tillämpas åt frekvenser under THz för att realisera låga förluster och strålscanningskapacitet med både hög förstärkning och apertureffektivitet, detta på grund av dess fullt metalliska egenskaper samt rotationssymmetri. I högfrekventa tillämpningar anses därför en geodetisk lins vara lovande i jämförelse med en fasstyrda gruppantenn eller andra strålformningstekniker. Ytterligare så kan polarisationsrotatorer med helt metalliska skärmar kan placeras vid linsöppningen för att realisera korspolariserade fält samt öka kanalkapaciteten hos geodetiska linser. I denna avhandling föreslårs en justerbar korspolariserad samt fullt metallisk geodetisk linsantenn centrerad runt 120 GHz. Den föreslagna designen innehåller två lager geodetiska linser och två polarisationsrotatorer placerade i sina respektive utgångar med respektive polarisatonsförskjutning på ±45°. Genom att använda en vriden vågledare för matningen så eliminerars läckaget som normalt följer av luftgapet mellan metallplattorna. Simuleringsresultaten visar att den korspolariserade linsen kan uppnå ett avsökningsområde inom vinklar ±60° men en skanningsförlust på 0,6 dB, detta med en apertureffektivitet på 90%. Slutligen föreslår vi en prototyp med hänsyn till mekaniska aspekter för att säkerställa robusthet i framtida tillverkning, montering och testning.

This thesis project investigates, analyzes, designs, simulates, constructs and tests a dual-axis solar tracker system to track the sun and concentrates the heat of the sunlight, using a Fresnel lens, into a small area, which is above of an evaporator, to increase the temperature of the seawater to convert it into freshwater. The dual-axis solar tracker was designed with the main objectives that the structure was portable, dismountable, lightweight, low cost, corrosion resistant, wires inside pipes, accurate, small size, follow the sun automatically, off-grid (electrical), use green energy (solar powered), and has an empty area right below of the lens. First, a 500 mm diameter flat Fresnel lens was selected and simulated based on an algorithmic method achieved by a previous PhD student at UNT using MATLAB®, to give the optimization lens dimensions. The lens profile was drawn with AutoCAD®, then output profile lens was simulated in COMSOL Multiphysics®. The objective was to provide the high efficiency, optimum and high precision of the focal rays and heat to the receiver of the evaporator. A novel dual-axis solar tracker system was then designed that is portable, dismountable, lightweight and corrosion resistant. The solar tracker tracks the sun in two axis of rotation automatically during the day time, maximizing the angles of inclination on each axis. After testing computer simulations, the dual-axis solar tracker system was constructed and tested. Last, a detailed cost analysis was performed of the entire project. The outcome of this work can be applied for desalination seawater purposes or other any Fresnel lens application that require a focal high temperature directed by dual-axis solar tracker system.

No description available.

No description available.

Doctor of Philosophy / Graduate Biochemistry Group / Dolores J. Takemoto / Eukaryotic cells possess a unique way to communicate with each other by passing metabolites and small molecules through protein pores that connect adjacent cells. Although there are many types and families of protein pores, connexins comprise a unique family. Six connexin monomers assemble into a hemichannel, which is transported to the cell membrane. An opposing cell membrane containing compatible connexin hemichannels is located and connected, forming an intercellular dodecameric protein complex. This results in a protein channel that connects two separate cytoplasmic compartments to each other. This type of channel is known as a gap junction. Connexin expression and function is commonly tissue specific. Of the 21 known human connexins, less than half are currently well characterized. Three connexins are expressed in the lens, connexin 43 (Cx43), 46 (Cx46), and 50 (Cx50). Of these three, Cx46 and Cx50 both have major functions in the mature lens. Cx46 functions as a major gap junction channel, which maintains mature lens homeostasis, while Cx50 possesses growth control properties in the lens. Cx46 expression is modulated in breast and bone tumors, and during ischemia. It is hypothesized that Cx46 provides resistance to hypoxia mediated cell death by prolonging survival. In this study, Cx46 expression was detected in human Y79 retinoblastoma cells. Decreasing the expression of Cx46 in nude mice carrying Y79 xenografts slowed early stage tumor growth. Y79 cells in culture survive for over 72 hours in 1% oxygen in vitro. C46 was upregulated in cultured lens cells when grown under hypoxia. Human lens epithelial cells, rabbit N/N1003A lens cells, and Y79 cells proliferated in 1% oxygen until Cx46 expression was depleted by use of siRNA. Protection from hypoxia-induced cell death was provided by transfection with the C-terminus of Cx46. We further determined that the promoter activity of Cx46 was increased in 1% oxygen. These results indicate that Cx46 would increase in response to hypoxia and suggest a role for Cx46 in protection from hypoxia. The studies demonstrate a novel function for Cx46 in cell survival during hypoxia.

The design of the flexure mount recently submitted to NASA Ames for the structural support of the primary mirror of the Space Infrared Telescope Facility (SIRTF) is presented. The flexure system must passively accommodate the differential thermal contraction between the glass mirror and the aluminum structure of the telescope during cryogenic cooldown. Further, it must support the one meter diameter, 116 kilogram (258 pound) primary mirror during a severe launch to orbit. Procedures used to establish the required radial compliance using computer programs NASTRAN and FRINGE are discussed. The parametric design program developed to study early concepts is presented. Methods of combining modal responses resulting from a displacement response spectrum analysis are discussed, and a combination scheme called MRSS, Modified Root of Sum of Squares, is presented. Modal combination schemes using MRSS, SRSS, and ABS are compared to the results of a Modal Frequency Response analysis.

Published Article / This paper is based on tests performed on die component specimens manufactured by EOS-DMLS (direct metal laser sintering) and LENS (laser engineered net shape) RP (rapid prototyping) technology platforms, as well as manufactured specimens machined out of preferred standard hot work steel DIN 1.2344. These specimens resemble typical components used in metal high pressure die casting tool sets. The specimens were subjected to a programme of cyclic immersion in molten aluminium alloy and cooling in water-based die release medium. The heat checking and soldering phenomena were analyzed through periodic inspections, monitoring crack formation and evidence of surface washout. At the end of the thermal tests, mechanical strength and hardness tests were performed to assess toughness and core resistance variations in relation to the initial conditions. Finally metallographic investigations were performed through optical microscopy on all the specimens considered. The outcomes of this research will be presented and used by the CSIR for further development and application of the assessed EOS-DMLS and LENS rapid prototyping technologies in rapid die manufacturing techniques and die design principles, including time and economic feasibility criteria to be applied when considering rapid die manufacture.