Beam-Steerable and Reconfigurable Reflectarray Antennas for High Gain Space Applications

Reflectarray antennas uniquely combine the advantages of parabolic reflectors and phased array antennas. Comprised of planar structures similar to phased arrays and utilizing quasi-optical excitation similar to parabolic reflectors, reflectarray antennas provide beam steering without the need of complex and lossy feed networks. Chapter 1 discusses the basic theory of reflectarray and its design. A brief summary of previous work and current research status is also presented. The inherent advantages and drawbacks of the reflectarray are discussed. In chapter 2, a novel theoretical approach to extract the reflection coefficient of reflectarray unit cells is developed. The approach is applied to single-resonance unit cell elements under normal and waveguide incidences. The developed theory is also utilized to understand the difference between the TEM and TE10 mode of excitation. Using this theory, effects of different physical parameters on reflection properties of unit cells are studied without the need of full-wave simulations. Detailed analysis is performed for Ka-band reflectarray unit cells and verified by full-wave simulations. In addition, an approach to extract the Q factors using full-wave simulations is also presented. Lastly, a detailed study on the effects of inter-element spacing is discussed. Q factor theory discussed in chapter 2 is extended to account for the varying incidence angles and polarizations in chapter 3 utilizing Floquet modes. Emphasis is laid on elements located on planes where extremities in performance tend to occur. The antenna element properties are assessed in terms of maximum reflection loss and slope of the reflection phase. A thorough analysis is performed at Ka band and the results obtained are verified using full-wave simulations. Reflection coefficients over a 749-element reflectarray aperture for a broadside radiation pattern are presented for a couple of cases and the effects of coupling conditions in conjunction with incidence angles are demonstrated. The presented theory provides explicit physical intuition and guidelines for efficient and accurate reflectarray design. In chapter 4, tunable reflectarray elements capacitively loaded with Barium Strontium Titanate (BST) thin film are shown. The effects of substrate thickness, operating frequency and deposition pressure are shown utilizing coupling conditions and the performance is optimized. To ensure minimum affects from biasing, optimized biasing schemes are discussed. The proposed unit cells are fabricated and measured, demonstrating the reconfigurability by varying the applied E-field. To demonstrate the concept, a 45 element array is also designed and fabricated. Using anechoic chamber measurements, far-field patterns are obtained and a beam scan up to 25o is shown on the E-plane. Overall, novel theoretical approaches to analyze the reflection properties of the reflectarray elements using Q factors are developed. The proposed theoretical models provide valuable physical insight utilizing coupling conditions and aid in efficient reflectarray design. In addition, for the first time a continuously tunable reflectarray operating at Ka-band is presented using BST technology. Due to monolithic integration, the technique can be extended to higher frequencies such as V-band and above

Design, fabrication, and characterization of functionally graded materials

“The aim of this research was to investigate the feasibility of fabricating custom designed, graded materials using Laser Metal Deposition (LMD) that will cater for functionality and unconventional repair. The ultimate goal of the project is to establish the versatility of LMD for fabricating advanced materials and tackling problems that have been conventionally difficult or in cases infeasible. In order to accomplish these goals, this research involved investigations into, the feasibility of using elemental powders as modular feedstocks, the feasibility of fabricating tailored gradients with these custom compositions, and finally leveraging the advantages of grading materials using LMD to successfully fabricate conventionally infeasible material systems. The copper-nickel material system was chosen for demonstrating the modular feedstock concept. While the use of elemental nickel lead to porosity issues, Delero-22 a nickel-silicon-boron alloy was identified as a viable substitute. A wide range of copper-nickel alloys were fabricated through the deposition of blended powder feedstocks. Also, using these blended powder feedstocks, graded material structures of copper-nickel alloys were successfully fabricated. Varying energy input through pulse width modulation of laser power was identified as a viable means for manipulating chemistry gradient within these graded materials. The influence of varying chemistry on mechanical properties was evaluated through the use of DIC coupled mini-tensile testing. A clear distinction in the strain field indicating the spatially varying chemistry was identified during tensile testing. Also, the feasibility of depositing on highly reflective alloys of aluminum such as Al2024 and Al6061 was also investigated. Leveraging the higher absorptivity of Al4047 and remelting during LMD, a strong metallurgical bond was obtained between the substrate and the deposit. Preheating the substrate was identified to increase the reliability and quality of deposition. The bond between the substrate and deposit was found to be stronger than the deposit --Abstract, page iv

An Experimental Study on Black Cotton Soil Stabilization by Using Terazyme

In developing countries like India the most important requirement of any project after performance criteria is its economical feasibility and serviceability criteria. The conventional methods are time consuming and are not economically feasible. Hence there is a need to find the other possible ways to satisfy the performance as well as economical criteria. These enzymes have been proven to be very effective and economical. Another advantage of the bio-enzyme is that these are environment friendly. The efficiency of bio enzyme depends upon the amount of dosage, type of soil and curing period. In our country vast areas consist of black cotton soils. As the conventional soil stabilizers like gravel, sand and others are depleting and becoming expensive day by day at a very rapid pace, it becomes necessary to look towards for alternative eco-friendly stabilizers as their substitute. Recently many Bio-enzymes have emerged as cost effective stabilizers for soil stabilization. One such type of bio-enzyme, Terazyme, has been used in the present work. The Terazyme effect on the unconfined compressive strength and on the atterberg limits were studied. The enzyme treated soil showing significant improvement in unconfined compressive strength values. The untreated soil has compressive strength as 71 kN/m2. After treating with Terazyme the soil showed significant improvement in strength. With curing period, the strength is increasing. The strength increment was found to be 300 percent. No significant improvement in liquid and plastic limit values with treatment of Terazyme enzyme. The compression index and coefficient of consolidation values decreasing with enzyme treatment for a prefixing curing period

Polymer colloids for catalysis in fluorous media and for colloidal crystalline arrays

Scope and Method of Study: Monodisperse charged polymer colloids in aqueous and non-aqueous dispersions have potential applications as membranes and catalysts. We chose poly(methyl methacrylate) polymer particles for the catalytic and colloidal crystalline filter fabrication applications. Micron sized poly(ethylhexyl methacrylate) (EHMA) cross-linked copolymers in fluorinated solvents were synthesized by dispersion polymerization using microwave heating for the catalytic applications. Sub-micron sized poly(methyl methacrylate) (PMMA) core-shell latexes in aqueous media were made by emulsifier-free emulsion polymerization for colloidal crystal films (CCF) making.Findings and Conclusions: Cationic EHMA copolymers slightly increased the hydrolysis of p-nitrophenyl hexanoate in fluorous media compared to the control experiment which lacked the polymer particles. PMMA CCF's fabricated by gravitational sedimentation method contained monodisperse FCC packed domains of 5-10 µm, point defects, and grain boundaries

Thermographic investigation of laser metal deposition

Laser metal deposition as an additive manufacturing technique has been proven to possess the capability for fabricating complex, intricate geometries and excellent material properties through material deposition. Accurate manufacture of such geometric features would require precise control over the material deposition process. The need of the hour are process monitoring and analyses mechanisms that are crucial in ascertaining the occurrence of the intended actions during deposition while also serving as effective learning tools. The current work involved developing and incorporating an Infra-Red (IR) camera as a process monitoring tool for laser metal deposition. Using the IR camera the thermal dynamics of the deposition processes under the control of the feedback systems were captured and analyzed to realize the changes in the material close to solidus temperature. The analysis confirmed the logic behind the control system and was successful in helping identify the ideal process parameters which were quantified using a set of experiments. The sub-sequent effort was focused on further disseminating thermographic data to attain details about the material above the solidus temperature. Employing image processing techniques pertaining to edge detection, regions that encompass the material above the solidus temperature were successfully identified. IR camera data was also used to track the regions of interest through the deposition and make other characteristic observations pertaining to phase change. To further test the sensitivity of this technique a series of experiments with varying power, track length and substrate size were performed. The developed methodology proved successful in identifying the regions of interest with a high degree of sensitivity and repeatability. Comprehensive insights into the physics of the process were also successfully obtained. --Abstract, page iii

Development of a Computer Algorithm for Generation of Primers for Nucleic Acid Sequence Based Amplification (NASBA)

Nucleic acid sequence based amplification (NASBA) is a primer based isothermal method of RNA/DNA amplification. Currently, primer design for NASBA has been restricted to hand creating sequences of oligonucleotides that must follow a set of rules to be compatible for the amplification process. This process of hand-creating primers is prone to error and time intensive. The detection of mutants, post amplification, also offers a benefit in point of care scenarios and the design of hybridization probes for sequences in the region of amplification is also an erroneous and time intensive process. By creating a program to design primers and hybridization probes based on the set of rules provided for a sequence of user input DNA or RNA, one can avoid costly errors in primers design and save time. Utilizing Python (a high-level object-oriented programming language), along with a series of bioinformatic libraries such as Biopython and UNAfold one can definitively choose the best primer sequences for a given sample of DNA

An approach to solve job shop scheduling problem

“A biotechnology device manufacturer needs to devise effective scheduling algorithms for its testing devices. A device is a configuration of machines, each of which performs a specific task, such as washing, reading and cleaning. These devices are used to test human samples to diagnose diseases like cholera, malaria etc. Each test is a job, which is to be processed on these machines for a specific amount of time. Every job has its own pre defined sequence. These samples are to be processed simultaneously on machines owing to constraint that as soon as one machine completes processing a sample, it should be immediately processed by another machine. This constraint is significantly known as no- wait constraint. Given a set of jobs the web application assigns an optimal start time for each job owing to no-wait constraint. This results in reducing the overall time taken to process the jobs, which is formally known as makespan. The main objective of the project is to minimize the makespan. The application is specific to laboratory platform, which helps them to test the samples in optimal time. The heuristic, which I have implemented, is designed with future advancements in mind. The application can be extended to test different heuristic procedures by keeping the time tabling intact. The development environment to be used in this project will require Microsoft Visual Studio, C#, ASP.NET, and other real time chart tools like Microsoft Silverlight.

A Mixed-Mode (I-Ii) Fracture Criterion For As4/8552 Carbon/Epoxy Composite Laminate

A majority of aerospace structures are subjected to bending and stretching loads that introduce peel and shear stresses between the plies of a composite laminate. These two stress components cause a combination of mode I and II fracture modes in the matrix layer of the composite laminate. The most common failure mode in laminated composites is delamination that affects the structural integrity of composite structures. Damage tolerant designs of structures require two types of materials data: mixed-mode (I-II) delamination fracture toughness that predicts failure and delamination growth rate that predicts the life of the structural component. This research focuses on determining mixed-mode (I-II) fracture toughness under a combination of mode I and mode II stress states and then a fracture criterion for AS4/8552 composite laminate, which is widely used in general aviation. The AS4/8552 prepreg was supplied by Hexcel Corporation and autoclave fabricated into a 20-ply unidirectional laminate with an artificial delamination by a Fluorinated Ethylene Propylene (FEP) film at the mid-plane. Standard split beam specimens were prepared and tested in double cantilever beam (DCB) and end notched flexure modes to determine mode I (GIC) and II (GIIC) fracture toughnesses, respectively. The DCB specimens were also tested in a modified mixed-mode bending apparatus at GII m/GT ratios of 0.18, 0.37, 0.57 and 0.78, where GT is total and GII m is the mode II component of energy release rates. The measured fracture toughness, GC, was found to follow the locus a power law equation. 2.08 ) (        = + − T m II C IC IIC IC G G G G G G The equation was validated for the present and literature experimental data.

Problems Of Improving Spoken Language Skills In Teaching Russian As A Foreign Language

While teaching Russian as a foreign language to undergraduate and postgraduate students in India, we observed that the learners quickly pick up writing skills, whereas their spoken language skills are not at the same level. There are many issues which need to be sorted out in order to improve spoken language skills. As written and spoken skills are different, we need to use different methods of teaching for each one of them. Since the first thing that is taught to students, who are learning a language, are alphabets, hence, initially the whole attention is turned towards improving their writing skills. Though, in the beginning, the students also do pick up an elementary level of spoken language, in the intermediate and advanced levels of learning, their spoken language skills suffer due to various factors. One of the main factors being the lack of exposure to the foreign language once the learners are out of the classroom. Since they continue to do homework, they keep in touch with the written skills. However, once they are out of the classroom, the learners and people around them use their own mother tongue or other native languages to speak. As a result, their spoken skills of the foreign language do not improve.Measures need to be taken for improving spoken skills: showing feature, as well as animation films; involving the students in discussions with the help of native speakers; providing audio books; showing them TV programs after class hours; involving learners in enacting Russian plays, etc. On the whole, artificial foreign language surroundings need to be created. Let us see how to motivate learners to speak as well as to write foreign language of their choice. Keywords: spoken skills, teaching Russian as a foreign language, learning problem

Automated restaurant orders using digital assistant

This disclosure describes techniques that enable a user to place orders for food using a digital assistant. An order for restaurant food pickup or delivery is received from a user. The digital assistant obtains additional details of the restaurant, e.g., from the restaurant website with the use of machine learning techniques to extract text from the website or from other information sources. With user permission, a call is made by the digital assistant to the restaurant to confirm availability of requested items and to complete the order. Details such as an amount of payment to be made, estimated time of pickup or delivery are obtained by the digital assistant. Upon successful placement of the order with the restaurant, a confirmation is provided to the user