Yes / A compact dielectric resonator antenna for ultra-wideband vehicular communication applications is proposed. Two cylindrical dielectric resonators are asymmetrically located with respect to the center of an offset rectangular coupling aperture, through which they are fed. Optimizing the design parameters results in an impedance bandwidth of 21%, covering the range from 5.9 to 7.32 GHz in the lower-band and a 53% relative bandwidth from 8.72 to 15 GHz in the upper-band. The maximum achieved gain is 12 dBi. Design details of the proposed antenna and the results of both simulations and experiment are presented and discussed.

No / A small dielectric resonator antenna has been designed for ultra wideband (UWB) communication system applications. The antenna element is a rectangular low permittivity ceramic block, with a dielectric constant of 9.4, and the modified T-shaped feed network includes a 50 ohm microstrip line to achieve strong coupling, and some bandwidth enhancement. The antenna performance is simulated and measured over a frequency band extending from 3100 MHz to 5500 MHz; the impedance bandwidth over this interval is 55.8% with VSWR <; 2, making the antenna suitable for UWB applications.

Block copolymer (BCP) phase segregation and self-assembly into two or more distinct domains are primarily dictated by two parameters: the block volume fraction, f, and the product of the segment-segment interaction parameter and the length of polymer chain, XN. The volume fraction determines a block copolymer's phase segregated morphology, whereas XN dictates its overall segregation strength, or phase stability. In order to achieve smaller domain sizes, the interaction parameter must be increased to compensate for the decrease in chain length. In the melt, PEO-b-PPO-b-PEO (Pluronic) triblock copolymer surfactants do not phase segregate primarily due to their low molecular weights and insufficient segregation strength, or low XN. Strong hydrogen bonding and selective interactions of PEO chains with homopolymers capable of hydrogen bonding, such as poly(acrylic acid) were shown to increase the effective segregation strength of the blend. Small angle X-ray scattering demonstrated highly ordered sub-10 nm domains resulting from phase segregation of the blends. The strong hydrogen bonding interaction between PEO and H-bonding homopolymers was also utilized to incorporate polyhedral oligomeric silsesquioxanes (POSS) into silicate films. In order to improve the compatibility between hydrophobic POSS with hydrophilic Pluronic copolymers, POSS-decorated acrylate monomer was copolymerized with acrylic acid. This eliminated the macrophase segregation between the BCP templates and POSS molecules. The inclusion of POSS is shown to increase the mechanical performance of the low-k films. A supercritical CO2 synthesis route enables the transport of silica precursors into the polymer blends. An increase of hardness of up to 1.8 GPa at k = 2.4 and 1.2 GPa for k = 2.1 was observed for these mesoporous organosilicate films. Finally, this work has also focused on the formation of ordered domains of the Pluronic surfactants into a ternary solvent system consisting of two liquid solvents and compressed CO2. Compressed CO2 can influence the compatibility of liquid solvents, inducing phase separation or phase mixing. CO2-induced phase separation of acetone and water and phase mixing of tetradecane and methanol were studied for the formation and breaking of nanoscale domains in the presence of Pluronic surfactants. Long-range ordered structures were observed using small angle neutron scattering.

<p> An improvement on the synthesis of a distributed RC notch filter, by computer-aided design techniques, is appraised. A brief presentation of the synthesis of thin-film RC tapered networks is made, along with applied uses of computer-aided design to RC distributed networks, particularly in the realizability of certain RC transfer functions.</p> <p> The preparation of the problem, accompanied by different methods of approach, is explained. Included are criticisms made, leading to the reasons for abandoning the more tasking ones.</p> <p> The Adjoint Network method of determining, gradients, with respect to circuit adjustable parameters, is evaluated fully, and the important use which it lends to the optimization problem is demonstrated. The outcome of the design approaches are given in tables, with theoretical responses compared in graphs. Actual circuit responses are indicated in photographs, and comparisons with theoretical responses are shown in graphs.</p> / Thesis / Master of Engineering (MEngr)

<p> This thesis is based on the studies of cross-linked network polymerization by measurements of dielectric permittivity and a study of the polymers formed by dynamic mechanical analysis. The network polymers are formed by reacting a trifunctional epoxy with three primary amines, namely, aniline, 3-chloroaniline and 4-chloroaniline. The manner in which the dielectric permittivity changes on polymerization was followed from the monomeric to the ultimately polymeric state, and the relaxation time and the distribution of reaction times was followed with reaction time. Isothermal measurements of the heat evolved during the reaction led to a determination of the number of covalent bonds formed at any instant of reaction time, thus the dielectric relaxation time was related to the number of covalent bonds formed during polymerization. The relaxation time increased progressively more rapidly with the increase in the number of covalent bonds formed under isothermal conditions as the reaction progressed towards completion. As the number of covalent bonds increased, a high-frequency, or low-temperature, relaxation process emerged. This was observed for both the time-variant (fixed frequency) and time-invariant (dielectric spectra) dielectric data.</p> <p> The extent of reaction at the gelation time deduced from the irreversible decrease in the dc conductivity on polymerization was 50% lower than anticipated from Flory-Stockmayer theory, but, the extent of reaction at the point of singularity agreed with the theory. As polymerization reactions occurred, both the static and high-frequency dielectric permittivities decreased with time. Data simulated for the dielectric behaviour for a fixed frequency during the course of polymerization were analyzed to confirm that the two analysis procedures (time-invariant and time-variant) yield the same parameters within 2-3%.</p> <p> The three, new, network polymers thus produced had unrelaxed and relaxed moduli that were in the ranges of 1.35-1.51GPa and 6.6-10.6MPa, respectively. GU of the three polymers decreased with increasing temperature and GR increased. The former effect has been attributed to mainly a decrease in the GR of the low-temperature, or high-frequency, β-relaxation process, and the latter to the increase in the temperature, and consequently, the increase in the entropy, as discussed in the entropy theories of the rubber modulus. The spectrum of the shear modulus cannot be superposed by shifting the spectra along the frequency scale alone. The three reasons discussed are; (1) GU and GR change with temperature, therefore the spectra differ in magnitude for each measurement temperature, (2) the presence of a temperature-dependent, frequency-independent background loss changes the magnitude of tan∅ with the temperature, and (3) the influence of secondary-, β-, or Johari-Goldstein relaxations causes deviations in the shape of the spectrum such that they cannot be superposed. It was determined that none of the three effects described contribute significantly to the changes in the isothermal spectra, and hence, the principle of the time-temperature superposition does not apply to the three polymers in this study. The three polymers produced have a mechanical loss peak at room temperature that is attributed to the β-relaxation process and whose magnitude is greater than that of polycarbonates. This suggests that the three new polymers produced here can absorb more energy at room temperature than the polycarbonates.</p> / Thesis / Master of Engineering (MEngr)

<p> It is known in the case of an electron gas that the Coulomb force between electrons is screened due to the density variation around the electrons. In a similar way the force acting between nucleons in nuclear matter may be appreciably different from the free nucleon-nucleon interactions. The main theme of this thesis is to examine the "Screening" effect of the nuclear force. To this end, first the dielectric formulation of the theory of an electron gas is reviewed. Relationship among the chain-diagram approximation, the random phase approximation and the dieledtric formulation is discussed in detail. These techniques are then applied to nuclear matter taking the one-pion exchange potential as an example. It is found that the screening effect on the nuclear force in nuclear matter is indeed quite appreciable. The validity of the approximations is discussed. </p> / Thesis / Master of Science (MSc)

Electronic devices are used for tasks such as keeping people connected, figuring out the contents of a package or detecting impurities in the air. The use of electronic sensors in short life cycle products has also begun to increase with the field of smart packaging. For example, RFID tags are used everyday in sorting facilities to identify packages and then discarded when the packaging is thrown away. Every year the world generates millions of tons of E-waste and most of it is exported, incinerated, or put in landfills. To mitigate the impact of electronics on the environment, it is essential that the next generation of disposable electronic devices are fabricated using environmentally friendly materials. For these materials to be considered for high throughput fabrication they need to be solution processable and biodegradable, all while having the necessary mechanical and electrical properties. This thesis focuses on the development of novel environmentally friendly dielectrics that can be used in capacitors and thin film transistors. A common environmentally friendly and biodegradable material used as a polymer dielectric is poly(vinyl alcohol) (PVA). Although PVA has a high capacitance it also has its drawbacks. Being mostly processed from aqueous solutions it is hard to form uniform thin films of PVA and it is sensitive to moisture which changes its capacitance. PVA is also a polar material which can cause charge trapping at the semiconductor/dielectric interface when used as a dielectric in the fabrication of organic thin film transistors (OTFTs). In this thesis we use different strategies such as blending dielectrics and stacking them to help improve the performance of PVA as a dielectric in OTFTs. In the first study, I demonstrate how low weight percentages of cellulose nanocrystals can be used to increase the viscosity of PVA without negatively impacting its dielectric properties. This led to better film uniformity and a larger number of functioning OTFTs. The second study focused on using a toluene diisocyanate terminated polycaprolactone (TPCL) polymer as a low-k barrier between PVA and the semiconductor. The TPCL led to an increase in OTFT performance and a large reduction in moisture sensitivity. For the third study, I improved the shelf life of the TPCL materials by replacing the toluene diisocyanate end units with UV crosslinking end units. The UV end units were protected unlike the TPCL end units allowing the polymer to remain stable under ambient conditions. The UV-PCL demonstrates similar resistance to moisture and dielectric properties to TPCL while being more stable and easier to use in traditional printing processes. My last study, investigates the use of a poly(lactic acid) (PLA) layer as a third layer in the TPCL/PVA/PLA dielectric system. The PLA layer acted as an intermediate between the substrate and PVA increasing the adhesion of PVA. Further the PLA layer improved OTFT performance and allowed for n-type single walled carbon nanotube transistors under ambient conditions. Finally, this work has demonstrated ways to improve the performance of PVA so that it can be used as an environmentally friendly dielectric in thin film, flexible and printed electronic applications.

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