Modelling and monitoring tools appropriate for the resin transfer moulding composites manufacturing route were developed in this study. A simulation of the curing stage of the process based on a finite elements solution of the non-linear heat conduction equation was implemented. The simulation involved appropriate submodels for the incorporation of thermal properties and cure kinetics. A novel non-parametric procedure which utilises interpolation applied directly to experimental Winefics data proved adequate for the simulation of chemical and structural phenomena occurring during the cure. The application of the heat transfer model was successful, the magnitude of thermal gradients was shown*to be significant and the character of degree of cure gradients temporary. An inversion of the heat transfer simulation based on genetic algorithms enabled an optihisation of the cure process parameters to be performed. The heat transfer simulation was combined with thermal monitoring results in order to achieve an extension of the local temperature measurements to the whole component. This combined scheme reproduced successfully the' temperature and degree of cure distributions. The same approach was implemented with similar outcomes using artificial cure monitoring results. Impedance cure monitoring was used in order to follow in real time the reaction progress. An interpretation was found for the manifestation of vitrification in the impedance signals. A new equivalent circuit representing accurately the behaviour of the resin system investigated was developed. A methodology which correlates the progress of cure with the imaginary impedance spectrum evolution was established. Dielectric flow monitoring techniques appropriate for the filling stage of resin transfer moulding were devised. Lineal sensors enabled monitoring of the progress of filling to be made in both conductive and non-conductive reinforcements.

This study is concerned with the association characteristics of solutions of alcohols in some non-polar solvents. The permittivities at 2 MHz and 25°C for solutions of the straight chain octanols in cyclohexane, carbon tetrachloride and benzene have been examined over the entire solute concentration range, with particular attention -1 being paid to the range below 0.1 molℓ⁻¹ By applying the Kirkwood- Fröhlich equation to these data, the apparent dipole moments of the alcohols as a function of concentration have been evaluated. These concentration dependencies have been correlated with infrared absorption results on the same systems to provide information on the sizes and configurations of the proposed hydrogen bonded multimers. It is concluded that, at very low solute concentrations, the alcohol molecules exist as monomers; but with increasing concentration, two types of hydrogen bonded multimers are formed, the first (at low concentrations) being of high dipole moment and the second (at higher concentrations) being of low dipole moment. At high concentrations, the molecules associate to form a three-dimensional network. Attempts have been made to determine equilibrium parameters for molecular models which are consistent with the qualitative understanding of the association behaviour. These parameters were obtained by applying least-squares, curve-fitting techniques to the low concentration permittivity data. A similar investigation has been conducted on solutions of 2,3,4-trimethyl-3-pentanol in the same solvents. The steric hindrance around the hydroxyl group of this alcohol modifies the association behaviour so that a three-dimensional network does not form at high solute concentrations. Proton magnetic resonance chemical shifts for the hydroxyl proton of this alcohol in carbon tetrachloride solutions have been measured. Attempts have also been made to determine equilibrium parameters which describe formation of the hydrogen bonded multimers. To extend this study to include solutes other than octanols, similar experiments have been conducted on solutions of t-butanol in hexadecane, a system which has recently been investigated by other workers using different experimental techniques. The association behaviour of this system is qualitatively similar to that of the straight-chain octanols. The combination of permittivity and infrared measurements, although proving extremely powerful in interpreting the association characteristics of dilute alcohol solutions, is less adequate at high solute concentrations. Attention was therefore directed towards dielectric relaxation and viscosity studies to investigate concentrated solutions. The relaxation times at 20°C of the low frequency dispersion have been measured for solutions of 1-propanol, 1-butanol, 1-hexanol, 1-octanol and 1-decanol in cyclohexane using time domain reflectometry techniques. Similar measurements have also been made on solutions of 1-butanol and 1-octanol in carbon tetrachloride and in benzene. The concentration dependence of the viscosities of certain of these systems has also been examined in an independent study. The ratio of the dielectric relaxation time to the viscosity, the "reduced relaxation time", is qualitatively similar for each system studied. This similarity leads to an explanation of the molecular process responsible for the low frequency dispersion in terms of the proximity of the hydroxyl groups in concentrated alcohol solutions and the fraction of the groups which are not involved in hydrogen bonding.

Field restrictions on E- and H-waves are examined for an inhomogeneous isotropic medium. Restrictions on E-and H-waves are, also, discussed for wave-guides of varying cross section, such as for example a circular-section waveguide having an axially dependent radius For an axially symmetric periodic structure with a slowly varying radius, an approximate wave equation is derived which is separable. The field problem is then reduced to finding the solution to Hill's equation. A treatment of electromagnetic waves in media with characteristics possessing finite discontinuities in the direction of propagation is developed. The development avoids the use of explicit boundary conditions. To illustrate the method, three examples are given. This method is extended to include media with characteristics possessing finite discontinuities in, and transverse to, the direction of propagation. Two examples are given. In the first an E-wave solution is found for a cylindrical waveguide loaded periodically with dielectric disc, the disc radius being smaller than the cavity radius. Two methods of solution are offered: one is a first mode approximation and the other is an approximate series solution. A short comparison is made between experimental measurements made on dielectric loaded periodic structures of the forementioned type and theoretical predictions based on the first mode approximation. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

[No abstract submitted] / Science, Faculty of / Chemistry, Department of / Graduate

In the first section of this thesis the simple Pierce Theory for the travelling wave tube is discussed and developed. The result of this analysis is a number of equations which produce information about gain and bandwidth. The next section of the thesis is devoted to a discussion of periodic structures with particular emphasis on dielectric loaded periodic structures. Finally the Pierce Theory is applied to the dielectric slow wave structure. Results are presented of a study performed to find a correlation between the physical dimensions of the dielectric structure and the gain-bandwidth properties of a travelling wave tube employing the structure. These results, which are in graphical form, can be used to eliminate the initial exploratory design work for travelling wave tubes of this type. A sample use is made of the design curves and the results are compared to a computational check to show both the usefulness and the limitations of the curves / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Dielectric relaxation of Fluoroform (CHF₋₃) is measured carefully in the density region (0.0009-0.28 amagat) where the molecular reorientational frequency is of the same order as the oscillating electric field of 30 MHz. The simple Debye model, which assumes that the dipole relaxes exponentially towards its equilibrium value characterized by a single relaxation time, is found to be inadequate to explain the experimental data. The Cole-Cole model, which assumes a distribution of relaxation times is tried. Agreement with experiment is only improved at densities below 0.03 amagat. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Metasurfaces are a novel class of optical devices, made up of an array of subwavelength scatterers that can allow unprecedented control of an optical wavefront. These devices can be fabricated using conventional nano and microfabrication processes en masse and have thin and lightweight form factor making them ideal for use in compact and miniaturized optical systems. In this thesis, I will first introduce the field of metasurfaces with a historical overview of the research and development in this field. Following the introductory section, I will demonstrate a design for broadband infra-red absorber based on the metasurface platform, demonstrating the ability of metasurface to control broad spectrum of light. Subsequently, optical wavefront engineering capability of metasurfaces is displayed by demonstration of multifunctional metasurface devices, including examples of multiwavelength metasurface lenses and holograms. An example of polarization multiplexed metasurface will also be discussed. As an extension of multiwavelength metasurface lens, a framework for correcting chromatic dispersion inherent in metasurface is presented. I will then demonstrate a strategy to design metalenses with broadband achromatic aberration correction for imaging applications and discuss fundamentals limitations on the extent of chromatic correction that can be achieved. This will lead to a section on multi-element metasurface design for correcting monochromatic aberration in addition to chromatic aberration for compact imaging systems. Finally, I will conclude the thesis with an outlook that points to application areas where metasurfaces, with their thin and light form factor are ideal alternative to replace many conventional optical devices.

No description available.

No description available.

No description available.