The design and construction of a microwave cavity, to be used in testing the electrical breakdown properties of titania ceramic, is described. The cavity is formed from cylindrical waveguide with a disc of titania centrally located in the cavity. Dimensions are so chosen that resonance is obtained in the H[subscript ol] mode at 3000 mcs. The cavity fields are derived and from them the theoretical cavity Q is found. Experimental values of Q are obtained from low power impedance measurements. Bethe's small-hole coupling theory is applied to the design of an iris to couple power to the cavity from the waveguide system. The dynamics of electrons in this test cavity are investigated. Time-averaged trajectories and upper limits to electron energies are derived from the Hamiltonian of the motion. With this information, the significance of electron bombardment and multipactor effects, in the ceramic breakdown, is discussed. The cavity is used to test glazed and unglazed titania ceramic specimens at high field strengths, using a 2Mw magnetron. In addition, the effectiveness of an aluminum-titania seal on the disc edge is investigated. It is found that, if suitable precautions are taken, the surface breakdown strength of titania is in excess of 50 Kv/cm when subjected to a purely tangential E field. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1983. / Vita. Abstract. Includes bibliographical references (leaves 294-299). Also available via the Internet.

Thesis (PhD) - Swinburne University of Technology, Industrial Research Institute Swinburne - 2006. / A thesis submitted to the Industrial Research Institute Swinburne, Swinburne University of Technology in fulfillment of the requirements for the degree of Doctor of Philosophy - 2006. Typescript. Includes bibliographical references (p. 183-193).

This thesis details the development of a novel microwave breast imaging system based on a faceted metallic chamber using magnetic field data in an air background. The chamber is simulated showing benefits over a cylindrical chamber. The use of magnetic scattered-field data collected on the inner surface of the chamber is shown to provide better reconstruction results compared to electric field data for breast tissue phantoms. Shielded half-loop probes are selected for use in the new system and prototypes are constructed. These probes are sensitive to magnetic fields and reject electric fields. An experimental faceted chamber is also constructed and used with the probes to image simple homogeneous targets as well as a simple breast phantom. Several possible measurement techniques and calibration methods for the new system are analyzed. Tumour detection in the simple breast phantom in an air background is achieved, validating the performance of the novel system. / February 2017

One of the most important areas of the application of industrial microwave technology for materials processing is curing polymers and polymer based composites, and this is currently in a state of considerable flux. Curing of thermosetting composites in multi-mode applicators and joining of a range of thermoplastics in ridged waveguides have been some of the major achievements in the field. This research extends the applications horizon of microwaves in the area of random fibre reinforced thermoplastic composites joining and places emphasis on the development of facilities and methodologies aiming at maximising bond quality. It discusses the fixed frequency microwave equipment used, including a 0.8 kW variable control power generator operating at 2.45 GHz, waveguide and a tuning piston designed for obtaining a standing wave at the seam of the butted and lapped test pieces. The effect of power input and cycle time is detailed together with the underlying principles of test piece material interactions with the electromagnetic field. The process of heterogenous joining, with filler material, or primer, of 33% by weight of random glass fibre reinforced nylon 66, polystyrene (PS) and low density polyethylene (LDPE), thermoplastic composites is mentioned together with the process of autogenous joining of 33% by weight of random carbon fibre reinforced polystyrene (PS) and low density polyethylene (LDPE). The weldability dependence on the dielectric constant, dielectric loss, and hence loss tangent of these materials is also described and investigated. Measurements of the dielectric properties were carried out using the waveguide transmission, probe kit and resonant cavity techniques. X-ray photoelectron spectroscopy for surface analysis was carried out to assess if the filler material had diffused into the parent thermoplastic composite materials. Bond strength measurements of the welded thermoplastic composites were obtained using tensile shear tests. A variable frequency microwave (VFM) facility was also used to join the thermoplastic composites and bond strength results obtained were compared with those procured by the fixed frequency microwave configuration. From the measured data of LDPE/GF (33%), PS/GF (33%) and nylon 66/GF (33%), it was found that at relatively high temperatures and frequencies, these materials became less reflective and permitted more microwave energy to be absorbed. At the same time, their dielectric loss factor increased with temperature and frequency and enabled more of the absorbed energy to be converted to heat. Therefore, within limits, higher temperatures and higher frequencies were more suitable for microwave-assisted joining of the three materials tested. As to the primer/filler, only liquid rapid Araldite was found to be the most favourable in microwave-assisted joining of fibre reinforced thermoplastic (FRTP) composites because of its considerably high value of loss tangent. Another important finding was that the dielectric probe method was found to be the recommended technique to use for measurements of �ՄS and tan �� in microwave joining of materials out of all the methods applied. However, for low loss materials, the values of tan �� need to be acquired through the resonance cavity method.

High-Power Microwaves (HPM) can be used to intentionally disturb or destroy electronic equipment at a distance by inducing high voltages and currents.This thesis presents results from simulations and experiments with a narrow band HPM source, the vircator. The high voltages needed to generate HPM puts the vircator under great stress, especially the electrode materials. Several electrode materials have been tested for endurance and their influence on the characteristics of the microwave pulse. With the proper materials the shot-to-shot variations are small and the geometry can be optimized in terms of e.g. output power or frequency content. Experiments with a resonant cavity added to the vircator geometry showed that with proper tuning of the cavity, the frequency content of the microwave radiation is very narrow banded and in this case the highest fields are generated. The vircator can be built in different geometries. Four different vircator types are investigated and the coaxial vircator is found to have advantages as a high radiated power and the possibility to vary the polarization during operation.Since HPM pulses are very short and have high field strengths, special field probes are needed. An HPM pulse may shift in frequency during the pulse and therefore it is very important to be able to compensate for the frequency dependence of the entire measurement system. The development and use of a far-field measurement system is described. / <p>QC 20121122</p>

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 102-112).

Thesis (M.S.)--Ohio State University, 1957. / Available online via OhioLINK's ETD Center

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