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A cylindrical waveguide resonator for the investigation of ceramic breakdown at microwave frequencies

University of British Columbia

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.

Text

2011-12-14

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http://hdl.handle.net/2429/39688

Electrical and Computer Engineering

University of British Columbia

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