High temperature superconducting devices

De Melo, Marcos Tavares (1997). High temperature superconducting devices. University of Birmingham. Ph.D.

DeMelo1997PhD_19274866_17538.pdf Text - Accepted Version Available under License All rights reserved. Download (4MB)

Abstract

This thesis is split into two main areas. The main objective of the first part is to obtain surface resistance values for superconducting thin films using a wide microstrip resonator. The thin films are deposited on only one side of a magnesium oxide (MgO) substrate. Thick films made by pyrolysis deposited on one side of zirconia (YSZ) substrate are also measured. The microstrip consists of a copper ground plane and a superconducting second conductor with MgO (or YSZ) dielectric spacer. An expression for the unloaded quality factor of the resonator is developed considering the effect of both thickness and penetration depth for superconducting thin film. The penetration depth is the same order as the thickness of the film. This calculation proved to be more accurate in the extraction of surface resistance from unloaded quality factor results. This is in comparison to the classical calculation which considers the penetration depth to be much less than the thickness of the film.

In the second part of this work a superconducting coplanar instantaneous frequency measurement (IFM) subsystem is investigated. In order to design the delay lines of the interferometers without bends, a slow wave structure is optimised to achieve the desired delay times. Keeping all the other parameters fixed and varying the finger length from 0.6 mm to 4.2 mm, coplanar strips interdigital delay lines are simulated, fabricated and measured for a frequency range of 0.5-3 GHz. In order to avoid the use of air bridges a special coplanar strip power splitter is optimised. Based on this power splitter, a coplanar unequal output impedance power splitter is designed to feed the different delays of each interferometer. Simulated and experimental results of characteristic impedances and group delay of the interdigital delays are used together to design the different delay lines required. Coplanar wave guide, coplanar strips, coplanar unequal output impedance power splitter and coplanar interdigital delay line are integrated without bends or air bridges. Two interferometers with delay differences of 0.6ns and 1.6ns are designed, fabricated and measured at the central frequency of 2GHz over a bandwidth of 1GHz. Theoretical and experimental responses are given together and are in good agreement. A prototype of a 2-bit IFM is measured, connecting the two interferometers. A high temperature superconducting coplanar IFM is proposed to overcome the additional loss.

Type of Work:	Thesis (Doctorates > Ph.D.)
Award Type:	Doctorates > Ph.D.
Supervisor(s):	Supervisor(s) Email ORCID Lancaster, Michael UNSPECIFIED UNSPECIFIED
Licence:	All rights reserved
College/Faculty:	Faculties (to 1997) > Faculty of Engineering
School or Department:	School of Electronic and Electrical Engineering
Funders:	Other
Other Funders:	CNPq-Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq), Ministery for Science and Technology of Brazil, UFPE (Universidade Federal de Pernambuco-Brasil)
Subjects:	T Technology > TK Electrical engineering. Electronics Nuclear engineering
URI:	http://etheses.bham.ac.uk/id/eprint/17538

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