Wide-band electromagnetic characterization of ionic and superconductors

This work concerns wide-band characterization of medium conductivity, high conductivity, and Type-II superconducting samples. For the lower range of conductivities, two variable impedance methods are considered. The impedance behind the sample is variable and chosen to maximize the sensitivity of the observables to the complex dielectric constant of the sample. This impedance is varied either by use of a variable short circuit behind the sample, or by using a fixed short with frequency as the variable. By replacing mechanical tuning with the frequency variable, the variable frequency method has the advantage of improved measurements and employs modern frequency swept sources and computer automation. A scalar method for measurement of the complex permittivity of the sample is explained, sources of errors are detailed, range and limitations on conductivity are discussed, and results of measurements of Teflon and silicon are presented. The effects on the observed complex permittivity caused by gaps between a sample and the conductors of a coaxial structure are also examined. A transverse resonance model is developed to examine how the variation of the observed data with frequency may be used to identify the existance of a gap problem, and to develop a relation between the observed and true values when the dimensions of the gap are known. Measurements of the ionic conductor, MEEP, were made in the frequency range of 10 Hz to 7.5 GHz, as a function of frequency, temperature, and salt concentration. Finally, four wide-band and a simple cylindrical cavity apparatus for the detection of changes in the conductivity of type-II superconductors with frequency and temperature are considered