One of the most exciting studies of contemporary physics is that of high temperature superconductor (HTS). Since its discovery, a large body of experimental and theoretical work by various groups has attempted to achieve a common understanding of this phenomenon. One of the main driving forces for applications centres on the possibility of new and improved microwave devices based on HTS materials, mainly due to the large reduction in the surface resistance that HTS has to offer. However, various problems need to be addressed before the use of HTS materials can be justified, for example fundamental issues such as the nonlinearity of these materials with respect to microwave power, which form the basis of this work. Microwave measurements were conducted on four magnetron sputtered and three laser ablated, Icm2 YBCO thin films, grown on LaAI03 and MgO substrates, respectively, employing the dielectric (rutile) resonator and coplanar resonator techniques. The low power response of the films was initially analysed, looking for clues to the underlying pairing mechanisms in these films. Power dependence and microwave intennodulation distortion (lMD) measurements were conducted between 12 K to 60 K to investigate the nonlinear response of the films, both in zero and finite dc (10 mT) fields. The effect of patterning on the microwave response of the films was also studied. From these measurements, it was observed that the microwave losses of these films are extrinsic in nature, probably a consequence of weak links/defects, and the results also show that films fabricated from the same technique can have significantly varying quality.

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Impedance spectroscopy (IS) is an important technique for monitoring and detection of biomaterials. In order to enable point-of-care systems, low-cost IS systems capable of rapidly measuring a wide range of biomaterials are required. This thesis presents two IS systems, one in Printed Circuit Board level and the other in Integrated Circuit level. The board level system is built for preliminary experimental data collection; it is capable of measuring impedance from 1KHz to 100KHz with 200mV signal injection into cell sample. Experimental results show that magnitude and phase error are less than 6.6% and 2.2%, respectively. An IC level IS front-end is also proposed which utilizes a time-to-digital converter (TDC) and a peak detector circuit (PDC) for quick measurement of both impedance phase and magnitude, respectively. Designed in a 0.18μm CMOS process, the front-end is capable of performing impedance measurements in 6μs at frequencies ranging from 100Hz-10MHz and with a 100Ω-1MΩ dynamic range. Simulation results with cell impedance models show that the system achieves <2.5% magnitude and <2.2 degree phase error. The front-end consumes 28mW total power and occupies 0.4mm^2 area.

The impedance response of a quadrupolar microelectrode array was studied over a wide frequency range to determine whether particles captured at the center of the array could be detected impedimetrically. The microelectrode array (denoted as DEP chip) uses dielectrophoretic forces to concentrate particles at its center. Initial results showed that there was a large electrode-silicon-electrode (ESE) capacitance which dominated at high frequencies. This capacitance was reduced by decreasing the electrode area and increasing the insulating layer thickness. These measures however proved fruitless as this capacitance was still significantly greater then the dielectric capacitance of the chip. This ESE capacitance can be eliminated through the use of a glass substrate so that the dielectric response of the chip dominates at higher frequencies. Since the ESE capacitance prevented experimental validation of impedance spectroscopy as a signal transduction method, computer simulations were performed. These simulations indicated that capture with the current DEP chips would not have a significant impact on the impedance of the chip. Decreasing the electrode gap distance and reducing the area of the electrodes, which is recommended for future work, can remedy this. As measureable changes in the dielectric capacitance of the chip are not possible, a reaction scheme was developed to translate the capture of viral particles into a change in medium conductivity. An ELISA type system was proposed where the viral particles would be functionalized with urease. This uease would then be used to degrade non-ionic urea into ionic products thereby increasing the medium conductivity. A model was formulated to predict the conductivity increase expected for low concentrations, and validated using higher concentrations of biotinylated-urease. Urease from commercial sources proved not to be a viable option as it does not possess a high enough activity to produce a significant conductivity change given the low concentrations of viral particles expected after collection. Urease with suitable activity is produced by the organism Ureaplasma urealyticum which has an activity of 180 000 µmol urea catalyzed min-1 mg urease-1. It is not recommended that this method be pursued further due to technical challenges that would be encountered. / Thesis (Master, Chemical Engineering) -- Queen's University, 2011-05-20 02:35:15.678

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