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Atrial fibrillation is a common cardiac condition which can place the patient at risk for many serious medical issues. Current interventional procedures employ cardiac ablation catheters guided using x-ray fluoroscopy imaging, which generates restricted two-dimensional images of the heart, and exposes the patient to a high dose of radiation. Three-dimensional catheter position data can be obtained and radiation exposure can be mitigated by using Magnetic Resonance Imaging (MRI) for this procedure. The magnetic field of the MRI machine can be strategically leveraged to steer and actuate a robotic ablation catheter, by energizing small embedded electromagnetic coils within the catheter tip. These coils however, may undesirably interact with the MRI machine’s rotating radio-frequency (RF) magnetic field, potentially leading to excessive heating of the catheter or power supply damage. This thesis aims to characterize the RF response of actuation coils used in a novel MRI guided catheter system, and design an actuation coil set prototype which can safely operate in the MRI environment. The proposed final actuation coil set consists of 3 coils wound over the catheter body, and aims to improve the RF behavior of the coil set by implementing improved design elements such as a new winding pattern, wire gauge variation, and utilization of capacitors within the system. The final prototype presented successfully meetsthe required standards and is able to perform desired actuations.

The A15 superconductor Nb3Sn has shown great promise to replace niobium as the material of choice for the construction of superconducting radio-frequency (SRF) accelerator cavities. It promises, at least on paper, greater efficiency and higher accelerating gradients, with the potential to enable the construction of smaller yet more powerful accelerators than can be constructed using niobium. Although the state-of-the-art performance of cavities coated with Nb3Sn has shown great potential, the achievable limits in cavity quality factor Q0 and accelerating gradient Eacc are still below that expected given theoretical limits. In this work we present and discuss results of experiments carried out to understand the current limitations on Q0 and Eacc, and propose methods to improve these further. We will conclude with an outlook to the future, and the prospects that Nb3Sn could enable.

The global energy and climate challenges have motivated development of innovative techniques to satisfy energy demand while minimizing emissions. To this end, hydrogen as an alternative energy carrier in the transportation sector is an attractive option. In addition, there is already a great need for hydrogen gas in several industrial processes such as hydro-cracking of crude oil to produce gasoline and production of ammonia and methanol. The current dominant methods of hydrogen production from fossil fuels are well-developed and have reached relatively high energy efficiencies (up to 85%), but these methods rely on non-renewable natural resources and produce carbon dioxide emissions. This work investigates the feasibility of hydrogen production by dissociating water molecules in a radio-frequency (RF) plasma discharge. In addition to the widespread usage of hydrogen gas, applications of water plasma have permeated in many areas of research, and information on basic behaviors of a water plasma discharge will provide fruitful insights for other researchers. An RF plasma source equipped with a double-helix antenna (m = 1 mode) and an applied axial magnetic field is designed to operate on water vapor. It is shown that water molecules are being dissociated in the discharge. Experimental results show that the rate of hydrogen production increases linearly with RF power in the absence of the applied axial magnetic field. With the magnetic field, the rate of hydrogen production increases from 250 to 500 W, and begins to saturate with RF power. Despite this saturation, it is shown that hydrogen increases with magnetic field strength at a fixed RF power. Further, the rate of hydrogen production increases with water input flow rate up to 100 sccm for a fixed RF power level, and begins to decrease at 125 sccm. This dissertation characterizes the rate of hydrogen production and plasma properties as a function of RF power, applied B-field strength, and water input flow rate. A zero-dimensional kinetics model is used to determine the theoretical energy efficiency.

With the ever increasing complexity of integrated circuits and constantly shrinking device sizes, the need to develop entire dystems on chip (SoC) has received a significant momentum. With this need,comes the responsibility of bringing about mature computer-aided design (CAD) techniques to handle the complexity of designing such systems. Although mature commercial techniques exist for designing the digital components in a system, design automation for the irreplaceable analog and radio-frequency (RF) circuits in a system remains incipient. Circuit sizing is one of the most important and challenging constituents of any analog design process. Given a set of high-level specifications and a circuit topology, sizing aims to determine the device dimensions and biasing information in order to meet the desired specifications. In this dissertation, we address two major problems ailing the sizing process. One of the most important challenges in analog synthesis is to design a circuit which meets the input specifications at the post-layout stage. The other problem we seek to address in this dissertation is the enormous time spent in sizing due to the overhead of running thousands of simulations for performance estimation. Analog and RF circuits are extremely sensitive to layout parasitics. This extreme dependence of the behavior of analog circuits, on layout-induced parasitics, is responsible for several silicon runs before a functional chip can be designed. We propose two techniques to introduce layout awareness during circuit sizing. The first approach is based on developing fast and accurate models of the layout parasitics. The parasitic capacitance models are used inside a circuit sizing framework to estimate the layout parasitics and account for them in the performance evaluation process. This approach relies on procedural layout generators (PLGs) for developing the parasitic models. The second approach proposed for layout-aware design draws a similarity between layout parasitics and process variables in a yield optimization problem. A two-step approach is proposed for identifying the worst case parasitic corners and for sizing in presence of these parasitics. A parasitic robust design is sought for which passes the post-layout validation test. Circuit sizing primarily comprises of two components: a search engine and a performance estimator. Stochastic combinatorial optimization techniques are used for exploring the design space. For each candidate design explored by the search engine, the circuit performance is estimated. Typically, the performance estimation time dominates the overall synthesis time. Most commercial approaches deploy a simulator-in-loop approach to the sizing problem due to the high accuracy desired from the estimation process. We propose two techniques for replacing the simulator with accurate and efficient performance models. Since the performance models allow a very quick evaluation of the circuit performance, their use helps in drastically reducing the time complexity of sizing. Unlike the existing macro-model driven sizing techniques, the proposed approaches guarantee to obtain accurate simulator validated design solutions. We propose a unified system which aims to resolve both the problems of computational complexity of performance estimation and performance closure at the layout stage in the same flow. The proposed system combines the ideas of parasitic modeling, design optimization in presence of worst case parasitics corners and performance macromodeling put forth in this dissertation to create high quality designs efficiently.

This thesis examines temperature dependence of magnetic susceptibility of the organic free radical galvinoxyl.

This thesis examines the operation and control of a radiofrequency ion source.