Digital Commons Network^™

An Optic Fiber Sensor For Partial Discharge Acoustic Detection, Xiaodong Wang

Dissertations

Partial discharge (PD) is a very common problem in operating power transformers and is one of the factors that could lead to failure of power transformers, leading to power outage and expensive repairs. The acoustic wave induced by PD can be measured and used for monitoring, diagnosing, and locating potential failures in power transformers.

The effects of the temperature of the transformer and transformer oil are one of the very important parameters in PD and these effects are investigated in detail. The Fast Fourier Transform (FF1') is used to synthesize the measured data and results show that for periodic PD …

Optimization Studies Of Thermal Bimorph Cantilevers, Electrostatic Torsion Actuators And Variable Capacitors, Wuyong Peng

Dissertations

In this dissertation, theoretical analyses and optimization studies are given for three kinds of MEMS devices: thermal bimorph cantilevers, electrostatic torsion actuators, and variable capacitors. Calculation, simulation, and experimental data are used to confirm the device behavior and demonstrate the application of the design approaches.

For thermal bimorph cantilevers, an analytical model is presented which allows theoretical analysis and quantitative optimization of the performance based on material properties and device dimensions. Bimorph cantilevers are divided into two categories for deflection optimization: either the total thickness is constant, or the cantilever has one constant and one variable layer thickness. The optimum …

A Micromachined Thermo-Optical Light Modulator Based On Semiconductor-To-Metal Phase Transition, Lijun Jiang

Dissertations

In this research, a micromachined thermo-optical light modulator was realized based on the semiconductor-to-metal phase transition of vanadium dioxide (VO₂) thin film. VO₂ undergoes a reversible phase transition at approximately 68 0C, which is accompanied with drastic changes in its electrical and optical properties. The sharp electrical resistivity change can be as great as five orders. Optically, VO₂ film will switch from a transparent semiconductor phase to a reflective metal phase upon the phase transition. The light modulator in this research exploits this phase transition related optical switching by using surface micromachined low-thermal-mass pixels to achieve …

A Microfabricated Microconcentrator For Sensors And Chromatography, Minhee Kim

Dissertations

The detection and quantitative measurement of trace components is a challenging task. The key component in such an instrument is the concentration step where the analytes are accumulated before the analysis. In this research, simple and inexpensive processes for the microfabrication of microconcentrator that can be used with sensors and as an injector in GC were developed. Analytes are selectively concentrated in the microconcentrator. Rapid electrical heating of the microconcentrator releases the adsorbed species as a 66 concentration pulse", which serves as an injection for the detection system. The relatively small size of the microconcentrator allows it to be heated …