Physics Commons^™

Structural, Transport And Magnetic Studies Of Perovskite Bi1-X Cax Mn O3, Hyungje Woo

Dissertations

This dissertation presents an investigation of the fundamental physics of the perovskite system Bi_1-xCa_xMn0₃. This material belongs to a group of simple perovskites called the manganites which are of technological importance for magnetic device applications as read-head sensors.

The Bi_1-xCa_xMnO₃ system is known to exhibit charge ordering (and high sensitivity to magnetic fields) for a much broader range of x than the well-characterized La_1-xCa_xMnO₃ system. However, the properties of Bi_1-xCa_xMnO₃ over the entire doping range are not well understood. …

Detection Of Vapor Phase Mercury Species By Laser Fluorescence Methods, Xiaomei Tong

Dissertations

Elemental and compound mercury are often both volatile and air stable. Several mercury species emissions have been identified in off-gases from industrial processes. The high toxicity of mercury species and the presence of mercury species in municipal waste and coal have prompted a demand for a cost-effective, accurate, and rugged technique for real-time, continuous detection of mercury species vapors. Real-time, continuous emission measurements are important for process control, monitoring, and remediation. At present, there is no commercial continuous emission monitoring (CEM) technique or instrumentation to reliably monitor volatile mercury species emissions from industrial stacks. Conventional measurement methods, such as cold …

Electrostatic Micro Actuators For Mirror And Other Applications, Xingtao Wu

Dissertations

Micro-electro-mechanical systems (MEMS) based electrostatic micro actuators are becoming important building blocks for innovations in optical signal processing and computing systems due to their inherently small size, high density, high speed and low power consumption. Generally, the principle of operation in these systems can be described as: an electrostatic attractive force causes a mechanical rotation, translation or deformation of a mirror plate, controlling the power, phase or direction of a light beam while it propagates through some medium or through free space. The fast paced, competitive research and development efforts widely being undertaken, both in academia and industry, are demanding …

Ultrathin Silicon Wafer Bonding Physics And Applications, Michael H. Beggans

Dissertations

Ultrathin silicon wafer bonding is an emerging process that simplifies device fabrication, reduces manufacturing costs, increases yield, and allows the realization of novel devices. Ultrathin silicon wafers are between 3 and 200 microns thick with all the same properties of the thicker silicon wafers (greater than 300 microns) normally used by the semiconductor electronics industry. Wafer bonding is one technique by which multiple layers are formed.

In this thesis, the history and practice of wafer bonding is described and applied to the manufacture of microelectomechanical systems (MEMS) devices with layer thickness on the scale of microns. Handling and processing problems …

Broadband Whole Package Fdtd Simulation, Shenjun Li

Dissertations

Whole package analysis is becoming more and more important with the rapid expansion of high frequency electronics. The motivation of this thesis is to find and implement a new method for broadband whole package simulation. 3-dimension (3-D) whole package Finite Difference Time Domain (FDTD) simulation result was first reported in detail in this thesis.

The FDTD method is a widely used full-wave time-domain simulation method used in the design and analysis for electromagnetic (EM) systems, such as antennas, wave propagating, and microwave circuits. Absorbing boundary condition (ABC), such as the perfect matched layer (PML) method, makes it possible to accurately …

Near-Field Imaging With Terahertz Pulses, Oleg Mitrofanov

Dissertations

High spatial resolution imaging is implemented with a novel collection mode near-field terahertz (THz) probe. Exceptional sensitivity of the probe allows imaging with spatial resolution of few microns using THz pulses with spectral content of 120 to 1500 microns. In the present study, the principle of the probe operation as well as the probe design and characteristics are described.

The probe performance is related to effective detection of radiation coupled into the probe aperture. Propagation of short single-cycle electromagnetic pulses through apertures as small as 1/300 of the wavelength is experimentally and numerically studied. Finite-difference time-domain method is used to …

Gated Multi-Cycle Integration (Gmci) For Focal Plane Array (Fpa) Applications, Haijiang Ou

Dissertations

In this thesis, the model and the theory of gated multi-cycle integration (GMCI) were first developed specifically for focal plane array dealing with repetitive or modulated image. The operational modes of GMCI include gated integration (GI), phase sensitive integration (PSI), multi-point summation, multi-point subtraction, multi-sample averaging and some of their combinations. Thus, the analytic theory of GMCI somehow unifies the theories of gated integration, phase sensitive detection, multiple summation and average. PSI works with background and/or dark current subtraction. As a result, the storage well of a pixel is mainly used for signal integration even if there exists a strong …

A Near-Infrared Filter System And Study Of Solar Umbral Dots At 1.6 Μm, Jingshan Wang

Dissertations

The observations of solar magnetic fields are very important because they influence events on the sun. Almost all of magnetographs in the world work in the visible wavelength and they are powerful instruments for measuring strong magnetic fields (above 1000 Gauss) on the sun. To measure the weak solar magnetic fields (below 1000 Gauss), a new filter system (magnetograph) working in near-IR wavelength has been developed in this work. This system includes an interference prefilter (FWHM - 40Å), a liquid crystal magnetic analyzer, a near-IR bireffingent filter (FWHM - 2.5Å), a near-IR Fabry-Perot filter (FWHM - 0.12Å), a near-IR InGaAs …

Software And Hardware Improvements For Digital Solar Magnetograph System, Shu Yang

Dissertations

Digital solar imaging systems have been widely used in solar observations. Their high resolution, high rate of image acquisition and convenience for off-line image processing have provided significant improvements to solar physics research. In this project, two digital magnetograph systems established at Big Bear Solar Observatory (BBSO) have been described. One is used to provide a high frame rate magnetogram system, and the other provides a real-time image alignment, i.e., a correlation tracker system.

The developed correlation tracker system consists of a high-speed 64x64 CCD camera, an EDT image grabbing board, an agile mirror, a D/A board and a Sun …