Typescript (photocopy)

Thesis (M.Eng.Sc.) - Dept. of Electrical Engineering, University of Adelaide, 1979. / Typescript (photocopy).

In the past, spectral analysis of Arctic Sea ambient noise has been carried out by octave band pass filtering and linear rectification, followed by analogue Integration. To relate this integral to the power spectral density of the noise, the amplitude distribution of the noise has been assumed to be Gaussian, giving rise to certain errors. A system is proposed which consists of a stage of variable gain followed by a polarity coincidence statistical wattmeter and measures the power spectral density of ambient noise after band pass filtering. The wattmeter will handle an input signal dynamic range of at least 20 dB and does so regardless of the statistical nature of the noise. This dynamic range is extended dynamically by controlling the gain of the driving stage. The gain level is automatically adjusted during a one minute "adaptive" time interval so that the noise delivered to the wattmeter is over the region of optimal system operation. Measurement of the power spectral density of the ambient noise is then made in the subsequent four minute interval. A prototype wattmeter has been constructed and tested. The gain level is determined by requiring that the noise not exceed fixed levels more than a certain percentage of the time. This automatic adjustment is carried out during a one minute adaptive time interval, and a relatively accurate measure of the mean square value of the noise is determined during the four minutes that follow. For purposes of testing the prototype, d.c. inputs and sinusoidal inputs of wide frequency and amplitude ranges were used. The actual root mean square value of the inputs was measured with a thermal milliammeter and a precision voltage divider. The results of these tests show the region of operation where the input-output relationship of the wattmeter is linear. From these results, suggestions are made.as to how the proposed system could be modified to replace the analogue system used for Arctic Sea ambient noise spectral analysis. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

by Kwong-hon Lee. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references (leaves [112-115]). / Chapter CHAPTER 1. --- INTRODUCTION / Chapter CHAPTER 2. --- PRINCIPLE OF ELLIPSOMETER / Chapter CHAPTER 3. --- MATHEMATICAL REPRESENTATION OF ELLIPSOMETRY / Chapter Section 3.1 --- Ambient Substrate / Chapter Section 3.2 --- Single Layer (Ambient-film substrate) / Chapter Section 3.3 --- Multilayer system (Isotropic Stratified planar structure) / Chapter CHAPTER 4. --- CLASSIFICATION OF ELLIPSOMETER / Chapter Section 4.1 --- Null-type Ellipsometer / Chapter Section 4.2 --- Photometric Ellipsometer / Chapter Section 4.3 --- Spectroscopic Ellipsometer / Chapter CHAPTER 5. --- CONSTRUCTION AND CALIBRATION OF THE SPECTROSCOPIC ELLIPSOMETER / Chapter Section 5.1 --- Design and construction / Chapter 5.1.1 --- Optical Assembly / Chapter 5.1.2 --- Electronic Circuit / Chapter 5.1.3 --- Micro-computer (Software) / Chapter 5.1.4 --- Modification of configuration / Chapter Section 5.2 --- Alignment and Calibration / Chapter 5.2.1 --- Alignment of Optical units / Chapter 5.2.2 --- Calibration of the system / Chapter 5.2.3 --- Measurements on standard samples / Chapter CHAPTER 6. --- ANALYSIS OF ELLIPSOMETRIC PARAMETERS / Chapter Section 6.1 --- Ambient-substrate model / Chapter Section 6.2 --- Ambient-layers model / Chapter 6.2.1 --- Parameter generator / Chapter 6.2.2 --- Least square fitting / Chapter 6.2.3 --- Choice of error function / Chapter CHAPTER 7. --- EXPERIMENTAL RESULT / Chapter Section 7.1 --- Spectra of Refractive index / Chapter 7.1.1 --- Low temperature MBE growth GaAs / Chapter 7.1.2 --- Amorphous Carbon / Chapter 7.1.3 --- High order x AlxGa1-xAs with different cooling rate / Chapter Section 7.2 --- Comparison of ellipsometric spectrum of SOI samples / Chapter 7.2.1 --- Difficulty in the analysis of multi-layer structure / Chapter 7.2.2 --- Silicon on insulator (SOI) / Chapter 7.2.2.1 --- The beam current effects / Chapter 7.2.2.2 --- Annealing after implantation / Chapter CHAPTER 8. --- CONCLUSION / Chapter Section8.1 --- Summary of the results / Chapter Section8.2 --- Suggestions for future work / REFERENCE / APPENDIX(A)MARQUART ALGORITHM / Chapter (B) --- CIRCUIT DIAGRAM

Thesis (M.S.)--University of Texas at Dallas, 2008. / Includes vita. Includes bibliographical references (leaves 62-63)

This dissertation centers on the development of a new helium microwave induced plasma. The analytical utility of this new plasma source is critically evaluated. To sustain the helium plasma a TM ₀₁₀ high efficiency microwave induced plasma, HEMIP, was used. The HEMIP is a modification of the original Beenakker cavity that precludes the use of external matching devices, such as the highly popular double tuning stub. The He-HEMIP was analytically characterized as an atomization source for metals and nonmetals with the use of atomic emission spectrometry (AES) and atomic fluorescence spectrometry (AFS). A torodial plasma was sustained in the cavity solely by the helium gas output of the nebulizer. Aqueous samples from a pneumatic glass nebulizer/Scott spray chamber were aspirated into the cavity without a desolvation apparatus. With AES, detection limits for metals and nonmetals were in the sub-ppm range. with AFS, detection limits for metals were determined to be in the low ppm to sub-ppb range and were found to be not statistically different from those reported for HCL-ICP-AFS. Linear ranges for AES and AFS ranged from four up to five and one-half orders of concentrative magnitude. The effect of sample uptake rate on the emission intensity was investigated. Ionization interferences were determined to be minimal and phosphate interferences were found not to occur. Development and characterization also included studies of the He-HEMIP's physical characteristics. Excitation and ionization temperatures were found to be approximately equal, suggesting that the He—HEMIP approaches local thermodynamic equilibrium. Evaluation of the He—HEMIP as a routine detector for sulfur during coal pyrolysis and coal extracted samples was investigated. Results showed that the He-HEMIP is selective and sensitive. Detection values compared favorably to those of certified coal samples. / Ph. D.