A project report sUbmitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering. Sandtoh, 1995. / Amplitude modulation, is the oldest modulation technique used for voice communication.It is the simplest and cheapest way to modulate and demodulate voice, and as a result, it did not lose much popularity in spits of the development of other, more efficient modulation technique. This project offers a new approach for AM demodulation. The two sidebands are separated and divided into many su-bands. The signals with the lowest noise level are solected and thier levels are individually adjusted according to signal conditions. The result is reduction of over 35 dB in continuous interference and about 15 dB in whit noise level. The new detector and about out-performs the conventional detectors in all aspects and can be used in applications where top performance is required and where mone is no object.

Neste trabalho, construímos um novo e versátil forno de crescimento de cristais pela técnica de Bridgman, o qual pode operar em temperaturas de até 2000 °C em alto-vácuo ou atmosferas inertes. Visto que o problema mais importante após o crescimento de um cristal por esta técnica é a aderência entre o mesmo e as paredes do caidinho, construímos também um sistema para tratamento do material de partida que eliminou este fenômeno. Este procedimento permitiu a obtenção de monocristais cilíndricos de NaI(Tl) transparentes, com alta qualidade e com cerca de 60 mm de comprimento e diâmetro de 20 mm. Utilizando a técnica de Czochralski, crescemos também vários monocristais cilíndricos transparentes de NAI(Tl) com comprimentos de 50 mm e diâmetros de 30 mm. Descrevemos também um método para eliminar o excesso de iodo dissolvido na fase líquida durante o processo de crescimento do cristal. Medidas de absorção ótica realizadas com os cristais de NAI(Tl) à temperatura ambiente e do nitrogênio líquido, mostram bandas de absorção características do Tálio próximas de 304, 291, 257, 249 e 236 nm. Através da relação entre a densidade ótica da banda de absorção em 304 nm e a concentração de tálio, estimamos o perfil da concentração deste elemento ao longo de um cristal crescido por Cz e por Bridgman. Através de espectroscopia de fluorescência encontramos, à temperatura ambiente, uma banda de emissão centrada em 425 nm. Protótipos de detetores foram construídos para avaliar as resoluções de energia dos monocristais crescidos pelos métodos de Bridgman e Czochralski. A performance dos detetores também foi analisada / In this work we constructed a new versatile Bridgman crystal growth furnace that can operate to 2.000 °C in high vacuum or in inert atmospheres. Since the most important post-growth problem in this technique is related with the adherence between crystal-crucible, we also developed an initial materials-treatment system that could prevent this phenomenon, by previously saturating with HI gas. These procedures allowed us to get clear and high quality NaI(Tl) cylindric single crystals up to 60mm length and 20mm diameter. Using the Czochralski technique, we also grew several clear NaI(Tl) single crystals with dimensions up to 50 mm length and 30 mm diameter. A method to prevent the excess of Iodine in the liquid phase during the crystal growth process is also described. Optical absorption measurements in NaI(Tl) single crystals, at room and liquid nitrogen temperatures, show characteristic Thallium bands near 304, 291, 257, 249 and 236 nm. Through the relationship between optical density of the absorption band at 304 nm and Thallium concentration, we could estimate the concentration profile through the entire crystal, grown by each method: Bridgman and Czochralski. By fluorescence spectroscopy we also find, at room temperature, one emission band near to 425 nm. Radiation detector prototypes were developed to evaluate the energy resolution of the single crystals grown by Bridgman and Czochralski methods. The performance of the radiation detectors is also analyzed

Micro-electro-mechanical Systems (MEMS) technology has revolutionized the micro/nano world by making micro/nano devices feasible. These devices allow more exploration and understanding of the micro/nano world. In this dissertation, we will discuss the measurement of wall shear stress in an integrated microfluidic system built by MEMS technology. Specifically, carbon nanotubes (CNTs) were used as the sensing element for gas-flow shear stress measurement in this work. CNTs have already been proven to have an excellent sensing response to temperature, pressure, and alcohol vapour. Based on the thermal sensing response of CNTs, the sensor was designed to operate using convective heat transfer principles in fluid flow. Dielectrophretic manipulation was used to batch fabricate CNTs on a PMMA substrate. The CNT sensor was then integrated into a PMMA microchannel, which was fabricated by a rapid prototyping technique using moulding/hot-embossing processes. The sensor responded to impinging flow as well as gas-flow shear stress. The sensor activation power was found to be linearly related to the 1/3 exponential power of the wall shear stress. With the measurements of an array of sensors, the flow profile of a microchannel with various types of flow could be studied. Compared with the conventional polysilicon sensor, the CNT sensor has the advantage of small dimensions, i.e. a greater spatial resolution for fluidic measurements, and low power consumption, i.e. it consumes ∼1,000 times less power than polysilicon sensors. Therefore, CNT sensors have a great potential to serve as an alternative to silicon-based sensors. / Chow, Wing Yin Winnie. / Adviser: Wen J. Li. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3743. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 105-110). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

by Poon Wing-chak. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1989. / Includes bibliographies.

by Lee Tin-wan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 79-84). / Abstracts in English and Chinese. / Chapter 1. --- Introduction / Chapter 1.1 --- Chemical sensors --- p.1 / Chapter 1.2 --- Quartz crystal microbalance --- p.5 / Chapter 1.3 --- Film immobilization technologies --- p.11 / Chapter 1.4 --- Research Outlines --- p.13 / Chapter 2. --- Saccharide detection by affinity mass sensor / Chapter 2.1 --- Concept of affinity mass sensor --- p.15 / Chapter 2.1.1 --- Affinity chromatography --- p.15 / Chapter 2.1.2 --- Basis of affinity mass sensor --- p.17 / Chapter 2.1.3 --- Saccharide sensing --- p.19 / Chapter 2.2 --- Experimental --- p.20 / Chapter 2.2.1 --- Flow-through cell --- p.21 / Chapter 2.2.2 --- QCA 917 quartz crystal analyzer --- p.21 / Chapter 2.2.3 --- Experimental setup --- p.25 / Chapter 2.2.4 --- Sensor fabrication --- p.29 / Chapter 2.2.5 --- Analysis procedures --- p.29 / Chapter 2.3 --- Results and Discussion --- p.30 / Chapter 2.3.1 --- Formation of boronate complex --- p.30 / Chapter 2.3.2 --- Response curve --- p.31 / Chapter 2.3.3 --- Ligand (APBA) immobilization --- p.32 / Chapter 2.3.4 --- Effect of various operating parameters --- p.35 / Chapter 2.3.5 --- Calibration and reproducibility --- p.38 / Chapter 2.3.6 --- Kinetics analysis --- p.39 / Chapter 2.3.7 --- Stability of sensor --- p.44 / Chapter 2.3.8 --- Determination of fructose in real samples --- p.44 / Chapter 2.3.9 --- Comparison with conventional saccharides sensors --- p.46 / Chapter 2.4 --- Summary --- p.47 / Chapter 3. --- Sol-gel fabrication of affinity mass sensor / Chapter 3.1 --- Principle of sol-gel method --- p.48 / Chapter 3.2 --- Encapsulation of organic molecules in sol-gel matrices --- p.51 / Chapter 3.3 --- Experimental --- p.53 / Chapter 3.3.1 --- Preparation of alkoxide solutions --- p.53 / Chapter 3.3.2 --- Film deposition on QCM --- p.55 / Chapter 3.3.3 --- Film characterization and surface analysis --- p.56 / Chapter 3.4 --- Results and Discussion --- p.57 / Chapter 3.4.1 --- Optimization of conditions for sol-gel process --- p.57 / Chapter 3.4.1.1 --- Choice of catalyst --- p.57 / Chapter 3.4.1.2 --- "H2O: TEOS ratio, R" --- p.59 / Chapter 3.4.1.3 --- Ligand loading --- p.60 / Chapter 3.4.1.4 --- Surface active agent --- p.60 / Chapter 3.4.1.5 --- Temperature --- p.61 / Chapter 3.4.1.6 --- Ageing and drying --- p.62 / Chapter 3.4.2 --- Characterization of APBA encapsulated film --- p.62 / Chapter 3.4.3 --- Performance of the sol-gel derived sensor --- p.65 / Chapter 3.4.3.1 --- Calibration --- p.65 / Chapter 3.4.3.2 --- Stability --- p.66 / Chapter 3.4.3.3 --- Selectivity --- p.68 / Chapter 3.4.4 --- Applicability of the sol-gel derived sensor --- p.69 / Chapter 3.4.5 --- Comparison between sensors fabricated via crosslinking method and the sol-gel method --- p.70 / Chapter 3.4.5.1 --- Surface uniformity --- p.70 / Chapter 3.4.5.2 --- Reproducibility in mass deposition --- p.72 / Chapter 3.4.5.3 --- Stability --- p.72 / Chapter 3.4.5.4 --- Sensitivity towards fructose standard --- p.73 / Chapter 3.4.5.5 --- Comparison of precision and accuracy --- p.73 / Chapter 3.5 --- Summary --- p.75 / Conclusion --- p.77 / References --- p.79 / Titles for tables --- p.85 / Captions for figures --- p.86 / Appendix I --- p.88 / Appendix II --- p.89 / Appendix III --- p.95

by Shao Bing. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (p. 111-122). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web.

This thesis describes a detection system for single molecules based on individual single-walled carbon nanotube field-effect sensors. The sensitivity, spatial confinement and transducer gain of the sensor is derived from a conductance controlled electrochemically created defect, which is also chemically reactive. An automated microfluidic system is designed to enable long and stable measurements of the carbon nanotube device in aqueous environment with temperature control of ±0.1°C. A probe DNA can be covalently attached to the defect through an amide bond and the conductance is modulated when a target DNA binds to the probe. As a result, the conductance shows a traditional random telegraph signal and fluctuates between a hybridized and melted state. By monitoring the conductance as a function of temperature, the kinetics and thermodynamics can be extracted, which are comparable to previous fluorescent correlation spectroscopy studies using optical fluorescent resonant energy transfer. By studying the fluctuation amplitude as a function of charge proximity, buffer concentration and solution potential, it is shown that the sensor is based on a field-effect. The sensor has a temporal resolution of 200 μs and a signal to noise ratio of 3-8 when continuously measuring for 30 seconds. By further reducing the parasitics, the sensor has the capabilities to detect biomolecule kinetics down to microsecond resolution, which could make it an attractive tool for single-molecule experiments with fast kinetics.

No description available.

Ng Tsz Ho. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 67-70). / Abstracts in English and Chinese. / ABSTRACT --- p.i / 摘要 --- p.ii / ACKNOWLEDGEMENTS --- p.iii / LIST OF FIGURES --- p.iv / LIST OF TABLES --- p.ix / Chapter CHAPTER 1 --- INTRODUCTION --- p.1 / Chapter 1.1 --- Background --- p.1 / Chapter 1.2 --- Literature Review --- p.3 / Chapter 1.3 --- Research Objectives --- p.5 / Chapter 1.4 --- Thesis Organization --- p.5 / Chapter CHAPTER 2 --- MODELING OF PIEZOELECTRIC SENSOR/GENERATOR --- p.6 / Chapter 2.1 --- Constitutive Equations --- p.6 / Chapter 2.2 --- Voltage Output of Piezoelectric Materials --- p.9 / Chapter 2.2.1 --- Short Circuit --- p.9 / Chapter 2.2.2 --- Open Circuit --- p.11 / Chapter 2.3 --- Sensitivity and Power Generation --- p.13 / Chapter 2.4 --- Modeling and Analysis of Sensor Structure --- p.23 / Chapter 2.4.1 --- Damping Ratio Estimation --- p.25 / Chapter (a) --- Half-power bandwidth method --- p.25 / Chapter (b) --- Linear interpolation method --- p.25 / Chapter 2.4.2 --- Trade-off between Resonant Frequency and Output Sensitivity of a Sensor --- p.29 / Chapter (a) --- Maximize Sme with constant wn --- p.31 / Chapter (b) --- Maximize wn with constant Sme --- p.33 / Chapter 2.5 --- Model Accuracy --- p.39 / Chapter CHAPTER 3 --- POWER HARVESTING --- p.41 / Chapter 3.1 --- Circuit Model --- p.41 / Chapter 3.2 --- Energy Storage --- p.47 / Chapter 3.3 --- Size Effect on Power Output --- p.49 / Chapter 3.4 --- Power Harvesting Circuit --- p.50 / Chapter 3.4.1 --- Performance of the Power Harvesting Circuit --- p.51 / Chapter (a) --- Power Harvesting Circuit Efficiency --- p.52 / Chapter (b) --- Useful Power Output --- p.53 / Chapter (c) --- System Efficiency --- p.56 / Chapter (d) --- Relationship between Input Excitation and Charge Time --- p.57 / Chapter 3.5 --- Harvested Energy for Wireless Transmission --- p.60 / Chapter CHAPTER 4 --- CONCLUDING REMARKS --- p.64 / Chapter 4.1 --- Sensor/Generator Design --- p.64 / Chapter 4.2 --- Potential Applications --- p.64 / Chapter 4.3 --- Conclusion --- p.65 / Chapter 4.4 --- Future Work --- p.66 / REFERENCES --- p.67 / APPENDIX --- p.71

by Lam Hiu-fung. / "Augustr 2004." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (p. 178-182). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.