Thesis (Ph. D.)--University of Hong Kong, 2000. / Includes bibliographical references.

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The thesis reports the results of the research carried out towards the development of an electrooptic sensor for DC and extra low frequency electric field measurement. Available cubic electrooptic crystals were compared from the sensor sensitivity point of view. A new figure of merit was used taking into account the attenuation of the electric field in the dielectric crystal and its shape. The effect of optical activity in 23 cubic crystals was analyzed using the concept of Poincare sphere. The cubic crystals were further characterised for the charge relaxation time constant to estimate their performance in DC field measurements. Crystals of Bismuth Germanate and Lithium Niobate were identified as suitable materials for the DC field sensor. The selected crystals were found suitable at extra-low-frequencies. DC field measurements, without the rotation of the crystal, were possible only with Lithium Niobate. However, its performance was influenced to a great extent by the effect of stimulated conductivity. The quarter-wave plate and the crystal of Lithium Niobate were identified as the main sources of temperature instability. A new method of temperature compensation of the quarter-wave plate is proposed. Due to the temperature instability of Lithium Niobate, mainly attributed to the pyroelectric effect and natural birefringence, it is difficult to use the sensor in practical applications. The performance of the sensor is significantly affected by the presence of an external space charge. The proposed method of its elimination using an artificial extension of the sensing element did not reduce the space charge effect adequately. The response of the sensor in a space charge environment was found to be linear and independent of the space charge density. This enabled measurements of static fields in a unipolar environment. The direct field measurements in bipolar environment suffered from a drift which is intolerable in practical measurements. The minimum detectable electric field of this sensor in the frequency range from 1 to 200Hz was 1V/m, with a signal to noise ratio equal to 0dB and a resolution of 1V/m. The static field measurements were limited to measurements of pulses with a duration of 200s, due to a long term drift of photodetectors. The minimum detectable level of DC electric field was 2.4kV/m.

Apresentaremos nesta tese três novos tipos de dosímetros de radiação, projetados para medir radiação X, na faixa de diagnóstico: o dosímetro de radiação fotoacústico pulsado, o dosímetro de radiação piroelétrico e o dosímetro de radiação piroelétrico pulsado. Estudamos também o dosimetro de radiação fotoacústico com o objetivo de compará-lo com os novos dosímetros desenvolvidos. Propomos uma metodologia para calibração de um dosímetro fotoacústico que prescinde da calibração de sua resposta em um campo conhecido de radiação ionizante. Apresentaremos um modelo teórico para explicar os resultados obtidos com o dosímetro de radiação piroelétrico pulsado. Os resultados encontrados mostram que os dosímetros desenvolvidos são do tipo calorimétrico, sendo a resposta deles linear com a taxa de fluência de energia da radiação X. / In this thesis we present three new types of radiation dosimeters, designed to measure X-rays in its diagnostic region: the pulsed photo acoustical radiation dosimeter, the pyroeletric radiation dosimeter and the pulsed pyroelectric radiation dosimeter. We also study the photo acoustical radiation dosimeter with the scope of to compare its characteristics with the characteristics of the new developed dosimeters. We propose a methodology for calibration of a photo acoustical dosimeter which doesn´t require the calibration of its response in a known field of ionizing radiation. We present a theoretical model to explain the results produced by the pulsed pyroelectric radiation dosimeter. The obtained results show that the developed dosimeters are of calorimetric type, being linear its response with the X-ray energy fluency rate.

Apresentaremos nesta tese três novos tipos de dosímetros de radiação, projetados para medir radiação X, na faixa de diagnóstico: o dosímetro de radiação fotoacústico pulsado, o dosímetro de radiação piroelétrico e o dosímetro de radiação piroelétrico pulsado. Estudamos também o dosimetro de radiação fotoacústico com o objetivo de compará-lo com os novos dosímetros desenvolvidos. Propomos uma metodologia para calibração de um dosímetro fotoacústico que prescinde da calibração de sua resposta em um campo conhecido de radiação ionizante. Apresentaremos um modelo teórico para explicar os resultados obtidos com o dosímetro de radiação piroelétrico pulsado. Os resultados encontrados mostram que os dosímetros desenvolvidos são do tipo calorimétrico, sendo a resposta deles linear com a taxa de fluência de energia da radiação X. / In this thesis we present three new types of radiation dosimeters, designed to measure X-rays in its diagnostic region: the pulsed photo acoustical radiation dosimeter, the pyroeletric radiation dosimeter and the pulsed pyroelectric radiation dosimeter. We also study the photo acoustical radiation dosimeter with the scope of to compare its characteristics with the characteristics of the new developed dosimeters. We propose a methodology for calibration of a photo acoustical dosimeter which doesn´t require the calibration of its response in a known field of ionizing radiation. We present a theoretical model to explain the results produced by the pulsed pyroelectric radiation dosimeter. The obtained results show that the developed dosimeters are of calorimetric type, being linear its response with the X-ray energy fluency rate.

Significant research efforts have been directed into smart home environments in the last decade creating abundant opportunities for the broader home services ecosystem to foster a wide range of innovative services. Research interest has been given on automatic identification and tracking of people within the home environment to support customised services such as care services for elderly and disadvantaged people to enable and prolong their independent living. Although various approaches have been proposed to tackle this problem, solutions still remain elusive due to various reasons (e.g. user acceptance). Literature reviews have indicated the need for an advanced non-tagged identification and tracking approach that is capable to provide the infrastructure support for realisation of context-aware services, satisfy users’ needs, and deal with the complexity of smart home environmental conditions. The aim of this study is to develop and implement an advanced approach that is capable to accurately detect, identify, and track people within opportune and calm home environment to be used as infrastructure for various application domains such as assisted living, healthcare, security and energy management. Accordingly, a novel multimodal approach for non-tagged human identification and tracking within home environment is proposed. The proposed approach combined floor pressure and PIR sensors through unique designed integration strategy aiming to merge the advantages of the two sensor types and overcome or minimise their weaknesses. The designed strategy enabled the PIR output signal pattern to afford explicit information indicating a person’s body surface area (size/shape). This information enhanced the identification accuracy, facilitated the custom designed smart floor, and reduced the overall cost. The conceptual framework of the proposed approach/strategy encompassed two key stages, hardware system design and implementation, and data processing. The hardware system design included the custom designed PIR and smart floor units. A test bed was designed and implemented for supporting the research studies, including proof of concept, concept demonstration, experimental and test cases studies. Data processing system has divided into different stages to accomplish the identification and tracking goals. First, the interested patterns were segmented and generated with threshold edge detection method and advanced pattern generation algorithm respectively. Second, limited set of features were extracted and selected from each pattern including ground reaction force GRF, gait, and body size/shape (PIR) features. Third, these features were merged at different fusion level, namely, feature-level and decision-level to provide comprehensive description about the person’s identity. Fourth, MLPNN multiclass classifier was adopted to process the feature vectors and recognise the person’s identity. Finally, the footstep patterns were tracked using weighted centroid tracking technique, in addition to MLPNN classifier to handle the footsteps association problems. Four test cases were designed and carried out to demonstrate, test, and evaluate the feasibility and effectiveness of the proposed non-tagged identification and tracking strategies/approach. The assessment outcomes have shown the potential of the proposed multimodal approach as an advanced strategy for implementation of an indoor non-tagged human identification and tracking system and to be used as infrastructure for supporting the delivery of various types of smart services within the smart home environments. In summary, the proposed multimodal approach has the potential to: (1) Identify up to 5 persons successfully with minimum 98.8% correct classification rate without tag, (2) detect, locate, and track multiple persons successfully without tag and the location error no more than 11.76 cm, approximately 1.5 times better in accuracy than the original set target (i.e. 30 cm), and (3) able to handle various tracking difficulties and solve 97.5% of data association problems.

Ferroelectric materials have been extensively studied theoretically and experimentally for many decades. Their ferroelectric, piezoelectric, pyroelectric, dielectric and electro-optical properties offer great promise in various applications such as non-volatile random access memory devices, non linear optics, motion and thermal sensors, and tunable microwave devices. Advanced applications for high dielectric constant insulators and nonvolatile memories in semiconductor industry have led to a meteoric rise of interest in the ferroelectrics recently. As most studied and technically important ferroelectric materials, lead zirconate titanate (PZT) and barium strontium titanate (BST) are widely investigated to understand their properties for potential device applications. Using radio frequency magnetron sputtering, single crystalline PZT and BST thin films have been achieved on SrTiO3 substrates, and been characterized for their structural and electrical properties. Eyeing their different potential applications, ferroelectric, pyroelectric and dielectric properties of PZT and BST thin films were studied. In addition, the introduction of bridge layers (nucleation or buffer layers) grown by molecular beam epitaxy (MBE) has been employed to facilitate the heterostructure growth of PZT thin films on GaN and BST thin films on sapphire substrates. Highly (111)-oriented perovskite PZT thin films were achieved on silicon-doped GaN (0001)/c-sapphire with a PbTiO3/PbO oxide bridge layer. And (001)-oriented BST thin films were grown on a-plane sapphire with an MgO/ZnO bridge layer. This dissertation also discusses the realization of PZT ferroelectric field effect transistors (FeFET). Two different 1T FeFET structures were successfully fabricated and their electrical properties were examined. Ferroelectric behavior was observed in the plot of source-drain current versus gate voltage where it exhibited a large counterclockwise hysteresis with 50% current modulation.

The performance of a novel micro-thermodielectric power generation device (MTDPG) was investigated in order to determine if thermodielectric power generation can compete with current portable power generation technologies. Thermodielectric power generation is a direct energy conversion technology that converts heat directly into high voltage direct current. It requires dielectric (i.e., capacitive) materials whose charge storing capabilities are a function of temperature. This property is exploited by heating these materials after they are charged; as their temperature increases, their charge storage capability decreases, forcing them to eject a portion of their surface charge to an appropriate electronic storage device. Previously, predicting the performance of a thermodielectric power generator was hindered by a poor understanding of the materials thermodynamic properties and the affect unsteady heat transfer losses have on system performance. In order to improve predictive capabilities in this study, a thermodielectric equation of state was developed that describes the relationship between the applied electric field, the surface charge stored by the thermodielectric material, and its temperature. This state equation was then used to derive expressions for the material's thermodynamic states (internal energy, entropy), which were subsequently used to determine the optimum material properties for power generation. Next, a numerical simulation code was developed to determine the heat transfer capabilities of a micro-scale parallel plate heat recuperator (MPPHR), a device designed specifically to a) provide the unsteady heating and cooling necessary for thermodielectric power generation and b) minimize the unsteady heat transfer losses of the system. The previously derived thermodynamic equations were then incorporated into the numerical simulation code, creating a tool capable of determining the thermodynamic performance of an MTDPG, in terms of the thermal efficiency, percent Carnot efficiency, and energy/power density, when the material properties and the operating regime of the MPPHR were varied. The performance of the MTDPG was optimized for an operating temperature range of 300 500 K. The optimization predicted that the MTDPG could provide a thermal efficiency of 29.7 percent. This corresponds to 74.2 percent of the Carnot efficiency. The power density of this MTDPG depends on the operating frequency and can exceed 1,000,000 W/m3.

The lithium tantalite [LiTaO3, abbreviated to LT] thin films were deposited on Pt/Ti/SiO2/Si substrates by spin coating with sol-gel technology and various rapid thermal processing in this thesis. By changing the annealed layers and heating temperature(500~800¢J), the effects of various thermal treatments on the thin films growth and the related properties are studied. Besides, the dynamic response of pyroelectric IR detector using LiTaO3 films was studied. In addition, the detector with back side etching was achieved by the anisotropic wet etching of back silicon substrate. The comparisons of detectors with and without backside etching were also investigated. Experimental results reveal that the annealed layers will influence strongly on grain size, dielectricity, ferroelectricity and pyroelectricity of LT thin films. With the increase of the annealed layers, the grain size of LT thin film increases slightly, and highly c-axis orientated LT films can be obtained for the twelve annealed layers. From 4 to 12 annealed layers, the relative dielectric constant of LT thin film increases from 35 up to 65, the dielectric loss (tand) decreases from 0.00637 to 0.00324, the coercive field (Ec) decreases from 84.79KV/cm to 46.23KV/cm, the remnant polarization (Pr) increases from 2.54 mC/cm2 to 7.36 mC/cm2, and the pyroelctric coefficient (g) increases from 2.18´10-8 C/cm2K up to 5.71´10-8 C/cm2K. In addition, the results also show that the LT thin film possesses the largest figures of merit Fv (3.02¡Ñ10-10 Ccm/J) and Fm (4.08¡Ñ10-8 Ccm/J) at heating temperature of 700¢J with twelve annealed layers. The voltage responsivities (Rv) measured at 70 Hz exists a largest value of 8398 V/W with twelve annealed layers. The specific detectivity (D*) measured at 200 Hz has the maximum value of 1.1¡Ñ108 cmHz1/2/W with twelve annealed layers. The results show that LT12 pyroelectric thin film detector exists both the maximums of voltage responsivity and specific detecivity. Therefore, optimizing the conditions of this study, LT12 thin film will be the most suitable for IR detector application. Finally, the voltage responsivities (Rv) of LT thin film increases from 8398 V/W to 9537 V/W, and the specific detectivity (D*) increases from 1.1¡Ñ108 cmHz1/2/W to 2.67¡Ñ108 cmHz1/2/W after backside etching. The results show that the detectivity can be improved after backside etching.