Magnetic Resonance Imaging (MRI) is a widely used soft tissue imaging technique that has gained considerable success because of its sensitivity to several tissue parameters. However, commercially available whole-body imaging systems with large encircling radio frequency (RF) and gradient coils are less efficient when the goal is to obtain detailed, high-resolution images with high specificity and sensitivity from localized regions of the body such as the female breast. This research addresses these problems by proposing a new design in RF coil development for breast cancer screening in a conventional 1.5T MRI system. The new design provides two resonant receiving modes that operate in a quadrature configuration, and a region of interest (ROI) that closely conforms to the shape of the female breast. We adopted an optimum design strategy that combined the analytic Biot-Savart intergral equation with the Method of Moment formulation in the development of electromagnetic models and simulation tools. These models were used to analyze the magnetic field distribution and the spatial field coverage, as well as the magnetic field uniformity in the ROI. Results from our analysis were employed in the construction of a highly scalable prototype. The validation of our design strategy is confirmed by comparisons with the commercial Ansoft HFSS v8.5 finite element package.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Com os recentes avanÃos da indÃstria de telecomunicaÃÃes se faz cada vez mais necessÃrio o desenvolvimento de matÃrias que apresentem altos valores de constante dielÃtrica, baixa perda dielÃtrica e uma boa estabilidade tÃrmica. Muitos materiais para rÃdio frequÃncia e microondas tÃm sido amplamente usados em uma variedade de aplicaÃÃes nestes segmentos. Destas aplicaÃÃes, as mais recentes tecnologias utilizam cerÃmicas com baixa temperatura de sinterizaÃÃo, materiais de baixo ponto de fusÃo, alÃm das caracterÃsticas citadas anteriormente. CerÃmicas dielÃtricas a base de Bismuto sÃo candidatas como materiais de baixa temperatura de sinterizaÃÃo e tÃm sido estudadas amplamente. Este trabalho apresenta o desenvolvimento e caracterizaÃÃo da sÃrie cerÃmica CaBi4Ti4O15 (CBT) com adiÃÃo em massa de triÃxido de bismuto, material conhecido por suas excelentes propriedades dielÃtricas, principalmente elevados valores de constante dielÃtrica. Esta sÃrie foi produzida a partir do mÃtodo cerÃmico convencional ou mÃtodo do estado sÃlido, com a utilizaÃÃo de moagem mecÃnica de alta energia e tratamento tÃrmico. ApÃs a sÃntese, foi adicionado o triÃxido de bismuto em diferentes concentraÃÃes para melhorar as caracterÃsticas elÃtricas desta matriz cerÃmica. A caracterizaÃÃo estrutural foi realizada por meio de DifraÃÃo de Raios-X com Refinamento de Rietveld. Um estudo da morfologia foi realizado atravÃs de Microscopia EletrÃnica de Varredura. Foram realizados experimentos para verificar o comportamento dielÃtrico das amostras, na regiÃo de rÃdio frequÃncia e microondas. No geral percebemos que esta matriz cerÃmica apresenta as caracterÃsticas desejÃveis para sua aplicaÃÃo na fabricaÃÃo de dispositivos eletrÃnicos como capacitores e antenas ressoadoras dielÃtricas. / With the recent advances in telecommunications industry, itâs increasingly required the development of materials which have high values of dielectric constant, low dielectric loss and a good thermal stability. Many materials for radio frequency and microwaves utilization have been largely used in a variety of applications in these segments. From these applications, the latest technology generally use ceramics with low sintering temperature, low melting point materials, in addition to the aforementioned characteristics. Dielectric ceramics based on Bismuth are candidates as low temperature sintering materials and have been studied extensively. This work presents the development and characterization of ceramic series CaBi4Ti4O15 (CBT) with addition of bismuth trioxide, which is currently known for its excellent dielectric properties, mostly by its high dielectric constant values. These series were produced by the use of conventional ceramic method or method of solid state, with the use of mechanical grinding of high energy and heat treatment. After the synthesis, was added the bismuth trioxide in different concentrations to improve the electrical characteristics of ceramic CBT. The Structural characterization was showed by X-ray Diffraction with Rietveld Refinement. A study of the morphology was accomplished by scanning electron microscopy (SEM). Experiments were performed to verify the behavior of dielectric samples, radio frequency and microwaves. In general we can realize that this ceramic standard mold presents desirable characteristics for its application in the manufacture of electronic devices such as capacitors and dielectric resonator antennas.

Made available in DSpace on 2016-04-27T17:05:59Z (GMT). No. of bitstreams: 1 Renato Pereira de Araujo.pdf: 1711666 bytes, checksum: b5ad19e844d9c137553ad64b03b603c7 (MD5) Previous issue date: 2015-03-02 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / For the visually impaired, identify which path to follow to reach the desired destination without assistance from healthy people is a challenge. To move in an unknown environment is required to interact with the mechanisms of information. However the visually impaired do not yet have a navigation system in indoor environments with real-time response that allows this this communication. This paper presents a device that allows interaction with the tactile floor to aid navigation and orientation. Through an audio interface, the device provides the visually impaired relevant information on the space around it and the navigation options available. The relevant information is disseminated using labels with radio frequency identification technology, integrated into a microcontroller and an audio playback card. Each label has an electronic product code that allows to identify it uniquely. The label installed in a standard place of tactile floor is linked to an audio file with information about the space and the available routes. The reader integrated development board reads the labels and sends the electronic code to the microcontroller, which in turn identifies the code and assigns this audio file to be played. The device was tested by a volunteer who found all labels positioned on the floor tactile alert, clearly identified its position and reached the desired destination without route errors. Used as a complement to tactile signage, this device provides an interaction between the visually impaired and the existing tactile signage. This project will directly contribute to society, providing a convenient navigation system for people with visual disabilities have greater autonomy / Para os deficientes visuais, identificar qual caminho deve ser seguido para chegar ao destino desejado, sem auxílio de pessoas hígidas, é um desafio. Para se deslocar em um ambiente desconhecido é necessária a interação com os mecanismos de informação. Entretanto os deficientes visuais ainda não contam com um sistema de navegação em ambientes internos com resposta em tempo real que possibilite essa comunicação. Este trabalho apresenta um dispositivo que possibilita a interação com o piso tátil para auxiliar a navegação e a orientação. Por meio de uma interface de áudio, o dispositivo proporciona ao deficiente visual as informações úteis sobre o espaço em seu entorno e as opções de navegação disponíveis. As informações pertinentes são difundidas utilizando etiquetas com tecnologia de identificação por rádio frequência, integradas a um micro controlador e uma placa de reprodução de áudio. Cada etiqueta possui um código de produto eletrônico que permite identificá-la de forma exclusiva. A etiqueta instalada em um local padronizado do piso tátil está atrelada a um arquivo de áudio com informações sobre o espaço e as rotas disponíveis. O leitor integrado a placa de desenvolvimento faz a leitura das etiquetas e envia o código eletrônico ao micro controlador, que por sua vez identifica o código e atribui a este o arquivo de áudio que será reproduzido. O dispositivo foi testado por um voluntário que encontrou todas as etiquetas posicionadas junto ao piso tátil de alerta, identificou claramente sua posição e chegou ao destino desejado sem erros de percurso. Usado como complemento da sinalização tátil, este dispositivo possibilita uma interação entre o deficiente visual e a sinalização tátil existente. Este projeto poderá contribuir diretamente para a sociedade, disponibilizando um sistema de navegação conveniente para que as pessoas com deficiência visual tenham maior autonomia

The increasing number of mobile devices challenges the current radio frequency (RF) networks. The conventional RF spectrum for wireless communications is saturating, motivating to develop other unexplored frequency bands. Light Fidelity (LiFi) which uses more than 300 THz of the visible light spectrum for high-speed wireless communications, is considered a promising complementary technology to its RF counterpart. LiFi enables daily lighting infrastructures, i.e. light emitting diode (LED) lamps to realise data transmission, and maintains the lighting functionality at the same time. Since LiFi mainly relies on line-of-sight (LoS) transmission, users in indoor environments may experience blockages which significantly affects users' quality of service (QoS). Therefore, hybrid LiFi and RF networks (HLRNs) where LiFi supports high data rate transmission and RF offers reliable connectivity, can provide a potential solution to future indoor wireless communications. In HLRNs, efficient load balancing (LB) schemes are critical in improving the traffic performance and network utilisation. In this thesis, the optimisation-based scheme (OBS) and the evolutionary game theory (EGT) based scheme (EGTBS) are proposed for load balancing in HLRNs. Specifically, in OBS, two algorithms, the joint optimisation algorithm (JOA) and the separate optimisation algorithm (SOA) are proposed. Analysis and simulation results show that JOA can achieve the optimal performance in terms of user data rate while requiring high computational complexity. SOA reduces the computational complexity but achieves low user data rates. EGTBS is able to achieve a better performance/complexity trade-off than OBS and other conventional load balancing schemes. In addition, the effects of handover, blockages, orientation of LiFi receivers, and user data rate requirement on the throughput of HLRNs are investigated. Moreover, the packet latency in HLRNs is also studied in this thesis. The notion of LiFi service ratio is introduced, defined as the proportion of users served by LiFi in HLRNs. The optimal LiFi service ratio to minimise system delay is mathematically derived and a low-complexity packet flow assignment scheme based on this optimum ratio is proposed. Simulation results show that the theoretical optimum of the LiFi service ratio is very close to the practical solution. Also, the proposed packet flow assignment scheme can reduce at most 90% of packet delay compared to the conventional load balancing schemes at reduced computational complexity.

Radio-frequency filters and oscillators are widely used in wireless communication and high-speed digital systems, and they are mostly built on passive integrated inductors, which occupy a relative large silicon area. This research attempted to implement filters and oscillators operating at 1-5 GHz using transistors only, to reduce the circuits’ area. The filters and oscillators are designed using active inductors, based on the gyrator principle; they are fabricated in standard digital CMOS technology to be compatible with logic circuits and further lower the cost. To obtain the highest operating frequency, only parasitic capacitors were used. Two new active-inductor circuits are derived from this research, labeled allNMOS and all-NMOS-II. The all-NMOS active inductor was used to design high-Q bandpass filters and oscillators, which were fabricated in TSMC’s 0.18-µm digital CMOS process. The highest center frequency measured was 5.7 GHz at 0.20-µm gate length and the maximum repeatably measured Q was 665. 2.4-GHz circuits were also designed and fabricated in 0.40-µm gate length. The all-NMOS-II circuit has superior linearity and signal fidelity, which are robust against process and temperature variations, due to its novel structure. It was used in signal drivers and will be fabricated in commercial products. Small-signal analysis was conducted for each of the active-inductor, filter and oscillator circuits, and the calculated performance matches those from simulations. The noise performance of the active inductor, active-inductor filter and oscillator was also analyzed and the calculated results agree with simulations. The difference between simulation and measured results is about 10% due to modeling and parasitic extraction error. The all-NMOS active-inductor circuit was granted a US patent. The US patent for all-NMOS-II circuit is pending. This research generated three conference papers and two journal papers.

This thesis addresses the problem healthcare facilities are having in maintaining proper food temperatures while transporting meals to patients after food has left the kitchen area. Induction heat has been a known method for generating heat for many years. The commercial food industry currently uses this technology, which is beginning to appear in the residential sector as well because of developments made by manufacturers. This study focuses on the top commercial brand models of induction heaters and the supporting materials currently used to create heat sources to maintain food temperatures in hospitals and long term care facilities. The research in this thesis includes data recorded from 6,000 total induction cycles from the 3 leading induction heating models. The focus of the research was to gather data concerning the models’ reliability to consistently create the intended inducement of radio frequency waves as well as deliver consistent temperature reactions from the recorded induction cycles. There were 18,000 temperature data points recorded during different time intervals for each of the induction cycles for the entire study. The results indicate the current technology not only is reliable in creating inductions fields but also in delivering consistent temperatures in the supporting materials being heated. Induction has been used historically as a fast heating process to treat large metal products and requires no direct contact to create or transfer heat to a surface (Rudnev et al., 2003). The speed and consistent application of heat transfer that has been derived by modern manufacturing induction practices makes it a logical use of existing technology to be applied in maintaining temperatures of food in the healthcare market. However, the focus for commercial equipment manufacturers has been to market products that can consistently maintain desired food temperatures, particularly in the healthcare industry. Traditionally, heating foods was accomplished by physically applying heat to areas where food is stored, in order to reach a certain temperature, and then working to deliver that food to the patient in a timely manner or before it cooled to temperatures that would be deemed too cold for consumption. If the food was too cold, before it was served to the patient, then it was typically micro waved in order to reheat the food. However, reheating food in the microwave is not only detrimental, but it also degrades food quality, texture, and visual presentation (Harvard Health, 2015). As a result, the effort demanded to deliver all foods to all patients, while the food is still at an ideal temperature, has resulted in an increased cost of labor. This is because healthcare facilities have had to hire additional workers to meet the demands placed on the nutrition department related to safe temperatures and speed of food delivery (Aladdin, 2013).

In wireless communication, the nonlinearity of a radio frequency (RF) power amplifier is an important issue for power amplifier designers. Since the nonlinearity is generated by the properties of physical components, it is hard to avoid it in producing power amplifiers. Power amplifier designers should know about the nonlinearity in order to compensate for it. A two-tone test is a relatively widely used method to measure the nonlinearity of a power amplifier, which means the third order intercept point (IP3) can be measured from the two-tone test. Through the two-tone test, researchers have proposed some formulae to present what the amplified Code Division Multiple Access (CDMA) signal is like. They derived formulae in terms of output power, bandwidth, IP3, and IP5 to express the amplified CDMA signal and further to Orthogonal Frequency Division Multiplexing (OFDM) signals. With the development of wireless communication, researchers put their interest increasingly in Multiple Input Multiple Output (MIMO) systems. A formula expressing amplified dual two-tone signals has been proposed. In their research, they discussed what the expressions of intermodulation and cross modulation are and what their locations are. In this research, dual band LTE-Advanced signals, whose modulation is OFDM are utilized, which means this research proposes a formula expression about the power spectrum of dual-band LTE-Advanced signals. Intermodulation and cross modulation caused by nonlinearity of power amplifiers are then specially discussed. This study will help RF designers to continuously compensate for them.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

<p>This master thesis deals with the study of ultra low power Low Noise Amplifier (LNA) for use inmedical implant device. Usually, low power consumption is required for a long battery lifetime andlonger operation. The target technology is 90nm CMOS process.First basic principle of LNA is discussed. Then based on a literature review of LNA design, theproposed LNA is presented in sub-threshold region which reduce power consumption through scalingthe supply voltage and through scaling current.The circuit implementation and simulations is presented to testify the performance of LNA .Besides thepower consumption simulated under the typical supply voltage (1V), it is also measured under someother low supply voltages (down to 0.5V) to investigate the minimum power consumption and theminimum noise figure. Evaluation results show that at a supply voltage of 1V the LNA performs a totalpower consumption of 20mW and a noise of 1dB. Proper performance is achieved with a current ofdown to 200uA and supply voltage of down to 0.45V, and a total power consumption of 200uW</p>

<p>This thesis work started with an extensive literature study in several areas, ZigBee, instruments and measuring methods. The knowledge was implemented in use with the ZigBee modules from the two manufacturers ITN and Chipcon along with ZigBee Software Stack. Measuring methods were developed and software in ZigBee software Stack was developed to use in the ZigBee modules for the measurements. Developing measurement methods and performing measurements was an iterative process for the different measurements. The aim was to characterize the ZigBee modules in the most important areas during the extent of this master thesis work.</p>