146 research outputs found
Characterization of systems for software defined radio
Mestrado em Engenharia Electrónica e TelecomunicaçõesEsta dissertação insere-se na área de electrónica de rádio frequência, mais
precisamente na caracterização de sistemas para rádios definidos por software
(SDR). Um SDR é aquele que possui a flexibilidade para sintonizar, filtrar,
ajustar a taxa de transmissão e controlar o tipo de modulação através de
software. O aparecimento de novas tecnologias no mercado obriga à utilização
de uma quantidade considerável de hardware nos dispositivos de
transmissão/recepção, assim uma solução consiste no uso de arquitecturas de
SDR onde a conversão do sinal analógico para digital é executada o mais
próximo possível da antena e, sendo depois todo o processamento efectuado
digitalmente. Assim, nesta tese, é apresentado um modelo comportamental
para receptores de SDR, que leva em conta os elementos chave da distorção
não linear. Além disso, são apresentadas algumas comparações entre
simulações e medidas usando sinais multi-seno e WiMax usando um receptor
ideal de SDR. Finalmente, é proposto um novo sistema de caracterização para
dispositivos de SDR.
ABSTRACT: This dissertation is related to the radio frequency area, more specifically to the
characterization of systems for software-defined radio. A software-defined radio
is one that has the flexibility to tune, filter, set the transmission rate and control
the modulation type only by software. The emergence of new technologies in
the market forces the use of a considerable quantity of hardware in the
transceivers systems, so a viable solution for this is to use SDR solutions
where the analogue to digital conversion is made closest possible of the
antenna and then make all the processing digitally. So, in this dissertation, a
behavioral model for SDR front end receiver evaluation, that captures the key
elements of the nonlinear distortion, is proposed. Moreover, some comparisons
between measured and simulated results under multisine and WiMax
excitations are presented using the ideal SDR receiver. Finally, a new
instrumentation system for characterization of SDR front ends is proposed
Modelling and detection of faults in axial-flux permanent magnet machines
The development of various topologies and configurations of axial-flux permanent magnet machine has spurred its use for electromechanical energy conversion in several applications. As it becomes increasingly deployed, effective condition monitoring built on reliable and accurate fault detection techniques is needed to ensure its engineering integrity. Unlike induction machine which has been rigorously investigated for faults, axial-flux permanent magnet machine has not. Thus in this thesis, axial-flux permanent magnet machine is investigated under faulty conditions. Common faults associated with it namely; static eccentricity and interturn short circuit are modelled, and detection techniques are established. The modelling forms a basis for; developing a platform for precise fault replication on a developed experimental test-rig, predicting and analysing fault signatures using both finite element analysis and experimental analysis. In the detection, the motor current signature analysis, vibration analysis and electrical impedance spectroscopy are applied. Attention is paid to fault-feature extraction and fault discrimination. Using both frequency and time-frequency techniques, features are tracked in the line current under steady-state and transient conditions respectively. Results obtained provide rich information on the pattern of fault harmonics. Parametric spectral estimation is also explored as an alternative to the Fourier transform in the steady-state analysis of faulty conditions. It is found to be as effective as the Fourier transform and more amenable to short signal-measurement duration. Vibration analysis is applied in the detection of eccentricities; its efficacy in fault detection is hinged on proper determination of vibratory frequencies and quantification of corresponding tones. This is achieved using analytical formulations and signal processing techniques. Furthermore, the developed fault model is used to assess the influence of cogging torque minimization techniques and rotor topologies in axial-flux permanent magnet machine on current signal in the presence of static eccentricity. The double-sided topology is found to be tolerant to the presence of static eccentricity unlike the single-sided topology due to the opposing effect of the resulting asymmetrical properties of the airgap. The cogging torque minimization techniques do not impair on the established fault detection technique in the single-sided topology. By applying electrical broadband impedance spectroscopy, interturn faults are diagnosed; a high frequency winding model is developed to analyse the impedance-frequency response obtained
Global Dynamic Characterization and Load Rating of Bridge Structures Utilizing Economical Dynamic Excitation Devices
Experimental modal analysis (EMA) of bridges and other civil structures can be used to acquire quantitative data describing their condition, and enhance opportunities for structural health monitoring and related fields. The use of EMA on civil structures has been limited by the high cost of the excitation devices that are required for the best data quality. The objective of the research reported herein is to evaluate a low-cost excitation system for multiple-input, multiple-output (MIMO) EMA, enabling the production of accurate estimates of the global behavior of in-service bridges.
The prototype excitation system is composed of consumer entertainment devices, namely tactile transducers and subwoofer amplifiers, which are capable of providing excitation in the range of 5 Hz to 200 Hz. The use of these devices in vibration testing is unprecedented, and their low cost allows approximately 30 structural degrees-of-freedom to be excited for the price of a single purpose-built laboratory shaker device. Methods are developed to systematically characterize the operational performance of the devices. Research and testing are also performed to optimize the techniques by which the system can be used for MIMO EMA of bridges.
The excitation system is then validated for MIMO EMA by dynamically characterizing a large-scale laboratory structure and comparing the results to those from traditional excitation methods. The system is then deployed on an in-service highway bridge, representing the first time that more than two shakers have been used in MIMO EMA testing of a bridge. The identification results using MIMO EMA are shown to be superior to those found using traditional excitation methods.
Finally, the identified modal parameters of the in-service bridge are used in load rating. Direct use of the modal properties of a bridge for load rating is unprecedented, and a relatively simple method to use measured modal flexibility to help determine live load demand is developed herein. The bridge load ratings calculated from the new method are compared to traditional methods.
In summary, a low-cost excitation system is optimized and systematically evaluated for MIMO EMA testing of civil structures, and the use of the system is validated in the laboratory and in the field. A new method to improve bridge rating reliability is then developed using the high quality modal parameters found via the optimized testing process
Modeling and experimental identification of vibrating structures: localized and distributed nonlinearities
L'abstract è presente nell'allegato / the abstract is in the attachmen
Characterization and modelling of software defined radio front-ends
Doutoramento em Engenharia ElectrotécnicaO presente trabalho tem por objectivo estudar a caracterização e modelação
de arquitecturas de rádio frequência para aplicações em rádios definidos por
software e rádios cognitivos. O constante aparecimento no mercado de novos
padrões e tecnologias para comunicações sem fios têm levantado algumas
limitações à implementação de transceptores rádio de banda larga. Para além
disso, o uso de sistemas reconfiguráveis e adaptáveis baseados no conceito
de rádio definido por software e rádio cognitivo assegurará a evolução para a
próxima geração de comunicações sem fios. A ideia base desta tese passa por
resolver alguns problemas em aberto e propor avanços relevantes, tirando
para isso partido das capacidades providenciadas pelos processadores digitais
de sinal de forma a melhorar o desempenho global dos sistemas propostos.
Inicialmente, serão abordadas várias estratégias para a implementação e
projecto de transceptores rádio, concentrando-se sempre na aplicabilidade
específica a sistemas de rádio definido por software e rádio cognitivo. Serão
também discutidas soluções actuais de instrumentação capaz de caracterizar
um dispositivo que opere simultaneamente nos domínios analógico e digital,
bem como, os próximos passos nesta área de caracterização e modelação.
Além disso, iremos apresentar novos formatos de modelos comportamentais
construídos especificamente para a descrição e caracterização não-linear de
receptores de amostragem passa-banda, bem como, para sistemas nãolineares
que utilizem sinais multi-portadora.
Será apresentada uma nova arquitectura suportada na avaliação estatística
dos sinais rádio que permite aumentar a gama dinâmica do receptor em
situações de multi-portadora. Da mesma forma, será apresentada uma técnica
de maximização da largura de banda de recepção baseada na utilização do
receptor de amostragem passa-banda no formato complexo.
Finalmente, importa referir que todas as arquitecturas propostas serão
acompanhadas por uma introdução teórica e simulações, sempre que possível,
sendo após isto validadas experimentalmente por protótipos laboratoriais.This work investigates the characterization and modeling of radio frequency
front-ends for software defined radio and cognitive radio applications. The
emergence of new standards and technologies in the wireless communications
market are raising several issues to the implementation of wideband
transceiver systems. Also, reconfigurable and adaptable systems based on
software defined and cognitive radio models are paving the way for the next
generation of wireless systems. In this doctoral thesis the fundamental idea is
to address the particular open issues and propose appropriate advancements
by exploring and taking profit from new capabilities of digital signal processors
in a way to improve the overall performance of the novel schemes.
Receiver and transmitter strategies for radio communications are summarized
by concentrating on the usability for software defined radio and cognitive radio
systems. Available instrumentation and next steps for analog and digital radio
frequency hardware characterization is also discussed.
Wideband behavioral model formats are proposed for nonlinear description and
characterization of bandpass sampling receivers, as well as, for multi-carrier
nonlinear systems operation. The proposed models share a great flexibility and
have the freedom to be simply expanded to other fields.
A new design for receiver dynamic range improvement in multi-carrier
scenarios is proposed, which is supported on the useful wireless signals
statistical evaluation. Additionally, receiver-side bandwidth maximization based
on higher-order bandpass sampling approaches is evaluated.
All the proposed designs and modeling strategies are accompanied by
theoretical backgrounds and simulations whenever possible, being then
experimentally validated by laboratory prototypes
Impedance Spectroscopy
This book covers new advances in the field of impedance spectroscopy including fundamentals, methods and applications. It releases selected extended and peer reviewed scientific contributions from the International Workshop on Impedance Spectroscopy (IWIS 2017) focussing on detailed information about recent scientific research results in electrochemistry and battery research, bioimpedance measurement, sensors, system design, signal processing
Microwave resonant sensors
Microwave resonant sensors use the spectral characterisation of a resonator to make high sensitivity measurements of material electromagnetic properties at GHz frequencies. They have been applied to a wide range of industrial and scientific measurements, and used to study a diversity of physical phenomena. Recently, a number of challenging dynamic applications have been developed that require very high speed and high performance, such as kinetic inductance detectors and scanning microwave microscopes. Others, such as sensors for miniaturised fluidic systems and non-invasive blood glucose sensors, also require low system cost and small footprint. This thesis investigates new and improved techniques for implementing microwave resonant sensor systems, aiming to enhance their suitability for such demanding tasks. This was achieved through several original contributions: new insights into coupling, dynamics, and statistical properties of sensors; a hardware implementation of a realtime multitone readout system; and the development of efficient signal processing algorithms for the extraction of sensor measurements from resonator response data. The performance of this improved sensor system was verified through a number of novel measurements, achieving a higher sampling rate than the best available technology yet with equivalent accuracy and precision. At the same time, these experiments revealed unforeseen applications in liquid metrology and precision microwave heating of miniature flow systems.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Bioimpedance sensors: a tutorial
Electrical bioimpedance entails the measurement of the electrical properties of tissues as a function of frequency. It is thus a spectroscopic technique. It has been applied in a plethora of biomedical applications for diagnostic and monitoring purposes. In this tutorial, the basics of electrical bioimpedance sensor design will be discussed. The electrode/electrolyte interface is thoroughly described, as well as methods for its modelling with equivalent circuits and computational tools. The design optimization and modelling of bipolar and tetrapolar bioimpedance sensors is presented in detail, based on the sensitivity theorem. Analytical and numerical modelling approaches for electric field simulations based on conformal mapping, point electrode approximations and the finite element method (FEM) are also elaborated. Finally, current trends on bioimpedance sensors are discussed followed by an overview of instrumentation methods for bioimpedance measurements, covering aspects of voltage signal excitations, current sources, voltage measurement front-end topologies and methods for computing the electrical impedance
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