The combined effect of group velocity dispersion (GVD) and nonlinearity limits the transmission distance of fiber optic communication systems. By designing a circuit that can model this effect and simulating it using the Block Oriented Systems Simulator (BOSS), we can study the pulse distortion and broadening that may occur. The nonlinearity considered here is self-phase modulation (SPM). A loop system is designed where each pass of the system corresponds to 200 km of fiber. The system mainly consists of a Butterworth bandpass filter which models the dispersion in the fiber and a VCO that imposes a phase modulation on the input signal thus modeling the intensity dependent phase shift due to SPM. By changing various parameters of the circuit, the dispersion limited distance, the nonlinearity limited distance and other related factors can be altered. With D=-0.04 ps/km.nm, the effect of changing the nonlinear limited distance and thus the nonlinear effect is studied and simulated. The results are compared with a simple theoretical model for pulse broadening that has appeared in the literature. Although the simulation results exhibit the same qualitative behavior as the theory, there are significant quantitative differences. The reason for these differences are discussed. / Master of Science

A generalized, discrete-time modeling and simulation program, applicable to any PWM, resonant or quasi-resonant converter, has been developed. From a circuit description, this program automatically generates state-space equations corresponding to each switching interval and performs time-domain simulations by using state-transition equations with a fast-convergence algorithm for topological changes. / M.S.

This study is a two part research project that describes and evaluates the efforts of the researcher to bring change in Cyprus' educational system, in the field of simple electric circuits. The objective of the first part was the assessment and evaluation of Cypriot STVE students' perceptions about simple electric circuits. The objective of the second part was to measure the effectiveness that conceptual change model-based instructional activities designed by the researcher had on changing students' misconceptions about simple electric circuits towards scientifically accepted ideas. Transformative mixed methods research design was used consisting mainly from an one-group pre-test post-test design with Determining and Interpreting Resistive Electric Circuits Concepts Test 1.2 as a research instrument, while interviews and field notes were used for triangulation. The findings showed that there was a significant improvement in students' understanding of simple electric circuit concepts that were taught using conceptual change model-based instructional activities. / Science and Technology Education / M. Sc. (Mathematics, Science and Technology Education)

This study is a two part research project that describes and evaluates the efforts of the researcher to bring change in Cyprus' educational system, in the field of simple electric circuits. The objective of the first part was the assessment and evaluation of Cypriot STVE students' perceptions about simple electric circuits. The objective of the second part was to measure the effectiveness that conceptual change model-based instructional activities designed by the researcher had on changing students' misconceptions about simple electric circuits towards scientifically accepted ideas. Transformative mixed methods research design was used consisting mainly from an one-group pre-test post-test design with Determining and Interpreting Resistive Electric Circuits Concepts Test 1.2 as a research instrument, while interviews and field notes were used for triangulation. The findings showed that there was a significant improvement in students' understanding of simple electric circuit concepts that were taught using conceptual change model-based instructional activities. / Science and Technology Education / M. Sc. (Mathematics, Science and Technology Education)

[pt] O ensino da Teoria dos Números Complexos durante o Ensino Médio é apresentado, por vezes, de uma maneira pouco representativa para os alunos levando em consideração a sua importância. Uma das lacunas que pode ser observada é a falta de exemplos de aplicações no cotidiano dos alunos o que, por fim, acaba não gerando significado no aprendizado para eles. No entanto, a aplicação dos números complexos é bem mais abrangente do que se possa imaginar, principalmente no campo das Ciências Exatas, tomando como exemplo a Engenharia. Este trabalho destina-se a ampliar a visão dos alunos do Ensino Médio apresentando aplicações e a maneira de como os Números Complexos são utilizados em outros contextos, assim como no estudo dos Circuitos Elétricos. / [en] The teaching of Complex Numbers Theory during High School is sometimes presented in a way that is not representative for students considering its importance. One of the gaps that can be observed is the lack of examples of applications in the students daily life, which, in the end, does not generate meaning in the learning for them. However, the application of the complex numbers is much more comprehensive than can be imagined, mainly, in the field of Exact Sciences taking as an example Engineering. This work is intended to broaden the view of high school students presenting applications and how Complex Numbers are used in other contexts, as well as in the study of Electrical Circuits.

Classiquement deux approches sont utilisées pour simuler les systèmes électroniques de puissance. La première, dite à topologie fixe, assimile les semi-conducteurs à des impédances de faible ou forte valeur en fonction de leur état. Les équations topologiques du système restent ainsi inchangées. Malgré sa simplicité, cette approche pose de sérieux problèmes de compromis entre précision des résultats et stabilité des méthodes numériques d'intégration. La deuxième, dite à topologie variable, assimile les semi-conducteurs à des connexions qui s'établissent ou disparaissent en fonction de l'état des semi-conducteurs. Il n'y a plus de problèmes de stabilité d'intégration ou de précision mais les équations topologiques du système sont dépendantes de l'état des interrupteurs. La détermination des conditions de transition (commutations) et la ré-écriture des équations sont des points délicats. Dans ce travail nous proposons une nouvelle approche, dite à topologie pseudo-variable qui combine les avantages des approches classiques sans en avoir les inconvénients. Les semi-conducteurs sont traités comme des dipôles comme dans les méthodes à topologie fixe, mais en fonction de leur état ils sont assimilés à des sources, de tension ou de courant, de valeur nulle ce qui leur donne une caractéristique idéale, comme dans les méthodes à topologie variable. La principale difficulté de cette nouvelle approche réside dans les contraintes algébriques, variables en fonction du temps, que les sources qui représentent les semi-conducteurs introduisent sur les variables d'état du circuit. Pour cette raison elle n'a, à notre connaissance, jamais été proposée. En adaptant au cas que nous traitons les techniques de partitionnement des coordonnées utilisées en mécanique de systèmes multicorps, nous montrons que ces contraintes peuvent être facilement prises en compte. Nous aboutissons ainsi à un algorithme de simulation à la fois très performant et bien adapté à la simulation des systèmes électromécaniques.

In this thesis work, a new distributed amplifier topology is discussed and applied to three different cases. The topology is based on dividing the frequency spectrum into channels and amplifying afterwards. The channelized and amplified signals are then combined at the output for broadband amplification. This topology is used in the design of a three channel 0.1-1 GHz amplifier with a gain of 14.5&plusmn / 0.6 dB. The design is fabricated, and then the measured and simulated results are compared. A second 0.1-1 GHz amplifier with 21&plusmn / 1 dB is designed in simulation environment with five channels. This five channel amplifier is fabricated and measured results are compared with the simulated ones. A 1-6 GHz three channel amplifier is also designed with a gain of 10.5&plusmn / 0.5 dB. Application of the proposed topology to three different designs shows promising results for future amplifier designs.

This thesis addresses the fabrication, evaluation, and analysis of the probe tip of a non-vibrating contact potential difference sensor. The non-vibrating contact potential difference (nvCPD) probe measures the work function variation on a conducting surface and recent experiments performed to measure the size of surface features have shown poor correlation between actual and calculated probe tip dimensions. In order to address this deficiency, experiments were done and an analytical model was developed, including fringe electrical fields, that predicts the shape of the nvCPD probe signal as a function of probe tip geometry, work function variation, and experimental parameters. Probe tips were constructed with varying geometric properties and experiments using these probe tips were compared to a model. There was good correlation of the nvCPD probe output for a known work function change and probe tip geometry. The effective area of the probe tip resulting from electrical field fringing is expected to increase with dielectric thickness to a finite value, based on pre-existing electrostatic models for a shielded parallel plate capacitor. The minimum fringe field obtained in these experiments was for a 3.18mm diameter probe tip with a dielectric thickness of 0.20mm. The fringe field diameter was 3.38mm at a fly height of 0.60mm, representing an effective probe tip area increase of 13%.

This thesis presents design, fabrication and testing of a number of multi-frequency band microstrip-fed re-configurable microstrip patch antennas. All re-configurable antennas are designed to change from one resonance frequency to another by an electronic control of RF MEMS switches, one at a time. Besides a fixed size slot on the patch, switches are placed in insets for satisfying better input match at each resonance frequency individually. Also some switches are placed into the slot for adding another resonance frequency to change the effective slot-length like effective inset length changing.To actuate the RF MEMS switches in the configured way, DC-stubs are also designed to apply required potential difference between switch ports and the carrier. These stubs exhibit RF-open at switch side to prevent any RF leakage, and DCground on the other side. That RF short-to-open conversion is accomplished together with feed structure / with a taper depending on the feed network selected. All devices introduced here are built by Microwave Research Group in Electrical and Electronics Department, Middle East Technical University. Depending on the sensitivity of structure, some devices are built by RF MEMS group in Microelectronic Production Plant for MEMS (METU &amp / #8211 / MET) during the thesis study. Therefore this study is the continuation of the first national work on fabrication of RF MEMS devices.

This study investigates the effect of methods of instruction (inquiry-based versus lecture instruction) and their interactions with students&rsquo / cognitive styles (field-dependent, field-mixed, and field-independent) and with other independent variables on 11th grade students&rsquo / physics achievement in and attitude toward electric circuits concepts in central district of Aydin. Lesson plans, instructional materials were developed for the inquiry-based instruction. Teachers&rsquo / regular classroom practices were accepted as lecture method. Physics achievement test, physics attitude scale, observation checklists, and GEFT were used as data collection instruments. Treatment was implemented to 298 11th grade students in central district of Aydin. Physics achievement test and physics attitude scale were administered to the students as pre and post tests while GEFT was administered only as pre test. MANCOVA was used as statistical analysis method to analyze data. The dependent variables of this study were the achievement (PSTACH) and attitude (PSTATT) scores of the students. The covariate and gender were used to statistically equalize the students&rsquo / characteristics. Group membership with respect to two groups (inquiry or lecture groups) was named here as &ldquo / MOI / methods of instruction&rdquo / (2 level categorical) and used as fixed factor of this study with the other group membership variables, students&rsquo / physics achievement pretest scores (PREACH), physics attitude pretest scores (PREATT), School, previous physics course grades (PPCG), cognitive style (CoS, 3 level categorical), and the interaction terms of MOI*PREACH, MOI*PPCG, PREATT*MOI*PPCG*CoS, MOI*PPCG*CoS, PREACH*School, and PREACH*PREATT. In general, inquiry instruction was effective than the lecture instruction with respect to PSTACH in electric circuits subject. However, there was not a significant difference in effectiveness of both methods in improving students&rsquo / attitudes toward electric circuits subject. In essence, each method of instruction was not effective on improving students&rsquo / attitudes toward electric circuits subject. Although, this study could not find any statistically significant interaction effect of MOI and other independent variables on students&rsquo / PSTATT scores, practical significance was investigated for the interaction terms.