In this study, we present analytical and experimental investigation of electrically actuated micro cantilever based resonators. These devices are fabricated using polyimide and coated with chrome and gold layers from both sides. The cantilevers are highly curled up due to stress gradient, which is a common imperfection in surface micro machining. Using a laser Doppler vibrometer, we applied a noise signal to experimentally find the first four resonance frequencies. Then, using a data acquisition card, we swept the excitation frequency around the first four natural modes of vibrations. Theoretically, we derived a reduced order model using the Galerkin method to simulate the dynamics of the system. Extensive numerical analysis and computations were performed. The numerical analysis was able to provide good matching with experimental values of the resonance frequencies. Also, we proved the ability to excite higher order modes using partial electrodes with shapes that resemble the shape of the mode of interest. Such micro-resonators are shown to be promising for applications in mass and gas sensing.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Includes bibliographical references (p. 115-120).

No description available.

Whispering Gallery Mode (WGM) microcavities have a wide range of applications from fundamental physics researches to engineering applications due to their ultra high quality factor (Q). For example, an ultra-high Q WGM cavity can be used as an bio/nanosensor since a nano particle bound to the surface of the cavity will result in a resonance wavelength shift. In the last decade lots of research have been conducted on this topic, as a result, WGM biosensors are emerging as one of the mainstream senors. This thesis presents an efficient beam propagation method (BPM) simulation tool to study the light propagation behaviour in WGM cavities. Using this tool, the perturbation of the cavity properties caused by a polystyrene nano bead attached to the surface of a WGM silica microcavity is investigated. Furthermore, we numerically verify a three times sensitivity enhancement by fabricating a nanohole at the surface of the WGM cavity sensor. In addition, we study the open cavity structures, cavity-waveguide coupling, huge WGM cavities, and deformed microcavities radiation. Finally, the impact of fabrication inaccuracy on asymmetric WGM cavities is investigated in terms of quality factor degradation. / Graduate

M.Ing. / During mineral exploration a whole lot of different exploration techniques can be applied. In this thesis the instrumentation used for electromagnetic surveying, which is only one of the prospecting techniques, is inspected. In particular the thesis will be about the transmitter of the single transmitter wide band receiver airborne electromagnetic prospecting system. A new power electronic topology is proposed in order to improve this transmitter. Before this is done a reference is first established. This is done in the form of the exponential transition inverter, which is the inverter that is currently applied as transmitter in South-Africa. Another reason for looking at this circuit topology is because it is the simplest way to realize the transmitter. During the analysis of this inverter topology all the proporties of the transmitter as a whole is also investigated. The main component of the transmitter, namely the transmitter coil is also discussed. This is followed by a summary of the properties of the exponential transition inverter in which the main shortcomings of this transmitter is discussed. The greatest of which is surely that pliable frequency spectra cannot be obtained. Subsequently resonance is viewed as a solution to the shortcomings. The main contribution of this is that the pliability of the frequency spectrum can be increased, because the capasitor in this circuit can easily be changed. It is however shown that a purely resonant circuit on it's own, also is not the solution. This leads to the improved inverter topology for the transmitter, namely the Kwasi resonant inverter. It is shown in detail that the Kwasi resonant inverter is a much beter option as transmitter then the exponential transient inverter. Since this circuit also has a capacitor in it, it is shown that pliable frequency spectra can be obtained. It is futher shown how the pliability of the frequency spectrum can be improved even more by deviating from conventional methods of switch control. Mathematical analysis, as well as an experimental setup, of the different inverter topologies, are used to illustrate all of the above mentioned. As a conclusion the only drawback of the Kwasi resonant inverter, namely high voltage peaks, is addressed. A solution to this problem is proposed in the form of two different voltage clamps. The best one of the two is identified and also implemented.

The consequences of fabricating Bragg gratings in various fibres, with or without hydrogen loading, and with varying laser power levels are explored. Three new techniques for fabricating chirped gratings are presented. Beams with dissimilar wavefront curvatures are interfered to give chirped gratings. With the same aim techniques of writing gratings on tapered fibres and on deformed fibres are also covered. With these techniques, a wide variety of gratings has been fabricated from the 'superbroad' (with bandwidths of up to 180 nm), small to medium bandwidth gratings with linear chirp profiles and quadratic chirped gratings. It is demonstrated that chirped grating can be concatenated to form all-fibre Fabry-Perot and Moiré resonators. These are further concatenated with chirped gratings to produce filters with narrow passbands and very broad stopbands. A number of other applications are also addressed. The use of chirped fibre gratings for dispersion compensation and femtosecond chirped pulse amplification is demonstrated. Chirped gratings are used as dispersive elements in modelocked fibre lasers producing ultrashort pulses. A chirped fibre grating Fabry-Perot transmission filter is used in a continuous wave laser that exhibits eleven simultaneously lasing wavelengths. Finally, the use of grating-coupler devices as variable reflectivity mirrors for laser optimisation and gain clamping is considered.

by Leung, Kowk-wa. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references (leaves 207-211). / Dedication / Acknowledgements / CHAPTER / Chapter 1. --- INTRODUCTION --- p.1 / Chapter 2. --- ANALYSIS OF A PROBE-FED HEMISPHERICAL DR ANTENNA --- p.13 / Chapter 2.1 --- Introduction --- p.13 / Chapter 2.2 --- Problem Formulation --- p.14 / Chapter 2.3 --- Single Cavity Mode Approximation --- p.33 / Chapter 2.3.1 --- Evaluation of Input Impedance --- p.33 / Chapter 2.3.2 --- Measured and Computed Results --- p.36 / Chapter 2.4 --- Rigorous Moment Method Solution --- p.47 / Chapter 2.4.1 --- Efficient Evaluation of GEz --- p.47 / Chapter 2.4.2 --- Moment Method Formulation for Input Impedance --- p.51 / Chapter 2.4.3 --- Evaluation of Z-matrix --- p.56 / Chapter 2.4.4 --- Evaluation of V-matrix --- p.62 / Chapter 2.4.5 --- Convergence Checks --- p.65 / Chapter 2.4.6 --- Measured and Computed Results --- p.91 / Chapter 2.4.7 --- Conclusion --- p.113 / Chapter 2.5 --- Theoretical Single Cavity Mode Radiation Patterns --- p.114 / Chapter 2.6 --- Conclusion --- p.117 / Chapter 3. --- ANALYSIS OF APERTURE COUPLED HEMISPHERICAL DR ANTENNA --- p.118 / Chapter 3.1 --- Introduction --- p.118 / Chapter 3.2 --- Problem Formulation --- p.120 / Chapter 3.3 --- Moment Method Solution --- p.133 / Chapter 3.4 --- Magnetic Field Green's Function of DR Antenna --- p.138 / Chapter 3.5 --- Efficient Evaluations of Antenna Green's Function and Yamn --- p.150 / Chapter 3.5.1 --- Modal Green's function of DR Antenna --- p.150 / Chapter 3.5.2 --- Evaluation of Yamn --- p.153 / Chapter 3.6 --- Single Cavity Mode Approximation --- p.155 / Chapter 3.6.1 --- Evaluation of Input Impedance --- p.155 / Chapter 3.6.2 --- Measured and Computed Results --- p.157 / Chapter 3.6.3 --- Conclusion --- p.165 / Chapter 3.7 --- Exact Modal Solution --- p.166 / Chapter 3.7.1 --- Convergence Checks --- p.166 / Chapter 3.7.2 --- Measured and Computed Results --- p.166 / Chapter 3.7.3 --- Conclusion --- p.187 / Chapter 3.8 --- Conclusion --- p.188 / Chapter 4. --- CONCLUSION --- p.189 / APPENDIX A PROOF OF EQUATION (2-16) --- p.192 / APPENDIX B DERIVATION OF EQUATION (2-43) --- p.193 / APPENDIX C DERIVATION OF EQUATION (2-44) --- p.196 / APPENDIX D PROPAGATION CONSTANT OF FIELDS INSIDE MICROSTRIPLINE --- p.198 / APPENDIX E NUMERICAL TECHNIQUE OF SPECTRAL DOMAIN INTEGRAL --- p.200 / APPENDIX F EXPERIMENTAL SET-UP FOR PROBE- FED DR ANTENNA MEASUREMENT --- p.203 / APPENDIX G EXPERIMENTAL SET-UP FOR APERTURE- COUPLED DR ANTENNA MEASUREMENT --- p.205 / REFERENCES --- p.207 / LIST OF PUBLICATIONS PRODUCED DURING THE STUDY A-l / INTERNATIONAL AWARD OBTAINED DURING THE STUDY B-l

Recientemente se ha abierto un nuevo campo de investigación en el área del electromagnetismo aplicado y de la ingeniería de microondas basado en el control de las propiedades electromagnéticas de ciertas estructuras periódicas artificiales conocidas como metamateriales. Debido a que las celdas constitutivas de este tipo de estructuras presentan unas dimensiones muy reducidas en términos de longitud de onda es posible diseñar, en base a este concepto, dispositivos que combinen un gran nivel de compactación y elevadas prestaciones. En esta tesis se han utilizado las propiedades de dichos medios para la implementación de filtros de microondas en tecnología planar. Particularmente se han desarrollado técnicas de síntesis que permiten el diseño de filtros con características controlables, en términos de ancho de banda, rizado en la banda de paso, colocación de ceros de transmisión en la banda de rechazo, etc. En este documento se pueden encontrar varios ejemplos de aplicación de estas técnicas, dando lugar a varios prototipos con respuestas en varios rangos de frecuencia, que van desde respuestas de banda estrecha hasta respuestas ultra anchas. / In the last years, a new research field in the area of applied electromagnetism and microwave engineering based on the control of electromagnetic properties of artificial structures has taken a great interest. These structures are known as metamaterials. Due to the small dimensions of its constitutive cells it is possible to design, based on this concept, devices that combine high performance and compact dimensions. This thesis concerns the application of metamaterial technology to the synthesis of microwave filters in planar technology. In this document can be found a design methodology for each cell of the structure according to the desired frequency response of the filter (bandwidth, pass band ripple, location of transmission zeroes, etc). This methodology is also applicable to the design of filters with standard frequency responses (Chebyshev, Butterworth, etc). The theoretical work is also supported with experimental results of several prototypes with different bandwidths, from narrow band responses to ultra wide band filters.

Integrated ring resonators have attracted a considerable interest in optical communications because of their small size and wide range of applicability. Here we consider several aspects of these devices, beginning with a tunable hybrid ring resonators consisting of a silicon over insulator (SOI) ring covered with a polymer layer in a variable electric field. Varying the field changes the polymer refractive index and consequently the resonance condition of the cavity. This device offers a large degree of optical confinement together with a high modulation speed. Subsequently, we design and present fabrication results for a Wavelength Division Multiplexing (WDM) multiplexer/demultiplexer formed from a series of ring resonators with two channels separated by 50 GHz each that is predicted to exhibit a free spectral range (FSR) of 100 GHz , signal dispersion less than 30 ps/nm and a signal cross-talk less than -23 dB. Finally, we analyze the application of the coupled ring waveguide circuit to rotation sensors based on the Sagnac phase shift. Here, however our analysis indicates that a single ring, of the same area exhibits a higher degree of sensitivity to rotational motion than a multiple ring circuit.

Micromechanical resonators are used in a variety of sensing and filtering applications. In these applications, the accurate performance of micro resonators depends on the sensitivity of these devices to a particular resonance frequency. This sensitivity is measured using the quality factor Q, which is the ratio of the total input energy into the device to the energy dissipated within a vibration cycle. A higher quality factor indicates a smaller resonance bandwidth, which makes the micro-resonator more effective in identifying a desired signal. Higher Q values result from reductions in dissipation losses. Dissipation losses occur through damping by the ambient fluid, anchor losses, thermoelastic damping, and other sources. The squeeze-film effect is of particular interest in micro-resonators as the fluid enclosed between the resonating components can provide significant dissipation. This work covers investigations into the air damping of oscillating micromachined resonators that operate near a fixed wall, which is parallel to the oscillating surface. The main portion of this work focuses on the theoretical and numerical investigation of the air damping of micromachined resonators when the surrounding gas (air) is in the Free-Molecule regime. Errors and limitations of previous theoretical models have been found and corrected. A molecular dynamics simulation code that is suitable to handle a more general class of resonators has been developed. This code has been used to find the quality factor of a microbeam resonator. The results from the code were compared to existing experimental results, and were found to have very good agreement in the free molecular regime. The simulation was then used to investigate the effects of the oscillation mechanics on the energy dissipation and quality factor. The second part of this work focuses on the region between the bottom surface of a laterally-oscillating disk resonator and the substrate. The compressibility effects of a 1 micron thick film of air on a laterally-oscillating disk resonator were investigated. The pressure perturbation for this case was found to be minimal, which means that the compressibility effects of the fluid film will negligible.