Recent advances in medical imaging have greatly improved the success of cardiovascular and intracardiac interventions. This research aims to improve capacitive micromachined ultrasonic transducers (CMUT) based imaging catheters for intravascular ultrasound (IVUS) and intra-cardiac echocardiography (ICE) for 3-D volumetric imaging through integration of high-k thin film material into the CMUT fabrication and array design. CMUT-on-CMOS integration has been recently achieved and initial imaging of ex-vivo samples with adequate dynamic range for IVUS at 20MHz has been demonstrated; however, for imaging in the heart, higher sensitivities are needed for imaging up to 4-5 cm depth at 20MHz and deeper at 10MHz. Consequently, one research goal is to design 10-20MHz CMUT arrays using integrated circuit (IC) compatible micro fabrication techniques and optimizing transducer performance through high-k dielectrics such as hafnium oxide (HfO2). This thin film material is electrically characterized for its dielectric properties and thermal mechanical stress is measured. Experiments on test CMUTs show a +6dB improvement in receive (Rx) sensitivity, and +6dB improvement in transmit sensitivity in (Pa/V) as compared to a CMUT using silicon nitride isolation (SixNy) layer. CMUT-on-CMOS with HfO2 insulation is successfully integrated and images of a pig-artery was successfully obtained with a 40dB dynamic range for 1x1cm2 planes. Experimental demonstration of side looking capability of single chip CMUT on CMOS system based FL dual ring arrays supported by large signal and FEA simulations was presented. The experimental results which are in agreement with simulations show promising results for the viability of using FL-IVUS CMUT-on-CMOS device with dual mode side-forward looking imaging. Three dimensional images were obtained by the CMUT-on-CMOS array for both a front facing wire and 4 wires that are placed perpendicular to the array surface and ~4 mm away laterally. For a novel array design, a dual gap, dual frequency 2D array was designed, fabricated and verified against the large signal model for CMUTs. Three different CMUT element geometries (2 receive, 1 transmit) were designed to achieve ~20MHz and ~40MHz bands respectively in pulse-echo mode. A system level framework for designing CMUT arrays was described that include effects from imaging design requirements, acoustical cross-talk, bandwidths, signal-to-noise (SNR) optimization and considerations from IC limitations for pulse voltage. Electrical impedance measurements and hydrophone measurements comparisons between design and experiment show differences due to inaccuracies in using SixNy homogenous material in simulation compared to fabricated thin-film stacks (HfO2-AlSi-SixNy). It is concluded that for “thin” membranes the effect of stiffness and mass of HfO2 and AlSi (top electrode) cannot be ignored in the simulation. Also, it is understood that aspect ratio (width to height) <10 will have up to 15% error for center frequency predicted in air when the thin-plate approximation is used for modelling the bending stiffness of the CMUT membrane.

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International Telemetering Conference Proceedings / October 17-20, 1994 / Town & Country Hotel and Conference Center, San Diego, California / With the development of the airborne telemetry technique, it will be demanded that the transmitting sets on the missiles are more reliable and smaller. A frequency modulation (FM) oscillator stabilized with a dielectric resonator (DR), which can operates in the S-band directly, is presented. The FM oscillator is of simple circuit, reliable operation in the stabilization, small size, light weight and low cost. It will have a certain prospect of application in the airborne telemetry transmitting sets.

Com hipóteses de simetria plana e que a distribuição inicial de cargas, ocupa totalmente a amostra (tocando os dois eletródios), estudou-se o problema do movimento de carga espacial livre (M.C.E.L.) monopolar, em sólidos isolantes, submetidos à uma d.d.p. conhecida. Utilizando o método das características, reduziu-se o problema à um sistema de duas equações diferenciais ordinárias,de ia. ordem. O método foi aplicado para as distribuições linear, exponencial e p ~ x -1/2 , sob condições de curto circuito. são apresentados gráficos relativos à evolução temporal do perfil da densidade de cargas e da corrente externa. Estes resultados são comparados com outros obtidos por um cálculo aproximado, baseado em princípios variacionais . / Assuming planar symmetry and an arbitrary charge distribution that spreads through the sample, the one-carrier free - space-charge motion is studied in insulators solids. Using the method of characteristics we can reduce the problem t o the resolution of a system of two ordinary first order differential equations. Results are applied for linear, exponential and S.C.L. current charge distributions , under short-circuit conditions, The charge distribution for several times and the discharge currents are presented. The results are compared with those coming from an approximated method, based on variational principles.

Um novo método de medida (SAM -Spectral Analysis Method) mostra que, devído a um erro sistemático tradicionalmente desprezado, os valores medidos de polarização espontânea do cristal líquido ZLI-3654 (Merck) não seguem o que é previsto pela teoria de Landau das transições contínuas. Porém, a variação da susceptibilidade elétrica relativa com a temperatura proporcional à (T Tc) IND.-1, onde Te é a temperatura onde ocorre o máximo da susceptibilidade ...... está de acordo com o modelo de Landau. A resposta em freqüência da constante dielétrica mostra que, a fim de minimizar a corrente iônica, as medidas de polarização elétrica devem ser realizadas em frequências acima de 20 Hz. Por sua vez, os valores dos ângulos de fase dos harmônicos da polarização, obtidos pelo novo método, indicam que a intensidade do campo elétrico aplicado deve ser inferior a 1, 1 x 10 IND.6 Vrms/m (em 23Hz) para que não ocorram instabilidades elctrohidrodinâmicas, Finalmente, o ajuste das amplitudes dos harmônicos da polarização elétrica obtidos pelo SAM aos parâmetros da equação de Landau-Kalatnikov mostra um bom acordo dos valores medidos com o modelo, em contraste com os valores de polarização espontânea, A solução da equação de equilíbrio, levando em consideração os parâmetros ajustados, mostra como seriam os valores da polarização espontânea sem os erros sistemáticos. / A new proposed measurement method (SAM - Spectral Analysis Method) shows that, due a traditionally neglected systematic error, the values of the measured spontaneous polarization cf the ferroeleotric liquid crystal ZLI-3654 (Merck) doesn\'t follow what is predicted by the Landau theory of continuous transition. In contrast, the decay of the relative electric susceptibility with the temperature (T) - proportional to (T Tc)-l, where Tc is at the maximum of the susceptibility - is in good agreement with the Landau model. The frequency response of the dielectric constant shows that the measurements of the electric polarization of the sample must be done at frequencies hígher than 20Hz to avoid the actíons of the ionic currents. The phase values of the electric polarization harmonics obtained by the SAM indicates that the electric field must be lower thau 1,1 x l06Vrms/m (at 23Hz) to avoid electrohydrodynamic instabilities, Finally, the fitting of the amplitudes of the electric polarization harmonics obtained by the SAM to the parameters of the Landau-Kalatnikov equation shows a good agreement with the model, in contrast with the spontaneous polarization measurements. The solution of the Landau model, considering the fitted parameters, predicts how should be the spontaneous polarization values without the systematic errors.

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

Um novo método de medida (SAM -Spectral Analysis Method) mostra que, devído a um erro sistemático tradicionalmente desprezado, os valores medidos de polarização espontânea do cristal líquido ZLI-3654 (Merck) não seguem o que é previsto pela teoria de Landau das transições contínuas. Porém, a variação da susceptibilidade elétrica relativa com a temperatura proporcional à (T Tc) IND.-1, onde Te é a temperatura onde ocorre o máximo da susceptibilidade ...... está de acordo com o modelo de Landau. A resposta em freqüência da constante dielétrica mostra que, a fim de minimizar a corrente iônica, as medidas de polarização elétrica devem ser realizadas em frequências acima de 20 Hz. Por sua vez, os valores dos ângulos de fase dos harmônicos da polarização, obtidos pelo novo método, indicam que a intensidade do campo elétrico aplicado deve ser inferior a 1, 1 x 10 IND.6 Vrms/m (em 23Hz) para que não ocorram instabilidades elctrohidrodinâmicas, Finalmente, o ajuste das amplitudes dos harmônicos da polarização elétrica obtidos pelo SAM aos parâmetros da equação de Landau-Kalatnikov mostra um bom acordo dos valores medidos com o modelo, em contraste com os valores de polarização espontânea, A solução da equação de equilíbrio, levando em consideração os parâmetros ajustados, mostra como seriam os valores da polarização espontânea sem os erros sistemáticos. / A new proposed measurement method (SAM - Spectral Analysis Method) shows that, due a traditionally neglected systematic error, the values of the measured spontaneous polarization cf the ferroeleotric liquid crystal ZLI-3654 (Merck) doesn\'t follow what is predicted by the Landau theory of continuous transition. In contrast, the decay of the relative electric susceptibility with the temperature (T) - proportional to (T Tc)-l, where Tc is at the maximum of the susceptibility - is in good agreement with the Landau model. The frequency response of the dielectric constant shows that the measurements of the electric polarization of the sample must be done at frequencies hígher than 20Hz to avoid the actíons of the ionic currents. The phase values of the electric polarization harmonics obtained by the SAM indicates that the electric field must be lower thau 1,1 x l06Vrms/m (at 23Hz) to avoid electrohydrodynamic instabilities, Finally, the fitting of the amplitudes of the electric polarization harmonics obtained by the SAM to the parameters of the Landau-Kalatnikov equation shows a good agreement with the model, in contrast with the spontaneous polarization measurements. The solution of the Landau model, considering the fitted parameters, predicts how should be the spontaneous polarization values without the systematic errors.

The use of the microstrip antenna has grown rapidly for the last two decades, because of the increasing demand for a low profile antenna with small size, low cost, and high performance over a large spectrum of frequencies. However, despite the advantages microstrip antennas provide, a number of technical challenges remain to be solved for microstrip antennas to reach their full potential, particularly if they are to be interfaced with monolithic circuits. The objective of this thesis is to examine novel methods for integrating and constructing broadband microstrip antennas, particularly at high microwave and millimeter wave frequencies where dimensions get very small and fabrication tolerances are critical. The first stage of the thesis investigates techniques to reduce the spurious feed radiation and surface wave generation from edge-fed patch antennas. A technique to reduce the spurious radiation from the edge-fed patch antenna by using a dielectric filled cavity behind the radiating element is explored. From this, a single element edge-fed cavity backed patch antenna was developed. Measured results showed low levels of cross polarization, making it suitable for dual or circular polarization applications. A 2 x 2 edge-fed cavity backed patch antenna array was also developed, which benefited greatly from this new technique due to the extensive feed network required. Furthermore, investigation into edge-fed cavity backed patches on high dielectric materials was also conducted. The measured impedance bandwidth of this edge-fed cavity backed patch is three times greater than the conventional edge-fed patch, and the gain increases to 5.1 dBi compared to 3.6 dBi. Further bandwidth enhancement of the single element edge-fed cavity backed antenna on high dielectric material was achieved by applying the hi-lo substrate structure. The hi-lo substrate structure produced an increase in the bandwidth to 26% from the 1.7% of the single element edge-fed cavity backed patch, while maintaining pattern integrity and radiation efficiency. Next, the development of a flip-chip bonding technique was investigated to enhance the fabrication accuracy and robustness of multilayer antennas on high dielectric materials. This technique was proven through simulation and experiment to provide good impedance and radiation performance via the high accuracy placement of the superstrate layer. The single element flip-chip patch antenna uses a high dielectric constant material for both the base and the patch superstrate, whereas the stacked flip-chip patch again uses a high and low permittivity material combination to achieve efficient wideband performance. Due to the high permittivity feed material, these antennas display the attributes required for integration with MMICs. The measured 10 dB return loss bandwidth of the single element was 4% with a gain of 4.6 dBi, whereas the stacked flip-chip patch showed very broadband performance, with a bandwidth of 23% with a gain of 8.5 dBi. The high accuracy placement and rigid attachment of the upper superstrat e layer via the flip-chip bonding technique also enables these antennas to be scaled up to millimeter-wave operational frequencies. The final section of this thesis is focused on developing a fabrication technique to enable the creation of a low permittivity layer at a nominated thickness.

<p> </p><p><p> </p></p><p><p><p> </p></p></p><p>MAX-phase materials are a new type of material class. These materials are potentiallyt echnologically important as they show unique physical properties due to the combination of metals and ceramics. In this project, spectroscopic ellipsometry in the spectral range of 0.06 eV –6.0 eV was used to probe the linear optical response of MAX-phases in terms of the complexd dielectric function <em>ε(ω) = ε1(ω) + iε2(ω<em>). </em></em>Measured data were fit to theoretical models using the Lorentz and generalized oscillator models. Data from seven different samples of MAX-phase materials were obtained using two ellipsometers. Each sample dielectric function was determined, including their infrared spectrum.</p>