O objetivo principal do presente trabalho é apresentar uma proposta que permita a combinação entre uma solução de captura de pacotes já existente e não muito flexível (sniffer) e o conceito de agentes móveis para aplicação em redes segmentadas. Essa pesquisa possui como foco principal a aplicação da técnica captura de pacotes em SDIs network based, utilizando para isso o modelo desenvolvido no ICMC (Cansian, 1997) e posteriormente adequado ao ambiente de agentes móveis (Bernardes, 1999). Assim sendo, foi especificada a camada base do ambiente desenvolvido em (Bernardes, 1999) visando as interações entre seus agentes e o agente de captura de pacotes. / The main objective of the current work is to present a proposal that allows the combination between an existent and not so flexible packet capture solution (sniffer) and the concept of mobile agents for application in switched networks. This research focuses the application of the packet capture technique in IDSs network-based, using for this purpose the model developed at ICMC (Cansian, 1997) and later adjusted to the mobile agents environment (Bernardes, 1999). Therefore, the base layer of the developed environment (Bernardes, 1999} was specified focusing the interactions between its agents and the packet capture agent.

"Microelectromechanical systems (MEMS) technology has been evolving for about two decades and, now it is integrated in many designs, including radio frequency (RF) switches characterized by µm dimensions. Today, designers are attempting o develop the ideal RF MEMS switch, yet electro-thermo-mechanical (ETM) effects still limit the design possibilities and adversely affect reliability of these microswitches. The ETM effects are a result of Joule heat generated at the microswitch contact areas. This heat is due to the current passing through the microswitch, characteristics of the contact interfaces, and other parameters characterizing a particular design. It significantly raises temperature of the microswitch, thus affecting the mechanical and electrical properties of the contacts, which may lead to welding, causing a major reliability issue. Advanced research was performed, in this thesis, to minimize the Joule heat effects on the contact areas, thus improving performance of the microswitch. Thermal analyses done computationally on a cantilever-type RF MEMS switch indicate heat-effected zones and the influences that various design parameters have on these zones. Uncertainty analyses were also performed to ensure accuracy of the computational results, which indicate contact temperatures on the order of 700˚C, for the cases considered in this thesis. Although these temperatures are well below the melting temperatures of the materials used, new designs of the microswitches will have to be developed, in order to lower their maximum operating temperatures and reduce temporal effects they cause, to increase reliability of the RF MEMS switches."

O objetivo principal do presente trabalho é apresentar uma proposta que permita a combinação entre uma solução de captura de pacotes já existente e não muito flexível (sniffer) e o conceito de agentes móveis para aplicação em redes segmentadas. Essa pesquisa possui como foco principal a aplicação da técnica captura de pacotes em SDIs network based, utilizando para isso o modelo desenvolvido no ICMC (Cansian, 1997) e posteriormente adequado ao ambiente de agentes móveis (Bernardes, 1999). Assim sendo, foi especificada a camada base do ambiente desenvolvido em (Bernardes, 1999) visando as interações entre seus agentes e o agente de captura de pacotes. / The main objective of the current work is to present a proposal that allows the combination between an existent and not so flexible packet capture solution (sniffer) and the concept of mobile agents for application in switched networks. This research focuses the application of the packet capture technique in IDSs network-based, using for this purpose the model developed at ICMC (Cansian, 1997) and later adjusted to the mobile agents environment (Bernardes, 1999). Therefore, the base layer of the developed environment (Bernardes, 1999} was specified focusing the interactions between its agents and the packet capture agent.

This dissertation presents the design, fabrication, and characterization of low-voltage capacitive RF MEMS switches. Although, RF MEMS switches have shown superior performance as compared to the existing solid-state semiconductor switches and are viable alternate to the present and the future communication systems, not been able to match the commercial standards due to their poor reliability. Dielectric charging due high actuation is one of the major concerns that limit the reliability of these switches. Hence, the focus of this thesis is on the development of low actuation voltage RF MEMS switches without compromising much on their RF and dynamic performances i.e., low insertion loss and high isolation. Four different switch topologies are studied and discussed. Electromechanical and electromagnetic modelling is presented to study the effect of various components that comprise a MEMS switch on the transient and the RF behaviour. The analytical expressions for switching and release times are established in order to estimate the switching and release times. An in-house developed surface micromachining process is adapted for the micro fabrication. This process eliminates the need for an extra mask used for the anchors and restricts the overall process to four-masks only. These switches are fabricated on 500 µm thick glass substrate. A 0.5 µm thick gold film is used as the structural material. For the final release of the switch, chemical wet etching technique is employed. The fabricated MEMS switches are characterized mechanically and electrically by measuring mechanical resonant frequency, quality factor, pull-in, and pull-up voltages. Since, low actuation voltage switches have slow response time. One of the key objectives of this thesis is to realize switches with fast response time at low actuation voltage. Measurements are performed to estimate the switching and release times. The measured Q-factors of switches are found to be in between 1.1 -1.4 which is the recommended value for Q in MEMS switches for a suppressed oscillation after the release. Furthermore, the effect of hole size on the switching dynamics is addressed. RF measurements are carried out to measure the S-parameters in order to quantify the RF performance. The measured results demonstrate that these switches need low actuation voltage in range of 4.5 V to 8.5 V for the actuation. The measured insertion loss less than -0.8 dB and isolation better than 30 dB up to 40 GHz is reported. In addition, the robustness of realized switches is tested using in-house developed Lab View-based automated measurement test set-up. The reliability test analysis shows no degradation in the RF performance even after 10 millions of switching cycles. Overall yield of 70 -80% is estimated in the present work. Finally, the experimentally measured results presented in this work prove the successful development of low actuation voltage capacitive RF MEMS switches and also offers that even with 0.5 µm thick gold film better reliability for MEMS switches can be achieved.

No description available.

Encrypted data transmission is becoming increasingly more important as information security is vital to modern communication networks. Quantum Key Distribution (QKD) is a promising method based on the quantum properties of light to generate and distribute unconditionally secure keys for use in classical data encryption. Significant progress has been achieved in the performance of QKD point-to-point transmission over a fibre link between two users. The transmission distance has exceeded several hundred kilometres of optical fibre in recent years, and the secure bit rate achievable has reached megabits per second, making QKD applicable for metro networks. To realize quantum encrypted data transmission over metro networks, quantum keys need to be regularly distributed and shared between multiple end users. Optical switching has been shown to be a promising technique for cost-effective QKD networking, enabling the dynamic reconfiguration of transmission paths with low insertion loss. In this thesis, the performance of optically switched multi-user QKD systems are studied using a mathematical model in terms of transmission distance and secure key rates. The crosstalk and loss limitations are first investigated theoretically and then experimentally. The experiment and simulation both show that negligible system penalties are observed with crosstalk of -20 dB or below. A practical quantum-safe metro network solution is then reported, integrating optically-switched QKD systems with high speed reconfigurability to protect classical network traffic. Quantum signals are routed by rapid optical switches between any two endpoints or network nodes via reconfigurable connections. Proof-of-concept experiments with commercial QKD systems are conducted. Secure keys are continuously shared between virtualised Alice-Bob pairs over effective transmission distances of 30 km, 31.7 km, 33.1 km and 44.6 km. The quantum bit error rates (QBER) for the four paths are proportional to the channel losses with values between 2.6% and 4.1%. Optimising the reconciliation and clock distribution architecture is predicted to result in an estimated maximum system reconfiguration time of 20 s, far shorter than previously demonstrated. In addition, Continuous Variable (CV) QKD has attracted much research interest in recent years, due to its compatibility with standard telecommunication techniques and relatively low cost in practical implementation. A wide band balanced homodyne detection system built from modified off-the-shelf components is experimentally demonstrated. Practical limits and benefits for high speed CVQKD key transmission are demonstrated based on an analysis of noise performance. The feasibility of an optically switched CV-QKD is also experimentally demonstrated using two virtualised Alice-Bob pairs for the first time. This work represents significant advances towards the deployment of CVQKD in a practical quantum-safe metro network. A method of using the classical equalization technique for Inter-symbol-interference mitigation in CVQKD detection is also presented and investigated. This will encourage further research to explore the applications of classical communication tools in quantum communications.

The frequency response analysis of switched networks plays a very important part in designing various kinds of power converter circuits. In this thesis two frequency response techniques for analyzing switching power converters are discussed. One method provides a mathematical description which treats the converter as a periodic time varying system. A linearized small signal model is subsequently derived. The major part of the thesis concentrates on this accurate exact small-signal technique. The derivation involves state space representation and the use of the time varying transfer function. A Fourier analysis is performed to show the relationship between the frequency response of the network and the time varying transfer function. The obtained expressions are in closed form. The method has proven to be exact. The complexity of this technique is overcome by automating its derivation in conjunction with a circuit simulator. An alternative method, relying only on a sampled-data representation, is also derived, which provides a less complicated algorithm. However the accuracy of this method suffers, particularly at high frequencies. The accuracy of the exact small-signal technique is verified by experimentation.

Molecular photoswitches are attracting much attention lately mostly because of their possible applications in nano technology, and their role in biology. One of the widely studied representatives of photochromic molecules is azobenzene (AB). With light, by a static electric field, or with tunneling electrons this specie can be "switched" from the flat and energetically more stable trans form, into the compact cis form. The back reaction can be induced optically or thermally. Quantum chemical calculations, mostly based on density functional theory, on the AB molecule, AB derivatives and related systems are presented. All the calculations were done for isolated species, however, with implications for latest experimental results aiming at the switching of surface mounted ABs. In some of these experiments, it is assumed that the switching process is substrate mediated, by attaching an electron or a hole to the adsorbate forming short-lived anion or cation resonances. Therefore, we calculated also cationic and anionic ABs in this work. An influence of external electric fields on the potential energy surfaces, was also studied. Further, by the type, number and positioning of various substituent groups, systematic changes on activation energies and rates for the thermal cis-to-trans isomerization can be enforced. The nature of the transition state for ground state isomerization was investigated. Applying Eyring's transition state theory, trends in activation energies and rates were predicted and are, where a comparison was possible, in good agreement with experimental data. Further, thermal isomerization was studied in solution, for which a polarizable continuum model was employed. The influence of substitution and an environment leaves its traces on structural properties of molecules and quantitative appearance of calculated UV/Vis spectra, as well. Finally, an explicit treatment of a solid substrate was demonstrated for the conformational switching, by scanning tunneling microscope, of a 1,5-cyclooctadiene (COD) molecule at a Si(001) surface, treated by a cluster model. At first, we studied energetics and potential energy surfaces along relevant switching coordinates by quantum chemical calculations, followed by the switching dynamics using wave packet methods. We show that, in spite the simplicity of the model, our calculations support the switching of adsorbed COD, by inelastic electron tunneling at low temperatures. / Um den technologischen Fortschritt zu gewährleisten, ist man in vielen technischen Gebieten auf der Suche nach neuen und leistungsfähigeren Materialien. In der Computer- und Informationstechnologie folgte daraus die stetige Miniaturisierung von Bauelementen. Molekulare Photoschalter sind häufig an biologischen Prozessen beteiligt und äußerst vielversprechend, auf diesem Gebiet Anwendung zu finden. Ein sehr umfangreich studiertes photochromes Molekül ist Azobenzol (AB). Diese Spezien können durch Licht, statische elektrische Felder oder elektronisches Tunneln von der energetisch stabilen trans Form zur geometrisch kompakten cis Form "geschaltet" werden. Die Rückreaktion kann optisch oder thermisch erfolgen. In dieser Arbeit werden vorwiegend auf der Dichtefunktionaltheorie beruhende quantenchemische Rechnungen von AB, AB-Derivaten und verwandten Systemen vorgestellt. Alle Rechnungen betrachten isolierte Moleküle, werden jedoch in Zusammenhang mit neuesten experimentellen Ergebnissen zu oberflächengebundenen AB-Schaltern gestellt. In einigen dieser Experimente wird angenommen, dass der Schaltprozess substratvermittelt erfolgt, indem dem Adsorbat ein Elektron zugeführt oder entzogen und so eine kurzlebige anionische oder kationische Resonanz erzeugt wird. Daher werden sowohl ionische AB berechnet als auch der Einfluss eines externen elektrischen Feldes auf die Potentialhyperfläche studiert. Weiterhin können Aktivierungsenergie und Reaktionsrate der thermischen cis-trans-Isomerisierung durch Art, Anzahl und Position verschiedener Substituenten variieren. Die Natur des Übergangszustandes wird daher intensiv erforscht. Mit Hilfe der Theorie des Übergangszustandes nach Eyring werden Reaktionsraten prognostiziert, welche gut mit experimentellen Daten übereinstimmen. Daneben wird die thermische Isomerisierung in einem Lösungsmittel unter Verwendung des polarizable continuum model untersucht, da der Einfluss des Substituenten und die Anwesenheit einer Umgebung zu Veränderungen der strukturellen Eigenschaften der Moleküle und dem quantitativen Verlauf der berechneten UV/Vis-Spektren führen. Abschließend wird unter expliziter Einbeziehung eines festen Substrates das elektronisch getriebene konformale Schalten von 1,5-Cyclooctadien (COD) an einer Si(001)-Oberfläche demonstriert. Zunächst wird die Energetik und die Potentialhyperfläche entlang der relevanten Schaltkoordinaten durch quantenchemische Rechnungen ermittelt und das Schaltverhalten durch Wellenpaketmethoden beschrieben. Trotz der Einfachheit wird gezeigt, dass ein derartiges Modell das elektronische Schalten von adsorbiertem COD bei niedrigen Temperaturen gut beschreibt.

Due to the low current ratings of the currently available silicon carbide (SiC) switches they cannot be employed in high-power converters. Thus, it is necessary to parallel-connect several switches in order to reach higher current ratings. This paper presents an investigation of parallel-connected normally-on SiC junction field effect transistors. There are four crucial parameters affecting the effectiveness of the parallel-connected switches. However, the pinch-off voltage and the reverse breakdown voltage of the gates seem to be the most important parameters which affect the switching performance of the devices. In particular, the spread in these two parameters might affect the stable off-state operation of the switches. The switching performance and the switching losses of a pair of parallel-connected devices having different reverse breakdown voltages of the gates is investigated by employing three different gate-driver configurations. It is experimentally shown that using a single gate-driver circuit the switching performance of the parallel-connected devices is almost identical, while the total switching losses are lower compared to the other two configurations. / <p>QC 20121116</p>

Microwave and millimeter wave switch matrices are essential components in telecommunication systems. These matrices enhance satellite capacity by providing full and flexible interconnectivity between the received and transmitted signals and facilitate optimum utilization of system bandwidth. Waveguide and semiconductor technology are two prominent candidates for the realizing such types of switch matrices. Waveguide switches are dominant in high frequency applications of 100 ? 200 GHz and in high power satellite communication. However, their heavy and bulky profile reinforces the need for a replacement. In some applications, semiconductor switches are an alternative to mechanical waveguide switches and utilize PIN diodes to create the ON and OFF states. Although, these switches are small in size, they exhibit poor RF performance and low power handling. <br /><br /> RF MEMS technology is a good candidate to replace the conventional switches and to realize an entire switch matrix. This technology has a great potential to offer superior RF performance with miniaturized dimensions. Because of the advantages of MEMS technology numerous research studies have been devoted to develop RF MEMS switches. However, they are mostly concentrated on Single-Pole Single-Throw (SPST) configurations and very limited work has been performed on MEMS multi-port switches and switch matrices. Here, this research has been dedicated on developing multi-port RF MEMS switches and amenable interconnect networks for switch matrix applications. To explore the topic, three tasks are considered: planar (2D) multi-port RF MEMS switches, 3D multi-port RF MEMS switches, and RF MEMS switch matrix integration. <br /><br /> One key objective of this thesis is to investigate novel configurations for planar multi-port (SPNT), C-type, and R-type switches. Such switches represent the basic building blocks of switch matrices operating at microwave frequencies. An in house monolithic fabrication process dedicated to electrostatic multi-port RF MEMS switches is developed and fine tuned. The measurement results exhibit an excellent RF performance verifying the concept. Also, thermally actuated multi-port switches for satellite applications are designed and analyzed. The switch performance at room condition as well as at a very low temperature of 77K degrees (to resemble the harsh environment of satellite applications) is measured and discussed in detail. <br /><br /> For the first time, a new category of 3D RF MEMS switches is introduced to the MEMS community. These switches are not only extremely useful for high power applications but also have a great potential for high frequencies and millimetre-waves. The concept is based on the integration of vertically actuated MEMS actuators inside 3D transmission lines such as waveguides and coaxial lines. An SPST and C-type switches based on the integration of rotary thermal and electrostatic actuators are designed and realized. The concept is verified for the frequencies up to 30GHz with measured results. A high power test analysis and measurement data indicates no major change in performance as high as 13W. <br /><br /> The monolithic integration of the RF MEMS switch matrix involves the design and optimization of a unique interconnect network which is amenable to the MEMS fabrication process. While the switches and interconnect lines are fabricated on the front side, taking advantage of the back side patterning provides a high isolation for cross over junctions. Two different techniques are adopted to optimize the interconnect network. They are based on vertical three-via interconnects and electromagnetically coupled junctions. The data illustrates that for a return loss of less than -20dB up to 30GHz, an isolation of better than 40dB is obtained. This technique not only eliminates the need for expensive multilayer manufacturing process such as Low Temperature Co-fired Ceramics (LTCC) but also provides a unique approach to fabricate the entire switch matrix monolithically.