Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: This dissertation presents a circuit-based design technique that leads to benefits in terms of the physical size, manufacturability, and exibility in the design of N-way conical line power combiners. An equivalent circuit model for the peripheral input ports of conical line power combiners is extracted, as well as empirical equations that allow the circuit element values to be calculated directly from the physical dimensions of the combiner, and vice versa. This allows for rapid optimization of various dimensions of the combiner at a significantly reduced computational cost compared to full-wave simulations. A design procedure is presented and a conical combiner designed with a measured reflection coefficient of better than -18 dB over a 46 % bandwidth around 10 GHz. The designed prototype is much smaller compared to previous designs while exhibiting similar performance. Design procedures for single-section and multi-section impedance tapered conical to coaxial line transitions are also presented, which can be used to simplify the design of conical combiners and reduce the manufacturing effort. Two combiners are designed, one with a single-section and one with a multi-section transition, and output port reflection coefficients of -23 dB and -17 dB over bandwidths of 20 % and 43 % around 10 GHz are measured, respectively. This dissertation additionally presents a method that can be used in general to improve the input port isolation of N-way power combiners without affecting their reciprocity. A simple S-parameter proof is presented, followed by a derivation of equations that can be used to estimate the worst-case performance. Some design examples are presented, showing that terminations can be used for isolation loads. A prototype based on microstrip transmission lines is manufactured and a much improved input port reflection and isolation performance of -15 dB and 20 dB is measured, respectively, compared to a simulated input port reflection coefficient of -2:5 dB and isolation of 2:5 dB before the method was applied. ii / AFRIKAANSE OPSOMMING: Hierdie proefskrif stel 'n stroombaangebaseerde ontwerpsmetode voor wat lei tot voordele in terme van die fisiese grootte, vervaardigbaarheid, en vryheid in die ontwerp van koniese lyn kombineerders. 'n Ekwivalente stroombaanmodel vir die voerpoorte word onttrek, asook empiriese vergelykings wat gebruik kan word om die stroombaanelement waardes vanaf die afmetings van die kombineerder te bepaal. Dit laat die ontwerper toe om verskeie afmetings van die kombineerder te optimeer teen 'n beduidende laer koste in vergelyking met volgolf simulasies. 'n Ontwerpsprosedure word voorgestel en gebruik om 'n koniese kombineerder te ontwerp en 'n weerkaatskoëffisient van beter as -18 dB met 'n bandwydte van 46 % om 10 GHz word gemeet. Die prototipe is aansienlik kleiner as vorige ontwerpe, maar toon soortgelyke werkverrigting. Ontwerpsprosedures vir enkel en veelvoudige deel koniese na koaksiale lyn oorgange word ook voorgestel, wat gebruik kan word om die ontwerp en vervaardiging van koniese kombineerders te vereenvoudig. Twee kombineerders word ontwerp, een met 'n enkel deel oorgang en een met veelvoudige dele, en onderskeidelike uittree weerkaatskoëffisiente van -23 dB en -17 dB oor bandwydtes van 20 % en 43 % word gemeet. Hierdie proefskrif stel ook 'n metode voor wat gebruik kan word om die intree poort isolasie van N-rigting kombineerders in die algemeen te verbeter, sonder om die wederkerigheid daarvan te beïnvloed. 'n Bewys van die metode word gelewer, gevolg deur 'n afleiding van vergelykings wat gebruik kan word om die slegste-geval werkverrigting af te skat. Verskillende voorbeelde van kombineerders word getoon waarop die metode toegepas is, en wys dat terminasies gebruik kan word vir die isolasie laste. 'n Prototipe gebaseer op mikrostrook transmissielyne word vervaardig en 'n verbeterde intreepoort weerkaatskoëffisient en isolasie van onderskeidelik -15 dB en 20 dB word gemeet, in vergelyking met 'n weerkaatskoëffisient van -2:5 dB en isolasie van 2:5 dB voordat die metode toegepas is.

The objective of the proposed research is to create new reconfigurable RF and millimeter-wave circuit topologies that enable significant systems benefits. The market of RF systems has long evolved under a paradigm where once a system is built, performance cannot be changed. Companies have recognized that building flexibility into RF systems and providing mechanisms to reconfigure the RF performance can enable significant benefits, including: the ability support multiple modulation schemes and standards, the reduction of product size and overdesign, the ability to adapt to environmental conditions, the improvement in spectrum utilization, and the ability to calibrate, characterize, and monitor system performance. This work demonstrates X-band LNA designs with the ability to change the frequency of operation, improve linearity, and digitally control the tradeoff between performance and power dissipation. At W-band frequencies, a novel device configuration is developed, which significantly improves state-of-the-art silicon-based switch performance. The excellent switch performance is leveraged to address major issues in current millimeter-wave systems. A front-end built-in-self-test switch topology is developed to facilitate the characterization of millimeter-wave transceivers without expensive millimeter-wave equipment. A highly integrated Dicke radiometer is also created to enable sensitive measurements of thermal noise.

published_or_final_version / abstract / Electrical and Electronic Engineering / Master / Master of Philosophy

The regulation and modulation of the serotonergic system is clinically significant in humans. Abnormally low levels of serotonin can result in depression and conditions like panic disorder, obsessive-compulsive disorder, social anxiety disorder, sudden infant death syndrome, and eating disorders. The mechanistic role of serotonin (5-HT) on the neural circuits related with these diseases is not definitively known. Drosophila is a simple model system that provides an advantage over vertebrates to modify genetically and for electrophysiological studies on identifiable cells. In this organism the sensory-CNS-motor circuit is modulated by 5-HT, octopamine (OA), and dopamine (DA), which gives one insight that these neuromodulators are playing a role in central neuronal circuits. The role of 5-HT in the behavior and development of Drosophila melanogaster larvae is being studied. p-CPA (para-chlorophenylalanine) blocks the synthesis of 5-HT by inhibiting tryptophan hydroxylase. The development, behavior and physiology in 3rd instar larvae are affected after feeding this drug. MDMA (3,4 methylenedioxyamphetamine), an analog of methamphetamine is a drug of abuse that has been shown to cause depletion of 5-HT from nerve terminals. It causes the 5-HT transporter to work in reverse. Thus, a dumping of 5-HT results. In Drosophila 3rd instar larva development, physiology and behavior are effected when MDMA is fed throughout their development period. Also at the fly neuromuscular junction, (NMJ) MDMA is causing more evoked vesicular release of glutamate from the presynaptic nerve terminal. Also using anti-sense expression of the 5-HT2dro receptor, role of 5-HT and one of its receptors is studied on development, physiology and behavior. Knock down of 5-HT2dro resulted in developmental delay. Physiology and behavior were also abnormal in these animals.

Modern cryptography responds to the need for security that has arisen with the emergence of communication appliances. However, its adapted integration in the wide variety of existing communication systems has opened new design challenges. Amongst them, this thesis addresses two in particular, related to hardware integration of cryptographic algorithms: constrained environments and side-channel security. In the context of constrained environments, we propose to study the interest of the Scalable Encryption Algorithm SEA for constrained hardware applications. We investigate both the FPGA and ASIC contexts and illustrate, using practical implementation results, the interest of this algorithm. Indeed, we demonstrate how hardware implementations can keep its high scalability properties while achieving interesting implementation figures in comparison to conventional algorithms such as the AES. Next, we deal with three complementary aspects related to side-channel resistance. We first propose a new class of dynamic and differential logic families achieving low-power performance with matched leakage of information to state of-the-art countermeasures. We then discuss a power consumption model for these logic styles and apply it to DyCML implementations. It is based on the use of the isomorphism existing between the gate structures of the implemented functions and the binary decision diagrams describing them. Using this model, we are not only able to predict the power consumption, and therefore attack such implementations, but also to efficiently choose the gate structures achieving the best resistance against this model. We finally study a methodology for the security evaluation of cryptographic applications all along their design and test phases. We illustrate the interest of such a methodology at different design steps and with different circuit complexity, using either simulations or power consumption measurements.

This thesis presents a method for parameter extraction of circuit elements from microwave filters. This diagnosis method can be applied to a sufficiently large number of filters and it can also be used in conjunction with a neural network model for filter design, greatly reducing development time. This thesis is an introduction of parameter extraction and circuit modelling through use of neural networks. It also presents an implementation of the proposed method as well as numerical results and validation data. Detailed implementation code is presented in the appendix.

Switched reluctance motor (SRM) has become a competitive selection for many applications of electric machine drive systems recently due to its relative simple construction and its robustness. The advantages of those motors are high reliability, easy maintenance and good performance. The absence of permanent magnets and windings in rotor gives possibility to achieve very high speeds (over 10000 rpm) and turned SRM into perfect solution for operation in hard conditions like presence of vibrations or impacts. Such simple mechanical structure greatly reduces its price. Due to these features, SRM drives are used more and more into aerospace, automotive and home applications. The major drawbacks of the SRM are the complicated algorithm to control it due to the high degree of nonlinearity, also the SRM has always to be electronically commutated and the need of a shaft position sensor to detect the shaft position, the other limitations are strong torque ripple and acoustic noise effects.

Approved for public release; distribution is unlimited / The goal of this thesis is the development of a programmable logic array (PLA) that accepts multiple-valued inputs and produces multiple valued outputs. The PLA is implemented in CMOS and multiple levels are encoded as current. It is programmed by choosing transistor geometries which control the current level at which the PLA reacts to inputs. An example of a 4-valued PLA is shown. As part of this research, a C program was written that produces a PLA layout. / http://archive.org/details/designofmultiple00koyo / Major, Republic of Korea Air Force

Metamaterials are artificially designed composite materials which can exhibit unique and unusual properties such as the negative refractive index, negative phase velocity, etc. The concept of metamaterials becomes prevalent in the electromagnetic society since the first experimental implementation in the early 2000s. Many fascinated potential applications, e.g. super lens, invisibility cloaking, and novel antennas that are electrically small, have been proposed based on metamaterials. However, most of the applications still remain in theory and are not suitable for practical applications mainly due to the intrinsic loss and narrow bandwidth (large dispersion) determined by the fundamental physics of metamaterials .In this dissertation, we incorporate active gain devices into conventional passive metamaterials to overcome loss and even provide gain. Two types of active gain negative refractive index metamaterials are proposed, designed and experimentally demonstrated, including an active composite left-/right-handed transmission line and an active volumetric metamaterial. In addition, we investigate the non-Foster circuits for broadband matching of electrically small antennas. A rigorous way of analyzing the stability of non-Foster circuits by normalized determinant function is proposed. We study the practical factors that may affect the stability of non-Foster circuits, including the device parasitics, DC biasing, layouts and load impedance. A stable floating negative capacitor is designed, fabricated and tested. Moreover, it is important to resolve the sign of refractive index for active gain media which can be quite challenging. We investigate the analytical solution of a gain slab system, and apply the Nyquist criterion to analyze the stability of a causal gain medium. We then emphasize that the result of frequency domain simulation has to be treated with care. Lastly, this dissertation discusses another interesting topic about THz spectroscopy of live cells. THz spectroscopy becomes an emerging technique for studying the dynamics and interactions of cells and biomolecules, but many practical challenges still remain in experimental studies. We present a prototype of simple and inexpensive cell-trapping microfluidic chip for THz spectroscopic study of live cells. Cells are transported, trapped and concentrated into the THz exposure region by applying an AC bias signal while the chip maintains a steady temperature at 37°C by resistive heating. We conduct some preliminary experiments on E. coli and T cell solution and compare the transmission spectra of empty channels, channels filled with aqueous media only, and channels filled with aqueous medium with un-concentrated and concentrated cells.

We summarize and present recent results in the field of infinite matroid theory. We define and prove basic properties of infinite matroids and we discuss known classes of examples of these structures. We focus on the topic of connectivity of infinite matroids and we link some matroid properties to connectivity. The main result of this work is the proof of existence of infinite matroids with arbitrary finite connectivity, but without finite circuits or cocircuits. Powered by TCPDF (www.tcpdf.org)