No description available.

Wireless systems, ranging from radio to optical frequencies, typically comprise two domains: the signal path and the local oscillator (LO) path. While signal processing is conventionally performed in the signal path, more recently, techniques that exploit LO-based signal processing are becoming increasingly popular. LO-based analog signal processing can be utilized for solving fundamental problems and for improving the performance of systems in a wide variety of applications that span radio to optical frequencies. In this dissertation, I explore LO-based signal processing to enable new functionalities and enhance performance in electrical, optical, and electro-optical circuits and systems. In the electro-optical domain, I use LO-based signal processing to improve the performance of a long-range Frequency-Modulated Continuous-Wave (FMCW) Light Detection and Ranging (LiDAR) system. As laser nonlinearity degrades the performance of ranging and imaging systems, it is essential to address this problem. In this dissertation, to linearize a laser, an integrated continuous-time Electro-Optical Phase-Locked Loop (EOPLL) is presented with a loop bandwidth equal to its reference frequency. Despite the high bandwidth, the proposed system is spurless, which is enabled by using Single-Sideband (SSB) and Harmonic-Reject mixing (HRM) techniques. These techniques are explored in Phase-Locked Loop (PLL) design for the first time. These features result in less area consumption and loss associated with the optical part of the system and increase the precision and accuracy of our long-range FMCW LIDAR significantly. In the electrical domain, I use LO engineering to address some of the challenges that exist in three different electrical systems including mm-wave Multi-Input Multi-Output (MIMO) systems, ultra-low power RF systems, and wideband mm-wave systems. In the first project, to alleviate the challenge of supporting a high data rate Input/Output (I/O) interface in a large-scale tiled mm-wave MIMO array, a single-wire interface (SWI) is used in this dissertation, and a 60GHz 4-element scalable MIMO transmitter (TX) prototype is designed. In our work, we use frequency-domain multiplexing (FDM) to simultaneously support the signals of four MIMO channels. Then, in our proposed FDM, HRM is utilized to generate the different frequencies at which the various IF signals are multiplexed. This enables us to multiplex and de-multiplex the four modulated signals simultaneously to/from the single-wire using multiple phases of only one LO. The technique proposed in this research significantly reduces the number of lines needed for LO and signal routing in a massive MIMO system. The second electrical project in this dissertation targets ultra-low power receivers at RF frequency. Wake-up receivers (WURX) are integral to reducing the power consumed by the main or primary RX in ultra-low power systems. Thus, the ability to share one antenna for both RXs is essential and results in a compact hybrid system. Furthermore, linearity and sensitivity are two fundamental criteria in these RXs. In order to improve the linearity of these systems, mixer-first RX architecture can be used for both RXs. However, mixer-first architecture has some drawbacks, like low gain and high noise figure (NF), which degrade the sensitivity of the system. Here, in our research, we implement a hybrid primary RX and WURX in which, first, a Quadrature Hybrid Coupler (QHC) is used to share one antenna between the two RXs and to achieve wideband input matching. Secondly, to address the problem of sensitivity in the mixer-first structure, we exploit a LO-assisted noise-canceling technique combined with a bottom-plate capacitor mixer-first receiver. This structure exploits implicit capacitive stacking which enables us to achieve passive LO-defined voltage gain, high linearity, and a low NF. In the last electrical project in this dissertation, I present a novel frequency-interleaved (FI) channel aggregation architecture for wideband mm-wave systems that relaxes the requirements of their Analog-to-Digital/Digital-to-Analog Converters (ADC/DAC) and consequently reduces the total cost and power consumption. In our proposed architecture, the input bandwidth is channelized into four sub-channels, which are individually up/downconverted from/to baseband, where they can be digitized with multiple lower rate subconverters. We use the idea of HRM in the channelizer to simultaneously down(up)convert four sub-channels with only one LO. Four chips, including two mm-wave RX and TX chips and two baseband RX and TX chips, are designed and tested to show the functionality of the entire system as a transceiver. Finally, I conclude this dissertation with an optical project which is a Silicon Photonic (SiP) simultaneous Mode and Wavelength Division (De)Multiplexer (MWD(De)MUX) for optical frequencies at C-band. I use an advanced 3D simulation tool, RSOFT software, to design and test this novel compact SiP structure. Our circuit uses a cascade of Mode Division Multiplexer (MDM) and Wavelength Division Multiplexer (WDM) stages for (de)multiplexing. A novel phase shifter introduced and used in this work is designed using two close waveguides on a CMOS compatible SiP platform, which results in reduced loss and size compared to conventional techniques.

In spite of electrogustometry having been in existence since the 1930s, there is no state of the art instrument to assess the electrogustometric threshold. A state of the art electrogustometer has been designed and constructed and tested for reliability and repeatability. This is based on embedded digital technology and is a semi-automatic, battery-powered portable instrument. Physical factors such as electrode area and stimulus duration affect the taste threshold but there are no recommended standards for these factors. Studies have been conducted to ascertain a recommended standard – a circular stainless steel electrode area of 28.5 mm2 and a stimulus duration of 2 seconds. While performing the test-retest assessment of the Sussex Electrogustometer, the new instrument, an anomaly was observed. Upon further investigation it was concluded that it was caused by alcohol consumed by a subject prior to the retest. Elaborate experiments were designed with the help of a neurologist and psychologist to understand the immediate effect of alcohol on taste for non-alcoholics. The results indicated an immediate improvement of taste for lower concentrations of alcohol and a delayed improvement for higher concentration. The studies were extended to understand the immediate effect of anaesthetics and smoking on taste which showed that taste deteriorated as expected. The new machine was used successfully in the clinical environment by local doctors and a report on their findings has also been included within this thesis.

Recently, the use of permanent magnets as magnetic field sources in biomedical applications has become widespread. However, usage of permanent magnets in magnetic resonance imaging (MRI) is limited due to their inhomogeneous magnetic field distributions. In this thesis, shape and geometry optimization of a magnet is performed. Moreover, placement of more than one magnet is optimized to obtain desired magnetic field distribution in specific region of space. However, obtained magnetic field distribution can not be used in the conventional MRI image reconstruction techniques. Consequently, an image reconstruction technique for MRI in inhomogeneous magnetic fields is developed. Apart from these, since any reconstruction technique requires signal data, an MRI simulator in inhomogeneous magnetic fields is constructed as a part of this thesis. Obtained results show that the theory developed in this thesis is valid. Consequently, new MRI devices that have permanent magnets as magnetic field sources can be constructed in the future.

In this thesis / analysis, design and implementation of a DC-DC converter with active clamp forward topology is presented. The main objective of this thesis is generating a rectified sinusoidal voltage at the output of the converter. This is accomplished by changing the reference signal of the converter. The converter output is applied to an inverter circuit in order to obtain sinusoidal waveform. The zero crossing points of the converter is detected and the inverter drive signals are generated in order to obtain sinusoidal waveform from the output of the converter. Next, the operation of the DC-DC converter and sinusoidal output inverter coupled performance is investigated with resistive and inductive loads to find out how the proposed topology performs. The design is implemented with an experimental set-up and steady state and dynamic performance of the designed power supply is tested. Finally an evaluation of how better performance can be obtained from this kind of arrangement to obtain a sinusoidal output inverted is thoroughly discussed

In this study, a model is developed to represent doubly-salient magnetic circuits and to fit finite element analysis for the aim of obtaining a set of normalized normal force, tangential force, and permeance variation data. To obtain the desired data FE field solution method is used. The reliability of finite element results have been verified by three steps / first, comparing the numerical results with analytically calculated permeance, second, by solving two switch reluctance motors and comparing the results with the measurements of static torque and flux linkage. The third step is by using the normalized data obtained by solving the model with the aid of an available software that is capable to predict the behavior of switched reluctance motors. Once the reliability of the data is assured, the desired data set is produced and presented in tables.

In this thesis, a wideband dual polarized microstrip antenna is designed, manufactured and measured. Slot coupled patch antenna structure is considered in order to achieve the wideband characteristic. Although rectangular shaped slot coupled patch antennas are widely used in most of the applications, their utilization in dual polarized antenna structures is not feasible due to space limitations regarding the positioning of two separate coupling slots for each polarization. For a rectangular slot, the parameter that affects the amount of coupling is the slot length. On the other hand when a H-shaped slot is considered, both the length of the center arm and the length of the side legs determine the coupling efficiency. This flexibility about the optimization parameters of the H-shaped slot makes it possible to position the two coupling slots within the boundaries of the patch antenna. Therefore, H-shaped slot coupled patch antennas are studied in this thesis. In order to investigate the effects of slot and antenna dimensions on the radiation characteristics of the antenna, a parametric study is performed by analyzing the antenna structure with a planar electromagnetic field simulation software (Ansoft Designer). By the help of the experience gained through this parametric study, a dual polarized patch antenna that can be used at the base station of a cellular system (DCS: 1710&ndash / 1880 MHz) is designed. Before manufacturing the antenna, dimensions of the antenna are re-tuned by considering a finite sized ground plane in the simulations. Finally, the antenna is manufactured and measured. An acceptable agreement is obtained between the measurement and the simulation results.

This dissertation is focused on the design, fabrication, and characterization of novel metamaterials in microwave and terahertz regions with the following outcomes: A planar &micro / -negative metamaterial structure, called double-sided SRR (DSRR), is proposed in the first part of this study. DSRR combines the features of a conventional split ring resonator (SRR) and a broadside-coupled SRR (BC-SRR) to obtain much better miniaturization at microwave frequencies for a given physical cell size. In addition to DSRR, double-sided multiple SRR (DMSRR), double-sided spiral resonator (DSR), and double-sided U-spiral resonator (DUSR) have been shown to provide smaller electrical sizes than their single-sided versions under magnetic excitation. In the second part of this dissertation, a novel multi-band tunable metamaterial topology, called micro-split SRR (MSSRR), is proposed. In addition to that, a novel magnetic resonator structure named single loop resonator (SLR) is suggested to provide two separate magnetic resonance frequencies in addition to an electric resonance in microwave region. In the third part, two different frequency tunable metamaterial topologies called BC-SRR and gap-to-gap SRR are designed, fabricated and characterized at terahertz frequencies with electrical excitation for the first time. In those designs, frequency tuning based on variations in near field coupling is obtained by in-plane horizontal or vertical displacements of the two SRR layers. The values of frequency shifts obtained for these tunable metamaterial structures are reported to be the highest values obtained in literature so far. Finally, in the last part of this dissertation, novel double-sided metamaterial based sensor topologies are suggested and their feasibility studies are presented.

Accelerometer sensors fabricated with micromachining technologies started to take place of yesterday&rsquo / s bulky sensors in many application areas. The application areas include a wide range from consumer electronics and health systems to military and aerospace applications. Therefore, the performance requirements extend form 1 &mu / g&rsquo / s to 100 thousand g&rsquo / s. However, high performance strategic grade MEMS accelerometer sensors still do not exist in the literature. Smart designs utilizing the MEMS technology is necessary in order to acquire high performance specifications. This thesis reports a high performance accelerometer with a new process by making the use of bulk micromachining technology. The new process includes the utilization of Silicon-on-Insulator (SOI) wafer and its buried oxide (BOX) layer. The BOX layer helps to realize interdigitated finger structures, which commonly find place in surface micromachined CMOS-MEMS capacitive accelerometers. The multi-metal layered CMOS-MEMS devices inherently incorporate interdigitated finger structures. Interdigitated finger structures are highly sensitive to acceleration in comparison with comb-finger structures, which generally find usage in bulk-micromachined devices, due to absence of anti-gap. The designed sensors based on this fabrication process is sought to form a fully-differential signal interfaced sensor with incorporation of the advantages of high sensitive interdigitated finger electrodes and high aspect ratio SOI wafer&rsquo / s bulk single crystal silicon device. Under the light of the envisaged process, sensor designs were made, and verified using a computing environment, MATLAB, and a finite element analysis simulator, CoventorWARE. The verified two designs were fabricated, and all the tests, except the centrifuge test, were made at METU-MEMS Research Center. Among the fabricated sensors, the one designed for the high performance achieves a capacitance sensitivity of 178 fF with a rest capacitance of 8.1 pF by employing interdigitated finger electrodes, while its comb-finger implementation can only achieve a capacitance sensitivity of 75 fF with a rest capacitance of 10 pF.

The management of parallel and series resonance conditions is important for ensuring that harmonic levels are managed on utility networks, and that shunt compensators are able to operate without constraints for various network conditions (states). For these and similar problems, harmonic impedance assessment of the ac network is required for the design of ac filter or shunt capacitor bank installations. This is particularly important for large installations connected to HV or EHV systems, because resonances at these voltage levels tend to be highly un-damped resulting in potentially damaging voltage and current amplification. The objective of this dissertation was to develop and demonstrate a design methodology which makes use of network impedance assessment methods to provide robust harmonic integration of large shunt compensators into a transmission and HVDC systems. The design methodology has two aspects. The first part considers network modeling, evaluation of different models and simulation of harmonic impedance. In the second part, methods of analyzing and assessing the simulated harmonic impedance are developed. A detailed step-by-step approach was taken in the development of the design methodology. The methodology was documented as a guideline and accompanied by the development of an Excel tool that can be used to assess the simulated harmonic impedance. The Excel tool permits a systematic assessment of the simulated network impedance where shunt compensators are integrated into transmission systems. The tool also ensures that the design of transmission and HVDC ac shunt compensation is optimally robust in terms of harmonic resonances. The theoretical and computational review has been tested and demonstrated on the existing Eskom Transmission system through several case studies. The results have shown the merits of the design methodology. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2013.