<p>This thesis addresses itself to what is considered to be one of the most general theoretical problems associated with the art of engineering design. A unified treatment is presented of production yield evaluation, worst-case design and yield optimization. The formulation is suited to nonlinear programming methods of solution.</p> <p>Viewed in its entirety the approach integrates the following concepts: design centering, assignment of component tolerances, post-production tuning, yield estimation for realistic distributions and modeling of response functions. Many of the ideas can also be used separately depending on the type of design evaluation required, the number of degrees of freedom involved and the availability and properties of suitable simulation programs.</p> <p>The thesis presents an analytical approach to yield and yield sensitivity evaluation. Basic to the approach is the discretization of the distributions by use of orthotopic cells to which suitable uniform distributions are applied. Multidimensional polynomials provide approximations to actual functions, which may be expensive to compute. Algorithms for updating and evaluating these polynomials are developed to permit efficient use of gradient optimization methods.</p> <p>Industrially oriented design examples are furnished to justify the theory. A telephone channel (lossy) bandpass filter is considered with relative insertion loss specifications to illustrate the analysis of yield. The cascade connection of nonideal, inhomogeneous sections of rectangular waveguides is considered from the worst-case design point of view. A current switch emitter follower involving transistors, a diode and a transmission line provides a challenging example for yield optimization including parameter correlations.</p> / Doctor of Philosophy (PhD)

<p>This thesis reports on a systematic investigation of the ion implantation damage in Si, Ge, GaP and GaAs at ≤50K. The damage has been measured "in-situ" using the channeling-backscattering technique. Implantation energies have ranged from 10-250 keV with Z₁ in the interval 2 ≤ Z₁≤ 81.</p> <p>The study has been divided into two parts, depending on Z₁. For low Z₁ (Z₁ < or ∼ 30), the damage profiles in Si, GaP and GaAs have been extracted at 50K. Discrepancies from the theoretical profiles are evident and can be accounted for in terms of the previously reported Z₁-oscillations in the electronic stopping powers. The radial distribution of displaced atoms is examined in these three materials by systematically introducing small misalignments (ψ ≤ 0.36 ψ₁) between the analyzing beam direction and crystal axis. This "Off-Axis" effect is examined as a function of Z₁, ion dose, and depth. Significant atom relaxations are concluded to extend perpendicular to the channel row by up to ~ 40% of the channel radius. While atom relaxations do not contribute to the measured damage at low ion doses, they can account for up to 50-70% of the measured damage at high ion doses. A quantitative model of the damage-done behaviour has been developed, in which the atom relaxation component is incorporated as being directly proportional to the measured damage.</p> <p>The number of displaced atoms/ion is found to be greater than the prediction derived from collision theory by up to an order of magnitude for high-Z₁ bombardment. Therefore, the second section of the thesis contains a detailed study of the effect for 7 ≤ Z₁ ≤ 81 in Si and Ge at 35K. The deviation is not an artifact of the channeling-bakscattering technique. It is concluded that an "energy-spike" may be initiated by the high-Z₁ bombardments; the energy-spike induces a local amorphous zone in the semiconductor, thereby accounting for the increased damage. A semi-empirical model of the data is developed, which divides the damage into collisional and energy-spike components. Extensive use is made of molecular ion bombardments, since they provide a simple method of varying the individual ion-induced collision cascade energy density; this allows for a test of the energy-spike concepts. It is concluded that spikes will influence the damage up to energies corresponding to a lower energy density limit of 0.1 eV/atom in Si and 0.01 eV/atom in Ge. The lower energy limit for spike effects is evidently «10 keV. In Si it appears that the amorphization process is best described by a thermal-spike mechanism, whereas in Ge, it is inferred that the athermal collapse of the unstable lattice is more probable. To support the arguments and concepts of the energy-spike, a Monte Carlo computer code has been written to simulate the collision cascade and provide insight into the parameters of the individual ion-induced cascades.</p> / Doctor of Philosophy (PhD)

<p>The problem of finding the characterizing parameters of an unknown linear discrete-time system "on-line" from the measurements of the input and output data is considered in detail. Two new algorithms for system identification have been proposed for the estimation of parameters of time-invariant single-input single-output systems. The first algorithm, called the Generalized Pseudoinverse, is the recursive version of the generalized least squares algorithm. The second algorithm, combining pseudoinverse and stochastic approx. algorithm, is an iterative scheme and found to be computationally more efficient than the first algorithm. The two algorithms have been used in a number of simulation problems to test the reliability and efficiency of the methods. A critical comparison of the new method with the existing algorithms has shown the new algorithm to be reliable in most of the problems considered. Also a new recursive pseudoinverse algorithm has been developed for identification of a multi-variable transfer function model.</p> / Doctor of Philosophy (PhD)

<p>This thesis describes dynamic stability modelling and analysis of balanced multimachine power systems where in addition to detailed generator, governor-turbine and excitation system simulation, the dynamics of the mechanical shaft system and electrical network are included. Eigenvalue and complementary eigenvalue sensitivity methods are used in the investigation of stability or lack thereof.</p> <p>A unified structure is presented in the formulation of a state space model for the complete system in terms of subsystem models. A wide variety of subsystem types and complexities can be accommodated including all present industry standard models. In addition, general models describing the dynamics of the mechanical shaft system and electrical network can be accommodated. The formulation approach further preserves the identity of the various subsystems, thus allowing ease of system modification or update.</p> <p>The overall modelling concepts are applied to a number of practical situations to demonstrate their applications. In particular, situations involving insufficient synchronizing torque, insufficient damping torque, interaction between turbine-generator and control equipment, interaction between turbine-generator and network dynamics and interaction between turbine-generator and asynchronous motor loads are examined.</p> <p>The concepts developed are also applied in the analysis of the interaction between the shaft dynamics of closely coupled identical generators. A method is presented for determining the shaft natural frequencies for an arbitrary number of identical units, in terms of two equivalents. The extent to which the shaft modes may be stimulated in feasible on-line experiments is investigated.</p> <p>Results and comparisons for alternative dynamic models are presented. It is shown that a single high order 'Benchmark' model which embraces all important dynamic effects, can be systematically reduced to models of reduced complexity - the basis for the reduction being the approximations normally applied in practice.</p> <p>The main contributions are:</p> <p>1. A systematic state-space equation structure which can include shaft and/or network dynamics has been developed. The formulation structure, which includes facility for eigenvalue sensitivity evaluation, can be applied in general problems involving electrical machine and system dynamic stability.</p> <p>2. A technique has been developed for deriving the multiplicity of normally considered low order power system models, from a single high order system model (Benchmark model). This permits the evaluation of a wide range of alternative models and also, the identification of sources of instability.</p> <p>3. The fundamentals of interacting shaft dynamics in closely coupled turbine-generators, have been examined. It has been shown that only two equivalents are necessary for the prediction of natural frequencies and mode shapes in a general N unit situation.</p> <p>4. Insights have been presented into the interpretation of eigenvalues as they reflect the various aspects of power system stability.</p> / Doctor of Philosophy (PhD)

<p>This thesis investigates some aspects of the theory of convolution and Fourier transforms on q-adic and multiplicative abelian groups, as well as their applications for solving various signal processing and system problems.</p> <p>A brief introduction to the importance and basic theory of convolution and Fourier transforms on locally compact abelian groups is given, followed by four major section:</p> <p>1. Subsequent to a comprehensive introduction of generalized Walsh functions, Walsh-Fourier analysis and harmonic differentiation on q-adic groups, a presentation is made of the theory of q-adic translation invariant linear systems from the point of view of both input-output and state-space description. This is followed by an analysis of the structure of Walsh transforms, so that is becomes possible to point to (and critically review) those engineering problems for which Walsh functions are suited to bring an optimal solution, as well as those problems for which they may bring suboptimal but efficient solutions.</p> <p>2. Signal processing in spaces of finite field-valued functions on finite abelian groups is investigated, emphasis being placed on the study of those linear operators whose eigenfunctions are the group characters. A harmonic differential calculus in finite fields is introduced.</p> <p>3. A study of the concept of frequency is undertaken with the objective of generalizing it to function spaces other than that of complex-valued functions on the real line. A generalized concept of frequency is proposed. An analysis of the relationship between the concepts of sequency and frequency proves unfounded the claims that the former is a generalization of the latter.</p> <p>4. The problem of analyzing signals formed of linear combinations of components having the same shape and location but different amplitude and widths parameters is investigated with the objective of providing a technique for its numerical solution. It is shown that this problem can be modelled as a convolution transform on a multiplicative abelian group. A brief introduction to the theory of Fourier transforms on multiplicative groups is presented, followed by the description of an efficient algorithm for performing the analysis. The problems pertaining to the practical implementation of this algorithm are discussed both in general terms and with reference to the analysis of multi-component exponential decays.</p> / Doctor of Philosophy (PhD)

<p>The problem of synchronizing earth stations to the switching sequence of the SDMA/SS-TDMA communications satellite system described by COMSAT Laboratories is examined in detail. System synchronization is discussed and two techniques for locking the time bases of all earth stations to the sync window of the satellite are described.</p> <p>It is established that synchronization for an individual earth station can be separated into three distinct modes of operation called the coarse search mode, the fine search mode and the tracking mode. Three different methods for achieving coarse search synchronization are described.</p> <p>In the fine search mode, the synchronization loop is analysed assuming that the pertinent earth station transmits sync bursts which are modulated by the sync window. Results of this analysis show that a receiver configuration employing an integrator provides a set of error detection characteristics which relate an error voltage measured in the earth station to the timing error measured at the satellite. It is shown that the average timing error is reduced to zero with successive transmissions of sync bursts around the loop.</p> <p>The timing error due to constant velocity satellite motion can be eliminated by employing a tracking network. The tracking network uses an integrator to adjust the earth station time base clock.</p> <p>A laboratory model, which closely approximates the actual physical model used in the theory, has been designed and constructed. The coarse search, fine search and tracking modes of operation are all included in this experimental study, and a provision which simulates satellite motion is described. Details of experiments, which confirm the theoretical predictions, are provided.</p> <p>The major contributions of the thesis are summarized below.</p> <p>(1) A technique for providing synchronization for all earth stations operating in the system, employing three control stations, is described.</p> <p>(2) A new technique for achieving coarse search synchronization using coded search signals has been developed.</p> <p>(3) Three new implementations of the sync burst have been described.</p> <p>(4) The behaviour of the synchronization loop has been analysed in detail and a concept using error detection characteristics has been explored.</p> <p>(5) A tracking network can be employed to eliminate timing errors caused by constant velocity satellite motion.</p> <p>(6) A laboratory model has been designed and constructed.</p> <p>(7) A special coherent receiver for demodulating bursts of PSK signals has been developed.</p> <p>(8) Results of experiments using the laboratory model are demonstrated to agree closely with theoretical predictions.</p> / Doctor of Philosophy (PhD)

<p>Skeletal muscles produce detectable electrical currents and voltages when they contract from any cause. The electrical potentials or electromyographic (EMG) signal is recorded from the muscle using suitable electrodes. The research presented in this thesis is concerned with the analysis and processing of electromyographic signals with a view to their use as a source of control for environmental control or other rehabilitation devices. An application of myo-electric control of a simple communication device for a cerebral palsied patient is presented. A model of the myo-electric source which can be used to stimulate EMG signals in real-time is proposed. The model algorithm has been tested for two different electrode systems and the results compared with real signals recorded using these electrode systems. A number of statistical parameters of the surface recorded EMG signal have been examined to determine which parameter is most suitable for myo-electric control. Finally, a pattern recognition algorithm is proposed which attempts to extract the motor unit recruitment and discharge frequency information present in the surface recorded EMG signal. The statistical parameters and the algorithm have been tested for six normal subjects, under isometric conditions.</p> / Doctor of Philosophy (PhD)

<p>Radiation returning from a target at low elevation to a radar can have a wide variety of characteristics. In general, we see return not only from the target itself, but from its image as well; this is the essence of multipath. The nature of this multipath depends on a number of factors, the most important of which is the roughness of the reflecting surface. The study of this return is essential in order that we may overcome the problems associated with target detection in multipath environments.</p> <p>In this thesis, methods of simulating diffuse multipath are discussed, and a hybrid system has been constructed which illustrates the effect of a phased array receiver on the observed radar return.</p> / Master of Engineering (ME)

<p>Phase-locked loops occasionally exhibit prolonged phase transients and are therefore not suitable for carrier recovery applications in time division multiple access (TDMA) systems. Instead, designers have, in several cases, used a single-tuned high Q filter in combination with an automatic frequency control. A non-linear differential equation model for such a system, called a "frequency locked loop" (FLL) is solved by computer to obtain the transient responses. The solutions obtained indicate that the FLL has fast and reliable carrier phase acquisition time compared to a phase-locked loop (PLL). Also, since the non-linear responses agree well with linear model responses, an equation based on the linear model is developed to determine worst-case acquisition time. It is shown that a limiter preceeding the single-tuned tank does not directly affect acquisition performance and will improve noise performance of the FLL. With a limiter, the FLL block diagram is equivalent to an FM feedback demodulator (FMFB) on which there is a large amount of existing literature. Using results from the literature, it is demonstrated how the FMFB will perform in the presence of Gaussian noise. Finally, a design procedure is recommended which takes into account the tradeoff between noise performance and acquisition/tracking ability and attempts to minimize the acquisition time for a given level of Gaussian noise.</p> / Master of Engineering (ME)

<p>The proposed methods of search and rescue (SAR) of mobile platforms use low altitude polar orbiting satellites to detect signals emanating from emergency locator transmitter (ELT) systems on board the distress platform. The uplink transmission receives a doppler shift due to the radial velocity of the satellite. Extracting the doppler from the signal is necessary for calculating the position of the ELT system. These ELT units were originally designed for reception by ordinary hand held receivers and detection by the human ear. For this reason the transmitters employ a distinct type of modulation often referred to as a chirp. Detection and estimation of the doppler by signal processing is complicated by this swept modulation. This dissertation compares two methods of spectral estimation, namely, Fourier analysis (in the form of an FFT algorithm) and the maximum entropy method (MEM) for application to ELT signals. The signals to be processed are divided into two categories, single and multiple signals. Multiple signal processing is necessary when two or more ELT systems are transmitting simultaneously and the time separation between transmissions is small enough to cause overlapping of signals in time. Results indicate that the enhanced detection capability by using the MEM offers a significant improvement in processing signals from an ELT.</p> / Master of Engineering (ME)