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The study of arterial wave propagation is essential to understand the physiopathology of the cardiovascular system, as waves carry clinically relevant information. Impedance analysis was used for such type of studies, where results were presented in the frequency domain, but it was difficult to relate specific events to time points within the cardiac cycle. Therefore, a mathematical tool called wave intensity analysis was developed, initially using measurements of pressure and velocity (PU approach). However, the need to acquire such measurements in a non-invasive, direct and simultaneous fashion led to the development of the DU approach, a type of wave intensity analysis carried out using vessel diameter and flow velocity waveforms, thus giving up the pressure measurement. It is the only available technique, at present, able to extract wave intensity information without relying on distally recorded pressure measurements and on non-simultaneous recordings. Due to its non-invasive nature for collecting the required measurements, this technique has a potential use in clinical and research settings to investigate physiological changes under rapid perturbations, such as the ones introduced by exercise. In this thesis, the DU approach is performed by only using an ultrasound device and to extract information about cardio-arterial interaction in the human common carotid artery. In the first experimental chapter of this thesis, a reproducibility study of common carotid DU-derived wave intensity parameters was conducted on a healthy young cohort, both at rest and during exercise (semi-recumbent cycling). Carotid diameter and blood flow velocity features, as well as wave intensity parameters such as forward compression, backward compression and forward expansion wave peaks and energies, were overall fairly reproducible. In particular, diameter variables exhibited higher reproducibility and lower dispersion than corresponding velocity variables, whereas wave intensity energy variables exhibited higher reproducibility and lower dispersion than corresponding peaks. Local wave speed, calculated via lnDU-loop, a technique based only on local measurements of diameter and velocity and often associated with the DU approach, was also reproducible. It is possible to conclude that the DU-derived wave intensity analysis is reliable both at rest and during exercise. In a subsequent study, DU-derived wave intensity analysis was performed on a young trained cohort to investigate the contribution of cardiac and peripheral vascular alterations to common carotid wave intensity parameters, under rapid physiological perturbations, such as semi-recumbent cycling at incremental workrates, and subsequent recovery. Judging by the increase in local wave speed, the common carotid artery stiffened substantially as workrate increased whilst peak and energy of the forward and backward compression waves also increased, due to enhanced ventricular contractility, which was associated with larger reflections from the cerebral microcirculation and other vascular beds in the head. However, the reflection indices remained unchanged during exercise, highlighting that the increased magnitude of reflections is mainly due to the enhanced contractility, rather than changes in vascular resistance, at least at the carotid artery in young healthy individuals. The forward expansion wave increased during exercise, as the left ventricle actively decelerated blood flow in late systole, potentially improving filling time during diastole. In the early recovery, the magnitude of all waves returned to baseline value. Finally, the X wave, attributed to the reflection of the backward compression wave, had a tendency to increase during exercise and to return to baseline value in early recovery. A further development of wave intensity analysis came with the reservoir-wave approach, able to separate, from the pressure and velocity waveforms, the component solely due to the reservoir volume, for the correct evaluation of backward- and forward-travelling waves. A number of issues, however, still remains, involving specifically the lack of consensus over the fitting technique and over the value of the asymptotic pressure value (P ∞),used for the determination of the reservoir waveform. Therefore, to give a contribution to the debate involving the more correct model for the pressure and velocity reservoir-wave approach, a study aimed to investigate various common carotid hemodynamic and wave intensity parameters, using different fitting techniques and values of P ∞ currently available in literature, was performed and described in the last chapter of this thesis. The study demonstrated that different fitting method and values of P ∞ could bring significant variations in values and trends of hemodynamic and wave intensity parameters. However, despite the changes in the shape of the reservoir pressure waveform, its peak and integral with respect to time tended to remain constant. This is an important feature, because both reservoir peak pressure and its integral have been used in clinical settings for the calculation of diagnostic indicators. The reservoir and excess velocity peaks, instead, changed more significantly. This outcome, together with the concomitant substantial change in excess pressure peak and integral, may greatly affect wave intensity parameters. Wave intensity parameters were, in fact, significantly more sensitive to fitting techniques and values of P ∞ than pressure parameters. Finally, the wave speed did not substantially change, leading to the conclusion that the calculation of local vessel distensibility and/or compliance, when calculated from the excess components of the waveforms, seemed insensitive to fitting techniques and values of P ∞.

A voltage controlled oscillator (VCO), that generates a periodic signal whose frequency is tuned by a voltage, is a key building block in any integrated circuit systems. A sine wave oscillator can be used for a built-in self testing where high linearity is required. A bandpass filter (BPF) based oscillator is a preferred solution, and high quality factor (Q-factor) is needed to improve the linearity. However, a stringent linearity specification may require very high Q-factor, not practical to implement. To address this problem, a frequency harmonic shaping technique is proposed. It utilizes a finite impulse response filter improving the linearity by rejecting certain harmonics. A prototype SC BPF oscillator with an oscillating frequency of 10 MHz is designed and measurement results show that linearity is improved by 20 dB over a conventional oscillator. In radio frequency area, preferred oscillator structures are an LC oscillator and a ring oscillator. An LC oscillator exhibits good phase noise but an expensive cost of an inductor is disadvantageous. A ring oscillator can be built in standard CMOS process, but suffers due to a poor phase noise and is sensitive to supply noise. A RC BPF oscillator is proposed to compromise the above difficulties. A RC BPF oscillator at 2.5 GHz is designed and measured performance is better than ring oscillators when compared using a figure of merit. In particular, the frequency tuning range of the proposed oscillator is superior to the ring oscillator. VCO is normally incorporated with a frequency synthesizer (FS) for an accurate frequency control. In an integer-N FS, reference spur is one of the design concerns in communication systems since it degrades a signal to noise ratio. Reference spurs can be rejected more by either the lower loop bandwidth or the higher loop filter. But the former increases a settling time and the latter decreases phase margin. An adaptive lowpass filtering technique is proposed. The loop filter order is adaptively increased after the loop is locked. A 5.8 GHz integer-N FS is designed and measurement results show that reference spur rejection is improved by 20 dB over a conventional FS without degrading the settling time. A new pulse interleaving technique is proposed and several design modifications are suggested as a future work.

The goal of this work was to design and evaluate a hydraulic Hardware-in-the-Loop (HIL) simulation system based around electric and hydraulic motors. The idea behind HIL simulation is to install real hardware within a physically emulated environment, so that genuine performance can be assessed without the expense of final assembly testing. In this case, coupled electric and hydraulic motors were used to create the physical environment emulation by imparting flows and pressures on test hardware. Typically, servo-valves are used for this type of hydraulic emulation, and one of the main purposes of this work was to compare the effectiveness of using motors instead of the somewhat standard servo-valve. Towards this end, a case study involving a Sauer Danfoss proportional valve and emulation of a John Deere backhoe cylinder was undertaken. The design of speed and pressure controllers used in this emulation is presented, and results are compared to data from a real John Deere backhoe and proportional valve. While motors have a substantially lower bandwidth than servo-valves due to their inertia, they have the ability to control pressure at zero and near-zero flows, which is fundamentally impossible for valves. The limitations and unique capabilities of motors are discussed with respect to characteristics of real hydraulic systems.

Localized detection of very small regularly placed magnetic systems, such as an array of tiny magnetic islands, has been of great interest to scientists for years because of their applications to data storage media. One such detection device, the micro-SQUID (microscopic superconducting quantum interference device), can be used to detect very small changes in magnetic flux. Most low Tc micro-SQUIDs (LTS) are made from aluminum or niobium. While an aluminum SQUID is relatively easy to fabricate, one often needs a low temperature system than can be cooled to 1K to see the critical current phenomenon. As a contrast, niobium which has a higher critical temperature, and a more complicated fabrication procedure due to its need to be fabricated in a extremely clean environment to achieve a reproducible value for its critical temperature, which is about 9.25 K. Such a SQUID will only need to be immersed in a helium bath for the superconducting transition to occur. Alternatives such as tin, indium and lead, which are soft superconductors, do not wet a silicon/silicon dioxide surface as easily as niobium and aluminum. However, the benefits of a successful implementation of these soft superconductors as SQUIDs could greatly outweigh their drawbacks in terms of reducing the amount of time necessary for fabrication and measurement as well as the low temperature system requirements. In this dissertation, the successful development of functional square and rectangular tin sub-microscopic SQUIDs for use as magnetometers is reported. The application of a germanium pre-nucleation layer, as a means of creating a electrically continuous path, offers an alternative to micro-SQUIDs fabricated under more in- volved methods as used in niobium SQUIDs. An image of the device surface showed that the roughness consisted of defects such as holes which gives rise to critical current fluctuations and vortex pinning due to magnetic hysteresis. However, the oscillations observed from several of these devices, were found to be smooth with sharp edges but with a diminished period of oscillation. Several devices were tested and their fabrication, measurement and characterization methods are described. Another important study incorporated in our analysis of these tin germanium SQUID included its reduction from the micrometer regime to its lowest functional ge- ometry. Moreover, to avoid the operational breakdown of a SQUID due to magnetic hysteresis and a diminution in sensitivity, the condition 2IcL / 0 had to be satisfied, where Ic is the critical current and L is the inductance of the device and 0 is one flux quantum 0 = h 2e = 20:86 gauss mm2. Experimental measurements showed that all of these devices had magnetic hysteresis and operated outside of this constraint. In addition, several devices exhibited extremely high critical currents when the temper- ature was lowered a few milli-Kelvin past the transition temperature. Furthermore, unstable regions were present in the minima of the modulations indicating that ad- ditional quantum effects were incorporated into the device as a result of screening currents and magnetic hysteresis behavior.

Dislocation loops in pressureless-sintered undoped BaTiO3 ceramics have been analysed via transmission electron microscopy (TEM). The Burgers vector b = [100] of the loops was initially determined by the contrast analysis of the g•b = 0 criteria combining with the inside-outside contrast method by which the sense of the Burgers vector was concluded. The vacancy nature were determined by adopting the inside-outside contrast analysis using the criteria of (g•b)sg being positive or negative when the loops were imaged under kinematical diffraction conditions of sg ¡Ú 0. High-resolution imaging of such loops has enabled us to confirm its vacancy nature, consistent with the contrast analysis. Further, the loops¡¦ Burgers vector was determined to be b = 1/2[100] and the loops were therefore negative partial dislocation loops lying in {200} where part of the TiO2-deficiency existed locally in the grains of sintered BaTiO3 ceramics was accommodated by the presence of vacancy loops. It is suggested that the extrinsic defects of both titanium and oxygen vacancies ( and ,) generated by the non-stoichiometry which gave clustered during sintering in air are responsible for the formation of the dislocation loops.

The focus of the present thesis is the circuit-level implementation of an excess loop delay compensation scheme which optimizes excess loop delay in Analog-to-Digital Converter(ADC) by using a programmable delay block and synchronizes the signal passing through Dynamic Element Matching block, used to mitigate mismatch effects of multi-bit Digital-to-Analog Converter(DAC). The proposed delay block has tuning range of T/10 to T/2 seconds, with a step size of T/30 seconds, where T is the time period (1.25 nanoseconds) of sampling signal (800 MHz) in high IF (200 MHz) Bandpass [sigma delta] ADC. The implementation details of the element rotation scheme used to calibrate the multi-bit DAC static error mismatch are also presented. Also presented is the design of high frequency highly linear Operational Transconductance Amplifier(OTA) targeted for continuous-time filters in a high resolution High Intermediate Frequency (200 MHz) Bandpass [sigma delta] ADC for Software Radio applications. Proposed OTA uses super source follower input stage to enhance its voltage-to-current conversion linearity. The design has been simulated using TSMC 0.18 μm CMOS process. The OTA has small signal transconductance of 0.9 mA/V, IM3 below -79 dB (for 0.3 Vpp input), Signal-to-Noise Ratio of 82 dB and power consumption of 6.8 mW, when tested in unity gain configuration.

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No description available.

Magnetic hysteresis modelling plays a crucial role in determining the electromagnetic properties of soft magnetic materials. A new approach to modelling is the use of recurrent neural networks, capable of time dependent, dynamic, sequential mapping. This research investigates the implementation and accuracy of this approach among other available hysteresis models. / Thesis (MEng(ElectronicsEngineering))--University of South Australia, 2004.