No description available.

No description available.

No description available.

No description available.

1-3 piezocomposites comprising of stiff piezoelectric ceramic rods embedded in a soft polymer matrix have considerable potential as the active component in ultrasonic systems for applications in such diverse fields as bio-medicine, SONAR and nondestructive testing. This is because of the ability to tailor the properties via adjustment of the ceramic pillar shape, size, type and distribution and by selection of the passive phase properties. This complex microstructure and its significant influence on resultant device performance has led to a requirement for sophisticated analytical tools to facilitate cost-effective optimisation at the design stage. This Thesis describes the use of finite element analysis to investigate the behaviour of 1-3 composites for different applications. Firstly, the influence of constituent material properties on the behaviour of thickness mode drive was studied via a combination of modal and harmonic analysis. This led to the creation of straightforward de sign rules relating to ceramic type, shape and distribution, in addition to the desired properties of the passive filler phase. The Thesis then describes the influence of mechanical loading and method of construction on composite transducer performance, over the complete range of volume fractions. Front face matching, fluid loading and mechanical damping via a backing block are considered and analysed with respect to composite transducer performance. This is extended using static analysis to include the behaviour of hydrostatic devices and the effect of adding stiffening plates. The theory is then augmented to encompass monolithic and diced imaging arrays. The influence of composite geometry, element dimensions and transducer separation is discussed with respect to sensitivity, cross-coupling and beam profile. Throughout the Thesis, the analytical work is supported by experimental evidence. This involved the manufacture of a comprehensive range of devices, followed by experimental studies on performance. Impedance analysis, transmission/reception sensitivities, surface displacement profiles and beam characteristics were all evaluated and the results compared with theoretical predictions. It is considered that the work described within the Thesis makes a valuable and original contribution to the field of 1-3 connectivity composite transducers. It should constitute a basis for ongoing theoretical work to improve further the performance of the devices.

Biological oscillators occur frequently in nature---and many systems, such as the growth of certain bacteria, are governed by the 24-hour circadian clock. Furthermore biological phase-locked oscillators, as identified by researchers, are clearly an integral part of the structure of the brain in humans, and in animals in general. Such systems are most conveniently investigated via computer models. This thesis describes the computer-modelling of phase-locked systems in which the oscillator is a cellular automaton---a device often used by scientists to model the growth or decay of populations within biological and other systems. The latter part of the thesis shows how these computer models have been implemented in a two-dimensional form using gate array technology, and results are presented to demonstrate the overall loop performance. It is not suggested that the phase-locked loops described in this thesis should be translated directly into practical commercial products---the primary objective of the research described being to originate a new type of phase-locked loop based around a novel variable frequency oscillator. However, the summary at the end of the thesis indicates how the designs might be modified so as to allow a direct silicon implementation.

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No description available.

Polarisation-based wavelength-division multi-/demulti-plexers (WDMs) and filters have been designed, constructed and evaluated. These are compact devices made from single-mode optical fibre possessing high linear birefringence. Ihe WDMs accept two input wavelengths in a common state of polarisation, and produce orthogonally polarised outputs which are spatially separated using a polarisation-selective element. The maximum separation demonstrated is 1.5 nm, and the minimum 0.04 nm, which is two orders of magnitude better than that achieved b most other in-line WDMs. A few metres of fibre only are required. Instantaneous cross- talk values below -15 dB have been measured experimentally, and theoretical analysis of the devices predicts that values below -28 dB should be attainable. Temperature sensitivity currently limits long-term cross-talk, but also offers the possibility of tuning the centre wavelength. Methods of reducing environmental sensitivity include judicious choice of fibre type and appropriate packaging of the WDMs. These techniques are investigated and discussed. Incorporation of the WDMs in optical fibre sensing networks is demonstrated, as is separation of frequency-shifted stimulated Brillouin scattered light, generated in a fibre, from the pump frequency. Filters are constructed using concatenated sections of birefringent fibre, positioned between two polarisers. Rotation of the polarisation azimuth between sections is achieved by twistíng portions of the fibre to induce circular birefringence. Thus devices are made from a single strand of linearly birefringent fibre, less than one metre in length. Passband widths and separations are selected b changing the number of twisted sections in the filter, and altering lengths and twist angles of sections. A minimum passband width ofI0 nm has been demonstrated, at a passband separation of60 nm. Environmental stability is suíciently good for the devices to be operated as passive components.

This thesis describes the development of a detailed set of step-by-step SVC system design procedures which allow manufacturers and operators to plan and develop optimum SVC systems for a given a.c. power transmission system. The validity of a typical svc system designed using the suggested procedures is investigated. The internationally recognised software package EMTP has been used as the primary Research tool, and principal features of this software, including those observed in the Research study also forms part of the discussion in the thesis. Previous conventional approaches to SVC simUlation have been restricted to simplified system models, and have only provided partial solutions to the design problem. In contrast, a detailed representation of three phase SVC systems using a time-domain approach is used in this research study in order to formulate a comprehensive design methodology. The SVC considered is for high voltage transmission applications, and is the TSC-TCR-FC type. A new optimisation program termed "OPTI-SVC" has also been developed to assist the SVC system design process. The system compensation limits must first be derived, and then for given equipment costs and system harmonic constraints, the program evaluates the optimum arrangement of the SVC primary system. Although certain simplifying assumptions are made and only those factors that can be taken into account analytically are considered, the program uses a worst case design philosophy in order to ensure acceptable performanceIn particular, Cost of the the program can minimise either the total svc system or the total harmonic voltage produced in the transmission system. In order to derive optimum control system settings, in particular for the SVC regulator, a structured trial and error approach has been developed. wi th the aid of the Astrom relay tuning technique, a good first estimation on optimum regulator settings for a given a.c. system condition can be obtained. The results are then systematically trimmed until a satisfactory system response is achieved. A three phase SVC system has been designed using the suggested approaches and applied to a generator fed transmission system. Realistic system data has been supplied by NEI Reyrolle Technology Limited. Simulated performance tests carried out demonstrate the correct functioning of the svc system against general accepted criteria, and hence the validity of the design procedure is established. As a primary research tool, the software EMTP has been proved to be very versatile although not user-friendly. Significant observations regarding the use of EMTP that are necessary to assist general users of the software package, are also revealed in the research study.