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Electronically focused ultrasonic transmitting arraysHosseini, S. January 1985 (has links)
This work describes a thirty-two channel programmable transmitter unit for driving an ultrasonic transmitting array using transducers with thickness resonances of up to 2 MHz. It has been developed to allow the performance of time delay focussed transmitting arrays to be thoroughly investigated before their eventual use in an imaging system. The unit will produce a pulse or continuous wave output which is programmable using either a microprocessor or a computer, in both amplitude and delay or phase. The unit's operation is discussed in some detail and the experimental underwater 1 MHz transducer array used for the functional tests is described. Results are presented showing the performance of the transmitting unit when used with this array and demonstrate that the system provides an effective tool by which a proper assessment of time delay focussing may be made. A computer prediction technique·has been introduced. The computer prediction of the field in the region in front of a focussed ultrasonic array has been obtained by the summation of the fields due to the individual array elements. The shape of the short duration acoustic pulses due to the individual elements is determined.by the electrical drive and transducer characteristics. The prediction technique is valid for any pulse shape which can be represented mathematically, however the results presented here have been limited to the pulse shape used in the experimental work. The algorithm used is suitable for a wide range of array formations and the close agreement of the practical and the simulation work shows the validity of the prediction technique. The experimental array has been used as the basis of a detailed investigation into the resolving power of focussed arrays and a number of results have been derived from this investigation. These are used to support extensive simulation studies and computer prediction techniques. The validity of the simulation techniques is assessed and the effect of considering each transducer in the array as a single small but finite sized centrally placed element is compared with that where each transducer is represented by a number of synchronously driven Huygens radiators. The significance of these results with respect to imaging is discussed. The effect on performance of system error is investigated and an assessment of the tolerance of the time delay technique to these errors is made.
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The design and performance of a hall-effect wattmeter for measuring continuous and controlled powerPanayiotides, L. A. January 1978 (has links)
No description available.
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The performance of a half-cycle per bit F.S.K. data transmission systemKeats, D. G. A. January 1974 (has links)
No description available.
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An investigation into methods of direct digital measurement of electrical quantitiesHunter, R. D. January 1971 (has links)
No description available.
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A study of computer methods in mobile radio planningDurkin, J. January 1969 (has links)
No description available.
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An investigation of control and feedback mechanisms in constant temperature anemometrySamman, A-R. January 1985 (has links)
No description available.
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A fibre optical strain sensorAllsop, Thomas David Paul January 1999 (has links)
Strain-sensing elements, fabricated in standard communications-grade single mode optical fibre, are increasingly being considered for application in structural health monitoring. The reason for this is the numerous advantages demonstrated by these devices compared with traditional indicators. This thesis describes work carried out on optical sensors at the University of Plymouth. The aim of this work was to achieve an optical fibre strain sensing system capable of measuring absolute strain with good resolution and having wide dynamic range, without bulky optical equipment and not susceptible to misalignment due to handling. Earlier work was devoted to study on an intrinsic Fabry-Perot interferometric sensor and an optical phase-shift detection technique. The sensing element investigated relied on the end face of an optical fibre as one mirror and the second mirror being a layer of Titanium Dioxide (TO2). Although some results are included, it was soon realised that this sensor had a number of problems, particularly with fabrication. As no simple solution presented itself, consideration was given to a sensor that made use of the change in reflectance of an intra-core fibre Bragg grating when the grating was subjected to strain. The bulk of work described in this thesis is concerned with this type of sensing element. The grating structure is inherently flexible and a number of structural formats were studied and investigated. The first and simplest grating considered was two linearly chirped Bragg gratings used in a Fabry-Perot configuration (a grating resonator). The sensor was tested using the sensing detection system and although the fabrication problems were overcome absolute strain measurement was unattainable. To achieve this end, a theoretical study of a number of grating structures was carried out using the T-matrix Formalism. Confidence in using this approach was gained by comparing the spectral behaviour of a proposed grating with results, which were given by another theoretical model for the same proposed grating. The outcome of this study was that two structures in particular showed promise with regard to absolutism (the measure of true strain) and linearity. Discussions held with the department of Applied Physics at Aston University about fabrication resulted in one of the proposed designs being abandoned due to difficulties of fabrication. The second structure showed more promise and fabrication attempts were put in hand. This grating is linearly-chirped with a Top-hat function and a sinusoidal perturbation as a taper function of the refractive index modulation. Experiments were performed, data were acquired and system performance for this sensor is presented. The thesis concludes that using such a fibre Bragg grating as the sensing element of a strain sensing system enables it to measure absolute strain without using bulky optical equipment. At present, the resolution of strain is limited by the quality of the grating being fabricated (anomalies on profile), this should improve once the fabrication technique is refined.
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An echo cancelling technique applied to an underwater acoustic data linkRoberts, S. J. Roberts January 1983 (has links)
No description available.
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A study of microwave sensor design and their use for moisture measurement in polymeric materialsAscroft, John T. January 1989 (has links)
No description available.
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Application of bit-slice microprocessors to digital correlation in spread spectrum communication systemsIsmail, Nabil Abd January 1983 (has links)
This thesis describes the application of commercially available microprocessors and other VLSI devices to high-speed real-time digital correlation in spread spectrum and related communication applications. Spread spectrum communications are a wide-band secure communication system that generate a very broad spectral bandwidth signal that is therefore hard to detect in noise. They are capable of rejecting intentional or unintentional jamming, and are insensitive to the multipath and fading that affects conventional high frequency systems. The bandwidth of spread spectrum systems must be large to obtain a significant performance improvement. This means that the sequence rate must be fast and therefore very fast microprocessors will be required when they are used to perform spread spectrum correlation. Since multiplication cannot be performed efficiently by microprocessors considerable work, since 1974, has been published in the literature which is devoted to minimising the requirement of multiplications in digital correlation and other signal processing algorithms. These fast techniques are investigated and implemented using general-purpose microprocessors. The restricted-bandwidth problem in microprocessor-based digital correlator has been discussed. A new implementation is suggested which uses bit-slice devices to maintain the flexibility of microprocessor-based digital correlation without sacrificing speed. This microprocessor-based system has been found to be efficient in implementing the correlation process at the baseband in the digital domain as well as the post-correlation signal processing- demodulation, detection and tracking, especiaJIy for low rate signals. A charge coupled-device is used to obtain spectral density function. An all-digital technique which is programmable for any binary waveform and can be used for achieving initial acquisition and maintaining synchronisation in spread spectrum communications is described. Many of the practical implementation problems are discussed. The receiver performance, which is measured in terms of the acquisition time and the bit-error rate, is also presented and results are obtained which are close to those predicted in the system simulations.
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