Electronic speckle pattern interferometry (ESPI) has become an established technique for surface deformation studies. However, difficulties remain in the practical use of ESPI, primarily because results require skilled and time-consuming interpretation. The work reported here has enabled automated acquisition and processing of ESPI displacement data. Further processing has enabled the components of surface strain and stress to be, determined automatically. Such measurements are of great importance for experimental fracture mechanics studies, a quantitative approach to measuring the severity of defects in a loaded structure. Having established the importance of experimental optical methods in fracture mechanics, and the particular advantages of ESPI, a study has been undertaken to determine whether ESPI can be used for quantitative fracture mechanics measurements. Automated analysis for in-plane displacement measurements with ESPI was achieved by the phase-stepping technique. Numerical differentiation of the displacement data allowed surface strain to be evaluated. The accuracy of such measurements was investigated, particularly with regard to speckle noise inherent in the data. Speckle noise limits the accuracy of all measurements, and a practical threshold for displacement and strain of ±0.03~m and ±6~strain was found. From these considerations, two new phase-stepping algorithms have been proposed for ESPI. The first offers improved accuracy by the way it eliminates speckle noise; the second has allowed phase-stepping of ESPI addition fringes for the first time. · In the past ESPI has been restricted to uniaxial measurements. A new interferometer design enabled displacement to be measured along two axes simultaneously: extension to three-dimensional sensitivity is discussed. Automated displacement and strain measurements, recorded with the dual-sensitivity interferometer, are presented for a cantilever loaded at its free end.

No description available.

No description available.

No description available.

The method of electrodeless conductivity measurement using two coils wound on toroidal ferrite cores in close proximity, coupled by the induced current in the electrolyte and operating in the audio range of frequencies has been used in process control since its introduction in the 1950s. It presents several advantages over the traditional method of measuring conductivity most important of which are stability, ruggedness, and maintenance free operation. Its major disadvantage is the large sample size required for correct operation. Despite its long established use in industry with various configurations of probe design, there is no published theory of its operation. A model of the probe operation is presented which takes into account the pattern of current flow induced in the electrolyte. This allows the electrolyte to be modelled as a resistance and the effect of geometrical factors upon this resistance is described. The operation of the probe can be represented by an equivalent circuit and theoretical expressions for the cell constant are derived. The correctness of this theory is confirmed by practical measurements. Factors affecting the performance of the probe such as operating frequency, cable length and coupling have been examined. The design and development of a conductivity meter which operates with an existing electrodeless sensor is described. It comprises analog circuitry which interfaces the sensor to a microcontroller. The microcontroller provides synchronisation, analog circuit control, calculations, display update, and interfacing with a small keyboard. A requirement that the meter be portable necessitated the minimisation of component count, cost and power consumption. Addition of reference curves for various chemicals stored in the microcontroller's EEPROM allows the instrument to be used as a concentration meter.

All of the single sideband systems currently being considered for the land mobile radio service transmit a pilot tone in addition to the wanted information. The pilot is required in the receiver for automatic gain control and automatic frequency control. In particular, a phase-locked loop is often employed to perform receiver frequency control. This thesis begins by presenting background information on phase-locked receiver design and the problem caused by excess time delay introduced into the loop of a conventional phaselocked receiver. A novel phase-locked loop configuration is introduced and shown to overcome the effects of the excess time delay. The same technique is shown to greatly improve the adjacent channel selectivity performance of a phase-locked receiver. Random phase and amplitude variations are impressed upon a signal transmitted through the land mobile multipath environment. After discussing several models of the propagation medium, some of the limitations it imposes on phase-locked SSB receiver performance are introduced.

The problems associated with single sideband (SSB) radio transmitters are primarily those of achieving both a spectrally clean output and a high DC to RF conversion efficiency. In the majority of applications the linearity of a transmitter is considered to be a more important requirement than efficiency, making the transmitter a poor convertor of DC into RF energy. An approach whereby both good linearity and efficiency may be obtained is known as the Polar-Loop Technique in which a large amount of negative feedback may be applied to a radio transmitter without compromising the stability of the RF amplifiers. This is achieved by resolving the SSB signal into polar coordinate form to produce two signals: one proportional to the instantaneous amplitude of the RF signal and the other to its instantaneous phase. These component are functions of the modulating signal and have bandwidths which are much lower than those of the RF circuits. By applying feedback in each component the excess phase shift introduced by the RF circuits into the feedback loops is small and consequently, a large amount of feedback may be employed without causing instability. This thesis is primarily concerned with the application of the Polar-Loop Technique to high frequency (HF) SSB radio transmitters. The early chapters of this thesis discuss the important aspects of HF transmitter design, practice and constraints together with methods of improving the linearity or efficiency of such transmitters. Subsequently, the Polar-Loop Technique is introduced and the properties and potential sources of spurious emissions from transmitters of this type are described. Several possible transmitter configurations suitable for broadband HF applications are presented and the problems associated with the implementation of HF Polar-Loop Transmitters are outlined. In order to demonstrate the properties and capabilities of transmitters based on the Polar-Loop Technique a 100 W broadband HF unit has been designed and evaluated and the results obtained using this transmitter are presented and described in detail.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 94-100). Available also in a digital version from Dissertation Abstracts.

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