Thesis (Ph. D.)--University of Wisconsin--Madison, 1968. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1982. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf 46).

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2009 / In acoustics, pulse echo methods are well known as a means of measuring time of Hight. Traditional techniques for generating acoustic waves in solid ferromagnetic waveguides include piezoelectric, capacitive and magnetostriction. Piezoelectric and capacitive techniques are preferred due to the inefficiency of magnetostriction caused by electro-mechanical coupling losses and the fact that most ferromagnetic materials show low levels of magnetostriction. The aim of this study was to optimise the magnetostrictive effects for sensing applications based on a ferromagnetic waveguide using the pulse echo method. The results obtained were implemented in the design of an acoustic thermometer. Two configurations for signal generation and recovery were examined, the use of a single wound copper coil acting as a transceiver coil, and the use of separate transmit and receive coils. Results obtained using the latter configuration indicated better signal to noise ratio's and provided the flexibility to manipulate the point of signal recovery. The pulse echo method was implemented and optimised. An acoustic thermometer based on an existing design was developed by inducing a partial reflection from a set position in the waveguide, defining a sensing probe. Awareness of the elastic properties of the waveguide material enabled the guaging of its temperature by measuring the acoustic pulse velocity in the probe. The accuracy of the instrument was increased through signal conditioning, examined together with cross correlation and an increased sampling frequency. Systematic errors were resolved through calibration, giving the instrument an overall accuracy of ±O.56"C for the range of temperatures between 2O"C and 400"C.

The theory of the phonon broadening of impurity spectral lines in homopolar semi-conductors is discussed within the framework of a Kubo-type formulation of the adiabatic dielectric susceptibility and the subsequent calculation of this using the double-time Green's function method. The basic assumption is the smallness of the interaction of the electrons (or holes) bound to impurity sites with the lattice vibrations. This interaction is then treated as a small perturbation of the independent systems of electron and vibrating lattice; the use of the adiabatic approximation is thereby avoided. The so-called decoupling of the infinite hierarchy of equations for the relevant Green's functions is discussed in detail and is given its justification in the present problem. In the case of nondegenerate electronic levels, the line-shape function is obtained explicitly in terms of the matrix elements of the electron-phonon interaction. It is found that the absorption line consists of a sharp peak with a width arising from a finite life-time of the unperturbed states due to the electron-phonon interaction and of a continuous background arising from the multi-phonon processes which accompany the optical absorption. In the degenerate case, a general method of obtaining the line-shape function is discussed and is illustrated in an example. The results are compared with those obtained by previous workers in the field. The general theory is applied to shallow impurity levels in silicon with the use of a modified hydrogenic model and a deformation potential description of the electron-phonon interaction; numerical estimates are made for typical contributions to the widths of the lines in both acceptor and donor cases. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

It is suggested that the stratosphere may-act as a wave-guide for certain types of acoustic-gravity waves. An isothermal layer model is proposed which introduces gravity terms into the equations governing wave propagation. An expression for the phase change on reflection at a boundary of the layer is derived. Numerical solutions to the equation for wave-guide, modes of propagation are obtained by the use of a digital computer. Results are given in the form of dispersion curves. Cutoff is found to occur at a frequency well above the Brunt resonant frequency for the stratosphere. The model stratosphere proposed in this study does not behave as a lossless wave-guide for gravity coupled acoustic waves. This is shown to be consistent with the results of a more complete study by Press and Harkrider. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

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Thesis (Ph. D.)--Open University. BLDSC no. DX226217.

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