pp. Price 3. 40 rubles.Professor Lyamshev, the current editor of the Soviet Acoustics Journal, has long played a significant role in Soviet work on acoustooptics. In 1980, he contributed an invited paper on the subject to the ICA in Sydney, Australia. In this short volume, he carries out a careful exposition of the theoretical basis of laser excitation of sound, beginning with the simplest cases and proceeding systemically through the more complicated.The first chapter concerns itself with laser excitation of sound in a homogeneous half-space, first with a free surface and then with increasing complications of rough surfaces. Chapter 2 takes up various possible materials in the second half-space, be it another liquid, a solid, or an inhomogeneous surface layer. Here, he also introduces FM modulation of the intensity of the exciting laser.Chapter 3 continues this exploration of the source, considering pulses of various shape, interactions in one and three dimensions, and the effect of bubbles on the sound generation.The effect of moving sources has been of interest in Soviet acoustics since the days of Blokhintsev in the late 40s, and Chap. 4 is devoted to effects produced by moving laser thermooptical sound sources. The theoretical analysis is then completed by a chapter on the laser generation of sound in solids, including surface wave excitation and solid waveguides.The last chapter in the book is devoted to experimental results, mainly for laser-induced sound in water, with a small amount of attention paid to excitations of surface acoustic waves in solids.
The condition for the maximum directivity from a spherical radiator is presented and it is shown that this directivity index is 20log N, where N is the number of consecutive modes excited. For superdirectivity, the relationship among the expansion coefficients is particularly simple and a closed-form expression for the beam-pattern function results. Using this method, a high directivity may be obtained no matter how small the sphere is, provided that the prescribed velocity distribution is maintained. Examples of the resulting beam patterns are given.
The condition for the maximum directivity from a spherical radiator is presented and it is shown that this directivity Index is 20 logN, where N is the number of consecutive modes excited. In this case, the relationship among the expansion coefficients is particularly simple and a closed-form expression for the beam pattern function results. Using this method, a high directivity may be obtained no matter how small the sphere is, provided that the prescribed velocity distribution is maintained. Examples of the resulting beam patterns are given.
The magnetostrictive properties of Hiperco, a magnetic alloy of iron, cobalt, and chromium, were investigated to determine its suitability as a material for electromechanical transducers. The relations between the magnetic and magnetostrictive characteristics of a material and its performance as a transducer element are reviewed and criteria for its evaluation established. The properties of Hiperco, measured after a suitable heat treatment had been determined, are discussed in relation to these criteria and a comparison made with nickel and Permendur. For operation at magnetic remanence Hiperco is shown to be as good as Permendur for hydrophone applications, but inferior to nickel and Permendur when used as an underwater projector at high power levels. When polarized above remanence maximum value of 0.17 for the electromechanical coupling coefficient is realized and operation as a projector is improved. Performance data are given for a small underwater transducer constructed of Hiperco operating at remanence.
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