Acoustic Waves In Crystals Research Articles

Two-dimensional plasmons (2DP) and acoustic waves in crystals

The interaction of 2DP with elastic waves in crystals opens up new interesting possibilities to control the wave processes in solids. The present paper deals with the coupled plasma-acoustic oscillations on the surface of crystals. The coupling takes place between the shear surface or bulk waves and the longitudinal waves in a plasma sheet. Such an interaction could be realized in the inversion layer of the MOS structures or in a thin film of a semimetal or a doped semiconductor deposited on the surface of a crystal, or at last for electrons over a film of liquid helium lying on a crystal substrate. The plasmons can generate both bulk and surface hypersound waves. The coupling between plasma and acoustic waves by means of piezoeffect and deformation potential is considered.

Propagation of acoustic waves in crystals of univalent mercury halides

AbstractSections through the surfaces of phase and group velocities of propagation of acoustic waves in Hg2Cl2, Hg2Br2 and Hg2I2 were ascertained. The relations between the directions of energy propagation and the directions of phase velocities were also established. It was found that the energy flux deviates from the A‐plane towards the [001] direction. The direction of the smallest velocity of propagation of acoustic waves in the A‐plane was found, too. The results of this study are interesting especially with respect to the practical utilization of some new types of acoustic and acousto‐optic elements.

Some Invariance Relations for Acoustic Waves in Crystals Deformed by Hydrostatic Pressure

Third order elastic coefficients can be determined by using experimental values of ultrasonic velocities and their changes by hydrostatic pressure. These elastic coefficients are correct only in the case when the experimental data satisfy some invariance relations. Propagation and polarization directions of crystals of Laue groups CI, CII, TI and HI fulfilling mentioned relations are given. [Russian Text Ignored.]

On diffraction and focusing in anisotropic crystals

This paper discusses various aspects of diffraction and focusing for waves in anisotropic crystals, and the concepts are applicable to electromagnetic, ultrasonic bulk, or ultrasonic surface waves in homogeneous but arbitrarily anisotropic crystals. A numerical technique based on an angular spectrum of plane waves representation is shown to produce theoretical intensity profiles in good agreement with acoustooptic probe measurements of the diffraction field of a slit-type ultrasonic transducer launching quasi-longitudinal and quasi-shear waves in quartz along on axis of extreme anisotropy where the wave normal and the direction of energy flow are separated by angles greater than 20°. A theoretical study of two-dimensional focusing structures for use in anisotropic crystals reveals that a launching transducer fabricated in the shape of the relevant group-velocity surface can be far superior in producing a well-defined focus to a structure having the shape of a circular arc. The computation techniques can be applied to obtain the diffraction field of any arbitrary aperture function and the examples described, theoretical and experimental, concern acoustic waves in crystals demonstrating extreme elastic anisotropies, in fact much more extreme than would be encountered in analogous cases of optical diffraction. Because of current relevance to device research, emphasis in the latter sections of the paper is placed on ultrasonic surface waves.

Amplification of Magnetization Waves in Ferromagnetic Conductors

AbstractA general linear theory of spin wave amplification similar to the theory of amplification of acoustic waves in crystals is presented which takes into account the space charge arising in the course of spin wave propagation in the crystal. The treatment is given for the case of an arbitrary orientation of the wave propagation vector and an external electric field with respect to the vector of crystal magnetic moment. It is found that in an approximation linear in the deviation from the unperturbed spin value the spin—spin interaction does not contribute to spin wave amplification. It is the spin—orbit interaction that contributes to the amplification in a linear approximation. The spin wave amplification factor proves to be proportional to the value of the direct current through the sample and attains appreciable values (about 25 cm−1) at rather weak currents (about 3.5 A/cm2) and wave vectors about 103 cm−1. With increasing wave vector the amplification factor diminishes inversely proportional to the first power of the wave vector in the case of time amplification, and inversely proportional to the second power of the wave vector in the case of space amplification.

Acoustic-Wave Propagation in Tetragonal Crystals and Measurements of the Elastic Constants of Calcium Molybdate

A complete analysis is given of the propagation of acoustic waves in crystals of the tetragonal system. The determination of the elastic constants from measurements of longitudinal- and shear-wave velocities in selected directions is discussed and experimental results for calcium molybdate are presented. The elastic constants in units of 1011 dyn/cm2 at 25°C are found to be c11=+14.47 ±2%,c33=+12.65±0.17%,c44=+3.69±0.17%,c66=+4.51±5%,c16=+1.34±50%,c12=+6.64±50%,c13=+4.46±2%.

Cavity Resonator for Piezoelectric Surface Excitation

The three-dimensional problem of surface excitation of acoustic waves in a piezoelectric crystal is examined. For practical conditions, it is found that the excitation of a given acoustic mode is proportional to the scalar product of the exciting electric field and the “excitation vector,” which is determined by the material constants of the crystal. The direction of this excitation vector is evaluated for some common orientations in crystal quartz. Details are given of a new type of double-tuned cavity resonator, which, by suitable choice of one or the other of its two resonant modes, is capable of providing an electric field at the surface of the piezoelectric crystal that has a substantial component along any preferred excitation direction. A field-probe technique has been used to determine both the amplitude distribution of the exciting electric field in the cavity and the resulting acoustic wave in the crystal. It is found that constant phase of excitation over the cross section of the acoustic beam is a prerequisite for obtaining good exponential-decay patterns for successive reflection of many echoes in the crystal. Selection of the appropriate resonant mode of the cavity has enabled excellent results to be obtained for the decay patterns, using various orientations of crystal quartz.