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SUMMARY This paper is in homage to Robert Stoneley for his many contributions to the analysis of acoustic wave propagation and, in particular, for his introduction of anisotropy into the computation of elastic surface-wave characteristics. The latter has proved to be fundamental to the industry which has grown up around the signal processing devices using surface acoustic waves. The problem reviewed here is that of the reflection of incident acoustic waves from planar interfaces of quite general geometries. The interface may consist of substrate and superstrate welded together, of periodic or non-periodic intervening layers between superstrate and substrate, of free surfaces or of layered free surfaces. Surface waves and layer waves are also included. The materials involved may be of arbitrary crystalline symmetry and may be piezoelectric. The goal is to summarize this range of reflection and transmission problems in a common transfer matrix formalism which is convenient for programming. The same format is used for all the problems and the size of the matrices depends not on the complexity of the interface geometry but only on the crystalline symmetry. The reflection results are expressed as scattering matrices linking the amplitudes of the modes propagating in the substrate and the superstrate.

Transmission properties of guided modes in liquid‐core cylindrical acoustic waveguides are investigated. It is observed that for each value of the circumferential order n the first mode becomes of Stoneley‐type above a certain frequency. There are two modes without cutoff frequencies, in contrast to only one mode in solid‐core waveguides. They are the first modes with n=0 and 1. The application of liquid‐core waveguides in sensor devices is pointed out and some preliminary experimental results are reported.

The effect of relative motion on the contact resistance between certain superconductors has been investigated. Results are presented for a variety of speed, pressure, and current conditions for lead-lead contacts of the slip-ring type in which one or both members are electroplated with a thin layer of normal metal.

In non-isotropic single crystals the normals to the wavefronts of elastic waves are not colinear with the vectors representing either the energy flow or the particle displacement. Calculations have been carried out on the propagation characteristics of sound waves in two particular trigonal crystals, α-quartz and sapphire.The development of the eigenvalue equation for the velocity and the formulae for the components of the displacement and energy-flow vectors are summarized. The assumption that the wave has a plane wavefront normal to a given direction leads to three solutions, one representing a quasi-longitudinal wave and the other two representing quasi-transverse waves. The velocities of propagation, directions of displacement, and directions of energy flow for the three waves have been calculated for many orientations of the wave normal. Detailed results for propagation near one of the pure-mode axes are presented.

A homogeneous dielectric sphere illuminated by a small external source of electromagnetic radiation will be free, because of its special symmetry, from all off-axis aberrations such as coma and astigmatism. If the only monochromatic aberration, namely spherical aberration, is not too excessive or if it is partially corrected by a suitably designed source, a sphere could be used for purposes of rapid scanning of a microwave beam through an angle of 360° of arc without moving the lens. This possibility was investigated by computations based on geometrical optics and on the diffraction theory of optical aberrations. The results suggest that a sphere of fairly small refractive index and less than about 30 wavelengths in diameter will produce a good diffraction image of a point source. Methods are also discussed of designing appropriate sources for use with larger spheres.

When the free surface is anisotropic, mode of elastic surface‐wave propagation can arise that has many of the properties of a normal surface wave but has a phase velocity higher than that of the transverse bulk waves in the corresponding direction. The pseudo surface wave is a coupled mode involving terms decaying rapidly beneath the free surface and a term representing a bulk wave radiating into the solid. For many choices of crystal and plane of propagation, the contribution of the bulk term over a range of directions is small enough that the energy of the wave is essentially concentrated within a few wavelengths of the free surface and flows parallel to the surface as with the normal elastic surface waves. Moreover, in certain specific directions, the bulk term disappears completely and the pseudo‐surface wave has all the properties of a normal surface wave. The method of computation of the characteristics of the pseudo surface waves is outlined here and typical results of velocity, displacements and e...

Detailed measurements at a wavelength of 3.2 cm have been made of the phase distribution in the diffraction image produced by an aberration-free lens illuminated from a point source. The behavior of the phase of the electric field is shown by contours of constant phase (wavefronts) in the plane of the image space containing the axis and the H-vector of the radiating source. The region of the image space considered extends from the solid dielectric lens to a surface somewhat beyond the focus. Results are also shown of the phase distribution measured within about one wavelength of certain phase singularities which occur at the minima of intensity on the focal arc and on the axis. In general, there is very good agreement between plots of measured phase contours and plots of phase contours previously calculated from scalar diffraction theory.

The effect of acoustoelectric interactions on the electrical impedance of a piezoelectric semiconductor (CdS) bar is analyzed. With the assumption that the acoustic damping is dominated by the electronic effects, the impedance undergoes substantial changes whenever the bar dimensions approach odd multiples of a half‐wavelength of sound. In the presence of a biasing drift field, the impedance behavior is drastically modified and, under conditions of acoustic amplification, the real part of the impedance becomes negative for some frequencies in the neighborhood of the mechanical resonances. A linear theory for this effect is presented and the magnitude of the impedance changes are illustrated by calculations for a (1‐cm) bar of CdS.

The paramagnetism of the color centers in smoky quartz is caused by the electron which is missing from a nonbonding oxygen orbital near an aluminum impurity. The effects produced by externally introduced microwave phonons on the spin-resonance signal from these color centers have been studied in detail as a function of the relative phonon and spin-resonance frequencies, the phonon power, the spectrometer power, the magnetic field angle, and the phonon polarization. As has been noted previously, these interactions do not conform with those observed in other paramagnetic crystals. Effects of an applied electric field on the resonance lines and various further experiments on the color centers in smoky quartz are reported; two in particular suggest that the ''hole'', the missing electron, makes thermally excited transitions between two different sites adjacent to a given impurity atom. One of the experiments is a measurement of the cross relaxation which takes place between the various lines of the spectrum, while the other is a measurement of the low-frequency dielectric loss found at liquid helium temperatures. An attempt is made to discuss the spin-phonon results in terms of such transitions for the holes. (Author)

The usefulness of the immersion–reflection technique for the measurement of the angular dependence of the dispersion curves for elastic surface waves in anisotropic thin-film, substrate combinations is demonstrated. The example chosen consists of gold films on a substrate of Y-cut lithium niobate, the latter being both highly anisotropic and piezoelectric. The velocity accuracy of the measurements is about ±0.3% and the frequency of operation is limited by the attenuation in the liquid medium in which the test specimen is immersed.

Sensor development plays a key role in the field of nondestructive evaluation and process control. The annual fiber optic sensor market alone is a multimillion dollar business (1). Acoustic waves are about five orders of magnitude slower than optical waves and can also be guided in cladded glass fibers, similar to optical fibers, with low loss and low dispersion (2–7). Fiber acoustic waveguides are believed to be a very attractive and basic component for further sensor development (8). In this paper a brief theoretical description of a weakly guiding acoustic fiber (7) is given. The material selection criteria for the core and the cladding of the fiber guide, the properties of single-mode operation, and some sensing mechanisms for temperature and pressure variations are discussed. The acoustic waveguide with a liquid core is also considered.

A review is presented of the dispersion properties of elastic waves propagating in thin layers on thick substrates, including the effects of crystal symmetry and piezoelectricity on mode coupling. The relation of these layer modes to plate, Rayleigh, and Stoneley modes and the displacement distributions for various asymptotic conditions is considered for both isotropic and anisotropic examples. [This work is supported by the National Research Council and the Defence Research Board of Canada.]