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Acoustic Beam Scanner

IP.com Disclosure Number: IPCOM000092282D
Original Publication Date: 1968-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 43K

Publishing Venue

IBM

Related People

von Gutfeld, RJ: AUTHOR

Abstract

This system is for scanning an acoustic beam repetitively by mechanically rotating or oscillating an anisotropic crystal. Acoustic waves in solids travel with a velocity whose magnitude is dependent on direction. In general, these velocities are quite anisotropic in single crystals, particularly those possessing cubic symmetry. The relationship between the energy and phase velocity is such that acoustic scanning can be achieved, such scanning not being available with electromagnetic waves. This results in applications to sonar, bio-acoustics, etc. The latter often requires acoustic beam scanning of body tissue.

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Acoustic Beam Scanner

This system is for scanning an acoustic beam repetitively by mechanically rotating or oscillating an anisotropic crystal. Acoustic waves in solids travel with a velocity whose magnitude is dependent on direction. In general, these velocities are quite anisotropic in single crystals, particularly those possessing cubic symmetry. The relationship between the energy and phase velocity is such that acoustic scanning can be achieved, such scanning not being available with electromagnetic waves. This results in applications to sonar, bio-acoustics, etc. The latter often requires acoustic beam scanning of body tissue.

The basic principle of this scanning device stems from the theory outlined by
M. J. P. Musgrave in which the mathematical relationship between acoustic energy and phase velocities in anisotropic media is given in detail for arbitrary directions. The device, drawing 1, consists of ultrasonic transducer A generating longitudinal waves having frequencies in the megacycle region, into a liquid B of matched acoustic impedance, or as closely matched to A as possible for efficient transmission. Transducer A, is mounted so that its emitting surface is at the center of the circular configuration as shown. The wave then enters, at normal incidence, a single crystal C in the shape of a disk with a hole in the center, polished on both inside and outside circumferences. Crystal C is capable of rotation, so that, if the viscosity of liquid B is low, little turbulence is produced from the circular motion. The rotation can either be continuous in one direction or oscillatory.

The nature and degree of scanning that occurs inside crystal C are shown in drawing 2, a typical phase and energy velocity diagram for an anisotropic single crystal. The magnitude of the acoustic velocity is represented by the distance from the origin 0 to a point on the curve and the direction of the acoustic velocity with respect to 0 - 0' is indicated by the polar angle alpha. Consider that the crystal and its wave surface are fixed with the wave entering the crystal from different directions. For a wave entering along direction 1 the energy and...