Accession Number : AD0437995

Title :   SYSTEMATIC ERRORS IN ULTRASONIC PROPAGATION PARAMETER MEASUREMENTS. PART I. EFFECT OF FREEFIELD DIFFRACTION.

Descriptive Note : Interim rept.

Corporate Author : NAVAL RESEARCH LAB WASHINGTON D C

Personal Author(s) : Del Grosso,V. A.

Report Date : 29 JAN 1964

Pagination or Media Count : 99

Abstract : Appreciable errors in sound speed and sound absorption determinations may be attributed to a neglect in applying appropriate corrections to situations closely approximating free-field conditions. The errors are shown to be more severe for the lower frequencies and shorter paths. For long paths the errors are generally such as to indicate an excessive loss in absorption measurements. In sound speed determinations over relatively long paths, the error leads to group velocities lower than the plane-wave phase velocity and to phase velocities, obtained by noniterative techniques, higher than the plane-wave phase velocity. A reduction in the size of such errors (which are not errors if corrected for) may be made by a judicious selection of a particular differential path, although certain intervals may result in an increased error. This report contains, principally, graphs and tables of relative pressure and phase measurements as a function of the distance perpendicular to the transducer element. These data have been compiled for various transducer-crystal radii and for various wavelengths of operation. The tables, especially, are set up to permit accurate reading of diffraction corrections, particularly for absorption measurements in relatively low loss liquids or for sound speed measurements over relatively short paths or path differences. (Author)

Descriptors :   (*SOUND, PROPAGATION), TABLES(DATA), ERRORS, ULTRASONIC PROPERTIES, ABSORPTION, MEASUREMENT, VELOCITY, DIFFRACTION, CORRECTIONS, GRAPHICS, TRANSDUCERS

Distribution Statement : APPROVED FOR PUBLIC RELEASE