SYSTEMATIC ERRORS IN ULTRASONIC PROPAGATION PARAMETER MEASUREMENTS. PART 1. EFFECT OF FREEFIELD DIFFRACTION
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.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 29, 1964
- Accession Number
- AD0437995
Entities
People
- V. A. Del Grosso
Organizations
- United States Naval Research Laboratory