FOCUSED SOUND FIELDS AND THEIR APPLICABILITY TO THE NON-DESTRUCTIVE TESTING OF MATERIALS.

The sound field of ultrasonic probes is determined by diffraction phenomena. This article describes their use for ultrasonic test problems. For the detection of very small reflectors, at greater distances, sound fields with very high intensity are required; for an exact determination of the shape of the reflectors however, highly concentrated sound fields are necessary. Both requirements can be fulfilled by focusing the sound field. It is shown that, independent of the type of focusing, the narrowing of the sound field is always due to the same interference effects. By means of characteristic examples of focused sound fields, the important effects to be considered when choosing appropriate probes can be detailed.