ACOUSTIC MICROSCOPY FOR SPHERICAL INCLUSION CHARACTERIZATION

In this paper a new nondestructive ultrasonic technique is developed t o distinguish small spherical voids from small spherical elastic and r igid inclusions. In many materials, such as light metal casting alloys , ultrasonic scattered echoes from void-type defects and heavy metal i nclusions used for strengthening purposes can give the ultrasonic sign al of the same order of magnitude. It is shown in this paper how one c an extract the phase information of the reflected signal to distinguis h the voids from solid inclusions. When phase-frequency curves are ext ended to the zero frequency, then voids and solid inclusions meet at t wo distinct points on the phase axis separated by a distance of approx imately 180 degrees. Thus voids and solid inclusions can be clearly di stinguished. Experimental results are verified by theoretical predicti ons. (C) 1996 Acoustical Society of America.