Ultrasonic in-line sensors for inclusion detection in liquid metals

A high temperature ultrasonic sensor for detecting inclusion particles in molten metals is presented. The sensor consists of a conventional piezoelectric transducer and a focused waveguide, and provides high spatial resolution measurements in molten metals in a pulse-echo mode at 10 MHz. A taper-shaped clad buffer rod is used as the waveguide. In order to design the waveguide, elastic wave propagation in the rod is evaluated by a numerical simulation using a finite difference method. Focusing ability of the acoustic lens fabricated at the end of the rod is also examined numerically. Using the developed sensor, backscattered echoes from alumina particles of 160 /spl mu/m suspended in molten aluminum at 1073 K have clearly been observed.