STRONG ULTRASONIC MICROWAVES IN FERROELECTRIC CERAMICS

It is well known that ferroelectric materials have piezoelectric prope rties which allow the transformation of electrical signals into mechan ical signals and vice versa. The transducer action normally is restric ted to frequencies up to the mechanical resonance frequency of the sam ple. There are, however, two mechanisms which allow transducer action in ferroelectric ceramics at much higher frequencies: one is the norma l piezoelectric effect in a ferroelectric ceramic in which the crystal lites have periodic domain structures, the other is a domain wail effe ct in which ferroelastic domain walls in a periodic domain structure a re powerful shear wave emitters. Both mechanisms give rise to extensiv e dielectric losses in ceramics at microwave frequencies.