4.3 Piezoelectric ceramics as ultrasonic transducers
Piezoceramics devices are widely used as ultrasonic transducers because they can generate
powerful ultrasonic waves useful for cleaning, drilling and welding, as well as to stimulate
chemical processes. Moreover, they act either as transmitters and receivers of ultrasonic
waves in medical diagnostic equipments and non-destructive material testing apparatus for
locating defects within a structure. Ultrasonic waves are mechanical vibrations that
propagate in a material as a consequence of a series of very small continuous displacements
of atoms and chain segments around their equilibrium positions. Displacements are induced
at neighbouring zones by the forces within a chain segment and between adjacent chain
segments, propagating in this way a stress-strain wave. Several kinds of ultrasonic waves
may propagate in solid materials: longitudinal waves, shear waves, Rayleigh waves (or
surface acoustic waves), Lamb waves (or plate waves). The most common method of
ultrasonic wave generation and detection uses longitudinal waves in which the
piezoceramic transducers are required to move like pistons at very high frequencies (from
20 kHz to hundreds of MHz) (Lionetto et al., 2004).
Recently the research interest in this field is focused on the development of suitable
transducers for the medical diagnosis