Piezoelectric ceramics in ultrasound

3203HD, a piezoelectric ceramic material manufactured by CTS, was developed in the 1980s to meet the requirements for medical ultrasound. This high dielectric constant, high electromechanical coupling coefficient material, which is known for its consistency and reproducibility, became the reference material for medical ultrasound imaging and is still used in many transducers today. However, material requirements for ultrasonic imaging have evolved leading to the need for new materials. In particular there has been a demand for higher dielectric constant materials and materials that offer good mechanical strength and performance at dimensions less than 50 microns. There are often property trade-offs to be considered when developing new materials. Substitution of various lanthanide ions into an existing piezoelectric material formulation shows that the dielectric constant decreases and the Curie point increases with increasing atomic number for the lanthanide ion. Dielectric properties are often less than predicted as the material cross-section decreases. Polished cross sections of a 2-2 composite structure reveal surface damage that is one grain deep on the ground and diced surfaces. An empirical model suggests that the effective dielectric constant of the damaged surface is lower than the bulk material, which causes the measured capacitance to be lower than expected.