Comparative performances of new KNN lead-free piezoelectric materials and classical lead-based ceramics for ultrasonic transducer applications

The purpose of this paper is to present the comparative study of a single-element transducer based on KNN and on lead-based ceramics. A thickness coupling coefficient of 35%, a sound velocity of 5800 m/s and a dielectric constant of 280 are found and make this material suitable for medium and high frequency applications. On the basis of these electromechanical properties, we have used the KLM model to predict the electroacoustic behaviour of a 10 MHz single-element transducer with two matching layers. We show that KNN transducers have performances intermediate between those of PT-based transducers and PMN-based transducers. Finally, performances of a KNN-based transducer are reported and discussed according to non-linear behaviour of the ceramic.