High permittivity ceramics for medical ultrasonic transducers: a study on the optimisation of processing parameters

The present paper describes the study of a material system in order to provide manufactures of medical transducers with a range of high sensitivity materials that can be tailored to their individual requirements. The focus of the investigation is to identify the optimum combination of the key material parameters of permittivity (dielectric constant) and electromechanical coefficient (K_t) for the highest possible transition temperature (T_c). Materials obtained by different processing conditions are characterised by their thickness mode coupling coefficient, dielectric, elastic and piezoelectric constants and by microstructural analysis. Relationships between these measurements and processing parameters are established. The ceramics are then used in both single-element and array transducer configurations. Simulated performances are presented (i.e. input impedance and sensitivity), to show the advantage of different materials according to the type of transducer