A functionally graded piezoelectric material created by an internal temperature gradient

Ultrasound transducers will have a broadband frequency characteristic if the relevant piezoelectric parameters could be graded in the thickness direction of the plate. As is well known, piezoelectric properties will fade away gradually if the material temperature approaches to the Curie point. From this viewpoint, we present a functionally graded piezoelectric material for broadband ultrasound transducers created by giving a temperature variation across a piezoelectric ceramic plate that has a relatively low Curie temperature. The distribution of the piezoelectric constant is estimated by comparing the measured impedance characteristic with that calculated by an equivalent network model specially derived by the authors for the plates with a graded piezoelectric constant