Miniature high frequency array transducers based on new fine grain ceramics

New fine grain ceramics have been developed for high frequency applications (i.e. 15 to 50 MHz). Modified lead titanate (MPT) and lead zirconate titanate (PZT) ceramics are prepared by either hydrothermal synthesis or hot isostatic pressing. Their fabrication is described, as well as results of microstructure analysis, which includes pore size and grain size distributions. The thickness mode piezoelectric, elastic and dielectric constants are measured and used as inputs for the design of 20 MHz linear array transducers with 32 elements of less than 100 μm width. The manufactured arrays are characterized in pulse echo operation and their centre frequency and bandwidth are compared to theoretical predictions. Finally, the radiation pattern of an element is measured and the effect of inter-element coupling is discussed. Performances are compared to those of PVDF-based transducers in view of intravascular imaging applications. The bandwidth is slightly lower but the sensitivity is much higher than those of PVDF devices. This is explained on the one hand by higher coupling coefficients and on the other by lower electrical input impedances due to higher dielectric-constants