High frequency single element transducer based on pad-printed lead-free piezoelectric thick films

A transducer for medical imaging was fabricated using a pad-printing process to deposit a curved lead-free thick film (KNN-based) on an electroded backing (porous KNN). First, the electromechanical properties of the pad-printed thick film were measured. An effective thickness coupling factor of 34% (similar to those obtained with the same composition by a screen-printing process) was obtained. The transducer has a f-number of 1.3 and a focal distance around 5 mm. The center frequency is at 12 MHz and the -dB bandwidth is 93% and a high sensitivity is observed. For the first time, images of human skin in vivo were obtained using a lead-free film. They are compared to those obtained with a PZT-based transducer.