Lead-Free Ultrasonic Phased Array Transducer for Human Heart Imaging

Substantial advancement has been made in recent years on lead-free piezoelectric materials, but up to date, it is still a challenge to make a true medical imaging ultrasonic array transducer with center frequency <3 MHz. There are two major obstacles: the difficulty of fabricating large enough uniform lead-free piezoelectric materials with high piezoelectric coefficient, and the severe electrical impedance mismatch of an array element to the imaging system due to the relatively low dielectric constant of lead-free materials compared to lead-based piezoelectric materials. We resolved these two issues by employing texture engineering and stacking piezoelectric-layer design, which allowed us to fabricate an 80 element phased array transducer with the center frequency of 2.9 MHz and a bandwidth >80% for human heart imaging. The high-quality lead-free (Ba0.95Ca0.05)(Ti0.94Zr0.06)O3 textured ceramic plate has the size of 23×22×0.8 mm3 with the piezoelectric constant d33 = 570 pC/N. Phantom imaging and internal clinical human heart imaging demonstrated that this lead-free phased array can produce comparable imaging quality to that of a commercial PZT-5H ceramic-based phased array transducer, which demonstrated the practicality of using lead-free materials to replace PZT ceramics in phased array transducers for medical imaging applications.