Variably polarized ceramic for passive aperture apodization

Large aperture transducers, such as those required for the crossed-electrode array geometry for three-dimensional real-time ultrasound imaging, introduce edge artifacts called range secondary lobes. These artifacts are attenuated through apodization; however, accomplishing apodization without introducing additional system channels or new material interfaces proves challenging. An alternative technique is presented where the piezoelectric response of a PZT ceramic is engineered to achieve apodization in a passive manner. By utilizing a sacrificial curved structure during polarization, a variable degree of remnant polarization is achieved across the expanse of the transducer while using a constant polarizing potential. Experimental measurement of poling parameters and finite-element simulations allowed the ceramic structure to be designed so as to accomplish appropriate apodization. This passive means of apodization complements the low-system complexity of the crossed-electrode array.