Design and fabrication of multiplexed two-dimensional transducer arrays using electrostrictive ceramic materials

Two-dimensional array transducers are essential for real time volumetric imaging. The implementation of receive mode parallel processing requires the transducer be designed with a wide transmit beam to allow multiple simultaneous receive beams. Unfortunately, this requirement has an associated increase in pulse-echo beamwidth that reduces contrast of subtle lesions. When the volumetric system is used for B-mode scanning, the wide transmit beam degrades image quality unnecessarily. It is hypothesized that a multiplexed two-dimensional array transducer can be developed to improve image quality of a volumetric scanner when it is used for B-mode scanning, while maintaining the capability of real time volumetric imaging. It is further hypothesized that 2-D array multiplexing can be achieved using the bias controlled sensitivity of electrostrictive relaxor ferroelectric materials.;The hypothesis was tested by analysis, development and evaluation of sparse random arrays and relaxor ferroelectric materials. Random array patterns with Gaussian and uniform element distributions were analyzed by computer simulation. A random array pattern was designed for each mode of the multiplexed transducer. Beamwidth was controlled by distribution of the 192 transmitter and 64 receivers, whereas the average sidelobe amplitude was determined by the number of elements. Bar mode piezoelectric properties of two prototype relaxor ferroelectric materials were measured and used in KLM transducer modeling. The materials exhibited high dielectric permittivity, but low electromechanical coupling and high dielectric loss. Bias circuits were designed to allow operation of the relaxor transducer with the existing phased array system. The 3.5 MHz, 82 x 82 multiplexed transducer was fabricated with 428 active elements. Element and array performance were in good agreement with predictions. Multiplexing was successfully accomplished with performance comparable to commercial multiplexors. The multiplexing system was integrated with the Duke phased array scanner and allowed rapid multiplexing between element patterns. Images of test phantoms indicated the element pattern for B-mode imaging had improved contrast when compared to the element pattern for volumetric imaging.