Improved Transducer Performance for 3D USCT

The latest generation of 3D ultrasound computed tomography (USCT) devices at KIT, developed for breast cancer screening, employs 128 transducer arrays distributed over a hemispherical aperture. The central element of the transducer arrays is a piezocomposite disk embedding 18 pseudo-randomly distributed single-PZT-fiber transducers. The current transducers exhibit isotropic ultrasound emission, a large bandwidth (134%), and a wide opening angle (43°). For transducer design optimization a previously developed finite element model was optimized by including a more realistic damping model for the passive materials. In this work we developed a new backing material based on large-grain tungsten powder and epoxy. The acoustic field of 17 single transducers with the new backing material was measured in an ultrasound testing setup. The bandwidth was increased substantially to 168%, accompanied by a minor decrease in sensitivity. Moreover, we studied the effects of matching layer thinning on transducer performance. A prototype transducer array was thinned and characterized in multiple steps. An increase in opening angle by 40% accompanied by an increase in sensitivity by 60% was achieved.