Geometry effect on piezo-composite transducers with triangular pillars

High frequency transducers/arrays made of piezo- composite materials have the advantages of lower acoustic impedances, which better match tissue and a flexibility that allows focusing without the use of an acoustic lens. However, developing a high-frequency piezo-composite material for such arrays is still a challenge due to the extremely small pillar dimensions required to avoid the interference from the lateral resonances. Recently, success in developing high-frequency transducers made of piezo-composite materials with triangular pillars has been reported. The use of triangular pillar piezo-composite material was shown to suppress lateral resonances that appear in square pillar composites. To further understand how the geometry of the pillars affects the lateral resonance, piezo- composite materials with different triangular pillar angles are investigated in this work. The performance of composite transducers with triangular pillar angles of 30deg, 40deg, 45deg, 50deg and 60deg were simulated using PZFlex. The electrical impedances of these different transducers show large differences in lateral resonances. The lateral resonances cause a secondary pulse to appear after the main pulse in the time response and ripples in the pass-band of the frequency response. This secondary pulse will produce a ghost in imaging and need to be suppressed. The simulation results show that the composite with a 45deg pillar angle has the lowest secondary pulse amplitude (-22 dB below the main pulse). The secondary pulse becomes larger when the angle deviates from 45deg. Composites with 30deg and 60deg angles have secondary pulse amplitude -15 dB and -10 dB below the main pulse amplitude, respectively. Experimental composite samples have also been fabricated and acoustical and impedance measurements compared with simulation predictions. Three composite transducers with pillar angles of 30deg, 45deg and 60deg were made from PZT5H and Epotek 301 epoxy. The electrical impedances and the pulse echoes were measured to compare with theoretical predictions.