ULTRA PRECISION GRINDING IN THE FABRICATION OF HIGH FREQUENCY PIEZOCOMPOSITE ULTRASONIC TRANSDUCERS

High frequency ultrasonic transducers are needed for high spatial resolution measurements in applications such as medical diagnosis and non-destructive testing. However, cost-effective fabrication of high performance transducers with frequencies above 20 MHz is challenging because of the need for a thin layer of active material. Piezocomposites are the material of choice in such transducers at lower frequencies, but current fabrication methods cannot easily achieve sufficiently thin active layers. Commercially, piezocomposite is usually finished to thickness by grinding, providing surface finish acceptable for most applications. However, conventional grinding is insufficiently precise for high frequency operation and is subject to undesirable intra-process variation. The most widely used alternative is precision lapping and polishing, but this is slow and therefore expensive. In the work reported here, an alternative process of ultra precision grinding was studied, using the Loadpoint PicoAce machine operating in the ductile machining mode. To determine the capabilities of this machine for piezocomposite processing, 1-3 connectivity material was fabricated using both a standard commercial process and a novel approach based on viscous polymer processing. Unsupported layers of piezocomposite of thickness much less than 100 mu m have been achieved with surface roughnesses of less than 1 mu m and minimal discontinuity between the ceramic and polymer phases. These results suggest that ultra precision grinding may have a role to play in practical implementation of high frequency piezocomposites for ultrasonic transducers.