High temperature ultrasonic transducers for monitoring of micro-molding

Thick film (90μm) piezoelectric ceramic ultrasonic transducers (UTs) have been successfully deposited on a barrel and a mold insert of a micro-molding machine by a sol-gel spray technique. The ball-milled bismuth titanate fine powders are dispersed into PZT solution to achieve the gel. The gel is then sprayed onto the substrate at room temperature. The films with desired thickness have been obtained through multilayer coating approach. Piezoelectricity is achieved using a corona discharge poling method. These UTs can operate at more than 500°C. The center frequency of ultrasound generated is 13 MHz and 6 dB bandwidth is 13 MHz. In the pulse/echo mode the ultrasonic signals have a signal to noise ratio of more than 30dB. The ability of these UTs to monitor the polymer properties in real-time at the barrel and the mold insert of the micro-molding machine during processing is demonstrated.