How about these "buzzer" shaped transducers:
http://www.annon-piezo.com/product/P...ic-cleaner.htm

The photos are small, I can't understand. The buzzer/transducer of the
ultrasonic is: diametre 40mm (1.5"), thickness 4mm (0.15"). The "normal"
transducers are about 1000g weight, the specific I suppose about 25g.