Electroacoustic sandwich transducers

Claim 1

AN ULTRASONIC WASHING DEVICE COMPRISING IN COMBINATION A CONTAINER FOR LIQUID ULTRASONIC TRANSMITTING MEDIUM, MEANS FOR FILLING SAID CONTAINER WITH SAID MEDIUM AND FOR EXHAUSTING SAID MEDIUM FROM SAID CONTAINER, A FITTING COMPRISING A METALLIC PLATE INTEGRALLY BONDED TO A SURFACE OF SAID CONTAINER, A BOLT FIXED AT ONE END TO SAID PLATE, AND THE OTHER END OF SAID BOLT PROTRUDING THROUGH SAID PLATE, AND AND ULTRASONIC TRANSDUCER REMOVABLY FASTENED TO SAID BOLT, SAID TRANSDUCER COMPRISING IN COMBINATION A PIEZOELECTRIC ELEMENT CONSTRUCTED TO VIBRATE IN A RESONANT-THICKNESS MODE OF VIBRATION, A PAIR OF METALLIC BACKING ELEMENTS FORMING WITH SAID PIEZOELECTRIC ELEMENT A SANDWICH THE ELECTRICAL THICKNESS OF WHICH APPROXIMATES A HALF-WAVE-LENGTH IN A RESONANT THICKNESS FREQUENCY OF SAID PIEZOELECTRIC ELEMENT IN THE DIRECTION OF VIBRATION THEREOF, SAID BOLT AXIALLY DISPOSED TO ENGAGE ONE END OF SAID SANDWICH TO FASTEN SAID SANDWICH TO SAID METALLIC PLATE AT SUBSTANTIALLY AN ANTINODE IN SAID RESONANT-THICKNESS VIBRATIONS, COUPLING SAID SANDWICH TO SAID PLATE IN CONTIGUOUS ULTRASONIC COUPLING RELATION INDEPENDENTLY OF THE PRESENCE OF RIGID BONDING MATERIAL AT THE INTERFACE BETWEEN SAID PLATE AND SAID SANDWICH.