Abstract: A driving circuit for ultrasonic tools which uses a piezoelectric transducer to convert ultrasonic electric signals into ultrasonic mechanical vibrations including a voltage-controlled oscillator which produces an output signal at a frequency that is proportional to an input voltage, a power amplifier stage having its input coupled to the output of the voltage-controlled oscillator, the power amplifier stage including an output transformer which couples the output of the power amplifier stage to the piezoelectric transducer, the power output transformer further acting as both an insulating transformer and a boosting transformer for the driving circuit and a feedback transformer coupled in series with the secondary side of the output transformer and the piezoelectric transducer, the feedback transformer having a secondary side through which a current flows which is proportional to the current flowing through the piezoelectric transducer, a phase comparitor which detects the phase difference between two signals

Abstract: A bearing for an air driven turbine operated dental handpiece of the type including a turbine rotor provided in a casing and having blade elements coupled to a shaft member. The bearing includes a first air bearing formed circumferentially about the shaft member, a second air bearing including a small gap formed between the end of the shaft and an inside surface of the casing and a means for introducing compressed air into the small gap and a pair of opposed magnets of the same polarity provided respectively in the end of the shaft member and the inside surface of the casing whereby the axial load on the turbine rotor is resisted not only by the second air bearing but also by the magnetic repulsive force of the magnets.