An ultrasonic oscillator drives a tool at a set frequency. An amplitude control runs the oscillator to set the vibration level. A frequency regulator joins the amplitude and the oscillator. A control feedback loop, in the frequency regulator, keeps handpiece linear dynamics. An operational transconductance...http://www.google.se/patents/US5421829?utm_source=gb-gplus-sharePatent US5421829 - Ultrasonic surgical handpiece and an energy initiator
