An Automatic Resonance Tracking Scheme With Maximum Power Transfer for Piezoelectric Transducers

This paper presents a novel cost-effective automatic resonance tracking scheme with maximum power transfer for piezoelectric transducers (PTs). The conventional approaches compensate the PT with complex power factor correction schemes or drive it in resonance using intricate loops with limited operating range. The proposed tracking scheme is based on a bandpass filter (BPF) oscillator, exploiting the PT´s intrinsic resonance point through a sensing bridge. It guarantees automatic resonance tracking and maximum electrical power converted into mechanical motion, regardless of process variations and environmental interferences. Thus, the proposed BPF oscillator-based scheme was designed for an ultrasonic vessel sealing and dissecting system, where accurate PT displacement regulation over a wide range of loads is required. An amplitude control for a switching power stage was developed to regulate the output mechanical motion and provide different power levels for the specific surgical functions such as sealing and dissecting. A proportional-integral compensator was developed to ensure stable operation under various loading conditions. The sealing and dissecting functions were verified experimentally in chicken tissue and glycerin.