Suppressing Bifurcation in Bolt-Clamped Langevin Ultrasonic Transducers Through AC Current-Driven Control

Bolt-clamped Langevin ultrasonic transducers are widely used in industrial, medical, and research applications attributed to their ability to generate high-power ultrasonic waves. Due to their large quality factor, it is important to hit the exact resonance frequency to achieve their maximum performance. Voltage-controlled excitation of these transducers often leads to bifurcation, a scenario where multiple valid phase angles result in varied power outputs at the resonance frequency. In this work, we model the nonlinearities that occur within the transducer via an extended Butterworth Van Dyke (BVD) model and use it to explain why an AC current-driven control suppresses the bifurcation. This involves modelling the damping behavior, which is subsequently verified through surface velocity measurements using a laser Doppler vibrometer. We propose a circuit that facilitates current-controlled AC voltage output, detailing its components and evaluating its impact on the transducer’s dynamics. Our method prevents impedance curve jumps and improves the transducer’s transient rise time from 12.7ms to 0.9ms and reduces the fall time from 6.9ms to 1.2ms, offering a fast and robust solution. Despite the increased complexity of the current-controlled circuitry, our findings demonstrate its efficacy in maintaining consistent performance near the resonant frequency, thus, opening new avenues for improving bolt-clamped Langevin ultrasonic transducers in applications such as acoustic levitation or ultrasonic cleaning.