In “Robust Transducer–Reflector Distance Control in Acoustic Levitation”, we introduce an automated approach for stabilizing the transducer–reflector distance in single-transducer acoustic levitators. The method uses a motorized linear stage together with a precision balance that measures acoustic radiation force as a direct indicator of cavity performance. Based on this signal, a physics-informed hill-climb algorithm first locates the resonance distance, while a physics-informed extremum-seeking controller maintains it under drift and disturbances.

The results show that the optimal cavity distance can be held reliably even when operating conditions change, such as through resonance-frequency drift or environmental variations. In long-term validation experiments, the acoustic radiation force remained within tight bounds for two hours, enabling stable levitation over extended periods. The publication builds on work we presented at IUS 2025 in Utrecht and extends it into a robust control strategy for long-duration acoustic levitation.