Noninvasive Flow Bubble Detection for Small Pipes Based on Piezoelectric Micromachined Ultrasonic Transducers

Ultrasonic flow bubble detection plays a significant role in industrial control and chemical production, as it enables noninvasive monitoring of hydraulic systems, oil degradation, and the progression of chemical reactions. However, the conventional bulk PZT ultrasonic transducers currently employed for bubble detection are characterized by their large size and limited integration capabilities with integrated circuits (ICs). This constrains their application for real-time and long-term monitoring in small-diameter pipes. This study highlights the potential of piezoelectric micromachined ultrasonic transducers (PMUTs) for real-time bubble detection in small pipes based on the principle of acoustic energy attenuation. The operating frequency of PMUTs has been theoretically optimized to enhance the performance of bubble sensing. Our fabricated PMUTs chips successfully measured bubbles in water, indicating an excellent linear relationship between the received voltages and bubble diameters within the 1-5 mm. Additionally, subsequent research indicates that environmental conditions, including temperature and flow medium types, have negligible impact on the bubble measurement. These results demonstrate the robustness of MUTs-based ultrasonic bubble detection techniques.