Highly-accurate and non-invasive flowrate monitoring for miniature pipelines using piezoelectric micromachined ultrasonic transducers

Abstract

Noninvasive and real-time flowrate measurement for small pipes is crucial in medical diagnostics and aviation hydraulic system health monitoring. However, current bulk PZT-based ultrasonic flowmeters are unsuitable for these scenarios due to their large size, high power consumption, and poor integration with ICs. This paper proposes a highly accurate and universal ultrasonic flowrate measurement technique for pipes with small diameters (≤ 15 mm) using piezoelectric micromachined ultrasonic transducers (PMUTs) by taking advantage of their miniaturized size, low power consumption, and superior integration capability. A clamp-on testing method is proposed for ultrasound transmitting and receiving. The inside liquid flowrate is measured based on the propagation time difference between the upstream and downstream ultrasound waves. To enhance accuracy, a unique PMUTs chip with a center circular element and an outer annular element is developed to improve acoustic pressure. Additionally, the incident angle and working frequency of ultrasound waves are optimized to reduce the interference caused by ultrasound wave superposition at the PMUTs and pipe wall interface. This optimization also improves acoustic energy transmission and response. The flowrate of water in a steel pipe is successfully measured, demonstrating excellent linearity (99.69%) between flowrate and time difference, with a high accuracy of 2%. Furthermore, flowrate testing for pipes with different diameters and pipe wall materials is experimentally demonstrated, showing widespread usability. The developed PMUTs-based flowmeter is versatile and compatible with common pipes, allowing compact integration in tight spaces, making it highly promising for practical applications.