A Small-Diameter PMUT-Based Ultrasonic Gas Flowmeter for Internet of Things

A small-diameter gas flowmeter utilizing scandium-doped aluminum nitride (ScAlN) piezoelectric micromachined ultrasonic transducers (PMUTs) is proposed for use as a sensor node in remote gas flow monitoring within the Internet of Things (IoT). The core component of the flowmeter comprises two transceivers based on PMUT chips and a $\pi $ -shaped pipe. The PMUT chip measures 4 mm $\times $ 4 mm and features a $4\times 4$ array of circular diaphragms, with a resonant frequency of ~172 kHz in air. The circuit board based on MSP430FR6043 MCU is used to realize the alternate transmission and reception of ultrasonic signals and the calculation of the flight time difference between upstream and downstream sound waves based on cross-correlation algorithm. The experimental results indicate that the developed small-diameter gas flowmeter has a flow measurement capability ranging from at least 2 L/h to 810 L/h, 690 L/h, and 156 L/h in channels with diameters of 6, 4, and 2 mm, respectively. The analysis of the test data for the three pipe diameters shows that the maximum relative errors are below ±1.7%, ±2.25%, and ±2.1%, respectively, and the maximum repeatability remains below 0.68%, 0.45%, and 0.18%, respectively. The developed gas flowmeter enables gas flow measurement in smaller-diameter pipes and demonstrates excellent performance. Therefore, for applications involving small gas channels, such as neonatal nasal catheters and hydrogen fuel cell gas pipes, the proposed small-diameter ultrasonic gas flowmeter based on PMUTs presents an effective solution. This solution offers significant advantages in expanding IoT application scenarios and demonstrates broad potential.