High Precision Liquid Level and Leak Detection Based on Capacitive Micromachined Ultrasound Transducer

This paper reports on a miniaturized liquid level sensor, that is sensitive to very small changes in the liquid level, and thus can also be exploited for leak detection particularly for small-volume fluid reservoirs, where sensor size and detection precision are crucial factors. The sensing principle is based on measuring the time of flight of the ultrasound signal to and from liquid / air interface using Capacitive Micromachined Ultrasound Transducer (CMUT). The sensor can be used in contact or non-contact modes, and is unaffected by fluid coating on sensor surface. The sensor was tested in contact mode for a liquid volume of ca. 725 ml, and proved to be sensitive to 0.2 mm level or 5 ml volume change. In non-contact mode, a smaller volume change was aimed where a 1 ml change was clearly distinguishable.