The use of piezoelectric materials in fluid level sensors is known. An existing design includes two piezoelectric sensor elements mounted opposite each other on the inside of a container. The sensor elements are both mounted at the level of interest. A first sensor element functions as a transmitter and is electrically excited with a voltage pulse or continuous frequency such that it transmits an acoustic signal. The second sensor element functions as a receiver of the transmitted acoustic signal. When both sensor elements are immersed in a fluid, the acoustic signal generated by the first sensor propagates through the fluid and is detected by the second sensor element, thereby indicating the presence of fluid at the level of the sensor elements. In the presence of air, the acoustic signal is not detected by the second sensor element, indicating that fluid is not present at the level of interest.
As noted, existing fluid level sensors often require intimate contact between the sensor elements and the fluid being detected. As well, because the sensor elements are typically mounted inside the container, the structural integrity of the container must be breached to install the sensor elements. As such, the container must usually be empty, or at least not have fluids at or above the level of interest, when the sensor elements are being installed.