Fluid depth sensor using surface acoustic wave resonator

Fluid depth measurement finds practical applications across various industries, including petroleum, water treatment processes, nuclear technology, and household appliances. Traditional methods include magnetic, radiation, linear variable differential transformers, LASER, pressure, capacitive, float, conductivity probe, fiber optics, ultrasonic, and triple bubbler sensors. Despite its promising attributes, such as suitability for low to very high-temperature environments, wireless interrogation, battery-less operation, and compact size, the application of piezoelectric Surface Acoustic Wave (SAW) sensors in fluid depth measurement has been comparatively unexplored in the current body of literature. This research presents a depth gauge engineered for fluid depth assessment employing a Surface Acoustic Wave (SAW) resonator. The apparatus comprises a 20 mu m thick aluminum diaphragm, with a quartz SAW resonator affixed to it. Employing an 868 MHz quartz SAW resonator enables the precise measurement of minute depth variations, with a remarkable sensitivity of 532 Hz/mm (equivalent to 0.61 ppm/mm), allowing for accurate detection of changes as small as 1 mm.