Development of a water level sensor using magnetostrictive materials

In this study, an active-mode water level sensor has been developed to distinguish between the interfaces in large capacity water tanks. The sensor must be robust to withstand forces due to moving water when filling or emptying the tanks, and should be able to work when the water tank is both in motion and still. A Galfenol-brass unimorph beam has been constructed, with Galfenol (an Fe-Ga alloy, magnetostrictive material) as the active layer. The beam is clamped at one end, and, when it is flexed, there will be a stress concentration near the clamped region. This change in stress can be measured by a magnetic field sensor, which can detect local changes in magnetic field. Two magnetic coils are used, one for alternating current (AC) magnetic field generation and the other for measuring the magnetic field response of the beam. The resonance frequency of the beam in air is 248 Hz, and 206 Hz in water. By choosing an operating vibrational frequency of 280 Hz, we can separate the pick-up coil voltage response due to differences in the surrounding environment. The sensor was mounted vertically in a water tank and the system was tested both as the water level increased and decreased, showing a 10% increase from not submerged to fully submerged. The relative sensor response was evaluated from room temperature (25 °C) to 80 °C, showing a 9.1% linear increase in voltage response in water, and 8.2% in air.