A Magnetic Field Response Sensor for Measurement of Liquid Levels

NASA’s Langley Research Center (www.larc.nasa.gov) recently reported on the development of a sensor. that allows wireless measurement of the level of liquid in closed, electrically-conductive containers such as metal fuel tanks. Magnetic Field Response sensors utilize the absorptive properties of a tuned circuit near the resonant frequency. A simple swept oscillator excites the circuit via magnetic coupling to the inductor, and records the amplitude response versus frequency. The frequency where the response is minimum—due to maximum coupling to, and absorption/radiation by the tuned circuit—corresponds to the value of the tuning capacitance. Thus, a variable capacitance and a fixed inductor are the only components necessary for a passive sensor.