Utilizing Electromagnetic-Acoustic Resonators for Liquid Level Sensing

Electromagnetic excitation of acoustic resonators sensors as an alternative to piezoelectric and capacitive acoustic sensors provides unique benefits of remote, multi-mode measurements. Utilizing out-of-plane modes of vibration, we have employed the devices as liquid level sensors. The resolution is not limited by the wavelength (as for time-of-flight ultrasonic sensors), since small frequency changes due to interference effects of the generated acoustic wave are evaluated. With standard lab equipment, a liquid level resolution as low as 3 mu m at 275 kHz has been achieved. To describe the physical mechanisms and predict measurement results, we present a refined model of the electromechanical interaction and compare simulated and experimental results. The model is based on an equivalent circuit description, where the compressional acoustic wave in the liquid is described as a lossy transmission line with an acoustic impedance depending on the liquid's properties.