Frieder Lucklum, Bernhard Jakoby,
"Non-contact liquid level measurement with electromagnetic–acoustic resonator sensors"
, in Measurement Science and Technology, Vol. 20, Nummer 12, IoP, Seite(n) 124002, 12-2009
Non-contact liquid level measurement with electromagnetic–acoustic resonator sensors
Sprache des Titels:
Electromagnetic–acoustic transduction represents an alternative to piezoelectric transduction
with unique properties and advantages for resonator sensors. We have shown that such devices
are suitable as mass microbalances similar to quartz crystal resonators, and as liquid density
and viscosity sensors by exciting a suitable in-plane mode featuring dominant shear vibration.
Generating out-of-plane vibrations we have applied these devices also as liquid level sensors.
In contrast to classic time-of-flight ultrasonic liquid level sensors, the resolution is not limited
by the wavelength, since small frequency changes due to interference effects with a standing
acoustic wave are evaluated. For this contribution we have extensively evaluated this liquid
level sensing and will present and compare new measurement and modeling results. The
model comprises electromagnetic–acoustic interaction with a lossy transmission line
representing the acoustic wave in the liquid. In impedance measurements with standard lab
equipment a resolution as low as 3 μm at a liquid level of 10 mm and an operating frequency
of 275 kHz has been achieved.