Abstract: The characteristic equation of Lamb waves in a solid plate with loading liquid on single side is derived. The disper- sion curve is also calculated. A new method monitoring the fixed liquid level is presented and implemented, based on the sensitivity of the characteristic parameters, such as, attenuation, of some Lamb wave modes to the presence of liquid. The results show that the presence of liquid has little influence on the phase velocity dispersion curve and energy velocity dispersion curve, but great influence on the attenuation disper- sion curve; the experimental results are in good agreement with the theoretical calculations and imply that this method is suitable for monitoring the fixed liquid level of large tanks.

Key words: Fixed liquid level measurement, Lamb waves, Large tanks