Optimization design of a Lamb wave device for density sensing of nonviscous liquid.

A Lamb wave device composed of a piezoelectric plate loaded with a nonviscous liquid layer is presented. The relation between the Lamb wave phase velocity and the liquid density can be used for liquid density sensing. In this paper, utilizing the partial wave theory, the concept of effective permittivity is introduced to analyze the Lamb wave's excitation and the phase velocity calculation under a certain liquid density. The interface between the Lamb wave device and the liquid layer is metallized to eliminate the influence of liquid electrical properties when sensing liquid density. Based on the theory model, the phase difference measurement method is adopted to study the device's sensitivity to liquid density. In order to achieve high sensitivity to liquid density with sufficient excitation efficiency of Lamb wave, the optimal parameters of the Lamb wave device including plate thickness and cut orientation are obtained by numerical calculation. The experimental results are found to be in agreement with the theoretical simulations, verifying the validity of the theory model and the practicability of the optimization design.