Theoretical Study of Quasi-Longitudinal Lamb Modes in SiN/c-AlN Thin Composite Plates for Liquid Sensing Applications

Abstract

The propagation of quasi-longitudinal Lamb mode along SiN/c-AlN thin composite plates was modeled and analyzed aimed at the design of a sensor able to detect the parameters change of a liquid environment, such as added mass and viscosity changes. Three modes were identified that have high phase velocity and quite good electroacoustic coupling efficiency: the fundamental quasi symmetric mode (qS0) and two higher order quasi-longitudinal modes (qL1 and qL2) with a dominantly longitudinal displacement component at one plate side. The velocity and attenuation of these modes were calculated for different liquid viscosities, and the gravimetric and viscosity sensitivities of both the phase velocity and attenuation were theoretically calculated.

Guided acoustic wave sensors for liquid environments

“…As an example, figure 5.1.4a-c shows the field profile of three quasi longitudinal modes, qS 0 , qL 1 , and qL 2 travelling in AlN(1.4 μm)/SiN(0.2 μm) plate: the corresponding SiN/AlN total thicknesses values H total / λ = (h AlN + h SiN )/λ values are 0.08, 0.80 and 1.6. As it can be seen, the condition U 3 << U 1 is verified on one plate side that is thus the one suitable for contacting a liquid environment [88]. The FEM of the field profile for the qS 0 , qL 1 and qL 2 modes at (h AlN +h SiN )/λ = 0.08, 0.8 and 1.6, respectively [88].…”

“…As it can be seen, the condition U 3 << U 1 is verified on one plate side that is thus the one suitable for contacting a liquid environment [88]. The FEM of the field profile for the qS 0 , qL 1 and qL 2 modes at (h AlN +h SiN )/λ = 0.08, 0.8 and 1.6, respectively [88].…”

“…The field profile of the a) qS 0 , b) qL 1 , and c) qL 2 modes in air[88].2D COMSOL Multiphysics software was employed to simulate the QL-S 0 , QL-S 1 and QL-S 2 modes propagation along the AlN(1.4 μm)/SiN(0.2 μm) composite plate while contacting the liquid (water) environment from the SiN side of the plate where the U 3 = 0 is satisfied, as opposed to the AlN side of the plate. As it can be seen in figure 5.1.5, the acoustic energy remains confined inside the plate[88].…”

“…Figure 31.The FEM of the field profile for the qS 0 , qL 1 and qL 2 modes at (h AlN + h SiN )/λ = 0.08, 0.8 and 1.6, respectively. Reproduced from[85]. CC BY 4.0.…”