Abstract
The propagation of surface acoustic Love modes along ZnO/glass-based structures was modeled and analysed with the goal of designing a sensor able to detect changes in the environmental parameters, such as liquid viscosity changes and minute amounts of mass supported in the viscous liquid medium. Love mode propagation was modeled by numerically solving the system of coupled electro-mechanical field equations and Navier–Stokes equations. The phase and group velocities and the attenuation of the acoustic wave propagating along the 30° tilted c-axis ZnO/glass structure contacting a viscous non-conductive liquid were calculated for different ZnO guiding layer thicknesses, added mass thicknesses, and liquid viscosity and density. The three sensor responses, i.e., the wave phase and group velocity, and attenuation changes are calculated for different environmental parameters and related to the sensor velocity and attenuation sensitivities. The resulted sensitivities to liquid viscosity and added mass were optimized by adjusting the ZnO guiding layer thickness corresponding to a sensitivity peak. The present analysis is valuable for the manufacture and application of the ZnO-glass structure Love wave sensors for the detection of liquid properties, such as viscosity, density and mass anchored to the sensor surface.
Highlights
Love waves are acoustic modes that propagate along the surface of a structure comprising a layer on top of a half-space, when the shear bulk acoustic wave velocity of the layer is slower than that of the substrate
We theoretically investigate the performance of a glass/ZnO Love wave sensor which is suitable for the fabrication of a biological sensing platform including Rayleigh wave-based microfluidic devices
The effect of the sensitivity dispersion of Love wave sensor is investigated, and we focused on the guiding layer thickness optimizing the mass sensitivity for the first Love wave mode
Summary
Love waves are acoustic modes that propagate along the surface of a structure comprising a layer on top of a half-space, when the shear bulk acoustic wave velocity of the layer is slower than that of the substrate. Love wave devices can be directly fabricated on silicon or glass substrate by using the thin piezoelectric film technology whose characteristics depend on the piezoelectric guiding layer thickness and on the c-axis tilt angle μ. A viscous Newtonian liquid is introduced that contacts the guiding layer free surface, and a complex wave velocity is defined for the three-layer system (substrate, guiding layer, liquid); the velocity and attenuation sensitivities to viscosity and to an added mass are calculated. Solutions to the wave equations are sought which decay to zero with depth below the surface x2 = 0 and in the liquid half-space; inside sought which decay to zero with depth below the surface x2 = 0 and in the liquid half-space; inside the guiding and added mass layers, the displacement varies sinusoidally.
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