Determining biosensing modes in SH-SAW device using 3D finite element analysis

Surface acoustic wave (SAW) sensors are electromechanical devices that exploit the piezoelectric effect to induce elastic (acoustic) waves which are sensitive to small perturbations: for example specific binding and recognition of disease biomarkers. Shear horizontal surface acoustic waves (SH-SAWs) are particularly suited to biosample analysis as the wave is not completely radiated and lost into the liquid medium (e.g., blood, saliva) as is the case, for example, in a device implementing Rayleigh waves. Here, using 3D finite element analysis (FEA) the nature of waves launched on a particular quartz device is investigated with respect to the cut of the quartz, the addition of gold guiding layers, and the addition of other linear elastic materials of contrasting acoustic properties. It is demonstrated that 3D FEA analysis showing the device's frequency shift with added guiding layer height reveals a proportional relationship in agreement with the Sauerbrey equation from perturbation theory. It is directly shown, given certain device parameters and a gold guiding layer, that shear horizontally polarized waves are launched on the surface with a dominant mode frequency around 250 MHz. This would be an appropriate biosensing mode in Point of Care (POC) testing for the particular properties of certain disease biomarkers delivered via a liquid medium.