A theoretical study of Love wave sensors mass loading and viscoelastic sensitivity in gas and liquid environments

The sensitivity of Love wave (also known as guided shear horizontal surface acoustic wave (SH-SAW)) sensors to mass loading and/or to viscoelastic change, in gas and liquid environments, is theoretically investigated. The objective is to present effective design parameters for Love wave sensors. The investigated sensor platform consists of a ST and AT-cut quartz substrate, a guiding layer, and a thin (poly)methylmetacrylate (PMMA) coating, used to simulate the chemically sensitive layer. The investigation process consists of computing optimal guiding layer thickness (resulting in the largest perturbation, hence the highest sensitivity), for increasing layer density and shear modulus that includes all available materials. It is demonstrated that the device sensitivity, in general, increases as the difference in bulk shear wave velocities between the substrate and the guiding layer. The relative importance of mass loading and viscoelasticity are discussed. First experiments to confirm this theoretical study lead us to bring up a material characterization technique which shows that literature material parameters are not usable for film materials.