Love waves dispersion by phononic pillars for nano-particle mass sensing

We present a design of a pillared phononic crystal based structure for Love wave manipulation to achieve high mass sensitivity. The structure is made of phononic micro-pillars constructed by stacking tungsten and SiO2 layers, distributed on a substrate designed for Love wave propagation. The multilayered pillar allows the creation of bandgaps, which leads to the existence of resonant modes where the elastic energy is confined within the SiO2 free surface layer of the pillar. We study particularly a resonant mode where this layer exhibits torsional mechanical motion which can only be excited by shear horizontal surface waves. We show that Love wave interaction with the torsional mode gives rise to a sharp attenuation in the surface wave transmission spectrum with a high quality factor. We also study the variation of the mass sensitivity of the system by evaluating the resonant mode's frequency shift induced by a mass perturbation using two theoretical approaches: a perturbation theory based approximation and a numerical method. The system presents very promising mass sensitivity which provides an interesting approach to increase the detection performance of Love wave based bio-sensors