Finite element analysis on tunable solid/fluid phononic crystal for surface acoustic wave bandgaps with various fluid heights

In this study, the propagations of surface acoustic waves (SAWs) in two-dimensional solid/fluid phononic crystal (PC) structures were investigated. The PC structures are composed of a periodic sequence of hollow pillars deposited on a semi-infinite substrate, which can be filled with various kinds/heights of fluid. Finite element analysis was used to study the characteristics of SAW bandgaps for the unit cell of PCs. The results showed that the distribution of bandgaps varies with the fluid height. Additionally, the change of bandgaps is more sensitive to mercury than water. Furthermore, transmission properties of SAWs for the PCs filled with different mercury heights are analyzed. It can be found that the PCs can inhibit the propagation of SAWs with a frequency corresponding to the bandgaps validly. Meanwhile, comparing with the transmission spectra, it could be concluded that the transmission troughs shift to lower frequency overall as the mercury heights increase. The results obtained in this study are instructive and meaningful for the practical design of tunable SAW PCs.