Nonlinear vibration of liquid droplet by surface acoustic wave excitation

Vibration of a liquid droplet is easily controlled by the Rayleigh surface acoustic wave (SAW). In the vibration of a liquid droplet, two cases are considered: free vibration and forced vibration when it is excited without and with SAW excitation, respectively. For the free vibration, the theoretical and experimental results have already been reported. In the forced vibration, when input excitation was increased, we had determined experimentally that vibration of a liquid droplet shows two nonlinear phenomena. One is, with the increase in SAW input voltage, resonance frequency decreases and vibration amplitude exhibits jump phenomenon. The other, in addition to the fundamental frequency, second and third harmonies, and 1/2 and 3/2 subharmonics are observed. In this report, we explain the two nonlinear phenomena qualitatively using the Duffing equation including the term of a nonlinear spring.