中文摘要：

实验研究了不同交流电频率下共面电极电润湿芯片上液滴的振荡行为特性．结果表明，在某些特定的输入频率下液滴出现共振，共振模态称为Pn（n=2，4，…），且实验获得的共振频率值与线性理论预测值吻合良好．在共振模态Pn下，液滴振荡对称，表面呈现n／2个波峰．在相邻共振模态间存在某个临界频率，此时液滴振荡对称，但很微弱，且接触线宽度和液滴高度的振荡相位关系发生转变．小于此临界频率时，液滴接触线延展至最大时呈液瓣状，且液瓣的位置通过液滴的收缩和延展在水平面内周期性交替，液瓣数目随着相邻共振模态阶数”的升高而增加．大于此临界频率时，液滴振荡左右不对称，具体表现为液滴表面波的传动．预期这些液滴的非对称振荡会产生更为混乱的内部流动，从而增强微流控液滴混合器的混合效率．

英文摘要：

An experimental study on droplet oscillations under AC electrowetting on dielectric （EWOD） with coplanar-electrodes configuration at different input frequencies was conducted. It was found that the droplet resonates at some specific frequencies, which agrees reasonably well with those predicted using a previous linear theoretical analysis, and the resonance modes is named P,, （n = 2, 4, …）. At resonance modes Pn, the droplet oscillates symmetrically with n/2 peaks appearing on the droplet surface. There ex ists a critical frequency between the adjacent resonance modes, at which the droplet oscillates symmetrically but very weakly, and the oscillation phase relationship between the contact line width and height of the droplet switches. At frequencies lower than this critical frequency, the contact line will form lobes whose number increases with the order of adjacent resonance mode and whose position alternates periodically in azimuthal direction through droplet spreading and receding. At frequency higher than the critical frequency, droplet oscillates asymmetrically with the transmission of ripples on the droplet surface. It is believed these asymmetric oscillations will produce more chaotic fluid flows inside the droplet than symmetric oscil lations and therefore can enhance the mixing efficiency in droplet-based microfluidics.