中文摘要：

采用声悬浮方法研究了自由液滴表面的毛细波形成机理,并利用主动调制声场技术激发了液滴的八阶扇谐振荡.实验结果表明,当声场调制频率接近液滴本征频率的两倍时,液滴将由轴对称受迫振荡向非轴对称扇谐振荡模态转变.实验与理论分析证实,参数共振是毛细波与扇谐振荡的形成原因.扇谐振荡的本征频率随液滴赤道半径的增大而减小,可通过修正的Rayleigh方程来描述.

英文摘要：

The suspension of liquid drops provides a preferable boundary condition for investigating various free surface phenomena.Here we report the observation of concentric capillary wave formed on the surface of drastically flattened water drops levitated in ultrasound.The measured wavelength of capillary wave accords well with that from the classic dispersion relation equation.The eighth mode sectorial oscillation of acoustically levitated drop is excited by the active modulation of sound pressure.It is found that these phenomena are due to parametric excitation.The capillary wave is induced when the parametric instability arises and ultrasound pressure exceeds a threshold pressure.The sectorial oscillations take place when the equatorial radius varies at twice the natural sectorial frequency of the levitated drop.The frequency of the eighth mode sectorial oscillation decreases with the increase of equatorial radius and can be well described by modifying the Rayleigh equation.Further analysis reveals the parametric excitation mechanism for this kind of oscillations.