Shape Oscillation of a Sessile Drop Under the Effect of Amplitude-Modulated High Frequency Magnetic Field*

The shape oscillation of a sessile mercury drop under the effect of high frequency amplitude-modulated magnetic field (AMMF) is investigated experimentally. It is a new method to excite shape oscillation of a liquid metal sessile drop, which is different from the case in the presence of a low-frequency magnetic field. The high frequency AMMF is generated by a solenoid inductor fed by a specially designed alternating electric current. The surface contour of the sessile drop is observed by a digital camera. At a given frequency and magnetic flux density of the high frequency AMMF, the edge deformations of the drop with an azimuthal wave numbers (modes n $=$2, 3, 4, 5, 6) were excited. A stability diagram of the shape oscillation of the drop is obtained by analysis of the experimental data. It is found that the same oscillation mode is excited in different frequency range, and the corresponding frequencies have a ratio of 2. This is a typical character of Mathieu-type parametric instability of a liquid drop.