Stability of liquid metal drops affected by a high-frequency magnetic field

The dynamic behavior of liquid metal drops submitted to a high-frequency magnetic field is investigated experimentally. The motivation for this study comes from the coating industry. In this industry, liquid metals showing a free surface held in a dome-type shape are evaporated by applying electromagnetic pressure. The Galinstan drops are placed on a curved glass plate. A ringlike inductor fed by an alternating electrical current generates the magnetic field. The surface contour of the drop is observed using a high-speed camera system. The data are analyzed by utilizing image processing methods. In the experiment, we vary the inductor current I and the drop volume V while the frequency is fixed at 20 kHz. Upon increasing the inductor current within the range 0 < I < I-C, we first observe a static axisymmetric squeezing. However, when the inductor current exceeds a certain critical value, i.e., I>I-C, these symmetric states become unstable to capillary waves. The critical current (critical electromagnetic Bond number) as well as the critical mode number, the critical frequency, and the amplitudes of the waves depend strongly on the volume (Bond number).