Sounds of Leidenfrost drops

We show that when a drop of water is maintained in its Leidenfrost regime, a sound in the form of periodic beats emits from the drop. The process of beat emission involves two distinct frequencies. One component is the frequency of beats itself, and the second is the frequency of sound in every beat which is emitted when one oscillation in the drop occurs. Experiments were performed by placing a drop of water over a concave metallic surface, and the beats of the drop were recorded by fixing a microphone above the drop. A video camera was also fixed above the drop to record its oscillations. Simple analytical techniques like Fourier and wavelet transforms of the audio signals and image processing of the videos of the drop were used to gain insight into the mechanism of the beat emission process. This analysis also helped us in studying the dependence of frequencies, if any, on the radius of the drop and the substrate temperature.