Tuning the resonant frequencies of a drop by a magnetic field

TL;DR

This study experimentally demonstrates how a static magnetic field can tune the resonant frequencies of a ferromagnetic nanoparticle-laden water drop on a superhydrophobic surface, by effectively altering its surface tension.

Contribution

It introduces a method to control drop oscillations via magnetic fields and models the magnetic influence as an effective negative surface tension without fitting parameters.

Findings

Magnetic field adjusts the drop's resonant frequencies.

Magnetic contribution acts as negative surface tension.

Model aligns well with experimental data.

Abstract

We report an experimental study of a magnetic liquid drop deposited on a superhydrophobic substrate and subjected to vertical vibrations in presence of a static magnetic field. It is well-known that a flattened drop of usual liquid displays oscillating lobes at its periphery when vibrated. By adding ferromagnetic nanoparticles to a water drop and varying the strength of the magnetic field, we are experimentally able to efficiently tune the resonant frequencies of the drop. By using conservation energy arguments, we show that the magnetic field contribution is equivalent to adding an effective negative surface tension to the drop. Our model is found in good agreement with the experiments with no fitting parameter.