  When the interface between a dielectric and a conducting liquid is excited by
an oscillatory electric field, electrostatic Faraday waves can be induced.
Here, we study the response of the interface to an AC electric field, which is
superposed by either a second AC field of different frequency, or by a DC
field. An algorithm based on light refraction at the fluidic interface is used
to obtain the spatio-temporal response of the Faraday waves, and the critical
voltage corresponding to onset of instability, the interfacial oscillation
frequency and the dominant wavelengths are determined. The influence of the
mixing ratio, which denotes the relative amplitudes of the different components
of the driving signal, is analyzed, and the experimental results are compared
with theoretical predictions. For AC/AC driving, gradual variations of the
mixing ratio can induce a jump of the pattern wavelength, which is a result of
the transition from harmonic to a subharmonic oscillation. For AC/DC driving,
the interface oscillates either harmonically or subharmonically, and the
response wavelength can be tuned continuously by adjusting the admixture of the
DC component. For both driving modes, the experiments show good agreement with
theory.

Fluid Dynamics