Experiments are carried out in a circular container
(178 mm diameter, 30 mm deep) as shown in Fig. 1. The
container is filled with a liquid whose depth is larger than
the wavelength of the perturbations at the surface. The
monochromatic forcing is varied in the range of frequencies
f0 ¼ 30–60 Hz, which results in Faraday wavelengths
in the range 8–14 mm. The dominant frequency of
the excited surface ripples is at the first subharmonic of the
excitation frequency, f ¼ f0=2. We define the supercriticality
as ¼ ða athÞ=ath, where a is the amplitude of
the vertical acceleration imposed by the shaker and ath is
the threshold for the parametric generation of Faraday
waves.
A diffusing light imaging technique is used to visualize
simultaneously the surface ripples and floating tracer particles,
as seen in Fig. 2(a). A 2% milk solution in water
provides sufficient contrast for the parametrically excited
waves to be observed and allows high resolution movies
(800 800 pixel) to be recorded in the range of speeds
80–120 fps by using the Andor Neo sCMOS camera. Black
floating particles are added on the fluid surface to visualize
the horizontal motion of the liquid. Particles are made of
carbon glass and have been plasma treated to reduce their
intrinsic hydrophobicity. The use of surfactant and plasma
t