Faraday waves at foam/liquid interface*

Monodisperse foams are produced in Hele-Shaw cells and submited to vertical oscillations. This leads to a destabilization of the interface bewteen the foam and the liquid bath. Faraday instability has been identified and characterized in terms of wavelength and destabilization threshold. The control parameters which are considered are: the frequencies of the oscillations, varying between $10$~Hz and $100$~Hz, the amplitudes of the oscillations, ranging from $1$~mm to $15$~mm and the bubble size, which is millimetric. Considering the foam as a continuous media, the waves at the interface can be linked to an effective surface tension of the interface, wich depends on the bubble size and the oscillation parameters. Results are interpreted with help of fast-cam recording and energy considerations. This study paves the way to a new continuous approach of liquid/foam interfaces.