Water–air interface deformation by transient acoustic radiation pressure

The deformation of a fluid interface by the acoustic radiation pressure has been used for surface tension measurements or to design exotic structures such as acoustic diodes. However, few studies focus on the characterization of the spatial characteristics of deformation induced by transient excitation, making research requiring precise spatial control of deformation challenging. This paper investigates experimentally and numerically the effects of transient excitation on deformation generated by an acoustic radiation pressure at the water–air interface. A numerical model using the finite-element method and based on theoretical background for permanent excitation is generalized to transient excitation. An experimental setup is developed to evaluate the maximum height of interface deformation for different durations and amplitudes of ultrasonic excitation using two complementary methods: the first using a camera and an edge detection algorithm and the other using a multichromatic confocal displacement sensor. Numerical and experimental results for a non-steady-state excitation show a quadratic evolution of the height of deformation as a function of incident pressure and also a linear increase as a function of the excitation duration. The evaluation of the deformation height induced by acoustic radiation pressure at a water–air interface for a transient excitation paves the way to applications requiring noncontact space-time interface modulation, such as subwavelength phenomena.