A synthetic jet is a time-averaged fluid motion generated by sufficient strong oscillatory flow downstream from a sudden expansion. The study of the interaction between the synthetic jet and an external flow is of great interest in particular for aeronautical applications. A network of such actuators could be used indeed on airplane wings for example to control, with a good energetic efficiency, the boundary layer separation in order to increase the lift or the laminar / turbulent transition for drag reduction. In this paper, the interaction of a sub-millimetric synthetic jet actuator with an external flow is experimentally studied. In these experiments, the actuation is ensured by acoustic excitations produced by a loudspeaker. Hot-wire anemometry is used for measurement of the velocity field in various functioning configurations (velocity of the transversal flow, actuation frequency,…). In most of the tested configurations, the boundary layer of the transversal flow is significantly modified by the synthetic jet, which shows that these types of actuators could be efficiently used for flow control purposes. A comparison with a continuous jet is finally performed.