A fluid injection.

The invention relates to an injector (7) having an injection axis (AB) and comprising: - a housing (2) comprising a cavity (20) axially, - an actuator (3) comprising an electro-active portion (30) and having o a first end face (31) extended by a penetrating member (33), and o a second end face (32) opposite the first (31), the actuator (3) being mounted in the housing (2) and the member (33) comprising a piston (330) engaged in the cavity (20) and forming a fluid connection between the actuator (3) and the housing (2), - excitation means for put the electro-portion (30) of the actuator (3) in vibration with a setpoint period t, According to the invention, the penetrating member (33) has a length (L) as the propagation time T wave the acoustic browsing satisfies the equation: T = [2n + 1] * [t / 4], where n is a multiplier, positive integer.