Automatic passive control of liquid positioning in microfluidic chips

A device for controlling liquid motion includes a substrate (10) of material having piezoelectric properties, and a system for controlling the motion of a quantity of liquid placed in contact with the substrate. The control system includes at least one interdigitated transducer (T1, T3, T5, T7), applied to the substrate (10) and designed for selectively generating a surface acoustic wave adapted to propagate on the substrate (10) and interact with the quantity of liquid. The control system further includes an acoustic resonator (30) which is placed on the path of the surface acoustic wave, and which is adapted to normally allow the forward transmission of the surface acoustic wave having a frequency equal to a resonance frequency of the acoustic resonator, and to reflect the surface acoustic wave back towards the transducer when the quantity of liquid is present within the acoustic resonator.