A bi-directional incoming air flow fan comprises a case in which is mounted a rotor that includes a plurality of rotary blades. The frequency variation unit being coupled to an end of the tuning support and adapted to vary the position of the tuning rods, as the tuning support is slid, according to the frequency band. A first outer electrode and a second outer electrode are fixed to the first or the second metallisation strips in order to electrically contact the piezoelectric actuator. Objects contained in storage volumes that are currently accessible to the portable computer are then synchronized between the base computer and the portable computer.