Microsystem for converting a pressure difference in a fluid into a mechanical movement, this microsystem having machined components of which at least one of the dimensions is less than 200 μm, this microsystem comprising: - an inlet nozzle for the compressed fluid and an outlet nozzle for the expanded fluid, - a first and a second arm (12, 14), at least one of which is movable, between which the fluid flows in order to pass from the inlet nozzle to the outlet nozzle while moving these arms relative to one another, - an upper plane and a lower plane between which the arms are interposed, these planes confining the flowing fluid between these arms, characterized in that: - the arms (12, 14) are formed in such a manner that, in the course of their movement relative to one another, they define at least one pocket of fluid moving away from the inlet nozzle in order subsequently to reach the outlet nozzle while increasing in volume at the same time, - each of the arms (12, 14) is mechanically connected to the same fixed lower plane according to one embodiment chosen from the group composed of a first embodiment and of a second embodiment, according to the first embodiment each of the arms (12, 14) is mechanically connected to the same fixed lower plane by means of a movement means (16, 18) allowing only a to-and-fro translational movement of each arm parallel to this lower plane and along non-co-linear directions, and according to the second embodiment the first arm is fixed with no degree of freedom on the fixed lower plane and the second arm is mechanically connected to this fixed lower plane by means of a movement means allowing said movement, relative to the first arm, which defines said at least one pocket of fluid moving away from the inlet nozzle in order subsequently to reach the outlet nozzle while increasing in volume at the same time, - the movement means comprises a point of anchoring to the fixed lower plane, and - said at least one movable arm (12, 14) is capable of moving relative to each of the upper and lower planes. - an inlet nozzle for the compressed fluid and an outlet nozzle for the expanded fluid, - a first and a second arm (12, 14), at least one of which is movable, between which the fluid flows in order to pass from the inlet nozzle to the outlet nozzle while moving these arms relative to one another, - an upper plane and a lower plane between which the arms are interposed, these planes confining the flowing fluid between these arms, - the arms (12, 14) are formed in such a manner that, in the course of their movement relative to one another, they define at least one pocket of fluid moving away from the inlet nozzle in order subsequently to reach the outlet nozzle while increasing in volume at the same time, - each of the arms (12, 14) is mechanically connected to the same fixed lower plane according to one embodiment chosen from the group composed of a first embodiment and of a second embodiment, according to the first embodiment each of the arms (12, 14) is mechanically connected to the same fixed lower plane by means of a movement means (16, 18) allowing only a to-and-fro translational movement of each arm parallel to this lower plane and along non-co-linear directions, and according to the second embodiment the first arm is fixed with no degree of freedom on the fixed lower plane and the second arm is mechanically connected to this fixed lower plane by means of a movement means allowing said movement, relative to the first arm, which defines said at least one pocket of fluid moving away from the inlet nozzle in order subsequently to reach the outlet nozzle while increasing in volume at the same time, - the movement means comprises a point of anchoring to the fixed lower plane, and - said at least one movable arm (12, 14) is capable of moving relative to each of the upper and lower planes.