A power generator including a converter with an electromechnical transducer and a magnetostrictive layer to convert a variation of a magnetic field into a mechanical deformation exerted on the transducer. There is a magnetic field source including a group of several permanent magnets. One of the group or the converter is movable, between first and second positions. The group has several first permanent magnets, one having an aspect ratio of between 1/10 and ten and most of the field lines that loop back do not pass through another first permanent magnet. The first permanent magnets are arranged such that the magnetic field induced inside the magnetostrictive material in the first position by one of the first permanent magnets is parallel to and in the direction opposite to the magnetic field induced at the same instant in the magnetostrictive material by the next first permanent.