NOVELTY - The device (10) has an electret (40) provided with a continuous layer with a series of projections (42) extending along a Z-direction perpendicular to that of a plane. The projections are distributed based on a degree of freedom with a step (P) less than course between an electrode (20) and the electret. The electrode has faces (21, 31) arranged opposite to the electret. The faces are distributed based on the degree of freedom with a step identical to the step of the projections of the electret.    USE - Device i.e. autonomous conversion device, for converting vibrational mechanical energy into electric energy to a vehicle.    ADVANTAGE - The electret can exhibit a high stability and enable generation of high capacity variations with small displacements, so that the amount of electrical energy can be generated with the device of a given size can be increased. The variation of significant capacitance per relative step size of the electret can be obtained from the authorized smoothness of structuring of the electret, so that the fine structure can be adapted to a wide range of vibration amplitudes. The device enables generating multiple electric alternations when the relative displacement of the electret is higher than the step. The polarity of the potential difference changes when the electret slides with an amplitude equal to half of the step size so as to maximize the electric quantity of recovered power when the electret traverses, so that effective electric energy transformation is carried out even when the amplitude of the sliding motion of the electret strongly varies in time with a limited sliding motion. The frequency of the potential difference generated at the boundaries of load is higher than the frequency of resonance of the resonant system or the frequency of vibration of the source of vibration by the stable electret due to continuous dielectric layer.    DETAILED DESCRIPTION - The electret is formed from a silicon oxide layer arranged on a silicon substrate. An INDEPENDENT CLAIM is also included for a method for manufacturing a device for converting vibration mechanical energy into electric energy.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of an electrical/mechanical conversion structure with an electret.    Step in an electret (P)    Device for converting vibration mechanical energy into electric energy (10)    Electrodes (20, 30)    Faces of the electrodes (21, 31)    Electret (40)    Projections (42)