Converter of a variation of energy to be harvested into a potential difference between two electrical terminals, the variation of energy to be harvested being a variation of magnetic field or of temperature, this converter comprising: - a transducer layer (52; 110; 120; 150; 194; 240; 254; 284; 300) extending essentially parallel to a reference plane and suitable for transforming the variation of energy to be harvested into a mechanical deformation, this transducer layer comprising, to this end: a number of first blocks (70-73; 116-118; 126-129; 152-155; 214-217; 270; 301-304) of magnetostrictive material or material with shape memory, these first blocks being delimited from one another by lateral edges, and regions without any first block, these regions being inserted between the lateral edges of these first blocks (70-73; 116-118; 126-129; 152-155; 214-217; 270; 301-304), - a piezoelectric layer (54, 58) formed from a single block of piezoelectric material or from a number of blocks of piezoelectric material attached alongside one another and fixed to one another with no degree of freedom so as to behave mechanically as a single block of material, this piezoelectric layer having inner and outer faces parallel to the reference plane, the inner face being fixed with no degree of freedom onto most of the transducer layer so as to undergo a mechanical stress exerted by this transducer layer, - a first (56; 60) and a second electrode of electrically conductive material extending essentially parallel to the reference plane along at least one of the faces of the piezoelectric layer to show an excess of electrical charges on one of these electrodes in response to the mechanical stress undergone by the piezoelectric layer, and the first blocks (70-73; 116-118; 126-129; 152-155; 214-217; 270; 301-304) each having a preferential axis of deformation parallel to the reference plane. - a transducer layer (52; 110; 120; 150; 194; 240; 254; 284; 300) extending essentially parallel to a reference plane and suitable for transforming the variation of energy to be harvested into a mechanical deformation, this transducer layer comprising, to this end: a number of first blocks (70-73; 116-118; 126-129; 152-155; 214-217; 270; 301-304) of magnetostrictive material or material with shape memory, these first blocks being delimited from one another by lateral edges, and regions without any first block, these regions being inserted between the lateral edges of these first blocks (70-73; 116-118; 126-129; 152-155; 214-217; 270; 301-304), a number of first blocks (70-73; 116-118; 126-129; 152-155; 214-217; 270; 301-304) of magnetostrictive material or material with shape memory, these first blocks being delimited from one another by lateral edges, and regions without any first block, these regions being inserted between the lateral edges of these first blocks (70-73; 116-118; 126-129; 152-155; 214-217; 270; 301-304), - a piezoelectric layer (54, 58) formed from a single block of piezoelectric material or from a number of blocks of piezoelectric material attached alongside one another and fixed to one another with no degree of freedom so as to behave mechanically as a single block of material, this piezoelectric layer having inner and outer faces parallel to the reference plane, the inner face being fixed with no degree of freedom onto most of the transducer layer so as to undergo a mechanical stress exerted by this transducer layer, - a first (56; 60) and a second electrode of electrically conductive material extending essentially parallel to the reference plane along at least one of the faces of the piezoelectric layer to show an excess of electrical charges on one of these electrodes in response to the mechanical stress undergone by the piezoelectric layer,