An axial displacement piezoelectric actuator , comprising an outer piezoelectric assembly of square-pipe construction and an inner piezoelectric reinforcement structure such that the outer piezoelectric assembly and the inner piezoelectric reinforcement structure support one another during operation to improve the bending and breaking resistance of the resultant actuator; and wherein the inner piezoelectric reinforcement structure comprises a plurality of inner active elements , either in the form of a square-pipe assembly or truss structures, wherein despite of active elements which make up the inner piezoelectric reinforcement structure having a width smaller than active elements which make up the outer piezoelectric assembly, the cut, axial length and thickness of active elements which make up the inner piezoelectric reinforcement structure are identical to the cut, axial length and thickness of the active elements which make up the outer piezoelectric assembly such that, during operation, the active elements of both the outer piezoelectric assembly and the inner piezoelectric reinforcement structure display the same axial displacement to support one another for the intended reinforcement effect, characterized in that the outer piezoelectric assembly comprises four outer active elements and said four outer active elements successively adjoin each other along their axial-length edges, with the aid of edge guides, to form a square pipe construction; in that the inner piezoelectric reinforcement structure comprises four first inner active elements which successively adjoin each other along their axial-length edges, with the aid of edge guides, to form a first inner square pipe reinforcement structure, and in that the four axial edges of said first inner square pipe reinforcement structure respectively abut, bonded with the aid of edge guides onto, corresponding inner surfaces of the outer piezoelectric assembly, forming diagonal truss support to the outer piezoelectric assembly. wherein the inner piezoelectric reinforcement structure comprises a plurality of inner active elements , either in the form of a square-pipe assembly or truss structures, wherein despite of active elements which make up the inner piezoelectric reinforcement structure having a width smaller than active elements which make up the outer piezoelectric assembly, the cut, axial length and thickness of active elements which make up the inner piezoelectric reinforcement structure are identical to the cut, axial length and thickness of the active elements which make up the outer piezoelectric assembly such that, during operation, the active elements of both the outer piezoelectric assembly and the inner piezoelectric reinforcement structure display the same axial displacement to support one another for the intended reinforcement effect, characterized in that the outer piezoelectric assembly comprises four outer active elements and said four outer active elements successively adjoin each other along their axial-length edges, with the aid of edge guides, to form a square pipe construction; in that the inner piezoelectric reinforcement structure comprises four first inner active elements which successively adjoin each other along their axial-length edges, with the aid of edge guides, to form a first inner square pipe reinforcement structure, and in that the four axial edges of said first inner square pipe reinforcement structure respectively abut, bonded with the aid of edge guides onto, corresponding inner surfaces of the outer piezoelectric assembly, forming diagonal truss support to the outer piezoelectric assembly. <EOS>