A piezoelectric polymer element such as a fibre or film is described, having a solid cross-section and a substantially homogeneous composition. A method of forming such a piezoelectric polymer element is also described. The method has the steps of extruding a polymer material and concurrently poling a region of the extruded material. Apparatus for forming such a piezoelectric polymer element is also described that comprises an extruder for extruding a polymer element from a granular feed and a pair of electrodes for applying an electric field across a region of the element concurrently with its extrusion. Also described is a piezoelectric construct having such piezoelectric polymer elements interposed between two conductive layers. A system for converting mechanical energy into electrical energy is described in which each of the piezoelectric construct' s two conductive layers is connected to a respective terminal of a rectifying circuit.