An electro-active element comprises at least one elongate member of electro-active material extending along a curve and having two pairs of electrodes spaced across the width of the elongate member radially of the curve. The electrodes of each pair extend along the length of the elongate member on opposite sides of the member for developing an electric field across a region of the member therebetween on activation. The material of the elongate member in each region is poled parallel to the electric field to be capable of activation in an expansion-contraction mode with a differential change in length of the two regions concomitantly with bending of the member parallel to the width of the member so that said bending is concomitant with relative rotation of the ends of the element about an axis on the inner side of the curve. The electro-active element may extend along a helix. The helix may itself extend along a curved axis resulting in a device which twists around the curved axis and concomitantly generates linear displacement between the ends of the device on activation. Similarly, devices formed from a plurality of elements coupled together to generate relative rotation and parallel may be arranged successively along a curved axis so that the resultant structure twists around the curved axis concomitantly relative displacement of the ends of the device occurs. The preferred method of manufacture is to form the elongate member form sintered material and subsequently apply electrodes to the sintered material this has the advantage that is unnecessary to co-fire the material during sintering.
