Abstract: An actuator that transforming electrical energy into mechanical energy (or vice-versa) that is particularly suited to portable applications requiring a high degree of efficient control, e.g. applications in which human-like movement needs to be simulated or interacted with. The actuator has a stator comprising electromagnetic sectors for generating phased electromagnetic fields around the stator and at least one cylindrical element (and preferably two such elements). The stator and the cylindrical element(s) are arranged concentrically around a central axis. The cylindrical element has permanent magnetic elements magnetized radially and arranged as one or more discontinuous helices. Phased magnetization of the stator causes the cylindrical element to rotate around the axis along a helical path, thereby exerting a longitudinal force along the axis.