a linear actuator includes a plurality of sub - modules disposed in adjacent array and adapted to translate reciprocally parallel to a common axis . a plurality of shape memory alloy wires extend generally linearly and parallel to the axis , and are each connected from one end of a sub - module to the opposed end of an adjacent sub - module . the sma wires are connected in a circuit for ohmic heating that contracts the sma wires between the sub - modules . the sub - modules are linked by the sma wires in a serial mechanical connection that combines the constriction stroke displacement of the sma wires in additive fashion to achieve a long output stroke . moreover , the sub - modules are assembled in a small volume , resulting in an actuator of minimal size and maximum stroke displacement . the sub - modules may be rods or bars disposed in closely spaced adjacent relationship , or concentric motive elements , with the serial mechanical connection extending from each motive element to the radially inwardly adjacent motive element , whereby the innermost motive element receives the sum of the translational excursions of all the motive elements concentric to the innermost element . the sma linear actuator includes a restoring spring assembly having a restoring force that decreases with increasing displacement to minimize residual strain in the sma components . the sma wires are connected for ohmic heating in various series and parallel circuit arrangements that optimize force output , cycle time , current flow , and ease of connection .