In 2004 Jansen et al. developed a linear actuator used as a drive module in an angular positioning mini-actuator [Jansen 2004]. In the same year 2004 Strittmatter (figure below) proposed a shape memory alloy actuator for the activation of a hydraulic valve [Strittmatter 2004] . When an electric current is applied, shape memory alloy wires contract and cause a movable ange to shift; the ange possesses a shaft that transfers the movement outside the closing screw. When energy supply is interrupted, an outside spring, not shown in figure, pulls the shaft back and the ange to the bottom of the closing screw.
Figure: SMA actuator by Strittmatter 2004. Linear device composed of (1)closing screw, (2) shaft, (3) guide plate, (4) ange, (5) SMA wires;