Prestrained Thin-Film Shape Memory Actuators Offer Rapid, Strong Response
Prior use of thin films of SMA materials has been confined to the deposition of films onto rigid substrates such as silicon, limiting their use to planar elements which are not amenable to the pre-straining required to obtain maximum shape memory strain recovery. Prior SMA cyclic actuator systems using wires, springs or sheets require users to impart strains into the martensitic phase of an SMA material before use, to provide biasing forces to reset the actuator to a starting position on cooling. These straining operations often require substantial mechanical complexity and are generally not applicable to thin films deposited onto rigid substrates.
Description of Technology
In the invention, the use of a polymeric substrate gives the actuator a carrier film that greatly facilitates handling and installation, while the thin, flat form of the SMA provides a large surface area for easy and secure attachment. Unlike currently available shape memory alloy (SMA) wires, sheets and plates, the thin, flat form of the SMA film of the invention maximizes heat transfer rate to allow more rapid cyclic actuation. Alternatively, two-dimensional membranes may be fabricated that may express a variety of adaptive mechanical responses to environmental stimuli or which may be controlled by externally applied energy input.
- Fast: Relative to prior shape memory elements, the larger surface area of the invention provides for rapid energy transfer and therefore fast response to stimuli.
- Strong: The duel layer technology combined with the pre-stress of the invention provides for more powerful action compared to prior elements.
- Scalable: The construction of elements can be scaled from micron dimensions to devices many centimeters in size.
The potential areas of application are very diverse and could include any range of mechanical opportunties to include biomedical devices and robotics. Automotive applications could include mirror positioning, lamp positioning, door locks, and engine controls. Aerospace applications could include antenna operators, solar panel controls, dynamic optical element controls, jet engine mechanical controls, and aerodynamic form alterations in flight. Optically, the devices could position optical elements intended to adjust reflectivity or absorption of visible, RF, IR, or particle beams. In fluid systems, these devices might provide fluid controls by diverting flow or adjusting turbulence.
The technology is still in a research and development phase. Specific research and design will be needed for specific applications as they are considered.
US Patent 7,690,621
For Information, Contact:
Michigan State University