Applications of Film and Foil-Based Shape Memory Alloy Devices

Shape memory alloys (SMAs) such as ‘nitinol’ are nowadays available in a wide range of semi-finished products. While two- and three-dimensional passive structures made from superelastic SMA foils and tubes – like e.g. medical stents – have been commercialized with great success, most SMA actuator products are on the other hand still based on simple structures like wires and coiled springs. However, planar actuators fabricated from SMA films or foils offer a number of specific advantages, including design flexibility, complex modes of motion and fast response times due to a favorable surface-to-volume ratio. The company memetis GmbH, a spin-off from Karlsruhe Institute of Technology (KIT), has committed itself to the commercialization of such planar actuators for linear motion, fluid handling, optics and other applications with small available installation space. A selection is presented in this contribution. As one of the first products, a miniaturized de-coupling mechanism for model trains has been introduced to replace a considerably bulkier electromagnetic drive. The mechanism is based on a planar meandering TiNi foil actuator pre-strained by a leaf spring. A second group of products includes components for fluid handling, like normally open (NO), normally closed (NC) and bi-stable miniature valves, which are operated by cross-shaped TiNiCu film actuators working in out-of-plane direction. Beyond these actuator applications, the possibility of performing solid-state cooling or damping with superelastic SMA foils is illustrated.