Graphical design for thin-film SMA microactuators

Simple graphical designs for bridge- and diaphragm-type actuators using shape-memory alloy (SMA) thin films are proposed. The performance (force and displacement) of these actuators is predicted on the basis of the stress–strain curves of an SMA film by introducing the material parameter K that represents the mechanical properties of both the austenite and martensite films. The methods of designing actuators are presented along with numerical examples and their validity is discussed, referring to some actual devices such as a microvalve and a micropump. A comparison of theory and actual device performance shows that the proposed design gives a useful approximation for practical applications. The advantage of the proposed design method is that, once the value of K is obtained for a given SMA film, one can design various actuators with various dimensions without detailed information about its mechanical properties.