Frequency response of TiNi shape memory alloy thin film micro-actuators

Relatively independent of the physical dimensions of micro-actuators based on shape memory alloys (SMA), the reported frequency response typically is capped at a few tens of Hz. The slow response agrees well with that of the rotating micro-actuators fabricated in this work. On the other hand, based on heat transfer analyses, a theoretical response time on the order of a few milli-seconds should be possible for scaled micro-actuators, thus implying a frequency performance of at least a few hundred Hz. Therefore it is concluded that the response of SMA micro-actuators may not be limited by heat transfer, but by the slow rate of phase transformation between the austenitic and the martensitic phases. This is consistent with the slow phase growth rate of about 0.3 μm/s observed using in-situ transmission electron microscopy.