Local annealing of complex mechanical devices: a new approach for developing monolithic micro-devices

The concept of monolithic shape memory alloys (SMA) micro-devices is to integrate all device functions within the same piece of material. This is very interesting in the field of micro-systems, because assembly is avoided. In such devices, the main problem is to create a reversible motion. Recently, the use of the two-way shape memory effect has been investigated. A simpler solution could be to integrate a pullback spring within the monolithic structure. This implies introducing shape memory properties only in some predefined parts of the material. In this paper, an approach based on local annealing of the material is proposed. The annealed parts will exhibit a shape memory effect and the remaining non-annealed parts will have an elastic behavior. Two methods of local annealing have been investigated. The first one is done by an electrical current, which needs a special design of the electrical path. The second one is done by local laser heating, which allows complete freedom in choosing the 'memory regions' of the material. With these tools, complex mechanical devices with active and passive parts can be designed. To illustrate this idea, two mechanical structures containing locally annealed parts are presented.