Thermal actuators

In figure 16a, a beam is machined from one material (e.g. silicon), and a layer of material with a different coefficient of thermal expansivity (e.g. aluminium). When the two are heated, one material expands faster than the other, and the beam bends (figure 16b). Heating may be accomplished by passing a current through the device; heating it electrically.

Figure 16.

Figure 16c shows a cavity containing a volume of fluid, with a thin membrane as one wall. Current passed through a heating resistor causes the liquid in the cavity to expand, deforming the membrane (figure 16d).

Whilst thermally actuated devices can develop relatively large forces, the heating elements consume quite large amounts of power. Also, the heated material has to cool down to return the actuator to its original position; so the heat has to be dissipated into the surrounding structure. This will take a finite amount of time, and may affect the speed at which such actuators can be operated.