Thermal actuator is a micromechanical device that typically generates motion by thermal expansion amplification. A small amount of thermal expansion of one part of the device translates to a large amount of deflection of the overall device. These are commonly either of the bimetallic type, or rely on the expansion of a liquid or gas. A beam is machined from one material, and a layer of material with a different coefficient of thermal expansively. When the two are heated, one material expands faster than the other, and the beam bends. Heating may be accomplished by passing a current through the device; heating it electrically. A cavity contains 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. 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.