Investigation of dynamic thermal behaviors of an electrothermal micromirror

It is well known that the heat transfer at microscale is quite different from that at macroscale, but the dynamic thermal behavior of micro-actuators with movable microstructures still lacks comprehensive investigation. This work presents a thorough study on thermal behaviors of an electrothermally actuated scanning micromirror, which has a 1 mm × 1 mm central mirror plate supported on four sides by four pairs of electrothermal bimorph actuators. The heat transfer from the thermal actuator to the ambience, including the substrate and the environmental air, are investigated experimentally with several different driving powers and various frequencies under natural convection, forced convection, and in vacuum. The results indicate that the heat conduction dominates the heat transfer process of electrothermal bimorph actuators, while the convection has little impact on the overall heat transfer even under strong forced convection. Furthermore, an equivalent circuit model of the electrothermal micromirror is developed and experimentally verified, from which the effective heat transfer coefficient of the electrothermal bimorphs is extracted to be in the range from 1900 to 2282 W/(m² K), which is one to two orders of magnitude larger than that at macroscale.