Modeling Optical Absorption for Heat-Induced Actuation of Single-Use Microgrippers

Report No. ARL-TR-6063
Authors: Christopher J. Morris
Date/Pages: July 2012; 32 pages
Abstract: Optical power represents a viable way to wirelessly actuate microsystems and minimize the need for conventional onboard power storage. One approach is to use mechanical stored energy in residually stressed thin films and trigger the release of this energy by mechanically softening a polymer through thermal or chemical stimuli. Building on past reports of circular arrangements of actuators based on this approach to form free-standing microgrippers, this report presents analytical and numerical thermal models that help interpret experimental measurements of actuation behavior as a function of applied optical power. The models showed that steady-state microgripper surface temperature rise ?ΔT was directly proportional to irradiance and microgripper size, which for the example of a 1.4-mm-diameter microgripper leads to a lower limit of 343 mW/cm2 to reach ?ΔT = 20 °C, at which actuation can be expected. The transient relationship between the time to the reach actuation temperature and irradiance I0 was found to range between a 1/I02and a 1/I0 power law, as the distance to a neighboring substrate ranged from zero to infinity. These results yielded reasonable predictions of microgripper closing temperatures in different experimental conditions, and successfully explained different the power law regimes observed.
Distribution: Approved for public release
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Last Update / Reviewed: July 1, 2012