Electrostatic actuated micro mirror supported on torsion beam. Two separate electrodes under each section allow the mirror to be tilted about the axis of the torsion beam. The mirror itself forms the third electrode. Micro mirrors have application in display technology (such as Texas Instruments DLP) and can also be used as optical switches in the telecommunications industry.
ANSYS Multiphysics can be used to perform coupled electrostatic-structural analysis on the device, and can also perform a fluid-structural analysis to compute the squeeze film damping that dominates the response time of these devices. In this application example a static coupled electrostatic-stuctural analysis is performed using ESSOLV. Other possible analysis capabilities are listed here:
The mirror, electrodes and surrounding air/dielectric is included and meshed in the model. The mirror and electrodes have an axis of symmetry, and the ESSOLV model used here is the half symmetry model. Below is the full mesh of the mirror without electrodes:
Here is the half symmetry model meshed. Only a small volume round the mirror is discretized since the external boundary is treated as a TREFFTZ domain. Note also that only the surface nodes of the two electrodes under the mirror are required in the model, they are treated as perfect electric conductors:
The ESSOLV macro automates the coupled electrostatic-structural solution process, the image below shows the voltage contours for the mirror in its initial position, i.e. no rotation:
The results for both the electrostatic and structural degrees of freedom present in the model are available for review in postprocessing. Here are the displacements of the mirror (red=positive/maximum displacement, blue = negative/minimum displacement). Also, the /EXPAND command can be used to expand the half symmetry model to gain a more realistic image:
These results show the stress in the mirror, concentrated in the torsion support beams which are subjected to the rotational torque produced by the electrostatic field:
