129 research outputs found
A soft actuation system for segmented reflector articulation and isolation
Segmented reflectors have been proposed for space based applications such as optical communication and large diameter telescopes. An actuation system for mirrors in a space based segmented mirror array was developed as part of NASA's Precision Segmented Reflector program. The actuation system, called the Articulated Panel Module (APM), provides 3 degrees of freedom mirror articulation, gives isolation from structural motion, and simplifies space assembly of the mirrors to the reflector backup truss. A breadboard of the APM was built and is described
Modeling of micro- and nano-scale domain recording by high-voltage atomic force microscopy in ferroelectrics-semiconductors
The equilibrium sizes of micro- and nano-domains caused by electric field of
atomic force microscope tip in ferroelectric semiconductor crystals have been
calculated. The domain was considered as a prolate semi-ellipsoid with rather
thin domain walls. For the first time we modified the Landauer model allowing
for semiconductor properties of the sample and the surface energy of the domain
butt. The free carriers inside the crystal lead to the formation of the
screening layer around the domain, which partially shields its interior from
the depolarization field. We expressed the radius and length of the domain
though the crystal material parameters (screening radius, spontaneous
polarization value, dielectric permittivity tensor) and atomic force microscope
tip characteristics (charge, radius of curvature). The obtained dependence of
domain radius via applied voltage is in a good quantitative agreement with the
ones of submicron ferroelectric domains recorded by high-voltage atomic force
and scanning probe microscopy in LiNbO3 and LiTaO3 crystals.Comment: 21 pages, 5 figure
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Control of micromachined deformable mirrors
A micromachined deformable mirror with pixelated electrostatic actuators is proposed. The paper begins with a physical description of the proposed mirror. Then a mathematical model in the form of a nonlinear partial differential equation describing the mirror surface deformations is derived. This model is used to derive the required voltages for the actuators to achieve a specified static deformation of the mirror surface. This is followed by the derivation of a static nonlinear feedback controller for achieving noninteracting actuation. Then the structure for a complete control system for wavefront correction is proposed. The paper concludes with a discussion of the physical implementation of the proposed control system
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