Yoshikazu Hishinuma

Piezoelectric unimorph microactuator arrays for single-crystal silicon continuous-membrane deformable mirror

Micromachined deformable mirror technology can boost the imaging performance of an otherwise nonrigid, lower-quality telescope structure. This paper describes the optimization of lead zirconium titanate (PZT) unimorph membrane microactuators for deformable mirrors. PZT unimorph actuators consisting of a variety of electrode designs, silicon-membrane thickness, and membrane sizes were fabricated and characterized. A mathematical model was developed to accurately simulate the membrane microactuator performance and to aid in the optimization of membrane thicknesses and electrode geometries. Excellent agreement was obtained between the model and the experimental results. Using the above approach, we have successfully demonstrated a 2.5-mm-diameter PZT unimorph actuator. A measured deflection of 5 /spl mu/m was obtained for 50 V applied voltage. Complete deformable mirror structures consisting of 10-/spl mu/m-thick single-crystal silicon mirror membranes mounted over the aforementioned 4/spl times/4 4 PZT unimorph membrane microactuator arrays were designed, fabricated, assembled, and optically characterized. The fully assembled deformable mirror showed an individual pixel stroke of 2.5 /spl mu/m at 50 V actuation voltage. The deformable mirror has a resonance frequency of 42 kHz and an influence function of approximately 25%.

Optimized Design, Fabrication and Characterization of PZT Unimorph Microactuators for Deformable Mirrors

This paper describes an optimization of PZT unimorph membrane microactuators in view of their application to deformable mirrors (DMs). PZT unimorph actuators of various electrode designs, silicon membrane thickness, and membrane sizes were fabricated and characterized. A mathematical model was developed to further assist the optimization of membrane thickness and electrode sizes, and excellent agreement with experiment was obtained. For a 2.5m diameter actuator with 2pm thick PZT and 15pm thick silicon membrane, the measured vertical stroke was 5.4pm at 50V. The measured resonant frequency of the unimorph actuator was 47kHz, far exceeding the bandwidth requirement of most DMs (-1kHz).

Piezoelectric unimorph MEMS deformable mirror for ultra-large telescopes

This paper describes the results of our demonstration on a proof-of-concept piezoelectric unimorph-based deformable mirror (DM) with continuous single-crystal silicon membrane. A PZT unimorph actuator of 2.5 mm in diameter with optimized PZT/Si thickness and design showed a deflection of 5 μm at 50 V. DMs consisting of 10 μm thick single-crystal silicon membranes supported by 4×4 actuator arrays were fabricated and optically characterized. An assembled DM showed a stroke of 2.5 μm at 50 V with a resonant frequency of 42 kHz and influence function of approximately 25%.

Piezoelectric microactuator technologies for wavefront correction in space

There is a need for ever-larger apertures for use in space based optical imaging systems. Requirements on optical instrumentation for future observations in space will place rigorous demands on wavefront quality. The design of such mirrors involves a balance between the utilization of ultra-lightweight mirror and support structures, and the active correction of the increased deformations due to these compromises in structural rigidity. Performing wavefront control with a primary mirror requires precision and stability over a large structure. The wavefront correction, therefore, can be partitioned in spatial frequency between the primary mirror and a tertiary deformable mirror (DM). To realize the full potential of new ultra-lightweight, active primary mirror, the large-stroke microactuator and DM technologies need to be developed. This paper presents a set of candidate components: linear microactuator technology and a piezoelectric unimorph-based large-stroke DM technology, in the context of a lightweight active mirror concept.

Active Membrane Using Electrostructure Graft Elastomer for Deployable and Lightweight Mirrors

An important requirement enabling future space missions is the availability of very large, deployed, re-configurable apertures for high-resolution imaging. Membrane-based architectures have the potential for very low aerial densities, which will enable large aperture space telescopes. Two major requirements for considering large apertures are: 1) a high degree of surface control coupled with a low-mass deployable capability and 2) an optical quality membrane mirror technology. Current state-of-the-art deployable aperture technologies have significant limitations in their ability to correct the surface figure following deployment. In this paper, a controlled deformation of silicon membrane mirrors using electroactive polymer has been demonstrated to overcome these limitations. We have designed, modeled, and fabricated Electrostrictive Graft Elastomer (G-elastomer)-based bi-layer membranes. The bi-layer mirror membranes maintain a good working condition after thermal cyclic tests, performed at temperatures between −50 °C and 150 °C. G-elastomer provides means to drive and control the deflection and curvature of reflective membranes. Several G-elastomer-based bi-layer structures have been optically characterized. This concept can be scaled to a deployable ultra-large mirror with a self-reconfiguration capability.Copyright