Curved mirrors of a proposed type would comprise lightweight sheets or films containing integral, biologically inspired actuators for controlling their surface figures. These mirrors could be useful in such applications as collection of solar energy, focusing of radio beams, and (provided sufficient precision could be achieved) imaging. These mirrors were originally intended for use in outer space, but it should also be possible to develop terrestrial versions.

Figure 1. IPMC Multifinger Grippers have been adopted as models from which designs of proposed shape-controllable mirrors would be developed.

Several prior NASA Tech Briefs articles have described a variety of approaches to the design of curved, lightweight mirrors containing integral shape-control actuators. The primary distinction between the present approach and the prior approaches lies in the actuator design concept, which involves shapes and movements reminiscent of those of a variety of small, multi-armed animals. The shape and movement of an actuator of this type can also be characterized as reminiscent of that of an umbrella. This concept can be further characterized as a derivative of that of multifinger grippers, the fingers of which are bimorph bending actuators (see Figure 1). The fingers of such actuators can be strips containing any of a variety of materials that have been investigated for use as actuators, including such electroactive polymers as ionomeric polymer/metal composites (IPMCs), ferroelectric polymers, and grafted elastomers.

Figure 2. The Focal Length of a Curved Mirror would be varied by using its shape actuators to vary its curvature.

A mirror according to this proposal would be made from a sheet of one of the actuator composites mentioned above. The design would involve many variables, including the pre-curvature and stiffness of the mirror sheet, the required precision of figure control, the required range of variation in focal length (see Figure 2), the required precision of figure control for imaging or non-imaging use, the bending and twisting moments needed to effect the required deformations, and voltage-to-moment coefficients of the actuators, and the voltages accordingly required for actuation. A typical design would call for segmentation of the electrodes on the actuators so that voltages could be applied locally to effect local bending for fine adjustment of the surface figure.

This work was done by Yoseph Bar-Cohen, Pantazis Mouroulis, Xiaoqi Bao, and Stewart Sherrit of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at under the Mechanics category. NPO-30487.

This Brief includes a Technical Support Package (TSP).
Mirrors Containing Biomimetic Shape-Control Actuators

(reference NPO-30487) is currently available for download from the TSP library.

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