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.
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.
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 www.techbriefs.com 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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Overview
The document presents a novel invention related to mirrors containing biomimetic shape-control actuators, developed by a team at NASA's Jet Propulsion Laboratory. This innovation addresses the challenges associated with traditional optical systems, particularly in achieving zoom capabilities without the drawbacks of lens-based systems. The primary problem identified is the difficulty in achieving a simple zooming action in mirror-based optical systems, which are preferred for their achromatic performance in space applications.
The invention proposes a fan-like arrangement of strips that can bend and conform to desired curvatures, allowing for adjustable mirror surfaces. This design enables precise control over both the quadratic and higher-order terms of the mirror's surface, which are crucial for maintaining image quality and correcting aberrations. Unlike conventional methods that rely on hydraulic, pneumatic, or mechanical forces, this approach offers superior surface controllability.
The document outlines the advantages of this technology, including the ability to deploy mirrors in a flat configuration and adjust their shape once in space, significantly saving on weight and volume. This capability is particularly beneficial for small satellites that can utilize large "umbrella" telescopes for astronomical or surveillance functions. The absence of gravity and wind in space further facilitates the control of the mirror shape.
Additionally, the invention has potential applications beyond imaging optics, including in antennas and solar collectors. The use of electroactive polymers (EAP) as the base material for the actuators promises high repeatability and robustness, enhancing the reliability of the system.
The document emphasizes that this technology is distinct from existing methods, as it allows for fine shape adjustments to correct aberrations and improve focusing accuracy. The innovative design and functionality of these shape-controlled mirrors position them as a significant advancement in optical technology, with implications for various fields, including space exploration and energy collection.
In summary, the document highlights a groundbreaking approach to mirror technology that leverages biomimetic principles to achieve adjustable optics, offering enhanced performance and versatility for future applications in space and beyond.
