United States of America As Represented by the Secretary of the Air Force

The United States of America As Represented by the Secretary of

James M Wilkes

Richard A Carreras

Dennis C Duneman

Dan K Marker

James R Rotge

Marvis N Gillum

Arthur H Waldie

An optical quality, freestanding, compliant membrane mirror is cast with a concave parabolic shape, and includes a substrate and a reflective stress coating. The stress coating is in compression and applies a tensile shear stress to the substrate that opposes and offsets the intrinsic stress in the substrate that would otherwise decrease the concavity. The stress coating generates a force to restore the membrane mirror to its cast concave parabolic shape when an external force deforms the mirror.

Parabolic membrane mirror having a shape-restorative force

A method for fabricating an optical quality, free-standing, compliant parabolic membrane mirror using an inverted parabolic mandrel created by rotating a liquid confined to a cylindrical polymer and applying a reflective optical stress coating once the substrate has hardened. The stress coating applies a tensile force to the substrate that offsets the stress in the substrate that would otherwise decrease the convexity, and also generates a force to restore the membrane mirror to its original convex parabolic shape when the mirror is deformed by an external force.

Method of centrifugally casting a parabolic membrane mirror having a shape-restorative force

A membrane mirror having an optical quality spherical shape maintained by differential pressure takes a near parabolic shape when a plunger-induced displacement of the central area of the mirror is introduced. The focal length can be adjusted by varying the differential pressure.

Plunger controlled, near-parabolic optical membrane mirror

A thin membrane is mounted on an optically flat circular outer ring and stretched over a smaller optically flat circular inner ring. Differential pressure is applied to the annulus formed between the inner and outer rings to prestrain the membrane and separately applied to the inner ring where the mirror figure will be produced. The inner ring has a doubly curved top surface and is optically fiat so that the membrane can freely move across the inner ring as incremental stress is applied via the annulus. A calculated combination of annulus stress and differential pressure on the inner ring produces an optical quality mirror figure in the inner ring area.

Active edge controlled optical quality membrane mirror

Physical properties relating to permeability and porosity of a material in a conveying fluid medium are determined in a device designed to measure the pressure differential between a first stream of fluid applied directly to the material in the medium and a second stream applied to a referencing plenum containing only the medium. The system is sensitive to the component of flow resistant imparted by the material itself without measuring the pressure drop across the entire thickness of material. The invention finds particular application in determining the permeability of cotton at various stages of the ginning operation for the ultimate purpose of monitoring and controlling the moisture content.

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Sandia Park, NM, United States of America

James M Wilkes