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Publication numberUS3855598 A
Publication typeGrant
Publication dateDec 17, 1974
Filing dateAug 29, 1972
Priority dateOct 23, 1970
Publication numberUS 3855598 A, US 3855598A, US-A-3855598, US3855598 A, US3855598A
InventorsKeller L
Original AssigneeHughes Aircraft Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Mesh articles particularly for use as reflectors of electromagnetic waves
US 3855598 A
Abstract
A non-woven mesh reflector for radio waves comprises two or more parallelly positioned layers of electrically conductive high modulus, high yield strength, inextensible fibers. The fibers in each layer extend parallel to each other and the fibers of one layer extend in a direction different from the direction of the fibers of the other layer. Examples of fibers include wires of beryllium, aluminum, stainless steel type 304, CHROMEL R, INVAR 36, and other alloys of the stainless steel INVAR type.
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Description  (OCR text may contain errors)

United States Patent 11 1 [111 3,855,598

Keller Dec. 17, 1974 [54] MESH ARTICLES PARTICULARLY FOR 3,286,259 ll/l966 Carman et al. 343/18 USE s REFLECTORS 0F 3,354,458 11/1967 Rottmayer 343/18 ELECTROMAGNETIC WAVES 3,513,474 5/1970 Gest et a1 343/915 [75] Inventor: Leon B. Keller, Palos Verdes FOREIGN PATENTS OR APPLICATIONS Peninsula, Calif. 758,090 9/1956 Great Britain 343/915 [73] Ass1gnee: gaghecsazltz rcraft Company, Culver Primary Examiner Eli Lieberman Attorney, Agent, or FirmJames K. Haskell; Lewis B. [22] Filed: Aug. 29, 1972 Sternfels 21 Appl. No.: 284,508

57 ABSTR CT Related US. Application Data 1 A [63] Continuation of Ser No 83 375 Oct 23 1970 A non-woven mesh reflector for rad1o waves comubandoned prises two or more parallelly positioned layers of electrically conductive high modulus, high yield strength, [52] U S Cl 343/840 343/897 343/915 inextensible fibers. The fibers in each layer extend [51] d 15/20 parallel to each other and the fibers of one layer ex- [58] Fie'ld 840 897 tend in a direction different from the direction of the fibers of the other layer. Examples of fibers include wires of beryllium, aluminum, stainless steel type 304, [56] References CM CHROMEL R, INVAR 36, and other alloys of the UNITED STATES PATENTS stainless steel INVAR type. 2,674,693 4/1954 Millett et a1. 343/915 3,224.000 12/1965 Bloetscher et al. 343/18 10 Claims, 3 Drawing Figures MESH ARTICLES PARTICULARLY FOR USE AS REFLECTORS OF ELECTROMAGNETIC WAVES This is a continuation of application Ser. No. 83,37 5, filed Oct. 23, 1970, now abandoned.

This invention relates to electrically conductive mesh articles characterized by being flexible yet inextensible and thermally stable. More particularly, but not necessarily exclusively, the invention relates to electromagnetic wave reflective articles and materials in mesh form which are electrically conductive, and are of exceptional light weight, flexibility and dimensional thermal stability, having a high modulus of elasticity and high yield strength. Such articles and materials may be readily formed and maintained in extremely accurate shapes.

The articles and materials of the present invention are especially useful for lightweight radar antennas and particularly where such antennas are to be used in remote or inaccessible terrestial places or in space, as on space satellites or celestial bodies (e.g., the moon).

Heretofore, it has been customary to utilize solid metal surfaces for the reflection of electromagnetic waves, especially radio waves, in such applications. These solid reflective articles have been produced from sheet metal, metal foil, or metal-coated substrates. Such applications noted above require radio wave reflectors to possess many diverse properties which often are incongruous and usually not achievable in solid structures. Thus, large size and low weight are usually required as well as flexibility and dimensional and structural rigidity, especially to environmental and maneuvering conditions. At the same time, the ability to be packaged in a small volume, as during transit to a space station or to a remote or relatively inaccessible locale on earth, and the ability to be deployed thereat into the correct shape, are desirable features. Heretofore some of these properties have been sought in approaches utilizing umbrella-like structures consisting of spokes and mesh, metallized polymeric films reinforced with plastic or foam capable of being hardened in space, or petaloid structures made of a large number of electroformed metal (i.e., nickel) segments which are mechanically unfurled. It will be appreciated that these various constructions have possessed disadvantages such as high weight per unit area of reflective surface (i.e., 0.1 to 0.3 lb./sq. ft. of deployed surface), mechanical complexity, poor dimensional accuracy, and low reliability. Perforated or expanded metal reflectors, or woven and/or welded wire grids have also been used with a sacrifice in lightness, flexibility, and foldability.

In contrast to prior structures, the conductive mesh articles and materials of the present invention are lighter by several orders of magnitude with respect to the comparable prior art constructions and exhibit flexibility and foldability prior to deployment into shape as well as being more dimensionally precise. Constructions achieved according to the present invention, for example, weighfrom 0.001 to 0.003 lb./sq. ft. of deployed surface. In the case ofa l-foot diameter paraboloid design made according to the invention, deviation from the true paraboloid was estimated to be i 0.125 inch compared to a predicted deviation of i 1.0 to i 3.0 inch for such paraboloids fabricated according to the prior art.

The present invention obtains these characteristics by being formed of an unwoven mesh of two or more layers of fibers having a high modulus of elasticity and a high yield strength and which are inextensible. The mesh can be formed into a smoothly contoured shape from the individual fibers or wires without such interweaving of the wires over and under each other. Such interweaving or crimping of the elements of a mesh or cloth is undesirable when a highly accurate and dimensionally precise shapeis required by some uses at the present invention. Interweaving or crimping cannot obtain such a shape due to the phenomenon know as crimp elongation" in which the fiber element elongates grossly when tension is applied to it, that is, the woven elements tend to elongate by straightening out when tension is applied to them. This effect is eliminated in the invention by deliberately refraining from interweaving the fibers, thereby eliminating stretching and deformation of the desired shape when it is deployed. In addition, it is also possible to make articles which possess a smooth, doubly curved shape without gaps, laps, seams, or discontinuities. The elimination of such discontinuities and inhomogeneities is essential to the production and maintenance of the precise shapes.

It is therefore an object of the present invention to provide an improved electrically conductive mesh article of prescribed shape and which is dimensionally accurate and stable.

Another object is the provision of such an article having a smoothly contoured shape.

Another object is to provide such an article which is easily produced and maintained.

Another object of the invention is to provide an improved mesh article of prescribed shape suitable for use as a reflector of electromagnetic energy.

Another object of the invention is to provide an improved electrically conductive mesh article of prescribed shape, which is dimensionally accurate and stable, of lightweight, which is flexible, and capable of being folded into a small volume prior to deployment into the prescribed shape.

Still another object of the invention is to provide an improved mesh reflector for radio waves wherein the mesh-forming elements and spaces may be precisely established and maintained.

These and other objects and advantages of the invention are realized by providing mesh-forming material or elements comprising fibers of high tensile strength, low

, elongation properties, and low coefficient of expansion which fibers are of, for example, beryllium, aluminum, or stainless steel.

By forming such fibers of appropriate diameters and by maintaining the prescribed spacing therebetween when formed into a mesh article, an excellent reflector of radio waves for a particular frequency thereof may be provided. Such mesh articles are light weight, flexible and foldable, and have a high modulus and a high yield strength. The mesh configuration is achieved by bonding the fibers together at their intersections. It was discovered that such mesh articles appear to possess what may be called a shape memory that aids considerably in deployment of the article to the desired shape after it has been folded.

The invention will be described in greater detail by reference to the drawings in which:

HQ. 1 is a perspective view partly in section of a mesh structure according to the invention;

FIG. 2 is an elevational view partly in section of a pair of intersecting fibers showing the same in greater de- For this material, as well as those others set forth in the above table, as well as other alloys of the stainless tail; and 5 fiber characteristics in manufacturing aprecisely shap- FIG. 3 is a perspective view of mesh r di wave ed mesh. These two properties are also the most imporflector according to the invention, tant characteristics in maintaining the deployed shape Mesh articles according to the invention are formed with high accura y under a variety of conditions. Howby threads or fibers having hi h tensile th, 1 ever, the ability of the mesh to be folded and packaged elongation, and a low coefficient of expansion. Suitable to in a Small Volume is dependent p the fiber diameter, fibers are available from beryllium and other metallic the modulus, and yifild strength according to the materials, which may be drawn from the molten state following relationship: into continuous fibers. Such fiber materials have properties which are suitable for use as mesh articles and which include: 15 R E X d/Zs Minimum Thermal Specific Bend Coefficient Specific Strength iiiLlS fQl' 522th. E :32:22 5123?: 52.22% psi lg psi l0" V inches Beryllium [.85 55 42 6.4 3.6 025 820 0.76 Aluminum 2.8 32 l0 l3 3.0 99 320 0.31 Stainless 8.0 80 28 [0.2 7l 97 280 0.35 Steel Type 304 INVAR 36 8.05 70 20.5 0.05 82 10 240 0.29 CHROMEL R 8.l5 90 31 10 H6 105 305 0.34

Trademark of Hoskins Mfg. CIL. Detroit. lll.

Referring to FIGS. 1 and 2, such inextensible fibers where R is the minimum diameter in inches to which a are stretched over a mandrel or surface having the defiber may be bent without causing a permanent kink, sired shape in parallel disposition so as to form a mesh 35 bend, or deformation; d is the fiber diameter in inches; structure with the desired mesh spacings and are bond- E is the modulus of elasticity in tension in pounds per ed together at their intersections with a bonding agent square inch, and s is the tensile yield strength in pounds or adhesive 12 preferably of the epoxide type although per square inch. in materials which exhibit no yield beother elastomeric and/or glassy adhesives may also behavior, the ultimate tensile strength may be substituted, employed. After curing or hardening the agent, a stable in which case the above formula provides the minimum mesh structure is obtained which is flexible and foldradius to which the fiber may be bent without breaking. able. Provided the fibers are not bent in an arc of smaller ra- In general, the fiber spacing is predetermined by the dius than given by the formula, they will tend to spring frequency of the radio waves to be reflected. The folback to their original shape without a permanent deforlowing table demonstrates the approximate relationmation. ln the table the minimum bend radius R has ship between fiber spacing and frequency to achieve been calculated for 0.002 inch diameter fibers. better than 95% reflectivity of the incident energy: When employed as a reflector for radio waves, the

' high porosity (95 percent at 8 GH of the mesh reduces solar shading problems to a minimum and further minimizes thermal distortions of the whole antenna and A spacecraft structural system. Likewise the low temperx/20. ature coefficient of the material essentially eliminates Band inches he's/Inch the thermal distortion problem in the reflecting surface VHF 300 39.4 M itself. At the same time, the high porosity of the mesh u 1200 9.8 0.6 2 permits the reflecting surface to be uniformly illumi- 238g 8'3 3 nated with minimum thermal gradients.

7000 0:104 As shown in H6. 3, a typical antenna structure 14 X 8000 0-093 11 according to the invention is a paraboloid mesh, the

- mesh being formed in the same operation as the paraboloid, yielding a smooth curved shape which is dimensionally stable and maintains its parabolic contour.'

AS noted Previously, a material Suitable fOY a mesh- Such an antenna mesh is essentially a network of fibers type reflector Of radio waves, especially for use in outer precisely spaced on a male mandrel of exafl paraboloispace, should be lightweight, strong, and electrically dal contour. The fiber spacing is predetermined by the conductive. The presently preferred fibers are of berylfrequency of the RF energy to be reflected. The fibers lium since it has a low density (1.85 gm/cc), a very high elastic modulus (42 X 10 psi), and a low coefficient of thermal expansion (6.4 X 10' per F).

of a first layer are all positioned on the mandrel and then the fibers of the second layer are placed over those of the first layer so that the planes of the layers are parallely disposed. The interweaving of fibers, as in normal cloth or screen, is avoided in the design of the mesh for the following reasons. The weaving of fibers causes a bending of the fibers at the cross-over points and the fiber is no longer a straight structural member able to support tensile loads without undue strain or elongation or stretching. Secondly, the interweaving of fibers complicates the fabrication of large meshes to an extreme degree because it requires weaving machinery to control the movement of each fiber as additional fibers are added to the pattern. The significance of this complication will be appreciated when it is considered that an antenna having a diameter of 120 feet and fibers per inch will require a total of 28,800 fibers having a total length of 660 miles.

According to the invention, the individual fibers are held in position and in correct relation to each other by bonding the fibers to each other at cross-over points or intersections. In this way, structural continuity is maintained throughout the mesh without deforming or bending the fibers. The fibers are laid individually in place in a predetermined winding pattern on a male mandrel of precise shape. Each fiber is bonded to a pcripheral ring and, after the entire mesh is in place, the fiber intersections are bonded. After removal of the mesh and ring assembly from the mandrel, it may be folded and packaged. A convenient way to fabricate the mesh structures of the invention is to machine grooves in the mandrel surface for retaining the fibers therein during assembly. These grooves may be V- shaped and only deep enough to accommodate the fiber. Small holes may be provided at the intersections of the grooves in order to free the fiber from the mandrel to permit unimpeded bonding.

Another method for fabricating a mesh structure for patterns other than geodesic is to spray a pressuresensitive adhesive on the mandrel. Fibers laid on the mandrel will therefore remain in position during bonding and may be warmed during application of the adhesive to insure adhesion or embedment into the surface layer. After completion of the mesh, the adhesive film may be chemically dissolved and the mesh removed from the mandrel. Vinyl or silicone-based adhesives and wax-like materials are satisfactory for this technique.

In applying the adhesive or bonding agent to the cross-over points of the fibers, it has been found that the adhesive wets and wicks between the intersecting fibers to form a small head. The adhesive bead cures to form a structural bond having a shear strength of from 2,000 to 3,000 psi. It is generally preferable, especially where the fibers are closely spaced and a mandrel without grooves is employed to place the first layer of fibers on the mandrel and bond each intersection of each fiber as the second and succeeding intersecting fibers are laid in place. This may be accomplished by mounting an adhesive applicator on the fiber feeding mechanism to precede the fiber and apply the adhesive thereto as it is fed onto the mandrel. After the first layer of fibers is complete, the adhesive applicator is adjusted in height to deposit a small amount, such as a drop, of adhesive on each fiber intersection location it passes over. The fiber being placed on the mandrel directly behind the adhesive applicator therefore encounters adhesive at each intersection.

An alternate and less complex procedure is to spray or brush the entire mesh with a dilute adhesive followed immediately with a dry brushing or blotting operation to remove excess adhesive except that which is wicked between intersecting fibers. While a thin resin coating might adhere to the upper surface of the fibers, the additional weight and stiffness added to the mesh would be negligible. As a variation of this method, a mask, either as a perforated sheet or tapes, it placed over the entire surface in such a manner as to expose only the intersection areas of the mesh. Adhesive may then be applied by brush, spray, roller, or the like to only the intersections. After the adhesive cures, the mask is removed.

The selection of a suitable adhesive for the bonding of the fibers is based primarily on ease of application and good wetting properties. A satisfactory adhesive giving excellent results is an amine-cured epoxy system. The joints resulting are formed by a resin bead approximately 1/32 inch in diameter. Typical adhesive for the purposes of the present invention comprises l00 parts of an epoxy prepolymer cross-linked by ten parts of diethylene triamine. The useful life of this adhesive system is 30 to 60 minutes at room temperature. Usually the adhesive system is prepared in gram batches and blended with 1 percent of a carbon black slurry to facilitate observability of the resin and the bead formed thereof. The epoxy resin cures to a hard glassy polymer in approximately 3 hours at room temperature. Flexible or rigid adhesive systems may be employed. Generally, with close fiber spacing of 10 per inch or more, it may be necessary to employ a low modulus, high elongation elastromeric adhesive to provide flexibility in the final mesh. Elastomeric properties may be imparted to epoxy adhesives by modifying them with polyamines. In addition, many silicone and polyurethane systems have the required properties.

All of the procedures described may be performed automatically and in multiple operations. Thus fibers may be laid down in gangs, in parallel courses using multiple reel, tension and feed assemblies. Also, the operation of bonding each intersection can be performed by simultaneously bonding a multiplicity of intersections with a properly designed multiple applicator.

One of the novel and advantageous features of a mesh article according to the invention is the fact that the article may be formed into a configuration having at least one axis of curvature and still be of one-piece or unitary structure. Previously, doubly-curved mesh articles, for example, had to be formed from a plurality of pieces which were joined together. The mesh articles of the invention are capable of being formed into such doubly-curved configurations without discontinuities and hence are referred to herein as unitary.

Although the invention has been described with reference to particular embodiments thereof, it should be realized that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

l. A folded antenna for radio waves comprising a peripheral support, a non-woven preformed flexible relatively inextensible mesh member secured to said support, said mesh member formed of solid, single-strand fibers intersecting one another and bonded together at each point of intersection, said fibers having a modulus of elasticity exceeding 10 X 10 psi and a yield strength exceeding 32 X 10 psi, said fibers selected from the group of materials consisting of beryllium, aluminum,

7 a first portion of said fibers extending in a common direction and lying in a common plane, a second portion of said fibers extending in directions other than the common direction in which said first portion lie and contacting said first portion fibers at points of intersection, said first portion being bonded to said second portion at the points of intersection, said fibers selected from the group of materials consisting of beryllium, aluminum, lNVAR 36, CHROMEL R, stainless steel type 304, and alloys of the stainless steel and INVAR type.

3. A foldable antenna for radio waves comprising a peripheral support, a preformed unitary flexible unwoven mesh member secured to said support, said mesh member having at least one axis of curvature and formed of intersecting solid, single-strandfibers of a modulus of elasticity exceeding X 10 psi and a yield strength exceeding 32 X 10 psi, with fibers extending in a common direction lying in a common plane different from the plane in which fibers extending in directions other than said common direction lie and bonded thereto, said fibers being selected from the group of materials consisting of beryllium, aluminum, lNVAR 36, CHROMEL R, stainless steel type 304, and alloys of the stainless steel and INVAR type.

4. A foldable antenna for radio waves comprising a peripheral support, a non-woven preformed flexible substantially inextensible mesh member secured to said support, said mesh member formed of solid, singlestrand fibers crossing one another at intersections and bonded together at the intersections, said fibers having a modulus of elasticity exceeding 10 X 10 psi and a yield strength exceeding 32 X 10 psi.

5. A foldable antenna for radio waves comprising a peripheral support, a preformed flexible substantially inextensible mesh member secured to said support, said mesh member formed of intersecting unwoven, solid, single-strand fibers having a modulus of elasticity exceeding 10 X 10 psi and a yield strength exceeding 32 X 10 psi, a first set of said fibers extending in a common direction lying in a common plane, a second set of said fibers extending in directions other than said common direction and crossing said first set at intersections, bonds securing said first set and said second set together at the intersections, said fibers being selected from the group of materials consisting of beryllium, aluminum, INVAR 36, CHROMEL R, stainless steel type 304, and alloys of-the stainless steel and INVAR type.

6. A foldable antenna for radio waves comprising a peripheral support, a preformed unitary flexible substantially inextensible mesh member secured to said support, said mesh member having at least one axis of curvature and formed of intersecting solid, singlestrand fibers having a modulus of elasticity exceeding 10 X 10 psi and a yield strength exceeding 32 X 10 psi with first fibers extending in a common direction lying in a common plane different from the plane in which second fibers extending in directions other than said common direction he, said first and second fibers bonded together at the intersections therebetween, said fibers being selected from the group of materials consisting of beryllium, aluminum, INVAR 36, CHRO- MEL R, stainless steel type 304, and alloys of the stainless steel and INVAR type.

7. A foldable antenna for radio waves comprising a peripheral support, a preformed flexible substantially inextensible mesh member secured to said support, said mesh member formed of at least two layers of intersecting solid, single-strand fibers having a modulus of elasticity exceeding l0 X 10 psi and a yield strength exceeding 32 X 10 psi, said fibers of a first of said layers extending in a first common direction and lying in a first common direction and lying in a first common plane, said fibers of a second of said layers extending in a second common direction different from the first common direction and lying in a second common plane different from the first plane, bonds affixing said fibers of said first and second layers at the intersections, said fibers being selected from the group of materials consisting of beryllium, aluminum, INVAR 36, CHRO- MEL R, stainless steel type 304, and alloys of the stainless steel and lNVAR type.

- 8. A foldable antenna for radio waves comprising a peripheral support, a preformed unitary flexible substantially inextensible mesh member secured to said support, said mesh member having at least one axis of curvature and formed of two layers of intersecting solid, single-strand fibers of a modulus of elasticity exceeding l0 X 10 psi and a yield strength exceeding 32 X 10 psi, said fibers of a first of said layers extending in a common direction and lyingv in a first common plane, said fibers of a second of said layers extending in a direction different from said common direction of said first layer and lying in a common plane and bonded to said first of said layers at the points of intersection therewith, said first and second common planes being parallel to each other, said fibers being selected from the group of materials consisting of beryllium, aluminum lNVAR 36, CHROMEL R, stainless steel type 304, and alloys of the stainless steel and lNVAR type.

9. A foldable antenna for radio waves comprising a peripheral support, a preformed flexible inextensible mesh member secured to said support, said mesh member formed of at least two layers of intersecting substantially inextensible solid, single-strand fibers, said fibers of a first of said layers extending in a common direction and lying in a common plane, said fibers of a second of said layers lying in a plane and extending in a direction other than said plane and said common direction of said first layer fibers and bonded thereto at the points of intersection therewith, said fibers being selected from the group of materials consisting of beryllium, aluminum, lNVAR 36, CHROMEL R, stainless steel type 304, and alloys of the stainless steel INVAR type.

10. A foldable antenna for radio waves comprising a peripheral support, a preformed unitary flexible mesh member secured to said support, said mesh member shaped as a parabola and formed of a first layer and a second layer of intersecting, substantially inextensible solid, single-strand fibers, said fibers of said first layer extending in a common direction and lying in a common plane, said fibers of said second layer extending in a common direction perpendicular to the common direction of said first layer and lying in a common plane consisting of beryllium, aluminum, lNVAR 36, CHRO- parallel to the common plane of said first fibers and MEL R, stainless steel type 304, and alloys of the stainbonded thereto at the intersecting points therewith, less steel INVAR type.

said fibers being selected from the group of materials

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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4609923 *Sep 9, 1983Sep 2, 1986Harris CorporationGold-plated tungsten knit RF reflective surface
US4812854 *May 5, 1987Mar 14, 1989Harris Corp.Electroconductive flexible reflective surfaces; microwave transmission
US5864324 *May 15, 1996Jan 26, 1999Trw Inc.Telescoping deployable antenna reflector and method of deployment
US7724203 *Sep 12, 2006May 25, 2010Cell Cross CorporationCommunication system, interface device, and signal carrying apparatus
US7898499 *Feb 15, 2006Mar 1, 2011Mitsubishi Cable Industries, Ltd.Electromagnetic wave shielding body
EP0336094A1 *Feb 22, 1989Oct 11, 1989PETOCA Ltd.Flexible materials for reflecting electromagnetic wave
Classifications
U.S. Classification343/840, 343/915, 343/897
International ClassificationH01Q15/14, H01Q15/16
Cooperative ClassificationH01Q15/161
European ClassificationH01Q15/16B