US3047860A - Two ply electromagnetic energy reflecting fabric - Google Patents

Description

July 3T,962 A. B. swALLcSw ETAL 3,047,860

TWO-FLY ELECTROMAGNETIC ENERGY REFLECTING FABRIC Filed Nov. 27, 1957 -2 Sl'leets--Sheefl l INVENTORS. B. Swa//Ow @L i j im July 31, 1962 A. vB. swALLow l-rrAL 3,047,850

TWO-FLY ELECTROMAGNETIC ENERGY REFLECTING FABRIC Filed Nov. 27, 1957 2 Sheets-Sheet 2 INVEN 0 S. vas iz'fz B @hand/er E. wal/ow,

BYL/W ,VH1/LIM ATTORNEYS.

B'h@ Patented July 3l, 1962 fcelllhandler E. Swallow, Jr., 65 Lyon St., Paw- Filed Nov. 27, 1957, Ser. No. 699,388 3 Claims. (Cl. 343-18) This invention relates to a reflector for electrical energy of the space type which is more commonly known as electromagnetic energy.

Reilectors of the type used for radio and radar radiation have heretofore comprised a sheet of metal or metal foil against which the electromagnetic waves were impinged and reflected; or a screen formed from intermeshed wires of metal, woven or formed to provide some type of open mesh construction; or a fabric coated or plated with metal. In each case the reflecting surface has had a relatively large weight per unit area and was subject (depending on the reflecting material used) to varying degrees of corrosion and of limited flexibility. In constructing reflectors of large refecting surface of any of the mentioned reflecting materials, relatively rigid and heavy frames had to be constructed to suspend or support the reflecting surfaces. Rellectors carried `aloft or suspended from balloons made out of such reflecting surfaces and frames are limited in size (and thus useful rellecting surface) by the weight of the material of the reflecting surface and supporting frames. Also such reflectors are awkward to package, transport, and erect. They also restrict the launching sites of balloon-s `from which they might be suspended to those places where the reflectors can carefully be handled during launching. Suspending such reflectors from a balloon also endangers the balloon by offering sharp edges Iand corners which might puncture the balloon. At the same time they inhibit the suspension of other objects from the balloon such as instruments by occupying space below the -balloon and using up a portion of the weight lifting power of the balloon.

One of the objects of this invention is to provide an electromagnetic wave reflector which may be simply and inexpensively formed.

Another object of the invention is to provide a rellector which will be of very light weight so that it may be easily suspended in the air.

Another object of the invention is to provide a reflector that will not corrode or change its reflective properties iu the presence of moisture or other corrosive elements in the atmosphere.

Another object of the invention is to provide ya reflector that is extremely flexible and will not lose its reflective properties under continual flexing or fluttering.

Another object of the invention is to provide a reilector which can be constructed within a balloon, collapsible with the balloon for ease of packaging storage, transportation and erection.

Another object of the invention is to provide :a reflector suspended inside a balloon which is self erecting on inllation of the balloon.

Another object of the invention is to provide a reflector of large reflecting surface that can be carried al-oft or mounted on the ground which is of extremely light weight, inexpensive and capable of storage in a small space.

Another object of the invention is to provide a rellector which may be easily formed by known netting machinery so that the cost of manufacture is exceedingly low.

Another object of the invention is to provide a reilector which is formed from metallic strands having an insulating covering that will reilect lall polarizations of electromagnetic energy by providing two plies of net so that the effective metallic conductors are arranged at right angles to each other.

Another `object of the invention is to provide a reflector vfor electromagnetic waves of a net or mesh material whose openings remain constant and need only be small enough to adequately reilect the waves of the frequency desired.

With these and other objects in view, the invention consists of certain novel features of construction, as will be more fully described and particularly pointed out in the appended claims.

In the accompanying drawings:

FIGURE l is a plan view of an open mesh with the strands arranged longitudinally in one direction the ties being omitted for clarity;

FIGURE 2 is a plan view of an open mesh with the strands arranged in a direction at right angles to the showing in FIGURE 2 with the ties omitted for clarity;

FIGURE 3 is a plan View of a fragment and on a larger scale showing the strands of either FIGURE l or 2 tied together.

FIGURE 4 is a plan view of the two plies shown in FIGURES l and 2 as superimposed one on the other;

FIGURE 5 is a perspective view of the end of a strand of the material which we use in this invention;

`FIGURE 6 is a View similar to FIGURE 5 of ya modified strand.

FIGURE 7 is a longitudinal sectional view of a dillerent modified form of strand;

FIGURE 8 is an edge view of the two-ply construction of FIGURE 4;

FIGURE 9 is a plan view of a modified woven mesh fabric;

FIGURE l0 is an elevation of the rellecting net in trihedral form;

FIGURE ll is a plan view of one section of the reilector shown in FIGURE 10;

FIGURE 12 is a sectional view of the balloon with the net therein in inflated relation;

FIGURE 13 is an elevational view of the balloon having the net therein in collapsed relation.

In proceeding with this invention, we utilize a strand of material comprising essentially a ribbon of aluminum foil which is encased within a non-metallic covering. A material known as Mylar or Daeron or some resin which may be heat sealed is suitable. This strand of material is then formed into an open mesh fabric with an arrangement so that the effective electrical conductors are at right angles to each other. A fabric so `formed is then shaped into a desired reflecting unit such, for instance, as three planes arranged at right `angles to each other in a trihedral form and suspended from the six corners. This arrangement may be placed within a balloon and fastened therein in any fashio-n for extending the surfaces as desired and the fabric construction accordingly permits collapsing of the balloon without any further manipulation.

With reference to the drawings and particularly FIG- URE 5, l0 designates a strand of material which is used in connection with this invention and has a core of aluminum ribbon 11 which is laminated with layers l2, 13 of a non-metallic material such as a polyester resin known as Mylar which is a polyester film made from polyethylene terephthalate, the polymer formed by the condensation reaction between ethylene glycol and terephthalic acid or Daeron which is a trademark for a synthetic polyester fiber made from methyl terephthalate and ethylene glycol. Vinyl coating capable of being heat set may be used as a covering.

The strand material may in some cases comprise a metal ribbon 1l as in FIGURE 6 with a vinyl coating 12 surrounding it on all sides. Again the metal ribbon 11 (see FIG. 7) may be twisted with a reinforcing synthetic yarn 11 such as nylon and then the twisted structure coated with a resin 13' to protect the metal. A net machine for making sh net may then be used to form this strand material into a fabric form consisting of a plurality of longitudinally extending strands 14, 15, 16, 17 and 18 which are zigzagged by the machine as at location 25 with the zigzags of one strand knotted with the zigzags of the other strand at their points of meeting 26. (See FIG. 3.)

In the showing of FIGURE 1, strands are illustrated in a plane parallel to the plane of the paper as extending vertically of the paper while in FIGURE 2 we have illustrated the same with the strands at right angles to the showing in FIGURE 1 or horizontal with reference to the paper. In this case, the similar reference numerals are applied except that they are given a prime designation.

Radar waves may be polarized, and it is found that if the strands of our reflector happen to extend in the same direction as the polarization, they will give good reflection, but if they happen to lbe at right angles to the polarization of the electrical energy waves, they will not give good rellection. This comes about since no contact is made at the points of meeting 26 due to the insulated character of the strand comprising the insulated covering 12, 13 about it. In order to overcome this lack of conductivity, we superimpose one ply such as shown in FIGURE 1 upon the other such as shown in FIGURE 2 and secure these in such relation in any suitable way such such as by heat setting them together so that the longitudinal extent of the strands will be at right angles to each other. Thus, we may provide for good reilective characteristics regardless of the polarization of the waves to be reflected, be they horizontal or vertical.

In some cases the mesh fabric used may be formed by weaving, as shown in FIGURE 9, a metallic core strand having a vinyl which may be heat set to cause the intermeshing strands to become fixed to each other. Thus, we provide warp strands 40 and filling strands 41 extending at right angles thereto. This formation will provide the electrical conductivity in right angular directions as is desired without superimposing one fabric on another. The points of crossing may be secured by heat and pressure to weld the points of crossing together.

The reflective properties of a net of this character also bear some relation to the waves which are to be reflected. So long as the wavelength of the radiation is longer than the sides of the openings in the net, they will be reflected. We may, however, with the use of this very soft like material provide a net with very small openings, in fact, sufficiently small so that they will be smaller than the shortest wave lengths which are now used, even in microwave frequencies. It is thought, however, that it would be best to have the openings of a diameter no greater than one sixth of the wave length of the wave which is to be reflected. Accordingly, the mesh net may -be formed with various size openings, depending upon the intended use to which it is to be put, the reflective properties, so far as the openings are concerned, being a direct function of the wave lengths of the electrical energy which is to be reflected.

Some reflective shapes have been found to be better than others to accommodate all directional transmissions; and in FIGURE 10, we have shown the net reflector as formed in a trihedral shape which is provided by forming three planes of reflective surfaces at right angles to each other and giving eight dierent pockets when suspended from a corner, which will cause very good reflection regardless of the direction in which the waves are transmitted. This very soft flexible net so formed may further be suspended from its six corners 30, 31, 32, 33, 34 and 35 in a balloon 36 so that it may collapse with the balloon or when the balloon is inilated, it will be stretched out to the form shown in FIGURE 10 and 12. Thus, the balloon may be in the collapsed form as shown in FIGURE 13 when not in use, and easily transported from one location to another.

We claim:

i1. A reflector for electromagnetic energy within a band of frequencies comprising two plies of open mesh net the strands of which comprise a metallic core with a non-metallic covering encasing the core with each of the strands in one ply extending generally in one direction without electrical conductive connection to adjacent strands and each of the strands in the other ply extending generally at right angles to said direction without electrical conductive connection to adjacent strands.

2. A reflector as in claim 1 wherein the openings in the mesh net are smaller than the shortest wave length within the band of frequencies of the energy to be rellected.

3. A reflector as in claim 1 wherein the strands in one ply lie in a zig-zag path in one direction and the strands in the other ply lie in a zig-zag path in the other direction, each ply of said strands being knotted at intervals with similarly extending strands.

References Cited in the ille of this patent UNITED STATES PATENTS 2,031,720 Lee et al Feb. 25, 1936 2,419,549 Griesinger et al Apr. 29, 1947 2,436,578 Korn et al. Feb. 24, 1948 2,463,517 Chromak Mar. 8, 1949 2,533,439 Elder Dec. 12, 1950 2,576,255 Hudspeth et al Nov. 27, 1951 2,812,570 Petersilie et al Nov. 12, 1957 2,888,675 Pratt et al. May 26, 1959 FOREIGN PATENTS 505,877 Great Britain May 18, 1939 758,090 Great Britain Sept. 26, 1956

Images