US3103662A - Inflatable eight-corner reflector - Google Patents

Description

Sept. 10, 1963 INFLATABLE EIGHT-CORNER REFLECTOR Filed May 19, 1959 EQDIO WAVE REFLECTIVE SHEET INVENTORS THOMFIS EDWARD HoRAcE GRAY JAMES Jones-mwrow HTTOIQNE Y T. E. H GRAY ETAL 3,103,662

United States Patent Company Limited, London County, England, a British company Filed May 19, 1959, Ser. No. 814,290 Claims priority, application Great Britain June 3, 1958 5 Claims. (Cl. 343-18) This invention relates to reflector devices for radio waves, and especially such devices used for radar purposes. The invention is concerned with such devices incorporating corner reflectors, comprising three plain reflective surfaces set mutually perpendicular to each other so as to define the internal corner angle of a cube. Such a reflector has the property of reflecting along a path parallel to their incident path waves striking any of its surfaces from any direction within the solid angle defined by the surfaces. In particular the invention is concerned with a device incorporating a reflector comprising eight corner reflectors with their apices coincident, as defined by both sides of three plane sheets intersecting each other at right angles. Such a reflector, which will be termed an octonary reflector, will reflect waves incident from any direction along a path parallel to their incident path. If each reflective surface of an octonary reflector is a right-angled triangle, the straight base edges of the triangular surfaces define the edges of an octohedron. For convenience such a reflector will be referred to herein as an octahedral reflector. If the triangles are isosceles the octahedron is regular.

It has been proposed to construct an octonary reflector of flexible radio wave-reflective sheet material which can easily be folded and packed for storage or when not required 'for use. These flexible reflectors must, however, be provided with some means for holding the sheets taut when in the erect position so that the reflective surfaces are all truly flat and correctly disposed in relation to each other. Rigid supporting members are not entirely convenient owing to storage difliculties and, if they are collapsible, the time that may be taken to erect them.

It has been proposed to mount an octonary reflector inside an inflatable spherical balloon of material permeable to radio waves by connecting the ends of the lines of intersection of the surfaces (the apices in the case of an octahedral reflector) to the internal surface of the balloon. This is a diflicult assembly since the parts must be secured together when the balloon is in its deflated condition, and if the connection points are not correctly positioned in the balloon, or if it expands unevenly on inflation, puckering of the reflective surfaces may result. Furthermore, if the balloon is to be made of material of low extensibility it is diflicult to construct the assembly with the desired accuracy owing to the problem of making a spherical or near-spherical balloon from essentially flat material.

According to the invention a reflector device for radio waves comprises an octonary reflector formed from flexible radio wave-reflective sheet material enclosed within and secured by its edges to an inflatable envelope of flexible material permeable to radio waves, of dimensions such that on inflation of the envelope the sheets of the reflector are held taut and in the desired relation to each other.

Since the edges of the reflector are secured to the envelope, the sheets of the reflector are not only pulled outwardly on inflation but the edges are themselves firmly held, restraining any tendency of the sheets to pucker.

The reflector and its envelope may be of any desired shape, but are preferably symmetrical.

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One embodiment of the invention is illustrated by way of example by the accompanying drawings in which:

FIGURE 1 is a perspective view of a regular octahedral reflector of the prior art.

FIGURE 2 is a perspective view of the reflector of our invention enclosed in its envelope and inflated in condition of use.

The reflector shown in FIGURE 1 is assembled from twelve identical sheets 1 of flexible radio wave-reflective material of right-angled isosceles triangular shape, secured together along their side edges 2 with their right-angled apices coinciding, so that their base edges 3, when the sheets 1 are all held taut and flat, define the edges of a regular octahedron.

The sheets 1 may be textile fabric, such as nylon mesh, with a metallic coating such as silver. Alternatively they may be formed from metal foil. They may be secured together along their edges 2 by any convenient means, for example by stitching or by adhesive. Preferably, however, the radio wave-reflective material is laminated to flexible plastic sheet for reinforcing it, and if the plastic is a thermoplastic the sheets 1 can be secured together by heat sealing.

The reflector shown in FIGURE 1, after assembly, is enclosed within an envelope of flexible radio wave-permeable material as shown in FIGURE 2. In this figure the envelope is shown in its inflated condition, in which it is substantially in the shape of a regular octahedron.

The envelope is assembled around the reflector from eight identical sheets 4 of the radio wave-permeable material, each of equilateral triangular shape with edges 5 of length equal to the edges 3 of the reflector. The sheets 4 are secured together and to the corresponding edges 3 of the reflector by these edges 5 so as to form a closed envelope which when inflated will be of the desired shape. One of the sheets 4 has an inflation valve 6 as shown, and some or all of the sheets of the reflector have openings for admitting inflating gas to all the compartments defined within the envelope by the reflector. Conveniently the tip of each corner 7 of the reflector may be cut off before assembling the envelope so as toprovide these openings.

On inflation the envelope is distended to its substantially octahedral shape, erecting the reflector and holding it in its position of use with the sheets 1 in the desired mutually perpendicular relation. Although the sheets 4 of the envelope may tend to belly out when inflated, so that the shape is not truly octahedral, the seams between the edges 5 and 3 Will remain straight so that the reflector sheets 1 are restrained from puckering.

The envelope sheets 4 may be formed from any flexible gas-impervious material which is permeable to radio waves, and they may be secured together and to the reflector along their edges by any convenient means providing a gas-tight joint. Preferably, however, they are formed from textile fabric of a long chain polymeric amide such as nylon impregnated with a plastic such as polyvinyl chloride or other thermoplastic which provides the desirable properties of toughness with low extensibility so that their distortion on inflation is small, and which can be secured together by heat sealing. When the reflector sheets also incorporate a thermoplastic as mentioned above, this provides a very strong seam.

With this embodiment, only two shapes of sheet are involved, the isosceles triangular reflective sheets 1 and the equilateral triangular sheets 4 of the envelope, so providing for simplicity and economy in manufacture.

Any convenient inflating gas may be used, depending upon the uses to which the reflector device is to be put.

0 For example, air or hydrogen may be used.

The invention provides a reflector device which can be erected quickly and simply by inflation and requires no other supports for holding its reflective surfaces in the desired relation. Furthermore, it can be stored easily and compactly. It is particularly suitable for use on life boats and life rafts, especially inflatable life rafts in which means may be provided for inflating the reflection device at the same time as the raft.

Having now described our invention what we claim is:

1. A radar reflector device for radio waves comprising sheets of radio wave-reflective sheet material lying in three planes which intersect each other at right angles to define eight corner reflectors having coincident inner apices, six outer apices and eight edges of the radio wave-reflective sheet material each of which edges extends between an adjacent pair of said outer apices, and an inflatable envelope of flexible material permeable to radio waves having at least eight outstanding edges, the outstanding edges extending in said planes of radio wave-reflective sheet material and the corner reflectors being enclosed within said envelope and secured to said outstanding edges thereof by their edges.

2. A reflector device according to claim 1 wherein the envelope comprises a plurality of sheets of the flexible radio wave-permeable material.

3. A reflector device according to claim 1 wherein the envelope when inflated is substantially in the shape of a regular octahedron having the same edge lengths as the edges of the radio Wave reflective sheets.

4. A reflector device according to claim 3 wherein the envelope has a single inflation valve, and the radio wave-reflective sheets have openings for admitting inflating gas to all the compartments defined between them and the envelope.

5. A reflector device according to claim 3 wherein the envelope is thermoplastic.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. A RADAR REFLECTOR DEVICE FOR RADIO WAVES COMPRISING SHEETS OF RADIO WAVE-REFLECTIVE SHEET MATERIAL LYING IN THREE PLANES WHICH INTERSECT EACH OTHER AT RIGHT ANGLES TO DEFINE EIGHT CORNER REFLECTORS HAVING COINCIDENT INNER APICES, SIX OUTER APICES AND EIGHT EDGES OF THE RADIO WAVE-REFLECTIVE SHEET MATERIAL EACH OF WHICH EDGES EXTENDS BETWEEN AN ADJACENT PAIR OF SAID OUTER APICES, AND AN INFLATABLE ENVELOPE OF FLEXIBLE MATERIAL PERMEABLE TO RADIO WAVES HAVING AT LEAST EIGHT OUTSTANDING EDGES, THE OUTSTANDING EDGES EXTENDING IN SAID PLANES TO RADIO WAVE-REFLECTIVE SHEET MATERIAL AND THE CORNER REFLECTORS BEING ENCLOSED WITHIN SAID ENVELOPE AND SECURED TO SAID OUTSTANDING EDGES THEREOF BY THEIR EDGES.,

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