Glass manufacturing – Processes – Reshaping or surface deformation of glass preform
Patent
1993-06-28
1995-06-06
Jones, W. Gary
Glass manufacturing
Processes
Reshaping or surface deformation of glass preform
65111, 264 11, 264 124, 359652, C03B 2300, B29D 1100
Patent
active
054218489
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for the fabrication of three-dimensional lenses with a variable refractive index.
Lenses with a variable refractive index, such as a Luneburg lens or a Eaton-Lippmann lens, are well known.
It is also known, e.g. from U.S. Pat. No. 4,288,337, that lenses with variable refractive indexes can be used as radar reflectors or, as is known from E. F. Buckley; "Stepped-Index Luneburg Lenses"; Electronic Design, Apr. 13, 1960, as part of an antenna system.
As Buckley has described in said article, it i s a known method for the fabrication of Luneburg lenses to use a hemispherical-shell construction with a given number of layers.
According to said US patent the layers for the fabrication of Luneburg and Eaton-Lippmann lenses can be produced by mixed dielectrics. Such a mixed dielectric can be obtained by mixing expanded particles selected from the group consisting of expanded polystrols, expanded polyethylenes, expanded polyurethanes, glass balloons and silica balloons, with metal-coated particles consisting of said expanded particles, surfaces of which have been coated with a thin film selected from the group consisting of chromium, aluminium, copper, nickel, gold, silver, and magnesium in proper proportions to obtain a desired eielectric constant the forming the same to the desired shape by the use of a binder.
From the article "A multiple-beam multiple-frequency spherical Lens Antenna System providing hemispherical Coverage" of M. A. Mitchel et al.; 6. International Conference on Antennas and Propagation (ICAP) 1989, Part 1, pp. 394-398 it is known that the relative dielectric constant, and by this the refractive index, of a dielectric material, such as polysterene, can be modified by a variation of density of said material.
Thereby hemisperical shells with given refraction indexes may be produced.
From U.S. Pat. No. 3,307,196 a method is known, which allows the production of a two-dimensional dielectric lens, such as a disk, by winding a ribbon, shut or strip type of module.
In the U.S. Pat. No. 3,307,196 it is proposed to fabricate a three-dimensional dielectric lens by the individual preparation of wound disks, which are superposed upon one another. The superposed disks are of successively different diameters and dielectric profile and could be formed, starting with individual substantially strip or ribbon modules, by cutting successively different lengths away from the high dielectric constant ends of said different strips, and then rewinding the resultant successively different length strips.
There are two disadvantages in the known methods for the fabrication of three-dimensional lenses. It is either possible just to approximate the variation of the refractive index required, which is dependent on the dielectric constant. 0r it is necessary to carry out a large number of steps. That means no easy and practical method for smoothly varying the refractive index has been achieved.
By using shells with different dielectric constants and thereby with different refractive indexes, reflection losses occur by which power is reflected from the dielectric boundaries.
It is an object of the invention, to present an easy method for the fabrication of lenses with a variable refractive index, which overcomes the deficiencies of the prior art.
The invention fulfills this object.
The method according to the invention allows to produce three-dimensional lenses with a variable refractive index n by wrapping a material with a given refractive index, e.g such as the known materials from U.S. Pat. No. 4,288,337, into the final shape of the lens to be produced.
It is an advantage of the invention to present a method for the fabrication with a reduced number of steps.
It is a further advantage of the invention to produce lenses with a better aperture efficiency by avoiding surface waves, which are set up at the spherical boundaries, and by achieving a more exact phase of the colliminated rays at the feed points, which makes the lens less frequency dependent.
When the material with the given refrac
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patent: 3023135 (1962-02-01), Wiltshire
patent: 3115271 (1963-12-01), Anderson et al.
patent: 3274668 (1966-09-01), Horst
patent: 3307196 (1967-02-01), Horst
patent: 4288337 (1981-09-01), Ota et al.
patent: 4482513 (1984-11-01), Auletti
Fujimoto Masahiro
Harrison David
Maier Gerhard
Griffin Steven P.
Herrmann E. P.
Jones W. Gary
Thomson Consumer Electronics S.A.
Tripoli J. S.
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