Electric heating – Microwave heating – Radiation protection
Reexamination Certificate
2003-10-29
2004-12-07
Leung, Philip H. (Department: 3742)
Electric heating
Microwave heating
Radiation protection
C219S739000, C174S034000
Reexamination Certificate
active
06828534
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a door with a viewing window for a microwave unit and, more particularly, to a door with a viewing window for a microwave unit, which comprises a metallic door frame, two glass panes held spaced from each other between the metallic door frame and a metallic screen for screening or blocking microwaves arranged between the glass panes, which is in conductive contact with the metallic door frame.
2. Description of the Related Art
Doors for microwave units typically have a viewing window, in order to be able to better observe the cooking process in the microwave unit. This viewing window comprises two glass panes arranged spaced apart from each other in a metallic frame. The glass panes are made from a high temperature-resistant glass. Since this glass is also transparent for microwaves to some extent, a screen is necessary in the metallic frame to block microwave radiation in the vicinity of the viewing window.
In the known microwave units this screen comprises a blackened perforated metallic plate, which is rigidly attached in the space between both glass panes and is in electrically conductive contact with the metallic frame. This comparatively heavy perforated metallic plate of course blocks the microwave radiation to the required extent, however it significantly impairs observation of the interior of the microwave unit.
SUMMARY OF THE INVENTION
It is an object of the present invention to construct the microwave unit door in regard to the metallic screen, based on the above-describe microwave unit door with viewing window of the above-described type, which comprises a metallic door frame, in which two glass panes are spaced from each other, and a metallic screen for blocking or attenuating microwaves between the two glass panes, which is in conductive contact with the metallic door frame, so that, on the one hand, the metallic screen provides the required blocking or attenuation of the microwave radiation, which means that the legally required limit for emission of microwaves from the microwave unit is not exceeded, and, on the other hand, the metallic screen does not impair observation of the interior of the microwave unit from a practical standpoint.
This object and others, which will be made more apparent hereinafter, are attained in a door with a viewing window for a microwave unit, which comprises a metallic door frame, two glass panes held spaced apart from each other between the metallic door frame and a metallic screen for blocking or attenuating microwaves arranged between the glass panes, which is in electrically conductive contact with the metallic door frame.
According to the invention the metallic screen comprises a woven fabric of thin metal fibers, which are woven together with a predetermined small spacing.
This fine woven fabric, as experimentation has shown, blocks or attenuates the microwave radiation to the required extent and surprisingly allows a practically completely unblocked or unveiled view of the interior to the microwave unit. There is practically speaking no noticeable blocking of the view.
The term “thin metal fibers” within the sense of the present invention means metal fibers each with a thickness in a range from 0.02 mm to 0.1 mm, preferably about 0.06 mm.
The predetermined small spacing between metal fibers, i.e. the distance between opposing sides of adjacent individual metal fibers, is preferably in a range of 0.09 mm to 0.5 mm and amounts to about 0.12 mm in a preferred embodiment.
In the simplest case the woven fabric has a so-called linen or plain weave, in which the warp fiber or thread alternatively passes over and under the weft fiber or thread. Also other weaves of the fibers, for example, a body weave, are of course conceivable.
So that the thin metal fibers have sufficient tear resistance, the metal fibers preferably comprise steel fiber.
In order to avoid light scattering effects, the woven fabric, as in the known case of the perforated plate, is blackened.
REFERENCES:
patent: 2958754 (1960-11-01), Hahn
patent: 3305623 (1967-02-01), Bakker et al.
patent: 4010343 (1977-03-01), Tanaka et al.
patent: 4631214 (1986-12-01), Hasegawa
patent: 4678699 (1987-07-01), Kritchevsky et al.
patent: 5012041 (1991-04-01), Sims et al.
patent: 6717047 (2004-04-01), Haselby et al.
Busch Dietrich
Leutner Kurt
Leung Philip H.
Schott Glas
Striker Michael J.
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