Electricity: conductors and insulators – Anti-inductive structures – Conductor transposition
Reexamination Certificate
2000-11-06
2001-11-27
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Anti-inductive structures
Conductor transposition
C361S816000, C174S034000
Reexamination Certificate
active
06323419
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to enclosures that are shielded from electromagnetic radiation and more particularly to such enclosures and doors that are provided with seals that achieve effective radio frequency shielding by simply closing the door.
DESCRIPTION OF THE PRIOR ART
It is common practice to place apparatus that emits electromagnetic radiation (EMR), or which is sensitive to radio frequency interference (RFI) within a shielded enclosure. When the enclosure must be frequently opened, the means for ensuring that the shielding will be restored when the opening is once again closed present problems. It is well known to provide the access door or panel with a forwardly directed blade along its perimeter that conductively engages separate sealing strips with springy contact fingers conductively held in a groove at the enclosure opening. U.S. Pat. No. 5,223,670 issued Jun. 29, 1993 to Hogan describes such an apparatus and the problems encountered. When cellular telephones are tested, they must be shielded from even the slightest stray radiation. Their emitted radiation must also be shielded when they are tested in a production facility. The closure must be repeatedly opened and closed, as each phone is tested in turn. The closure must be easy to open and close. The unit should take up little space.
LIGI TOOL AND ENGINEERING, INC. OF POMPANO BEACH, Fla. has been producing the RFI-100 Radio Interference Test Box for this purpose. It provides 80 decibel isolation up to 3 GHz. It employs a beryllium copper spring finger strip held captive in the cover that cooperates with a flange extending from the enclosure opening. The strip is series 97-542 produced by INSTRUMENT SPECIALTIES OF DELAWARE WATER GAP, Pa., U.S. Pat. No. 3,504,095. The fingers are spaced apart farther than is desirable to permit some bending of the straight strip. Because the strip cannot be bent through a radius of less than 3 inches, the overall dimensions of the apparatus are larger than is desirable. Construction needed to hold the strip in place adds to the cost. It would be desirable to have a greater degree of shielding, a smaller enclosure, and one that was less costly to produce.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a means of shielding an openable closure that would enable providing smaller radii, greater shielding, less costly construction, and longer useful life without maintenance. The invention comprises a closure seal and an openable RFI shielded enclosure for testing electronic equipment. The seal of the invention comprises a generally U shaped conductive spring finger strip seated in a groove in the cover. The strip comprises a continuous web with springy fingers extending downward therefrom. The strip is comprised of eight portions, four corner portions with small radius, and four straight portions closely adjacent to one another to make an effectively continuous perimeter. The strips are formed into the final desired curved and straight shapes prior to heat treatment. A short flange extends from the housing and is designed to fit into the strip, forcing the fingers of the strip apart to press the legs against the opposed walls of the groove. This provides spring biased electrical contact between the housing, the springy fingers, and the walls of the groove.
These and other objects, features, and advantages of the invention will become more apparent when the detailed description is studied in conjunction with the drawings in which like elements are designated by like reference characters in the various drawing figures.
REFERENCES:
patent: 3504093 (1970-03-01), Roberson
patent: 4069618 (1978-01-01), Geiss
patent: 4677251 (1987-06-01), Merewether
patent: 4760214 (1988-07-01), Bienia et al.
patent: 4794206 (1988-12-01), Weinstein
patent: 4817337 (1989-04-01), Lahita
patent: 4929802 (1990-05-01), Schaepers et al.
patent: 5223670 (1993-06-01), Hogan
patent: 5585599 (1996-12-01), Schwenk
Catalog p. 67, Instrument Specialties, PA, No date.
Blum Alvin S.
Ngo Hung V
Reichard Dean A.
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