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Biased-Coil Design for Electromagnetic Shielding of Enclosure Joints

IP.com Disclosure Number: IPCOM000119993D
Original Publication Date: 1991-Mar-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 4 page(s) / 134K

Publishing Venue

IBM

Related People

Yanker, GM: AUTHOR

Abstract

Prevention of EMC/EMI leakage at seams and joints of electrically conductive enclosures is the primary objective of this design. Disclosed is a simple method for using common coiled wire (such as music wire) to economically and effectively accomplish this objective.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Biased-Coil Design for Electromagnetic Shielding of Enclosure Joints

      Prevention of EMC/EMI leakage at seams and joints of
electrically conductive enclosures is the primary objective of this
design. Disclosed is a simple method for using common coiled wire
(such as music wire) to economically and effectively accomplish this
objective.

      Referring to Fig. A, shown are end and top views of both
electrically conductive male side 1 and conductive female side 2 of a
cover enclosure which are designed to provide an EMI-gasket type of
seal when joined together in conjunction with an electrically
conductive spring coil 3.

      Spring coil 3, which is essentially a round spiral coil in its
free state, is nested in a coil-retaining channel 4 which runs the
length of female side 2 of an enclosure cover.  Channel 4 has a
cross-section that approximates a "C" shape such that it has an open
slot 5 which runs lengthwise along channel 4.  The width of the open
slot 5 is less than the free-state outer width of the spring coil 3,
so that the coil is retained from escaping through open slot 5.  For
ease-of-assembly purposes, the width across open slot 5, however, is
chosen great enough to allow the spring coil 3 to be "stuffed" into
channel 4 through open slot 5, provided the coils first are biased
(laid-over) at an angle at time of insertion.  Such insertion can be
done manually or with the aid of an assembly tool.

      When installing spring coil 3 into channel 4, the laid-over
coils will try to spring back toward their original position, but
will be prevented from doing so by the smaller channel width "X"
chosen between the walls of the channel 4.

      The width "X" of channel 4 is chosen to be narrower than the
outer width of spring coil 3, so as to cause the spring coils to be
retained at a biased or laid-over position, with their angle "Y"
relative to their free-state orientation (see top view) to be about
35 degrees, more or less.  The depth "Z" of channel 4 is chosen to
allow a slight vertical clearance for spring coil 3.

      Referring to Fig. B, when the blade edge of conductive male
side 1 is inserted into channel 4 of the female side 2 as shown, the
spring coils 3 are pushed aside and angle "Y" increases.  The result
is a snug, predictable, and reliable EMI seal.  If there is no space
be tween the coils before the male side 1 is inserted, the stack
height of the spring coil 3 along its axis will be observed to
increase.  A key discovery within this disclosure is that, for very
large coil stack heights, it is important that the coils be
pre-separated (stretched and anchored at both ends of the channel 4.
Without pre- separation, the stack height along a lengthy spring coil
3 will need to grow and slide a prohibitive amount within the channel
4 and cause prohibitive insertion forces. Extra-generous coil
pre-separation is also a design key factor that can reduce cost of
the spring...