Double-action gasket assembly for EMI/RFI shielding

The present disclosure describes an elongated, articulated gasket assembly which finds particular application in the EMI/RFI shielding of the gaps between adjacent panels of a metal cabinet, such as that used in a mainframe computer. The gasket assembly is characterized by its double-action capability, that is, it may be wiped in either direction under a compressive force, without sustaining any damage. Likewise, the gasket assembly exhibits excellent durability during the routine handling of the panels. Finally, since installation of the present gasket assembly does not restrict movement of the panels, a desired panel may be removed during service procedures without affecting any other panel.

BACKGROUND OF THE INVENTION 
In the operation of electronic equipment, it is necessary to shield against 
electromagnetic emissions. When the equipment is housed in metal cabinets, 
as is the case, for example, with a mainframe computer, the gaps between 
the panels which enclose a side of the cabinet, pose an EMI/RFI shielding 
problem. 
In order to shield the gaps between adjacent panels or between a panel and 
the cabinet housing, there are presently available from different 
manufacturers gasket-like shields. One such manufacturer is Instrument 
Specialties Company, Inc., which offers two types of beryllium-copper 
finger contact strips sold under the trademark "Sticky Fingers" and 
identified in the advertising literature with U.S. Pat. No. 3,504,095. In 
the first-type strip, an adhesively coated section supports one end of 
each of the arched fingers, the other end of which is unsupported and free 
to move. In performing a shielding function, the gasket must be either 
directly compressed by the mating surfaces by a force directed 
perpendicularly to the gasket as with a panel pressed against the housing 
frame, or compressed with a wiping action by a force directed laterally to 
the gasket as occurs in the gap between adjacent coplanor panels when one 
panel is moved in a direction substantially orthogonal to its planar 
surface into position relative to an adjacent panel. The difficulty with 
the last mentioned commercial gasket is that the fingers are fragile and 
are designed to be wiped in only one direction--from their supported ends 
toward their free ends. If mounted between adjacent panels, extreme care 
must be exercised when removing a panel, because manual contact with the 
shielding fingers in a direction opposite to the wiping direction will 
severely damage the fingers and compromise the integrity of the shield. To 
preclude such damage, a flange may be provided on a panel edge within the 
gap area which may be grasped during panel removal, thereby protecting the 
gasket fingers. The flange is also necessary if a direct compression mode 
is used since the gasket would normally be mounted on the flange. Use of 
such a flange is undesirable since it restricts the movement of the 
panels. Thus, it may be necessary to open an adjoining panel before a 
panel with a flange may be opened. To open multiple panels to access a 
particular location in the cabinet can become time consuming for the 
service personnel. Moreover, the cost of the cabinet is increased since, 
for example, in the case of lift-off panels, it may be necessary to 
fabricate and stock several panel types to achieve the desired cabinet 
configuration. 
As was mentioned hereinbefore, the manufacturer of "Sticky Fingers" offers 
a second type of gasket described in its advertising literature as the 
newest version. This second type was designed to be less susceptible to 
damage than the first type. As indicated in the literature, it includes a 
U-shaped end as part of the adhesively coated longitudinal section, which 
is adapted to retain the free movable end of the fingers when the 
enclosure doors are open, so as to protect against accidental damage to 
the strip's fingers. While offering some improvement relative to the first 
type of gasket, the second type is still adapted to be wiped in only one 
direction. If the gasket is grasped in a direction opposite to the wiping 
direction, during panel removal, the fingers tend to exit the U-shaped 
retainers and to be bent backward and damaged. Thus, it has been expedient 
to mount even the second type of gasket on panels which have a protective 
flange as described hereinbefore. Accordingly, the restrictions on panel 
removal still apply. 
What is desirable is an EMI/RFI shielding gasket which may be installed on 
the panels of a cabinet structure without a flange and the accompanying 
restriction of panel movement; which may be compressively wiped in either 
lateral direction; which is more durable than those described herein; and 
which is relatively immune to damage from normal handling of the panels 
during service procedures. The double-action gasket assembly of the 
present invention fills such a need. 
SUMMARY OF THE INVENTION 
In accordance with the present invention there is provided a double-action 
gasket assembly comprised of a one piece elongated, articulated beryllium 
copper structure and a substantially planar stainless steel carrier 
enclosed thereby. 
More specifically, as seen in cross section, the segments of the beryllium 
copper structure comprise an arcuate section having opposed extremities 
bent toward each other to form a respective pair of spaced-apart, coplanar 
sections. The carrier is disposed within the bends of the structure and is 
contiguous with the surfaces of the pair of coplanar sections. The carrier 
provides a means for attaching the gasket to a mounting surface such as 
the edge of a panel. At the same time, the carrier surface is designed to 
be slightly offset from the adjacent mounting surface, in order to permit 
the beryllium copper structure to slide against the last mentioned surface 
without interference by the carrier. Also, the structure is loosely 
mounted on the carrier to permit the pair of coplanar sections to contact 
the mounting surface and to slide in either direction thereon in response 
to the compressive wiping of its arcuate section, without incurring 
damage. At the same time, the attachment is firm enough to keep the 
structure from coming loose from the carrier when the mounting surface is 
routinely handled. 
Other features and advantages of the present shielding gasket assembly will 
become apparent in the detailed description thereof which follows.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 illustrates the prior art "Sticky Fingers" shielding gasket 1 
installed on the edge of the panel 2 and adapted to be compressively wiped 
in the direction of the arrow by the adjacent panel 3, thereby shielding 
the gap formed between the panels. Under compression, the extremity of 
finger 4 of the gasket 1 moves within the U-shaped enclosure 5. However, 
should it be necessary to remove panel 2, it is apparent that in the 
absence of flange 6, the panel would normally be grasped along the edge 
upon which gasket 1 is installed. Movement of the panel 2 in a direction 
away from frame 7, may involve contact with the finger 4 which dislodges 
it from the U-shaped enclosure 5 and bends it backward, thereby damaging 
the gasket seal. Flange 6 provides a hand hold for the panel 2 which 
minimizes the need for manual contact with the gasket 1. On the other 
hand, flange 6 restricts movement of the panels 2 and 3. If it is 
necessary to remove panel 2, panel 3 must first be removed, because of the 
flange interference. 
FIGS. 2, 3, 4 and 6 illustrate respectively plan, side, end view and 
section view of the double-action gasket assembly 10 of the present 
invention. With general reference to the last mentioned figures, an actual 
operative embodiment of the assembly 10 is comprised of a unitary 
elongated, articulated beryllium copper structure 12 and a substantially 
planar stainless steel carrier 18 enclosed thereby. It should be 
understood that the various materials identified herein as being used in 
the assembly 10, the physical dimensions of the materials, and other 
parameters are provided solely for purposes of example, and the invention 
is not to be construed as being limited thereto. 
As seen in FIGS. 2 and 3, the segments 14 of the articulated structure 12 
are formed by regularly spaced slits 16 in the structure. The segments 14 
as seen particularly in FIG. 4 comprise an arcuate section 14a having 
opposed extremities bent toward each other to form a respective pair of 
spaced-apart coplanar sections 14b. The carrier 18 is partially enclosed 
within the bends of the structure 12 and lies upon the copolanar sections 
14b. The carrier includes apertures 20 formed therein for receiving 
push-in type rivets 22 to mount the gasket assembly 10 to a mounting 
surface. As seen more clearly in FIG. 4 and FIG. 6, the area of the 
carrier surrounding the head of a rivet 22 includes a depression 24 to 
permit the depressed area of the carrier surface to contact the mounting 
surface (such as 28 or 30 in FIG. 5) and to offset the remaining carrier 
surface a predetermined distance from the mounting surface. A distance of 
0.010 inches has been found to be satisfactory. The offset permits the 
coplanar sections 14b of the beryllium copper structure 12 to slide 
against the mounting surface without interference from the carrier 18 when 
a laterally directed wiping force is applied to the arcuate section 14a. 
not attached to the carrier 18 except by the shape of its bends between 
the arcuate section 14 a and the coplanar sections 14b. As seen in FIGS. 2 
and 6 slots 26 in the last mentioned sections homologous with and 
partially surrounding the depressions 24 in the carrier 12 provide 
clearance such that the sections 14b are not captured between the 
depressions 24 and the mounting surface. This attachment method is loose 
enough to permit the coplanar sections 14b of structure 12 to slide in 
either direction when the arcuate section 14a is subjected to wiping 
forces without being damaged. However, the attachment of the structure 12 
to carrier 18 is firm enough to permit routine handling of the assembly 10 
without having it come apart. 
As seen in FIG. 5, the assembly 10 may be installed on the edges of panels 
28 and 30 which are mounted in a frame 32. Panel 34 is assumed to have 
moved in a direction perpendicular to and toward frame 32 and has 
compressed the arcuate section 14a of the beryllium copper structure 12, 
causing the pair of coplanar sections 14b to slide further apart from each 
other, concurrently moving toward and ultimately contacting the edge 
mounting surface of panel 28. Since the assembly 10 is capable of double 
action, panel 34 may wipe the structure 12 in either direction, as during 
panel installation and removal relative to frame 32, without damage. The 
structure 12 mounted on panel 30 is in a non-compressed state. Panel 30 
may be installed against frame 32, at which time, the adjacent panel 36 
will wipe against the structure 12 and the gap formed between adjacent 
panels will be shielded by the gasket assembly. Since panel flanges are 
not required with the present assembly, any of the panels 28, 30, 34 or 36 
may be individually removed without disturbing the remaining panels. 
In conclusion, there has been disclosed an EMI/RFI shielding gasket 
assembly, characterized in that it is of simple construction and easy to 
mount, yet effective for its intended purpose; has a double-action 
capability which not only increases its versatility but also renders it 
relatively immune to damage during operation and routine handling; and may 
be installed in adjacent panels of a cabinet enclosure without restricting 
movement of any panel. It is apparent that depending upon the particular 
application, changes and modifications of the gasket assembly may be 
desirable. For example, although beryllium copper has been indicated for 
the compressive structure, other spring-type electrically conductive 
materials might be employed. Also, the materials may be plated to minimize 
corrosion effects. As to the carrier portion of the assembly, although a 
stainless steel plate 0.625 inches wide by 0.020 inches thick has been 
used, in an actual operative embodiment of the invention, the carrier may 
be formed of any rigid material, not necessarily an electrical conductor, 
and may deviate appreciably from the given dimensions. These and like 
changes and modifications, insofar as they are not departures from the 
true scope of the invention, are intended to be covered by the claims 
which follow.