Datasheet

Anywhere high speed electronics are
present, their operating frequencies
usually must be controlled within specified
government designated regulations. The
radio frequencies emitted can interfere
with other nearby electronic equipment as
unwanted RFI/EMI, radio frequency
interference / electromagnetic interference
When a solid enclosure is not practical,
due to the need for access panels,
controls, doors, vents or seams, RFI
shielding gaskets are used to maintain
electrical contact between mating
surfaces. See figure 5.
The shielding effectiveness of an
enclosure is a function of the wavelength of
the frequencies involved versus the length
of the longest openings. See figure 6.
A proper gasket installation effectively
reduces the slot length. Low compression
force is very desirable to facilitate easy
closing of mating surfaces.
Correct installation of the dual elastomer
gasket between mating surfaces of an
enclosure slot assures continuous
electrical coupling along its axis, and long-
term shielding effectiveness.
Effectively, the shielding gasket is a
connector of one mating surface to another.
This permits the electronic enclosure to
respond as one continuous absorber of the
undesirable high frequency energy by
limiting the passage of these radio waves.
FREQ
UENCY (Hz)
ATTENUATION vs. FREQUENCY
ATTENUATION
(dB)
10K 100K 1M
E field
H field
10M 100M 1G 10G
140
120
100
80
60
40
20
0
% COMPRESSION OF
TUBULAR GASKETS
BETWEEN
TWO PLATES
SURFACE RESISTANCE
(ohms)
FORCE (lb./in.) REQUIRED
TO COMPRESS
0
SHIELDING EFFECTIVENESS (dB)
0
7% 14% 21% 26% 35% 42% 49%
56%
0.75
0.60
0.45
0.30
0.15
0
10
8
6
4
2
compression force
surface resistance
% ATTENUATION
ATTENUATION RATIO
20 40 60 80 100 120
0
1,000,000:1
100,000:1
10,000:1
1,000:1
100:1
10:1
99.9999
99.999
99.99
99.9
99.0
90.0
typical
dual elastomer
performance
Figure 3:
Figure 4:
Figure 2:
Figure 6:
Figure 7:
Figure 5:
FREQUENCY (Hz)
1M
SHIELDING
EFFECTIVENESS (dB)
10K 100K 10M
INSTALLATION BETWEEN MATING PANELS
TYPICAL ELECTRONIC ENCLOSURE
100M 1G 10G
100
50
0
COMPRESSION FORCE -
(Kg) lbs.
.10
(2,5)
0
(0)
.20
(5,1)
.30
(7,6)
COMPRESSION DISTANCE - in. (mm)
.40
(10,2)
.50
(12,7)
0
(113) 250
(90) 200
(68) 150
(45) 100
(23) 50
copper fingers
meshes
other elastomers
0.01 meter (.4")
0.10 meter (4")
1.0 meter (40")
10.0 meters (394")
slot attenuation (dB) = 20log l/2l
slot length = l
dual elastomers
4
performance specifications
minimizing the effects of enclosure openings
The full potential of dual elastomer
gasket technology is now being realized.
Shielding effectiveness with an attenuation
of 110dB in the frequency range of 30 MHz
to 1GHz is attainable (MIL SPEC G-83528,
para 4.6.12) (Figure 2).
Any design used to block the RF signal
between its source and a receiver is an
electromagnetic interference (EMI) shield.
The measure of this ability to attenuate RF
is shielding effectiveness (SE), which is
expressed in decibels, (dB), the ratio of field
strength on one side of the shield to the
other side. Figure 4 shows the relationship
between shielding effectiveness (in dB), the
attenuation, and attenuation percentage.
ULTRA-VANSHIELD
®
dual elastomer
gaskets typically exceed 110dB shielding
effectiveness regardless of shape, size or
compressed state beyond 10% of relaxed
height.
The silicone rubber foundation is
most resistive to permanent deformation,
contaminant’s and other environmental
influences.
The accelerated aging data on page 3,
table 2, exhibits very high performance
results at elevated temperatures and
repeated compressions over extended time
periods.
The same continued performance
under most application conditions can be
expected. Due to the pliable properties of
the unfilled elastomer core, these
extrusions promise to have the best
possible aging and long-term shielding
properties (Figures 3 & 4).