ORBIT FR Low Frequency Absorbers - AEP-EM Series - Manual (Page 2)

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1/ Description
Low Frequency absorbers should be used in order to
reduce the multiple refl ection and resonant conditions
typical in shielded rooms at frequencies from 30 MHz to
1000 MHz. The use of these materials allows for grea-
ter repeatability of tests performed within a shielded
room. Due to the extremely long wavelength at 30 MHz,
conventional pyramidal absorbing materials must be ex-
tremely thick because the performance of the absorber
drops off rapidly as the material becomes less than one
quarter wavelength in thickness. In order to minimize this
roll off and improve the overall loss characteristics, AEMI
has developed low frequency absorber using special
materials. These materials have proven to be extremely
effective in medium size shielded rooms.
2/
A unique graded dielectric approach
The EM material is essentially a pyramidal front mate-
rial properly loaded to match successive layers of gra-
ded dielectric foam. This design allows for the proper
matching of the material to free space by initially provi-
ding a tapered impedance match through the pyramidal
front.
After the energy has entered the material, it is then suc-
cessively passed on to higher and higher dielectrically
loaded layers which enhance the energy dissipation cha-
racteristics. It is through this gradual change in dissipa-
tion that high loss at low frequencies can be achieved.
The design of this graded dielectric approach provides
the user with 33% more lossy dielectric material than
the use of conventional pyramidal material of equal size.
This added dielectric material provides increased per-
formance at low frequencies. The graded design also
increases the wide angle performance of these products
with respect to conventional pyramidal materials. Typical
performance increases at normal incidence are 3-6 dB
and 6-10 dB at wide angles.
3/ A high fl exibility of use
Another feature of this series is its ability to be stacked.
This allows the engineer to provide a temporary wall of
absorptive material for the elimination of hot spots in a
shielded facility. This mobility also gives the freedom to
alter the test environment whenever conditions and re-
quirements change. Resonance of the shielded cavity
can be altered at will by the proper placement of this
series of absorbers.
4/
Specifi cations
AEP-12-EM AEP-18-EM AEP-24-EM AEP-36-EM AEP-48-EM
Height in 12 18 24 36 48
cm 30.5 45.7 61 91.4 121.9
@ 30 MHz dB 6 9
@ 50 MHz dB 8 12 16
@ 100 MHz dB 9 11 14 21 27
@ 250 MHz dB 19 21 26 30 34
@ 500 MHz dB 26 29 32 36 39
@ 1000 MHz dB 32 35 38 41 44
Weight lbs/pc. 10 16.5 17 27 36
kg/pc. 4.5 7.5 7.7 12.2 16.3
Absorption @
Normal Incidence
AEP-24 EM mechanical drawing
12’
’
12’
’
24’
’ 24’
’
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