Shielding Effectiveness Evaluation and Optimization
of Resonance Damping in Metallic Enclosures
R. Araneo
#1
, G. Lovat
#2
, S. Celozzi
#3
#
Department of Electrical Engineering - Sapienza, University of Rome
Via Eudossiana 18, 00184 Rome, Italy
1,2,3
rodolfo.araneo,giampiero.lovat,salvatore.celozzi@uniroma1.it
Abstract— The evaluation of the shielding effectiveness of
metallic enclosures with apertures containing metallic objects
and excited by arbitrary sources is the main topic of this work.
The shielding effectiveness is computed through an integral
formulation based on the Method of Moments which makes use of
a fast computation of the enclosure Green functions. Absorbing
artificial materials are also designed and proposed to damp the
resonant fields excited inside the enclosure in order to improve
the shielding performance.
I. I NTRODUCTION
The analysis of the interaction between an electromagnetic
(EM) field and a metallic enclosure is a classical shielding
problem [1]. Metallic enclosures are usually adopted to reduce
the EM coupling between their inner volume and the outer
world. However, important couplings are often caused by
the unavoidable presence of apertures, necessary for many
practical purposes, such as ventilation. Also in the presence
of apertures the aperture-cavity system is resonant, although
its resonant frequencies move slightly from those of the
corresponding closed cavity, and the quality factor is no more
infinite. In any case, at the resonant frequencies the shielding
effectiveness (SE) of the system deteriorates dramatically. The
SE of enclosures is strongly dependent on the number, shape,
and thickness of the apertures, on the presence of internal
loads, and on the type of the radiating EM source, which can
be modeled as an impinging uniform plane wave or a dipole.
In recent years the shielding problem involving enclosures
has been addressed by means of analytical approximate for-
mulations [2] and several numerical methods [3]-[6]. However,
a simple comparison of these works reveals that different
analyses have led to dramatic differences in the SE evaluation.
In this work, we study the SE of several configurations
of enclosures of practical interest by means of an integral-
equation (IE) approach [7]-[8]. Such a method allows for
an efficient analysis of metallic enclosures with apertures of
arbitrary shape and thickness, possibly loaded with 2-D or 3-
D objects, and excited by arbitrary EM sources. The shielding
problem is solved through a mixed-potential formulation of
the Method of Moments (MoM). The results are compared
with those obtained through different full-wave commercial
software, showing the accuracy of the proposed approach and
its superior performance in terms of computational cost.
Finally, in order to improve the SE, some absorbing artificial
materials are proposed to damp the excited resonant fields. The
design of these artificial materials is carried out by solving
an auxiliary and simpler 2-D problem which allows for the
proper tuning of the constitutive parameters and next the
geometrical features of the particles constituting the filling
artificial absorber can be determined by using quasi-dynamic
formulas for effective parameters obtained through homoge-
nization procedures. As a final step, the designed materials are
inserted inside the 3-D enclosures and the whole problem is
studied through a full-wave analysis by modeling the artificial
absorbers as homogeneous (possibly dispersive) materials.
II. PROBLEM FORMULATION
The EM problem under analysis is sketched in Fig. 1: a
cavity with perfectly conducting (PEC) walls and dimensions
ℓ
x
×ℓ
y
×ℓ
z
is excited by either an electric or a magnetic dipole
of unit amplitude placed inside or outside the enclosure. The
walls of the enclosure may have a finite thickness t, and one
or more apertures of arbitrary shape are cut on one of the
enclosure walls (i.e., that located at the plane z = l
z
). Finally,
the enclosure can contain one or more PEC objects of arbitrary
shape. The electric shielding effectiveness SE
E
(the magnetic
shielding effectiveness could be used as well) of the enclosure
at a given point r is defined as
SE
E
= 20 log
E
inc
(r)
|E(r) |
(1)
where E
inc
(r) and E (r) are the electric fields at the point
r due to the radiating dipole sources without and with the
enclosure, respectively.
l
y
l
x
l
z
J
im
, M
im
y
r
r
im
x
O
z
z=l
z
z=l
z
+t
Pec
Aperture A
u
n
u
z
S
Region 1 - Cavity
Region 3 - Free space
EM
G
C
HM
G
(3)
HM
G
C
HJ
G
C
EJ
G
C
M
A
e
i
M
e
A
i
Region 2 - Aperture
HM
G
S
HM
G
M
Fig. 1. Geometry of the metallic rectangular enclosure.
2010 Asia-Pacific International Symposium on Electromagnetic Compatibility, April 12 - 16, 2010, Beijing, China
978-1-4244-5623-9/10/$26.00 ©2010 IEEE 528