UAq EMC Laboratory
Dept. of Electrical Engineering
67040 Poggio di Roio
University of L’Aquila - Italy
5.4.2.1.
Shielding Standard Problem
G.Antonini, M.Italiani, W. Michelli, A.Orlandi
January 2006
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I. Introduction
Computing the shielding effectiveness of an enclosure is very complex, because it involves a lot of different
phenomena. For example, electrical and geometrical parameters of the material of the walls, apertures and grids,
joints and contacts (connections) (including the use of gaskets, springs, overlaps,…), internal and external
cabling, cable feed-through or connectors, internal boards and back panels all affect the field levels. In most
cases, the total shielding effectiveness is determined by the combination of all these effects, some with greater
impact than others. As a consequence, determining the shielding effectiveness of a real enclosure is not a
simple. For this problem, a complex metal enclosure has been defined, as shown in Figure 1. This enclosure
includes an internal source and apertures with different holes sizes.
II. Problem Description
The following four cases have been analyzed from the the electromagnetic model shown
a) With no shield
b) With small holes and large hole
c) With small holes only
d) With large hole only
For each one of them the magnitude of the electric field has been evaluated and for the cases b),c),d) the SE
(Shielding Effectiveness) at a distance of 3m away from the front side of the enclosure is found.
The geometrical dimension of the entire structure is shown in Figure 2. The analysis has been performed in the
frequency range 0.1GHz - 2GHz.
Enclosure Dimensions and Materials (Figure 2):
The enclosure is of dimension 370mm x 90mm x 300mm (x, y, and z axis). The walls are made up of Perfect
Electric Conductors (PEC) with a thickness of 2mm.
Aperture Dimensions (Figure 2):
• Large hole: 80mm x 60mm whose bottom left corner is placed at x = 275mm and y = 15mm
• Small holes: The small holes are organized as a matrix of 4 rows and 17 columns. Each small hole is
2mm x 2mm. The holes matrix bottom right corner is placed at x = 104.5mm and y = 38mm. The
spacing between each small hole is 2mm.
ElectroMagnetic (EM) Source Description: Dimensions, Materials and Location (Figure 3):
The EM source like a PCB is simulated as follows: A metal plane made of PEC material and of dimensions
260mm x 0.017mm x 280mm. Over the metal plane a dielectric substrate made of FR4 with dielectric
permittivity of εr = 4.7 and of dimensions are 260mm x 0.25mm x 280mm is placed. No dielectric losses are
considered. A trace in PEC material is placed over the dielectric substrate (microstrip configuration); the
trace is of dimension 0.4mm x 0.017mm x 280mm and is centered on the plane perpendicular to the slotted
panel. A heatsink (solid metal rectangular object) in PEC material of dimension 160mm x 20mm x 100mm
is centered at 5mm above the reference plane covering the trace.
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In the EM source, the plane, with the trace, is placed horizontally in the enclosure and is 10mm away from
the front panel and 10mm above the bottom enclosure wall.
The metal plane (representing the PCB reference plane) and the trace over a dielectric is driven by constant
amplitude harmonic excitation of 1.0 volt in the frequency range of 0.1 GHz to 2 GHz. 50ohms termination
is used at the source and load.
III. Results and Discussion
The simulations were performed using the Finite Integration Technique (FIT) [1, 2].
Figure 4a shows the position of the excitation in the electromagnetic model. A discrete port [2] applied between
the metal plane and the trace is used to model the voltage source as shown in Figure 4b. The lumped element of
50Ω is also modelled using a discrete port (Figure 4c). The excitation signal is a transient waveform as in
Figure 5. To record the electric field components at a distance of 3m, three probes (each probe to record one
particular component Ex, Ey, Ez of the electromagnetic field in a specified location during the transient analysis)
has been used. The location of the probes are at P(x = 185mm, y = 45mm, z = 3000mm) as shown in Figure 6.
The boundary conditions are set as illustrated in Figure 7.
For the four considered cases a), b), c), d) the magnitude of the electric field at a distance of 3m from the front
panel of the enclosure are computed and compared.
E( f ) = E x2 ( f ) + E y2 ( f ) + E z2 ( f )
The comparison is shown in Fig. 8.
The SE has been evaluated for the cases b), c), d) and they have been compared in Figure 9.
The SE is defined as follows
E
SE = 20 log w / o
Ew
Ew/o is the electric field assessed for case a) (that is without shield)
Ew is the electric field assessed for the cases b), c), d) respectively
IV. RESULTS & DATA SETS
For each case a), b), c), d) an ASCII file with the computed magnitude of the electric field at a distance of 3m
and a frequency range of 0.1 GHz to 2 GHz is available. The file names are indicated below.
a)
b)
c)
d)
With no shield (Ew/o) Æ
With small holes and large hole Æ
With small holes only Æ
With large hole only Æ
ASCII file name:
ASCII file name:
ASCII file name:
ASCII file name:
5421_E_noshield.txt
5421_E_small_large.txt
5421_E_small.txt
5421_E_large.txt
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Each of the above mentioned files has two columns 1. Frequency in GHz 2. E in V/m.
For each case b), c), d) an ASCII file with the computed SE at a distance of 3m and for frequency range of 0.1
GHz to 2 GHz are available. The file names are as indicated below
b) With small holes and large hole Æ
c) With small holes only Æ
d) With large hole only Æ
ASCII file name: 5421_SE_small_large.txt
ASCII file name: 5421_SE_small.txt
ASCII file name: 5421_SE_large.txt
Each of the above mentioned files has a two columns 1. Frequency in GHz 2. SE in dB.
On request (orlandi@ing.univaq.it) the CST STUDIO SUITE 2006 [2] models used for the simulations are
available.
a)
b)
c)
d)
With no shield (Ew/o) Æ
With small holes and large hole Æ
With small holes only Æ
With large hole only Æ
CST model archive:
CST model archive:
CST model archive:
CST model archive:
5421_noshield
5421_small_large
5421_small
5421_large
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Fig. 1 - View of the electromagnetic model of the metal enclosure.
Fig. 2 - Geometrical dimensions of the enclosure; small holes and large hole. (All dimensions are in mm).
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Fig. 3 – Geometrical description of the source structure: metal plane, FR4 dielectric substrate; heat sink (all dimensions
are in mm).
DISCERETE
PORT
AS VOLTAGE SOURCE
DISCRETE
PORT
AS
50Ω LOAD
Fig. 4a – Overview of the positions of the discrete port and lumped element.
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Fig. 4b - Discrete port as voltage source and its settings.
Fig. 4c - Discrete port as 50Ω load.
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Fig. 5 - Excitation signal at the discrete port.
Fig. 6 – Electric field probes distribution.
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Fig. 7 - Boundary condition settings.
Electric Field Magnitude Comparison
0
-50
EdB [V/m]
-100
-150
5421 noshield
5421 small large
5421 small
5421 large
-200
-250
-300
0
0.2
0.4
0.6
0.8
1
1.2
Frequency [GHz]
1.4
1.6
1.8
2
Fig. 8 - Electric Field Magnitude comparison.
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SE Comparison
140
5421 small large
5421 small
5421 large
120
100
SEdB
80
60
40
20
0
-20
-40
0
0.2
0.4
0.6
0.8
1
1.2
Frequency [GHz]
1.4
1.6
1.8
2
Fig. 9 - SE comparison.
References
[1] T. Weiland, “A Discretization Method for the Solution of Maxwell’s Equation for Six Component Fields”,
Electronics and communication, (AEÜ), Vol.31 (1977), p. 116.
[2] Computer Simulation Technology, CST STUDIO SUITE 2006 Manual – ver. 2006.0.0 - , Vol I, II ,
www.cst.de.
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