IPC-TM-650 EN 2022 试验方法.pdf - 第594页

IPC-2-5-15-1 Figure 1 Shielding Effectiveness T est Setup IPC-TM-650 Number 2.5.15 Subject Guidelines and Test Methods for RFI-EMI Shielding of Flat Cable Date 10/86 Revision A P a g e4o f5 电子技术应用 ｗｗｗ．ＣｈｉｎａＡＥＴ．ｃｏｍ

100%1 / 824
These
readings are taken with both open and short circuits on
the radiating bare wire.
6.4
It
should be noted that although a shield may be quite
effective in protecting a cable system, tests should be made
to determine the affect the shielding materials have on the
internal electrical cable properties.
In a cable system handling high-speed digital pulses, the
choice of shielding materials can greatly affect important
transmission characteristics. If a shield is applied to suppress
strong magnetic fields and a ferromagnetic material is used,
which has a low conductivity, it will create a direct capaci-
tance coupling between adjacent signal carrying conductors.
This coupling will cause an increase in the crosstalk between
signals and will also distort the output rise time of the pulse.
If shielding is necessary on a sophisticated transmission line
system, a few tradeoffs might be necessary to obtain the opti-
mum operating conditions.
T
able 1
Metal
Relative
Conductivity
G
Relative
Permeability
u
Properties
of Various Metals
at 150 KHz
Properties of Various Metals
at 400 MHz
Absorption
Loss in db
A
Magnetic
Reflection
Loss in db
R
H
Electric
Reflection
Loss
in db
R
E
Absorption
Loss
in db
A
Magnetic
Reflection
Loss in db
R
H
Electric
Reflection
Loss
in db
R
E
Silver
1.05 1 1.34 34.7 198.5 6.92 48.9 155.7
Copper 1.00 1 1.31 34.5 198.3 6.76 48.7 155.5
Gold 0.70 1 1.09 32.9 196.7 5.65 47.1 154.0
Aluminum 0.61 1 1.02 32.4 196.1 5.28 46.6 153.4
Magnesium 0.38 1 0.80 30.3 194.1 4.17 44.5 151.3
Cadmium 0.23 1 0.63 28.1 191.9 3.24 42.3 149.1
Nickel 0.20 1 0.58 27.5 191.3 3.02 41.7 148.5
Iron 0.17 1,000 17.06 1.07 160.6 88.14 11.8 117.8
Tin 0.15 1 0.50 26.3 190.0 2.62 40.5 147.3
Steel, 1045 0.10 1,000 13.10 0.0001 158.3 67.6 9.8 115.5
Lead 0.08 1 0.37 23.6 187.3 1.91 37.7 144.5
Mu-Metal 0.03 80,000 64.13
*
7.3
134.0 331.17 0.93 91.2
Permalloy 0.03 80,000 64.13
*
7.3
134.0 331.17 0.93 91.2
Stainless
Steel
0.02 1,000 5.85 -1.3 151.3 30.23 4.2 108.5
*
V
alid only if incident field does not saturate metal.
Calculations are for a 0.0025 mm thick shield 2.5 cm away from the radiating source.
IPC-TM-650
Number
2.5.15
Subject
Guidelines
and Test Methods for RFI-EMI Shielding of Flat Cable
Date
10/86
Revision
A
P
age3of5
电子技术应用　　　　　　　ｗｗｗ．ＣｈｉｎａＡＥＴ．ｃｏｍ
IPC-2-5-15-1
Figure
1 Shielding Effectiveness Test Setup
IPC-TM-650
Number
2.5.15
Subject
Guidelines
and Test Methods for RFI-EMI Shielding of Flat Cable
Date
10/86
Revision
A
P
age4of5
电子技术应用　　　　　　　ｗｗｗ．ＣｈｉｎａＡＥＴ．ｃｏｍ
IPC-2-5-15-2
Figure
2 Connection of Copper Wire
IPC-TM-650
Number
2.5.15
Subject
Guidelines
and Test Methods for RFI-EMI Shielding of Flat Cable
Date
10/86
Revision
A
P
age5of5
电子技术应用　　　　　　　ｗｗｗ．ＣｈｉｎａＡＥＴ．ｃｏｍ