SJH 20524-1995 (SJ20524-1995)

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SJ 20524-1995
SJ
ELECTRONIC INDUSTRY STANDARD
OF THE PEOPLE’S REPUBLIC OF CHINA
FL 3971
Measuring methods
for shielding effectiveness of materials
ISSUED ON. MAY 25, 1995
IMPLEMENTED ON. DECEMBER 01, 1995
Issued by.
Ministry of Electronic Industry of the People’s Republic of
China
Table of Contents
1 Scope ... 3 
2 Reference files ... 3 
3 Definitions ... 3 
4 General requirements ... 4 
5 Detailed requirements ... 6 
Recommended method to measure near-field shielding effectiveness of
conductive wire, conductive film, conductive rubber and other flat-plate type
materials ... 12 
Other methods to measure near-field shielding effectiveness of conductive wire,
conductive film, conductive rubber and other flat-plate type materials ... 14 
Additional information... 16 
Measuring methods
for shielding effectiveness of materials
1    Scope   
1.1 Subject content
This standard specifies the measuring methods of flat-plate type electromagnetic
shielding material, such as non-conductive material coating or plating-layer, metal mesh,
conductive film, conductive glass, and conductive dielectric plate against plane wave
shielding effectiveness.
1.2 Applicable scope
This standard is applicable for measurement of flat-plate type electromagnetic shielding
materials, such as metal film, non-conductive material coating or plating-layer, metal mesh,
conductive film, and conductive glass, and conductive dielectric plate against plane wave
shielding effectiveness.
2    Reference files 
GB 6113-85 Electromagnetic Interference Measuring Instrument
GJB 72-85 Terminology of Electromagnetic Interference and Electromagnetic
Compatibility
GJB/Z 25-90 Design Guideline on Earthing, Lapping and Shielding of Electronic
Equipment and Facility
3    Definitions 
Except for terms specified in this standard, other terms shall comply with GJB 72.
3.1 Shielding effectiveness (SE)
Under the same excitation level, the ratio of power or voltage received when there is or
there is not shielding materials; it is expressed in logarithm. That is.
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Where.
SE - shielding effectiveness, dB;
V0 - received voltage without shielding materials;
V1 - received voltage with shielding materials;
P0 - received power without shielding materials;
P1 - received power with shielding materials.
4    General requirements 
4.1 Measurement condition
a. Ambient temperature. 23 ± 2°C;
b. Environmental relative humidity. 45% ~ 75%;
c. Atmospheric pressure. 86 ~ 106 kPa;
d. The samples shall be kept in the above-mentioned environment for 48 hours before
test.
e. Environmental electromagnetic noise shall not have impact on measurement result.
4.2 Test equipment
4.2.1 Signal source
Frequency range. 1 MHz ~ 1.5 GHz;
Maximum output power. + 13 dBm;≧
Output impedance. 50 Ω;
Voltage standing wave ratio. < 2.0.
4.2.2 Electromagnetic interference measuring instrument
Working frequency range shall be consistent with the signal source phase; the
measurement error shall meet the requirements of GB 6113.
4.2.3 Flange coaxial test device is shown in figure 1;
Frequency range. 5 KHz ~ 1.5 GHz;
measurement, shall be subject to this reading value. Therefore, compression force of
each load sample are ensured to be the same, and repeatability of measurement is
improved to avoid measurement error caused by difference pressure;
f. Measuring equipment applied in this standard must have enough dynamic range, which
means the dynamic range of the measuring equipment shall be greater than the
dynamic range of flange coaxial test device;
g. Before the load sample is measured, measurement shall be carried out to the reference
sample; and measurement data shall be recorded as pass-through status data;
h. If there is standard sample, calibration shall be made to the flange coaxial test device
by using standard sample. It can determine whether the entire system works in normal
state. The standard sample is polyester film with single gold plating. The surface
resistance is 5 + 2Ω per unit area. The shielding effectiveness is 32 ±3dB;
i. Because the background noise may affect the sensitivity of the receiver, therefore, when
shielding materials with shielding effectiveness over 60 dB are measured, double layer
shielding or semi-rigid cable shall be used;
j. Before the measurement is carried out, the testing personnel shall be specially trained
and accumulate experience to ensure that the measurement results are correct and
repeatable.
k. The measurement system shall be well grounded;
l. When measurement is carried out, measurement results shall be given at least at such
frequency points at 30MHz, 50 MHz, 100 MHz, 300 MHz, 500 MHz, and 1GHz etc.
5.2 Measurement methods
When the flange coaxial testing device is used to measure shielding effectiveness of
materials, the common measurement methods are. signal source/electromagnetic
interference measuring instrument (interference receiver) measurement, tracking signal
source/spectrum analyzer measurement, and network analyzer measurement.
5.2.1 Signal source/electromagnetic interference measuring instrument (interference
receiver) measurement
a. Connect the measurement device according to figure 4, directly connect the signal
source which meets requirements of 4.2.1 in this standard to one end of this device
through 10dB attenuator, and the other end of this device shall be connected to the
electromagnetic interference measuring instrument (interference receiver) by 10dB
attenuator. Pay attention to make the measurement cable as short as possible during
measurement;
A2 Specification and dimension of double shielding box measurement device
Double shielding box dimension. 180mm X 120 mm X 160 mm;
Sample dimension. (76.2 ± 3.2 mm) X (152. 4 ± 3.2 mm);
Sample thickness. 4 mm;≦
Frequency range. 1 ~ 30 MHz;
Dynamic range. 50 dB;
Connector. BNC.
vertical electric field component and the horizontal magnetic field component of the
traverse measurement hole. Therefore, the double TEM cell is able to simulate high and
low impedance field at the same time. The basic method of measurement is similar to
other methods. It’s the same that incident power P0 and transmission power P1 are
respectively measured out by not adding and adding the sample to the window. The
shielding effectiveness of the materials can be obtained based on formula (B1).
The features of this method are. because the field is built inside the waveguide room, the
input power required is low and no electromagnetic interference will be caused to the
surrounding equipment and personnel. The disadvantage is that it is rather difficult to
install the fixed tested materials, especially it is much more difficult on how to reduce the
contact resistance. Moreover, it is easy to produce leakage or ground loop, therefore the
dynamic range is only 50 ~ 60 dB.
Additional information. 
This standard shall be under the jurisdiction of China Electronics Standardization Institute.
This standard is drafted by China Electronics Standardization Institute.
Main drafters of this standard. Wang Qing, Jiang Quanxing, Zhang Linchang, Wu Fan,
and Ma Fuhua.