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《ASTM D4935测试平面材料电磁屏蔽效果的标准方法》该标准ASTM D4935-10是关于测定平面材料对平面、远场电磁波电磁屏蔽效果的测试方法。标准中的数字表示首次采纳或修订的年份，括号内的数字则表示最近一次修订或复审的年份。编辑上的修改会用上标epsilon（'）表示。 1. 范围 1.1 本测试方法提供了一种程序，用于测量平面材料对于平面远场电磁波的电磁屏蔽效能（SE）。通过对测量数据的分析，可以计算出磁性（H）源的近场SE值。对于电学上薄的样品，可以从这些数据中推算出近场SE值。然而，这种方法对于电场（E）场的SE值的计算有效性及适用性尚未得到证实。 1.2 测量方法的有效频率范围为30 MHz到1.5 GHz。这个范围并非绝对，而是基于在较低频率时因位移电流减少导致的耦合效应下降，以及在较高频率时由于测试样品支架尺寸导致的横向电磁模式（TEM）之外的模式激发。在这个范围内可以选择任何离散频率进行测量。对于电学上薄的各向同性材料，如果其导电率、介电常数和磁导率不随频率变化，可能只需要在少数频率下进行测量，因为远场SE值将与频率无关。如果材料不是电学上薄或者其参数随频率变化，应在感兴趣的频带内进行多个频率的测量。 1.3 本测试方法不适用于电缆或连接器。 1.4 单位——标准中所使用的SI单位被视为标准。标准中未包含其他度量单位。 1.5 本标准并不旨在解决所有安全问题，也不提供或暗示任何关于安全的保证或责任。此标准为电磁屏蔽效能的测试提供了统一的准则，有助于确保不同研究和应用中材料屏蔽性能的准确评估。通过使用该方法，可以更好地理解材料如何阻止或减弱电磁波的传播，这对于电子设备的保护、信号干扰的控制、无线通信的优化等领域具有重要意义。同时，对于材料参数的频率依赖性进行了考虑，使测试更具全面性和科学性。在实际应用中，根据具体需求选择合适的测试频率和方法，能有效提升电磁屏蔽效果的评估质量和精度。

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Designation: D4935 - 10

Standard Test Method for

Measuring the Electromagnetic Shielding Effectiveness of

Planar Materials

This standard is issued under the ?xed designation D4935; the number immediately following the designation indicates the year of

original adoption or, in the caseof revision, the year of last revision. A number in parenthesesindicates the year of last reapproval. A

superscript epsilon (′) indicates an editorial change since the last revision or reapproval.

1. Scope

1.1 This test method provides a procedure for measuring the

electromagnetic (EM) shielding effectiveness (SE) of a planar

material for a plane, far-?eld EM wave. From the measured

data, near-?eld SE values may be calculated for magnetic (H)

sources for electrically thin specimens.

2,3

Electric (E) ?eld SE

values may also be calculated from this same far-?eld data, but

their validity and applicability have not been established.

1.2 The measurement method is valid over a frequency

range of 30 MHz to 1.5 GHz. These limits are not exact, but are

based on decreasing displacement current as a result of

decreased capacitive coupling at lower frequencies and on

overmoding (excitation of modes other than the transverse

electromagnetic mode (TEM)) at higher frequencies for the

size of specimen holder described in this test method. Any

number of discrete frequencies may be selected within this

range. For electrically thin, isotropic materials with frequency

independent electrical properties of conductivity, permittivity,

and permeability, measurements may be needed at only a few

frequencies as the far-?eld SE values will be independent of

frequency. If the material is not electrically thin or if any of the

parameters vary with frequency, measurements should be made

at many frequencies within the band of interest.

1.3 This test method is not applicable to cables or connec-

tors.

1.4 Units —The values stated in SI units are to be regarded

as standard. No other units of measurement are included in this

standard.

1.5 This standard does not purport to address all of the

safety concerns, if any, associated with its use. It is the

responsibility of the user of this standard to establish appro-

priate safety and health practices and determine the applica-

bility of regulatory limitations prior to use.

2. Referenced Documents

2.1 ASTM Standards:

D1711 Terminology Relating to Electrical Insulation

3. Terminology

3.1 De?nitions —For de?nitions of terms used in this test

method, refer to Terminology D1711.

3.2 De?nitions of Terms Speci?c to This Standard:

3.2.1 dynamic range (DR), n—difference between the maxi-

mum and minimum signals measurable by the system.

3.2.1.1 Discussion —Measurement of materials with good

SE require extra care to avoid contamination of extremely low

power or voltage values by unwanted signals from leakage

paths.

3.2.2 electrically thin, adj —thickness of the specimen is

much smaller (<

100

) than the electrical wavelength within the

specimen.

3.2.3 far ?eld, n—that region where vectors E and H are

orthogonal to each other and both arenormal to the direction of

propagation of energy.

3.2.4 near ?eld, n—that region where E and H are not

related by simple rules.

3.2.4.1 Discussion —The transition region between near

?eld and far ?eld is not abrupt but is located at the distance

close to λ/2πfrom a dipole source, where λis the free-space

wave length of the frequency of the source. This concept of

regions is further blurred by reradiating as a result of scattering

by re?ecting materials or objects that may be distant from the

source. The interior of metallic structures often contains a

mixture of near-?eld regions.

3.2.5 shielding effectiveness (SE), n—ratio of power re-

ceived with and without a material present for the same

incident power.

This test method is under the jurisdiction of ASTM Committee D09 on

Electrical and Electronic Insulating Materials and is the direct responsibility of

Subcommittee D09.12 on Electrical Tests.

Current edition approved May 1, 2010. Published June 2010. Originally

approved in 1989. Last previous edition approved in 1999 as D 4935–99.DOI:

10.1520/D4935 –10.

Wilson, P. F., and Ma, M. T., “ＡStudy of Techniques for Measuring the

Electromagnetic Shielding Effectiveness of Materials, ”NBS Technical Note 1095,

May 1986.

Adams, J. W., and Vanzura, E. J., “ShieldingEffectiveness Measurements of

Plastics, ”NBSIR 85-3035, January 1986.

For referencedASTM standards, visit the ASTM website, www.astm.org, or

contactASTM Customer Service at service@astm.org. For Annual Book of ASTM

Standardsvolume information, refer to the standard ’ｓDocument Summary pageon

the ASTM website.

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3.2.5.1 Discussion — SEis usually expressed in decibels

(dB) by the following equation:

SE5 10log

(1)

where:

= received power with the material present, and

= received power without the material present.

If the receiver readout is in units of voltage, use the

following equation:

SE5 20log

(2)

where:

and V

= respective voltage levels with and without a

material present.

According to these equations, SE will have a negative

value if less power is received with the material present than

when it is absent.

4. Signi?cance and Use

4.1 This test method applies to the measurement of SE of

planar materials under normal incidence, far-?eld, plane-wave

conditions (E and H tangential to the surface of the material).

4.2 The uncertainty of the measured SE values is a function

of material, mismatches throughout the transmission line path,

dynamic range of the measurement system, and the accuracy of

the ancillary equipment. An uncertainty analysis is given in

Appendix X1 to illustrate the uncertainty that may be achieved

by an experienced operator using good equipment. Deviations

from the procedure in this test method will increase this

uncertainty.

4.3 Approximate near-?eld values of SE may be calculated

for both E or H sources by using measured values of far-?eld

SE. A program may be generated from the source code in

Appendix X2 that is suitable for use on a personal computer.

4.4 This test method measures the net SE caused by

re?ection and absorption. Separate measurement of re?ected

and absorbed power may be accomplished by the addition of a

calibrated bidirectional coupler to the input of the holder.

5. Apparatus

5.1 A basic equipment setup is shown in Fig. 1.

5.2 Specimen Holder —Physical dimensions of a specimen

holder are given in Annex A1 . The specimen holder is an

enlarged, coaxial transmission line with special taper sections

and notched matching grooves to maintain a characteristic

impedance of 50 ? throughout the entire length of the holder.

This impedance is checked in accordance with 7.1, and any

variations greater than 6 0.5 ? are corrected. There are three

important aspects to this design. First, a pair of ?anges in the

middle of the structure hold the specimen. This allows capaci-

tive coupling of energy into insulating materials through

displacement current. Second, a reference specimen of the

same thickness and electrical properties as the load specimen

causes the same discontinuity in the transmission line as is

caused by the load specimen. Third, nonconductive (nylon)

screws are used to connect the two sections of the holder

together during tests. This prevents conduction currents from

dominating the desired displacement currents necessary for the

correct operation of this specimen holder.

5.3 Signal Generator, a source capable of generating a

sinusoidal signal over the desired portion of the frequency

range speci?ed in 1.2. A 50-? output impedance is needed to

minimize re?ections caused by mismatches. Precision step

attenuators are useful in increasing the effective dynamic range

for SE measurements.

5.4 Receiver, a device with a 50-? input impedance capable

of measuring signals over the same frequency range as the

signal generator in 5.3. A wide dynamic range is desirable to

achieve a wide dynamic range of measured SE values.

Typically, either a spectrum analyzer or a ?eld intensity meter

is used.

5.5 Coaxial Cables and Connectors —These are devices for

connecting power between speci?c components without caus-

ing interference with other components. These should all have

a 50-? characteristic impedance. Double-shielded cables pro-

vide lower leakage than single-shielded cables. Type N con-

nectors provide more reliability and less leakage than BNC

connectors. Precision 14-mm connectors give lower mismatch

errors and are more reliable under heavy usage than other

connectors but are more expensive and are not used on most

generators or receivers.

5.6 Attenuators —These are devices used to isolate the

specimen holder from the signal generator and the receiver.

Their main purpose in this system is for impedance matching.

A10-dB, 50-? attenuator should be used on each end of the

specimen holder. The material under test usually causesa large

re?ection of energy back into the signal generator. This may

also cause variations of the incident power by changing the

generator impedance loading. Use of a bidirectional coupler

allows monitoring and correcting any changes in incident

power as a result of this loading. Attenuators greater than 10

dB will excessively decrease the dynamic range of the mea-

surement system.

6. Test Specimens

6.1 The reference and load specimens shall be of the same

material and thickness. Both are shown in Fig. 2. Dimensions

are shown in Fig. 3. The load specimen can be larger than the

outer diameter of the ?ange on the holder but keeping them to

the dimensions shown in Fig. 3 will expedite handling.

6.2 Specimen thickness is a critical dimension. For the best

repeatability of SE measurements, reference specimen and load

specimen shall be identical in thickness. For this test method,

two specimens are considered to have identical thickness if the

FIG. 1 General Test Setup

D4935 - 10

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