ASTM D4935-99

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An American National Standard
Designation: D 4935 – 99
Standard Test Method for
Measuring the Electromagnetic Shielding Effectiveness of
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Planar Materials
This standard is issued under the fixed designation D4935; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (ϵ) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 Thistestmethodprovidesaprocedureformeasuringthe 2.1 ASTM Standards:
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electromagnetic (EM) shielding effectiveness (SE) of a planar D1711 Terminology Relating to Electrical Insulation
material due to a plane-wave, far-field EM wave. From the
3. Terminology
measured data, near-field SE values may be calculated for
,
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magnetic (H) sources for electrically thin specimens. Elec- 3.1 Definitions—For definitions of terms used in this test
method refer to Terminology D1711D1711.
tric (E) field SE values may also be calculated from this same
far-field data, but their validity and applicability have not been 3.2 Definitions of Terms Specific to This Standard:
3.2.1 dynamic range (DR)—the difference between the
established.
1.2 The measurement method is valid over a frequency maximum and minimum signals measurable by the system.
3.2.1.1 Discussion—Measurement of materials with good
rangeof30MHzto1.5GHz.Theselimitsarenotexact,butare
based on decreasing displacement current due to decreased SE require extra care in order to avoid contamination of
extremely low power or voltage values by unwanted signals
capacitive coupling at lower frequencies and on overmoding
(excitation of modes other than the transverse electromagnetic from leakage paths.
3.2.2 electrically thin—the thickness of the specimen is
mode (TEM)) at higher frequencies for the size of specimen
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holder described in this test method. Any number of discrete much, much (< ⁄100) less than the electrical wavelength within
the specimen.
frequencies may be selected within this range. For electrically
thin, isotropic materials with frequency-independent electrical 3.2.3 far field—thatregionwhereEandHareorthogonalto
each other and also to the direction of propagation of energy.
properties of conductivity, permittivity and permeability, mea-
3.2.4 near field—that region where E and H are not related
surements may be needed at only a few frequencies as the
far-field SE values will be independent of frequency. If the by simple rules.
3.2.4.1 Discussion—The transition region between near
material is not electrically thin or if any of the parameters vary
with frequency, measurements should be made at many fre- field and far field is not abrupt, but occurs approximately λ/2π
from a dipole source, where λ is the free-space wave length of
quencies within the band of interest.
1.3 This test method is not applicable to cables or connec- the frequency of the source. This concept of regions is further
blurred by reradiating due to scattering by reflecting materials
tors.
1.4 This standard does not purport to address all of the or objects that may be distant from the source. The interior of
metallic structures often contains a mixture of near-field
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- regions.
3.2.5 shielding effectiveness (SE)—the ratio of power re-
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. ceived with and without a material present for the same
incident power.
3.2.5.1 Discussion—It is usually expressed in decibels by
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This test method is under the jurisdiction of ASTM Committee D-9 on
the following equation:
Electrical and Electronic Insulating Materials and is the direct responsibility of
Subcommittee D09.12 on Electrical Tests.
P
1
SE 510 log ~decibels,dB! (1)
Current edition approved April 10, 1999. Published June 1999. Originally
P
2
´1
published as D4935–89. Last previous edition D4935–89 (1994) .
2
Wilson, P. F., and Ma, M. T., “A Study of Techniques for Measuring the
where:
Electromagnetic Shielding Effectiveness of Materials,” NBS Technical Note 1095,
May 1986.
3
Adams, J. W., and Vanzura, E. J., “Shielding Effectiveness Measurements of
4
Plastics,” NBSIR 85-3035, January 1986. Annual Book of ASTM Standards, Vol 10.01.
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D4935–99
5.3 Signal Generator—A source capable of generating a
P = received power with the material present, and
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sinusoidal signal over the desired portion of the frequency
P = received power without the material present.
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range specified
...