The ASTM D 4935-10 standard evaluates the shielding effectiveness of planar material for a plane, far-field electromagnetic wave. An illustration of such is shown below. The samples under test must be electrically thin for a near field magnetic field (H) calculation. Electric field shielding effectiveness can be calculated for far-field as well, but applicability has yet to be established.
Measurements are to be taken within a frequency range of 30 MHz – 1.5GHz. However, these limits are not exact. The limits are generally based on decreasing displacement current as a result of decreased capacitive coupling at lower frequencies.
For an electrically thin isotropic material, measurements are needed at only a few frequencies. If the material is not electrically thin, measurements are made at many frequencies within the band of interest.
Scope of ASTM D 4935-10 Lab Testing
ASTM D4935-10 EMC testing applies to the measurement of shielding effectiveness of planar materials under normal incidence, far-field, plane-wave conditions. The uncertainty of the measured shielding effectiveness 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 provided in the ASTM D 4935-10 test standard 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.
This test method measures the net shielding effectiveness caused by reflection and absorption. Separate measurement of reflected and absorbed power may be accomplished by the addition of a calibrated bidirectional coupler to the input of the holder.
The final test report includes test specimen identification and measured values of shielding effectiveness at each frequency of measurement. Values of shielding effectiveness are noted as exceeding the DR of the system when the measured values from 8.7 that are within 10 dB of the smallest detectable signal of the measurement.
Expert ASTM Shielding Effectiveness Compliance
In addition to ASTM D4935 EMC testing, Keystone has a full scope of expertise including environmental and package testing such as accelerated aging, vibration, and cold chain. Our team strives to give our customers more time and energy on product development instead of testing.
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