ASTM D 4935-99 Standard Test Method for Measuring the Electromagnetic Shielding Effectiveness of Planar Materials
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Our ASTM D 4935-99 testing allows customers to test materials of various sizes. We offer nearly immediate scheduling and often have test reports delivered with one week of the test program being completed.
If you need expert ASTM D-4935-99 shielding effectiveness testing, we are the test lab for you. Please Contact Us or Request a Quote to get started. The remainder of this page offers an overview of the ASM D4935-99 test standard.
Summary of ASTM D4935-99 Compliance Testing
STM D 4935-99 EMC testing provides a procedure for measuring the electromagnetic shielding effectiveness of a planar material. The measurement is due to a plane-wave, far-field electromagnetic wave. From the measured data, near-field shielding effectiveness values may be calculated for magnetic sources for electrically thin specimens.
Electric field shielding effectiveness values may also be calculated from this same far-field data, but their validity and applicability have not been established. The measurement method is valid over a frequency range of30 MHz to 1.5 GHz.
These limits are not exact, but are based on decreasing displacement current due to decreased capacitive coupling at lower frequencies and on overmoding (excitation of modes other than the transverse electromagnetic mode 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-field shielding effectiveness 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. This test method is not applicable to cables or connectors.
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 appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
ASTM D 4935-99 Terminology and Calculations
Some of the terminology of the standards includes dynamic range, which is the difference between the maximum and minimum signals measurable by the system. It is important to note that the measurement of materials with good shielding effectiveness require extra care in order to avoid contamination of extremely low power or voltage values by unwanted signals from leakage paths.
The term electrically thin applies to the thickness of the specimen is much, much (<1/100) less than the electrical wavelength within the specimen. A far-field is the region where electric and magnetic are orthogonal to each other and also to the direction of propagation of energy. Conversely, near-field is the region where electric and magnetic are not related by simple rules.
The standard states that the transition region between near field and far field is not abrupt, but occurs approximately λ/2π from a dipole source, where λ is the free-space wavelength of the frequency of the source. This concept of regions is further blurred by reradiating due to scattering by reflecting materials or objects that may be distant from the source. The interior of metallic structures often contains a mixture of near-field regions.
Lastly, shielding effectiveness is the ratio of power received with and without a material present for the same incident power.
Scope of ASTM D 4935-99 Compliance
ASTM D 4935-99 is the test method that applies to the measurement of shielding effectiveness of planar materials under normal incidence, far-field, plane-wave conditions (electric and magnetic tangential to the surface of the material).
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 given 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.
Approximate near-field values of shielding effectiveness may be calculated for both electric or magnetic sources by using measured values of far-field shielding effectiveness. A program may be generated from the source code that is suitable for use on a personal computer.
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.
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In addition to shielding effectiveness testing, we also provide ESD testing, EMC testing, indirect lightning testing, and many other forms of product certification testing. We also have a full mechanical testing and package testing lab.