ASTM D4935-18 Standard Test Method for Measuring Electromagnetic Shielding Effectiveness of Planar Materials

Material Testing

ASTM D4935-18 Standard Test Method for Measuring Electromagnetic Shielding Effectiveness of Planar Materials

Developed by the American Society for Testing and Materials (ASTM), the ASTM D4395 standard provides a method for measuring the electromagnetic shielding efficiency of a planar material for a plane, far-field electromagnetic wave. From the measured data, near field shielding efficiency values ​​for magnetic sources for electrically thin samples are calculated. Electric field shielding efficiency values ​​are also calculated from the same far field data, but their validity and applicability have not been determined.

ASTM D4935-18 Standard Test Method for Measuring Electromagnetic Shielding Effectiveness of Planar Materials

The full name of this standard is as follows: ASTM D4935-18 Standard test method for measuring the electromagnetic shielding effectiveness of planar materials.

Measurements made within the scope of this standard are valid in the frequency range of 30 MHz-1.5 GHz. However, these limits are not firm. This test method is based on reduced displacement current as a result of reduced capacitive coupling at lower frequencies and excessive modification at higher frequencies for the described specimen holder size, ie excitation of modes other than the transverse electromagnetic mode.

Any number of discrete frequencies in this range should be selected during the tests. For electrically thin, isotropic materials, for frequency-independent electrical conductivity and permeability properties, far field shielding efficiency values ​​are frequency independent. Therefore measurements are only required at a few frequencies. If the material is not electrically thin or if any of the parameters vary with frequency, measurements should be made at several frequencies within the baseline band.

By the way, the test method presented in this standard does not apply to cables or connectors.

Briefly, this test method is valid for measuring the shielding efficiency of planar materials under normal domain, far field and plane wave conditions.

The uncertainty of the measured shielding efficiency values ​​is a function of mismatches in the material's transmission line path, the dynamic range of the measuring system, and the accuracy of the auxiliary equipment. An uncertainty analysis is included in the standard appendix to show the probability of uncertainty achieved by an experienced user using good equipment. Deviations from the processes in this test method increase this uncertainty.

This test method measures the net shielding efficiency value caused by reflection and absorption. The measurement of reflected and absorbed power is performed by adding a calibrated bidirectional coupler at the inlet of the holder.

ASTM D-4935 shielding effectiveness test focuses on planar materials. However, this standard does not claim to address all safety concerns for use. It is the responsibility of the person applying this standard to establish appropriate safety and health practices and to determine the applicability of regulatory restrictions prior to use.

Dynamic range refers to the difference between the highest and lowest signals measured by the system in accordance with the ASTM D4935 standard. The term electrically thin means that the thickness of the sample is much smaller than the electrical wavelength in the sample. The far field is the region where the vectors are perpendicular to each other and both are perpendicular to the direction of propagation of energy. The near field is the region where vectors are not associated with simple rules. Ultimately, the shielding efficiency is the ratio of the power taken with and without a material for the same event force.

In many applications, due to the effect of higher and higher frequencies, the shielding efficiency values ​​of the materials are expanding to frequencies well above 1 GHz. In addition, energy efficiency requirements require the use of lightweight protective materials such as composites, especially in aerospace applications. A typical concern with composite materials is their internal homogeneity.

Our organization, among numerous tests, measurement, analysis and evaluation studies, with its trained and expert staff and advanced technological equipment, within the framework of national and international standards, provides standard test method services for measuring the electromagnetic shielding efficiency of planar materials within the scope of ASTM D4935-18 standard. gives.

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