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How is Shielding Tested to Determine Shielding Effectiveness?

Keystone Compliance specializes in shielding effectiveness testing, a critical aspect of EMC/EMI compliance.

We offer comprehensive support, from developing the test plan to issuing the final report. Additionally, our laboratory is equipped with advanced facilities, including seven specialized chambers and a range of ground plane and ESD workstations.

Antenna Setup in Shielding Effectiveness Testing

A critical phase in shielding effectiveness testing is the antenna setup, which is meticulously engineered to measure signal attenuation—a fundamental indicator of a material’s capability to shield against electromagnetic interference. This setup involves:

Two Antennas: One acts as a transmitter, sweeping through the necessary frequency range, while the other serves as a receiver, capturing the field strength. This dual-antenna configuration is essential for evaluating the sample’s attenuation characteristics.

Dynamic Range Calculation for Accurate Results

Dynamic range calculation is a prerequisite for accurate shielding effectiveness testing, ensuring the reliability of the test outcomes. This process involves:

Verification Steps

Before assessing the sample, the testing procedure includes a verification phase to establish the dynamic range, comparing the signal strength with and without a barrier. This calculation is vital for confirming the precision of the measurements and ensuring that the sample’s shielding performance is accurately represented.

Electric and Magnetic Fields

The differentiation between electric and magnetic fields is crucial for a comprehensive analysis of shielding effectiveness, encompassing:

Far-Field Measurements

In far-field measurements, the focus is on the interaction between electric and magnetic fields when they are orthogonal to each other. This orthogonality signifies the direction in which the electromagnetic energy propagates through space.

Far-field conditions typically occur at distances greater than a few wavelengths away from the source of radiation. In this region, the electromagnetic waves spread out and the intensity of the fields decreases with distance.

This type of measurement is crucial for understanding how electromagnetic waves emanate from an antenna or a similar source and interact with shielding materials at a distance. It helps in assessing the effectiveness of the shielding in blocking or attenuating radiated electromagnetic energy.

Near-Field Measurements

Contrastingly, near-field measurements address the electromagnetic field’s behavior in close proximity to the antenna or source.

In the near-field region, which extends to about one wavelength away from the source, the relationship between electric and magnetic fields is more complex. Here, the fields do not necessarily propagate as radiative electromagnetic waves but can have significant reactive (non-radiative) components.

This proximity effect is crucial for analyzing how shielding materials behave when exposed to electromagnetic fields that have not yet formed into uniform waves.

Near-field testing provides insights into the material’s ability to absorb or reflect electromagnetic energy before it transitions into the far-field region, offering a more nuanced understanding of shielding performance in real-world scenarios where sources of EMI might be close to sensitive equipment.

Cable Shielding

In the realm of EMC/EMI compliance testing, the specialized testing for cable shielding stands out as a pivotal evaluation process. This type of testing is dedicated to understanding and quantifying how well a cable’s shielding properties protect against the intrusion or escape of radio waves, electromagnetic fields (EMF), and electrostatic fields.

The primary goal is to ensure that cables can perform effectively in their intended environments, minimizing interference that could affect device functionality or data integrity. Here’s a closer look at the key factors and methodologies involved:

Key Factors in Cable Shielding Effectiveness

  • Material Properties: The composition of the shielding material plays a significant role. Metals like copper, aluminum, and tin are commonly used for their conductive and magnetic properties, which are essential for reflecting or absorbing electromagnetic energy.
  • Thickness of the Shielding: The thickness of the material directly impacts its ability to attenuate electromagnetic interference (EMI). Generally, thicker shields offer better protection, but practical limitations such as flexibility and weight must also be considered.
  • Physical Characteristics of the Shielded Volume: The dimensions and shape of the cable, including the layout and spacing of internal conductors, affect how electromagnetic fields interact with the cable. Optimal design can enhance shielding effectiveness by reducing the cable’s susceptibility to interference.
  • Frequency of the Fields of Interest: Shielding effectiveness varies across different frequency ranges. High-frequency signals may require different shielding strategies compared to low-frequency signals, due to differences in wave behavior and penetration capabilities.

Why Partner with Keystone Compliance?

Partnering with Keystone Compliance means accessing a team of skilled engineers and a laboratory accredited to ISO-17025 standards, known for producing globally recognized test reports. Our comprehensive testing services are designed to give clients the confidence they need to navigate the complexities of EMC/EMI compliance.

To evaluate the shielding performance of your materials, cables, products, or facilities, Keystone Compliance is ready to provide expert assistance. Contact us to discuss your needs, request a quote, and learn why many manufacturers trust us for their shielding effectiveness testing requirements. Visit our website at www.keystonecompliance.com for more information.

 

For more information on shielding effectiveness testing, please follow the corresponding links:

Shielding Effectiveness
ASTM D 4935-10
ASTM D 4935-99
IEEE 299
MIL-STD-285
MIL-STD-907B
MIL-STD-1377
MIL-G-83528