Chambers
Design Considerations for EMC Test Chambers
By Don MacArthur
Digital stock image display cropped close-up view of an open electromagnetic compatibility (EMC) anechoic chamber; The thick, shielded door is open, revealing the interior walls lined with pyramid-shaped foam absorbers; A section of the interior wall is digitally highlighted in bright blue; The exterior has a white roll-up door on the left
E

lectromagnetic compatibility (EMC) test chambers are critical facilities where electronic devices are tested for their ability to function properly without emitting or being affected by electromagnetic interference (EMI). Designing an EMC test chamber requires careful consideration of several factors to ensure accurate and reliable testing. This article explores the key design considerations for EMC test chambers, focusing on material selection, chamber size, and configuration.

Material Selection
The materials used in the construction of EMC test chambers play a pivotal role in their performance. The primary materials to consider are RF absorbers and shielding materials.

RF Absorbers

  • Types of RF Absorbers: There are various types of RF absorbers, including ferrite tiles, pyramidal foam absorbers, and hybrid absorbers. Each type has its unique properties and applications. Ferrite tiles are effective at lower frequencies, while pyramidal foam absorbers perform well at higher frequencies. Hybrid absorbers combine the benefits of both types.
  • Performance Characteristics: The effectiveness of RF absorbers is measured by their reflection loss and absorption efficiency. High-quality absorbers should offer high reflection loss, ensuring minimal RF reflections within the chamber, and high absorption efficiency to reduce the incidence of standing waves and reflections.
  • Installation Considerations: Proper installation of RF absorbers is crucial for their performance. Absorbers should be evenly distributed and securely attached to the chamber walls, ceiling, and floor to ensure consistent performance across the entire testing area.

Shielding Materials

  • Types of Shielding Materials: Common shielding materials include galvanized steel, copper, and aluminum. These materials are chosen for their high conductivity and ability to attenuate electromagnetic fields.
  • Shielding Effectiveness: The effectiveness of shielding materials is measured by their shielding effectiveness, which quantifies the material’s ability to block or attenuate electromagnetic fields. High-quality shielding materials should provide effective attenuation across a wide frequency range.
  • Structural Considerations: The structural integrity of the shielding materials is important to maintain a continuous and effective shield. Overlapping seams, conductive gaskets, and proper grounding are essential to prevent leakage and ensure a complete shield.
Chamber Size and Configuration
The size and configuration of EMC test chambers are critical factors that influence their effectiveness and versatility.

Chamber Size

  • Determining Size Requirements: The size of the chamber should be determined based on the type of equipment to be tested and the test procedures. Larger chambers are required for testing larger devices or systems, while smaller chambers are suitable for individual components or small devices.
  • Compliance with Standards: The chamber size should comply with relevant standards and guidelines, such as CISPR 16-1-4 and ANSI C63.4, which specify the minimum dimensions and clearances for EMC testing.
  • Future-Proofing: Consider future testing needs and potential growth when determining the chamber size. Designing a slightly larger chamber can accommodate future testing requirements and avoid the need for expensive modifications.

Configuration

  • Chamber Layout: The layout of the chamber should facilitate easy access to the device under test (DUT) and testing equipment. Adequate space should be provided for test personnel to move around and set up equipment.
  • Antenna Positioning: Proper positioning of antennas is crucial for accurate measurements. The chamber should allow for adjustable antenna mounts and clear line-of-sight paths between the antennas and the DUT.
  • Control Room: A separate control room adjacent to the chamber allows for remote operation and monitoring of tests. This setup minimizes interference and ensures safety for test personnel.
Summary/Conclusion
Designing an effective EMC test chamber requires careful consideration of material selection, chamber size, and configuration. RF absorbers and shielding materials play crucial roles in ensuring accurate and reliable testing by minimizing RF reflections and attenuating electromagnetic fields. Proper chamber size and configuration are essential for accommodating different types of equipment and testing requirements while complying with relevant standards. By considering these factors, engineers can design EMC test chambers that provide accurate, reliable, and efficient testing environments, ultimately ensuring the electromagnetic compatibility of electronic devices.

By adhering to these best practices, engineers can ensure that their EMC test chambers are equipped to handle the rigorous demands of compliance testing, providing a reliable environment for evaluating the electromagnetic performance of electronic devices.

References and Further Reading
  1. Henry W. Ott, Electromagnetic Compatibility Engineering, Wiley, 2009.
  2. Tim Williams, EMC for Product Designers, Fifth Edition, Newnes, 2016.
  3. Louis T. Gnecco, Design of Shielded Enclosures: Cost-Effective Methods to Prevent EMI, Newnes, 2012.
  4. R. Timothy Hitchcock and Robert M. Patterson, Radio-Frequency and ELF Electromagnetic Energies: A Handbook for Health Professionals, Wiley, 1995.
  5. IEEE EMC Society, “IEEE Std 1128-1998 – Recommended Practice for RF Absorber Evaluation in the Range of 30 MHz to 5 GHz,” IEEE Xplore.
Share this story:
Back to Issue