NSA 94-106 Shielding Effectiveness Testing
The NSA 94-106 shielding effectiveness testing standard provides requirements for the installation and performance of shielded enclosures to attenuate electromagnetic radiation. The requirements of NSA 94-106 apply to all associated and auxiliary facilities furnished as part of a shielded enclosure.
As a leader in EMC regulatory compliance testing, Keystone Compliance assists electronic equipment manufacturers with shielding effectiveness testing. Meeting the NSA, IEC, EN, and other EMC testing requirements can be challenging. Not only do we understand the challenges, but we help guide companies through the process.
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Summary of EMI Attenuation Testing of NSA-94-106
Design and Construction
This phase of the shielding procedures emphasizes the importance of maximizing electromagnetic attenuation in designing and constructing enclosures. Considerations for reliability, materials, and ease of assembly/disassembly must be accounted for.
The enclosure’s size will match the contract specifications. Likewise, the contractor chooses noncorrosive shielding materials unless specified otherwise. Joints must be bolted from the inside unless it’s a double-walled design.
Lastly, the structure must be defect-free, with surface coverings and support systems as specified in the contract. The structure must resist damage from noncorrosive liquids or moisture without affecting its attenuation properties
Performance
The shielded enclosure must meet the requirements for electromagnetic attenuation. Isolation devices are required for all lines penetrating the enclosure, ensuring no degradation in attenuation, with the power isolation system providing at least 100 dB insertion loss.
A single ground lug connected to the shield surface must ensure proper grounding.
Reliability
The shielded enclosure will be subject to varying floor loads, repeated use of access doors, and continuous use of the HVAC and electrical filters.
When maintained by the manufacturer’s preventative and routine maintenance instruction, it shall retain the specified attenuation for a minimum of five years without retightening of bolts (if used), seams, or other major maintenance.
Materials and Warranty
All materials must be new, undamaged, and of high quality. Contractors are required to guarantee the performance of the enclosure for five years.
Quality Assurance
The document details the responsibilities of the contractor in terms of inspections and tests to ensure the enclosure meets the specified standards.
Additional Requirements
Includes specifications for access doors, HVAC systems, power and line isolation, and grounding.
Access doors must be sturdy, ensuring complete closure to meet attenuation requirements. HVAC ducts should maintain proper airflow without compromising the enclosure’s attenuation.
HVAC ducts must not restrict airflow for proper AC operation. The contractor must ensure the installation doesn’t reduce the enclosure’s sound attenuation.
NSA 94-106 EMI/RFI Shielding Testing Procedures
The contractor is responsible for performing all inspections before submitting for the contracting officer’s representative approval. They can use their own facilities or any approved commercial lab, and inspection records must be available to the Government. The Government can also conduct inspections if necessary to ensure compliance with requirements.
A continuous wave (CW) source covering 1 kHz to 10 GHz, along with magnetic and electric field antennas, will be used for testing. Magnetic field antennas cover 1 kHz to 1 MHz, while electric field and plane wave antennas cover 1 kHz to 10 GHz. Receivers or spectrum analyzers must measure attenuation from 1 kHz to 10 GHz as per Figure 1.
Magnetic/Electric/Plane Wave Test
Attenuation tests will be conducted with antennas 61 cm apart (plus wall thickness) for magnetic (1 kHz to 1 MHz) and electric fields (1 kHz to 10 MHz). Plane wave tests are done with antennas 6 meters apart (if possible) and 5.1 cm from the wall for frequencies of 100 MHz to 10 GHz.
Tests are conducted around the entire enclosure, including doors, ducts, and penetrations, and across at least four locations, covering 180 square feet each.
Results must be documented, and the lowest attenuation recorded. The Government may require additional tests at specific frequencies or locations.
Filter Insertion Loss
All installed isolation devices must be tested for insertion loss or attenuation. Power filters will be tested per MIL-STD-220A and installed on the enclosure for attenuation tests.
Additionally, power filters must also be tested for voltage drop (max 2%) under half and full rated current. They must operate under full load for 10 hours, with the case temperature increase not exceeding 25°C (77°F) above ambient.
Importance of NSA-94-106 Certification Testing Process
Testing shielded enclosures is crucial for several reasons:
- Ensuring Compliance: Testing ensures that the enclosure meets specific electromagnetic attenuation standards set by regulatory bodies or contractual agreements. Compliance is vital for maintaining operational integrity in sensitive environments.
- Reliability: By conducting rigorous testing, manufacturers can verify that the enclosure will perform reliably over time, maintaining its shielding effectiveness under various conditions, including mechanical stress, environmental changes, and prolonged use.
- Security: Shielded enclosures are often used to protect sensitive equipment from electromagnetic interference (EMI) and prevent eavesdropping or data leakage. Testing ensures that the enclosure effectively shields against external and internal electromagnetic threats, safeguarding sensitive information.
- Quality Assurance: Testing provides a way to assess the quality of materials, construction, and assembly, ensuring that the enclosure will function as intended without defects that could compromise performance.
- Safety: Proper testing can prevent hazards associated with electromagnetic interference, such as malfunctioning equipment or compromised safety systems, which could lead to accidents or operational failures.
How often should NSA-94-106 testing be performed?
The specification recommends that shielded enclosures be reviewed and potentially retested every three years or sooner if there are changes in the operational environment, such as new equipment installation, modifications to the enclosure, or updates in applicable standards.
Can NSA-94-106 testing be conducted on-site, or does it need to be in a lab?
NSA-94-106 testing can be conducted on-site, especially for large installations. On the other hand, shielding testing can also be done at a laboratory if the enclosure can be transported. On-site testing ensures that the enclosure performs as expected in its actual operating environment.
What are the most common issues found during NSA-94-106 testing?
Common issues include insufficient attenuation at critical frequencies, improper installation of seams or gaskets, degradation of shielding materials over time, and failures in grounding or power isolation systems. These issues can compromise the effectiveness of the enclosure and require remediation.
What documentation is needed to prove compliance with NSA-94-106?
Documentation typically includes detailed test reports, maintenance records, materials certifications, and any certificates of compliance issued by the testing provider. This documentation must be kept up-to-date and available for audits or inspections.
The Impact of Electromagnetic Shielding on Various Industries
Testing shielded enclosures is vital for ensuring that they perform as expected, particularly in industries where electromagnetic interference can have significant consequences on security, safety, and operational reliability.
Defense and Military
Shielded enclosures are critical in defense and military applications to protect communications and electronic equipment from EMI and to secure sensitive operations against electronic surveillance.
Telecommunications
Telecom companies use shielded enclosures to protect equipment in data centers and communication hubs from electromagnetic interference that could disrupt signals or degrade performance.
Medical
In the medical industry, shielded enclosures protect sensitive diagnostic and treatment equipment. This includes equipment such as MRI machines, CT scanners, radiotherapy machines, endoscopes, pacemakers, and more.
Aerospace
The aerospace industry uses shielded enclosures to protect avionics and other critical systems from EMI. This is crucial for the safety and reliability of aircraft operations.
Research and Development
Laboratories and research institutions use shielded enclosures to conduct experiments and develop technologies that are sensitive to electromagnetic fields.
Manufacturing
Manufacturers of electronic components and systems use shielded enclosures to test products for EMI compliance. This ensures that they meet industry standards before being released to the market.
Expert Shielding Effectiveness Certification Testing Laboratory
In addition to NSA 94-106 testing, Keystone has a full scope of expertise including environmental and package testing such as accelerated aging, ingress protection, and vibration. Keystone has a full lab of test equipment which permits us to provide short lead times on scheduling.
Our team strives to give our customers more time and energy on product development instead of testing.
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