Shielding effectiveness testing is a critical process used to determine the ability of an electrical or electronic enclosure to shield against electromagnetic interference (EMI) and radio frequency interference (RFI). This testing is important because electronic equipment is becoming increasingly sensitive to electromagnetic interference, and it is essential to ensure that electronic systems are protected from unwanted electromagnetic emissions.
The shielding effectiveness of an enclosure is determined by exposing it to an electromagnetic field and measuring the amount of electromagnetic energy that penetrates the enclosure. The shielding effectiveness is then calculated as the ratio of the electromagnetic energy inside the enclosure to the electromagnetic energy outside the enclosure.
There are several test methods that are commonly used for shielding effectiveness testing, including resonant cavity, waveguide, and transfer impedance methods. These methods differ in the type of electromagnetic field used, the equipment and materials required, and the complexity of the test setup.
One of the key benefits of shielding effectiveness testing is that it helps to ensure the reliability and functionality of electronic and electrical equipment in the presence of electromagnetic interference. By exposing electronic equipment to an electromagnetic field and measuring the amount of electromagnetic energy that penetrates the enclosure, the shielding effectiveness of the enclosure can be determined, and improvements can be made if necessary.
Another benefit of shielding effectiveness testing is that it provides a common reference for the design and development of electronic equipment, which helps to ensure the compatibility and interoperability of electronic systems across different platforms and networks. This is particularly important in military and aerospace applications, where shielding effectiveness is critical to ensure the security and reliability of these systems.
What Materials Block or Absorb RF?
Metal is the best material to block electromagnetic energy. The metal could be sheet metal, metal screens, or metal foam. However, metal is rigid, heavy, and expensive. Because of this, other materials have been created to provide the RF blocking properties of metal without the drawbacks. These materials are lighter, flexible, and sometimes less expensive.
Resins and fabrics are designed with RF blocking material woven. Likewise, some paints, inks, and coatings have RF blocking properties. These materials often consist of a carrier metal loaded with very small particulates of another metal such as nickel or copper. Copper is used for RF shielding because it absorbs electromagnetic and RF waves.
What Items Should be RF Shielding Tested?
As a shielding effectiveness test lab, Keystone Compliance tests a variety of products. Material samples are just one of the many items we can test. With technology advancements, manufacturers must push the envelope and find more flexible and cost-effective materials that can block RF. Some of the materials we have tested include: fabrics, resins, glass, paints, and inks.
The majority of our RF shielded testing involves cables and entire electronic devices. In testing an electronic device, we are essentially testing the enclosure.
There are two focuses when testing an enclosure. First, we test how well an enclosure keeps RF noise generated by the device inside the device. It is important that the device’s operations do not interfere with other devices. The second consideration is how well the device keeps outside electromagnetic noise outside of the device. It is equally important that a device’s operations are not interrupted by other devices or signals.
When testing an enclosure, the most common points of concern are cables, fans, and inputs/outputs. Essentially, what are the holes in the enclosure, and are the gaskets, filters, insulation, and other components sufficiently blocking RF.
The last test item we test are facilities. The most common facilities are military, medical, industrial, and utilities. Electromagnetic Pulse (EMP) attacks are a growing concern and have prompted new standards and hardening requirements.
How is electromagnetic shielding testing completed?
The process of shielding effectiveness testing depends on what is being tested. The testing or materials for RF shielding is completed by having two connected EMC test chambers with a shared wall. This shared wall has an opening in which the material sample is placed. The RF shielding test lab will place a receiving antenna in one chamber and a transmitting antenna in the second chamber. Then, the transmitting antenna will transmit a set of RF waves. Lastly, the receiving antenna will record all of the electromagnetic signals received.
To determine how well shielding material performs, labs conduct an analysis of what was transmitted and received. Any RF noise transmitted but not received was effectively blocked.
To test electronic devices, an EMC test chamber is used. First, an EMC test engineer will operate the device to be tested. For part of the testing, a receiving antenna receives and records all of the EMI generated by the device. Upon completion, a transmitting antenna will transmit signals at the device. The objective is to determine if there are unacceptable impacts on its operation.
Acceptable and unacceptable criteria generally depend on the device and its purpose. For instance, a blip on the screen of a video game might be acceptable. Whereas a blip on an aircraft navigation system might not. The test standard often details what is acceptable and what is not.
Testing the shielding effectiveness of a facility is similar to the testing of a material sample. Antennas are placed on both sides of the structure. The structure could be a vent, a wall, a window, a door, or any other physical barrier. Next, one antenna is to be receiving and the other transmitting radio frequencies.
The shielding effectiveness of facilities is important for certain industries such as military, aerospace, health care, and industrial facilities.
Expert Shielding Effectiveness Compliance Testing
Keystone Compliance has developed the reputation of being a leader in electromagnetic shielding testing. Our engineers not only provide testing but can also assist in the design and implementation of shielding effectiveness test improvements. Please contact us for more information on how Keystone Compliance can assist you with determining and improving the RF shielding of your product.
Common RF Shielding Test Standards:
- ASTM D 4935-10: Standard Test Method for Measuring the Electromagnetic Shielding Effectiveness of Planar Materials
- ASTM D 4935-99: Standard Test Method for Measuring the Electromagnetic Shielding Effectiveness of Planar Materials
- IEEE 299-2006: Measuring The Effectiveness Of Electromagnetic Shielding Enclosures
- MIL-DTL-83528C: General Specification For Gasketing Material, Conducting Shielding Gasket, Electronic, Elastomer, EMI / RFI
- MIL-G-83528B: General Specification for Gasketing Material, Conducting Shielding Gasket Electronic, Elastomer, EMI / RFI
- MIL-STD 1377: Measurement And Effectiveness Of Cable, Connector, And Weapon Enclosure Shielding And Filters In Precluding Hazards Of Electromagnetic Radiation To Ordnance
- MIL-STD-188-125-1: High-Altitude Electromagnetic Pulse (Hemp) Protection For Ground-Based C4I Facilities Performing Critical, Time-Urgent Missions (Transportable Systems)
- MIL-STD-188-125-2: High-Altitude Electromagnetic Pulse (Hemp) Protection For Ground-Based C4I Facilities Performing Critical, Time-Urgent Missions (Transportable Systems)
- MIL-STD-285: Military Standard For Attenuation Measurements For Enclosures
- MIL-STD-907B: Engineering, Design, And Shielding Effectiveness Criteria For Shelters (Expandable & Non-Expandable)