Shielding Effectiveness Test
Shielding effectiveness testing determines the ability of material and enclosures to block electromagnetic and radio frequency (RF) signals. A shielding effectiveness test lab like Keystone Compliance, can assess samples of materials, enclosures and complete facilities.
What are the objectives of shielding effectiveness testing?
The shielding can be designed to accomplish one of three goals.
The first goal is to keep certain RF signals within the enclosure of the device. As part of the product certification process, electronic devices must undergo Electromagnetic interference (EMI) testing. EMI testing determines if there are signals generated by the device under test that are outside of the acceptable range and limit. These RF signals could significantly impact other electronic devices in its proximity. These impacts can include communication interruptions, data loss and system malfunctions.
The second goal of shielding effectiveness testing is to block external EMI from impacting the device under test. All of the potential impacts mentioned in the previous paragraph can be realized by the device under test if its enclosure is not properly shielded. Areas of vulnerability can include cables, input and outputs, fans, points of ingress, gaskets, seals and controls.
The third objective is a combination of the two. A properly-shielded device will effectively retain all RF energy in its enclosure and keep all external RF isolated. The amount of RF allowed in or out will depend on the purpose of the device, its functionality and its placement of operation.
How is shielding effectiveness testing completed?
The method of completing shielding effectiveness testing will depend on the size and composition of the sample. As previously mentioned, testing can occur on material samples, enclosed devices and entire facilities.
Testing materials for shielding effectiveness involves two connected EMC test chambers with a shared wall. The shared wall has a window in which the sample is securely placed. The shielding effectiveness test lab will place a transmitting antenna in one chamber and a receiving antenna in the other chamber. The transmitting antenna will begin transmitting a predetermined set of signals. The receiving antenna will record all of the signals received. Essentially, all signals that are transmitted but not received will be considered shielded by the material.
Testing electronic devices is completed by placing the device in an EMC test chamber. The EMC test engineer will power the device and ensure it is in an operating mode. For one aspect of the testing a receiving antenna receives and records all of the EMI generated by the device. Once that is complete, a transmitting antenna will transmit signals at the device to determine if there are unacceptable impacts on its operation. The term unacceptable will depend on the device. For instance, a blip on the screen of a child’s toy might be acceptable whereas the blip on a medical device used for surgery might not. The determination of what is acceptable and what is not from a signal standpoint is spelled out in the test standard.
The testing of the shielding effectiveness of a facility is completed very similar to the testing of a material sample. An antenna is placed on either side of the structure. This could be a door, a wall, a window, a vent or any other physical barrier. One antenna transmits and the other receives. Shielding effectiveness of facilities is very important for certain industries such as military, aerospace, health care and industrial facilities.
What about the shielding of cables?
Electromagnetic shielding is also an important characteristic of cables. The shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. The amount of reduction can vary based on the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest. Also impacting the effectiveness of the shielding is the size, shape and orientation or apertures in a shield to an incident electromagnetic field. Electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as RF Shielding.
What type of materials can be tested?
Being recognized as one of the best shielding effectiveness test labs in the world, Keystone Compliance has tested a number of different sample types. Our engineers have tested metal, glass, plastics, other resins, fabrics and combinations of materials. We have also tested specific rooms to entire installations. Our equipment allows us to test to any shielding effectiveness test standard. However, we can also work with companies to develop custom test programs.
As a shielding effectiveness test lab, Keystone Compliance works with engineers to not just measure the shielding effectiveness of their product, but design and implement shielding effectiveness test improvements. Please contact us for more information on how Keystone Compliance can assist you with determining and improving the shielding effectiveness test of your product.
Common shielding effectiveness 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
- IEC 61000-5-7: Degrees of Protection Provided by Enclosures Against Electromagnetic Disturbances (EM code)
- 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)