What Is EMI Shielding Effectiveness and How to Measure It?

23 Sep What Is EMI Shielding Effectiveness and How to Measure It?

In order to ensure the proper functioning of the various sophisticated electronic devices used today, it is vital, among other things, to protect them from radio and electromagnetic interference. Excellent products are built with shielding components that have been tested for EMI shielding effectiveness. Understanding this critical metric provides reassurance that the devices chosen will hold up without worrying about interference from outside forces.

What Is EMI Shielding Effectiveness?

Because all electronics emit magnetic and electrical energy, interference is possible, causing devices to malfunction. Even unintentional interference can lead to severe problems. For example, a blimp of interference in a child’s toy doesn’t affect much. However, that same tiny bit of interference in a medical device can be devastating.

Shielding materials work to decrease and eliminate electromagnetic interference (EMI) and radio frequency interference (RFI). Today’s electronics have many components that need protection from interference, such as computers, microprocessors, broadcasting receivers, medical devices, measuring instruments, and navigation systems. Knowing how well shielding materials work (i.e., their effectiveness) provides the protection required to ensure the devices can function properly and safely.

There are several types of EMI products on the market that can be integrated into a device design where EMI shielding is crucial. These EMI products include honeycomb vents, conductive shielding gaskets, fingerstock gaskets, metalized fabric gaskets and conductive elastomers, all of which contribute in their own way to increased EMI protection and effectiveness.

What Are the Objectives of Shielding Effectiveness Tests?

Quality products have end-user objectives in mind. EMI shielding effectiveness tests are no different and accomplish three main goals based on how the device is designed:

1. Keep specific radio frequency signals within the enclosure of the device. Under EMI testing, it is determined if an electronic device generates signals within an acceptable range and limit.
2. Another objective is to block external electromagnetic interference from affecting the tested device. When an enclosure is not adequately shielded, it can be impacted by EMI. Areas most vulnerable include cables, fans, input and outputs, gaskets, seals, and controls.
3. The final objective is to measure if a device is capable of retaining all RF energy within its enclosure while keeping all external RF out. Each device is different and has unique tolerances based on its functionality and placement of operation.

How to Measure EMI Shielding Effectiveness

Shielding effectiveness is measured in different ways. One of the principal indicators is called attenuation. It is the difference between an electromagnetic signal’s intensity before shielding and then after shielding. Attenuation is measured in decibels (dB). This measurement corresponds to the ratio of shielded and unshielded devices in the field.

Generally, a signal’s intensity or amplitude decreases further away from the interference from the device. The lowest effective shielding falls within the range of 10-30 dB, and high levels of protection fall between 60 and 90 dB. It is possible to hit exceptional protection when shielding reaches over 90dB in attenuation.
Measuring an electronic devices’ attenuation is accomplished through four standard tests, including:

1. Open Field Test: Often used with finished products, open field testing is designed to simulate usage under normal conditions. Utilizing an available site that is free from other metallic equipment, antennas are situated at a variety of distances from the electronic device being tested. The open area allows for measurements of radiated field strength and conductive emissions.
2. Coaxial Transmission Line Test: This type of testing is used for comparative testing. It measures lane-wave field electromagnetic wave radiation in planar material. First, a reference testing device is placed in close proximity to the planar material. Measurements of voltage at multiple frequencies are recorded. Next, a load device is placed near the material, and those voltage readings at various frequencies are recorded. Finally, the measurements are compared to establish the ratio of power received both with shielding and without shielding.
3. Shielded Box Test: For testing frequencies less than 500 megahertz, a shielded box is used. This sealed box has an opening on one side in which a shielded test subject is inserted. Next, a coated shielding is placed over the opening. Then, electromagnetic signals from inside and outside of the box are compared. All transmitted and received emissions are measured. Once complete, the ratio between the signals determines the shielding effectiveness of the test device.
4. Shielded Room Test: If it’s vital to determine a device’s susceptibility, a shielded room test is a practical choice. Two shielded rooms with a wall in between them are used. One room holds the device being tested, while the other room holds the sensors. It is customary to have shielding leads used to minimize errors from external signals. This test is often used when it is difficult or impossible to diminish or eliminate ambient noise in an area.

What Kinds of Materials Can be Tested?

Because plastic housings are increasingly being used, and many plastics are insulators, it is imperative to utilize conductive shields to ensure proper protection is possible. It is not only plastics that need protection. Other types of materials should be protected, as well. Many different types of materials can be tested for shielding effectiveness, including metal, glass, plastics, fabrics, and a combination of materials.

Protect Delicate Equipment with Quality EMI Shielding Products

Without EMI shielding, electronic devices will fail to perform their respective roles. Failure is not an option when telecommunication, medical or aerospace devices are on the line. EMI shielding effectiveness testing ensures that devices will perform as they should when in use.

Finding the best EMI products is possible with help from a dependable, value-added supplier. The ID Group can assist you with fingerstock gaskets, metalized fabric gaskets, conductive elastomers, and conductive foam gaskets. It is possible to not only obtain standardized EMI shielding, but we can also help you find customized solutions for your specialized equipment.

Learn more about how The ID Group can help protect your equipment from EMI and RFI. Contact us, request a quote, or browse our EMI products now.