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What is EMI Shielding Effectiveness?

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    Electromagnetic interference (EMI) is pretty much everywhere in the modern world. EMI comes from external signals that reach an electronic device and interfere with the device’s signals. It can impact all kinds of functions, rendering some devices completely useless. 

    Hundreds of thousands of devices rely on the ability to send and receive electromagnetic signals without interruption, so engineers had to come up with a solution. That solution is called EMI shielding. It’s the principle of designing devices to contain materials and objects that protect against interference from external electromagnetic signals.

    If you’re doing research about EMI shielding, you’re almost sure to come across the term, “EMI shielding effectiveness.” That’s what we’re going to cover in this post. Read on to learn more about this topic.

    Modus Advanced supplies EMI components to OEM's that develop world-class devices. We’re here to help you take your design from concept to fully formed reality. Contact us to learn more.

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    Better understand EMI Shielding and how to fit it into your 

    Definition of EMI Shielding Effectiveness

    Let’s begin with a quick definition of EMI shielding effectiveness. This term is a key measurement used when discussing EMI shielding devices and implements. 

    What is EMI Shielding Effectiveness?

    EMI shielding effectiveness measures how effectively a device protects against EMI. This metric is essentially measured as the difference in strength or intensity of an electromagnetic signal before shielding and after shielding.

    That’s a relatively simple definition for what amounts to a very complex topic. See below to have your lingering questions answered in full.

    EMI Shielding Effectiveness FAQs

    If you have questions about EMI shielding effectiveness, the Modus team has the answers. Read on.

    What Causes EMI?

    EMI can come from a wide variety of sources, but the two major categories are man-made EMI and natural EMI. 

    Computer circuits, cellular networks, power lines, ignition systems, cellular devices and microwave devices are examples of man-made sources of EMI. For natural EMI, the most common culprits are lightning, solar flares and auroras.

    These sources of EMI can send electromagnetic signals toward a device by conduction or radiation. The former involves the signal traveling over a conductive surface — often from within the same device as the item that’s being interfered with. The latter involves electromagnetic signals wirelessly traveling through space to reach a device and cause interference. Radiated EMI commonly occurs with lightning strikes and cellular networks.

    How is EMI Shielding Effectiveness Calculated or Measured?

    The primary measurement for EMI shielding effectiveness is called attenuation. This is simply a measurement of the strength of the interfering signal at two points: before the device is shielded and after it is shielded.

    As a measurement, attenuation is expressed in decibels (dB). The intensity of the signal being measured is referred to as amplitude. 

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    How Do Materials Affect EMI Shielding?

    In electronic devices, EMI shielding is primarily achieved by creating seals (often in the form of EMI gaskets) that prevent signals from entering a sensitive area of the device. 

    EMI gaskets typically use a base material of silicone or fluorosilicone, but these materials do not attenuate disruptive signal strength. However, the base material contains a filler material that does the work of shielding against disruptive external signals. Common EMI filler materials include the following:

    • Silver
    • Silver aluminum
    • Silver nickel
    • Silver copper
    • Nickel graphite

    Each of these materials comes with different properties and prices, so it’s important to consider both budget and your EMI shielding effectiveness requirements when choosing a filler material.

    Learn more about EMI shielding materials in this guide.

    What is the Military Standard for EMI Shielding Effectiveness?

    Any electronic device designed for use in military applications must meet the standards of MIL-STD-285. This standard lays out the EMI shielding effectiveness requirements for military devices. 

    The minimum effectiveness under MIL-STD-285 is 100 dB at frequencies between 20 and 10,000 hertz. Commercial-grade EMI shielding materials tend to have less stringent standards.

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    EMI Shielding Resource Center

    Visit our complete EMI shielding resource center. 

    Why is EMI Shielding Important?

    Electromagnetic interference (EMI) can disrupt electronic devices, equipment, and systems that are used in critical applications. Examples include medical, military, and aerospace electronics; mass transit systems; industrial touch screens; and navigation and vehicular control systems - just to name a few.

    For engineers, it's important to recognize how electromagnetic energy (EME) in the application environment can cause interference. Without this basic EMI awareness, you may design gaskets that lack adequate protection against electromagnetic fields in the radio frequency (RF) spectrum, the part of the electromagnetic spectrum with frequencies from 3 kHz to 300 GHz. RF waves form the basis of radio technology, but they can also transmit signals that interfere with wireless communications.

    Learn more about the importance of EMI shielding in this article.

    How can You Increase EMI Shielding Effectiveness?

    The primary factor which will improve your EMI shielding effectiveness is the material you choose to create EMI shielding gaskets. 

    Learn more about available materials in this EMI shielding materials in this guide.

    Do EMI Materials Provide a Strong Environmental Seal?

    Depending upon the type of gasket you have in your design, if you’re hoping to create both an EMI shield and a solid environmental seal, you might be a little disappointed. If you're using a dispensed Form-in-Place EMI gasket: unfortunately available materials rarely make for a highly effective seal. Gasket materials that contain fillers do not tend to make strong seals over the long term. Another great option is Nolato’s Compashield Extrusions that do a great job handling both EMI shielding and environmental sealing requirements.

    However, there is a possible solution. You may be able to dispense two different form-in-place (FIP) gasket materials — one that contains a filler material and acts as an EMI shield and another that functions as an effective environmental seal.

    For Highly Effective EMI Shielding, Go with Modus

    EMI shielding effectiveness is an important measurement of quality for any device that is meant to protect against EMI. At Modus Advanced, we’re all about quality. It’s central to everything we do, and that extends to the EMI gaskets and other parts we manufacture for our customers.

    For sensitive electronic devices and complex designs, you need high-quality manufacturing. That’s what our team offers. If you would like to work with us, we’re ready to hear from you. Just give us a call at (925) 960-8700 or contact us online.


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