Protect Your Electronics With Formidable EMI Shielding
Every single day, we encounter electromagnetic interference, also known as EMI. Garbled conversations and dropped cell phone calls; The "noise" your radio makes when you drive under power lines; crackles on your phone lines during lightning storms. EMI can create inconveniences, but there are much more dire repercussions to EMI.
Generated by many natural and manmade factors, EMI can be the cause of data losses, system failure and in some catastrophic cases, the loss of life.
As anyone who’s ever ridden an airplane knows, you must turn your cell phones off during takeoff and landing to minimize EMI with flight control systems. Your cell phone signals can also interfere with critical, life-saving hospital equipment. And in construction zones, two-way radios can inadvertently set off explosive blasting caps.
Without basic EMI awareness, you may design products that are susceptible to interference and won’t function properly in the presence of electromagnetic energy. EMI shielding shouldn’t be a luxury, and in many cases, it’s a regulatory requirement.
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Below, we’ll take a deeper dive in the fundamentals of EMI, discuss electromagnetic compatibility and outline your design choices when considering electromagnetic energy and its potential effect on your product, and others around it.
What is EMI?
A fundamental principle of electromagnetics states that electromagnetic fields are generated whenever charged particles are accelerated – charged particles such as electrons.
The operation of electronic devices rely on the routing of electrons around intricate circuits. And in order for this routing to occur, those electrons must be accelerated. The byproduct then, is the generation of EM fields; which brings us to EMI.
EMI is the term that describes what happens when external electromagnetic fields disrupt (or adversely affect) the normal operation of an electronic circuit or device. It also describes what happens when the electromagnetic energy emitted from one device adversely affects the operation of another device.
National and International Standards regulate how much electromagnetic energy a device can emit. Proper EMI shielding is also a common requirement to ensure compliance with these standards. With the growing adoption of increasingly-interconnected sensors, wearables and household appliances – and even the advent of autonomous vehicles – the need to manage and control EMI is only increasing.
What is EMC?
EMC stands for electromagnetic compatibility, a discipline that concerns itself with the methods and techniques that ensure electronic devices can operate normally in common electromagnetic environments.
The strength of the EM fields that a circuit generates is dependent on a multitude of factors, and careful design of circuit boards is key to minimizing undesirable effects at the source. Similarly, proven design techniques can minimize the "susceptibility" of a circuit to interference from outside EM sources. But even if you follow best design practices, it’s often necessary to implement additional EMI shielding measures.
How to Protect Against EMI
EMI always involves three elements, at least one of which must be addressed to thwart the interference:
- A source
- A victim
- A path
The following mechanisms are EMI shielding approaches used to protect devices from electromagnetic interference:
A common technique for shielding electronic circuits from external interference is to enclose them within conductive Faraday cages. Named after the English scientist Michael Faraday, these cages are made of a continuous covering of conductive mesh material. Some of the best materials used to construct Faraday cages are expanded metal foils because they are lightweight, flexible, formable and electrically continuous.
When an external electrical field meet the Faraday cage's expanded metal foil, the electric charges are distributed such that they cancel the field's effect in the cage's interior. You can also use Faraday cages to "contain" EM energy within your device and prevent your electronics from disturbing other devices.
EMI Shielding Gaskets
EMI shielding gaskets are mechanical devices fabricated from metal sheets and formed into shapes that fit electronic housings or enclosures. EMI gaskets establish a conductive path or covering along seams and openings in electronic enclosures. They block potential difference across its surface and creates a smooth current flow.
Dated EMI shielding gaskets used thin metal sheets as a covering, but they would deform under greater pressures. And once damaged, the gaskets were susceptible to leakage in and out of electronic circuits. Modern EMI shielding materials use flexible metal screens, wires, foams or expanded foils. The latter are formed from solid metal foils in a “slit-and-stretch” process.
Unlike the woven mesh, expanded foils are electrically continuous and exhibit consistent and predictable conductivity. They also conform readily to complex surfaces without the risk of fraying or unraveling.
Conductive Silicone and Composite Enclosures
Particle-filled silicone is another option used to shield against EMI for their resistance to sunlight, water and different temperatures. Composite materials such as carbon fiber reinforced plastics (or "CFRPs") are also growing in popularity do to their excellent strength-to-weight ratio.
Conductive silicones and CFRPs generally lack the conductivity to completely protect against EMI, however. When used to replace metal components, these enclosures are typically reinforced by an expanded foil or mesh gasket for added strength. The flexible, open-area structure of expanded metal foil is highly compatible with composite manufacturing processes. They’ve proven to be a viable "conductivity enhancer,” effectively fabricating strong, lightweight shielding enclosures.
Shield Your Product from EMI
Whether you’re motivated by designing a device for the longevity of its electrical components, meeting electromagnetic energy regulations or both, proper EMI shielding is essential to building the best product. With unique needs, however, how you choose to protect against EMI depends on your specific product.
Consider these several techniques and how each would perform within your product. If you want to know more about EMI shielding and expanded foil gaskets, discover more of our articles, and subscribe to our blog to learn the latest technological trends.
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