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Everything You Need to Know About EMI Shielding

Written by Sue Chambers | May 12, 2020 7:32:14 PM

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If radio waves and signals were visible and tangible, you wouldn't be able to move from one end of your home to another without tripping. The very device from which you're reading this article probably has a wireless signal.

What keeps those signals from crossing? How are you able to answer your cell phone without the signal crossing over your WiFi connection on your laptop and causing a disruption?

These disruptions are electromagnetic interference. We do not see them much because of effective electromagnetic interference shielding, otherwise known as EMI shielding. 

Keep reading to learn everything you need to know about EMI shielding and the materials that keep your signals in check. 

What is Electromagnetic Interference (EMI)?

Have you ever been listening to the radio only for it to go to crackly for a moment and then back? During that few seconds of static, someone's cell phone rang, be it in your home, across the street, or across town. The cell phone signal temporarily interrupted your radio signal. 

It's like your radio was looking for one signal but grabbed another. This is electromagnetic interference. 

EMI occurs whenever one source disrupts another source's signal. Engineers will also refer to EMI as RFI, or radio frequency interference. While the above example illustrates an annoying result of EMI, this type of interference can cause more than just missing a few bars on your favorite song. 

Specifically, it impacts electrical circuits through induction, electrostatic coupling, or conduction. This means it can either prevent the device from doing its job or can cause it to fail completely. 

Types of EMI

Two types of EMI exist. 

Narrow-band EMI happens typically to radios, TV stations, and mobile phones because it occurs over a discrete frequency. Signals cross and devices malfunction. Typically a consumer can just tune out the disruption that will not cause damage to equipment. 

Broadband EMI occurs over a broader spectrum since it occupies a large part of the electromagnetic spectrum. Broadband EMI is the type of EMI that can cause the most damage to your devices. 

You notice this type of interference most when you're using a device with a digital data link.

Something as simple as a worn brush of a motor can cause EMI. A fluorescent light with defects indicate EMI.

When you start your car, your ignition can cause EMI. The same kind of interference can come from the igniter in a jet engine. Defects in power lines will cause the same interference as well.

In each of these cases, the devices you're attempting to use could receive several different transmitted frequencies, mix them up, and then send them out over a broad spectrum. 

Interference over radio frequencies is the most common type of interference in the electromagnetic spectrum. Energy radiated by circuits, power lines, lightning, lamps, and even motors and engines causes this interference. 

You may notice EMI at home when your device doesn't do what you want it to. The same problem at work, though, in a commercial environment can cause ruined hardware, lost data, and wasted productivity. 

Where does EMI Come From? 

Electromagnetic interference can come from both man-made and natural sources.

The sun, specifically solar flares, and lightning can naturally cause electromagnetic interference. 

Older devices with worn-out shielding or no EMI shielding materials at all can experience problems because of EMI. Also, large equipment that puts out a big signal or that just has a large volume can cause interference. Machinery and electrical equipment, for example, can generate stray magnetic or electric fields that cause trouble for precision research applications. 

Big, moving equipment like elevators, heavy machinery, HVAC equipment, and even vehicle traffic will cause interference. Basic communications devices can cause it as well as general radio signals. 

In short, you cannot avoid EMI. It's everywhere, and the fact that our devices do not pick up more interference is a modern miracle of technology.

This modern miracle is EMI shielding. 

What is EMI Shielding and How Does It Work? 

With all of the problems that EMI causes, you can see why EMI shielding matters. Our devices need some sort of protection from picking up the wrong signals and security in picking up the right signals. 

EMI shielding increases their success. 

EMI shielding is a material that prevents electromagnetic interference. It consists of a metallic screen that absorbs the interference transmitted through the air. 

EMI shielding ultimately exists to protect the electronics of your device. The shield, or metallic screen, surrounds either your sensitive electronics or transmitting electronics in your device.

As signals reach your device, the screen absorbs them, causing a current within its body. A ground connection or a virtual ground plane then absorb this current. 

The EMI shield absorbs transmitted signals before they reach any sensitive circuits on your device, and it keeps your protected signal clean.

Your smartphone is a great example of why you need an EMI shield. You have tons of sensitive, intricate electronics working all at once to make your display say what it says. An EMI shield prevents random signals and waves from frying those sensitive electronics. 

Examples of EMI Shielding

You can find EMI shielding anywhere you find sensitive electronic equipment requiring isolation from outside electromagnetic fields. 

So in the medical industry, this means EMI shielding goes on equipment like AM/FM emergency service transmission and other communication devices. It also goes on any patient monitoring equipment and even on pacemakers. 

In the world of data and tech, EMI shielding prevents anyone from accessing data you store on an RFID chip or embed in a different device. 

Engineers will also use EMI shielding material with air-gapped systems to increase security for military, government, and financial systems. 

Whenever you have any device or appliance with sensitive electronics, you need EMI shielding to protect it from unseen electromagnetic fields. The naked eye cannot see all the potential interference in the air. EMI shielding protects you from that. 

What Are EMI Shielding Materials? 

EMI shielding materials consist of one of three types of metal but come in a variety of forms. Sometimes engineers will use a combination of materials to create the best EMI shielding solution. 

Pre-Tin Plated Steel

Pre-tin plated steel costs less than the other metals used in EMI shielding, but it works well for lower frequencies, typically in the kHz range up to the lower GHz range. Carbon steel, in particular, provides low-frequency shielding properties that the other metals do not provide. It also protects the steel from corrosion and ultimately rust. 

Copper Alloy 770 / Nickel Silver

Copper alloy 770 is also commonly known simply as alloy 770. It consists of copper, nickel, and zinc. People use it most often because it resists corrosion so well. 

Copper alloy 770 works best as an EMI shield for mid kHz range up into GHz. It has a permeability of 1, which means it is ideal with MRI machinery where magnets cannot be present. 

Copper

Copper is different than the copper alloy 770. Of all the metals in EMI shielding, copper is the most reliable because it works best at reducing both magnetic and electrical waves. You can find copper in just about any place needing EMI shielding from hospital equipment to basic home computers. 

Copper costs more than other alloys or pre-tin plated steel. It does, however, have a higher rate of conductivity, which makes it so effective as an EMI shield. 

Aluminum

Because of its strength-to-weight ratio and high conductivity, aluminum can work well as an EMI shield material. Compared to copper, aluminum has nearly 60 percent of conductivity. 

Aluminum has a downside, though. It corrodes more easily than the other metals and has high oxidation properties. Oxidation will compromise the integrity of the metal, making it weak. 

EMI Shielding Gaskets

A gasket is a seal that fills the space between two surfaces. EMI shielding gaskets work in a similar way except they exist to protect electronics from interference. 

EMI shielding of the past consisted of metal sheets that fabricators formed into specific shapes to fit into housing or enclosures. This worked well for thin metal sheets of aluminum, copper, and steel. If weathering or time deforms the sheets, the sheets stay in the same shape, and the circuits they're supposed to protect will leak. 

EMI gaskets look like a sieve or ruggedized touchscreen made from particle-filled silicones. These gaskets work well in the heat as well as the cold, making them an ideal solution for EMI problems. 

Plus, they're easy to fabricate, and the materials do not cost much. 

EMI Shielding Film and Foil

EMI shielding tape, film, and foil each have their place in the EMI shield marketplace. 

EMI materials can take many shapes. For example, conductive silicones work well as window films that help shield electronics from magnetic and electrical waves in commercial settings. 

The material and form of the EMI protection depend solely on the type of electronics that need the shielding and the frequencies involved. 

For example, technicians will use metallic foil or plaited braid to shield equipment wires. You can also use coaxial cables with EMI shields built into the wire construction. Technicians will wrap wire bundles in foil or they will apply cable braid over an entire construction. 

Even the connectors have EMI shielding with braiding or foil attached to the metal covers giving the appliance or device complete protection. 

For a printed circuit board, the shielding has a ground plane built into it and a metal box over the sensitive elements. Technicians then surround the delicate components with a Faraday cage arrangement. 

Audio speakers have an inner metallic casing that blocks EMI specifically caused by common nearby elements like microwaves or televisions. 

When magnetic fields have less than a 100 Khz range, you can use conductive points and magnetic materials. Technicians will also use sheet metal, metal foam, conductive plastics, or mesh metal screening. 

Shieling foil tapes have specific characteristics that make them ideal for EMI shielding. They resist corrosion and are flame retardant. They're also flat and embossed which makes them ideal for shaping around odd corners and shapes. 

You can find shielding tapes in several places: 

  • Ground panels for electronic cables and connectors
  • Keyboard devices
  • Around individual electronic components and cables
  • In the seams and holes in shielded rooms. 
  • Electro-medical devices
  • Doors and panels of electronic cabinets
  • Around outside of coils, relays, and other electrical components that could attract broadband EMI emissions
  • Used around the outside of coils, relays, and other components to prevent broadband EMI emissions

EMI Shielding Foam

EMI shielding can also come in the form of carbon foam. The EMI shielding foam will shield anywhere from 100 Mhz to 20 GHz, even though it has no metallic components. Foam has a distinct advantage as an EMI shielding material because of its flexibility. It serves more than one function. 

For example, some foam provides fire protection. It also lasts longer in harsh environments than metal would, weighs less than metal, and does not corrode. It's also environmentally friendly. 

EMI Shielding Silicone

Silicone typically cannot conduct electricity. However, if you embed metal in the silicone, you create a conductive material that can work well as an EMI shield product. 

Plus, silicone is flexible. Manufacturers can die cut it to fit whoever you need the EMI shielding. Automotive, aerospace, satellite communication, and electronic industries have all used EMI shielding silicone in their products. 

Many like silicone because it resists sunlight and water. It can tolerate a range of temperatures as well. This is why we see silicone used in environments with extreme heat and cold, like aerospace engineering

Current EMI shield silicone has nickel-graphite in it which effectively shields radio frequencies between 20 and 10,000 Hz. 

Many Products, One Use  

Not all EMI shielding is made alike, but they all do the same thing: prevent unwanted interruptions in transmissions. Electromagnetic interference can destroy a machine. Shields keep this damage from happening. 

Modern technology has provided us with a variety of options made from a variety of materials to prevent unwanted interference. 

If you're looking for EMI shielding materials or adhesive solutions, we can help. Contact us. We are the experts.