If you could touch radio waves and signals, you wouldn't be able to move from one end of your home to another. In fact, the device from which you're reading this article probably has a wireless signal.
But what keeps those signals from crossing? How can you answer your cell phone without the signal disturbing the WiFi connection on your laptop?
Customers often approach us with designs that shield against electromagnetic interference. Their innovative solutions, combined with our flexible material knowledge and machines, generate product components that prevent EMI disturbances.
Luckily for all of us, EMI is a problem that can be solved with proper protections. Keep reading to learn everything you need 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 crackly for a moment? During that few seconds of static, be it in your home, across the street, or across town, someone’s cell phone could’ve rung and interrupted your radio signal.
Electromagnetic interference (EMI) occurs whenever one source disrupts another source's signal. In the previous instance, your radio was looking for one signal but latched onto another. Engineers also refer to EMI as Radio Frequency Interference (RFI).
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. EMI can not only prevent devices from doing their jobs but also cause them to fail completely.
TYPES OF EMI
There are two types of EMI: narrow-band and broadband EMI.
Narrow-band EMI typically happens to radios, TV stations, and mobile phones because it occurs over a discrete frequency. Signals cross and devices malfunction. Usually, a consumer can 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, and you’ll notice this type of interference most when using a device with a digital data link.
Where Does EMI Come From?
Electromagnetic interference can come from both man-made and natural sources.
EMI EXAMPLES
When you start your car, your ignition can cause EMI. The same kind of interference can come from the igniter in a jet engine or defects in power lines.
Interference over radio frequencies is the most common type in the electromagnetic spectrum. Energy radiated by circuits, power lines, lightning, lamps, and even motors and engines causes this interference.
In each of these cases, the devices you're attempting to use might receive several different transmitted frequencies, mix them up, then cast them out over a broad spectrum.
You’ve probably noticed EMI at home when your devices don’t do what you want. However, the same problems in a commercial environment can cause ruined hardware, lost data, and wasted productivity.
Large equipment that puts out a big signal, or has a considerable volume, can cause interference. Big, moving equipment like elevators, heavy machinery, HVAC equipment, and even vehicle traffic will cause interference. The same goes for basic communications devices as well as general radio signals.
Older devices with worn-out shielding or no EMI shielding materials might experience or lead to EMI problems. For example, machinery and electrical equipment can generate stray magnetic or electric fields that cause trouble for precision research applications.
The sun, specifically solar flares, and lightning, can cause electromagnetic interference naturally.
In short, you cannot avoid EMI. EMI is everywhere, and the fact that our devices don’t pick up MORE interference is a modern miracle of technology. Yet, there’s a reason our devices are able to sift through the noise: EMI shielding.
What is EMI Shielding and How Does It Work?
With all of the problems EMI causes, you can see why EMI shielding matters. Our devices need protection from picking up the wrong signals and security in picking up the right ones.
EMI shielding is done using materials that prevent electromagnetic interference.
EMI shielding ultimately exists to protect the electronics of your device. EMI shields often consist of a metallic screen that surrounds your sensitive electronics or device insides and absorbs the interference transmitted through the air.
Signals reach your device, causing electronic currents. A ground connection, or a virtual ground plane, then absorbs this current. The EMI shield absorbs transmitted signals before they reach any sensitive circuits on your device, keeping your protected signal clean.
Your smartphone is an excellent example of why you need an EMI shield. Morden phones consist of many sensitive, intricate electronics working simultaneously to operate your display. An EMI shield prevents random signals and waves from causing trouble within 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, 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 military, government, and financial security.
Whenever you have any device or appliance with sensitive electronics, you need EMI shielding to protect it from unseen electromagnetic fields. The naked eye can’t see all the potential interference in the air, but EMI shielding protects you from it regardless.
EMI Shielding Gaskets
A gasket is a seal that fills the space between two surfaces. EMI shielding gaskets work similarly, 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. Usually, these materials consisted of thin aluminum, copper, and steel metal sheets. If weathering or time deforms the sheets, 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 and the cold, making them an ideal solution for EMI problems.
Plus, EMI gaskets are easy to fabricate, and the materials don’t cost much.
What Are EMI Shielding Materials?
EMI shielding materials often consist of one of three metal types 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 other metals don’t offer. It also protects the steel from corrosion and rust.
COPPER ALLOY 770 / NICKEL SILVER
Copper alloy 770 is also commonly known simply as alloy 770. It consists of copper, nickel, and zinc. Engineers use it most often because it resists corrosion well.
Copper alloy 770 works best as an EMI shield for the mid-kHz range up to GHz. Its permeability is 1, which means it is ideal with MRI machinery where magnets cannot be present.
COPPER
Copper is different from 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 almost any place needing EMI shielding, from hospital equipment to basic home computers.
Copper costs more than other alloys or pre-tin-plated steel. However, it does have a higher conductivity rate, making it 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.
The disadvantage of aluminum is that it corrodes more quickly than other metals and has high oxidation properties. Oxidation will compromise the integrity of the metal, making it weak.
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 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 caused by common nearby elements like microwaves or televisions.
When magnetic fields are less than 100 kHz, you can use conductive points and magnetic materials. Technicians will also use sheet metal, metal foam, conductive plastics, or mesh metal screening.
Shielding 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, making them suitable 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 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 wherever you need the EMI shielding. Automotive, aerospace, satellite communication, and electronic industries have all used EMI shielding silicone in their products.
Many people 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 extreme heat and cold environments, like aerospace engineering.
Current EMI shield silicone has nickel-graphite, effectively shielding radio frequencies between 20 and 10,000 Hz.
How Do I Achieve Good EMI Shielding?
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, but shields prevent the damage from happening.
Modern technology has given us a variety of EMI shielding options made from carefully chosen materials to prevent unwanted interference. Yet, each device has its own unique shape, materials, and design.
When you’re seeking to shield a product successfully, you’ll likely look into having custom parts made for your design. Consider evaluating your design for manufacturability to help you prepare for future production.
Originally published: May 12, 2020
