About every 11 years the sun's magnetic field flips. North becomes south and south becomes north. This change causes solar storms on the sun's surface that send solar flares careening towards Earth.
These flares are dangerous to our infrastructure.
In 1859 there was little in the way of electronic technology other than telegraphs. At the time there was no such thing as EMI shielding. So when a huge solar flare crashed into Earth, it generated enough EMI to stop communications and electrocute operators.
With all our advanced technology, could you imagine if that happened today? How much of your equipment would get damaged because it isn't protected? Do you even know?
If not, this article is the right place to start learning. Read on to find out more.
What Is Electromagnetic Interference?
EMI occurs when electromagnetic energy from an external source affects an electrical system. The disruption can range anywhere from minor interruptions to severe damage.
Examples of EMI
Cell phones can interfere with the sensitive equipment of an airplane. That's why the crew asks you to turn them off during takeoffs and landings.
When you hear static on a phone call, that's often caused by EMI. There could be a nearby, low-flying plane or it could be some other disturbance.
Loud noises from a microphone are often caused by cell phones communicating with a tower during a call. Even something as simple as an electric egg beater can interfere with a radio signal.
EMI Versus EMC
EMC stands for Electromagnetic compatibility. It means that an item has electromagnetic shielding that prevents its energy waves from affecting other devices.
Most household electronics get rated for EMC. This includes TVs, laptops, cell phones, tablets, etc.
What Is Electromagnetic Energy?
Electromagnetic energy is energy expressed in waves. It's everywhere and comes in many forms.
Types of Electromagnetic Energy
Each type of energy has a unique use, frequency range, and wavelength.
- Uses: Voice communications, data transfers, radio broadcasting
- Frequency Range: 3 Kilohertz (kHz) to 300 Gigahertz (GHz)
- Wavelength: 10 millimeters (mm) or longer
- Uses: Heat sources for microwave ovens, communications over high-bandwidths, radar
- Frequency Range: 3 GHz to 30 Terahertz (THz)
- Wavelength: 10 mm to 100 micrometers (μm)
- Uses: Heat-sensitive thermal imaging, heat sources, therapy
- Frequency Range: 30 THz to 400 THz
- Wavelength: 100 μm to 740 nanometers (nm)
- Uses: Light sources for visibility, lasers, electronics screens
- Frequency Range: 400 THz to 800 THz
- Wavelength: 740 nm to 380 nm
Ultraviolet Waves or Sunlight:
- Uses: Microbe elimination, Sterilization, UV lamps for tanning beds
- Frequency Range: 8 × 10^14 Hertz (Hz) to 3 × 10^16 Hz
- Wavelength: 380 nm to 10 nm
- Uses: Internal medical examinations, art, quality control
- Frequency Range: 3×10^16 Hz to 3×10^19 Hz
- Wavelength: 10 nm to .01 nm
- Uses: Cancer treatments, Nuclear warfare, Aerospace telescope technologies
- Frequency Range: More than 10^18 Hz
- Wavelength: Less than 10 picometers (pm)
When trying to prevent EMI it's important to understand what type of energy you want to block. Different materials are more effective at stopping different kinds of energy.
Additionally, if you use a perforated shielding medium, you must ensure the holes aren't large enough for the energy waves to escape.
What Is EMI Shielding?
Electromagnetic shielding is a barrier that covers electronics to prevent EMI. It is also sometimes referred to as radiation shielding.
RF Shielding and Magnetic Shielding
EMI shielding is the umbrella term that encompasses all types of EMI. RF shielding and magnetic shielding are two sub-types of EMI shielding.
RF shielding is specific to the blocking of radiofrequency electromagnetic radiation. Shields effective at blocking RF waves as well as other types of waves are sometimes called EMI/RFI or EMF shields.
Magnetic shielding is a little different since you can't block a magnetic field the same way you can electromagnetic energy. This is because a magnet's field lines run from its north pole to its south pole and monopole magnets don't exist.
Instead, you must redirect the magnetic field lines. You can achieve this by separating two magnets with a magnetic barrier.
When doing so, the magnetic field lines of the magnets will interact with the barrier. This causes the lines of both magnets to bounce back before reaching the magnet on the other side. Because the magnetic lines of the magnets can't interact, their impact on each other is either decreased or nullified.
Much of today's technology requires magnets to work. Like EMI, you must prevent magnetic interference or it can impede the operation of other magnetic devices. Some shields combine conductive and magnetic mediums to prevent interference from both EMI and magnetism.
Skin Effect and Skin Depth
Alternating currents have a tendency not to go through the center of a solid conductor. Instead, they travel closer to the surface. This is called the skin effect.
Skin depth is how far underneath the surface of a conductor a current will travel and decreases as frequency increases.
In an EMI shield, you want a material with enough skin depth to prevent a frequency from penetrating. You can determine skin depth with this calculator.
Why Is Shielding Important?
We are in the age of science fiction. Everywhere we turn there are electronic devices. Each one can interfere with another if it isn't properly shielded.
The main goal of an electromagnetic shield is two-fold. It isolates a device's energy so it doesn't affect anything else and blocks external energy from getting in.
Without shielding, electronics wouldn't function as designed or may even stop working altogether.
EMI shielding is important because it can prevent:
Brownouts and Blackouts
Brownouts are any type of partial service outage, while a blackout is a full outage. Brownouts and blackouts are not limited to power outages.
Electrical Fast Transitions or EFTs
If there is a power outage and a transfer sequence is in place, you'll start receiving power from a generator. When this happens, it's called an EFT. If there is an EMI, you can experience unwarranted EFTs.
Static on Phone Lines
If you were to remove the plastic jacket from a phone line you'd see another layer covering the wires. This second layer is usually a metallic foil or metallic plaited braid that protects the lines against EMI. It is a type of RF shielding that reduces static during phone calls.
A power fault is any abnormality in an electrical current. A short circuit is an excellent example of a power fault, but it is not the only kind. Power faults are sometimes caused by an EMI.
Types of EMI Shielding Materials
There are many types of EMI shielding materials and new materials are getting introduced all the time.
When deciding which shielding material to use, you need to consider shielding effectiveness (SE). SE is the strength of the intruding electric field in comparison to a device's electric field. Shielding effectiveness is measured in decibels (dB).
This Shielding Effectiveness Calculator can help you determine your specific needs.
Aluminum is a cost-effective shielding material for ultra- to super-high radio waves. It's high conductivity and strength-to-weight ratio make it an excellent choice for EMI shielding. Keep in mind though that aluminum is non-ferrous so you can't use it to block magnetic forces.
Additionally, fabricating EMI shields of aluminum present some challenges as it is difficult to solder. You'll also have to keep an eye on any shield made of aluminum as it can corrode over time.
Copper is a very versatile metal. It's highly conductive, capable of blocking Radio waves and magnetic. This makes it an ideal choice for applications that require all three types of shielding. Copper's malleability means you can use it in a wide array of devices.
It's also easy to combine with other metals to form alloys like brass making it even more adaptive. Copper's only real drawback is its price tag when compared with other materials.
Steel's strength and durability made it a prime candidate for early EMI and magnetic shielding.
It's not very versatile and is effective at blocking low-frequency waves only. Its rigidity makes it difficult to work with when used in tight spaces. You could use thin sheets of steel instead, but the sheets often deform under the pressure created when sealing the shield.
For these reasons, steel sees less and less use as technology advances and new alloys are created. If you do opt for a steel shield, carbon and stainless steels are the most effective.
Nickel is both inexpensive and effective. It's durable, hard and conductive. You can use nickel as an EMI shield on its own or combine it with other metals to form magnetic alloys.
Mu-metal is a new alloy designed for EMI shielding. Nickel and Iron are the main elements of Mu-metal making it both soft and magnetic.
It can block both electronic and magnetic fields and is very permeable. Because of its malleability, Mu-Metal is easy to work into thin sheets for efficient application.
Conductive Rubbers Like Silicone and Neoprene
Silicone has a very high tensile strength. It is also flexible and resilient. Neoprene is compressive and generally useful.
Conductive rubbers are often used to make sealing EMI shielding gaskets that seal enclosures.
Types of EMI Shield Devices
There are almost as many kinds of EMI shield devices as there are applications for them. You can get both solid and perforated shields for most material and design types.
EMI Enclosures are the simplest type of shield. They create a Faraday cage effect by surrounding the equipment it protects. Enclosures come in solid and perforated forms depending on the application.
For example, a microwave uses a perforated enclosure so you can see inside, but the holes are too small for the waves to escape.
EMI gaskets made of conductive rubbers or metals can shore up any gaps left between enclosures and equipment. Gap sealed enclosures provide more comprehensive protection.
Faraday cage enclosures are bulky and add weight to a device. This makes them impractical for use with small devices like phones tablets and computer components.
EMI Coatings are almost like paint mixed with conductive metals that form a shield. Coatings are very flexible because you only need to brush them onto a surface for them to work. They also take up no extra space and have no added weight, unlike other shielding options.
On the downside, it only takes a single scratch to compromise the protection.
EMI filters block high frequencies while allowing low frequencies to pass through. As a rule, they get built into the power sources or switches they're protecting.
Because filters don't block all EMI, you can only use them in certain situations.
Foil Shielding Tape
Foil shielding tape uses thin pieces of conductive metal with an adhesive to shield electronics.
Tapes are flexible, easy to use and form-fitting. You can cut them into any size or shape and they weigh next to nothing. These qualities make them an excellent choice for EMI protection when working with small electronics.
Because you can customize tapes to fit your equipment perfectly, there is less waste which saves you money. Their versatility means you can also use them for anti-static masking, mechanical protection, static charge grounding, component cushioning.
Additionally, you can get foil tapes in almost any type of metal. Some options include:
- Stainless steel
When buying tape, you must take tensile strength into consideration to avoid damage to the shield.
Conductive Fabric Shields
Conductive fabric isn't fabric in the traditional sense. It's more like a metallic textile with similar physical properties to that of fabric.
It either uses a fabric substrate like nylon or polyester combined with metal or nothing but metal. Like fabric, it drapes and is easy to work with. You can add an adhesive to help hold it in place or hang it over the equipment you intend to protect.
To increase effectiveness you can add an elastomer core to the fabric, but even with that addition, it is still among the weakest shield options available. For this reason, you should only use conductive fabrics when you only need a moderate amount of protection.
Additionally, you have to watch for surface corrosion when working with metallic fabrics.
Get Shielded Today!
Now that you know more about EMI, it's time to get shielded. Strouse can help with that. We offer top of the line EMI shielding tapes for an array of purposes.
We provide foil tape made of aluminum, copper, stainless steel and many other metals in any of the following forms:
- Individual die cuts in custom shapes, sizes, and formats
- Rolls of tape cut to custom widths
- Custom die cuts on a roll or sheet of material
This helps you improve the efficiency of your assembly lines by allowing you to pick the delivery method that best suits your process.