Electromagnetic signals are everywhere. When lightning strikes, it releases electromagnetic energy. Solar flares also cause large amounts of electromagnetic radiation. More common sources of electromagnetic signals are manmade devices such as electric motors, generators, microwave ovens, and fluorescent lights.
Electromagnetic signals cause electromagnetic interference (EMI) that can affect the performance of electronic equipment. Problems can range from disruption of other signals to data loss, security risks, and device failure.
The History of Electromagnetic Interference Challenges
Engineers have been grappling with EMI since the advent of radio communications in the early 20th century. By the 1930s, standards were developed around electromagnetic compatibility (EMC), which seeks to control the unintentional emission and propagation of electromagnetic energy by electronic equipment through grounding, shielding, or filtering.
In the 1970s, the U.S. Federal Communications Commission established legal limits on electromagnetic emissions. In the mid-1980s, the European Union followed suit with its own requirements. These regulations continue to evolve as the world has become increasingly crowded with electronic equipment.
EMI vs. EMF
Before we dive into shielding principles, it’s important to define common terminology. EMI and EMF are often used interchangeably, but they are technically different.
EMF
EMF stands for electromagnetic fields. It’s essentially a measure of electromagnetic energy. These fields can be natural or manmade. EMF is everywhere electricity or communication signals are present. It’s the parent term that encompasses many other specific frequencies such as radio, microwave, gamma, ultraviolet, etc.
EMI
EMI stands for electromagnetic interference, which is the result of EMF. It describes situations where electromagnetic emissions disrupt an electrical path or circuit. The origin of this interference can be either man-made or natural.
EMI vs RFI
EMI and radio frequency interference (RFI) are related but distinct concepts. When EMI is caused by radio frequency (RF) spectrum emissions, it’s referred to as RF interference (RFI).
EMI Types
Electromagnetic interference is classified into two types: residential and natural EMI.
Residential (Man-Made) EMI
Residential EMI describes the energy that escapes cables, wires, or components. Man-made EMI could come from laptops, Bluetooth devices, microwaves, etc. An example would be analog TV static. As EMI increases, the static gets worse.
Natural EMI
Natural EMI results from natural phenomena such as solar flares, lightning or auroras. The same analog television example is relevant to natural EMI as well as residential EMI. In 2002, a US House of Representatives debate was interrupted and distorted due to a solar flare episode.
EMI Transmission
EMI can be transmitted by conduction or radiation.
Conducted EMI
Conducted EMI means the sources are in physical contact. A power line is a good example. Conducted EMI would occur when various devices are connected to the same circuit. Turning one on will cause another to malfunction.
Radiated EMI
Radiated EMI is a lot more common. This type of EMI describes interference among devices that aren’t in direct contact with one another.
Broadband vs. Narrowband EMI
EMI is further divided into two categories: broadband and narrowband EMI.
Broadband EMI
When it affects a large portion of the frequency spectrum, it’s called “broadband” EMI.
Narrowband EMI
When it affects a narrow range of frequencies, it’s called “narrowband” EMI.
Measuring EMI
EMI is commonly measured via a spectrum analyzer, an oscilloscope, or a broadband RF field meter.
Spectrum Analyzer
This tool measures the frequencies in a signal to measure if EMI is present and at what frequency.
Oscilloscope
These identify EMI on high-voltage signals by measuring signal amplitude vs. time domain. They are often used in tandem with spectrum analyzers.
Broadband RF Field Meter
Measures the amount of EMI in a given area. A common tool for general analysis.
What Is EMI Shielding?
Electromagnetic signals flow through the air and aren’t stopped by sheetrock walls. That’s why Wi-Fi connections work throughout your home or office. You need certain types of materials to block electromagnetic signals. EMI shielding is made of one or more of these materials.
Michael Faraday discovered this principle in 1836. He enclosed a “cage” with a mesh of conductive material, now known as a “Faraday cage.” An electric current that contacts the cage causes electrical charges in the conducting material that cancel out the effect. The interior of the cage is protected from the electrical charge. The same principles work for EMI. An electronic device placed inside an area encased with EMI shielding won’t be affected by the electromagnetic signals.
How is EMI Shielding Measured?
Electromagnetic interference effectiveness is measured by attenuation. Attenuation is the measurement of a signal at a point before and after it is shielded. The attenuation is expressed in decibels (dB) with the intensity of that signal. The dB levels between 10 dB and 30 dB would be the least effective shielding, while 60 dB to 90 dB is highly effective, and 90 dB to 120 dB is deemed exceptional.
EMI Shielding Materials
The most commonly used EMI shielding materials include copper, aluminum, and steel. Each has different properties that can influence the selection. Factors to take into consideration include effectiveness, cost, and resistance to corrosion.
Copper
Copper is highly conductive, making it an effective shield against EMI. It can be manufactured into a wide range of shapes and installed quickly. It is also durable and resistant to oxidation. Although it can be expensive, it is generally considered the best EMI shielding material. It is widely used in everything from MRI facilities to IT equipment.
Copper alloy 770, also known as alloy 770 and nickel silver, is an alloy of nickel, copper, and zinc. It resists corrosion and works well at shielding frequencies in the mid-kilohertz to gigahertz range.
Aluminum
Aluminum is only about 60 percent as effective as copper at EMI shielding, but it has other properties that can make it a good choice. It is malleable, has a high strength-to-weight ratio, and is great at thermal and electrical conductivity. Aluminum is also less expensive than copper but is subject to oxidation and will corrode if exposed to weather.
Steel
Steel is the least effective of the three materials in terms of signal attenuation. Cold-rolled steel offers better EMI shielding properties than other types. Pre-tin-plated steel works well across a wide range of frequencies, and the tin plating helps prevent corrosion. It is a good low-cost alternative and offers the magnetic shielding properties that copper and aluminum lack.
EMI Shielding Applications
Methods and materials used for EMI shielding depend on the application and the frequencies to be attenuated. Two common use cases are security and real device testing.
Protection Against Eavesdropping
Highly sensitive applications and data, such as those related to national security and critical infrastructure, require shielding to prevent eavesdropping. These use cases generally require a SCIF (sensitive compartmentalized information facility) that meets the strict requirements of the TEMPEST specification. SCIFs are found in places where security is paramount, such as the Pentagon and the White House. However, SCIFs are often room-sized and are cost-prohibitive for most needs. A purpose-built, shielded cabinet can provide information security without the expense of building a SCIF room.
Real Device Testing
Mobile app developers often need the ability to test various devices and must isolate them so that their wireless signals don’t interfere with one another. Traditionally, developers had to improvise a real device testing environment. However, a properly shielded server cabinet can be used to test mobile devices and applications that require RF attenuation.
Enconnex EMI Shielded Cabinets
Shielding against EMI at the data center level is expensive. A better approach is to utilize properly shielded cabinets. Enconnex developed the DefenseShield enclosure to deliver military-grade performance in a lightweight, cost-effective solution.
DefenseShield is purpose-built to provide 85 dB of attenuation against EMI and RF signals from 1 MHz to 10 GHz. It enables you to isolate sensitive systems and data from threats such as EMI and power analysis side channels. Our DevShield product is nearly identical in form and creates a real device application test environment that can support hundreds of devices in a single enclosure. Simply add more cabinets to scale from an R&D lab to a data center with thousands of devices.
But DefenseShield is more than just a Faraday cage. It offers key features that reduce costs and simplify management. Fifty percent lighter than competitive products, DefenseShield is easy to ship, install, and integrate into the data center. It also provides the airflow needed to support high-density applications, with ten powerful, long-life fans. Additionally, we offer a wall-mounted version capable of 90 dB of attenuation at frequencies ranging from 1 MHz to 10 GHz.
Customize your enclosure with various power options, shelves, and other components from Enconnex. We’re here to help you minimize the impact of electromagnetic interference and meet your most demanding requirements. Get in touch today.
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