What Are Electromagnetic Interference and Electromagnetic Compatibility Measurements, and Why Do We Care?
Fundamental design checkpoints of new products generally focus on the designs of mechanical, electrical and software systems. On the whole, EMI/EMC design falls by the wayside for many companies, including preparation for certification testing.
When designing a new product, it's best to ask yourself:
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Has there been consideration in preliminary testing in my product for compliance early in the design cycle?
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What if I've reached the testing and evaluation phase of the process only to discover that I cannot release the product to market because it did not meet the global EMI/EMC regulations?
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Have I ever considered the potential cost and time impact of being late in the product release?
If any of the above answers give you cause for concern, then you now realise that testing your product early in the design cycle to make sure it works appropriately in an EMI/EMC environment is just as important as the basic mechanical and electrical design to make it function.
In this blog, we’ll discuss the basics of EMI/EMC pre-compliance testing – something all electronic products should undergo much earlier than full certification testing. Typically EMI/EMC compliance testing certification occurs very late in the development process and test failures are almost always encountered. If you did pre-compliance testing earlier on, fixing these test failures is far easier and less costly.
What is EMI/EMC anyway?
EMI and EMC stand for electromagnetic interference and electromagnetic compatibility respectively. EMI is the unwanted electromagnetic energy either radiating in free space or conducting down I/O and/or power cables. This unwanted energy can come from any electronic device and is considered interference when the energy makes another device malfunction. EMC is the ability of electronic devices to all operate in harmony in an environment, including unwanted EMI. This can also include wanted electromagnetic energy in the form of intentional radiation off antennas such as WiFi.
All electronic products, whether it be your tablet or your TV, must eventually pass EMI/EMC compliance tests to be certified before they can be brought to market. This certification testing is performed to demonstrate that a device will not electromagnetically interfere with another electronic device in close proximity and in turn, not be interfered with from the other devices.
To get your device certified, there are four basic types of EMI/EMC phenomena a device must pass:
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Radiated emissions
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Conducted emissions
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Radiated immunity
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Conducted immunity
Emissions are concerned with the amount of unintentional electromagnetic energy emitted from your device. As stated earlier, it can happen in the form of radiated electromagnetic energy or conducted electromagnetic energy conducting down interface cables and/or power cables. The intentional radiation of an antenna is also considered a radiated emission and also must undergo certification testing to ensure the radiated energy is effectively controlled.
Immunity is concerned with how susceptible your device is to electromagnetic energy being emitted from surrounding devices. For example, if you were a patient in a hospital hooked up to a medical device, would you want that device to malfunction by electromagnetic energy from other devices in close proximity? Unless you've got your malpractice lawyers on speed dial, this wouldn't be optimal. The device malfunction can be created by either radiated or conducted electromagnetic emissions (EMI).
Who requires this?
Here again, a device cannot be placed on the market (sold) without having proven to meet the EMI/EMC regulations. Regulatory bodies, like the Federal Communications Commission (FCC) in the United States (US), set up EMI regulations that devices are tested against. As you would expect, standards vary from one device to another – meaning intentional and unintentional radiated emissions have different requirements. Similar radiated and conducted emissions requirements exist globally. Much of the standards development activity is now handled by the International Electrotechnical Commissions (IEC).
Immunity regulations are not as widespread globally. Although immunity requirements are most prevalent in Europe, similar requirements are being adopted in many other countries. For example, medical device approval in the US by the Food and Drug Administration (FDA) requires compliance with both emissions and immunity regulations.
In addition, countries such as Taiwan and Japan have adopted many of the IEC standards which include both emissions and immunity. In some cases, these standards are adopted with minor changes which are typically called “country-specific deviations."
So what do you recommend?
EMI/EMC testing is very expensive, but what makes it the most expensive is failing test requirements at the end of the design cycle when a device is ready to be released. At that point making changes to a device is the most painful and you risk having to do design revisions and throwing off your entire schedule. That’s why it’s important to do some pre-compliance testing for your device during the design cycle well in advance of sending it in for certification compliance testing.
The further any device design is down the path to completion, the more painful it is to make changes to correct test failures. In addition, it becomes less likely that the problem can be solved at the board level or internal to a device in general. At that point, the focus typically becomes a packaging solution. This is primarily due to the complex integration of components and sub-subsystems that are purchased to be integrated into your design. You have little to no control over the EMI/EMC performance of these integrated parts.
Get to the point already
Based on this unknown, a packaging approach to address EMI/EMC issues is a sound way to end up with a solid design. Materials such as EMI gaskets, shielded windows and shielded vents can be incorporated into a design at any time. Typically, the earlier the better in pre-compliance testing will have the least impact with regard to cost and time.
Another important reason to use a packaging approach to your EMI/EMC design is that you not only need to be concerned with what your device may radiate (emissions) but you also need to be concerned with keeping outside unwanted electromagnetic interference out of your device so that your device does not malfunction (immunity).
