Electronics Insight
16. February 2022
Reading time: 18 Min.

What is EMC? Basic knowledge of electromagnetic compatibility

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Table with keyboard and computer in a room with a bunch of pointy gray structures coming from the walls

In this five-part EMC blog series, we will walk you through a basic understanding of EMC. By the end of this series, you should be able to start your designs while keeping EMC concerns in mind up-front.

In this first post, we’ll give you an overview of EMC and how it may concern you and your company. Once you understand what EMC is, we'll then talk about chip bead ferrites and understanding datasheets in our next post. Then we'll move on to defining the losses and details of insertion loss calculation. And finally, we'll finish up with a discussion about clamp-on ferrites.

But first — what is EMC?

What Is Electromagnetic Compatibility (EMC)?

First things first: EMC is not to be confused with EMI.

Every electronic device emits EMI, or electromagnetic interference. How that affects your device and other electronic devices is where EMC comes in.

EMC, or electromagnetic compatibility, is concerned with how well your product interacts with other products within its environment.

The world is a busy place, and it's filled with tons of EMI. Your job is to make sure that your device does not cause any unintentional failures to other devices and, at the same time, protect your device from the EMI caused by others.

In short, in order to be electromagnetically compatible, you need to prevent emissions and have high immunity. So please keep this statement in mind as we move forward in the blog series; it will be key to our discussion.

EMC Regulations

There are many types of electronic devices in the world that provide many types of different applications — that's an obvious thing.

The level of products ranges from very simple to very complicated. The impact of a failure of one of these devices may be harmless, or it may be life-threatening.

Therefore, there are many regulations for EMC to ensure the safety of electronic devices and make sure there aren't any unintentional failures caused by EMI. There are special electronic components for this purpose.

IEC is a worldwide standard, and EN is a European standard. We won't get into the details of every standard here, but we want to show you these very specific regulations for several different industries, such as medical equipment, industrial equipment, information technology, and so on. It is very important that you're aware of what regulations your product needs to meet in order to bring your product to market.

It's not up to manufacturers of EMC components like Würth Elektronik or EMC labs to tell you what standards you need to meet. You will need to know this for yourself when you're getting your product tested at the EMC Lab for certification.

The EMC Lab will definitely be able to point you in the right direction, but at the end of the day, it is your responsibility to understand those standards.

Types of EMI

There are a few different types of EMI. Understanding these types will help you identify what might cause any EMI issues you'll encounter.

  • First, we have conductive coupling, which is a physical coupling path that is formed by a direct contact. An easy example is a cable or wire. Keep in mind that conductive coupling could also occur with any trace on a printed circuit board (PCB) or even a metal enclosure.
  • Then, there's radiative coupling, which occurs over the air. Because every trace on a PCB is a potential antenna, it is also a potential coupling path.
  • Next, we have capacitive coupling, which is specific to an electric field. It occurs when a varying electrical field exists between two adjacent conductors. For instance, when you have two plates with a potential difference separated by any space, you essentially have a capacitor.
  • Finally, there’s inductive coupling, which is specific to the magnetic field. This occurs when you have a varying magnetic field between two parallel conductors. This causes parasitic induced voltages.
  • This means that in high-voltage applications, capacitive coupling will dominate. In high-current applications, inductive coupling will dominate.

Example of EMI

Here, we're using an old picture as an easy example of what EMI looks like.

On the left, you see a picture taken from an old television. Since it was not designed for EMI, the old TV is very susceptible to EMI and the failures caused in its environment. The picture on the right shows the results of this type of interference.

So put the picture into a real-life scenario: You’re watching TV, and somebody decides to come in and vacuum the living room. The result of the EMI emitted by the vacuum is a distorted screen, like the image on the right. Not a pretty picture.

Luckily, standards have now been put in place to prevent this type of situation.

Electromagnetic Compatibility

As stated previously, in order to be electromagnetically compatible, you need to both prevent emission and have high immunity. Emission is concerned with EMI leaving your device, and immunity is concerned with EMI entering your device.

There are two types of each of these: conducted and radiated. Conducted is a direct connection, like a wire or cable, whereas radiated is transmitted through the air.

We like to use the flu example when discussing this topic. Picture a situation in which the flu bug is going around. People may choose to wear surgical masks.

Now, they can wear these for two different reasons. If they have the flu and don't want to spread it to others, they're using this flu mask to prevent emission. If they don't have the flu but don't want to catch it from others, they're using the mask to increase immunity.

CISPR 22 vs. FCC 15

As we mentioned, there are a number of EMC regulations out there. Two regulations we run into quite often are CISPR 22 and FCC 15.

CISPR 22 tests for conducted noise at 150kHz to 30MHz. It tests for radiated noise at 30MHz to 6GHz.

FCC 15 tests for conducted noise at 450kHz to 30MHz. It tests for radiated noise at 30MHz to 40GHz or the fifth harmonic of the highest frequency.

This means that anytime you have a frequency above 10MHz, you should start considering that there's a common mode noise issue. The chances are higher that it's common mode noise above 10MHz, but it's not a guarantee. It's possible to have differential noise above 10MHz, but this doesn't happen very often.

This image shows conductive and radiated test performed at the same frequency, broken down into Class A and Class B. Class A is for commercial, industrial, and business environment equipment. Class B is for residential environment equipment. The tests for Class A are more stringent because of the environments they’re operating in.

By reading this article you have now taken the first step and learned more about the topic of electromagnetic compatibility.

Stay tuned and learn more about EMC in the following blog posts:

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