You can’t wave a wand and magically cure conduction noise… But you can find the cause and countermeasures! (Part 2)

Hello, everyone. I’m Akatani, a manager for EMI test & solution service.

Continuing on from my previous blog, today I will explain a way to suppress conducted emissions with an example.

When I face a non-conformity of conducted and radiated emission, I imagine “leaking water from a pinhole somewhere on a bucket”. The same story holds true for EMI suppression. Even for a product that has been well considered for EMI suppression, if it exceeds the standard’s criteria, there must be a leak (cause) in the design.

It’s really hard to find these leaking holes. Have you ever supposed how much easier it would be to suppress conducted or radiated emissions if you could see them, haven’t you? I wondered many times I wish I was able to see them with my own eyes.

Surprisingly, such a system (Electromagnetic Field Visualization System) has already been available and has made this engineer’s dream real! Wow! It’s amazing how far technology has come!

The system captures an EUT (Equipment under test; such as PCB, product itself, and so on) with a camera and uses a near field probe to scan the EUT’s surface and superimpose the measured electromagnetic field intensity levels on the image to map the noise emissions.

 

 

When I was selecting equipment to introduce into our anechoic chamber, I found this and thought, “This is exactly I am looking for!”, so I installed it right away.

This Electromagnetic Field Visualization System is available for customers who use our anechoic chamber rental service.

Then, I’ll tell you an example of a way of solution for conducted emission using Electromagnetic Field Visualization System in a schematic diagram.

The following figure obtained by the Electromagnetic Field Visualization System shows an electromagnetic field distribution of a PCB of a product that doesn’t conform to a conducted emission criteria. (The more red the area, the higher the noise level. Blue area does not have the effect of noise)

 

 

As you can see, the noise in question is confined to a small area, suggesting an ideal design. But actually, the conducted emission caused from this noise was leaking into the power cable. Why?

The problem was hidden behind the way assembling this PCB into the case, actually.

 

 

As you can see in this figure, when we assembled the PCB into the case, we also had to place the power cable inside the case and connect it to the connector on the PCB, then a part of the cable was lying right above the noise source. Even though the noise energy on the PCB is ideally confined, such configuration leads not only to propagate it as a conducted emission from the noise source to the power cable by inductive coupling, but also to cause a radiated emission from the power cable.

In such a case, you just need to review the internal cable wiring so as not to get affected by the noise source so that the noise level is significantly improved.

 

Example of revised internal cable wiring

The solution for conducted emission seems quite simple as a hindsight. But designers midst of seeking solutions wonder if there are some faults in their design and will try everything they can think of. Of course, that approach will still get you to the answer, but it takes an overwhelming amount of time and effort.

In order to solve EMI problems effectively, we have introduced the latest equipment such as an Electromagnetic Field Visualization System and a Δ Type Line Impedance Stabilization Network (LISN).

We will support your EMI solutions efficiently by utilizing these facilities. In addition, you can also use them by yourself as our anechoic chamber rental service, so please feel free to contact us.

 

 Copyright © 2020 Wave Technology Inc. all rights reserved.