Minimizing Electro-Magnetic Interference (EMI) for product approval

Recently I had an urgent call from a past client to help him resolve an EMI problem which exceeds its limits. He had supported me before, and I could not say no to him as his team tried to resolve the EMI problem for months.

I was involved in EMI back when I was in Philips Electronics back in 1982 ! I had only documented this EMI project in 1983 (page below). That project accelerated my Philips Electronics career, as back then even the engineers in Eindhoven HQ could not resolve this problem.

I was familiar with EMI as I designed and set up the Outdoor US FCC radiation measurement site with HP Spectrum Analyzer and Rotating Table at the top of the TP1 Building and the German FTZ radiation test facility.

I was concerned that my EMI knowhow might be outdated. However, helping a friend is helping without any commercial terms in mind.

I had to rely on my basic knowledge of Magnetic Fields and Finite Element Method (FEM) background when I did my Ph.D in 1979 (page below)!

With these past basic understanding of Electro-Magnetic fields and my Electronic Hobby background, I help to identify the sources of EMI, which came from the switch mode power supplies and cabling and unshielded opening.

In the Test Laboratory, there was a R&S Spectrum Analyzer (picture below) used with the shielded room. The upper yellow chart is the Spectrum Graph without EMI suppression solutions while the lower green noisy chart is the Spectrum Graph with EMI shielding.

During the investigation, I used my $ 30 Medium Wave Radio with a Ferrite Antenna to trace for the EMI sources for the lower harmonics. It was good enough to help pin point the EMI sources.

Without a proper $ 10.0 M EMI test setup, I had to improvised and rely on my poor man EMI kit to evaluate the EMI blocking solutions, which consist of only Aluminum Food Trays, Baking Foils and conductive Tapes.

Finally, we found the EMI sources and exit areas. We then add an Aluminum shield inside machine to reduce the EMI signatures. During the investigation, the metal screen sheet was replaced with mild steel but it could not suppressed the EMI as the Eddy currents back suppression is better in conductive Aluminum than mild steel.

The Final setup met the EMI requirement.

Do not look at the problem as one huge problem. The Fundamental Engineering Understanding is important in Engineering. Most problems can be broken down into smaller manageable problems to isolate and understand stage by stage.