Taming the Dragon: Understanding and Focusing on EMI

Medical Device & Diagnostic Industry Magazine
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An MD&DI July 1998 Column

Scott Roleson sometimes characterizes himself as an amateur radio operator who lost control of his hobby. He says ham radio has been a passion since he was a kid, and so it was a natural progression from that into the electronics technologies and engineering. An electromagnetic compatibility (EMC) and telecommunications engineer with Hewlett-Packard in San Diego, Roleson wrote this month's EMI Field Notes starting on page 54. The article is based on work he did to help understand and quickly identify electromagnetic interference (EMI) radiation.

"If antennas can be designed to produce certain radiation patterns, then in some cases, it should be possible to infer the antenna-like structures in electronic equipment by looking at the EMI radiation pattern," Roleson says. As part of his amateur radio experience, things like antennas are interesting to him.

After getting his master's degree from the University of Arizona (Tucson), Roleson got a call from Hewlett-Packard. They had a product being redesigned and one problem they had was with EMC. "They wanted to have someone concentrate on EMC. I had been studying circuit design, antennas, and everything except EMC. When I started working in 1982 as an EMC engineer on a specific project, that was my sole job for about a year and a half. I succeeded for the most part in taming the dragon. But that was what it took. It wasn't so much my skill, but it was the focus. It was important to have someone focused on EMC," he says.

Scott Roleson says it's vital to know EMI.

Fascinated by the project, Roleson was able to use a lot of his background in antennas. One of the first things he did tapped into this knowledge. "I needed some way of going inside the product and figuring out what was radiating and why. I developed a magnetic field probe using the concept of a loop antenna. I built a classical loop antenna about as big around as your finger—a very small probe—and was able to use this effectively to get inside the circuitry, find the offending sources, and understand the emissions," he says.

It's vital to understand the fundamentals of an electromagnetic problem before trying fixes, he says. Understanding the physics and the underlying rationale enables the engineer to find several possible solutions. It's important, he says, to choose a solution that meets not only the technical requirements but also the project's cost and time constraints. "You can't do that unless you have many solutions to choose from," says Roleson.

A big issue facing EMC engineers now, he explains, is ever-increasing clock speeds. As clock frequencies increase, there's more energy at higher frequencies, which means shorter wavelengths. The shorter wavelengths are the key parameter for assessing resonance and determining how a structure relates to the energy wavelength associated with it. "In the old days, we had slower clock speeds and the wavelengths of these emissions were fairly long. The energy that was available was in a much lower frequency than the actual resonant frequencies at which the equipment would have resonated."

As technology moves to do things faster, smarter, smaller, and cheaper, Roleson says EMC engineers must find ways to design devices that can operate compatibly with multiple pieces of equipment. "Those factors conspire against electromagnetic compatibility unless the designers are really aware of EMC." From an engineer's point of view, he says, the challenge is to be a good designer in a chosen field and still know enough about EMC to do the whole job. "It's not sufficient to just be a good microprocessor designer. One must understand the electromagnetic consequences of the design and how to make it not only meet its primary function but also be compatible with other products."

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