What I Learned this Month

I attended the 2011 IEEE EMC Symposium in Long Beach and encountered a number of exciting companies, people and products. The Canadian company EMSCAN is one of these.

Their EMxpert can measure, plot and analyze the current distribution in circuit boards at specific frequencies. It uses an array of high bandwidth magnetic field sensors on a flatbed which picks up the near field magnetic field from a circuit board.  When the board is turned on, return currents in the planes generate local magnetic fields with frequency components based on the signal’s spectrum and a spatial distribution and magnitude based on the current distribution.

When you superimpose on the map of the current distribution, the component outlines on the board you get an immediate visual clue about where currents are actually flowing on the board. Usually the currents on the bottom of the board that can be sensed outside the bottom are due to the power and ground distribution, but may also relate to the aggregate of signal returns. You might use this information to consider adding more capacitors to reduce the local currents and reduce the near field radiated emissions.

The near field external magnetic fields are not always a direct indication of far field radiated emissions, but it offers a new window into what’s going on with a functional board. 

Each magnetic field pick-up-loop sensor can measure the spectral response of the current.  Depending on the specific signal, you will see frequency components at harmonics of the signal.

You can then sit at one frequency and scan across the array to measure the peak amplitude of the magnetic field, at that frequency. This maps the current distribution at that frequency in the board that leaks through to the bottom. 

On my visit to the EMSCAN booth, I recorded this short video demonstration performed by Cedric Caudron, an applications engineer with EMSCAN in which he walks through the process of looking at the spectrum, the current distribution, then adding a capacitor and showing that the current distribution in the planes is reduced by adding the capacitor. It’s pretty darn cool.