Near-field scanners let you see EMI

June 27, 2016 // By Arturo Mediano
I love near field probes because they let me "see" magnetic and electric fields with an oscilloscope or with a spectrum analyzer. They let me locate sources of emissions in board, cables, and systems. Near-field scanners also let you see emissions, particularly all over a board. That's hard to do with a single probe.


There are several EMI/EMC scanners on the market today such as those from EMSCAN, DETECTUS, and Api, and others. A scanner is essentially a series of near-field probes placed in a grid. Thus, it can produce an image of a board's emissions that's more consistent and repetitive than you can get by manually scanning a board with probes.


The EMxpert scanner from EMSCAN is one such scanner, which I use in my lab. Here's an example of how I used it to evaluate a decoupling network for a training course. Figure 1 shows a scanner with a scan area 21.8 cm x 31.6 cm scanning a PCB under test.



Figure 1. A PCB under test on top of the near field scanner. (Photo; author)


The scanner consists of thousands of loops spaced so that it provides resolution of less than 1 mm. Frequency range goes from 50 kHz to 8 GHz, depending on the model. The loop antennas are sensitive down to -135 dBm and a high-speed electronic switching system provides real-time analysis in less than 1 sec.


EMI scanners let you quickly analyze and compare design iterations and optimize hardware design. I use them for troubleshooting and for teaching. Here, I'll use it to demonstrate how a decoupling network can reduce emissions from a board.