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In the paper "Synthetic Sensors: Towards General-Purpose Sensing" by Gierad Laput, et. al, they use a 100 mH inductor as an EMI (electromagnetic interference) sensor. They have not provided much details on the board (shown below)

enter image description here

I was wondering what a circuit would look like which the inductor can be an ADC input to a microcontroller. Thanks for any ideas.

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    \$\begingroup\$ Roll-back to what you want to achieve - don't start with an under-defined product with no provenance that I can see. What do you want to achieve? \$\endgroup\$
    – Andy aka
    Sep 14, 2020 at 9:20
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    \$\begingroup\$ I am trying to build a platform to collect sensor data for building ML models. Specifically I'd like to understand how to get EMI data from an inductor as input to a uC. \$\endgroup\$
    – M-V
    Sep 14, 2020 at 13:47
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    \$\begingroup\$ @Andy-aka In figure 5 the authors clearly show some signal picked up by the inductor when a microwave oven is on. While the microwave emission itself is at 2.4GHz, the power electronics in the microwave may radiate at a variety of other frequencies. For example, the plot also shows a signal received when the microwave door is closed due to the interior light switching on or off. \$\endgroup\$
    – Josh
    Oct 6, 2020 at 16:50
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    \$\begingroup\$ I would suggest reading the conference paper for more information (it will do a better job than me!), it's actually quite interesting. They combine signals from several sensors to feed into an event detection system. For EMI, they take a spectrum of the signal from the inductor and use that as an input to their classifier. See my answer below, you can detect a lot of distinct appliances that emit in the 100-250kHz band. So "some signal" is an FFT/spectrogram of whatever is picked up by the inductor acting as an antenna. \$\endgroup\$
    – Josh
    Oct 6, 2020 at 17:30
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    \$\begingroup\$ A microwave might not be the best example. There may be appliances which emit a burst of broadband EMI when you power them on, without any obvious audio signal. gierad.com/assets/supersensor/supersensor.pdf \$\endgroup\$
    – Josh
    Oct 6, 2020 at 17:39

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You can see one design from the Elektroscluch [0]. It seems to be as simple as connecting an inductor to ground and then feeding the "positive" end into an amplifier (and in your case an ADC). I don't see why you need two inductors here. This circuit uses one.

Given the sampling rate of 500kHz (if you copy the paper), you might want to put in a low pass filter around 200-250kHz anyway. On the PCB in the supersensor papre it looks like there may be an RC filter just off to the right, which maybe feeds into an op-amp buffer (unity gain amp) U8. That's a guess though, since there's no schematic.

Their conference paper does cite a couple of references that may be useful, but they seem to be more related to power line monitoring, not inductive/contactless. For example:

https://ubicomplab.cs.washington.edu/publications/electrisense/ https://ubicomplab.cs.washington.edu/publications/lightwave/

Both these papers show that lots of interesting emission in the low 100s of kHz which matches with the sampling rate in the paper.

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[0] https://github.com/LOM-instruments/Elektrosluch-3-plus/blob/master/hardware/elektrosluch_schematic.pdf

Another example they cite is the Syntonistor project from CMU - that seems closer, although a lot of the conditioning circuitry here doesn't seem to be on the Synthetic sensor PCB (but who knows, we only have a photo of the top side). Also it's designed to detect 60Hz, but you could tap off the signal just after the inductor.

https://www.andrew.cmu.edu/user/agr/projects/syntonistor/

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