Pick up Electromagnetic Field of a Human - Page 1
Forum section: electronics / projects

author: Bskitter
author_rank: Regular Contributor
timestamp: September 21, 2016, 02:16:03 am
content: Hello Guys I recently had a chat with a friend of mine about how one could pick up the electromagnetic field of a human.He mentioned that you would need some very sensitive hall effect sensors in some differential configuration to filter out unwanted noise.But in short has anyone here made a circuit that can get a basic reading of the field ?Would be interesting to see the results.Byron

author: zlymex
author_rank: Frequent Contributor
timestamp: September 21, 2016, 02:35:24 am
content: I would rather go for capacitive detector or static voltage to sense the change of electrostatic field around human body.A simple capacitive detector could be an LC oscillator with open capacitor(just a metal plate).

author: edavid
author_rank: Super Contributor
timestamp: September 21, 2016, 03:54:01 am
content: Humans don't really produce an electromagnetic field. You have to glue electrodes to them to measure anything electrical.Hall effect devices are never very sensitive. They are used to detect strong magnetic fields only.So, double fail for your friend.

author: NottheDan
author_rank: Frequent Contributor
timestamp: September 21, 2016, 04:08:37 am
content: Quote from: zlymex on September 21, 2016, 02:35:24 amThey already madea musical instrumentout of that.

author: jitter
author_rank: Frequent Contributor
timestamp: September 21, 2016, 05:25:14 am
content: Quote from: evb149 on September 21, 2016, 02:44:14 amSource?

author: technotronix
author_rank: Regular Contributor
timestamp: September 21, 2016, 06:11:08 am
content: Some millimetre wavelength radiation and some infra red both are the result of the temperature of the body.

author: jitter
author_rank: Frequent Contributor
timestamp: September 21, 2016, 10:49:29 am
content: Somehow I doubt that is what OP was getting at...

author: MosherIV
author_rank: Super Contributor
timestamp: September 21, 2016, 11:15:55 am
content: QuoteReally?? So every time a neuron fires and the tiny electrical current that flows does not generate a tiny magnetic field.QuoteI agree, that the magnetic field produced by nerve pulses are too small to measure with Hall effect sensors.In any case, these tiny magnetic fields are likely to be swamped by1. the earth's magnetic field2. Any near by electrical stuff.

author: Gyro
author_rank: Super Contributor
timestamp: September 21, 2016, 11:43:49 am
content: The major emission in the from humans in the electromagnetic spectrum is long wave IR, using a PIR sensor is the logical way of detecting this (or a thermal camera of course). I agree it may not be what the OP was intending but it's very hard to argue with how it's almost exclusively done in practice.

author: DaJMasta
author_rank: Super Contributor
timestamp: September 21, 2016, 03:03:24 pm
content: Passively measuring em fields from a human is going to be difficult. As mentioned, the electrical things going on are quite small and you need to be very sensitive and very close to find them in the noise. Aside from just going to IR or another tech, I think capacitive testing is probably a decent bet - same tech the theremin uses - and basic setups can detect fingers at a few inches, with some tweaking and a decent sized plate, you should be able to get at least a little more distance.I don't know if this is viable, but what about active field sensing? Basically generating an em field and then monitoring it for changes induced by a human's proximity. Not sure if it is viable because I don't know what power level such a field may need to be, but If you're only detecting the presence of a person, maybe it wouldn't be prohibitive to make an air-core inductor that can tell when it becomes a flesh-core inductor.

author: Len
author_rank: Frequent Contributor
timestamp: September 21, 2016, 03:15:41 pm
content: Quote from: jitter on September 21, 2016, 05:25:14 amhttps://en.wikipedia.org/wiki/Black-body_radiation#Human_body_emission

author: Fungus
author_rank: Super Contributor
timestamp: September 21, 2016, 05:42:42 pm
content: Quote from: Bskitter on September 21, 2016, 02:16:03 amI assume you mean "at a distance".Hall effect sensors? No way. Not gonna happen. Electrical signals in nerves are simply too small to measure. They're also going to be fairly randomly oriented so they'll cancel each other out.A capacitive sensor is the way to go.

author: trophosphere
author_rank: Frequent Contributor
timestamp: September 21, 2016, 07:52:47 pm
content: There have been attempts at obtaining ECG/EMG/EEG signals from human subjects via capacitive coupling termed "non-contact dry electrodes" which technically is electric field based and works at a distance of millimeters. You would basically need a very high impedance amplifier (easily obtainable with op-amps today) with circuitry to handle saturation and noise.Review article here

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 22, 2016, 12:59:27 am
content: https://en.wikipedia.org/wiki/Ampullae_of_LorenziniHow to use them is left as an exercise for the reader.

author: Dago
author_rank: Frequent Contributor
timestamp: September 22, 2016, 04:11:59 am
content: It kinda sounds like you want to do something similar as a MEG machine doeshttps://en.wikipedia.org/wiki/MagnetoencephalographyWhich detects the magnetic fields caused by neurons firing in the brain with superconductive SQUID-sensors. Needless to say it is a rather expensive machine. The sensors alone (which total maybe a few square centimeters of silicon) cost a six figure sum total (worked in a company which manufactured and tested those).