Accurate EMF detection

Hi,

I’m new to this forum. I’m a software engineer and know only a little about electronics. I’ve done some projects with Arduino (and Raspberry Pi). For this project, I want to detect the radiation “spikes” off of a smartphone. The states I want to detect/sense are 1) when the screen is off/idle, and 2) when the screen comes on by the device being swiped. I don’t care about when data goes out, when data comes in or when a call is being made. I read this article: https://macintoshhowto.com/hardware/emf.html and EMF measurements were taken in various states and various distances. Most states are < 1000 mV/m (I’d like to detect these low radiation states). Note, when talking on the phone the EMF is 10,000 mV/m which is considered high in the paper I posted above.

What I did was some research and found “a lot” of EMF detectors using Arduino. The ones where you connect a wire (antenna) to an ADC port, along with some resistance and then light an LED or turn on a buzzer, etc. These work but are not accurate as it seems they pick up not only electric fields but also static electric fields and I can’t get it to pick up the states from my iPhone. Again, I’m more of a software engineer and not an engineer that understands a lot about electric, electronics, and radiation.

This is kind of what I want to duplicate: I used a Fluke Pro3000 tone detector (for finding non-active wires). If I use that and get close to my iPhone when the screen is off, the buzzer gets louder and you get a “distinct pattern (with or without airplane mode off)”. When I swipe the phone the buzzer on the Fluke gets way louder and if I touch an icon or press a number of the phone causes the same behavior (even a louder buzzing sound). Moving away from the iPhone, the buzzing sound gets softer. How does the Fluke do this?

For a proof of concept, the phone could be right near the antenna on the Arduino board. If I can detect these states when close to the antenna (a piece of wire) then I can go to an engineer that understands radiation in regards to antennas, etc. They can build something for me including the right kind of antenna. Preferably one that can read the radiation from 12-15 inches away.

I know I just made this simple (in my head at least). I know it is much harder to do which is why I’m reading out to you. Note: I do have a high-precision A/D D/A hat for a Raspberry Pi that I could use if necessary to prove the concept. It has a 24 bit A/D channels. I also can buy other parts if necessary for the Arduino and/or Raspberry Pi.

As I said, I’m more of a software engineer. Any help would be appreciated. Thank you in advance!

The EMF of interest is probably radiated over some band of frequencies. What are those frequencies?

I would expect them to be quite high, and totally out of range of ADC sampling rates.

Thanks for replying. From the study noted in my initial post, the researcher had an EMF detector that had the range of frequencies from 50MHz to 3.5GHz.

When thinking about the Fluke, it has to measure at least 60Hz(?) (picking up signals from a wall outlet) all the way to 5GHz (WIFI). At least from my tests at my house.

I thought maybe the radiation from the iPhone was at an extremely low frequency (ELF). I read a little about ELF and EMF. But, I probably got something mixed up. I know the iPhone has a screen refresh of 60Hz and some may go to 120Hz when the screen comes on. But, these are probably two different things. That is, the radiation level and the screen refresh rate.

I wonder then if a software-defined radio that has a range of 50MHz to 3.5GHz like the EMF meter used in the study could pick up the signal states? When this project came my way, the first thing I did was use a software-defined radio but it wasn't the same frequency ranges as the study used. Do you think it would be worth me buying another software-defined radio and try it out on my Mac/Windows machine as just a test?

Sure, try out an SDR. Keep in mind that the transmitter in your smartphone radiates several Watts on the cell phone bands, even when idle (i.e. pinging towers).

Ok, I will buy an SDR in that range and give it a try.

What do you mean by “accurate” Do you have the means to calibrate your instrument?

Paul

Thanks for your reply.

I was trying to calibrate the antenna and ADC by monitoring the values and plotting the values. But, I captured static electricity, and I saw spikes when I touched the antenna. I also could see spikes by an AC outlet and also my WIFI. But, it did not pick up my iPhone. As I mention, I only care about radiation detection when the device goes from screen off to screen on with a swipe. I want to detect when the screen goes on. I know when it is swiped something increases as I proved it with the Fluke Pro3000.

I'm probably missing something huge. The other post mentioned frequency. I was going to try a SDR to see if I can pick up the spike.

You can't possible see "static" electricity because it is "static", not moving. You are adding your body to the antenna when you touch it and see the results.

How exactly is your screen activated? Is it LED or is it LCD with a back light? There is no signal to be seen if it is LED. It is not a raster scan like the old analog TV sets.

Paul

Thanks for telling me about the static electricity.

When you say screen, do you mean when I touch my iPhone screen (that is what I can't detect but the Fluke toner does)? If so, my iPhone has a retina display. If that isn't the screen you meant, can you expound about what you meant? Thank you in advance!

rchicone:
Thanks for telling me about the static electricity.

When you say screen, do you mean when I touch my iPhone screen (that is what I can't detect but the Fluke toner does)? If so, my iPhone has a retina display. If that isn't the screen you meant, can you expound about what you meant? Thank you in advance!

You really, really, really, need to research exactly how your phone works, in detail. I have never owned one and probably won't.

A touch screen may operate in several ways. The most common may still be an array of IR emitters on two adjacent sides and IR receptors on the other two sides. Interruption of the beams meant your finger is doing something.

Another way, is to have the screen coated with an array of wires that are invisible to your eye. Same pattern as the IR. Touching the screen makes several of the wires connect.

Those are really old methods and are doubtlessly replaced by other ways.

So what your Fluke is sensing is unknown to me and with some actual research on your part you can find out. Probably make friends with your phone repair service.

Paul

Your phone is active all the time and within a couple of centimeters your phone will emit anything in the range of its local oscillator, CPU clock frequency and its LTE/UMTS/GPRS/WiFi network circuitry all the time.

When the Pro3000, which is not intended to be used for EMF measurements, comes in close proximity of the phone, it's receiving 20 - 30V/meter of EM fields and no wonder it starts buzzing. Try holding the phone near your stereo amplifier, car radio or computer speakers. Chances are you'll hear that same pattern from the EM interference.

As it is its purpose for a phone to emit such EM waves, it is an intentional radiator and should be treated as such.

For wanting to investigate EM fields in the 50Mhz - 3.5Ghz range, you'll need a lot of antennas to cover the frequency bands. From around 10 feet to less than an inch.

Leroy2007:
Your phone is active all the time and within a couple of centimeters your phone will emit anything in the range of its local oscillator, CPU clock frequency and its LTE/UMTS/GPRS/WiFi network circuitry all the time.

When the Pro3000, which is not intended to be used for EMF measurements, comes in close proximity of the phone, it's receiving 20 - 30V/meter of EM fields and no wonder it starts buzzing. Try holding the phone near your stereo amplifier, car radio or computer speakers. Chances are you'll hear that same pattern from the EM interference.

As it is its purpose for a phone to emit such EM waves, it is an intentional radiator and should be treated as such.

For wanting to investigate EM fields in the 50Mhz - 3.5Ghz range, you'll need a lot of antennas to cover the frequency bands. From around 10 feet to less than an inch.

To investigate the voltage you just need a single short wire To investigate the magnetic field, you need a loop of wire to create a transformer.

For very wide band antenna look for a log periodic antenna.

Paul

Leroy2007:
Your phone is active all the time and within a couple of centimeters your phone will emit anything in the range of its local oscillator, CPU clock frequency and its LTE/UMTS/GPRS/WiFi network circuitry all the time.

When the Pro3000, which is not intended to be used for EMF measurements, comes in close proximity of the phone, it's receiving 20 - 30V/meter of EM fields and no wonder it starts buzzing. Try holding the phone near your stereo amplifier, car radio or computer speakers. Chances are you'll hear that same pattern from the EM interference.

As it is its purpose for a phone to emit such EM waves, it is an intentional radiator and should be treated as such.

For wanting to investigate EM fields in the 50Mhz - 3.5Ghz range, you'll need a lot of antennas to cover the frequency bands. From around 10 feet to less than an inch.

This is so very helpful to me. Thank you so much. I really don't want to investigate that entire range of frequencies. I want the frequency or range of frequencies to detect mobile phone states (do not want any data, just state changes). States like screen going off to on, a swipe, a password entered. Essentially, I want to know when the device is first starting to be used. Would it be at the ELF range or more like the medium range or ? I've seen some researchers detect mobile device EM (but when processor-intensive apps are running) at the 150MHz - 300MHz frequency. I'll use the loop antenna, as Paul mentioned.

jremington:
Sure, try out an SDR. Keep in mind that the transmitter in your smartphone radiates several Watts on the cell phone bands, even when idle (i.e. pinging towers).

Only the old analog network used that kind of power, these days typically it will be much less than 1W, and 1W is the maximum. In a dense cell network the distance to the nearest base station is low, so low power is used. Out in the sticks you might get upto full power.

To measure radiation you'll need a set of probes (near field) / antennas (far field) and an RF spectrum analyser.

To estimate emissions an RF detector might be better than nothing. Basically some germanium/back diode(s) /resistors/capacitor and a voltmeter.

MarkT:
Only the old analog network used that kind of power, these days typically it will be much less than 1W, and 1W is the maximum. In a dense cell network the distance to the nearest base station is low, so low power is used. Out in the sticks you might get upto full power.

To measure radiation you'll need a set of probes (near field) / antennas (far field) and an RF spectrum analyser.

To estimate emissions an RF detector might be better than nothing. Basically some germanium/back diode(s) /resistors/capacitor and a voltmeter.

Thank you, again.

I did get a small near field loop antenna probe. I can now detect EMF from a mobile device (and other places). At first, I was using the straight antenna until Paul straightened me out. I now know there is a difference between EF and EMF.

rchicone:
I did get a small near field loop antenna probe. I can now detect EMF from a mobile device (and other places).

To help others in the future (and to satisfy my curiosity :slight_smile: ), what probe did you get (make/model please)? And if you made the probe from parts, please post a schematic.

Paul_KD7HB:
You can't possible see "static" electricity because it is "static"

An electroscope can measure static electric fields by induction. Coulomb Meter, -1999 to 1999 nC - Digital Electroscope - For Use In El — Eisco Labs

DaveEvans:
To help others in the future (and to satisfy my curiosity :slight_smile: ), what probe did you get (make/model please)? And if you made the probe from parts, please post a schematic.

Sure thing. I bought this from Amazon: https://www.amazon.com/gp/product/B01MXJJ0YW/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

If it for a particular device but I didn't use it that way. It is my input to my ADC. I hope this helps you!