Antenna for detecting EM fields

Using Arduino Sensors
#1

Hi Folks,

I'm looking for an antenna expert. I want to detect EM within a 3-foot range. I see a lot of Arduino projects using a straight wire. That detects EF and not EM. I currently can measure EM using a near field loop antenna (https://www.amazon.com/gp/product/B01MXJJ0YW/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1). This antenna works great. Now I want to expand the range. Can anyone suggest what kind of antenna I may need? The frequency would be in the low to medium frequencies (I think). I don't know anything about antennas except that they are complicated.

Thank you in advance!

#2

Is this the same project from your other topic?:

#3

Do not cross post.

#4

rchicone:
The frequency would be in the low to medium frequencies (I think). I don't know anything about antennas except that they are complicated.

Terms like 'low' and 'medium' are very subjective, you need to be more specific.

#5

If your antenna coil is working now, you extend the range by AMPLIFYING the signal, not changing the antenna coil.

If you want to start over, make a loop antenna about 3 feet in diameter with, perhaps 100 turns of wire. But then you pick up all the noise from local power lines.

Paul

#6

srnet:
Terms like 'low' and 'medium' are very subjective, you need to be more specific.

Not for radio frequencies.

low frequency is 30kHz to 300kHz, medium is 300kHz to 3MHz

#7

rchicone:
Hi Folks,

I’m looking for an antenna expert. I want to detect EM within a 3-foot range. I see a lot of Arduino projects using a straight wire. That detects EF and not EM. I currently can measure EM using a near field loop antenna (https://www.amazon.com/gp/product/B01MXJJ0YW/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1). This antenna works great. Now I want to expand the range. Can anyone suggest what kind of antenna I may need? The frequency would be in the low to medium frequencies (I think). I don’t know anything about antennas except that they are complicated.

Thank you in advance!

Near field means either electric field or magnetic field that’s not necessarily propagating distantly.

If both near fields are present at the same frequency and at the right sort of ratio, then that’s
likely to propagate distantly anyway.

antennas for electric field are simple, a short conductor sticking out near the object of interest, and shielded
elsewhere.

A magnetic antenna is usually a shielded coil of wire, with the shield cut so it doesn’t act as a shorted turn.
This will only respond to magnetic field due to the shielding.

Either will detect far field as well, but near field is usually far larger in magnitude so we don’t worry about this.

For any antenna we have to chose its impedance, centre frequency and bandwidth, which is where it gets much more technical.
Broadband antennas have to have a fairly constant impedance across the whole band to be useful, good examples are horns and log-periodic antennas. Such antennas are often used for measurement.

Narrow band antennas are used for radio transmission and reception, and they are almost always resonant with
the resonance peak a bit wider than the band of interest - this helps with selectivity by rejecting other bands.

Near field antennas for measurement are normally broadband, not resonant.

Near field antennas for power transfer are resonant however, to ensure the power ends up in the right place.

If you want a 3 foot near-field range your antenna will need to be of similar dimension, by the definition of near-field.

#8

A single-turn magnetic loop antenna can be made from coax cable, as per: https://www.eng.mu.edu/~richiej/seminar/aidi.pdf

#9

As I recall, "near field" means within 10 wave lengths of the emitter.

Paul

#10

Magnetic near field falls off as 1/r^3, irrespective of wavelength, where r is the typical dimension of the emitting coil/conductor. Often r is << wavelength, so the field has effectively vanished long before a single wavelength. Far field is better though of as being when you are many times r away from the radiating structure. Electric near field drops as 1/r^2, and far field drops as 1/r (since energy is proportional to field squared, power falls off as 1/r^2 in radiation).

In quantum electrodynamics far-field is more straightforwardedly defined as beyond the range of virtual photons (virtual photons mediate electric and magnetic fields, real photons are those that escape to radiate and are detectable directly).

#11

pert:
Is this the same project from your other topic?:
https://forum.arduino.cc/index.php?topic=666322

It is for the same project. I wanted this post to concentrate on antennas that are needed for a range of 15-20 inches from the device giving off EM.

#12

rchicone:
It is for the same project. I wanted this post to concentrate on antennas that are needed for a range of 15-20 inches from the device giving off EM.

You need to supply some effort in testing what you already know about sensing the electric field.

Paul

#13

pert:
Is this the same project from your other topic?:
https://forum.arduino.cc/index.php?topic=666322

I didn't realize I was cross-posting. This post is specifically for antennas now that I got the loop probe to work.

#14

Paul_KD7HB:
If your antenna coil is working now, you extend the range by AMPLIFYING the signal, not changing the antenna coil.

If you want to start over, make a loop antenna about 3 feet in diameter with, perhaps 100 turns of wire. But then you pick up all the noise from local power lines.

Paul

I just bought an amplifier module to do some experimenting. Thanks again, Paul.

#15

I wasn't accusing you of cross-posting (though there was some chance this could have turned into a cross-post, depending on how the discussion evolved).

I posted that because I thought that, it was for the same project, there might be some context in the other thread that could be useful to people answering.

#16