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
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.