Questions tagged [near-field]
The near-field tag has no summary.
25 questions
2 votes
1 answer
151 views
Problem in locating and stopping radiation from an ethernet phy and RMII signaling
An FCC unintentional radiators test is failing at 550MHz, after probing with a near field probe the source was located to these areas of the PCB (shown below in black circles). The RMII is running at ...
- 93.4k
0 votes
0 answers
55 views
How to trigger a circuit when getting close to it physically?
Context : A relative of mine is working on a game. They would like to be able to have an event to start when getting close to say 50cm to an object (any direction). What would be a way to implement ...
1 vote
1 answer
125 views
Is there a simple approximation for B-field strength of a loop antenna when driven at 10 GHz?
I have a near-field loop antenna that I'm applying a microwave field to at 10 GHz. I'd like to have it interact with a small magnet that is much smaller than the loop. Here's a picture with the little ...
- 370
1 vote
1 answer
93 views
Maximizing magnitude of fields created by an antenna
I have a small loop antenna (\$C\$ = circumference<< \$\lambda\$ ). I am interested in the fields created by this loop at a distance \$D\$ along the z axis also small compared to \$\lambda\$. I ...
- 549
1 vote
2 answers
112 views
Electrically long loop antenna with homogenous near B field inside antenna loop
I wanted to know is it possible to create a loop antenna that functions in a way like a high frequency helmholtz coil. Because a helmholtz coil is usually made with multiple turns of wire having high ...
- 47
0 votes
0 answers
110 views
RF Power measured using near field probe
I'm trying to measure the TX signal strength of an intentional transmitter at 2.4 GHz. I'm using a near field probe and can clearly see the signal, but the amplitude is less than I was expecting - it'...
- 61
0 votes
2 answers
195 views
Why do we want detaching field lines in an antenna?
I have some questions about the link between the intuitive explanation for why an antenna radiates (based on this video) and the Maxwell equations. Q1. The video starts by saying that "an ...
- 3,660
0 votes
0 answers
53 views
Receive Antenna Design Consideration in Dual Antenna LF RFID System
I am working on constructing a loop antenna pair for an LF RFID application. The antenna is quite large (4' x 6'). I was able to successfully wind a transmit (Tx) antenna and tune it such that it ...
- 31
1 vote
0 answers
204 views
Radiated Emissions problem
This is regarding some Radiated Emissions testing unintentional radiator. We did a pre-scan of our product and we got the following EMI signature. Critical frequency is at 314.986 MHz Polarization is ...
- 710
1 vote
0 answers
48 views
Near-end scan different frequency magnetic field propagations in ideal DC source
I installed a simple PCB on Ansys siwave. I defined the power lines. And I defined an ideal voltage source that gives only 18 V on the pins. I set the near fields analysis as you can see. ...
- 824
2 votes
1 answer
741 views
E field probe or H field probe to detect
I have a board that is failing radiated EMC tests. There are narrowband spikes with 50 MHz intervals (300 MHz, 350 MHz, 400 MHz, etc.) I believe it has something to do with a clock (I suspect so since ...
- 141
1 vote
1 answer
279 views
How should I use characteristic mode analysis for antennas that are needed for near field imaging?
I am designing an electrically small microstrip patch antenna, and its "radiative" near field (r = wavelength) reaches quite long enough for the whole imaging region. Basically, I don't need ...
0 votes
0 answers
396 views
Why is the near-field radius of a small antenna lambda/2PI?
If I have a small antenna, the near-field is said to extend to \$\frac\lambda{2\pi}\$: The outer boundary of the reactive near-field region is commonly considered to be a distance of \${\textstyle {\...
- 21
0 votes
1 answer
214 views
Can PN7150 NFC controller deactivate RF Interface?
I have used the PN7150 NFC chip from NXP in autonomous polling mode with LPCD disabled. I can detect NFC Tag and can see NFC coil signals are changing as the NFC tag is detected. PN7150 VDDTx current ...
0 votes
1 answer
658 views
Near Field from a Dipole Antenna
What are the equations defining the near field of a half-wave dipole antenna? What is the rate of decay of E-field and H-field in the near field (both reactive and radiative zones)? How are the ...
- 179