# Questions tagged [near-field]

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1 vote
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### 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 ...
1 vote
60 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 ...
• 395
1 vote
54 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 ...
• 31
19 views

### How are the currents induced by the E-field and H-field flows on a sphere? [duplicate]

Please correct me if I am wrong? We consider a sphere made of thin metal, with a radius of 1 m, at 20 km distance from an AM transmitter operating at 1 MHz. The alternating current in the transmitter ...
• 1
38 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
106 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 ...
• 3,550
29 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 ...
• 21
1 vote
110 views

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 ...
• 554
1 vote
41 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. ...
• 756
394 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 ...
• 131
1 vote
144 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 ...
255 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
195 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 ...
410 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
125 views

### Near-field microwave antenna design

How to I design an antenna which produces a strong field within the antenna, but doesn't radiate out or reflect back to the source? (as much as possible) I'd like ideally to have a planar structure (...
• 3,511
1 vote
80 views

### Using a far field UHF RFID in the near field range

I have a 902 MHz to 928 MHz UHF 8dBi far-field RFID antenna connected to a reader. I want to read RFID tags. What will be the consequences if I used this UHF antenna in the near field range when it is ...
• 2,391
333 views

### How to get rid of 19kHz electrical fields

The mains of my German flat has 19kHz electrical fields on hot, neutral and! ground wire. I don't have to get rid of them entirely but I want to achieve 20dB reduction while sitting in front of my ...
• 123
668 views

### Does this sensor measure electrical or magnetic fields (with oscilloscope)

I want to measure electrical and magnetic fields of the frequency 50Hz to 1MHz with my oscilloscope. For electrical fields I learned that any bunch of metal will work. For magnetic field derivation ...
• 123
4k views

### NFC standards ISO 14443, ISO 15693 and ISO 18000-3. Which of them are most supported by smartphones?

I want to do this: mobile app <-> NFC <-> microcontroller, in order the MCU can communicate with Android or iOS apps via NFC hardware. I have two options of low-cost NFC chips, these chips don'...
• 657
1 vote
49 views

### Prevent Reception from an Extended Distance (Beyond Design)

I have a magnetic field that is being induced onto a power line by a transmitter, which is following the length of the power line to the receiver. The receiver communicates via a loosely coupled coil ...
292 views

### Implement a data protocol between a smartphone and a MCU via NFC hardware?

If I'm able to develop a mobile app which is able to use the NFC hardware of a smartphone to write/read through it. And if I have a board containing a MCU and a NFC transponder like the IC from ST ...
• 657
132 views

### Why do LF RFID tags use near field and why is reading distance longer with UHF RFID?

Why do LF/HF RFID tags use the near field (magnetic coupling) and not the far field? Well, I guess it's easier. The two antennas can just be modeled as a "transformer" and power transfer is straight ...
• 1,326
1 vote
2k views

### Designing 60hz antenna to detect electric field

I am working on designing an antenna to detect 60Hz electric field. I came across the microstrip antenna being used to detect the field. Before designing the antenna I wanted to maek sure this is the ...
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