# Questions tagged [em]

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82 views

Let's consider the case of linear dipole antenna or Hertz dipole. I know that the antenna acts as a transducer and it radiates the E-M waves due to the acceleration and decelaration of the electrons ...
58 views

### Question on spark gap transmitter circuit

I am trying to understand how basic electromagnetic communication works. From what I understand, spark-gap transmitters were the first wireless devices made by man. A couple of circuits I found online ...
• 1
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### Finding constant in electrostatic equation given only charge

So in a region of free space with zero charge, all I'm given is that the electrostatic potential V is given by: $$V(x,y,z) = kz(x^2) y + 2y - 6y(z^3)$$ [Volts] To find the constant k, would I have to ...
67 views

### Need RF advice (NFC antenna VS GND pour)

I'm currently working on a design who involve a NFC chip (ST24DV) who need to be on the board as it's used to communicate with a smartphone. Here is the picture of the antenna: There is a LED on the ...
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40 views

### A circularly polarized EM wave is perfectly absorbed by any interface?

According to the Fresnel equations, the effective reflectivity of an arbitrarily polarized electromagnetic wave is given as: $$\Gamma = \frac{\Gamma_p + \Gamma_s}{2} ,$$ where $\Gamma_p$ and \\$\...
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70 views

### Detection range of unintentional emissions by battery powered video recording devices?

I have read about unintentional radiators, but wonder about what their unwanted emissions detection range can be in low background noise, referring to battery powered motion-sensor activated video ...
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1 vote
23 views

### How do I EM-Extract a subcircuit and define a different em/drawing-layer than the original circuit in AWR?

I have a 4-layer project in AWR/MWOffice and have built a parameterized microstrip inductor schematic (named "spiral") with a "Line Type" of layer1 that I wish to reuse on another ...
• 872
1 vote
39 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 ...
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139 views

### How, exactly, does the 'input signal' wave(s) modify the carrier-wave of a radio signal? [closed]

I cannot find a simple (or really, not-so-simple) explanation of how mixing the high-frequency carrier wave with the lower-frequency input signal works... Is it entirely due to constructive and ...
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125 views

### Simulation of 2D vs 3D electromagnetic waves

If you using a simulation tool that allows you to simulate behaviour electromagnetic waves in an environment. What differences are there in terms of doing the simulation in 2D vs 3D? Does doing the ...
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47 views

### Inconsistent performance of circularly polarized antenna

I have a circularly polarized patch antenna for an RFID reader, with a gain of 8dBi and bandwidth from 914MHz to 919MHz and an axial of 0.34dB. I have read that using a CP RFID patch antenna means ...
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72 views

### Effects of wood on UHF transmission

I have set up the following scenario in gprmax. From the results obtained using the software, I realized that when I increased the wood thickness the power received at the receiver increases instead ...
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1 vote
116 views

### Why is a horizontal rod a full wavelength oriented radially to a broadcast antenna not the best receiving antenna

I have always struggled to get a good physical understanding of Electromagnetic waves. I've done the whole Maxwell's equation approach, wrote boundary element solver tool but cannot rationalize that ...
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### Power received by RFID tag

Power calculation from E and H field Following from the previous post above. The user provided me with some assistance however I am still a bit unclear on how to apply the equations provided. Could ...
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76 views

### Power calculation from E and H field

I am using gprMax to simulate my design. The design is shown in the picture. It consists of an RFID system inside a steel structure. The transmitting antenna is placed in the middle of the container ...
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1 vote
53 views

### EM propagation analysis

I have an antenna which runs at 917MHz located inside a metal structure that measures in at 6m long, 2m wide and 1.9m high. The exact location of this antenna will be in the center against the length ...
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51 views

### Interpretation of data

I hope this question meets the standards of this platform, if not please inform me of how I can improve it. I was trying to design an antenna and I have done so. I am planning on using this antenna ...
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68 views

### Conceptual question about Frii's equation

That's a pretty basic one but for some reason I am stuck now: Suppose I have a transmitter that transmits Ptx=4W_EIRP with an ideal, omni-directional antenna. The power applied to the antenna ...
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361 views

### FDTD simulation for beginners using matlab

My previous posts are as follows: 1.Mitigation of dead zones when applying circular polarized antenna 2.Standing waves modes inside a cavity resonator 3.Visual understanding of EM fields within a ...
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82 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 ...
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95 views

### Multimode cavity resonator

From my previous posts Insight into cavity resonators, Visual understanding of EM fields within a rectangular metal container I have slowly gained a better insight into cavity resonators and thereof. ...
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1 vote
2k views

### Distance requirements in antenna arrays?

Antenna array is a broad term and it encompasses at least the following concepts: MIMO or massive MIMO: for spatial multiplexing beamforming: increasing the SNR (at transmitter or receiver) by ...
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427 views

### Insight into cavity resonators

Modes of a waveguide As shown in the link above, they show how these modes work for various values of m, n, and p. However, where is the antenna/ source of radiation placed within the cavity? From ...
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307 views

### Visual understanding of EM fields within a rectangular metal container

I have the following scenario setup inside a rectangular metal container. The container size is 12.03m by 2.39m by 1.84m (lxbxh). Additionally, inside the container I have placed 4 antennas equally ...
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41 views

### Not full-wave signal transmission?

Is it possible to transmit half-wave signals repetitively, like repetitive "north" magnetic fields like going from 0-1 Gauss "north" and repeat however many times per second without going 0-north-0-...
1 vote