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Questions tagged [electromagnetism]

The kind of magic without which all of this wouldn't be possible. This tag should be used for questions about the **physics** of the fields that charged particles create and how these fields interact. It should not be used for all questions involving electromagnetism, that would be everything on the site.

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29 views

Analogy electric circuit and magnetic circuit - Power

Here are a table which do the analogy between electric circuit and magnetic circuit. Nevertheless, there is no analogy with power dissipation … Nevertheless, It is said that in a transformer with an ...
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2answers
294 views

Why are the poles of the stator and rotor taken differently in the picture below?

The rotor and stator in the picture below have the same orientation of flux lines yet the are taken as opposite that is flux lines leaving the stator is taken as a South Pole while flux lines leaving ...
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24 views

How to create optimal solenoid actuator

I would like to create a solenoid like this one: It should be powered by 5V and of course I want it to take as little current as possible. I know it will probably still take a current of around 0.75, ...
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1answer
46 views

Calculation of magnetic field saturation inside coil core

I want to try to make an electromagnet, but I don't have soft-iron available. I've read that ferrite MnZn are suitable as soft-iron to create a high efficiency magnets with the inconvenient of lower ...
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2answers
999 views

How many watts does a 40 MHz radio frequency signal create?

I am new to the study of electromagnetic frequencies and electrical engineering as a whole. I am trying to understand how to convert a radio frequency into energy, or calculate the power density of ...
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29 views

Meaning of “raised structure” in microwave networks

Can you help me to understand what "raised structure" means and why it determines the following property of the S matrix? Reference: here.
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3answers
71 views

How does the magnetic field in a servo motor acts according to the PWM signal?

I have read about servo motors but have problem grasping the main idea of obtaining fixed position by the magnetic field. The servo motor position is said to be controlled by PWM signal. And a toy DC ...
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41 views

Using one electrical pump for multiple hoses [migrated]

I'm currently trying to figure out a cheap way to build a cocktail machine. For now the machine should have about 20-30 possible input liquids. These liquids should remain in their original bottle ...
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17 views

Time Domain Measurements with Vector Analyzer

In my university I have done some time domain measurements with a VNA (by using the transform operation of the instrument). Precisely, I have selected the measurement of the real part of S11 while ...
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1answer
90 views

Is it logically explainable that current is lower when torque higher?

I am modelling a motor with a little simulation script. The principle is: Input is the traction force needed to be provided by the motor Output is the current to be provided to the coil of the motor (...
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1answer
122 views

Why isn’t this way of generating electricity well documented / not at all?

After looking up different examples of inducing a voltage in a coil on Google and Youtube, I cannot find this being a known way of generating a voltage. In the image the brown arrow is the direction ...
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84 views

Is a rotor of an electrical motor charged with electricity?

This might seem to be dumb question, but as far as I understand it: An electrical motor is made of a rotor and a stator. The stator is electrically powered: it has a solenoid and current passing into ...
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1answer
34 views

Possible to measure EEG signals with an AM receiver antenna/circuit?

I'm having trouble understanding the importance of placing EEG electrodes directly on the skin. I used to think the reason for this was to pick up voltage differences between points on the skull, the ...
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2answers
51 views

Definition of quality factor as function of frequency

I have seen that some electrical components (which contain R,L,C elements) datasheets shows the curve of the quality factor Q with respect to frequency, and not simply its value at the resonance ...
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1answer
20 views

Meaning of coupling factor for a resonance cavity

I was reading this paper about resonant cavities, and on page 6 it introduces the concept of coupling factor β, which is defined as the ratio between the power loss in the total circuit (including the ...
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1answer
86 views

Back EMF in an inductor with an AC supply

If a pure inductor is supplied with an AC voltage we will always have AC current and time changing electric field in the circuit. That always changing electric field will cause changing magnetic field ...
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1answer
72 views

How strong are eddy current brakes?

I really just need a rough estimation. How strong are eddy current brakes? For example, if I use a solenoid that has 800 turns with up to 2 amps going through it, and I have the not ferromagnetic ...
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1answer
31 views

Magnetic field expression in a rectangular waveguide

I was reading the chapter of Fundations of Microwave Engineering (Robert E. Collin) about transmission lines and waveguides, and I have a question about the electromagnetic field in a rectangular ...
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36 views

How does Solenoid works? How do I calculate its output power? [duplicate]

Here is a solenoid valve. It is a normally closed, which is mean, it is normally closed the valve. Vice versa, there is also normally open, which is mean, it is normally open the valve until it ...
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1answer
67 views

How to block / lessen EM-radiation/signal from home Wi-Fi router? [closed]

1) What materials and how can I use to completely block radiation from two antennas of my WiFi router? 2) What materials and how can I lessen by 20-50% radiation/signal from the third router antenna? ...
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1answer
75 views

Why does rotor of synchoronous generator accelerate during faults?

I don't understand the electrical torque in a generator. Isn't the counter torque related to the armature current in the generator? Why does electrical torque decrease during fault in lines that ...
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1answer
30 views

Attenuators in Waveguides

Let's consider for instance a rectangular waveguide with TE01 mode. As shown here, a possible attenuator may be realized with a metal card placed so that it is tangential to the electric field. Here ...
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1answer
26 views

Reflection Coefficient with Electric Field and Voltage

In different situations the input reflection coefficient (of a waveguide, of a transmission line etc) is defined differently. Wikipedia says: The reflection coefficient may also be established ...
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45 views

Tesla Coil not working

I made a simple miniature Tesla Coil following a youtube tutorial (https://youtu.be/AehL3BodduE) As you can see in the photos, I 3-D printed a PVC pipe like piece and wound two copper wires one over ...
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1answer
23 views

Measurement of Isolation in a Directional Coupler

I want to measure the isolation of the following directional coupler (for more details of that specific component, go here). Isolation can be evaluated through the scattering parameter S21, but how ...
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3answers
93 views

Importance of EM to microwave design?

I am curious, how important is a general understanding of electromagnetics to microwave circuit design? I have looked at Pozars book which provides some background on EM and transmission lines in the ...
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50 views

Magnetic locks with paramagnetic materials

Well I was wondering why magnetic locks are made of an electromagnet and a ferromagnetic material and not an electromagnet and a paramagnetic material. The magnetic attraction between the ...
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2answers
65 views

Why do current transformers saturate with high short circuit currents?

When there is a severe short circuit current due to the faults in transmission lines ,sometimes current transformers get saturated.Voltage of the faulty line drops sharply but ct still saturates.As ...
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2answers
188 views

If induced voltage (back-emf) is equal and opposite to applied voltage, what drives the current?

Suppose we have a circuit with a voltage source, a switch open and an inductor all in series. If we close the switch, the potential difference of the voltage source is instantaneously applied to the ...
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2answers
176 views

How much electromagnetic/electric radiation does laptop/computer emit? [closed]

How much electromagnetic or electric radiation does laptop emit? I don't know in what measurement system you have to answer, but at least, I want to get the answer which should be enough "research" ...
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1answer
41 views

Example of computation of S matrix

Let's consider the slide 1 of this material. I have understood the computation of S11, but not that of S21. I do not understand: - why there is the circuit with V and two impedances Z0 and there is ...
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1answer
23 views

Computation of the Scattering Matrix of a Transmission Line

let's consider this transmission line (with losses) in which a and b denote respectively the reflected and the incident waves at each port: This exercise asks to find its scattering parameters ...
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24 views

Why do we get Non uniform plane waves along a transmission line?

I get that wave propagation will take place but why TEM mode is the only possible mode that can exist? And also why it is non-uniform?
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35 views

induced voltage in coil due to moving magnet

I am trying to calculate the voltage induced in a zylidric coil by a moving permanent magnet that is placed near the coil. To simplify calculations, assume that the permanent magnet is also a zylinder ...
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1answer
28 views

Orientation of Loop Antenna (receiving mode)

I have done some measurements through a loop antenna similar to that shown in the following picture (all the informations included do not refer to my antenna, it is a picture used only to show its ...
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29 views

Why current distribution of a receiving dipole antenna depends on incident frequency?

When an incident EM wave hits the antenna, the electric field is parallel to the whole wire and start moving all electrons on it simultaneously. I understand that the current at the ends should be ...
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4answers
80 views

Voltage on a Transmission Line with Ideal Conductors

Let's consider a transmission line with Perfect Electric Conductors. We know that if an external AC source is applied, we get a voltage waveform between the conductors which is function of the ...
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11 views

Evaluation of Dominant Mode in a Circular Waveguide

I was doing the analysis of a circular waveguide (precisely, a wave guide with half - circular section of radius a, as shown in the following picture, and in which the shell is a Perfect Electric ...
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34 views

TEM Propagation in Infinite Ferrit Medium

I have realised a question on Collin's Foundations of Microwave Engineering book which is related to TEM propagation in infinite ferrit medium. I could not find a way to establish to relate positive ...
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1answer
36 views

Transmission Line with Short Circuit and Inductor as Loads

let's consider this situation in which the two ports of a transmission line are connected to a short circuit and to an inductor: The transmission line is supposed to be lossless. My book makes a ...
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1answer
15 views

Scattering Matrix with Power Waves and Voltage Waves

I read that for a given N-port network there are two different conventions about defining the incident and reflected waves. This is the first convention: This is the second convention (we see that ...
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14 views

One Port Microwave Active Network Electrical Model

let's consider an active one port network: My book does an analysis of it by considering the Poynting Theorem, in which we consider the contributions of active sources (electric and magnetic current ...
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1answer
69 views

Magnetic force and Coulomb force

Lets have 2 electrons travelling with some speed relative to a static observer. The force between those 2 electrons will be the Coulomb force and the magnetic force. Is it forbidden from the laws of ...
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0answers
9 views

Evaluation of the dominant mode in a waveguide

In a waveguide, the dominant mode is defined as the propagation mode with the lowest cutoff frequency. Now let's consider a structure in which the lowest cutoff frequency occurs for two different ...
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2answers
33 views

Improving a permanent magnet alternator. Replacing magnets / reducing air gap

In the case of a 3 phase PMA radial flux type, used as a wind turbine, with magnets on the surface of the rotor, is it safe or even doable to stack another magnet with the same geometry on top of the ...
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2answers
58 views

Magnetic force as a function of PWM frequency

Consider an experiement with a DC source feeding an coil with a constant DC current I. The coil with an iron core attracts a magnetic plate with mass m with force F. The force F is higher than Fm and ...
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24 views

Parabolic wave equation, electric and magnetic field definitions

The split step solution for Parabolic Wave Equation (PWE) applied to the tropospheric propagation problem is: $$u(x+\Delta x, z)=e^{ikM(z)10^{-6}\Delta x}\mathfrak{F}^{-1}[e^{\frac{-ip^2\Delta x}{2k}}...
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20 views

Time Domain Analysis with Vector Network Analyzer

I have done some measurements with a VNA in time domain (by using the transform operation of the instrument). Precisely, I have selected the measurement of S11 (reflection coefficient at port 1 of the ...
0
votes
1answer
26 views

How do I solve transformer numericals with additive polarity?

Ok, so for subtractive polarity in transformers(dots at the same side of the windings) E1/E2=N1/N2 But if it's subtractive polarity E1 and E2 are out of phase so shouldn't E1/E2=-N1/N2 Edit: Ok here ...
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2answers
81 views

Can an induction motor be used to generate power?

Induction motors do not have magnets in them, instead the magnetic field the outer coils generate creates electricity, and subsequently magnetic field, in the inner coil. This means those motors need ...