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.
1,605
questions
4
votes
1
answer
233
views
How does energy travel in the system in a conducted RF immunity test,?
I have a question regarding some conducted RF immunity (IEC 61000-4-6) tests. We inject noise starting at 150kHz until 80MHz. The signal injected is AM at 80%. The level is 20Vrms.
Here is the setup ...
0
votes
1
answer
94
views
What is the utility of inductors in circuits? [closed]
I was wondering what all the possible purposes of inductors in electrical circuits are.
Inductors, as I understand, are wires wrapped in a helical pattern around some sort of solid material or simply ...
0
votes
0
answers
62
views
How can I calculate the coupling coefficient between two coils?
I have two planar, circular coils of different number of turns, inductances, and radius, stacked on top of each other. How can I calculate their coupling coefficient (k) based on their properties and ...
-1
votes
1
answer
43
views
Charges in receiving antenna and polarization if alternating current is changed to stay high
A dipole antenna receiver placed in parallel to a dipole antenna transmitter will have a current induced in the opposite direction to the current in the transmitter. This causes charges (electrons and ...
4
votes
3
answers
1k
views
Why is it not standard practice to integrate the output of an antenna?
This is a follow up question from my question answered here:
Why does a loop antenna not measure the differential magnetic field?
Essentially I just found out today that we are actually measuring the ...
0
votes
0
answers
37
views
Advancing PCB Design Knowledge: Seeking Resources for EMC, Analog Signals, RF and More
I'm designing 4 layer, 2 sided pcbs with MCU, radio module, digital sensors (i2c, UART..) and analog ones (4-20 mA, 0-10V). All on an average budget of 50 uW. Everything is quite slow here, 115200 ...
1
vote
2
answers
123
views
How does electricity flow if circuit is not complete? [closed]
https://youtu.be/oI_X2cMHNe0
What is he saying at 13:20? How can bulb glow if the circuit is not complete?
0
votes
0
answers
39
views
How to create RF source in CST Studio
I have designed a microstrip patch antenna in CST studio and I want to test its efficiency for energy harvesting. Having followed some youtube videos, I understand creating a waveguide port across the ...
0
votes
0
answers
267
views
Transformer Phasor Diagram And Circuit Diagram
I have been reading the construction of a practical transformer and facing difficulty in understanding the phasor diagram of it.
When we connect \$V_1\$ supply to the primary side, say \$V_1 = sin(wt)\...
0
votes
1
answer
74
views
UPML and tensor multiplication?
I am studying uniaxial perfectly matched layers.
In order to absorb outgoing waves we introduce a tensor S (I have anderstood how it is calculated)
\begin{bmatrix}
\frac{s_y s_z}{s_x} & 0 &...
0
votes
0
answers
72
views
Help with circuit for school
I am doing a project for school with two friends. We are going to make a DIY metal detector. We are using a source as our circuit. Can someone help us describe what is happening in the circuit?
0
votes
0
answers
32
views
Is this Molex flexible antennas feeding method consider insert or probe feed? what is the most accurate way to simulate it in HFSS?
I want to do some data augmentation to the radiation pattern of an off-the-shelf flexible antenna (in terms of bending, material, size...etc). To get started I tried my best to recreate the trace ...
0
votes
2
answers
49
views
Understanding voltage in simple electromagnet and DC motors
I made a simple electromagnet with enameled copper wire wrapped many times around a metal allen wrench. I attached the electromagnet to my PSU and it works great, but I do not understand the voltage ...
0
votes
1
answer
46
views
Fundamental Question - how does magnetic permeability work for weak signals?
This is basically a physics question. If a sophisticated answer is needed, please go for it.
The standard explanation of magnetic permeability is something like this:
In a ferromagnetic material, ...
0
votes
0
answers
79
views
Metal detector discrimination problem
I was experimenting with discriminating metal detector
I'm using TX coil about 28cm diameter, and 0.9mH with 470nF capacitor- pushing about 5Vpp sin wave from a signal generator
The RX coil also about ...
5
votes
3
answers
1k
views
Building an MRI safe video camera (e.g. webcam)
I would like to use a small camera inside an MRI. The eye-tracking cameras that are commercially available are both too expensive and also not suitable for my purposes.
How would one go about making a ...
0
votes
1
answer
80
views
How do I create an AC electromagnet for a particular type of field generator?
I’m trying to generate a special sort of field in a spherical spinning iron core using two orthogonally oriented coils.
One single-layer coil of 18 AWG magnet wire is wrapped directly onto most of the ...
1
vote
0
answers
49
views
Formula relating attenuation and loss tangent in EM wave propagation?
in this previously answered question, a relation is established between the attenuation and loss tangent in EM waves. The formula given is the following:
$$ \alpha = \frac{\omega}{c} \cdot \sqrt{\frac{...
1
vote
1
answer
710
views
Parallel magnetic circuit with 2 air gaps
I have the following ferromagnetic core.
N = 300
core thickness = 5 cm
relative permeability = 2000
the air gap's efective area rises 5%.
1 A going through the coil
I need to know the flux going ...
0
votes
2
answers
152
views
Voltage generated by individual coils goes down the larger the number of coils
I'm trying to make my own alternator & study the physics behind it.
So I have a circle of magnets rotating over 4 coils, forming a square (90 degrees each).
When I remove 3 coils from the square ...
1
vote
2
answers
50
views
EMF Sensors - Tri-axial Inductors vs Tri-axial Magnetometers
I took apart a bunch of EMF sensors (such as this one) and found that almost all of them instead of having a magnetometer inside, have usually three inductors. In the case I just shared, it has 3 33mH ...
0
votes
2
answers
120
views
Equation relating alternating magnetic field strength to induced voltage in search coil
I have a search coil (loop area A, N turns) placed normal to an alternating magnetic field with equation B(t)=Bp.sin(2.pi.f.t), B=field strength at time t, Bp=peak field strength, f=frequency, t=time. ...
2
votes
3
answers
714
views
Moving magnet frequency over a coil
It's my understanding that :
Changing magnetic field over a coil induce current in the coil itself.
Current running through a coil makes it magnetic. (To put it simply)
Can these 2 rules affect ...
4
votes
3
answers
949
views
Understanding the flux linkage in transformers
I am having difficulty understanding the concept of flux linkage in transformers, particularly how the secondary winding receives its flux when all the flux is said to be confined to the iron core. I ...
1
vote
2
answers
113
views
Analysing the behaviour of inductor in the circuit
Suppose we have an L circuit with DC power supply of emf \$\mathscr{E}\$
simulate this circuit – Schematic created using CircuitLab
By KVL,
\$\mathscr{E}=L\frac{dI}{dt}\$.
This suggests that \$\...
1
vote
1
answer
96
views
What's the best solution for creating a magnetic field around a small cylinder?
I'm a beginning electronics hobbyist so forgive the naive question.
I'd like to have a small cylinder (1cm radius, 3-4cm length) where I could control a magnetic field around the cylinder with voltage....
0
votes
0
answers
62
views
Making an automated chessboard [duplicate]
I want to create an automated chessboard. At the moment, I'm making the project and deciding what technology to use to detect which piece is at what position and how to move them. I'm not so skilled ...
0
votes
1
answer
54
views
In what direction does skin effect take place?
I'm working with some problems with coaxial cylinders and the currents driven in those when considering high frequencies. In such cases, the skin depth has to be taken into consideration.
One thing I ...
1
vote
1
answer
39
views
Why do we still need to calculate the equivalent exciting current \$I_{eq}\$ when we have the exciting current \$I_F\$ already?
Here is the compound DC machine schematic:
The equivalent exciting current is \$I_{eq}=I_F+\frac{N_{SE}}{N_{SH}}I_A-\frac{F_{AR}}{N_{SH}}\$
\$F_{AR}\$: the equivalent magnetomotive force of armature-...
1
vote
1
answer
35
views
Angular speed and voltage-intensity
I have a square frame with 200 windings rotating in a magnetic field B=0.2T. If I increase the angular speed of rotation of the frame will only the voltage increase? will the electric current also ...
0
votes
2
answers
160
views
Why is only the electric field considered in the calculation of the total radiated power of an infinitesimal dipole above ground?
I don't understand how the average energy density and total radiated power of an infinitesimal dipole above a conductive surface is being calculated and why the magnetic field is not being considered ...
1
vote
1
answer
105
views
Can a solenoid be made of copper strips?
Could a coil of copper strips instead of copper wires be used as a solenoid? Are there any real world examples of making solenoids out of strips of copper?
2
votes
0
answers
99
views
Analytical solution for the characteristic impedance along vertical wire over PEC ground plane (at given point h)?
For the purpose of TL transformer simulation I need a solution for the characteristic impedance of vertical wire, with radius a, at the infinitesimally short segment - not point, at the height h above ...
0
votes
0
answers
60
views
Equivalent circuit of spiral resonator metamaterial
I require equivalent circuit for two sided square spiral resonator for metamaterials.
I have found the equivalent circuit for one side, according to this paper:
https://www.researchgate.net/...
0
votes
0
answers
123
views
AC - impedance for a coaxial cable
Problem
I want to calculate the AC impedance for a coaxial cable. A rough image is presented below:
Because we have an AC current, suppose that the skin depth, which we can define as \$\delta\$ is ...
2
votes
2
answers
574
views
Why must an antenna be connected to ground?
My physics textbook states that connecting one plate of a capacitor to ground and replacing the other end with wire makes an antenna. So is an antenna really a capacitor? Does one end really need to ...
0
votes
3
answers
197
views
Torque on generator due to reactive power
Since reactive power goes back and forth from load to generator, so when reactive power goes from load to generator this should manifest as torque that's exerted on the rotor right? (like that of a ...
1
vote
3
answers
731
views
How does this toaster fix work?
Let's pretend your toaster need a little fix. Pulling the lever down, it does not stay low and immediately jump to its rest position. Apart from this, manually keeping the lever down, toasts your ...
0
votes
2
answers
130
views
How can energy be stored in a magnetic field?
A magnetic field can be thought of a vector field of force on electrons. Basically this can be thought of a some area that attracts or repels electrons.
It is said that inductors are able to "...
10
votes
2
answers
717
views
Parallel decoupling capacitors: Is inductance reduced?
Background
In general, when placing decoupling capacitors in parallel, their capacitances add and their compound ESR is reduced (like for parallel resistors). But I am a bit uncertain if/how this ...
0
votes
2
answers
54
views
Is power dissipation constant for a given mass of copper generating a given magnetic field?
What I mean, is that for a given field and a given mass of copper coil, power dissipation is independent of the form of that copper, whether thick wires or thin.
Is it true?
2
votes
3
answers
362
views
Does infinite magnetic permeability (e.g. for an ideal transformer) violate conservation of energy?
The ideal transformer is supposed to have infinite magnetic permeability.
Creating infinite magnetic field lines from a finite applied field sounds like... a violation of conservation of energy or ...
2
votes
0
answers
146
views
ESD problem and how to solve
We have a problem with contact discharge of 3kV on a housing part. The PCB with the PHY are installed in an aluminum lower part with plastic upper part (dimensions approx. 80x80x80mm). The contact ...
0
votes
2
answers
86
views
calculating magnetic field strength (H) of half wound solenoid or toroid
at school, I learned that the magnetic field strength(H) is defined by the Number of turns*current/Length. is the length in the formula the length of the coil or the core? so if an iron rod is 10cm ...
0
votes
0
answers
15
views
Query on labeling directions for electric force
On the second part of the problem, is my assumption correct? Do I even need to put the sign? or is the magnitude alone suffices as the answer?
0
votes
0
answers
58
views
Electric field intensity problem
I have done two solutions regarding this problem. One with the unit direction and one with no direction (magnitude only.)
All of these solutions are an exact copy of how my professor answered a ...
0
votes
0
answers
50
views
Calculate potential between two rods
Suppose we got four thin, long and parallell conductors with charges shown in the image below. Each conductor has a radius \$ r\$ and length \$ l\$ . Our problem is to find the potential between the ...
0
votes
0
answers
77
views
Voltage seen at load which has open circuit in parallel
If I send a sinusoidal signal down a transmission line, say with a source and line impedance of 50 ohms. Then if I have a 50 ohm load, in theory, there are absolutely no reflections.
If however, I ...
1
vote
1
answer
295
views
How does the electric field inside a conductor remain zero?
I'm learning about current in conductors, and came across the statement that "The electric field inside a perfect conductor is zero", this is frequently explained used Gauss´s Law by saying ...
-3
votes
2
answers
119
views
How do we maximize core and winding losses in an electromagnet (and calculate them) for variable DC input?
Bigger Picture:
Imagine a magnet approaching the solenoid with some initial constant velocity on \$v_0\$ on x axis. The approaching magnet will induce an EMF and induced current in solenoid. We want ...