Questions tagged [electromagnetic]

Electromagnetism, or the electromagnetic force is one of the four fundamental interactions in nature. This force is described by electromagnetic fields, and has innumerable physical instances including the interaction of electrically charged particles and the interaction of uncharged magnetic force fields with electrical conductors.

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25 views

Enhance sensivity of my magnetic field measuring setup

I have the following magnetic field measuring setup: Picoscope 2204A 16m wounded up bell wire connected to tip and ground clip as search coil antenna Now I want to enhance the sensivity for 50Hz to ...
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How strong should a magnet be to detach the magnetic locks? [closed]

I know that security tags can be removed by using the magnets. But how can I determine the strength of these magnets that can detach the tags? And does the same strength be applicable to ...
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What are some quick, cheap hacks for determining the source of EMI in my house?

TL;DR - Without dumping a bunch of money, is there a quick MacGuyver-y way to help diagnose what's causing the EMI in my house? Longer - I have the curse that I'm a little too technical to be helped ...
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35 views

EMP Halbach Array

Let's say I have a horizontal facing halbach array with equal north and south poles aligned one after the other, and a large circular gap in between them. If I fire an EMP gun through it, wouldn't the ...
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2answers
202 views

Reed switch only triggers with scope probe connected

I've run into a very odd problem. I've created the attached circuit, designed to cut power supply when a magnet is brought near the device. It works perfectly with the reed switch disconnected from ...
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How much high is the amplitude of stator-MMF of 3-phase 2-spp integral slot winding type machine as compared to 3-phase1-spp machine of same type?

Details: No. of POLES=2; i.e 1-pole pair SPP= slots per pole per phase In my case, amplitude of MMF of 3-phase 1-spp machine= 0.75; Then what should be the amplitude of MMF for 2-spp machine ? Is it ...
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99 views

DC through an inductor

I get that the frequency is zero hence the voltage is consequently zero according to the the equations, but any current through a conductor should produce a magnetic field. I also understand that ...
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142 views

Series RLC circuits

Suppose a series RLC circuit has its resonance frequency f_r. If we apply AC current of frequency f_r to this series RLC circuit then circuit has maximum current as output. My question is little bit ...
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179 views

Why don't stepper motors ring indefinitely?

I don't have much of a EM background but I have used stepper motors for things. What's not clear to me is why don't stepper motors ring indefinitely? Excluding physical friction, what actually causes ...
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1answer
23 views

How do we choose refractive index value in optical fiber design?

It is known that, given two media with refractive indeces \$n_1\$ and \$n_2 < n_1\$, if rays come from medium 1 they will be totally reflected if their angle of incidence is higher than the ...
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Create electromagnetic waves using Lc tank circuit

Electromagnetic waves are produced by the motion of a dipole and suppose we have top and bottom points then the negative and positive charges must oscillate between those 2 points. However an LC ...
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How does the shield of a coaxial cable work?

let's consider a coaxial cable with only two conductors (the core and the external metallic shield), and let's consider the case in which it propagates TEM mode at a certain frequency: My question is:...
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What is the physical meaning of the dispersion equation of an antenna?

I have a basic doubt about the role of the dispersion equation of an antenna. There are many situations (grounded dielectric slab, optical fibers etc) in which it is written, so I will put here an ...
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Is there a way to measure the magnetic field of a digital device and mask it?

I was reading this report: https://www.fanaticalfuturist.com/2018/05/hackers-find-a-way-to-neutralise-faraday-cages-to-exploit-air-gapped-systems/ It says how researchers used magnetic field ...
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1answer
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Off-the-shelf electromagnet with deterministic pole

I looking to buy an electromagnet (12v) and there are a lot of them out there on amazon and ebay in all kinds of size and shapes -some are round, some are rectangle, etc. However, in my application, ...
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Friis transmission equation: how do I consider power loss along other directions?

I do not understand a basic concept about Friis transmision equation between two antennas: where Dt and Dr are the antenna directivities (with respect to an isotropic radiator) of the transmitting ...
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33 views

Far field radiation and spherical waves

I have a basic doubt about electromagnetic waves emitted by a certain source. Depending on the shape and on the physical properties of the antenna, its electromagnetic waves may have different ...
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1answer
51 views

Hidden wire detector, using resistor

We have on the collector of the first transistor is a resistor at 1000 ohms , could you tell us what function this resistor performs in this place and how to argue that it is at 1000 ohms
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Magnetic field in the center of a coil

I have a closed core with a coil attached to it and metal inside the core. The N is 100, I is 100mA and l = 300mm. I have computed the magnetic field B = (μ0 * μr * N * I) / l. But I have also given ...
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80 views

Transformer at no load [duplicate]

I have been reading about the working of transformers at "no load" condition, that is when no load is connected to secondary side of the transformer. I don't understand why the transformer still draws ...
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1answer
59 views

Does the letter k in electromagnetics represent wavenumber inside a cosine?

I am having a intellectual debate with a colleague on whether k (in this equation below) represents the wavenumber k (that is used in electromagnetics) or does k in this question not refer to ...
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Hidden wire detector using BJT transistors

I made a hidden wire detector from this tutorial. It works, but I'm not quite understand why. Here is the circuit: I used 2SC1815 transistors and the value of R ...
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1answer
40 views

Matrix has a voltage drop on a coil that should not be receiving any current

I am making a matrix of electromagnets (each with about 120 Ohms resistance) and I am using a circuit like this for the columns (low side of the switch): simulate this circuit – Schematic ...
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Depletion region (space charge region) width calculation

Calculation of depletion region width requires the knowledge of permittivity of the material as shown below. \${\displaystyle w\approx \left[{\frac {2\epsilon _{r}\epsilon _{0}}{q}}\left({\frac {N_{...
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3answers
44 views

Spherical waves in far field region

in my antennas book (I do not put its reference because it is not in english) it is written that, at high distance from the source, the electromagnetic field radiated by it is a spherical wave. This ...
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1answer
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Digital to analog design question

I need some help with a circuit that will accept a digital input (0V-5V) and output 5V at 40mA for 200ms when the input goes high (5V), then drop to 20mA until the input drops low (0V.) I had thought ...
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Can a metallic rectangular waveguide support hybrid modes?

Studying the basics of guided waves in metallic rectangular waveguides, filled with homogenous dielectric material, I see that there is always a distinction between TE and TM modes. I understand that ...
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How do i set up an offset antenna?

How do i set up an offset antenna? I have two offset antennas. 1 for receiving and the other one for transmitting, they are at the same altitude. I don't know how to set up the angle because the beam ...
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26 views

Radiation pattern and propagation direction

I have a basic doubt about how to read a radiation pattern. Let's consider precisely the power pattern: it represents how the power is distributed along all directions in space. For instance, this ...
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1answer
80 views

Is Gauss's law still valid near the speed of light?

When the speed of the charge is close to the speed of light, is Gauss's law still valid? As far as I know, the invention of Gauss's law preceded the theory of special relativity, so if the answer is ...
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1answer
34 views

Understanding series open stub tuning

I recently had an assignment where I had to use open stub series tuning to find a way to maximize power delivered to the load from the generator. I understand that power delivered to the load is ...
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1answer
36 views

Dielectric slab waveguide

let's consider the so called dielectric slab waveguide (references for image and equations: here, page 53): I do not know much about it, I know only that it is a planar guiding structure which is ...
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1answer
27 views

Elliptical polarization and waveguides

It is known that a generic harmonic electric field which propagages in free space has an elliptical polarization (if you want to read the proof, look at this, slides 72 - 99). My question is: what ...
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2answers
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Electromagnetic compatibility problem with an hairdryer

I wanted to ask you if you could give me an explanation of this electromagnetic compatibility problem. I connected my (fully working) TV to a certain electrical socket in my house. I have also a ...
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3answers
203 views

Why should signals in circuits propagate much slower than the speed of light?

I've read a couple of other topics (such as this one and this one) about the lumped circuit abstraction requiring that signal timescales (i.e. the period of the highest frequency signal component) be ...
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1answer
125 views

Harrington rod from spinal fusion might be acting like a human EMF antenna [closed]

In 1994, I had a spinal fusion surgery to correct Scoliosis which was a result of my medical condition, Spinal Muscular Atrophy Type II. I've used a wheelchair my entire life. Because my upper body ...
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20 views

Formula for calculating the MMF and its harmonics of n-Phase PMSM with integral slot winding (slot per pole per phase =1 & 2)?

Data\Prerequisites: Integral slot winding full pitch winding Slot per pole per phase = 1 and 2 (two different possibilities) Number of phases : n = 3,4,5,6,7 Assume number of turns = N and current to ...
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1answer
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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 ...
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1answer
86 views

Need a solenoid to pull a Nerf Gun trigger

I'm looking for a solenoid that be used to pull the trigger of a Nerf gun. Using a strain gauge I determined that you need about 1 kg of force to pull the trigger, and the travel of the trigger is ...
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16 views

Ultrasonic transducer

Can a small ultrasonic transducer be retro fitted to the fuel bowl of a motorcycle carburetor. For the purpose of using sound waves to maintain clean jets. And possibly lengthen the longevity of the ...
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2answers
72 views

Why are E and B field in phase in far-field electromagnetic wave propagation?

I am very frustrated with the fact that the E and B field of an EM wave are in phase in the far-field case. Before I get into this question I am letting you know that I already read this link related ...
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3answers
177 views

What happens to parts of induction cooker magnetic field not covered with the pan?

An induction cooker works like this. There's a flat coil of wire under the cooker surface which is connected to a source of high frequency AC and it produces an oscillating magnetic field with field ...
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37 views

Conductor loop magnetic field in the middle

Why I have to take in the formula \$ H = \frac I l \$ the diameter and not the radius of a conductor loop when I want to know the magnetic field-strength in the middle of it. I have a conductor loop ...
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2answers
64 views

Calculating the intensity of an electromagnetic wave

I’m a bit confused when it comes to calculating intensity versus energy of a wave. If I’m given an electronmagnetic wave with an energy of 1 eV, how do I calculate its intensity ? I know intensity is ...
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1answer
91 views

Electromagnetic waves antenna via microcontrollers (Transceiver and receiver)

I have two Arduinos: Mega and Nano, and 2 steel pieces of wire as antennas which I stuck directly in the pin slots. I've setup my Mega2560 to generate an alternating current on one of its pind (PWM ...
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1answer
65 views

Speed and efficiency of solenoid train?

I'm talking about a simple solenoid train as shown in below image that works on the same principal as a homo-polar motor. It consists of an electric cell (AA or AAA type) whose terminals are fitted ...
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1answer
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Is it possible to get Flux in a magnetic circuit with zero mmf?

From an Example that I stumbled upon on A.E. Fitzgerald's book on electric Machines. He assumed that there is flux in a circuit with zero mmf. Which I find very confusing. I would appreciate it if ...
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66 views

When a coil is wrapped around a ring of non magnetic material, is the path length (l) the circumference or the diameter of the ring?

I'm doing some practice questions on magnetic fields: A coil of 300 turns is wound uniformly on a ring of non-magnetic material. The ring has a mean circumference of 40cm and a uniform cross-...
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2answers
45 views

What is the effect of the reflection coefficient?

I know that the reflection coefficient is the ratio of the backwards wave with the forward wave in terms of the characteristic and load impedances. But what does this mean? Does this represent a loss ...
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33 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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