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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Advice on mounting 4 wire video door phone with electromagnetic lock

I need some advice for mounting a video door phone with electromagnetic lock, using 4 wires only and a single power supply. The actual model is HIKVISION DS-KIS202 This is a diagram of what I want ...
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1answer
46 views

Electromagnetic waves antenna via microcontrollers (Transceiver and receiver)

I have two Arduinos: Mega and Nano, and 2 steel pieces of wire as an antennas which i sticked directly in the pins slots. I've setup my Mega2560 to generate an alternating current on one of its pin (...
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49 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
35 views

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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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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38 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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31 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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5answers
161 views

Electromagnetic 7-segment flip display: H-Bridge alternatives?

I have an electromagnetic 7-segment flip display which has 28 electromagnets for 4 digits. They run on 20V, have a 7.5W power rating and need alternate polarity applied to switch between the 'on' and ...
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71 views

Electromagnetic door locks in series or parallel

I am planning to add two 12V electromagnetic door locks to a door. Should they be connected in series or parallel to the power supply? Or is it advised for each to have its own power supply? The Power ...
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2answers
64 views

What can I use to increase efficiency of inductive wireless energy transfer instead of factory manufactured ferrite plates?

The Context I am a hobbyist with no education in electrical engineering. I am working on a DIY project trying to make water resistant rechargeable bicycle lights. I am doing this as a hobby for fun ...
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165 views

Copper Coil and Electromagnetic Induction

Waiting for answer Does mixing thickness of wires affect the Induction? What I mean is that I've like some 2mm and 1mm copper wires joined together. Basically I remove insulation on copper wire ends ...
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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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53 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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151 views

Impulse response function single coil

How can I measure the impulse response function of a single coil - like an electromagnetic shaker? The construction of a second winding would be difficult. I was thinking about a T/R switch but there ...
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1answer
34 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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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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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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28 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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69 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
27 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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60 views

Radio static caused by windscreen wipers

I was driving past a radio station transmitter of the radio station I was listening to. I turned on my windscreen wipers, which caused a noticeable static to be emitted through the speakers for the ...
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177 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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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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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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4answers
82 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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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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1answer
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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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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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25 views

Propagation Constant Expression in a Transmission Line

let's consider a generic transmission line: Its wave vector Kz is equal to: where Then, I read also that it is true that: where does this relation come from?
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57 views

Help with analysis of a signal that generates high frequency

I am trying to understand this circuit: In circle 1: I don't know why we make two capacitor in noise circuit, we can't do just one? In circle 2: The tuned circuit consists of capacitor C1 and ...
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1answer
37 views

Waveguides Equivalent Circuits

I was reading in a book how to derive the equivalent circuits for TE, TM, TEM modes of a generic ideal (without losses) waveguide. After some computations, it found this equivalent circuit for TE ...
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Electric Field in a Multi - Cell Cavity

let's consider a multi cell cavity like this one. The image has been taken from here. My question is about the magnitude of the electric field inside it. Let's consider each single cell of this ...
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3answers
126 views

Magnetron Working Principle

I was reading this simple description of magnetron working principle. Can you explain me why when electrons go near the cavities, they start to resonate at microwave frequency? I do not see the link ...
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35 views

Tuning Resonant Cavities

I have seen that some resonant cavities are equipped with some external screws, called tuners, which can be used to vary the resonance frequency. Can you explain me the physical reason with which to ...
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Charge Distribution on a Microstrip Line

let's consider a microstrip line connected to a voltage source V0 (applied between the strip and GND plane). According to foundation for microwave engineering (collin) book, the surface charge density ...
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Interface Conditions between Dielectrics inside a Waveguide

let's consider a general waveguide with two ideal dielectrics inside it: Let's consider the interface condition about the tangential electric field: Generally E = E(x,y,z), where z is the axis of ...
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Microstrip Voltage Boundary Condition

I was reading some notes about a microstrip line. Here the scheme with the reference system: In this scheme (sorry for the bad quality of the picture) the upper strip is represented as a charge sheet ...
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2answers
81 views

Coaxial Cable Resonance

let's consider a coaxial cable of length L and see what happens at port 1 when port 2 is left open. Let's consider what is written on these slides: 1) I do not understand the reason of this graph. In ...
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3answers
83 views

Frequency dependence of S21

I have done a measurement with a vector analyzer in which I have connected a certain coaxial cable to the two port of the instrument. Precisely, I have got a measure of the phase of S21 of this type:...
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4answers
30 views

Phase of Scattering Parameters

I do not understand the meaning of the phase of scattering parameters. Let's consider for instance a two port network, and let's focus on S21. I know that its absolute value represents a ratio ...
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1answer
86 views

How can we calculate the force of attraction between a coil and a ferromagnetic object?

As the question states I’m trying to figure out how I can calculate the force of attraction between the magnetic field of a solenoid (coil) and a ferromagnetic object. I suppose we should somehow ...
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1answer
35 views

Interface conditions and surface current density

let's consider the interface condition for magnetic field strength: 1) I do not have a clear idea of what js represents. If I have understood it correctly, it is a linear density ([A/m]) of a surface ...
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1answer
33 views

Is it possible to influence the working behaviour of a simple dc motor with an outside electromagnet?

I am using a simple DC-Motor 9V like this one. Now, I am curious about what influence an outside magnet / magnetic field would have on the working behavior of this motor? I would like to use the ...
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2answers
198 views

Propagation 'speed' of EM waves in air versus through conductive material

This paper I was reading said: "At a high level, the propagation speed of EM waves through conductive materials is SLOWER than their speed in air". Don't conductive materials intrinsically have less ...
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1answer
58 views

Create a continous variable force on object

I have a component that I need to press to another component with ideally max 200 Newton of force. I want to be able to to control this force. E.g I should be able to have half the force or 1/10 the ...
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1answer
43 views

Cut-off frequency in ideal waveguides

it is known that in an ideal waveguide (with a perfect electric conductor and with non-dispersive and non-conductive dielectric) there is a cut-off frequency, for each mode, such that for higher ...
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Expected E-field results vs simulation results

In the below question I wanted to know how they are getting the expect result of .74u for the e field, e field should be v/m it works out correctly for this simple example but as soon as I change the ...
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1answer
39 views

Transmission Line Mismatch Simulation

I found an interesting simulator for transmission Lines. I can set a precise value for the load and then see what happens. For instance, let's suppose Z0 = 50 Ohm and let's consider these cases: 1) (...
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1answer
64 views

Excitation of a resonant cavity

let's consider this picture in which a cylindrical resonant cavity is excited through a waveguide. I have some questions: 1) Why is it called "Magnetic Coupling"? I thought this excitation simply ...

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