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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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common-mode noise in single-ended parallel wire
As we all know that common-mode voltage is the average of voltages in two lines Vcm = (V1+V2)/2. So as shown in the figure below, a transmission line composed of two parallel wires above a ground ...
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How can I generate a noisy environment to test my PCB?
I am developing a PCB project but i want to use the PCB in noisy environments (which usually contains 7.5-45 kW multiple motors with frequency inverters and also ignition transformers). I made some ...
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Why is it said that for efficient transmission of radiation, antenna size should be comparable to wavelength of the radiation? [closed]
I have found it across many texts but I am confused about the reason why is it so? Is this related to radiation resistance?
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DC Chopper Operation in SMES Design
I'm reading a paper on a superconducting magnetic energy storage (SMES) power control system. One large superconducting inductor (L1 in the figure below) is charged up by a 10kA power supply. Once ...
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Why is magnetic field not accounted for in the theory of CRO
I’m reading the chapter on Oscilloscopes in Cooper’s Electronic Instrumentation and Measurement Techniques.
Nowhere in the theory of the working of CRO (like deflection sensitivity) does he take into ...
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Momentary over-excitation voltage circuit
I want to control an electromagnetic brake (fail-safe brake) used along with a servo motor. A microcontroller will control the trigger signal for the electromagnet coil.
Electromagnet requirements:
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Guided propagation in transmission lines
Can you help me on understanding why we may say this transmission line the propagation is guided and there is not any radiation?
It is a 2-conductors transmission line, in which the conductors are ...
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Power Radiated by an antenna
I have read that the power radiated by an antenna is equal to the flux of the Poynting vector through any closed surface that includes the antenna.
This fact is for instance exploited to calculate ...
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Magnetic Monopoles and Magnetic Current Densities
I see that in electronic engineering the Maxwell equations are written with also some terms which represent the magnetic charge and the magnetic current densities. I was told they are inserted only to ...
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Microstrip propagation mode
I have a trivial question about EM propagation in a microstrip line.
Why do the electric and magnetic fields have the following lines? Which are the physical laws (Maxwell etc) for determining them?
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Why is a clamp meter unaffected by nearby wires?
I understand a clamp meter works by measuring the magnetic field generated by current flowing through a wire.
It's well known that clamping 2 wires carrying the same current in opposite directions ...
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Steel vs iron for linear solenoid plunger
How much more force would an iron plunger provide than a steel plunger? From what I’ve read it seems like it would be much better, but I have no idea where to buy an iron rod.
Also, how much of an ...
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Marchand balun layout
For this marchand balun schematics in ADS, how to instruct the ADS layout generator to use coil shape (for area saving in IC) ?
Besides, anyone have any experience with planar layout of marchand ...
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The role of solenoid's wire diameter?
I'm not an expert in the electromagnetic field and need to design a solenoid actuator with 1 kg force approx. I am wondering if I change the wire diameter of the coil, what happens in solenoid's ...
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Can torque angle of motor be positive?
For any motor text say that, the rotor field follows the stator field with a certain torque angle. And in case of generator, the stator field follows the rotor field with a negative load angle. The ...
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Physics of Dirty Electricity? [closed]
I've been reading about "dirty electricity" lately and while I know there's much controversy whether it causes adverse health effects this question is not about that subject. I'm simply trying to ...
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Total current in a closed loop using Ampere's Circuital Law
I would like to reassure my concept on this question:
I have 2 different ways to solve this question:
Determining the direction of current in the loop using right-hand solenoid loop and adding ...
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Two modes of electrostatic force with charged capacitors?
During a charged state of a capacitor (Regardless of the type of capacitor),
Simple parallel plate:
.png
Parallel plate with dielectric material in the gap:
]3
Supercapacitor:
How is the ...
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Moving a capacitor in a time varying or non-time varying magnetic field?
1) If a simple parallel plate capacitor connected to a circuit, and discharging, were to move in an exterior magnetic field, what would happen to the interior region?
Interior region components:
...
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Is it possible to convert the audio signal from a smartphone's headphone jack into radiowaves? [closed]
I was watching a video of someone using his smartphone and a custom designed coil to make a metal detector.
The smartphone was connected to the coil via headphone jack.
I couldn't understand how he ...
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Supercapacitor and an applied exterior magnetic field?
I'm curious of the effects of an exterior magnetic field to a Supercapacitor, in both states of charging & discharging.
If the Supercap. is placed inside an area where an exterior magnetic field \...
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