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Questions tagged [magnetics]

Important to inductors, transformers, generators, motors, magnetic fields, inductive heating, magnetic storage, permanent magnets

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33 views

Determining magnetic flux density of a closely wound toroidal coil

I am using David K. Chengs's Fundamentals of Engineering Electromagnetics book. In chapter 5/question 5.2, there is a given closely wound toroidal coil, and it asks what is the magnetic flux density ...
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31 views

Why does the receiver coil voltage of this WPT circuit decrease at varying rates as the distance between the transmitter and receiver coil changes

The circuit below is a circuit that wirelessly transfers power via inductive coupling. I used a digital oscilloscope and measured the output voltage of the receiver coil at varying distances between ...
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2answers
74 views

How does a hall effect wheel speed sensor work?

I have been researching how a wheel or crank speed sensor works in vehicles and am having a hard time finding a hard truth. I think I understand how it works simply. That the sensor detects a change ...
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1answer
38 views

Difference series resonant and LLC DC/DC converter

What is the exact difference between a series LC resonant converter and an LLC converter. From a topological perspective, they seem to be exactly the same. I believe that for an LLC, also the ...
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3answers
2k views

Does this experiment show that Kirchhoff's Law hold when there's a changing magnetic field involved in a circuit?

In this video, the electrical engineer and youtuber Mehdi Sadaghdar (ElectroBOOM) disagrees with another video from professor Walter Lewin. Basically, professor Lewin shows in an experiment that if ...
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1answer
41 views

Proper connection of choke coil in ethernet magnetics

I need to use the medical ethernet magnetics by Pulse HXU6200NL (it is the only 2MOPP medical-certified PoE magnetics I can find). These are of the rather common transformer/choke coil topology. My ...
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2answers
100 views

Double ethernet magnetics for a passive medical application

I am designing medical data acquisition equipment that requires moderately fast data transfer. As part of the design we are using a custom 100BASE-T PoE architecture (and cabling) to the data ...
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2answers
32 views

Optimizing magnetic field force of a coil

For a personal project, I've done a redesign of Samy Kamkar's MagSpoof project. Basically, it is possible to use an electromagnet, h-bridge, and microcontroller to trick a magnetic card reader into ...
2
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1answer
120 views

What is the purpose of perpendicular “smaller” magnets in between the main magnets in a rotor of a motor? had never seen this before. Do they help?

I am trying to build my own generator at home for fun, I saw on a video in youtube https://www.youtube.com/watch?v=YsSm65DAcCg where the guy placed smaller magnets in between the main magnets of the ...
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0answers
26 views

Measuring a magnetic field using a loop

I am trying to use a loop to measure oscillating and pulsing magnetic fields. Using Faraday's Law (N - number of coil turns, B - magnetic field, A - area of coil, t - time) I should be able to ...
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3answers
197 views

Wireless power transfer - Inductive vs. resonant mode

When talking about how wireless power transfer is done, the standards (e.g Qi) distinguish between inductive and resonant mode. (Link) They claim that when the units are in very close proximity it is ...
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0answers
53 views

Cable Side and Physical Side of a PoE Magnetics

I am reading the datasheet of PoE Magnetics. I am not able to understand which side belongs to cable side and which belongs to ...
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0answers
55 views

Dolby HX PRO implementation on existing tape recording deck

I'm experimenting the implementation of Dolby HX PRO's IC into an old stereo Fostex tape deck to improve high frequency and headroom capabilities. HX PRO works as a dynamic processor with the BIAS ...
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0answers
49 views

Pulsed a magnetic field, what would be a suitable way to pulse a high current?

I would like to pulse a magnetic flux of up to 25 mT, for an experiment. I would like the pulses to be as short as possible 60-70 ns. I have a solenoid, 10 cm in length, 5 cm diameter with 7 turns, ...
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0answers
50 views

How strong is the field of a magnetic strip on a credit card?

How strong is the field of a magnetic strip on a credit card? In other words, at the typical distance of a read head, say 0.001" how strong is the magnetic field from the stripe? (Note this is NOT a ...
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2answers
131 views

Detecting very small magnetic movements

I am looking for techniques and methods to detect very small linear magnetic movement caused by a bar magnet. Imagine a bar magnet that can produce yaw and pitch but with extremely low frequency and ...
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2answers
67 views

Is there a way to make an experimental magnetic head?

I recently had a magnetic stripe on my bank card fail and I was curious to find out the exact nature of the corruption which would require scanning the surface of the stripe and determining its ...
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0answers
116 views

In an induction cooktop, what happens to the coils resistance when there is no pot? Does it vary between pots? How does the appliance respond?

An induction cooktop (or an induction rice cooker) uses a copper coil with a high-frequency alternating current going though. The magnetic flux heats any iron-alloy pot placed above. But what ...
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2answers
40 views

Can I create a continous gap in iron powder cores?

The iron powder core material, as you may know, has a continuous air gap in its structure. However, do you think it is possible to add a continuous air gap (for example 1mm) to the iron powder cores? ...
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1answer
60 views

Toroid coating got scratched

Will there be any performance effect if the torroid coating gets scratched?
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0answers
120 views

Magnetic field in the air gap of a transformer core

I am trying to calculate the magnetic field, Hg, and have been looking these formulas. I would like to know if I am on the right track, as something is not working out for me. From these with a ...
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0answers
38 views

Alternate formulation for the Neumann formula

I'm currently learning about the Neumann formula for the calculation of the mutual inductance between thin current filaments. However, for future purposes I want to find an alternative formulation of ...
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0answers
40 views

Can a CM choke saturate due to the leakage inductance?

On a 3-phase common-mode choke, if the three currents sum to zero, then it will theoretically never saturate. I understand that the leakage inductance stores energy in the core. Can the three phases ...
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3answers
45 views

Magnetic field direction

How do I know the direction of magnetic field produced by a bar magnet, assume a electron present side to the magnet ?
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2answers
227 views

Increase the pulling force of a solenoid with a permanent magnet [duplicate]

I have a number of solenoids I would like to use in a project. The problem is that they're not quite powerful enough so I've been trying to come up with ways to increase the their pulling force ...
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1answer
48 views

Calculating the magnetic flux density in cylandrical coordinates near a neodymium disc magnet

I am looking for an analysis of a disc magnet, I have heard there are 2D analaysis and 3D. Could someone point me in the right direction of a paper or some academic text on the matter. I don't mind ...
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1answer
32 views

90 degrees phase shifted magnetic fields

If we have a closed magnetic circuit with two primary coils and one secondary coil wound on it. The primary coils are wound such that unlike poles are adjacent. Both primary coils are using rectified ...
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2answers
61 views

Do MRI magnets oscillate due to parasitic capacitance?

Moved here from SE Physics. Do MRI magnets oscillate during charging or even during persistant mode due to parasitic capacitance? What problems can this cause? I am planning a low temp ...
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3answers
112 views

Why is the magnetic field around a bar magnet represented by iron filings?

Why would we use iron filings to display a magnetic field interaction and then teach this as the unaffected field of a magnet? Iron affects the field itself. This is analogous to an observer ...
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1answer
57 views

Simple Stepper motor for my experiment?

To graduate (Grade 12 or Year 12), I need to do an self-thought experiment in Physics. I decided to do something about stepper motor because I learned that they use this type of motor for robot arms. ...
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3answers
122 views

Circuit approximation of Induction in guitar pickups

I was trying to learn the way basic guitar circuits work, the other day, and I stumbled upon a thing that I couldn't fully understand. According to this site, a simple guitar circuit can be made as ...
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2answers
309 views

Metal detector coil SHIELDING?

Many designs of coils, of metal detectors, are shielded (Faraday shield). Should this be used in a gravity-fed detector (like the sketched one)? What's the shield for? NOTE: The coils are arranged ...
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0answers
46 views

Calculation of stray magnetic field from substation transformers

Say I want to assess the magnetic field attributed to some substation equipment and the cables in the substation area. Calculating the contribution from the cables and busbars are for my purposes done ...
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0answers
57 views

Toroidal Inductor magnetic field question

I need confirmation of my understanding of the magnetic field induced by a toroid inductor. What think is: The magnetic field B or H encircles the vector lines of A... A being the curl B. A ...
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1answer
115 views

Tranformer Output waveform

If input to a transformer is square/triangular, draw its output voltage waveform. This problem was asked in one of my recent interviews, please help me with this problem.
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0answers
161 views

Relationship between brushless coil inductance and back EMF as a function of phase angle

In general, does the inductance across the coils of a brushless motor have the same waveform as the back EMF? That is, if back EMF is sinusoidal, should I expect the inductance to be sinusoidal [with ...
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0answers
54 views

Falling Marble Sensor

I'm really building a sort of Rube Goldberg machine that students will assemble in order to guide a falling ball down through a series of gates/openings, where I need to detect when they're successful ...
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2answers
133 views

Saturating magnetic field in an inductor without heating

I am building an RL series circuit with a toroidal inductor that I am winding on my own. The toroid is made of steel (low carbon, I believe, but not 100% sure) and has about 280 turns of 22 gauge wire....
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0answers
48 views

Understanding maxwell's equations

I'm trying to use the fundamental maxwell's equations to see how this expression was derived: ∇⋅ (E⋅ E+ c^2 B⋅ B) = − ∂/∂t(E⋅B-E⋅B)+ 1/ε (B⋅J - J⋅B) c is 1/sqrt(ue). I have found the cross product ...
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1answer
53 views

Strong H fields: electronic items susceptible to thier damaging effects and how to shield them

This is another question related to magnetic fields. I'm trying to determine the thickness of copper foil that would be required to shield common electronic items from H fields of about 133 A/m over ...
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1answer
63 views

Energies of the fields in a plane wave, attenuated and unattenuated

This is a combination of two of my previous questions (question 1 and question 2) which are related. I'm trying to learn both how energy is carried in the electric and magnetic components of a plane ...
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1answer
166 views

EMI difference between Ferrite (powdered iron) and Iron

In an EMI application where I'm applying a snap on style ferrite core around a cable. What's the difference / benefit of the typical powdered iron type and just using a similarly sized piece of iron ...
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2answers
84 views

Energies carried by electric and magnetic fields in plane waves

This is a newbie question. I'm trying to understand what I think must be a very basic concept with an obvious answer, but I want to be sure. Do plane wave electric and magnetic fields of equal ...
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3answers
64 views

The electric and magnetic components of far field EMR and shielding thereof

This is a newbie question. I'm pretty sure of the answer, but I would like confirmation. I found this thread in this forum that came close to what I was looking for, but I think my question is ...
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2answers
85 views

Magnetic Locks mods [closed]

What about magnetic locks? Two questions.. Does armature plate need be exact size as magnetic mate? Id like to get a bigger one milled so i dont have to use lasers to check perfect alignment. ...
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1answer
61 views

magnetic hall effect sensor

I'm currently working on building a density based traffic light model. I want to use the magnetic hall effect sensor to detect the number of the cars passing, so the idea that I have is to place the ...
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0answers
34 views

Any deleterious effect from very strong, close magnets on NiMH cells over time?

This question probably isn't a perfect fit for this SE, but I did find this question: Will placing a strong magnet near my electric skateboard Li-Ion Battery pack damage or discharge it? This is a ...
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1answer
558 views

Ethernet magnetics - PHY side center tap isolation

I am designing a PCB that will use a Microchip KSZ9896C 6-port Gigabit Ethernet Switch. In the datasheet (section 7.2) they state that : "the four transformer center tap pins on the KSZ9896C chip ...
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1answer
80 views

Why transformers Secondary magnetizing inductnace and Secndary inductace are Not Considered while doing filter calculation for output ?

Why transformers Secondary magnetizing inductnace and Secndary leakage inductace are Not Considered while doing filter calculation for output ? Why most transformer datasheet only mention ...
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1answer
135 views

What is the relationship between field strength and efficiency in a DC motor?

This refers to a DC motor with permanent magnets. What is the relationship between the efficiency of the motor and the magnet field strength?