Physics - Electromagnetism - Eddy Currents and Applications
Image source: https://en.wikipedia.org/wiki/Eddy_current
Introduction
Hello it's a me again Drifter Programming! Today we continue with Electromagnetism to get into Eddy currents and their Applications, which is an interesting topic :) So, without further do, let's get started!
Eddy currents
During Electromagnetic Induction, currents that flow in closed loops and are circulating like swirling eddies in a stream are being induced by changing magnetic fields. These currents are therefore called Eddy currents. We can create them when moving a conductor through a magnetic field or when a magnetic field surrounding a stationary conductor is varying. Anything that causes a magnetic flux change can produce eddy currents. The magnitude/size of the induced eddy current is proportional to the size/strength of the magnetic field, the area of the loop, the rate of change of magnetic flux, and inverse proportional to the resistivity of the conductor. Like any other current, eddy currents also produce their own magnetic field. Because of Lenz's law the direction of the induced current's magnetic field will oppose the change of the magnetic field which created it.
So, to sum it up:
- Any electrically conductive object will conduct an induced current if it is placed in a changing magnetic field (Electromagnetic Induction)
- Eddy currents are circular induced currents AND
- Eddy currents generate their own magnetic fields
From all this we can clearly see that Eddy current is a form/type of induced current with a special and useful behavior which has a lot of applications that we will get into now!
Applications
Electromagnetic braking
Ordinary (friction) brakes convert kinetic energy into heat energy. Another type of brake, that is used to stop rollercoasters cars and trains, is the so called Eddy current brake. Let's consider a railroad train that's a huge solid block of copper mounted on wheels. Let's say that it's moving along at a high speed and that we want to stop it. Let's say that a giant magnet is next to the track and that the train has to pass nearby. As the copper approached the magnet, eddy currents are being induced inside the copper, which produce their own magnetic field. Eddy currents in different parts of the copper would try to work in different ways.
As the front part of the train approached the magnet, eddy currents try to generate a repulsive magnetic field, which slows down the copper's approach to the magnet. As the front part passed by, being slowed down already, the eddy currents would start generating an attractive magnetic field that tries to pull the train back again, slowing it down again. The kinetic energy lost by the train as it slows down again (like in friction brakes) turns into heat energy, heating up the copper as the eddy currents swirl inside it. Rollercoaster cars use magnetic brakes that work on this exact principle!
There are mainly two types of eddy current brakes:
- Linear brakes -> used in train tracks and rollercoasters, where the track works as a part of the brake
- Circular brakes -> based on a static electromagnet that applies magnetism and creates eddy currents in a rotating metal disc
Eddy current brakes have some big advantages:
- quiet
- frictionless
- wear-free
- little or no maintenance
- no smell or pollution
- regenerative braking technology (store energy for reuse)
The drawbacks are:
- the little experience we have using them
- problems by interfering with train signaling equipment
- the heating and expansion of rails could prove to be an issue when many trains brake in quick succession
Testing of materials
The detection and measurement of the magnetic fields that are produced by eddy currents make it possible for us to learn things about conductive materials whitout even contacting them. For example, the electrical conductivity of a material can be determined by the strength of the eddy currents that form.
The so called ECT (Eddy Current Testing) is an electromagnetic testing technique which is usually used to inspect ferromagnetic materials. For example, a copper wire can be connected with an alternating electrical current. The produced magnetic field oscillates at the same frequency as the current running through the coil. When the coil approaches a conductive material, currents opposed to the ones in the coil are induced in the material, forming eddy currents.
Cracks and other breaks in the surface of a material will prevent eddy currents from forming in that region of the surface and so eddy currents can also be used to detect cracks in materials! This type of testing of materials is referred to as nondestructive testing or NDT in short. NDT technicians and engineers can use eddy currents to find cracks and many other flaws in airplanes and other systems, where bad things happen if a part brakes.
Other
Some other applications of eddy currents include:
- Repulsive effects and levitation
- Attractive effects
- Vibration and position sensing
- Zip Line Brakes
- Free Fall Devices
- Eddy current adjustable-speed drives
- Electromechanical Induction Meters
- Induction heating
- Displacement/Proximity sensors
- Vending machines
- Sheet Resistance Measurement
- Mechanical speedometers
- and more...
REFERENCES:
- https://www.magcraft.com/blog/what-are-eddy-currents
- https://www.nde-ed.org/EducationResources/HighSchool/Electricity/eddycurrents.htm
- https://www.explainthatstuff.com/eddy-current-brakes.html
- https://www.eddyfi.com/technologies/eddy-current-testing-ect/
- https://www.princeton.edu/ssp/joseph-henry-project/eddy-currents/eddy_wiki.pdf
Previous posts about Electromagnetism
Electric fields:
Getting into Electromagnetism -> electromagnetim, electric charge, conductors, insulators, quantization
Coulomb's law with examples -> Coulomb's law, superposition principle, Coulomb constant, how to solve problems, examples
Electric fields and field lines -> Electric fields, Solving problems around Electric fields and field lines
Electric dipoles -> Electric dipole, torque, potential and field
Electric charge and field Exercises -> examples in electric charges and fields
Electric flux:
Electric flux and Gauss's law -> Electric flux, Gauss's law
Applications of Gauss's law (part 1) -> applying Gauss's law, Gauss applications
Applications of Gauss's law (part 2) -> more Gauss applications
Electric flux exercises -> examples in electric flux and Gauss's law
Electric potential:
Electric potential energy -> explanation of work-energy, electric potential energy
Calculating electric potentials -> more stuff about potential energy, potential, calculating potentials
Equipotential surfaces and potential gradient -> Equipotential surface, potential gradient
Millikan's Oil Drop Experiment -> Millikan's experiment, electronvolt
Cathode ray tubes explained using electric potential -> cathode ray tube explanation
Electric potential exercises (part 1) -> applications of potential
Electric potential exercises (part 2) -> applications of potential gradient, advanced examples
Capacitance:
Capacitors (Condensers) and Capacitance -> Capacitors, capacitance, calculating capacitance
How to solve problems around Capacitors -> combination, solving problems, simple example
Electric field energy and density -> Electric field energy, energy density
Dielectric materials -> Dielectrics, dielectric constant, permittivity and strength, how to solve problems
Electric capacitance exercises -> examples in capacitance, energy density and dielectrics
Current, resistance and EMF:
Electric current -> Electric current, current density
Electrical resistivity and conductivity -> Electrical resistivity, conductivity, thermal coefficient of resistivity, hyperconductivity
Electric resistance -> Resistance, temperature, resistors
Electromotive Force (EMF) and Internal resistance -> Electromotive force, internal resistance
Power and Wattage of Electronic Circuits -> Power in general, power/wattage of electronic circuits
Electric current, resistance and emf exercises -> exampes in all those topics
Direct current (DC) circuits:
Resistor Combinations -> Resistor combinations, how to solve problems
Kirchhoff's laws with applications -> Kirchhoff's laws, how to solve problems, applications
Electrical measuring instruments -> what are they?, types list, getting into some of them, an application
Electronic circuits with resistors and capacitors (R-C) -> R-C Circuit, charging, time constant, discharging, how to apply
RC circuit exercises -> examples in Kirchhoff, charging, discharging capacitor with/without internal resistance
Magnetic field and forces:
Magnetic fields -> Magnetism, Magnetic field
Magnetic field lines and Gauss's law of Magnetism -> magnetic field lines, mono- and dipoles, Flux, Gauss's law of magnetism
The motion of charged particles inside of a magnetic field -> straight-line, spiral and helical particle motion
Applications of charged particle motion -> CERN, Cyclotrons, Synchrotrons, Cavity Magetron, Mass Spectrometry and Magnetic lens
Magnetic force applied on Current-Carrying Conductors -> magnetic force on current-carrying conductors/wires, proofs
Magnetic force and torque applied on current loops (circuits) -> magnetic force on current loops, magnetic moment and torque
Explaining the Physics behind Electromotors -> tesla, history and explaining the physics behind them
Magnetic field exercises -> examples in magnetic force, magnetic flux, particle motion and forces/torque on current-carrying conductors
Magnetic field sources:
Magnetic field of a moving charged particle -> moving charge, magnetic field, force between parallel charged particles
Magnetic field of current-carrying conductors -> magnetic field of current, Biot-Savart law
Force between parallel conductors and the magnetic field of a current loop-> force between parallel conductors, magnetic field of current loop
Ampere's law and Applications -> Ampere's law, applications
Magnetic materials -> Magnetic materials, classification and types, material examples
Displacement current -> Displacement current, Extension of Ampere's law
Exercises in Magnetic field sources -> examples all around magnetic field sources
Electromagnetic Induction:
Electromagnetic Induction and Faraday's law -> Electromagnetic Induction, Experiments, Faraday's law
Motional Electromotive Force (Emf) -> Motional Emf, Faraday's law and motional emf, generalization
Lenz's law and Induced Electric fields -> Lenz's law, Induced Electric Fields
And this is actually it for today's post! Next time in Physics we will get into Maxwell equations as a whole...
C ya!
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very interesting topic
This is what causes the inability of cars to move from the railway as the train approaches???
Haha I don't think so...
Cars usually have rubber tires which of course don't conduct electricity and so aren't affected by the rails. The inability can be explained by the non-uniform surface that the car has to drive on. The bumpy track of course makes it much more difficult for cars to move on then on a "normal" road.
But, I don't put my hand in the fire :P There still might be some effect on cars, but this effect cannot be that strong that it doesn't let cars to move on...