MAGNETIC LEVITATION PDF
PDF | Magnetic levitation is a way of using electromagnetic fields to levitate objects without any noise. It employs diamagnetism, which is an. PDF | This book provides a comprehensive overview of magnetic levitation( Maglev) technologies, from fundamental principles through to the. al appendixes plus pdf-print of web sources enclosed. Finished at 27/ Synopsis: The purpose of this project is to study an existing magnetic levitation.
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The shinkansen, and other similar high-. Figure 1 Different Propulsion Methods of Conventional Electric Railways and Superconducting Maglev Guideway. N. N. The magnetic field is the medium by which the force is transferred. Maglev systems utilize the fundamental physics of electric currents experiencing forces-. speed maglev train uses non-contact magnetic levitation, guidance and propulsion systems Here is the pdf file of calculation regarding the force and solenoid.
The position can then be used to determine how much current the electromagnet must receive. To prevent oscillations however, the rate of change of position must used as well. The position information can easily be differentiated to acquire the speed information required.
Electromagnetic levitation works via the magnetic force of repulsion. Using repulsion though makes a much more difficult control problem. The levitating object is now able to move in any direction, meaning that the control problem has shifted from one dimension to three. There is much interest in levitation due to its possible applications in high speed transport technology. These applications can be broadly referred to as MagLev, which stands for magnetic levitation.
The MagLev cradle is a system designed by Bill Beaty. It is able to levitate a small rod magnet for a few seconds at a time. This system suffers from serious instability. As such levitation can only be maintained for a few seconds. The MagLev cradle uses rapid switching circuits to control current to the electromagnets. If the bar magnet falls too close to the electromagnet, the circuit switches on, thus applying more repelling force.
If the bar magnet rises too high above the electromagnet, it turns off, thus removing the repelling force. The system developed for this thesis uses the position sensing technique employed by the magnetic cradle. Hall Effect sensors are placed on each of the electromagnets in the system. Each electromagnet and its current control circuitry operates as an independent system to levitate part of a bar magnet.
The Hall effect sensor is a device that senses magnetic flux. It is also capable of detecting the magnetic flux orientation. The circuitry is configured such that is magnetic flux is detected; the system will energize the electromagnet in order to make the net magnetic flux with the hall effect sensor zero. Therefore this system electronically simulates the Meissner effect by repelling both north and south poles of a magnet. Experiments were also done to investigate various configurations of electromagnets in order to achieve stable magnetic levitation.
Initial tests revealed that besides position sensing, speed information was required as well. This was achieved by adding a phase lead circuit, which negated the phase lag caused by the electromagnet an inductive load and the control circuitry. Different configurations of electromagnets were used to attempt to levitate a bar magnet. The main problem that was soon identified was that of keeping the levitating bar magnet in the area above the electromagnets.
Despite moving the electromagnets closer and further apart, the bar magnet could not be effectively trapped above the electromagnets. Thus current system lacks the control circuitry required to achieve stable electromagnetic levitation. At present, pairs of electromagnets can effectively levitate part of a bar magnet which is supported at one end.
If the necessary control circuit required to effectively hold the levitating bar magnet in position above the electromagnet can be designed, then a working system can be quickly realised.
The Levitron top levitating above its permanent magnet base. A magnet levitating above a superconductor Fig3: Diagram showing the basic control arrangement of a magnetic suspension system.
Diagram showing the physical model of a magnetic suspension system. Diagram showing a simple phase lead circuit Fig6: Picture showing a magnetic suspension system in action. Diagram showing a simplified arrangement of electromagnets to levitate a train.
Diagram showing the physical setup of the MagLev cradle. A diagram showing a systems view of a magnetic levitation device. Shows a possible physical arrangement for a magnetic levitation system. Shows the physical dimensions of the electromagnets used. Circuit diagram of a one opamp current control circuit Fig Circuit diagram of a current control circuit with the addition of phase lead.
Circuit diagram of a current control circuit using two opamps. Circuit diagram of a two opamp current control circuit with the addition of a transistor stage gain limiting resistor. Diagram showing the physical layout of the magnetic repulsion tests.
Circuit diagram of the two opamp current control circuit with the addition of phase lead. Diagram showing the physical layout of the partial magnetic levitation tests.
Diagram showing sensor positioning modifications Fig Diagram showing the physical layout of the 4 electromagnet full levitation test. Diagram showing the physical layout of the 5-electromagnet magnetic levitation tests. Physical layout of the 6 electromagnet magnetic levitation tests.
Kelvin C: In other words, it is overcoming the gravitational force on an object by applying a counteracting magnetic field. Either the magnetic force of repulsion or attraction can be used. In the case of magnetic attraction, the experiment is known as magnetic suspension. Using magnetic repulsion, it becomes magnetic levitation.
Attempts were made to find the correct arrangement of permanent magnets to levitate another smaller magnet, or to suspend a magnet or some other object made of a ferrous material. It was however, mathematically proven by Earnshaw that a static arrangement of permanent magnets or charges could not stably magnetically levitate an object Apart from permanent magnets, other ways to produce magnetic fields can also be used to perform levitation.
When a magnet is moving relative to a conductor in close proximity, a current is induced within the conductor. This induced current will cause an opposing magnetic field. This opposing magnetic field can be used to levitate a magnet. This means of overcoming the restrictions identified by Earnshaw is referred to as oscillation. Electrodynamic magnetic levitation also results from an effect observed in superconductors. This effect was observed by Meissner and is known as the Meissner effect.
This is a special case of diamagnetism. This thesis will mainly deal with electromagnetic levitation using feedback techniques to attain stable levitation of a bar magnet. This can be simply proved as follows: At a point of equilibrium the force is zero.
If the equilibrium is stable the force must point in towards the point of equilibrium on some small sphere around the point.
However, by Gauss' theorem, s F x. Thus the result can be circumvented under certain conditions. At the atomic level there is a type of levitation occurring through forces of repulsion between particles. This effect is so small however, that it is not generally considered as magnetic levitation.
The Levitron uses an arrangement of static permanent magnets to levitate a smaller magnet. Below this temperature, they become superconductors, with an internal resistance of zero. They attain a relative permeability of zero, making them the perfect diamagnetic material.
This allows them to maintain their repelling magnetic field as long as a foreign source of magnetic flux is present. Thus the tendency for instability can be removed by constantly correcting the magnetic field strength of the electromagnets to keep a permanent magnet levitated.
Thus, it causes the electromagnet to behave like a diamagnetic material. It is a patented device that performs magnetic levitation with permanent magnets. The base consists of a carefully arranged set of permanent magnets.
The object that is levitated is a circular permanent magnet inside a spinning top shape. Harrigan found that the instability described by Earnshaw could be overcome by having the levitating magnet spin at high speed. This gyroscopic motion provides a simple solution to the spatial instability problem defined by Earnshaw.
Harrigan was able to determine the speed above which the levitating magnet would have to spin in order to maintain stable levitation. If the angular speed was too slow, the gyroscopic stabilising effect would be lost.
The spinning top shape for the levitating magnet was adopted in order to reduce the drag caused by air friction as the top spins. Thus it would be able to spin for longer. He also found that as the top spins, a diamagnetic effect occurs. The motion of the spinning levitating top relative to the base magnets causes a current to be induced in the spinning top.
The induced currents set up a magnetic field which opposes the base magnets in such a way that it tries to slow the rotation of the levitating top, causing the levitating time to be reduced.
Thus the Levitron uses ceramic magnets and ceramic materials instead of conducting metals. This reduces the induced currents and thus the unwanted opposing magnetic fields.
This allows the top to spin for longer. Because the air friction and induced currents cannot be completely eliminated however, the levitating effect cannot be maintained or controlled. Image from: Martin D. Simon, Lee O.
Three-dimensional cell culturing by magnetic levitation
Heflinger The Meissner effect is a phenomenon that occurs when certain conductors are cooled below their critical temperature which is typically 0 K.
It was observed that under this condition the conductor would become a superconductor, and would in fact repel magnetic fields of any orientation. In other words, a piece of superconducting material cooled to below its critical temperature will repel a magnetic south pole or a magnetic north pole, without having to move it.
In a conventional conductor such as copper, if a magnet is brought in proximity to it, an electric current is induced in the copper. Due to the fact that copper is not a perfect conductor however, the induced current quickly dies away due to the internal resistance present in the conductor. When the current disappears, the magnetic field collapses along with it. Thus, this induced current and its accompanying magnetic field are only observed when the nearby magnet is moving.
The movement of the nearby magnetic field would then constantly stimulate the induced current and the opposing magnetic field. This phenomenon explains the damping effect that a copper plate in close proximity has on the movement of a magnet.
As can be seen from the above explanation, theoretically, if the induced current did not dissipate due to the resistance of the conductor, then the accompanying magnetic field should persist as well.
This is in effect, what happens in a superconductor cooled to below its critical temperature. There is zero resistance inside the superconductor, and so the induced current and its accompanying magnetic field would not dissipate, even if the magnet stopped moving. This causes a magnet brought close to a cooled superconductor to be repelled, regardless of which magnetic pole the superconductor is exposed to. The opposing magnetic field induced in a superconductor can become so strong that it can effectively match the downwards force on a nearby magnet caused by its weight.
The resultant effect observed is that a magnet, placed above a cooled superconductor, can remain there, stably levitated. As Earnshaw showed, simple magnetic repulsion is not sufficient to maintain stable levitation. This problem is solved at the molecular level.
Within the superconductor are impurities, i. These areas, although small, are big enough to allow regions of the magnetic field from the nearby magnet to penetrate the superconductor.
If the magnet moved, the magnetic field would have to move with it. But because the magnetic field is unable to penetrate the superconductor in any other area, the magnetic field is effectively locked in place.
This is what holds the magnet in place above the superconductor and keeps it stably levitated. This is known as flux pinning.
A magnet levitating above a superconductor Image from: The object that is to be levitated is placed below an electromagnet only one is required , and the strength of the magnetic field produced by the electromagnet is controlled to exactly cancel out the downward force on the object caused by its weight. This system works via the force of attraction between the electromagnet and the object. Because of this, the levitating object does not need to be a magnet; it can be any ferrous material.
This further simplifies the design considerations. This produces the basic feedback arrangement depicted below. A possible physical arrangement is shown below. Electromagnet Position Sensor Levitating Object Supporting Stand There are various ways to sense the position of the levitating object. One way is optically. A beam of light is shone across the bottom of the electromagnet and detected at the other side.
As the object obscures more and more light indicating that the object is getting closer to the electromagnet the electromagnet controller limits the current more and more.
As the object drops away from the electromagnet, more light is exposed to the sensor, and the current to the electromagnet is increased. This system can prove difficult to properly set up, as the alignment of the light source and the light sensor is critical.
Also critical is the shape of the levitating object, because the rate at which light is obscured or exposed should be linear as the object rises and falls. This will produce the best results.
The position can also be sensed capacitively. A small metal plate can be placed between the levitating object and the electromagnet. The capacitance between the levitating object and the metal plate can be sensed and used to determine the distance between the two.
The advantage of this system is that the capacitance between the plate and the object is always linear regardless of the shape of the levitating object. The capacitance is given by the following equation. The disadvantage of this solution is that the metal plate placed below the electromagnet may have undesired effects on the magnetic behaviour of the system.
If the material is ferrous, its proximity to the electromagnet and its shape would alter the resultant magnetic field shape in the area of the levitating object.
Also the circuitry required to sense the capacitance accurately is fairly complex and sensitive to circuit layouts. Another means of position sensing is via ultra sonic sound transmitters. These work on the concept of sonar.
A chirp sound signal is transmitted and the time taken for the signal to return after bouncing off the levitating object is used to determine its distance. This however, is a very complex solution given the simplicity of the system?
If the magnet attempts to jump up towards the top magnet, the top plate prevents it from doing so, too.
What is really counter intuitive in this situation - especially for physicists - is that the minute forces created by the practically non-magnetic matter and very rapidly decaying with distance, are sufficient to keep the fine balance between magnetic and gravitational forces. The photograph shows a prototype of a new generation of passive magnetic bearings based on the described principle. Unlike in the case of superconducting bearings, there is no need to cool the device with liquid nitrogen or helium and there is no magnetic friction.
Importantly, there are no restrictions on either the size or weight of levitating objects, nor very strong magnetic fields are required. Our magnetic bearings can be made of only permanent magnets and are intrinsically frictionless.
They can be either less than a centimeter in size to support high-speed rotors or many meters large to support flywheels for energy storage weighing many tons. The latter would require many permanent magnets distributed above a heavy levitating objects.
Of course, the diamagnetically stabilised levitation is unlikely to be a panacea for every application where magnetic bearings were previously considered.
However, they can take over in some cases or be incorporated in design in others. In order to show how easy it is to achieve levitation when you know how!
These kinds of systems typically show an inherent stability, although extra damping is sometimes required.
Relative motion between conductors and magnets[ edit ] If one moves a base made of a very good electrical conductor such as copper , aluminium or silver close to a magnet, an eddy current will be induced in the conductor that will oppose the changes in the field and create an opposite field that will repel the magnet Lenz's law. At a sufficiently high rate of movement, a suspended magnet will levitate on the metal, or vice versa with suspended metal.
Litz wire made of wire thinner than the skin depth for the frequencies seen by the metal works much more efficiently than solid conductors. Figure 8 coils can be used to keep something aligned. The net effect is to more than triple the lift force. Using two opposed Halbach arrays increases the field even further.
Oscillating electromagnetic fields[ edit ] Aluminium foil floating above the induction cooktop thanks to eddy currents induced in it. A conductor can be levitated above an electromagnet or vice versa with an alternating current flowing through it. This causes any regular conductor to behave like a diamagnet, due to the eddy currents generated in the conductor.
This effect requires non-ferromagnetic but highly conductive materials like aluminium or copper, as the ferromagnetic ones are also strongly attracted to the electromagnet although at high frequencies the field can still be expelled and tend to have a higher resistivity giving lower eddy currents.
Again, litz wire gives the best results. The effect can be used for stunts such as levitating a telephone book by concealing an aluminium plate within it. At high frequencies a few tens of kilohertz or so and kilowatt powers small quantities of metals can be levitated and melted using levitation melting without the risk of the metal being contaminated by the crucible. This can be used to levitate as well as provide propulsion.
Diamagnetically stabilized levitation[ edit ] Permanent magnet stably levitated between fingertips Earnshaw's theorem does not apply to diamagnets. Diamagnetic levitation can be inherently stable.
A permanent magnet can be stably suspended by various configurations of strong permanent magnets and strong diamagnets. When using superconducting magnets, the levitation of a permanent magnet can even be stabilized by the small diamagnetism of water in human fingers. Diamagnetic materials cause lines of magnetic flux to curve away from the material.
Specifically, an external magnetic field alters the orbital velocity of electrons around their nuclei, thus changing the magnetic dipole moment.Damping of motion is done in a number of ways: external mechanical damping in the support , such as dashpots , air drag etc.
Electromagnets are similar to other magnets in that they attract metal objects, but the magnetic pull is temporary. If two magnets are mechanically constrained along a single axis, for example, and arranged to repel each other strongly, this will act to levitate one of the magnets above the other. A linear motor propulsion coils mounted in the track is one solution.
Table 1 shows the elements of superconductors from Type 1, which they are all consists of Figure 3.
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