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How Maglev Works
Maglev 2000

History of transportation

Superconducting maglev

Learning to levitate

Two key inventions

Null flux suspension

Null flux geometries

LSM propulsion

How the M-2000 system works

M-2000 guideways

M-2000 Vehicles

Superconductors

Maglev FAQ



Learning to levitatenull flux geometries

There are many geometric forms of Null Flux guideway loops. All of the various geometries share a common feature. The null flux guideway loop is wound so that when the vehicle is at the symmetry point of the loop, the net magnetic flux through the loop circuit is zero. Since the net magnetic flux is zero, the induced current in the loop is also zero.

If the vehicle magnet moves away from the symmetry point in any direction, the magnetic flux through the loop circuit becomes non-zero, causing an induced current to flow in the loop circuit.

The direction of the induced current is always such that the resultant magnetic force acts to push the vehicle magnet back towards the symmetry point.

When the superconducting (SC) loop on the vehicle is exactly halfway between the upper and lower halves of the null flux guideway loop circuit, the net flux through the circuit is zero, because the top half loop is wound in the opposite direction from the bottom half loop. (The + and - signs in the guideway loop circuit indicate the winding direction).

If the vehicle SC loop moves downward from the center symmetry point of the null flux guideway loop, an induced current and magnetic force develop so as to push the vehicle loop upwards. If the vehicle loop moves upwards, an induced current and magnetic force develop so as to push the vehicle loop downwards.

In an actual maglev system where the vehicle has a non-zero weight, the vehicle SC loop rests at a stable position slightly below the symmetry midplane. At this position, the induced current in the null flux guideway circuit generates a magnetic lift force that equals the downwards weight of the vehicle. Any external force that tries to move the vehicle away from this suspension point is automatically countered by a change in the induced current and magnetic lift force.

The null flux configuration permits the use of much stronger superconducting magnets in the vehicle than are possible using a conducting sheet or simple loop guideway. As a result, for a given magnetic levitation force, the induced current in the null flux loops is much smaller than for a conducting sheet or simple loop guideway. This greatly reduces the power losses in the guideway.

The same null flux principle applies to the "Figure of 8 loop." When the vehicle SC loop is centered on the "Figure of 8 loop," the net magnetic flux through the "Figure of 8" loop circuit is zero. If the SC loop moves to the left or right, a net magnetic flux results, inducing a current that pushes the SC loop back to its centered position.

The "Figure of 8 loop" is laid on the horizontal surface of a planar guideway and provides a horizontal restoring force if the vehicle is subjected to an external horizontal force, i.e., a cross wind. The "Figure of 8 loop" can also be vertically oriented. In the vertical orientation it provides both vertical lift and a vertical restoring force to the equilibrium suspension point. The vertical "Figure of 8" configuration is used on the side walls of the Japanese maglev U-shaped guideway.

Still another null flux configuration is formed by connecting the #1 and #2 guideway loops on the sidewalls of a U-shaped guideway. When the maglev vehicle is centered between the null flux loops, the net magnetic flux and current in the null flux circuit are zero. If an external force tries to push the vehicle either left or right, a net current and horizontal magnetic force develops in the null flux circuit pushes the vehicle back to its centered position.

Using the null flux suspension, the magnetic drag force on the vehicle can be made much smaller than the air drag force. At 300 mph, the air drag force is typically about 5 to 10% of the vehicles weight, while the magnetic drag force is about 1 % or less.


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