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
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
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.
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.