Translational Halbach arrays:
A Halbach array is a special arrangement of permanent magnets which augments the magnetic field on one side of the device while cancelling the field to near zero on the other side. In the diagram, the magnetic field is enhanced on the bottom side and cancelled on the top side (a one-sided flux).
The pattern (on the front face; left, up, right, down) of permanent magnets can be continued indefinitely and have the same effect. It is roughly similar to many horseshoe magnets placed adjacent to each other, with alternating polarity.
Moving Halbach arrays over a conductor results in an induced current through the conductor and consequently an opposite magnetic field is created. At a particular threshold velocity the induced magnetic field is strong enough to cause levitation over a series of such conductors. These arrays can be placed in a stable configuration and then insatlled in the devices.
High frequency oscillating electromagnetic fields:
A conductor can be levitated over an electromagnet with a high frequency alternating current flowing through it, this causes most conductors to behave as diamagnets because of the eddy currents induced in it. As eddy cureents cause opposing fields to be genrated it results in repulsion of the conductor.
Applications:
Magnetic levitation transport is a form of transport system that suspends, guides and propels vehicles via electromagnetic force. Using this we can achieve great levels of riding comfort and also very high speeds- almost in the region of 500 to 600 kmph. This is mainly due to the fact that there is no friction encountered whatsoever as there is no mechanical contact between the vehicle and any other surface. Only resistance is provided by air which too can be minimised by proper aerodynamic design.
The high speed potential of maglevs could prove to be a major competiton for airline routes of shorter distances . The world's first commercial application of a high-speed maglev line is the IOS (initial operating segment) demonstration line in Shanghai that transports people 30 km (18.6 miles) to the airport in just 7 minutes 20 seconds (top speed of 431 km/h or 268 mph, average speed 250 km/h or 150 mph).
Maglev technology has very minor similarities with the existing train technology thus it has to be designed as separate transport systems.
Technology
As previously mentioned maglev technolgy works mainly on three types of supension, namely the EDS, EMS and Inductrack.
Inductrack
This technique has a load carrying ability that is dependent on the speed of the vehicle as it depends on currents induced in an electromagentic array by permanent magnets. The permanent magnets are installed in the cart horizontally for lift and vertically for stability. The array of conducting loops is in the track. The magnets and cart are unpowered except by the speed of the cart.
Inductrack uses Halbach arrays for stabilization. Halbach arrays are arrangements of permanent magnets that stabilize moving loops of wire without electronic stabilization. Halbach arrays were originally developed for beam guidance of particle accelerators. They also have a magnetic field on the track side only, thus reducing any potential effects on the passengers.
Lift and propulsion
Germany and Japan are foremost in maglev research, creating and testing several new designs. An example of one of the designs is: The train can be levitated by the repulsive and attractive forces of the like or unlike poles of the magnets rspectively. The train is propelled by a linear induction motor on the track or on the train or on both. Since a strong magnetic field is required, large coils are placed along the track which create the required field.
Stability
Since magnetic bearings using only electromagnets and permanent magnets are unstable, diamagnetic and superconducting magents are used for a stable levitation of the train. Some conventional designs electromagnets that have electronic stabilization. This system works by constantly measuring the bearing distance and adjusting the electromagnet current accordingly.
Magnet Weight
The weight of the large electromagnet is a major design issue. A very strong magnetic field is required to levitate a massive train, so conventional maglev research is using superconductor research for an efficient electromagnet.
Pros and cons of different technologies
Each implementation of the magnetic levitation principle for train-type travel involves advantages and disadvantages. Time will tell as to which principle, and whose implementation, wins out commercially.
