The electromagnetic suspension EMS uses attractive force system to levitate. The train’s levitation magnet will be attracted to the conductors on the underside of the guideway. The attractive force between them will overcome the gravitational force. This will in turn levitates the train on the track.The guidance magnets on the other hand guides the train so that the side of the track will not have contact with the train, creating friction and damages the train. The guidance magnets will also guide the train so that it will follow the direction of the guideway track.
From the figure above, we can see that the train is wrapped around the track. Because of this, the EMS train is a safer train and comfortable. The regulated levitation of the train makes the train levitates even when traveling at low speed. The magnetic field intensity inside the passenger compartment is also small so it is safe for passengers with pacemakers or passengers carrying magnetic storage such as credit card or hard disk. Its intensity is comparable to the earth's magnetic field and far below the field intensity of a hair dryer, an electric drill or a sewing machine.
In the event of a power failure, the EMS maglev train is equipped with an emergency battery power supply so that the maglev train will not crash onto the guideway.
The most successful EMS maglev train so far is called the Transrapid system and it is currently being used by the MagLev in Shanghai, China. It is also being used in Germany.
Electrodynamic Suspension
The electrodynamic suspension (EDS) train has been developed by Japanese engineers. It uses magnets that has same polarity (refer to figure above) to create repulsive force between levitation magnet and guideway magnet. This repulsive force then will be high enough to overcome gravitational force and allows it to levitate.The main difference between EDS maglev train and EMS maglev train is that EDS maglev train use super-cooled, superconducting electromagnets. This superconducting electromagnet can conduct electricity even after the power supply has been shut off for example in the event of a blackout. In the EMS system, which uses standard electromagnets, the coils only conduct electricity when a power supply is present. By chilling the coil at frigid temperatures, Japan’s EDS system saves energy. However, the cryogenic system uses to cool the coils can be expensive.
One potential drawback in using the EDS system is that maglev trains must roll on rubber tires until they reach a liftoff speed of about 62 miles/h (100 km/h). Past the liftoff speed, the train will levitate and the rubber tires will no longer in contact with the guideway. However, Japanese engineer say that the wheels are an advantage if a power failure caused a shutdown of the system. The EDS train is impressively capable to levitate nearly 4 inches (10cm) above the guideway.
Since EDS train will induce a high intensity magnetic field, the passenger section of the train will have to be shielded from the magnetic field or else it will be dangerous for passengers with pacemakers and damages magnetic data storage such as credit cards and hard drives.
Inductrack
The inductrack is a newer type of EDS that uses permanent room-temperature magnets to produce the magnetic fields insted of powered electromagnets or cooled superconducting magnets.Permanent magnets had not been used before because scientists thought that they would not create enough levitating force. The Inductrack design bypasses this problem by arranging the magnets in a Halbach array. The magnets are configured so that the intensity of the magnetic field concentrates above the array instead of below it. They are made from a newer material comprising a neodymium-iron-boron alloy, which generates a higher magnetic field.
The track is actually an array of electrically-shorted circuits containing insulated wire. In one design, these circuits are aligned like rungs in a ladder. As the train moves, a magnetic field the repels the magnets, causing the train to levitate.
There are two Inductrack designs: Inductrack I and Inductrack II. Inductrack I is designed for high speeds, while Inductrack II is suited for slow speeds. Inductrack trains could levitate higher with greater stability. As long as it's moving a few miles per hour, an Inductrack train will levitate nearly an inch (2.54 cm) above the track. A greater gap above the track means that the train would not require complex sensing systems to maintain stability.
The Inductrack II design incorporates two Halbach arrays to generate a stronger magnetic field at lower speeds.
As of now, there is still no commercial version of inductrack or full scale system prototype.
