Theory
How does a Maglev work?
Maglev is short for Magnetic Levitation, so a Maglev is a train that works by means of Magnetic Levitation. On board of a Maglev are several powerful electromagnets located on each side of the train. These electromagnets a cooled down to about 77K using liquid Helium and liquid Nitrogen ¹. When the elec-tromagnets are cooled to that point they become ”Superconducting Magnets”. This means that when placed in a magnetic field, the field will bend around the magnet. As a result of this the magnet is locked in place.
These electromagnets are made of Niobium-Titanium alloy, which is used because it’s a type-II superconductor ². These superconductors also have the highest critical current and highest critical applied magnetic force (up to 15T, but it is usually used for electromagnets with a magnetic force of 10T), if one of those critical points are surpassed the superconductivity is destroyed.
The rails of the Maglev are made out of a ”floor” and 2 walls. This ”floor” contains the power supply for the train itself. The walls contain 2 rows of coils, 1 row for the propulsion and 1 for the guidance of the train. The so-called ”guidance coils” are coils wound in an 8-figure and placed vertically next to each other. This 8-figure is what causes the so called ”nullflux”, ”nullflux” is when electromagnets are exposed in a magnetic field. Because the potentials of the electromagnets cancel out due to the opposite poles in the 8-figure, the magnet can be centered so no currents flow and the magnet will stay in that position. If the magnet moves out of its centered position currents will begin to flow and the canceled out potential won’t hold. Because of the increase in potential, the magnet will correct itself back to its centered position. This ”nullflux” is used by the Maglev to keep the train in the air.
For the propulsion the so-called ”propulsion coils” are used. These coils have a long shape and overlap with each other. For this propulsion system a controlled alternated current is needed, where the amplitude of the current can be modified. When the amplitude is changed the speed is changed, if the wave function of the current is changed out of phase a break force is applied.
How do electromagnets work?
To be able to explain how they work, it should first be explained what electromagnets precisely are. Electromagnets are on the highest level simply magnets which are created through the existence of an electric current, meaning that the power of the magnet can be controlled depending on how big the current is ³. This also means, that contrary to static magnets, the location of the magnetic poles can be controlled by simply switching the direction the current flows in. The reason the magnetic field is created is because any electric current generates a small magnetic field around it, as defined by Ampère’s circuital law ⁴. If the current in a wire flows towards you, the magnetic field flows counterclockwise around the wire, and vice versa (see figure 1). This means that if we take, for example, an isolated copper wire, and form it into a series of loops, the flow of the magnetic fields that are created by the current are concentrated in the center of the loop, and all flow in the same direction, which causes the magnetic poles to appear (see figure 2) ⁵. This is what creates an electromagnet. The properties of an electromagnet can be adapted by using a wire of a different material, by changing the amount of loops, or by modifying the amount of power that flows through the wire ⁶. This all should be taken into account when using an electromagnet.
One of the problems when using electromagnets is the heat that is generated by the resistance provided by the material the current has to flow through. This often results in the materials melting and/or other damage done to the magnet. Thankfully, there’s a special kind of electromagnet, which is often employed for real-world Maglevs, called a ”Superconducting Magnet”. The special property of this kind of magnet is that it generates no heat at all, because the material that’s used for the coil provides no resistance 7 . A material that provides no resistance to an electric current is called a ”Superconductor”. Such a material is created by cooling down certain materials below their characteristic critical temperature 8 . There’s many benefits to using superconducting magnets in a Maglev, but the most prominent is the ability to be able to apply as much power as necessary without having to worry about the generated heat, which grants the ability to create as strong a magnetic field as necessary.
What effect does a piece of metal in the middle of the coil have?
What is better, connecting the electromagnets in series or parallel to each other?
Can we make a static magnet levitate using electromagnets?
How much mass can we levitate?