By Ian Gonzalez Lopez.
During the XIX century the world was set in motion fueled by vapor machines. The Industrial Revolution delivered big changes in the way different products were made, led the way into mass production and also set the engines going for new modes of transportation. Trains were a part of that evolution, and a crucial one, since the combination of their speed and the ability to transport heavy loads made it the main traveling method for long distances, both for goods and people. At that time, even the development of an area could be measured by how many railways were being constructed near it. But those times have long gone, steam engines no longer power the transportation through the world.
The technology changed, and electrical power turned out to be the main source of energy for household and industrial technologies, and in the transportation sector, the evolution of the car gave petroleum based fuel a prominent role which, although it seems it could be replaced at some point, it still holds. The constant advancement of transportation is mainly focused on its speed, a vehicle that can get faster from A to B is regarded as a better option against another that takes more time. In the case of trains, the main impediment for gaining speed is the friction of the wheels, as well as the energy needed to move all the weight.
To cope with the advancement in other sectors the trains evolved, and the ones that have the leading technology nowadays use some of the most interesting physical phenomena in their design, something that seems rather esoteric and out of a sci-fi movie: levitation.
What a better way of moving in land than not touching it? We are talking about magnetic levitation trains, commonly referred as maglev trains. With this kind of technology the replacement of wheels for a levitation mechanism not only increased the speed of the trains, but also the comfort of those who ride it. The noise of the wheels against the rails and the one made by the engine are not present anymore, and instead of having a bumpy ride depending on the tracks, the journey is smooth. This innovation in trains is credited mainly to Eric Laithwaite, but in reality there were multiple different prototypes around the globe, including the ones from Herman Kemper, which all shared the idea of magnetic levitation and the aspiration of being able to have a means of transportation that would not touch the ground. The principle behind it is rather simple: opposing magnetic poles are attracted and the ones with the same polarity are repelled between them. So, given a sufficiently large magnetic field, if the force that pushes an object upwards is the same as the one pushing it downwards (gravity), then the object would remain in the air, as the acting forces cancel each other out. But is it really that easy? How does the train actually moves and does not simply stay levitating at one spot? Well, in order to understand how this works it is necessary to explain the different systems involved in the magnetic levitation of trains. There are two different types of mechanisms that are currently used in maglev trains: electromagnetic suspension (EMS) and electrodynamic suspension (EDS). In the first system, the train contains a series of electromagnets that generate the magnetic forces used to levitate. In this case those forces are extremely sensible to the distance between the rail and the magnets, so in order to work correctly the electromagnets of the train are electronically controlled and have a special feedback system designed to compensate the forces. The main advantage of this type of levitation is that it works no matter the speed of the train, as opposed to EDS, which does not work at low speeds.
The second way of levitation is the electrodynamic suspension. In this case not only the train exert a magnetic field, but also the tracks, and levitation is achieved with the attraction and repulsion of both fields. While the magnetic field in the train is achieved with magnets, the track acts as an electromagnet to create it. What is the difference? In the latter case, the magnetic field is produced by the effect of passing current, commonly known as electromagnetic induction. The main advantage of this type of levitation is that it does not need the feedback system that EMS does, but on the other hand its disadvantage is that at low speeds the generated magnetic field is not strong enough to levitate the train.
In the case of EDS the tracks need current flowing through it and this leads to other curious physical properties involved in maglev trains. In simple terms the electrical energy is just the flow of electrons from one point to another. As it is commonly known, the electricity needs a conductor so the electrons can flow from one point to another, and a property of the conductors is the resistance they oppose to the moving electrons. What occurs is a loss of electrical power, the same electrical energy that is put into one extreme of the conductor is not the same as the one going out, and this loss is actually transformed into heat. Regarding this loss there has been a lot of research made and it points specifically towards one goal: achieve superconductivity. As was stated before, each conductive material has an inherent resistance, which describes how much of the current that passes remains there. What is described as superconductivity is achieved when the resistance of a conductor equal to zero, which also equals to a zero loss of electrical current. As of today this still remains an objective for scientists, since there is no material that in normal conditions behaves in this way, although it is possible to make certain materials superconductive by lowering their temperatures near to absolute zero and applying also a magnetic field to them to reduce certain internal forces.
It is evident that if the electrodynamic suspension system of certain maglev trains need a current to pass through the tracks, they also need a power supply for this electrical energy. Since trains are intended to cover large distances and the passing of electrical current along the tracks is what generates the electromagnetic field, hence the importance of superconductors when talking about maglev trains. Be it electromagnetic suspension or electrodynamic suspension, both mechanisms share the same principle of moving trains though levitation. This type of movement has not only speed as a benefit, but also an economical one. Since there is no more friction between wheels and rails there is no need to replace them. All the pieces that constantly wear out because of movement in traditional trains are not present in maglev trains. If the magnetic levitation trains have all this advantages, how come they are not more widely uses? Well, one of the main reasons they are still outside of the mainstream transportation is incompatibility, as it is not possible to simply “upgrade” a current railroad system to turn it into a maglev network. The trains, the tracks, the power supply and everything is drastically different.
In order to change a traditional train line to a maglev one it has to be totally replaced. Nowadays there are many countries that have maglev trains, like Japan and China, and many more have plans to develop systems which use them. But, although there seems to be a lot of benefits for this form of transportation the question still remains, will they ever become mainstream?
Will the glory of the steam transportation machines ever return in the form of maglev trains? Even when the scientific logic point towards this direction, there are always other factors that matter even more in the world scenario: the usage of coal as fuel, the skills of the conductors of traditional trains, the whole structure and infrastructure of railway companies, you name it. Maybe we don’t have flying cars as of today, but we do have levitational trains, and they may or not be the future of land transportation.
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Templeton, G. 2015. “What are superconductors, and when will we all get maglev trains and unlimited electrical power?” in Extreme Tech.
Available at: https://www.extremetech.com/extreme/208651-what-is-superconductivity
Bonsor, K. “How Maglev Trains Work” in How Stuff Works.
Available at: https://science.howstuffworks.com/transport/engines-equipment/maglev-train.htm
Kingsland, P. 2018. “Will maglev ever become mainstream?” in Railway Technology. Available at: https://www.railway-technology.com/features/will-maglev-ever-become-mainstream/
Wikipedia, 2018. Maglev. Available at: https://en.wikipedia.org/wiki/Maglev