Good vibrations for railways
Originally published on TrackTalk [December 2015]
Brian Wilson and the Beach Boys might have sung about Good Vibrations in 1964, but for railways, and their neighbours, vibrations are usually anything but good.
Vibrations in the railway environment are induced by interactive forces at the wheel-rail interface, which cause track components like rails and sleepers to move and transmit vibrations, or Rayleigh waves, into the ground.
The length of these waves varies depending on the type of train; freight trains travelling at low speeds generate low frequencies, while passenger trains which tend to travel faster usually emit higher frequency waves, which are more likely to impact nearby buildings and people.
Despite the best efforts of researchers and railways to mitigate these problems, the phenomenon persists. But what if there is a way to use these vibrations for good?
Bell Labs is attempting to do exactly this through a process known as vibration energy harvesting, which involves converting vibrations from everyday environments into electricity.
This technique utilises electromagnetic induction and the principles of momentum conservation and velocity amplification. Current commercial applications use a single magnet moving up and down a coil to generate electricity, which is known as a one-mass system where the power generated is proportional to the square of the velocity of the magnet. However, Bell Labs has taken this a step further.
“What we have invented is an entirely novel technique that uses multiple masses, or multiple magnets,” says Dr Domhnail Hernon, head of the Efficient Energy Transfer Department at Bell Labs. “We can substantially increase the velocity of the magnet moving within that coil, which means we can substantially increase the amount of energy we can convert from the local vibrations into useful energy.”
In its simplest form, in a single mass system the velocity of dropping a ball after impact is dependent on the height from which it is dropped. However, by introducing multiple masses of varying velocities the ball will rebound after impact at a speed not visible with the naked eye.
So how might this technology apply to the rail environment?
In theory with extensive vibrations from passing trains and passengers walking at busy stations the potential for this application is significant. However, any deployment needs to be realistic: it should avoid using copper cables to collect the energy and modify the existing rail infrastructure.
Bell Labs’ solution is a battery-sized application which is straightforward to apply and is able to feed autonomous equipment with energy, meaning that next-generation radio sensors and other communications devices could all be powered by energy harvesters. “This is what we’re looking to commercialise and bring to the network of 2020,” Hernon says.
While discussions are underway about licensing and introducing this application, some researchers are taking it a step further.
By incorporating it into micro-electro mechanical (MEM) chipsets, which can utilise the same principles and technology, but are 0.02-1mm in size, they are on the verge of revolutionising how we power infrastructure. Indeed we may soon be deploying these sensors, and M2M technology, almost anywhere that we can feel Good Vibrations.