Trains’ vibrations could provide power for monitoring tunnels

Aug 08, 2011 by Lisa Zyga feature
The power unit at the railway sleepers/ties in the Lotschbergbasis-tunnel in Switzerland can harvest enough energy to power wireless sensor nodes with a radio frequency interface. Image credit: M. Wischke, IMTEK

(PhysOrg.com) -- Traffic tunnels are often built in some of the most rugged and remote areas, which subjects them to extreme environmental forces while making them difficult to access. Ideally, the structural health of tunnels could be monitored in a way that requires minimal human maintenance while ensuring that the tunnels are consistently safe to drive through.

In a typical monitoring system, an array of sensors placed throughout the tunnel or other structure provides continuous monitoring, giving an early warning sign of any problems, such as damage due to corrosion or impact. When batteries are used to power the sensor arrays, replacing the batteries becomes an expensive and time-consuming endeavor.

With this drawback in mind, researchers are developing a power unit that harvests the vibrations from passing traffic to power the nodes of a structural health for tunnels. The power harvesting unit could reduce maintenance costs and improve the performance of the .

The researchers, Martin Wischke and coauthors from the University of Freiburg in Germany, have published their study on the new power supply concept for monitoring systems in a recent issue of . The study is part of the AISIS project funded by the Federal Ministry of Education and Research.

“[Currently,] railway tunnels feature very few structural health monitoring devices,” Wischke told PhysOrg.com. “Our system can be easily mounted to any tunnel, whether it is a new building or an old one. The installation of the is quite easy, flexible, and time- and cost-effective, which are advantageous attributes compared to wired monitoring systems. Thus, our system is especially suited for refitting and upgrading older tunnels to improve security.”

When the researchers first started investigating the use of vibrations from passing vehicles as an energy source, they found that no detailed data on the vibrations in traffic tunnels was available. So to begin, they investigated the vibrations in two tunnels: the Pfander-tunnel, a road traffic tunnel near Bregenz, Austria; and the Lotschbergbasis-tunnel, a high-speed train tunnel in Switzerland. They placed acceleration sensors in both tunnels to measure the vibrations from passing traffic. In the road tunnel, the sensors were monitored for a 3-5-minute period every hour, while each passing train was monitored in the train tunnel (more than 500 trains total).

When analyzing the vibrations, the researchers found that they could determine which acceleration signals represented cars and which signals represented trucks in the road tunnel. In the train tunnel, they could determine each train’s structure, such as the number of axles and the wagon sizes. They could also identify passenger trains based on their smaller accelerations, which are a result of better wheels and suspensions to improve passenger comfort.

In terms of usable energy, the researchers found that only the vibrations in the train tunnel were sufficient for harvesting; vibrations at various locations along the road tunnel were too small to be useful due to vehicles’ suspensions and pneumatic tires. While the vibrations in the train tunnel were strongest directly on the railroad track, the researchers decided to forego mounting a harvester on the rail because screw holes pose problems, such as causing cracks. Instead, the researchers mounted vibration harvesters on the railroad sleepers/ties due to the larger space and easier access, even though the vibration amplitudes are smaller there than at the rail.

The researchers then designed, fabricated, and tested a piezoelectric vibration harvester capable of harvesting vibrations across a broad frequency, since each train produces a slightly different frequency spectrum. The energy is then stored in a capacitor and supplied to the sensor system when needed. In order to ensure safe handling of the harvested energy, the researchers designed an ultra-low power control circuit that monitors the storage capacitor voltage and disconnects the sensor circuit from the capacitor if not enough energy is available. While other power control circuits exist that consume several microwatts to operate, the new circuit’s simple design enables it to run on a current of just 70 nA.

In the future, the researchers plan to make some improvements to the system, including expanding the harvested frequency spectrum and increasing the power output, and then prepare the system for industrial applications. In addition to energy harvesting, the system could be used in railway traffic surveillance, since details about the passing train (such as the quality of the wagon wheels and wagon weight) can be derived from the vibrations.

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More information: M. Wischke, et al. “Vibration harvesting in traffic tunnels to power wireless sensor nodes.” Smart Mater. Struct. 20 (2011) 085014 (8pp). DOI:10.1088/0964-1726/20/8/085014

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TheJonalist
not rated yet Aug 09, 2011
Why must the unit be exposed to the visible surface of rails? Wouldn't safety define a better location as being fused to the rails underneath surface in a waterproof container that can be serviced over time? Has the researchers done further experimentation in which a automotive application for placement of a device inside the wheels affixed to the hub or even the shock assembly, be considered a valued power generation potential? Ford Motor Company did not include a Power Generation Shock Absorbers to their new Electric Car, all they say is that they have braking power generation capability. I also consider the potential of rocks and debris hitting a surface under a vehicle to create power, this could create a monitoring capability as well to determine the safety of roadways in consideration to the amount of debris which is present allowing highway studies to conclude whether to upgrade the roadway or to wait for further analysis when the debris reaches a certain level, plus Airports.
antialias_physorg
not rated yet Aug 11, 2011
Why must the unit be exposed to the visible surface of rails? Wouldn't safety define a better location as being fused to the rails underneath surface in a waterproof container that can be serviced over time?

Since the rails are already present such placement would be very expensive. Putting the senosrs on the railway sleepers is very cheap (and since we're talking about the monitoring of tunnels weather effects should be minimal and there should be litle chance of water damage)

Has the researchers done further experimentation in which a automotive application

No. Otherwise they'd have published that. The power generating capacity for piezoelectrics there is minimal. When considering the viability of power generation two things have to be taken into account: magnitude and frequency (in addition to cost). E.g.: The frequency of stuff hitting the underside of a car is very low - as is the energy transmitted.
bobtrain
not rated yet Aug 16, 2011
As the rail tunnels are electrified, why would batteries even be considered. Induction currents should be available to power anything.
Jim1138
not rated yet Aug 17, 2011
How about an RFID type of device? A transmitter on the leading car or engine to power up the device and a second transmitter on the last car to read back the data. Nothing would need to be attached to the rail or sleeper.

No reason why a device could not be bonded with adhesive to the underside of the rail. Could use a clip to hold the device in place while the adhesive cures. An automated installer could be used if speed is important.

bobtrain: getting power from the high-voltage catenary for use in a miniature low-voltage device would be problematic as well as hazardous to anyone in the tunnel. Getting energy from the very low-voltage, high-current in the rail would be difficult for a strap-on device. You would not want to interrupt the circuit.

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