Technology Focus series: Vibration based energy harvesters and railways
Last updated: December 2018
What are vibration based energy harvesters?
Vibration based Energy Harvesters (VEH) consist of electromagnetic (EM) and piezoelectric based harvesters (PE), both converting mechanical vibration into electrical energy. PE have high commercial availability while EM can function on lower frequencies with higher current and power levels. The energy acquired by vibrations is often used to power sensors, measuring performance parameters and enabling the management of systems. VEH are often organised in Wireless Sensors Network (WSN) in remotely placed systems with consistent vibration, reasonably fixed frequency and high amplitude. This technology is important because it can acquire data with minimal power, by operating on an event-driven sleep mode.
What industries use them and why?
The aerospace industry uses WSN for helicopters’ health and usage monitoring systems including condition detection, wear features and backlashes. VEH present a feasible solution in helicopters because of the presence of high vibration (consistent with rotor’s RPM) and impracticability of wiring or battery replacement. As a result, allowing reduced maintenance, failure detection and prediction.
The technology is widely used in the construction industry, particularly in monitoring the parametric and structural performance of bridges. The wireless sensor networks offer detailed inspections and long-term monitoring that is autonomous and energy independent. The data acquired can be managed in a cloud-based manner with the help of modelling tools.
How will it impact the rail industry?
The railway industry can use VEH to power sensors located in the infrastructure and the train. This technology can provide vibration-generated energy to power sensors, reducing costs and creating independency from the gridline. VEH can create a wider system by powering more sensors in remote areas, monitor ambient conditions and manage both vehicle-tracking and lightning information. Furthermore, it can reduce maintenance/inspection hours as there is no need to replace batteries or check wiring. Another application of this technology can be in powering wearables, allowing to keep track of the wellbeing of workers.
What is the current state of R&D?
Indian Railways has just introduced the ‘Smart Coach’ train, in which VEH on the axle box will power sensors that can predict defects on tracks, bearings, and wheels.
University of Utah is researching on increasing the power outcome by determining the optimal volume and orientation of crystal structure of different piezoelectric materials. In the future, they intend to increase the efficiency of harvester by incorporating a magnetic component to account for inactive periods.
Contemporary research by Penn State University is assessing the possibility of using VEH to harvest natural vibrational energy from the human body, to power wearable and implantable devices. Recent developments in electronics are made in the fabrication of wireless grain-sized sensors (‘smart dust’) powered by VEH that can be applied inside a wagon to monitor conditions
What uncertainties remain?
The environment’s changing conditions alternate the frequency of vibration, decreasing the reliability of the system. For harvesters to meet energy demands, their natural frequency should be tuned to the trainload dominant frequency. As the number of people or quantity of commodities transported (trainload) changes, tuning might be lost because of speed variability, decreasing the amount of energy harvested.
WSN powered by VEH often demonstrate ‘black box’ behaviour and more explanation is needed to increase usability. For instance, if the data collected is used to diagnose or predict faults, human decision makers should be able to understand the underlying relationships to approve the outcome of the WSN.
What should the rail industry do?
The rail industry should research and consider implementing these sources of power instead of the battery approach to power sensor nodes and track-side electrical infrastructure. Based on the readiness levels and other industry applications, this technology has the potential to decrease dependency on the gridline and create a wider system. Implementing this technology could enable optimum node placement and to creating a network that is fully covering the system.
Moreover, it presents an option of being combined with other power generation methods, creating a more versatile system. In the short term, it can allow more frequent monitoring of vehicles, infrastructure and the wellbeing of workers if wearable technology is implemented. In the long-term future, it is an opportunity to improve safety, reliability, reduce human inspection and to an extent predict faults, bringing the railway closer to its future ambitions of high- speed intelligent trains.