Power S
ince ancient times, we’ve been trying to harness ‘free’ energy, perhaps starting with sailboats, then windmills, water- powered mills and, more recently, items
such as solar cells, geothermal heating and even self-winding watches. These days, two large trends are colliding to take the concept of ‘energy harvesting’ to new extremes: our ability to harvest energy – whether from the sun, vibrations, thermal differences or even RF energy in the air – using small-scale devices such as those based on MEMS has improved tremendously; on the other hand, we’ve developed systems that require very little energy to operate. Scientific software and
36 SCIENTIFIC COMPUTING WORLD
from thin air
Researchers have come up with ever more efficient ways of tapping the free energy that surrounds us, whether from heat, light, vibrations or radio waves. Paul Schreier examines some of the advances being made
Network, which is funded by the UK EPSRC (Engineering and Physical Sciences Research Council). The presentations are available online at
http://eh-network.org/events/ dissemination2011.php and provide a good beginning resource for anyone looking for detailed information on this subject beyond the overview in this article.
Energy in motion One of the oldest mechanisms for harvesting energy is motion. These days, small power generators using vibrations are becoming popular, especially in industrial settings with large machinery, but also even from an automobile or a person moving. Mains- powered machines, though, make an excellent vibration source because they have a repeatable frequency component. This is important because all vibrational energy harvesters are in essence a mass/spring- tuned resonator. The device’s resonant frequency is tuned to match that of the source to produce the maximum amount of displacement in the mass/spring structure and thus maximum power output. A large supplier of such devices is
Perpetuum Ltd, in Southampton, UK. Rather than taking the traditional approach of having an oscillating mass traverse a stationary magnetic field, that company moves the magnetic structure, which has more mass, and keeps the coil fixed. As a result, its PMG FSH unit (Fig. 1) charges an external storage device with up to four mA at 5V. All this is done in a can-shaped unit with a diameter of 68mm and a height of 63mm. Compared to other devices in this article,
Fig. 1: A wireless sensor node from Pruftechnik performing conditioned monitoring powered by a Perpetuum vibrational energy harvester at a Yorkshire Water waste-treatment plant
computer-aided tools have provided valuable help in developing these systems. Today, the most widespread application
for energy harvesters is self-powered wireless sensors in industrial processes. Because there’s never a need to replace batteries in such devices, a network of self-powered sensors produces immediate benefits, including the avoidance of costly wiring and deployment in inaccessible locations, not to speak of lower maintenance costs. Some very interesting findings and trends
along these lines were presented just last February in London at the first information event conducted by the Energy Harvesting
this one is somewhat large, but it also has a larger power rating. Company president Roy Freeland says they could achieve more power in a given volume with a denser proof mass such as tungsten; he adds that their devices are already close to the theoretical maximum efficiency. However, they are finding that their harvesters produce more than enough power for many applications and have plans for smaller versions. Meanwhile, with its Insight Mesh unit, GE Bentley uses one harvester to power four sensors whereas the first version used one for each sensor. Taking motion-to-energy almost to the
other extreme is the ECO 100 from EnOcean GmbH. It is intended for switches that control lights or HVAC systems. Here, the mere process of pushing the switch generates between 150 to 250µJ of energy, sufficient to read a switch’s position and send information about which button was pushed to a remote control unit that then performs the desired action. When used indoors, the
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