Millimetre scale energy harvester generates electricity from vibrations

The new device is smaller than a one pence piece and is specifically designed to turn the cyclic motions of factory machines into energy to power wireless sensor networks. "In a tiny amount of space, we've been able to make a device that generates more power for a given input than anything else out there on the market," said Khalil Najafi, one of the system's developers and chair of Electrical and Computer Engineering at the university. "Long lasting power is the greatest hurdle to large scale use of pervasive information gathering sensor networks," he continued. "If we were to look at the ongoing life cycle expenses of operating a wireless sensor, up to 80% of the total cost consists solely of installing and maintaining power wires and continuously monitoring, testing and replacing finite life batteries. Scavenging the energy already present in the environment is an effective solution." To create the device, Najafi and his team built a complete system that integrated a high quality energy harvesting piezoelectric material with the circuitry that made the power accessible. "There are lots of energy sources surrounding us," he explained. "Lightning has a lot of electricity and power, but it's not useful. To be able to use the energy you harvest, you have to store it in a capacitor or battery. We've developed an integrated system with an ultracapacitor that does not need to start out charged." The active part of the harvester that enables the energy conversion occupies just 27 cubic millimetres, according to the researcher. In addition, the packaged system, which includes the power management circuitry, has a bandwidth of 14 Hertz and operates at a vibration frequency of 155 Hertz. "Most of the previous vibration harvesters operated either at very high frequencies or with very narrow bandwidths and this limited their practical applications outside of a laboratory environment," Najafi said. "The new harvester can generate more than 200 microwatts of power when it is exposed to 1.5g vibration amplitude. The harvested energy is processed by an integrated circuitry to charge an ultracapacitor to 1.85V. In theory, these devices could be left in place for 10 or 20 years without regular maintenance. They have a limitless shelf time, since they do not require a pre charged battery or an external power source." With the market for power sources for wireless sensor networks in industrial settings expected to reach $450million by 2015, Najafi believes the technology could have applications in medicine as well as in the automotive industry. "They could be used to power medical implants in people or heat sensors on vehicle motors," he concluded.