The quarter-sized device mounted on a platform  (Source: Arman Hajati)
The new microchip has a bridge-like structure that's attached to the chip on each end with only a single layer of PZT added

MIT researchers have developed a microelectromechanical system (MEMS) the size of a U.S. quarter that is capable of harvesting energy from low-frequency vibrations. 

Sang-Gook Kim, study leader and professor of mechanical engineering at MIT, and Arman Hajati, co-author and Ph.D student at MIT, have created a microchip with an increased frequency range and power density that can draw power from vibrations like humming machinery and foot traffic.

While wireless sensor networks have a myriad of potential, from tracking environmental pollution to monitoring activity along an oil pipeline, the technology is limited by its energy consumption. A wireless sensor’s batteries need to be changed occasionally, and replacing these batteries can be difficult. 

Harvesting energy from 
environmental vibrations is not new, but current techniques can be problematic. For instance, many scientists have used a small microchip with layers of piezoelectric materials (PZT) (which naturally accumulate electric charge due to mechanical stress) glued to the top of a small cantilever beam. When the chip is exposed to vibrations, the beam moves vertically up and down, which stresses the PZT layers and builds up an electric charge. 

The problem with the cantilever approach is that the beam has a resonant frequency, which means a particular frequency where it moves the most, and outside of this frequency, the movement "drops off" along with the power generated. Scientists have attempted to fix this problem simply with more cantilever beams and PZT layers, but this can be expensive and wasteful.

Now, Kim and Hajati have developed a 
new design that addresses these issues. They've designed a microchip with a bridge-like structure that's attached to the chip on each end. A single layer of PZT is then added to the bridge with a small weight in the middle of it. When tested, the researchers found that their new device was able to respond to a variety of different frequencies. Also, it was able to generate 45 microwatts of power with only one layer of PZT. 

"Our target is at least 100 microwatts, and that's what all the electronics guys are asking us to get to," said Hajati. "For monitoring a pipeline, if you generate 100 microwatts, you can power a network of smart sensors that can talk forever with each other using this system."

"It seems as though my state-funded math degree has failed me. Let the lashings commence." -- DailyTech Editor-in-Chief Kristopher Kubicki

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