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