A new energy harvesting device converts low-frequency vibrations into electricity. The device, the size of a U.S. quarter, is shown mounted on a stand. Photo: Arman Hajati via MIT
While the concept of gathering energy from small vibrations is not new and has been in use for some time now, the devices aren't particularly efficient. MIT is changing that, however, with a new tiny energy harvester than can turn a wider range of vibrations into energy, making it 100 times more powerful than similarly sized devices.
MIT reports that in order to find a better solution for charging wireless sensors, researchers came up with a device the size of a US quarter that can harvest energy from low-frequency vibrations. This is perfect for charging wireless sensors on bridges, pipelines, and other structures that need to be monitored but where constant access is difficult or limited.
The device is called a microelectromechanical system, or MEMS, and because of the broad range of vibrations it can pick up, it is far more effective at generating power. The solution comes with a new approach to creating a piezoelectric device.
Various groups have gravitated toward a common energy-harvesting design: a small microchip with layers of PZT glued to the top of a tiny cantilever beam. As the chip is exposed to vibrations, the beam moves up and down like a wobbly diving board, bending and stressing the PZT layers. The stressed material builds up an electric charge, which can be picked up by arrays of tiny electrodes.
However, the cantilever-based approach comes with a significant limitation. The beam itself has a resonant frequency -- a specific frequency at which it wobbles the most. Outside of this frequency, the beam's wobbling response drops off, along with the amount of power that can be generated.
...Instead of taking a cantilever-based approach, the team went a slightly different route, engineering a microchip with a small bridge-like structure that's anchored to the chip at both ends. The researchers deposited a single layer of PZT to the bridge, placing a small weight in the middle of it.
"To get around the power constraint [of wireless devices], researchers are harnessing electricity from low-power sources in the environment, such as vibrations from swaying bridges, humming machinery and rumbling foot traffic. Such natural energy sources could do away with the need for batteries, powering wireless sensors indefinitely," reports MIT.
The device could be created for less than $1 each, which makes it possible to commercialize it and create a complete package of a wireless sensor with a charging package.
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