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article imageTiny device generates energy from low-frequency vibrations

To get around the time consuming task of changing batteries on arrays of wireless electronic sensors, MIT researchers innovated a tiny device that harvests energy from low-frequency ambient vibrations, such as those traveling along bridges and pipelines.
The U.S. quarter-sized energy harvester is an ultra-sensitive, new microelectromechanical systems (MEMS) design, constructed of the synthetic piezoelectric ceramic perovskite material lead zirconate titanate (PZT) that accumulates an electrical charge in response to pressure (like naturally occurring piezoelectric materials such as quartz crystals), and is capable of detecting a wider range of vibrations than earlier cantilever-based small energy harvesters, allowing it to generate about 100 times the power, according to MIT News, reporting on the research team's paper about the project, that was published in Applied Physics Letters:
MIT mechanical engineering professor Sang-Gook Kim explained, "There are wireless sensors widely available, but there is no supportive power package. I think our vibrational-energy harvesters are a solution for that."
Other research groups have worked with a cantilever energy harvester design, consisting of a small microchip with layers of PZT glued to the top of a cantilever beam that builds an electric charge by wobbling up and down in response to vibrations -- but vibrations outside the optimum frequency of the beam generate less power.
Co-author Arman Hajati described the problem: "In the lab, you can move and shake the devices at the frequencies you want, and it works. But in reality, the source of vibration is not constant, and you get very little power if the frequency is not what you were expecting." But using more cantilevers and PZT layers to address this shortcoming through a "power in numbers" approach is wasteful, and too expensive, when a single-layer MEMS device would cost less than $1, the researchers claimed.
Instead, according to MIT's report, Kim and Hajati used a bridge-like structure anchored to the microchip at both ends, covered with a single layer of PZT, a new design that increases the bandwidth, or frequency range, of the device, and maximizes the amount of energy generated by the device per square centimeter, or its power density.
When the team tested the new device, they found it could respond to a wide range low frequencies, and calculated it could generate 45 microwatts of power -- two orders of magnitude of improvement over most cantilevered designs at a fraction of the cost, MIT News reported.
Other research groups have designed traffic-powered wireless bridge sensors, mini-generators powered by random environmental vibrations, mini-power-plants for aircraft and human-gait-powered chargers for portable electronics, ScienceDaily reported.
More about MIT piezoelectric energy harvesting, piezoelectric energy harvesting, power from small vibrations, device harvests energy from small vibration, Energy generation
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