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posted by janrinok on Sunday July 21 2019, @12:22PM   Printer-friendly
from the just-what-we-knee'd dept.

The group describes the technology in Applied Physics Letters, from AIP Publishing. An energy harvester is attached to the wearer's knee and can generate 1.6 microwatts of power while the wearer walks without any increase in effort. The energy is enough to power small electronics like health monitoring equipment and GPS devices.

"Self-powered GPS devices will attract the attention of climbers and mountaineers," said author Wei-Hsin Liao, professor in the department of mechanical and automation engineering.

The researchers used a special smart macrofiber material, which generates energy from any sort of bending it experiences, to create a slider-crank mechanism -- similar to what drives a motor. The authors chose to attach the device to the knee due to the knee joint's large range of motion, compared to most other human joints. "These harvesters can harvest energy directly from large deformations," Liao said.

Due to the continuous back-and-forth the material will encounter when the wearer walks, every time the knee flexes, the device bends and generates electricity. This means the harvester can "capture biomechanical energy through the natural motion of the human knee," according to Liao. Previous wearable energy harvesters took advantage of the vibration caused in the device as a result of motion, which comes with drawbacks regarding efficiency.

"The frequency of human walking is quite slow, which significantly decreases the energy-harvesting capability," Liao said. Because the group's device uses a different method, it bypasses this limitation.

The prototype weighs only 307 grams (0.68 pounds) and was tested on human subjects walking at speeds from 2 to 6.5 kilometers per hour (about 1 to 4 miles per hour). The researchers compared the wearers' breathing patterns with and without the device and determined that the energy required to walk was unchanged, meaning that the device is generating power at no cost to the human.

[...] The article, "Macro fiber composite-based energy harvester for human knee," is authored by Fei Gao, Gaoyu Liu, Brendon Lik Hang Chung, Hugo H. Chan and Wei-Hsin Liao. The article appeared in Applied Physics Letters on July 16, 2019 (DOI: 10.1063/1.5098962) and can be accessed at http://aip.scitation.org/doi/full/10.1063/1.5098962.


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  • (Score: 3, Interesting) by RamiK on Sunday July 21 2019, @02:01PM (2 children)

    by RamiK (1813) on Sunday July 21 2019, @02:01PM (#869632)

    300 grams "at no cost to the human"? They measured it, right?

    Being a macrofiber likely means it's designed to substitute the pants' knee area so as long as it weights about the same as jeans inch-for-inch and doesn't introduce significant resistance, it won't matter.

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  • (Score: 2) by JoeMerchant on Sunday July 21 2019, @04:24PM

    by JoeMerchant (3937) on Sunday July 21 2019, @04:24PM (#869656)

    The reason it doesn't generate significant resistance is because it doesn't generate significant power.

    Ordinary pants take more than 1.6 microwatts to deform while you're walking, not a shock that you could extract that much power from bending piezo elements, or whatever they're using.

    We looked at "zero power" solutions for implantable device sensors - one I developed a small way was a piezo element that could wake the microprocessor when the patient "taps" on the device - the tapping motion would cause a flex in the piezo (springboard with a weight on the end arrangement), which created enough voltage to trigger a wakeup of the MSP430. When not being activated: zero power draw. There wasn't enough potential energy in the piezo springboards of ~2004 to make it worthwhile trying to extract operation energy from them while encased inside a titanium shell, but if that same piezo material was applied across a joint like the knee, it certainly could light LEDs while you walk.

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  • (Score: 2) by legont on Sunday July 21 2019, @05:01PM

    by legont (4179) on Sunday July 21 2019, @05:01PM (#869666)

    Yeah, mountaineers climb wearing jeans.

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