Piezoelectric backpack straps are harvesting otherwise-wasted, ambient energy and converting it into electrical energy that can power or recharge portable electronic devices.
Mechanical engineers Jonathan Granstrom and Joel Feenstra from Michigan Technological University, Henry Sodano from Arizona State University, and Kevin Farinholt from NanoSonic, Inc have designed a backpack with straps that will capture the energy generated by the movement of a hiker's backpack and turn it into enough voltage to power small electrical devices.
The straps operate in the same way as a traditional backpack but are made of polyvinylidene fluoride (PVDF), a strong, flexible material that feels very similar to nylon. This material is piezoelectric and contains embedded electrodes to harvest the energy produced by the friction of the straps rubbing on the wearer's shoulders and this energy can be stored in a battery or capacitor.
The backpack would be able to power devices that require small amounts of energy such as a GPS unit, or a hiker could charge up a headlamp or handheld computer whilst walking during the day and use these devices at night.
"In general, we want to accumulate the power before using it; for example you could walk for 20 minutes then have enough power to talk for 2.5 minutes on your cell phone," Sodano says.
Someone shouldering a heavy pack, such as a soldier in the field, could generate 45.6 milliwatts of power walking two or three miles per hour. That's enough wattage to power small electronics - or, it could be accumulated for later use without the need to carry spare batteries, thus lightening a soldier's load.
With the overabundance of personal electronics in everyday life, the energy harvesting backpack will have many uses from hiking backpacks, school backpacks or travel luggage to use by soldiers.
Top Image: Energy harvesting backpack. (Source: Physorg)
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