Power Bites: Personal Power

Got a little brother with energy to spare? Maybe he could drive your CD player instead of driving you nuts! New inventions that convert human power into electricity make that notion a very real possibility.

Think about walking or jogging. The pressure of your foot striking the pavement is a form of mechanical energy. Several engineering groups are successfully building “heel-strike” mechanisms that will capture that mechanical energy and convert it into electrical energy. The key to this technology? Electroactive polymers. These human-made plastics generate an electric charge when they are compressed or bent. When placed inside the heel of a boot or shoe, electroactive materials become power generators as each step stretches and squashes them into performance.

Making these electricity generators function inside the boot heels of soldiers is the aim of engineers at SRI International in Palo Alto, CA, and at the Massachusetts Institute of Technology (MIT) in Cambridge, MA. The trick has been to develop a durable material capable of sufficient energy output that can be electronically interfaced with the devices needing power. SRI International has created a rugged electricity-generating material that meets these needs. When engineered into boot heels, the system is expected to generate enough electricity from eight hours of walking to power the wearer's communication device, GPS (global positioning system), and night vision goggles. Engineers at MIT are working on their own microscale version of an energy-harvesting system. It uses a mini-hydraulic mechanism to collect energy from foot pressure. This mechanism then supplies the degree of pressure needed to activate an electroactive material with high electrical output.

Both the SRI International and the MIT boot generators are months away from field-testing, but prospects look good. This new technology will eliminate batteries, lighten pack loads, and extend power availability. Not to mention—maybe?—be applied to little brothers with excess energy!


Of, involving, moved by, or operated by a fluid, especially water, under pressure.

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  1. What has been one of the challenges facing researchers developing uses for electroactive polymers?
    [anno: Answers may vary but could include that developing an electroactive polymer that is durable enough to withstand the repeated pressures from walking while still generating enough energy.]
  2. Researchers are hoping to develop these materials and eliminate battery packs. If an electroactive polymer in a boot heel is collecting energy to power personal devices, how would the devices get the power? Think about what you learned about circuits in Lesson 2. Draw a diagram that shows a person wearing a pair of boots with electroactive polymers in the heels. The person wants to power a GPS unit worn on the belt. How would the boots power the GPS unit? Show how the energy would flow in this circuit. Label the power source, conductor, and the object using the current.
    [anno: Diagrams will vary but should show a device in the boot labeled as the power source, a wire running between the boot and the GPS unit labeled as the conductor, and the GPS unit as the object using the current.]