Researchers in Germany have taken a significant step towards harnessing the energy that is generated through walking by engineering two separate devices that can generate power from specific aspects of the human walking gait.
Presenting their results today, 15 January, in IOP Publishing’s journal Smart Materials and Structures, the researchers have created a “shock harvester” device that generates power when the heel of a shoe strikes the ground and a “swing harvester” device that generates power when the foot is swinging.
Both devices can fit comfortably into the sole of an ordinary shoe and have been designed to power a pair of next-generation, wearable electronics. It is hoped the devices can put an end to the constant replacement and disposal of batteries, which is not only costly but potentially damaging to the environment.
Lead author of the paper Klevis Ylli, from the Hahn-Schickard-Gesellschaft Institute for Micromachining and Information Technology, said: “The devices have been developed as parts of projects with specific applications in mind. The shock harvester was developed to charge the battery of an indoor navigation system and increase its operating life.
“The swing harvester was developed as part of a self-lacing shoe for the elderly. The shoe would detect when a user steps into it and lace itself up, as well as open up again when required. The harvesting device would generate the energy for the closing mechanism.”
Both energy harvesting devices generate power by exploiting the motion between magnets and coils. As the magnetic field of a moving magnet passes by a stationary coil, a voltage is induced and an electric current is generated.
In the “swing harvester” device, the swinging of the foot accelerates a stack of 14 magnets through a set of coils. The “shock harvester” device is placed in the heel of a shoe and when it strikes the ground a spring-loaded set of magnets begins to vibrate.
The “swing harvester” is 41 mm wide and 70 mm long and can generate an average power output of 0.84 mW. The “shock harvester” had a width and length of 40 mm and 60 mm respectively and has been able to generate a maximum of 4.13 mW of power when a test subject was travelling at 5 km/h on solid ground.
Both of the energy harvesters were used to power a temperature sensor in a shoe. The harvesters were able to generate enough power for the temperature readings to be wirelessly transmitted over 10 m to a handheld device and could send up to seven transmissions for each step that was taken.
Going forward, the researchers plan to develop the devices further by testing them on a larger set of subjects and optimising the device parameters to fully capitalise on the large amount of power generated by the human walking gait.