London: A team of German researchers has built shoe-sized devices to harvest power from the act of walking that can be used to power wearable electronic sensors without the need for batteries.
Two separate devices have been developed, a "shock harvester" that generates power when the heel strikes the ground and a "swing harvester" that produces power when the foot is swinging, the BBC reported.
Klevis Ylli from HSG-IMIT said that they have tried to power a wireless transmitter and to power a simple sensor. One application they are working on is indoor navigation which means they have sensors within the shoe that measure the acceleration of the foot, the angular velocity and the magnetic field.
Ylli added that from the data from these sensors, people could calculate how far they have travelled and in which direction.
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.
Ylli continued that the energy they generate is still relatively small, in the three to four milliWatt (mW) range at their peak and this generated power scales with size, but if people want to be able to reasonably integrate such a device within a shoe sole, they have to work with strict constraints, like a small height and limited length of the device.
He concluded that they believe they have built comparatively small devices, considering the power output.
He said the swing harvester was developed with the intention of making a self-lacing shoe for the elderly. The shoe would detect when a user stepped 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.
The study is published in the journal Smart Materials and Structures.