Scientists in Germany have created two new devices that can generate power from walking. The "shock harvester" generates power from the striking of a person's heel off the ground, while the "swing harvester" produces energy from the swinging motion of the foot as walking takes place.

The devices, described in the journal Smart Materials and Structures, fit into the sole of a shoe and can be used, their inventors say, to power wearable electronics. They've already been used to power a temperature sensor in a shoe and send the readings to a device 10m away. 

Each step that was taken generated enough power to allow seven temperature transmissions. Both devices create voltage and current when a moving magnet passes a stationary coil.

“The devices have been developed as parts of projects with specific applications in mind," said the paper's lead author Klevis Ylli, from the Hahn-Schickard-Gesellschaft Institute for Micromachining and Information Technology. "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.”

The “swing harvester” is 41mm wide and 70mm long and can generate an average power output of 0.84 mW. The “shock harvester” had a width and length of 40mm and 60mm 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.

The full paper can be accessed here: http://iopscience.iop.org/0964-1726/24/2/025029