German researchers have built two devices that can fit in a shoe and harvest energy from the act of walking.
The devices were designed with wearable electronics in mind hoping to replace batteries and the constant need to charge them. The 'shock harvester' generates power when the heel strikes the ground and the 'swing harvester' creates energy when the foot swings.
The results were presented in the journal Smart Materials and Structures and the prototypes could be the basis for other devices such as a self-lacing shoe for the elderly, according to researchers.
“The devices have been developed as parts of projects with specific applications in mind,” said lead author Klevis Ylli from HSG-IMIT, a research centre in Villingen-Schwenningen, Germany.
“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.
The amount of energy that can be generated is rather small, ranging from one to four milliWatt (mW) when a test subject is travelling at 5km/h on solid ground.
Although it couldn't produce enough energy to charge a smartphone, which would normally require 2,000mW, the devices open up new possibilities for sensors and other devices.