Electromechanical and Electronic Integrated Harvester for Shoes Application

Energy harvesting allows making sensors or transmitters electrically autonomous. Several studies have been proposed but most cases lack electrical and mechanical parts integration and practical application purpose. Here, with the aim of supplying a Bluetooth step-counter placed in the sole of a training shoe, a complete system is presented. It consists of amagnetoinductive transducer embedded with an electronic interface for power conditioning and exploits only the energy recovered by the impact on the ground. A phi 27 x 16 mm cylindrical device containing the transducer, the electronic interface, the step-counter electronics, and the protective shell is developed. Energy recovery derives from the magnet-free oscillation following the shoe impact. The proposed interface exploits pulse-width modulation to perform transducer output rectification and to emulate optimal load impedance while charging a storage capacitor. Numerical and experimental analysis show effective optimal resistive load emulation and energy recovery gain of 2 compared with the standard ac-dc interface. Prototypes have been manufactured and tested. Considering a sample footstep, energy recovery is 360 mu J against 400 mu J dissipated on optimal resistor. Mean energy recovery over a complete run is 644 mu J/footstep. In spite of variable excitation, energy recovery at each footstep is larger than the required and allows the step-counter transmitting the information.