Piezoelectric energy harvesting from human movement: exploiting foot swing excitations

Piezoelectric materials are capable of converting energy from mechanical vibration to electrical energy. Piezoelectricity stands for pressure electricity and is a property of special crystalline materials including quartz, Rochelle salt, tourmaline, and barium titanate 1 .Piezoelectricity is generated when dielectric materials that have developed a polarization are subjected to mechanical strain deformation. The mechanical strain produces a biasing forcer arrangement of atoms there by creating polarization and thus an electric field 2-3. Conversely, when a piezoelectric material is subjected to an electric field, it will cause a mechanical deformation with in its structure. In both conditions, changing the direction of the applied force, (mechanical or electrical), will generate a change in the direction of the effect 2-3. Harvesting mechanical energy from human motion is an attractive approach for obtaining clean and sustainable electric energy to power wearable sensors, which are widely used for health monitoring, activity recognition, gait analysis and so on. This research studies a piezoelectric energy harvester to convert mechanical energy to electricity using human motions. The harvester exploits walking swing and shock excitations and could be embedded to the shoe. Series of magnets can amplify the foot acceleration in swing phase. The harvester contains a cantilever beam that can vibrate based on foot acceleration and magnetic excitation. Two MFC materials are attached to the beam in parallel to increase the current. The maximum voltage of 50 V AC can be generated in resonance frequency that it could be converted to the DC by using bridge circuit to save in the capacitors or batteries.