Piezoelectric energy harvesting from floor using wounded PVDF films

Energy harvesters of PVDF can be used to power small electrical loads or wireless sensor systems. Simple technologies are sufficient for the fabrication of these harvesting modules. Critical process step is the polarization of the piezoelectric material. Main piezoelectric parameters depend strongly on the polarization material. Particularly, the electric field strength and the polarization temperature influence the remanent polarization of PVDF. Dielectric breakdowns of the film at higher temperatures prevent a sufficient polarization. At least, all modules were polarized at a field strength of 100 – 120 MV/m and a temperature of 90°C.

Modules with dimensions of 165mm × 95mm × 1.5mm were used to power a commercial available “development kit for Energy Harvesting Wireless systems” (EnOcean ‘EDK 300’). The modules possess of 20 layers of PVDF. Each module was connected via a standard four diode full rectifier bridge with the development kit EDK 300. Positioned underneath a parquet floor (thickness=10mm), the modules converted mechanical energy of footsteps into electricity. Goal of these investigations were to find out configurations suited to generate a sufficient energy level to supply the operation of the EDK 300. Two capacitors in the development kit are used to start the operation of the kit (C₁=470μF) and to store converted energy (C₂=0.25F). Already a few steps onto one module were sufficient to charge C₁ and to start the operation of the EDK 300. Following steps (>100) produced energy which was stored in C₂.