Piezoelectricity Of The PVDF Based Composite Films And Its Applications In Small Energy Collection

With the development of integrated circuit technology and the improvement of the efficiency of energy harvesting using piezoelectric materials,it has become possible for low-energy-consumption devices such as wireless sensors to be self-powered by collecting energy from surrounding environment.Compared with the conventional power supply method,energy harvesting by piezoelectric devices has many advantages like convenient installation,free maintenance and environment-friendly etc.In this research,nano-silicon dioxide/polyvinylidene fluoride?SiO₂/PVDF?composites were fabricated.Their piezoelectric properties were studied through energy harvesting experiment.The main work are as follows:?1?In order to improve the piezoelectricity of the PVDF film,a unique process was developed to make piezoelectric film samples.According to this process,nano-SiO₂ particles are added into the PVDF matrix during the solution casting process.The SiO₂/PVDF film is stretched uniaxially at high elongation rate to increase the amount of?-phase in the composite,and then it is polarized at high voltage after being coated with conductive silver paste which performs as electrodes.?2?A series of tests were conducted to investigate the performance of the piezoelectric composite films using a cantilever beam system.The energy harvesting capacity of the energy converter was also analyzed.The results show that the loading of the nano-SiO₂ particles can significantly improve the piezoelectric properties of the PVDF composite.In general,more nano-SiO₂results in higher piezoelectricity.However,when the weight fraction of the nano-SiO₂ particles is greater than 2%,the performance improvement approaches the upper bound gradually.The beam's vibration frequency also has influence on the piezoelectric properties of the composite.?3?An energy harvesting system based on cantilever-piezoelectric film was set up.The energy conversion capability of the system was evaluated by charging a capacitor using the rectifier circuit.The influences of the content of nano-SiO₂particles and the vibration frequency of the cantilever on the energy harvesting capability of the SiO₂/PVDF films were analyzed.Experimental results indicate that more nano-SiO₂ particles and higher vibration frequency are both helpful to increase the open circuit voltage significantly.In addition,the maximum charging efficiency is higher when charging a capacitor with small capacitance.The SiO₂/PVDF composite is a type of flexible material,therefore it may have great potential to be applied to small energy harvesting and self-powered wearable devices.