Simulation And Fabrication Of Piezoelectric Energy Harvesting Based On PVDF

With the development of net of thing and wearable device, it’s more and more difficult to use traditional battery as their power supply. At the same time, there is much energy wasted around us, harvesting energy from the environment is becoming realistic. Among the various unused energy, vibration draws the most attention due to its widely spread, high energy density and relative easiness to harvest. Here piezoelectric energy harvester(PEH) was studied in this paper by which mechanical energy was directly transformed into electric energy. Typically, piezoelectric ceramics is adopted in traditional PEH. However, there are some inherent disadvantages such as low toughness, relatively high Young’s modulus, environment pollution and so on. Previous calculation indicates that poly(vinyldene fluoride)(PVDF) is a very promising substitution as the power density is as high as piezoelectric ceramics in resonant mode and higher than piezoelectric ceramics in non-resonant mode. However, up to now the performance of cantilever PVDF PEH is much less than predicted by more than two orders of magnitude. In this paper, we are dedicated to make higher output PVDF PEH.Based on previous work, we firstly conduct a partially coupled analysis on PVDF PEH. By interpreting the piezoelectric equation assuming the cantilever was in harmonic vibration, we got the relation between average output power and excitation amplitude, frequency, external resistive load. As this model is rather simple and ignores a lot of details, a more precise model named couple finite element circuit analysis(CPC-FEM) was introduced. Here finite element software and circuit analysis software were combined together to simulate the performance of PVDF PEH. This detailed analysis was focused on the influence of shape parameters, vibration source and external resistive load. Further analysis and discussion was conducted based on the result and we found that the output performance was only limited by resonant frequency and PVDF allowance stress, irrelevant of vibration acceleration and other shape parameter. Besides there is a series of optimum T/L2 values when vibration source and maximum PVDF allowance stress are given, and this optimization process is to increase the maximum stress in PVDF by nature.Based on this theory, we fabricated two PVDF PEH devices. One is the prototype device with 5.2mm × 20 mm × 3.1mm in dimension; the other is optimized device with 5.2mm × 20 mm × 6.1mm in dimension. The resonant frequency was 82.7Hz and 34.4Hz respectively. Both devices were measured under 5m/s2 resonant frequency excitation and optimum resistive load. The output power was 6.0μW and 112.8μW respectively. If enhancing the vibration excitation to 10m/s2, the output power will reach 259.5μW.This optimization greatly enhanced the output power which is much higher compared with previous work. After that, this device was modeled using both methods in this paper. Both models are in concordance with the measured results, while the result of CPC-FEM was more closely matched, which is another proof for the effectiveness of the simulation. Finally, we make a conclusion and propose the future research directions in this field.