Characterization And Construction Of The PVDF Energy Harvester On Human Walking Pressure Energy

The human body has inexhaustible abundant energy,which can be collected during walking and can provide a good source of energy for continuous power generation in daily walking.Especially the energy generated by the foot is very popular with researchers.Because piezoelectricity has the advantage of directly converting mechanical energy into electrical energy,the use of piezoelectricity to harvest human energy is currently a hot topic.Based on the researches at home and abroad,this paper conducts a study on the piezoelectric energy harvesters to harvest the energy of the foot from three aspects of structural design,theoretical research and experimental research.Firstly,considering the performance of PVDF piezoelectric films and the limitations of the structure of the shoes,four types of piezoelectric energy harvesters,flat plate type,C type,arch type and zigzag type,were designed and fabricated to harvest foot energy,and preliminary discussions of their output performance were held.The C type structure was compared with the existing arched structure,and the advantages and disadvantages were compared.Based on the above researches and analysises,the advantages of the C type piezoelectric energy harvester harvesting the energy from the foot were preliminarily discussed.The flat plate type and C type piezoelectric energy harvester element were selected as the main research objects,and the corresponding array structures were designed,they are array flat plate type piezoelectric energy harvester based on flate plate type piezoelectric element and the spherical piezoelectric energy harvester based on the C type piezoelectric element.The energy density of the flat plate type,C type,piezoelectric energy harvester are0.5333?W/cm~3,1.0417?W/cm~3,1.5500?W/cm~3 and 3.3583?W/cm~3 respectively,under a 500N impact force at a frequency of 1 Hz.By analyzing the characteristic parameters of a single wave of the energy harvesters,the methods of characterizing electric energy and their relationship under impact force were determined,and the output performance of different structures was analyzed.At last,the problems and matters needing attention that occur when PVDF piezoelectric films are made into corresponding piezoelectric films and combined with substrate layer were summarized.Secondly,a series of studies have been carried out on the flate plate type piezoelectric energy harvesters.Through the related theory,the output performance relationship among the three piezoelectric harvesters which are the whole piezoelectric element(unsegmented electrode,UE)energy harvester,the two half-sheet piezoelectric element in series(segmented electrode in series,SES)energy harvester,and two half-sheet piezoelectric element in parallel(segmented electrode in parallel,SEP)energy harvester were calculated.Then,in the impact force experiment,the experiment results of the three energy harvesters were verified to be consistent with the theoretical results.During the fabrication process of the flat plate type energy harvester,it was found that the different insulation layers have a certain influence on the output performance of the harvester.When the upper and lower insulation layers are all made of PE cling film,the peak peak output voltage of the corresponding energy harvester is the largest.The effect of the static load on the output performance of the flat plate type was studied.When the weight of the mass is within 5 kg,the curve of the peak peak voltage over load can be fitted to a power function,the correlation can reach 0.99389.In the study of the small gravity experiment,the peak peak output voltage of the flat plate type piezoelectric energy harvester increases as the weight of the proof mass increases and it is also increases as the falling height increases.Under the simple harmonic force experiment,with the increase of frequency,the peak peak output voltage of the flat plate type piezoelectric energy harvester increases accordingly.When placing the energy harvester directly on the heel of the shoe,it can be found that as the walking frequency increases,the peak peak output voltage increases accordingly.When the treadmill speed is 6km/h,the peak peak output voltage can reach 13.4V.By analyzing the characteristic parameters of the single waveform under the simple harmonic force and walking,the methods of characterizing electric energy and their relationship under impact force were determined,the effect of the different excitation methods on the characteristic parameters of the flat plate type was studied.The performance of the flat plate type piezoelectric energy harvester under multiple cyclic pressures was studied.It can be seen that the peak peak voltage of the flat plate type piezoelectric energy harvester has great fluctuation when pressed,and the peak peak voltage after 1600 cycles is almost the same with the previous peak peak voltage,the energy harvester still maintains good piezoelectric performance.Then,a array flat plate type piezoelectric energy harvester based on flate plate type piezoelectric element was placed on the insole at the heel of the shoe.Various output performances were studied.The output voltage of the single energy harvester element in the array flat plate type piezoelectric energy harvester and the output voltage of the array flat plate type piezoelectric energy harvester in the same situation were tested,found that there is basically no phase difference between the two piezoelectric elements in the array flat plate type piezoelectric energy harvester.Therefore,when testing the DC output,in order to reduce the loss of the output of the rectifier bridge to the piezoelectric energy harvester,it is possible to select the way of connect the piezoelectric element before rectification.The output performance of the array piezoelectric energy harvester when the piezoelectric elements are directly connected in parallel was studied,with a load of 510k?,the human walked on a treadmill running at 3 km/h,with an available effective voltage of 0.1350V,an effective current of 0.2648?A,and an average power of approximately 0.0358?W.The piezoelectric energy harvester unit in the array energy harvester was connected in series and then connected to a rectifier bridge,and then connected with a capacitance.The capacitance was measured when the human was running on a treadmill running at3km/h.The measured capacitance stores 11.84?C charge in 4 minutes,and the voltage at the capacitor are linear correlation with walking time,the correlation is0.96763.When the piezoelectric energy harvester unit in the array energy harvester is connected in parallel before connected to a rectifier bridge,the charge of 58.93?C can be stored in the capacitor for 4 minutes.The voltage across the capacitor is exponentially related to the walking time,and the correlation is 0.9906.In addition,a C type piezoelectric energy harvester has been studied.The theoretical model of large deformation of C type piezoelectric energy harvester was introduced,and the influence of the size of the energy harvester on the output performance was analyzed.The problems encountered in the forming process of C type piezoelectric energy piezoelectric energy harvester and their solutions were discussed.The effect of the static load on the output performance of the C type piezoelectric energy harvester was studied.When the weight of the mass is less than the critical value that make the height of C type piezoelectric energy harvester to decline,the output voltage of the energy harvester is low,and it increases sharply as it reaches the critical value.When the weight of the mass is larger than the critical value that make the height of C type piezoelectric energy harvester decline 5mm,even the decline height of the energy harvester remains the same,the output voltage increases with the weight of the mass increases.The effect of the length of the piezoelectric sheet and the vertical height of the energy harvester on the output performance was also investigated:As the length of the piezoelectric sheet increases,the peak peak output voltage of the C type piezoelectric energy harvester increases,and as the vertical height of the piezoelectric energy harvester decreases,the peak peak output voltage increases.The electricity output theoretical value and the electricity output experimental value of the C type energy harvester with a height of 3 cm were also compared.The electricity output experimental value can reach 31.4%of the theoretical value,when the length of the piezoelectric element is 4 cm.By analyzing the characteristic parameters of the single waveform of the C type piezoelectric energy harvester,it is proved that the variation of the length of the piezoelectric sheet and the height of the energy harvester can affect the relationship between the characteristic parameters.Finally,the spherical piezoelectric energy harvester was studied.In the fabrication process,taking into account the problems occurred in the C type piezoelectric energy harvester experiments,the structure of the spherical piezoelectric energy harvester were optimized.Due to the aramid filament bundle occasionally slides into the spring steel slit when the C type energy harvester deformed and when it returns to the initial shape,the screws and nuts are used to solve this problem and to fix the piezoelectric energy harvester elements in the spherical type piezoelectric energy harvester.Considering the loss of the output performance of the C type piezoelectric unit when it is made into a spherical structure,three kinds of C type,circular and spherical energy harvesters were fabricated and their performances were studied.Compared with the output voltage of C type piezoelectric energy harvester,the biggest loss of the spherical piezoelectric energy harvester can reach 25%,which is larger than that of a circular one.In the experimental study,under the same conditions,the output performance of each piezoelectric unit of the spherical array piezoelectric energy harvester and the output performance of the piezoelectric units in series connection were tested.Found that the result of the series output voltage is much smaller than the sum of the output voltage of each unit,therefore there is a phase difference between the various piezoelectric energy harvester units.The sum of the output voltage of each unit after rectification and the output voltage of the series of each unit after rectification output is substantially the same,note that each unit rectification before connection can improve the output performance.The performance of spherical type piezoelectric energy harvester under multiple cyclic pressures was studied.It can be seen that the peak peak voltage of the spherical type piezoelectric energy harvester after almost 600 cycles is almost the same with the previous peak peak voltage and is not declined,the energy harvester still maintains good piezoelectric performance.The piezoelectric units of the spherical type harvester are rectified then connected in parallel and then connected to a 680k?resistor,and the drop height of the spherical type harvester is fixed at 5mm,the available effective voltage is 0.2158V,the effective current is 0.3174?A,and the average power is0.0685?W when put foot on the harvester at a frequency of about 1Hz.After each piezoelectric energy harvester unit was rectified and then connected in parallel,and then connected with a capacitance.The capacitance was measured under pressing by foot at a frequency of about 1 Hz.The measured capacitance can store 14.48?C charge within 4 minutes.and the curve of stored energy over time can be fitted to an exponential curve,the correlation is 0.98106.The amount of charge generated and the comfort of the array flat plate type piezoelectric energy harvester are better than that of the spherical piezoelectric energy harvester.