Basic Research On Application Of Relaxor Ferroelectric Single Crystal In Wearable Piezoelectric Energy Harvester

With the development of microelectronics industry and the technology of the Internet of Things,wearable and portable electronic devices have achieved experienced tremendous advancements.These devices often integrated with eyeglass,clothes,wristwatches,etc.,already find a wide range of applications including entertainment,human body health monitoring,navigation,medical treatment and wireless communication,and change every aspect of our day-to-day life.However,the energy density of their chemical battery is increased so lowly that it now can't meet the power demand of portable electronics,which restricts their application with long-time requirement.Especially for some embedded/implantable electronic devices,such as pacemakers,replacing batteries is not only a technical problem,but also a great threat to the lives of patients.Piezoelectric energy harvesting is a most hopeful technology to address this problem,which means scavenge mechanical energy from human body and transfer it to electrical energy to supply power to low consumption electronics based on direct piezoelectric effect,extending the battery life or realizing the self-powered of these devices.However,the current wearable piezoelectric energy harvesting technology still has the drawbacks of low output power,which is insufficient for the power consumption of most portable electronic devices,and inability to achieve balance between output performance and human comfort.In this thesis,based on high-performance relaxor based ferroelectric single crystals PIN-PMN-PT and PMN-PT,we have designed and prepared two types of energy harvester to solve these problems,namely the macro-flexible piezoelectric energy harvester and cantilever-based rigid resonant piezoelectric energy harvester,which are tend to harvest the strain energy and the inertial vibration energy induced by human motion,respectively.We do researches on these devices from optimization of piezoelectric materials and design of device structures,to analysis of device models and characterization of these devices.Finally,we have achieved a self-powered heart beat table using our energy harvester.The main research results we achieved are as follow:1)We significantly enhanced the piezoelectric properties of the relaxed ferroelectric single crystals with low PT content by using Alternating Current Polarization(ACP),and reduced the dielectric loss of single crystals to Direct Current Polarization(DCP)levels through aging.Under the optimum ACP conditions of f=30 Hz,Vp=1.2 k V/mm and 10 cycles,the piezoelectric constant d33 of PMN-26 T single crystal with the size of 5×5×0.5 mm3 and the cut of <001>L×<110>W×<1-10>t can reaches as high as 1680 p C/N,which is 37% higher than that of samples by DCP.The dielectric constant of the sample also increases from 5100(DCP)to 6700(ACP),while their dielectric loss increases from 0.5%(DCP)to 1.46%(ACP).Aging experiments show that after 60 days,the piezoelectric and dielectric constant of samples by ACP remain almost the same value,but their dielectric loss reduced to 0.3-0.6% which is comparable to samples by DCP.The performance of the ACpolarized PMN-26 PT sample reached as high as that of DC-polarized PMN-30 PT,which greatly improved the utilization the whole PMN-PT single crystal.2)We proposed the concept of “Macro-Flexible Piezoelectric energy harvester”(MFPEH),which means using the high performance bulk materials rather than nano materials to prepare the flexible piezoelectric energy harvester for improvement of their output performance.An array-type MF-PEH with the structure of ABS flexible substrate/PI flexible circuit board/PIMNT wafer array was designed and fabricated by using bulk piezoelectric PIMNT single crystal.When bended to a radius is 5.04 cm(the calculated average strain induced in the PIMNT is 0.225%),the device can generate an open circuit voltage of 23.2 V and short-circuit current of 105 mA.And under an optimum impedance of 500 kW,the maximum instantaneous output power of the device reaches as high as 0.25 m W,which is 50% higher than the best reported PMN-PT nano generators.3)A plastic-composite-plastic(PCP structure)sandwich structure MF-PEH was designed and prepared by using a PIMNT single crystal/epoxy 2-2 composite,which greatly improved the flexibility of the MF-PEH while maintaining excellent output performance.The bendable radius of this MF-PEH can be less than1.05 cm,which is 1/5 of the previous array-type MF-PEH.Under a bending radius of 1.05 cm and 4.2 Hz excitation frequency,the open circuit voltage and short circuit current of the device reach 12.9 V and 29 mA respectively,with a maximum instantaneous power density of 0.28 m W/cm3 at a matching impedance of 400 k?,which is comparable to that of the array-type MF-PEH.In addition,we replace the parallel plate electrodes in the device with IDE electrodes,the dielectric loss of the prepared piezoelectric energy harvester is greatly reduced from 0.1 to 0.01 @1 k Hz.Under the bending radius of 2.2 cm and the excitation frequency 0.39 Hz,the open circuit voltage and the short circuit current reach as high as 54.2 V and 6.7 mA,respectively.The maximum instantaneous power is 105 mW,corresponding to a power density of 0.64 m W/cm3,which is 2.3 times that of the parallel plate electrodes based PCP structure MF-PEH.4)Combining the advantages of low-frequency resonance cantilever beam and high performance double-sandwich structure,we present a Shear-mode-based CANtilever Driving Low-frequency Energy harvester(S-CANDLE).The device utilizes a cantilever beam to absorb mechanical energy from low frequency vibration source and efficiently transfer the pressure to the double-sandwich structure,which can turn the pressure into shear stress of PMNT wafer.Both the theoretical analysis and experimental results show that the stress amplification factor of the system is greater than 100,and increases with the increase of the proof mass.With an excitation acceleration of 0.4 g and an excitation frequency of 40.5 Hz,the device with a proof mass of 13.5 g the can generate voltage of 60.8 V and power of 390 mW,corresponding power density of 21.6 m W/cm3,which is 5 times more than that of cantilever energy harvester.5)Combining the piecewise-linear-stiffness cantilever beam and double-clamped stress amplify structure,we prepared a collision-type cantilever driving doubleclamped PMN-PT energy harvester.On one hand,a block was added on the vibration direction of the cantilever so that the cantilever will impact with the block during vibration,leading to chaotic motion and expanding the bandwidth.On the other hand,to increases the output power,we design a double-clamped PMN-PT structure to increase the distance between the neutral plane of the PMNT wafer to that of the cantilever.The experiment results show that the bandwidth of the device expands with the decrease of collision distance d.Under the excitation accelerations of 58.5 Hz and 0.3 g,the open-circuit voltage and output power of the device with d=0.66 mm reaches as high as 26.2 V and 1.15 m W,respectively,and the bandwidth is 7.3 Hz,both of which are an order of magnitude higher than that of cantilever energy harvester with the same size.6)For the construction of self-powered portable/wearable electronics systems,we used the MF-PEH to harvest mechanical energy from human knees and successfully prepared a self-powered heart rate table.When attached to the back of the knees,the previous IDE based PCP structure MF-PEH can generate an the open circuit voltage of 20 V to and light 12 red LEDs instantaneously during walking;and an open circuit voltage of 30 V is generated during running.With the highefficiency energy management circuit LTC3588,the rechargeable ML414 lithium battery can be charged from 0.4 V to 2.35 V by the device after 1 hour's running,which can successfully operate the heart rate table.