Flexible Buckled Piezoelectric Vibration Energy Harvesters And Its Applications In Self-powered Microelectronic Systems

With the quick development of a lot of wireless sensing nodes in the context of artificial intelligent Internet of Things(AIo T),as well as the lead restriction of the closed environment,the batteries have been become the main energy supply method.However,due to the limited lifetime of batteries along with maintenance difficulties,environmental pollution and potential safety risks,the development of energy harvesting technology is promoted to replace the battery in some cases,to solve this energy supply unsustainable problem.However,most of the vibration sources'frequencies in the environment are below 100 Hz or even 10 Hz.Traditional silicon-based piezoelectric energy harvesters are limited by stiffness,which makes it difficult to obtain effective and stable output at low frequency.At the same time,with the rapid development of flexible electronics,wearable electronics,and implantable medical electronics,there is an increasing demand for flexible piezoelectric energy harvesting technologies due to their compatible and easily integrated advantages.The method of chemical-mechanical polishing on flexible substrate will be proposed to realize the high-performance piezoelectric energy harvesting technology.In this thesis,we study the high performance flexible vibration energy scavenging mechanism,design theory and its fabrication process,and investigate its self-powered microsystem via the developed energy harvesters,the main contents are as follows:(1)A finite element analysis model was established to investigate the influence of multi-layer piezoelectric composite structrual sizes,substrate stiffness and environmental excitation acceleration on the performance of the piezoelectric energy harvesters.The simulated results demonstrate the optimal lengh of the cantilever-based energy harvester can increase the maximum output power by one times.It can be explained that the high average strain distribution of the piezoelectric layer is the main reason for obtaining high output energy conversion characteristics.(2)A fabrication technique of multi-layer piezoelectric composite structure based on a flexible beryllium bronze foil substrate is proposed,and single-crystal vibration energy harvesters with different piezoelectric layer layout lengths based on the flexible piezoelectric composite structure are prepared.The output performance of these cantilever energy harvesters was tested and analyzed,and the results verified the effectiveness of the optimization method of piezoelectric thin film partial layout in improving the output performance,and the normalized power density was increased by nearly seven times.In addition,a bimorph fabrication process based on a flexible beryllium bronze substrate was further developed to prepare a bimorph vibration energy harvester with optimized piezoelectric layer layout length,which increased the normalized power density by five times and doubled the power density compared to the bimorph energy harvester with the same length of the piezoelectric layer and the substrate layer.(3)The theoretical model of the free vibrating piezoelectric energy harvester based on flexible buckled structure was created,and the vibration displacement of central point and output voltage were analyzed under the different excited accelerations and applied frequencies.Meanwhile,the nonlinear vibration and broad bandwidth characteristics of the flexible buckled harvester were revealed,and the forced vibration performance of the flexible buckled piezoelectric composite structure was further investigated through the finite element simulation model,and the influence of the stiffness ratio between the piezoelectric layer and substrate layer and the external load mode on energy output were discussed.(4)The microfabrication process of a flexible buckled piezoelectric energy harvester based chemical and mechanical polishing technique was proposed and realized.As the testing results the bandwidth of about 15 Hz for this harvester at the amplitude of2.0 g excitation acceleration was obtained,as well as the maximum effective output power of 0.6 m W and the maximum effective output power density of 150 m W/cm³,with the normalized power density of 0.36 m Wcm^-3g^-2Hz^-1,to verify its broadband characteristics.Then,the broadband piezoelectric energy harvester integrated with double buckled structures was also developed to realize stable and wide bandwidth by combining the high-frequency offset of the nonlinear hardening and the low-frequency offset feature of the nonlinear softening mechanisms.(5)The flexible rotated-driven piezoelectric energy harvesting conversion model under forced vibration load was established to analyze the vibration output mechanism under low-frequency forced vibration excitation conditions.Moreover,the rotating gear mechanism was designed to convert low-frequency rotating mode into high one,and the piezoelectric rotational vibration energy harvester with eight typical nonlinear flexion bridges was proposed and fabricated to avoid the frequency dependence The experimental results show that the maximum open-circuit output voltage of 19 V and the maximum effective output power of 8.9 m W for this proposed harvester were obtained at a rotational frequency of 8.3 Hz.Finally,the flexible buckled piezoelectric rotational energy harvester is deployed to supply the electrical energy for commercial tire pressure monitoring system with normal work.(6)We proposed an implantable flexible energy harvester to scavenge the collision kinetic energy from cardiac apex during the periodic contraction and relaxation process of the porcine heart and its electrodynamic properties were investigated.The maximum short-circuit current of 30?A was obtained by in vivo experiments in adult pigs,which was about 15 times higher than that of similar studies,and the feasibility of this developed implantable piezoelectric energy harvesting technique to achieve a self-powered pacemaker was verified.Meanwhile,the feasibility of an epicardial pacing strategy was studied to solve the problem of pacing leads arrangement for a self-powered pacemaker.As a result,the pacing strategy with both leadless and self-powered pacemaker system was realized.