Research On Wideband Vibration Energy Harvesting System And Lead-Free Nano Generator Based On Piezoelectric Effect

The Internet of Things technology and wireless sensor network technology have enjoyed a rapid development and are widely applied in such fields as field tracking,project condition monitoring,human health monitoring and smart homes.However,traditional chemical batteries used in the technologies have the shortcomings of large-sized,lifetime-limited,difficultly-replaced,high-cost and environmentally polluted.It is of great research significance and practical value to collect environmental vibration energies and provide real-time power supply for the low-power wireless sensor monitoring devices.The piezoelectric vibration energy harvesters have the advantages like environmental friendliness,high energy density,strong disturbance interference capability,simple structures and easy to integrate and miniaturize,are becoming more and more attractive compared with the electromagnetic and electrostatic vibration energy harvesting.Traditional piezoelectric capturing system has the defects including high inherent frequency,narrow work bandwidth,low energy conversion efficiency with circuit and fragile with piezoelectric ceramics materials,which is unable to meet the new requirements of wearable,miniaturization,portable devices and so on.The design of low-frequency broadband piezoelectric vibration energy harvesting structures,energy conversion and storage circuits,and preparation of piezoelectric composite materials and their applications in nano-generators and piezoelectric harvesting structures have been studied in this dissertation.?1?A low-frequency vibration-based interdigital piezoelectric energy harvester and voltage synchronous control processing circuit have been developed.The proposed vibration pick-up structure consists of a rectangular flexible frame and five identical cantilever beams interdigitally bonded to it.Experimental results showed that the designed harvester exhibited a 460%increase in bandwidth compared with the single cantilever beams harvester and the maximum output power of the system could reach up to 18.8?W at an acceleration of 1 g.The efficiency of the proposed circuit was calculated as72.3%and increased by 25%compared with that of the SEH circuit.In addition,the efficiency of the system could reach up to 70.11%when the system was used as power supply of an actual temperature sensor.?2?Vibration energy harvester with unsymmetrical,interdigital pick-up structure and energy management circuit has been designed,fabricated,and characterized.The harvesting system exhibited asymmetry by adjusting the width of five single cantilever beams and the height of Fe mass on the interdigital piezoelectric energy harvesting structure.The working bandwidths of 11.2 Hz at simulation and 12.3 Hz at experiment have been gained for the designed structure.Experimental results showed that the proposed harvester could generate the output power of about 151.3?W?5.91 times of the symmetrical interdigital vibration energy harvester?with an acceleration of 1 g,which could maintain the normal work of a given electronic device?containing18 light emitting diodes?by using a matched energy management circuit.?3?A neat 3*n element energy harvester array exploiting multi-vibration modes separation technique,has been designed,fabricated,and characterized.The vibration modes of the system were separated to achieve the effect of wide frequency band by adjusting the width and mass height of the three single cantilever beams in each row using COMSOL finite element simulation software.A considerable wideband of 15.6 Hz at simulation and 13 Hz at experiment with 3*5 array energy harvester has been gained in a very low frequency range?below 50 Hz?,with an acceleration of 1 g.Experimental results showed that the adjusted 3*5 array harvester could generate the output power of about 2.1 mW at an 8 Hz resonant frequency with the optimum load resistance350 k?.Meanwhile,the half-power?1.05 mW?bandwidth could reach up to15.3 Hz.The bandwidth and the output power of the array energy harvesting system were significantly improved by exploiting the proposed vibration modes separation technique.?4?The high-performance BaTiO₃/C/PDMS lead-free piezoelectric composite films have been fabricated and characterized.The synthesized BaTiO₃/PDMS/C composite nanogenerator exhibited an output voltage of approximately 7.43 V with periodically beating from a vibrator,which was increased by 143%compared with the piezoelectric nanogenerators?PNGs?without C mixture.The maximum power was shown to reach up to approximately 7.92 mW with a load resistance of 2 M?when the C content of composite was 3.2 wt%.The generated electric energy could be effectively stored by the energy storage capacitor?47 mF?and was successfully used to light a commercial red light-emitting diode?LED?.Moreover,the unsymmetrical interdigital harvesters with BaTiO₃/PDMS and BaTiO₃/C/PDMS piezoelectric materials have been fabricated and-3dB bandwidth of harvesters increased from 8.7 Hz?without C?to 9.3 Hz?with C?.?5?The high performance composite films based on BaTiO₃/Graphene Oxide/polydimethyl siloxane?BaTiO₃/GO/PDMS?with different GO content have been fabricated and developed.GO with large specific surface and strong fluidity was employed as a carbon-based conductive phase material to form micro-capacitors in the ferroelectric composite and thus enhance the piezoelectric performance of the sample.The as-prepared BaTiO₃/GO/PDMS composite films with 0.6 wt%GO showed a dielectric constant of 185 and a conductivity of 8.5?10^-5 S/m.A remanent polarization of 13.47?C/cm² can be obtained,which is 28%higher than that of the pure BaTiO₃/PDMS films.Meanwhile,the synthesized BaTiO₃/GO/PDMS composite film exhibits a maximum output voltage of?7.71 V,which is almost 2.78 times higher than that without GO.The performance of lead-free piezoelectric nanogenerators is significantly enhanced after compounding with GO materials.Moreover,the unsymmetrical interdigital harvester with BaTiO₃/GO/PDMS piezoelectric materials has been fabricated.The results indicated that the output voltage of the harvester compounding with GO increased and-3dB bandwidth of harvesters increased from 8.7 Hz?without GO?to 11.2 Hz?with GO?.