Research On Characteristics Of Two-layer Cantilever Piezoelectric Energy Harvester

With the development of electronic technique, network technique and communication technique in recent years, it becomes a must to apply various electronic products in our life, and except for the basic function of those equipments, people pay great attention to experience when applying, this will make electronic devices to be more and more intelligentized. For microtransducers widely used in networks and systems, they always have small size and large number, and their scattered location as well as difficult maintenance put power components on high-level requirements. Using energy harvesting technique for converting various kinds of power in environment to electric energy can make electronic devices break the tether bring by traditional power source, it now becomes an important research field and attract a lot of attention.Among different types of energy harvester, piezoelectric device has the most broad prospects. Mechanical vibration exists everywhere and output large power density, it creates favorable conditions for piezoelectric energy harvester's development. Some one-layer cantilever piezoelectric products have appeared, but two-layer devices'research only stays at modeling stage. Because two-layer piezoelectric energy harvester has some peculiar advantages, it is meaningful to do research work about devices'characteristics.The thesis is aimed at figuring out how system parameters affect two-layer cantilever piezoelectric energy harvester output performance. Here, device model and its fixture were designed and fabricated, testing system was established, simulation steps and code were completed, experimental data and simulation data were compared, and some conclusions and suggests were obtained. The specific work is as following:The energy harvester model consisted of upper and under cantilever, two space blocks and one mass block. Upper and under cantilever consisted of support layer, PZT layer, electrode layer and wire, the size of cantilever was 50mm×8mm×0.6mm; Different space blocks were used to make device models with different parameters, the four sizes were 18mm×8mm×10mm,12mm×6mm×10mm,9mm×8mm×10mm and 7.2mm×10mm×10mm, and the uniform mass was 1.4g; The weights of three different mass blocks used were 10.5g, 6.7g, and 4.2g. The fixture consisted of middle axle, fixed upper jaw, fixed under jaw, movable nut and movable screw, it's specifically used to clamp energy harvesters with various thickness. In addition, the reliability of device model and fixture was checked.In conditions of 4mm distance between upper cantilever and under cantilever and 5m/s2 acceleration of vibration, devices with three different mass blocks which separately weighed 10.5g, 6.7g and 4.2g were tested, the results showed that the larger mass loaded, the lower resonance frequency and the higher resonant voltage with devices; In conditions of 4.2g weight of mass block and 5m/s2 acceleration of vibration, devices with four different distances which separately were 4mm, 6mm, 8mm and 10mm between upper cantilever and under cantilever were tested, the results showed that the larger the distance, the higher resonance frequency and the lower resonant voltage with devices, furthermore, the distance impacted device's resonance frequency weakly but device's resonant voltage obviously. During the experiment, the device with mass block of 10.5g and distance of 4mm between two cantilevers showed the best performance, it had a resonance frequency of 43Hz and a resonant voltage of 11.5V under 5m/s2 acceleration.After finite element simulation on the energy harvester model was done by ANSYS software, simulation results and experimental results were compared, the conclusion was found that the device's performance could get better by increasing the weight of mass block, decreasing the distance between two cantilevers or increasing the length of cantilever, however, the width of cantilever made almost no impact on device's performance. Consequently, there are two key points in device's MEMS fabrication: increasing equivalent load mass on free end of cantilever in limited space and decreasing the distance between two layers of cantilever of energy harvester.The thesis not only showed a two-layer cantilever piezoelectric energy harvester appropriate for low-frequency environment, but also offered a systematic method which combined physical modeling and finite element simulation to research device's performance, there are three advantages with this method: It can reduce failures caused by unreasonably choosing system parameters in fabrication; It can avoid incorrect conclusion caused by carelessness in ex-parte work; It can find import factors which impact device's performance so as to promote the development of micro manufacturing technology.