A Two-dimensional Piezoelectric Vibration Energy Harvester And Its Directional Sensing Application

In the past decades,microelectronics,wireless sensor networks and micro-nano electromechanical systems have developed rapidly.How to supply power to numerous sensors or sensor nodes in various environments efficiently has been becoming an urgent problem.Batteries in traditional power supply have short service life,bulky and not environmentally friendly.They need to be recharged or replaced regularly.With the exploration and discovery of unknown areas,more and more wireless sensor network nodes are distributed in harsh situations.If we still use the existing methods to replace new batteries for wireless sensors regularly,it obviously needs a lot of manpower and material resources.Another way of power supply-Installation of wires,not only expensive installation,maintenance troubles,but also very prone to safety accidents.Scavenging energy from the surrounding environment and converting it into electricity is considered a promising alternative to batteries or wires.Therefore,energy acquisition technology has become a hot research direction.Among many energy harvesters,piezoelectric vibration energy harvesters(PVEHs)have been studied extensively due to simple structure,large power density,easy integration with microsystems and without external power input.Nowadays,increasing the energy conversion efficiency of the piezoelectric vibration energy harvester(PVEHs)and widening the operating frequency bandwidth is one of the main objectives of current research.In addition,it is a research hot spot to design the harvester that can collect vibration energy from multiple excitation directions,because the vibration source in the actual environment may come from different directions.However,in reality,both the frequency and the direction of many vibration resources are changeable simultaneously.Traditional cantilever PVEHs can only effectively collect vibration energy in a single direction.If the excitation comes from the direction outside the bending direction of the cantilever beam,the output power of the cantilever PVEH will decrease significantly.In fact,the frequency and direction of many vibration energy sources can be changed at the same time.Therefore,how to harvest multi-directional vibration energy efficiently is becoming a hot issue recently.However,the effect of vibration direction on the piezoelectric energy harvester has not been noticed.In order to solve the problem that the traditional horizontal cantilever piezoelectric vibration energy harvester mentioned above can only effectively collect vibration energy in a single direction,a cylindrical cantilever radial array piezoelectric vibration energy harvester is proposed to collect two-dimensional(2D)vibration energy.By using the piezoelectric array axial distribution on the flexible cylinder to make vibration energy harvester,it can collect vibration energy in any direction on the two-dimensional(2D)plane.At the same time,we introduce a new concept called angle bandwidth,which can describe the ability to obtain two-dimensional vibrational energy.The specific research content and results of this paper are as follows:1.The number and arrangement of polyvinylidene fluoride(PVDF)thin film of the piezoelectric vibration energy harvester with axial symmetric distribution of piezoelectric array(4 PVDF films distributed uniformly and symmetrically),as well as the influence of series and parallel connection mode on the angle bandwidth and output performance were studied.Cylindrical axial distribution of piezoelectric vibration energy harvester array bandwidth of the angle of a single PVDF is 89.2°,larger than the horizontal cantilever beam structure harvester(65.2°)in bandwidth 24°,collect more direction performance increased by 30%.The axisymmetric position(180° apart)of PVDF thin film reverse series-parallel can significantly improve the output performance of harvester:The excitation conditions were 3 m/s2 and 66.5 Hz,in reverse series,the output voltage reaches 11.6 V,which is double of the output voltage of a single PVDF;in reverse parallel operation,the output power reaches 13.5?W,1.6 times greater than the output power of a single PVDF.2.The axial distribution of array asymmetrical design of piezoelectric vibration energy harvesters,namely when four PVDF adjacent land arrangement,and has a bandwidth of 89.2° angle compared to a single PVDF,four adjacent PVDF series of angle bandwidth can be increased to 106.3°(increased by 17.1°),Than conventional horizontal cantilever piezoelectric vibration energy harvesters(65.2°)41.1°.In addition,the increase in the number of PVDF and the change in the connection type had little effect on the frequency bandwidth(FB),both within the range of 13-14 Hz.The magnitude of the excitation acceleration cannot change the magnitude of the angular bandwidth,just as the magnitude of the excitation acceleration cannot increase the frequency bandwidth.3.When the piezoelectric vibration energy harvester mentioned in this paper is distributed axially symmetrically in the piezoelectric array,it can be directly used as a direction sensor without external power supply and additional energy storage circuit.According to the output signal of each PVDF thin film element during vibration,not only the four special vibration directions of excitation angle 0=0°,45°,90°and 135°can be directly judged,but also the vibration direction can be judged according to the magnitude and phase relationship between the output signals.Combining energy acquisition with sensor,the function of self-powered direction sensor is realized.