Dynamic Study Of Flow-Induced-Vibration Energy Harvester And Its Self-Powered Wireless Sensing Applications

With the rapid development of the Internet of Things(Io T)and the popularity of wireless sensors,using active power supply or traditional chemical batteries will face many problems such as higher workload and pollution.Therefore,self-powered wireless sensors through environmental energy harvesting are becoming an important research trend.Piezoelectric energy harvesters(PEHs)have attracted great interest in solving the power supply problem of wireless sensors.PEHs based on smart structures and physical principles have been extensively studied.Currently,the frequency bandwidth and the energy harvesting efficiency are two urgent issues to be solved in practical applications.By combining the advantages of magnetically non-linear,frequency up-conversion and down-conversion and array-type structures,this thesis proposes flow-induced-vibration piezoelectric energy harvester(FPEHs)for use in flow fields or in environments where rotational motion can be provided.Firstly,in order to reveal its dynamic characteristics,a corresponding mathematical model is established based on theories such as Euler-Bernoulli beam and Lagrange equation,while the gravity coefficients in the derived mathematical model are qualitatively analyzed to reveal the softening and hardening effects.The equations for the magnetic potential energy and magnetic force between the rotating magnet and the tip magnet are established based on the magnetic dipole theory.The effects of excitation frequency,magnet gap,mounting configuration and piezoelectric beam length on the dynamic characteristics of the FPEH are theoretically analyzed.Next,the FPEH experimental platform was built and the corresponding experimental verification was carried out.The results show that under low frequency excitation conditions,the FPEH can convert the low-frequency rotational motion(<10 Hz)of the piezoelectric beam into high-frequency vibration through a frequency up-conversion mechanism,effectively increasing the working bandwidth and improving the efficiency of low-speed rotational energy harvesting;when the excitation frequency is too high(>15 Hz),the piezoelectric beam can regain a large amplitude through a frequency down-conversion mechanism.The adoption of an 8mm magnet gap improves energy harvesting efficiency more than other gap distances.In addition,the softening,stiffening effect due to the gravity of the tip will give the forward beam a wider bandwidth than the inverse beam.Array structures made up of different lengths of piezoelectric beams have also been shown to have an extremely wide operating bandwidth(0.5 Hz-30 Hz).Finally,a complete self-powered system was built,yielding an optimum load resistance of around 150 KΩ for the FPEH and a peak output power of 177.53 μW for a single 90 mm forward beam at this load.The average charging power of the FPEH over 50 s was 41.63 μW and 76.84 μW for excitation at 100 rpm and 200 rpm,respectively,enabling the Bluetooth Tire Pressure Monitoring System(BLE-TPMS)to send signals at different intervals to meet the needs of wireless sensors operating in different conditions.In summary,this thesis shows through in-depth theoretical analysis as well as experimental verification that the proposed FPEH harvest energy with higher efficiency and wider operating frequency(0.5 Hz-30 Hz),proving the application potential of the FPEH and providing a valuable theoretical guidance and experimental basis for solving the self-powered solution of wireless sensors.