Design And Research Of Rotational Energy Harvester For Ultra-low Frequency Excitation

As an energy solution for traditional chemical batteries,environmental energy harvesting technology is able to convert energy in the environment into electrical energy that can drive micro low-power devices,thereby realizing the self-powered wireless sensor network.With characteristics of wide existence and stable,vibration energy in the environment becomes the key research object in energy harvesting field.Considering that vibrations in the environment are mostly in the low-frequency or even ultra-low frequency range,designing an energy harvester that is capable of effectively collecting the vibration energy of ultra-low frequency becomes the current research hotspot.In order to collect the vibration energy of ultra-low frequency,the structure is designed in this thesis that has the ability to convert the vibration into high-speed bi-directional rotation motion,and mainly works by the special winding method of elastic string and inelastic string.Based on the structure,the prototype of bi-directional electromagnetic rotational energy harvester is designed and manufactured.The main research contents of this energy harvester are as follows: Firstly,the electromechanical coupling model of the energy harvester is established,and the time-domain voltage waveform and output power of the energy harvester are obtained by simulation.Secondly,under different excitation amplitudes and the physical parameters of the energy harvester,the relationship between the output power of the energy harvester and the vibration frequency is obtained on the experimental platform,and the reasons for the inconsistency of state of time-domain voltage waveform at high frequency(5 Hz)and low frequency(2 Hz)are analyzed.The maximum output power is 5.1m W under the experimental platform.Finally,the energy harvester is applied to harvest human motion energy,and the converted energy is able to drive the micro low-power devices to work normally.Compared with other typical energy harvesters for exploiting human motion energy,the bi-directional electromagnetic rotational energy harvester has the advantages of high energy density and compact structure.When the rotation direction of the rotor changes,partial energy of the system is dissipated,which is not conducive to maximize the collected rotation energy.For this issue,the structure is designed that is capable of converting the vibration into uni-directional rotation motion.Based on the structure,the uni-directional hybrid rotational energy harvester prototype is designed and manufactured that consists of Electromagnetic Energy Harvester(EMEH)and Triboelectric Nanogenerator(TENG).The main research contents of this energy harvester are as follows: Firstly,due to the special fixed method of friction material,the TENG is able to realize the automatic conversion of working mode between non-contact TENG and contact TENG.Through the open-circuit time-domain voltage waveform of TENG with the changing speed,it shows that the TENG can realize the automatic conversion of working mode.Secondly,the relationship between the output power of energy harvester and the vibration frequency is explored under different excitation amplitudes and number of magnets.The open-circuit voltage and load voltage of EMEH and TENG are obtained on the experimental platform.The maximum power of EMEH and TENG are 40 m W and 300 μW,respectively.Finally,the energy harvester is used to harvest the hand motion energy,and the generated alternating current is rectified and stored to drive the hygrothermograph and timer.The results show that the low power device is able to start normally from sleep mode and work steadily.In summary,the two rotational energy harvesters designed in this thesis is able to effectively harvest ultra-low frequency energy in the environment,and drive micro-power devices to wake up from sleep mode and work stably.The practical application in this thesis illustrates the great potential of the two energy harvesters in realizing wireless sensor networks,and demonstrates the effectiveness of energy harvesting technology.