Optimized Design Of A Multi-stage Force Amplifying Magnetostrictive Walking Vibration Harvester

Vibrating energy harvesters,capable of converting mechanical energy into electrical energy,have attracted unprecedented interest in both academia and industry.This is because they have great potential for harvesting human activity-induced energy and energy from around the body to drive low-power wearable biosensors and electronics,micro-robots,and implantable biomedical devices.The harvesting of vibrational energy from living organisms suffers from irregularity and instability.The harvester should have a strong ability to amplify the weak vibrations of the organism to further improve the utilisation of the vibrational energy.In order to make the harvester better adapted to the harvesting of human walking vibration energy,this thesis firstly designs the structure of the harvester so that the harvester can harvest human walking vibration effectively,and then can improve the output capacity of the harvester.On the basis of the magnetostrictive inverse effect mechanism,this thesis proposes a magnetostrictive vibration harvester using Terfenol-D,which generates electrical energy when subjected to the walking vibration of the human body.A multi-stage force amplification mechanism,including a wedge mechanism,a micro-lever mechanism,and a bridge mechanism,is integrated into this magnetostrictive walking vibration harvester to amplify weak foot vibrations.A detailed mathematical model of the multi-stage force amplification process is established and the three main mechanisms are analysed mathematically separately to determine the initial structural dimensions of the harvester.The design and analysis are then optimised from the three viewpoints of the harvester structure,i.e.the vibration energy domain,the offset magnetic field arrangement method,i.e.the magnetic energy domain,and the selection of the key parameters of the coil,i.e.the electrical energy domain,respectively.Finally,experimental tests are carried out to analyze the effect of the force amplification mechanism on the output performance of the harvester,by using the data collection method firstly to test the actual force amplification of the harvester.The effect of the three bias magnetic field arrangements of the proposed harvester on its output performance is further verified.It is concluded that the best output performance of the harvester is achieved under the bias magnetic field arrangement with a closed magnetic circuit of the highly permeable material nickel and permanent magnets.Matched load resistance experiments have shown that the best output performance is obtained when the internal and external resistance of the harvester is similar,and that the matched load resistance is small compared to that of the piezoelectric vibration harvester.A comprehensive test of the harvester is completed on this basis.The harvester has good output performance under continuous low frequency excitation,and the harvester can generate peak voltage of 4.13 V and peak power of 426.4m W when fully compressed.When the harvester is placed on the human foot for energy harvesting,the peak power output is 213.16 m W at an average acceleration of 2.5g for plantar impact during jogging and 371.43 m W at an average acceleration of 4g for plantar impact during jogging.The results of this study suggest that the combination of a rod-shaped Terfenol-D and a force amplification mechanism can lead to the design of a bio-vibration energy harvester with excellent performance and more suitable for self-powered wearable electronic devices.