Study On Interaction Of Permanent Magnet Applied In Vibration Energy Harvesting System

In recent years,with the development of industrialization and the gradual increase in production capacity,the demand for energy keeps increasing.At the same time,the pollution to the environment has become more serious.It`s necessary to find a green and sustainable new energy source.On the other hand,low-power portable device and wireless communication technology have a rapid development.At present,continuous power supply for tiny devices becomes one of the bottleneck.The traditional power supply,due to its large size,short lifetime,has great restrictions on the working environment of these devices.As a ubiquitous phenomenon in the environment,vibration has a high usable energy density.Therefore,the object thesis based is the harvesting system of vibration energy in the environment.The main development goals of vibration energy harvesting technology are enhancing the harvesting efficiency and improving the adaptability to different vibration.Because the interaction between permanent magnets has the characteristics of nonlinearity,more energy harvesting systems have begun to consider the participation of permanent magnet interaction in the structural design,which can realize two above goals simultaneously.Hence,the interacting magnetic force plays an important role in the energy function and dynamic model of the system permanent magnets participate.Accurate analysis of magnetic interaction is the key to design of vibration energy harvesting system and exact prediction of output response.Based on the interaction of permanent magnets in the vibration energy harvesting system.the theory of interaction of permanent magnets is studied with three equivalent models of magnetization current,magnetic charge and magnetic dipole.The modeling methods are summarized regarding the permanent magnets of three common shapes,cuboid,cylinder and sphere,in the vibration energy harvesting system,and detailed magnetic force expressions are given.Through the verification of magnetic force measurement experiments,the calculation accuracy of different equivalent models and the applicability to different shapes of permanent magnets are compared.The equivalent magnetizing current,magnetic charge and magnetic dipole "cluster" model all have similar high accuracies for the rectangular and cylindrical permanent magnets.Since the single magnetic dipole model cannot describe the local shape details of the permanent magnet,it only performs well when interval between magnets is much larger than the sizes of magnets.For spherical permanent magnets,the single magnetic dipole model has the same high calculation accuracy as magnetizing current and magnetic charge models,because only sphere is the topological form of a dipole as a filled dot,to which single magnetic dipole is equivalent,the volume parameter is sufficient to describe the shape of sphere.A new magnetic dipole "cluster" modeling method has been proposed based on the magnetic dipole theory.This thesis comparatively analyzes the relationship between the magnetic charge model and the magnetic dipole model both in macro and micro scale,the equivalence of the two models is affected by the interval between magnetic charges.Therefore,the magnetic dipole "cluster" model can only be used to describe magnets with a small distance between the magnetic poles,namely small thickness of magnet.Specially,this paper also reports a special phenomenon when permanent magnets with large different sizes interact.When unlike magnetic poles are close to each other,as the interval decreases,the magnetic repulsion will be turned to attraction.An irreversible magnetic pole reversal occurs in a local area of the larger permanent magnet.The irreversible movements of load line and working point of permanent magnet is introduced to explain this special phenomenon.Also,the prospect of related applications of this phenomenon is given.At last,using the magnetic force calculation method studied in this paper,an improved magnetic force analysis of the classical bi-stable cantilever beam vibration energy harvesting system is carried out.The characteristics of the magnetic force and effect on the potential function of harvesting system are discussed.Then,this thesis also designs a new structure with spherical permanent magnets that can collect vibration energy in any direction,and also analyzes the characteristics of magnetic force,gives the potential function and predicts the output response.