Design And Optimization Of Electromagnetic Induction Devices By Finite Element Analysis

Electromagnetic induction is the basis of most electrical appliances and power equipment.To improve the overall performance of the electromagnetic induction devices,it is necessary to analyze the distributions of electric and magnetic fields around and inside the device in order to guide the structure modification and material selection for the devices.However,the analysis of electric and magnetic fields involves integral and differential operations,and the complex problems of electric and magnetic fields cannot be analyzed by analytical methods.With the improvement of numerical analysis theory and computer performance,the use of finite element analysis is expected to solve these complex electromagnetic problems.Based on the analysis of the basic principle of electromagnetics and the improvement of theoretical analysis method,finite element analysis was employed in this work to study the distribution and influence factors of electric field and magnetic field for the household induction cooker,transcranial stimulator,and magnetic induction hyperthermia.The design and optimization of these different devices are carried out according to the practical requirements.This work lays a foundation for further improving the performance of the devices.For the induction heating(IH)technology of domestic induction cooker,the factors that affect the overall energy efficiency of IH system is analyzed by theoretical derivation.The finite element analysis model is established,which verifies the correctness of the theoretical derivation.The quantitative analysis results on the influence factors of the energy efficiency were obtained.The results showed that,for the IH system with a certain structure,the correct selection of the cooker pan materials can make the equivalent resistance of induction cooker in IH system to be 1,by which the highest overall energy efficiency can be obtained.When analyzing the influence of induction cooker on system energy efficiency,it is necessary to consider the combined effect of relative magnetic permeability and conductivity of cooker pan material.For the soft magnetic strips used in the induction cooker,a higher relative magnetic permeability()can lead to a higher energy efficiency of the system.However,whenis over 3000,further increase incannot significantly increase the energy efficiency.In addition,the structure design also has a certain influence on the energy efficiency.It is found that adding L-shaped strips in IH coil can improve the inductance of coil disk,but it is not helpful to improve the energy efficiency.In view of the uneven heating problem of common household induction cooker,a mathematical model was established in this work.The origins of local overheating were theoretically explained,and the improvement approaches were put forward.Based on both theoretical analysis and finite element method,the structure of single IH coil is adjusted,and the heating effects of different coils are calculated by combined magnetic and thermal analysis.The results showed that the heating uniformity of single IH coil can be effectively improved by modifying the winding numbers at different positions.According to the calculation results,an optimized IH coil disk was prepared,and the actual heating effect was measured.The results demonstrated that uniform heating can be achieved by optimizing the coil structure.Compared with the approaches proposed by other scholars to improve the heating uniformity by using double coil,multi-coil and magnetic resonance coupling coil,the method in this work has the advantages of compatibility with the existing power circuit,low cost and easy realization.Transcranial magnetic stimulation(TMS)is a powerful tool for studying brain function in neuroscience and has been proved to valid for medical treatment.In this thesis,the finite element method is used to analyze the distributions of electric field induced by different TMS coils.The structure optimizations are proposed for different coils to solve the problems of stimulation accuracy and stimulation depth.By adjusting the coil structure or introducing a high permeability core and a magnetic shielding layer for the coils with different structures,such as single circle coil,single cone coil,ring-shaped figure-8 coil,disk-shaped figure-8 coil,traditional double cone coil and eccentric double cone coil,the stimulation accuracy has been improved,The results show that for the single circular and single conical TMS coils,the electric field intensity can be increased by modifying the coil structure to make it close to the head.For the ring-shaped 8-shaped coil,a small size U-shaped magnetic core is added in the center of the coil,which can effectively improve the stimulation accuracy along the direction of the magnetic core.When a magnetic shielding layer is added between the coil and head,the shape and size of the shielding layer can be modified to improve the stimulation accuracy.In the eccentric biconical coil,adding a magnetic core in the center can also improve the accuracy.H-coil is one type of TMS coil for deep brain stimulation.Here a simplified H-shaped coil is used to analyze the influence of structure parameters on the stimulation effect.According to the distribution of the electric field in the brain produced by the coil,the value of₈(6)((9)?₈(6)(0)×100%was used as a criterion to judge the stimulation depth.Because the working part of H-coil is usually located in the front of the head,the electric field intensity generated by the coil outside the stimulation target can be effectively reduced by adding a shielding layer between the H-coil and head.As a result,the safety of the stimulation can be improved.As a new type of tumor treatment technology,magnetic induction hyperthermia(MIH)has higher targeting effect than traditional treatment methods,and it can effectively reduce the pain of patients.Firstly,based on the working principle of MIH,the magnetic inductions of different IH coils in vivo were analyzed and it is found that the distribution of magnetic field can be modified by changing the position,number and shape of the coil.Secondly,the influence of the angle between cylindrical heat source and magnetic field on heat generation power was analyzed,and the results show that,when the heat source axis is parallel or perpendicular to the magnetic field,the heat generation power is the largest.It is suggested to use a spherical heat source to eliminate the influence of the heat source position on the heat generation power.The larger the size of the spherical heat source is,the larger the heat generation power is.A hollow heat source can effectively improve the heating rate.Finally,the amorphous Fe-Zr-B ribbon was prepared by experiment,and the electrical and magnetic properties of the ribbon were measured.The heat generation characteristics of the heat source made of multilayer amorphous ribbons in alternating magnetic field were analyzed by theory and finite element analysis.To sum up,the finite element method was employed in this thesis work to systematically analyze the IH system of household induction cooker,transcranial magnetic stimulation coil,and IH system for hyperthermia.By means of theoretical analysis and experimental verification,the reliability of finite element analysis in solving the electromagnetic induction problems is demonstrated.The theoretical models and finite element analysis model proposed in this work provide ideas and directions for the optimization of related devices.The present work is helpful to the design of electromagnetic induction devices.