Mnzn High Permeability Core Materials And Devices For Broadband Networks

With the development of digital telecommunication and network,it is a keyproblem of the miniaturization,wide band and wide temperature characteristic of thepassive device.This thesis is selected and researched in combination with this tendancyand needs.Firstly, we researched the high permeability MnZn ferrite cores materials,which arewidely used in communication and network digital transformers. In the paper, highpermeability Mn-Zn ferrites have been prepared by the newly mixed-oxide route.Theprescribed quantities of Fe₂O₃,Mn₃O₄and ZnO as the raw materials were mixed in aball mill.After being calcinated, the obtained ferrite powder was granulated and pressedinto toroidal shapes,mixing with PVA. Then, they were sintered under nitrogenatmosphere and the magnetic performances were tested. During the process ofreseach, the effects of calcinating temperature,sintering temperature sinteringatmosphere, a small amount addition of many different oxides on the magneticparameters of high permeability Mn-Zn ferrite were investigated. The results show thatthe choice of calcinating temperature have much effects on the determination ofsintering temperature and magnetic parameters of the products; the proper sinteringatmosphere can improve the maganetic performance of high permeability MnZn ferrites;P205 addition improves the microstructure of the ferrite materials and accelerate graingrowth; MoO₃ and CaCO₃ addition not only increase the average grain size and initialpermeability, but also improve the frequency characteristic and the porosity in ferrites;the liquid phase of ferrite including Bi₂O₃ in sintering atmosphere induces the uniformgrowing of ferrite grain. Through large quantities of experiments, we make progressmainly in raising frequency domain permeability and resisting the second harmonicdistortion,thus we improve the performance of the materials used in digitaltelecommunication and network.The ferrite materials parameters are as follows-μ_i≥10000, B_s≥380mT(10KHz,25℃,800A/m),η_B≤0.2×10^-3/T(10KHz,25℃,1.5～3mT), T_c≥120℃, f_r≥400KHz.Secondly, we used the high permeability MnZn ferrite materials that we developed to research wide-band transformer which is applied to ADSL network. In the research,we introduced the parameters and design method of ADSL transformer and discussedthe influence on the transformer of some parameters,such as the permeability, turns ratio,maganetic flux density, air gap. Finally, we designed the ADSL transformer by EXP7maganetic core. For the ADSL transformer, insertion loss is less than 0.5dB and the totalharmonic distortion (THD) satisfied the needs of 80dB.