Preparation Of Yttrium Iron Garnet Ferrite With High Dielectric Constant And Design Of Microwave Devices

Yttrium iron garnet ferrite（YIG）,as one of the important microwave magnetic materials,has been widely concerned with its unique and excellent performance and has been used in various microwave devices.With the current rapid development of microwave communication technology,microwave devices are required to be miniaturized and integrated in the direction of advanced systems,and their circuit size needs to be smaller and smaller,therefore,many performance parameters of YIG ferrite materials such as permeability,dielectric constant,saturation magnetization strength,ferromagnetic resonance linewidth,etc.have been put forward more stringent requirements.Among them,dielectric constant is an important physical parameter to characterize the dielectric property or polarization property of the material,which is one of the important performance indicators for designing microwave ferrite devices,and improving the dielectric constant of the material plays a crucial role in reducing the size of the device.The main work of this thesis is to prepare high dielectric constant YIG ferrite materials by solid-phase reaction method based on the excellent properties of pure YIG,and to discuss the realization path of high dielectric constant YIG materials and their applications.Firstly,the basic theory of garnet ferrite,such as microstructure,magnetic origin and ion doping law,was analyzed for the subsequent work such as modification of yttrium iron garnet ferrite materials by ion doping.Next,based on the theory of dielectric constant,the highly polarized ion Bi³⁺was introduced to partially replaceY³⁺,and the YIG ferrite samples were prepared by the conventional oxide method,and the microstructure and electromagnetic properties of the samples were characterized and analyzed by X-ray analyzer（XRD）,scanning electron microscope（SEM）,vibrating sample magnetometer（VSM）and electromagnetic property test.The effect of ionic substitution of Bi³⁺on the properties of YIG ferrite was investigated.The results show that Bi³⁺can effectively enhance the dielectric constant of the material,and the prepared ferrite material can reach a maximum dielectric constant of about 25,but it will inevitably increase the magnetic loss of the material.After determining the optimal Bi³⁺content,the effect of Z⁴⁺andV⁵⁺substitution on YIG was investigated.It is found that the appropriate amount of Z⁴⁺can reduce the larger ferromagnetic resonance linewidth due to the introduction of Bi³⁺,but it is still higher than the linewidth value of pure YIG;V⁵⁺can significantly reduce the sintering temperature of the material without affecting each property of the material.Secondly,based on the prepared YIG material,its magnetic permeability spectra was analyzed in detail,and an improved magnetic permeability spectra fitting method was proposed.Compared with the traditional method,the fitting accuracy was improved,and the new fitting results were in better agreement with the Snoek limit,which is helpful to study and analyze the magnetization mechanism of magnetic materials.Finally,based on the working principle of the circulator and related electromagnetic field basic theory,the experimentally prepared high dielectric constant yttrium iron garnet ferrite material was applied to the design of the circulator,and after simulation and optimization,the circulator designed at the center frequency meets the requirements of return loss,isolation degree,insertion loss,voltage standing wave ratio and other indexes,and the device size is significantly reduced,and the initial miniaturization of the device design is achieved without affecting the performance.