Manipulation Of The Permeability Spectra Of NiCuZn Ferrite Applied In HF-VHF Frequency Range

As the ongoing development of electronic industry,the requirement for passive device are getting higher and higher,in order to meet the demand of electronic equipment.The NiCuZn ferrite,as a basic material for many kinds of passive devices,needs to be further improved.This material should possess high permeability and low loss in wide frequency band.In this paper,we have systematically studied the characteristic to meet to demand of the device applied in HF-VHF frequency range.Specifically,we have studied the characteristic of the permeability spectra of the NiCuZn ferrite and the manipulation method of damping coefficient function.We also studied how to make the material possessing high permeability and low loss material applied in HF-VHF frequency range.At last,for applications in electromagnetic shilding sheet and ferrite antenna,the NiCu Zn ferrites have been studied specifically.The main contents are as follows:Firstly,we have studied the permeability spectra of monodomain and multimodomain NiCuZn ferrites.When the damping coefficient is fixed as frequency-dependent,the agreement between the fitting permeability spectra and measured permeability spectra of domain and multidomain ferrite has been remarkably improved.Further study shows that the steepness of the ascent stage of the permeability spectra is influenced by the functional relationship between damping coefficient and the frequency.Meanwhile,the peak value and peak width of the imaginary peameability spectra are also be influenced by the above relationship.By introducing the concept of the domain acrossing grain boundary,we have discussed the physical interpretation of the damping coefficient function.The peak width of the imaginary permeability spectra of spin rotation is narrow.We theorized that monodomain design and damping coefficient function design can be treated as new technology methods to regulate the peameability spectra of the NiCu Zn ferrite applied in HF-VHF frequency range.Secondly,we have studied the main factors and the manipulation mechanism of the damping coefficient function experimentally.We have investigated the influence of the grain size,composition,additive on the damping coefficient function,respectively.Additionally,we have analyzed the reason why the damping coefficient function is influenced by the above factors by means of domain precession.The results show that the anisotropy field of the material has been influenced with the changement of the grain size,the formulation and the additives.As a result,the damping coefficient function will be changed.Thirdly,we have investigated the method for achieving the material possessing broad band,high permeability and low loss,applied in HF-VHF frequency range.We establish the effective criterion for evaluating the characteristic of broad band,high permeability and low loss: the product of the initial permeability ?i and upper limit frequency fd of straight low frequency range.The formula of this product is ?i×fd.The fd is defined using the differential method.Adopting monodomain design,increasing Snoek limit or changing damping coefficient function will enhance ?i×fd.Finally,we have investigated the NiCuZn ferrite specifically for applications of the electromagnetic shielding sheet and ferrite antenna.We have summarized out the design guideline for the material applied in electromagnetic shielding sheet.Monodomain design and damping coefficient design are all adopted to prepare the material with good properties for electromagnetic shielding sheet application.We have prepared the sample displaying equivalent high permeability and permittivity,as long with low loss factor at the frequency of 200 MHz,by using monodomain design and Co doping.Using this material as substrate,a miniaturized T-DMB(Terrestrial Digital Multimedia Broadcasting)antenna with good properties was designed.