The Research On Ferrite Used For NFC Antenna

In this thesis, in order to achieve high real permeability and low imaginarypermeability NiCuZn ferrite for NFC antenna, the influences of Ni/Zn proportion,additive and process conditions on the magnetic properties the NiCuZn ferrite have beenthoroughly analyzed. The optimized NiCuZn ferrites were chosen to manufacture theflexible ferrite sheets and their properties were tested. The main results are as follows:1. The influences of Ni/Zn proportion on the microstructures and magneticproperties of Bi-modified NiCuZn ferrites were investigated. Also according to thedesigning standards， the optimum ration of Ni/Zn content was obtained. Then theeffects of sintering schedule on the densification, microstructures and magneticproperties were researched. Results show that some Bi³⁺ions enter into the spinel latticegradually and consequently improve the microstructural uniformity and densificationwith the increase of calcination temperature. The permeability could be improved withraising the sintering temperature and extending the sintering time appropriately.2. Effects of substitution of Al³⁺and Co²⁺, the Bi³⁺content on the magnetics andmicrostrure of NiCuZn ferrites were investigated. With the increase of Al³⁺ions,permeability and Bs decreased monotonously while the effect on magnetic loss was notsignificant. The permeability and average grain size of samples increased firstly thendecreased with the increase of Bi³⁺ions. And the second phase appears with highcontent of Bi³⁺ions. The Co²⁺substitution in Bi-modified NiCuZn ferrites showed goodmagnetic properties at a low sintering temperature.3. Effects of Co₂O₃、V₂O₅and Bi₂O₃additive on magnetic properties and themicrostructure of NiCuZn ferrites were investigated. The substitution of Co²⁺couldincrease the cut-off frequency, reduce the magnetic loss effectively and improvetemperature stability. Doing sintering additives V₂O₅and Bi₂O₃could reduce thesintering temperature and the optimum adding amounts were0.5wt%and1wt%respectively.4. Powder prepared by solid phase reaction method was used to make ferrite sheetswith different sizes, thicknesses and cutting depths. The influences of sintering temperature、sintering time and ferrite sheet thickness on reading and writing distance ofNFC antenna were researched.