| With the application and popularization of high frequency electronic and electric technology,in order to avoid the interference of electromagnetic wave in the operation of electronic equipment and damage to human health,microwave absorption materials and mechanisms have always attracted the attention of researchers.In addition,the military field has always had a strong demand for microwave absorption materials for radar band.Up to now,although various wave-absorbing materials have been characterized in published journals,most of them still remain in the superficial characterization stage such as sample preparation and reflection loss calculation,without in-depth analysis of wave-absorbing mechanism,regulation of wave-absorbing properties and design of wave-absorbing materials starting from the target frequency band.Therefore,there are still many problems to be explored in the field of microwave absorption.With high-frequency of electronic and electrical devices and the development of wide band gap semiconductor(WBG),in order to realize the full potential of the high frequency application potential of WBG,it is urgent to develop a kind of high frequency soft magnetic material which can effectively work in matching frequency band of WBG.The oriented Y2Fe17N3-δ/PU composite with low volume fraction has higher initial permeability and natural resonance frequency,and can obtain excellent impedance matching at high frequency.In this paper,Y2Fe17N3-δ magnetic powders are prepared by reduction diffusion method innovatively.Y2Fe17N3δ#SiO2 magnetic powders are obtained by coating.Oriented Y2Fe17N3-δ/PU and Y2Fe17N3-δ@SiO2/PU composites with different volume fractions are prepared and their electromagnetic parameters are measured.Based on the interfacial reflection model and λ/4 interference cancellation theory,impedance matching,phase matching and the strongest reflection loss are directly related to regulate properties,and the variation of reflection factor((?))and effective absorption bandwidth(EAB,RL<-10 dB)with frequency is analyzed.Based on the design objectives of "thin thickness,light weight,wide band and strong reflection loss",the absorbing materials are designed and the absorbing properties are compared from the specific frequency band(X-band,Ku-band).For example,with thickness of 1.49 mm and 1.16 mm,the EAB of Y2Fe17N3-δ/PU(20 vol%)can cover the X-band and Ku-band respectively,and their RLmin are-13.78 dB and-11.66 dB respectively;with thickness of 1.94 mm and 1.40 mm,the EAB of Y2Fe17N3δ@SiO2/PU(20 vol%)can cover the X-band and Ku-band respectively,and their RLmin are-30.91 dB and-50.01 dB respectively.Based on the source of the reflection loss peak,the effective absorption bandwidth formula is derived from the microwave amplitude,and the calculated results agree well with the experimental results.Y2Fe17N3-δ/PU soft magnetic composite(SMC)with high volume fraction not only has high saturation magnetization,but also has the potential to break the Snoek limit and obtain high initial permeability and high natural resonance frequency,which can be used as the soft magnetic material matching WBG.In this paper,oriented composite materials with volume fraction of 65%,irregular spherical Y2Fe17N3-δ/PU(SA1),flake Y2Fe17N3-δ/PU(SA2)and large diameter-thickness ratio flake Y2Fe17N3-δ/PU(SA3)with different molding pressures are prepared.The high frequency losses of them are measured and separated.The degrees of plane orientation(DPO)of SA1,SA2 and SA3 molded at 150 MPa are 95.81%,97.14%and 98.78%;the initial permeability are 7.2,14.4 and 16.8;the core losses are 4615.15 kW/m3,2246.05 kW/m3 and 807.91 kW/m3 at 3 MHz and 8 mT;the performance factors are 8.68,14.02 and 33.05 respectively at 500 kW/m3 and 10 MHz.The above data indicate that for oriented Y2Fe17N3-δ/PU composite,flake Y2Fe17N3-δ magnetic powder with large diameter-thickness ratio is beneficial to improve high frequency soft magnetic properties and reduce core loss.Among them,SA3-450 has the best high-frequency magnetic properties and the lowest core loss.The initial permeability of SA3-450 is 18.3.The core loss of SA3-450 is 623.88 kW/m3 at 3 MHz and 8 mT.The performance factor of SA3-450 is 40.28 at 500 kW/m3 and 10 MHz.These results indicate that 450 MPa is the most suitable molding pressure for large diameter-thickness ratio flaky Y2Fe17N3-δ/PU oriented composite. |
