Research On Nonlinear Loss Charateristics Of Yttrium Iron Garnet Material Under Action Of The Microwave Narrow Pulse

The miniaturization and integration of electronic equipment increase its sensitivity to strong electromagnetic pulse interference.High power microwave(HPM),one of the strong electromagnetic pulse,has the characteristics of narrow rise edge and puls width and high peak power,which can cause electromagnetic damage to sensitive components of electronic system.Therefore,the research on the protection technology and mechanism in the HPM environment has been paid more attention by scholars all over the world.Ferrite is an important microwave functional material.Under the high power microwave,the instability process of spin wave in ferrite can be excited.The amplitude of the excited spin wave increases exponentially with time,leading to a large loss of the energy.However,the traditional nonlinear loss theory,that ferrite limiter is based on,takes long microwave pulse or continuous wave pulse as the condition,which is not suitable for HPM environment containing rich pulse time domain waveform parameters(pulse width,power,rise time,etc.).In particular,there are few research about the characteristics of nonlinear loss effect of ferrite under narrow pulse condition.The thesis is helpful to understand the mechanism and law of nonlinear loss effect of ferrite under narrow pulse of microwave,and provide technical basis for subsequent HPM protection.The influence of HPM pulse rise time parameters on the nonlinear effect of ferrite is discussed in this thesis.Based on the classical theory of ferrite nonlinear effect,a threshold theory model of ferrite nonlinear effect considering waveform parameters including rise time and signal power is proposed.The transmission line model of nonlinear effect of yttrium iron garnet ferrite(YIG)material was established,and the numerical relationship of nonlinear effect of ferrite under different pulse fronts,power parameters and external magnetic field conditions was expounded.Finally,the YIG nonlinear effect microstrip model under different frontier parameters in X-band was developed,which was composed of polycrystalline YIG substrate with size of50mm×12mm×0.7mm,saturation magnetization of 1800 Gs and relative dielectric constant of 14.5,and 50 ohm microstrip line with length of 50 mm.Experimental study of high power microwave injection was carried out under different external bias magnetic fields.Experimental data and theoretical results were compared and analyzed.This thesis research shows that under the conditions of external bias magnetic fields ranging from 500 Gs to 1100 Gs,rise edge parameters ranging from 40 ns to 600 ns,and maximum injection power about 150 W,the calculated results of nonlinear effect threshold theoretical model are in good agreement with the experimental data.The threshold power of the ferrite nonlinear effect is related to the front edge of microwave pulse.The smaller the rise edge leads to the higher the threshold of the nonlinear effect is,and the threshold is about 60 W and 1W at the rise edge of 40 ns and 600 ns,respectively.When the rise edge exceeds 400 ns,the threshold tends to the long pulse threshold or continuous wave threshold.For the same rise edge,the higher the input power leads to the higher the nonlinear loss,and the corresponding nonlinear loss can be up to 10 d B for the pulse(rise edge:600ns and power:150W).For the same input power,the larger the frontier parameter has the higher the nonlinear loss.When the input power is about 100 W,the nonlinear loss generated by the pulses(rise edge:100ns to 600ns)is about 3d B to 9d B.