| The plasmas sheaths in the hypersonic velocity of reentry can seriously threat communication, which is opaque to the electromagnetic wave. There have been many categories to make the plasmas sheaths appear transparent, for example, using high frequency laser or strong magnetic. Other suggestions are to destroy the plasmas sheaths by electrophilic injection or by vehicle reshaping. But such solutions have high cost and are not well supported by existing infrastructure. On the other hand, the parameters of the plasmas sheaths easily affected by the electromagnetic field, even the weak magnetic field, can produce nonlinear effect. The nonlinear effect in plasmas sheaths provides a new idea to solve the problem of blackout communication.Three aspects in the plasmas sheaths, which are the electromagnetic wave propagation characteristics, the nonlinear interaction of three wave, and frequencymodulated signal propagation characteristics, are analyzed and simulated in detail. The expressions of the attenuation coefficient and the phase factor of the electromagnetic wave are expounded and analyzed in detail. The rules of the carry and frequency-modulated signal attenuation are numerically showed. The field equation of the electromagnetic wave incident plasma sheath is deduced. The results show that the electromagnetic wave suffers from attenuation to frequencies lower than the plasma frequency.Secondly, from the field equation of the incident wave, the mechanism of the nonlinear three wave interaction is discussed. From the fundamental equations of electromagnetic field, the transmission of the incident wave and Stokes wave in the plasma sheath are simulated. The density distribution of the plasma sheath is improved, and the parabolic distribution and double exponential distribution are analyzed for the influence of the nonlinear three-waves interaction. Research shows that the Stokes wave generated by the nonlinear effect is more easily to be received by the aircraft under the double exponential density distribution.Finally, the transmission of the frequency modulation signal is analyzed and numerically showed. From the expression of energy flux density, the power change of incident wave and Stokes wave in nonlinear process is analyzed. The study shows that when the baseband frequency is 2MHz and the maximum frequency deviation is 200 KHz, the transmission of electromagnetic wave in the plasma sheath is only considered fixed amplitude attenuation.The study shows that the electromagnetic wave frequency is lower than the plasma frequency, and the signal has a serious attenuation. The nonlinear effect of electromagnetic wave and plasma sheath can excite the new frequency of the electromagnetic mode, and realize the transmission of information. |
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