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After entering the near space, a layer of plasma sheath is formed outside the hypersonic vehicles due to the hightemperature and high-pressure environment. The plasma sheath, which characteristic frequency is similar to microwave, will cause serious impediment to communication signal. This phenomenon is known as the blackout problem. With the rapid development of aerospace industry, plasma sheath blackout has become an urgent problem to be solved. Current research shows that increasing the frequency of electromagnetic wave higher than the plasma characteristic frequency can effectively reduce the shielding effect of plasma. The frequency of terahertz (THz) wave is much higher than microwave, it can propagate through plasma sheath, which provides an effective method to solve the problem of plasma sheath. In this paper, a theoretical model of plasma is established, and the transmission properties of THz wave in plasma is simulated using scattering matrix method. Then a kind of plasma jet is produced in laboratory environment according to dielectric barrier discharge. And the experiments of a broadband THz source and THz time-domain spectrum transmission in this kind of plasma and a 2.52 THz wave reflection imaging of target under plasma shelter are carried out respectively. The transmittance increases with frequency under 0.5 THz and becomes stable at 100% over 0.5 THz, and the result of experiments and simulation are in good agreement. Both theory and experiments show that THz wave has good penetration in plasma jet and can detect targets behind plasma, and this study will lay a theoretical foundation for solving the plasma blackout problem of hypersonic vehicle in near space.
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