THz application
2015, 44(12): 3690-3695.
The plasma sheath produced in the progress of entry or reentry flight has attracted much attention as it would impact the propagation of electromagnetic wave. This plasma sheath is a group of weakly ionized gas in general and has the ability to influent the communication between aero craft and ground. Sometimes the existence of this plasma sheath even cloud cause the communication blackout which is not desirable. To improve this problem plenty of researches have done, some of the researches mentioned that raising the wave frequency could be one way. The development of intensive terahertz sources broke up the restrain of electromagnetic wave in microwave range, there comes out several researches on the interaction between terahertz wave and plasma. Computational fluid dynamics was used in numerical simulating of a thermodynamics and chemical nonequilibrium flow over the aero craft to calculate the electromagnetic characteristics of plasma layer. Four flight scenes and different incidence forms were taken to discuss the interaction between terahertz wave and plasma sheath. And the propagation of terahertz wave along with different paths was discussed. From the simulating results, terahertz wave is capable to transmit in the plasma sheath with high electron density when the flight height is lower.
2015, 44(12): 3696-3700.
The extinction characteristic of graphite smoke at 337 m was calculated on the basis of Mie scattering model. And the extinction characteristics of it at conventional infrared bands(3-5 m, 8-12 m) and representative wavelength of laser(1.06 m) were calculated later. The results indicate that the mass extinction coefficient(MEC) of the smoke at 337 m is smaller by 1-2 orders of magnitude than that of other wavelengths or wavebands. Then, the transmission experiments about two kinds of smoke with different diameters of graphite particles were conducted respectively at those wavelengths and wavebands mentioned above. Finally, the MECs at 337 m, 1.06 m, 3-5 m and 8-12 m were deduced, and corresponding experimental results were contrasted. The MECs of two kinds of smoke at 337 m are all less than 0.045 m2/g, and the values at other wavelengths or wavebands are further higher than it. The final results demonstrate that THz wave of 337 m has stronger penetration capacity for smoke.
