Plasma has been of great interest to engineers and scientists during the past few decades due to its wide applications. Besides, the plasma-sheath-caused lose of communication (i.e. re-entry blackout) that happens when a spacecraft re-enters the earth atmosphere is still a problem to be solved. The microwave characterisation of shock tube excited plasma has been an important method for exploring the transmission and reflection of microwave signals in plasma. The existing frequency sweep or multi-frequency technologies are not desirable for the characterisation of high-speed time-varying plasma generated in shock tubes. Hence, in this paper a novel signal-frequency approach is proposed to measure both electron density and collision frequency of plasma in shock tube. As frequency sweep is not required in this method, it is extremely suitable for characterising the shock tube excited high-speed time-varying plasma. The genetic algorithm is applied to extract electron density and collision frequency from the reflection coefficient. Simulation results demonstrate excellent accuracy for electron density within 1 0 10 ～ 1 0 12 c m ? 3 and collision frequency within 5 × 1 0 10 ～ 1 0 12 H z . This work paves the way for a fast and compact microwave reflection measurement of shock tube generated plasma.
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机译：在过去的几十年中，等离子体由于其广泛的应用而引起了工程师和科学家的极大兴趣。此外，当航天器重新进入地球大气层时发生的等离子体鞘引起的通讯中断（即重新进入停电）仍然是有待解决的问题。激波管激发等离子体的微波表征一直是探索微波信号在等离子体中的传输和反射的重要方法。现有的扫频或多频技术对于表征激波管中产生的高速时变等离子体是不理想的。因此，本文提出了一种新颖的信号频率方法来测量电子密度和激波管中等离子体的碰撞频率。由于此方法不需要扫频，因此非常适合表征激波管激发的高速时变等离子体。应用遗传算法从反射系数中提取电子密度和碰撞频率。仿真结果表明，电子密度在1 0 10〜1 0 12 c m？范围内具有极好的精度。 3，碰撞频率在5×1 0 10〜1 0 12 H z之内。这项工作为快速，紧凑地测量激波管产生的等离子体的微波反射铺平了道路。
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