真空中高功率微波下介质材料击穿破坏的实验研究

Experimental research on damage of dielectric materials under high power microwave in vacuum

介质窗材料的击穿破坏限制了高功率微波(HPM)的产生和传输,严重阻碍了高功率微波技术的发展。为认识微波下介质材料的击穿破坏现象和机制,本文针对常见的几种介质窗材料(PTFE、PMMA、LDPE及HDPE)在真空中开展了微波击穿破坏实验。实验采用X波段微波源,其输出微波的频率为9.4GHz,功率为1GW,微波模式为TE11。研究了不同材料的微波击穿破坏特性,并针对PTFE介质材料考察了表面加工槽及打磨处理对其微波击穿的影响。对微波破坏后样品进行形貌分析,发现破坏通道与微波电场有着密切的关系,材料的表面加工处理对击穿破坏有显著的影响。通过对不同破坏程度样品的研究,提出了介质材料在微波作用下的破坏发展过程,即破坏初期为材料表面的点状破坏,随着破坏程度的加深,形成贯通的树枝状破坏通道,且破坏通道从材料的表面向内部延伸,最终导致材料的失效。

Breakdown of dielectric window materials limits the generation and transmission of high power microwave （HPM）,which blocks the development of microwave technology. In order to study the physical mechanism of this phenomena,the dielectric breakdown experiments with several kinds of dielectric window materials,i.e.,PTFE,LDPE,HDPE and PMMA,are performed under HPM with the power level of 1GW at 9.4 GHz in vacuum,and the model of microwave is TE11. The HPM breakdown characteristics of different materials are obtained,and the influence of different surface treatments for PTFE with notching and polishing on its breakdown characteristics is also studied. Based on the photography analysis of destroyed dielectric samples,it is found that,the breakage phenomena significantly occurred on the surface of dielectric window along the direction of microwave electric field,and the damage status is greatly affected by the different surface treatments. By studying the samples with different damage,the development of dielectric breakdown under HPM is proposed,it is considered that the earlier damages present small circular aperture on the surface of material,then develop into perfoliate channels on the surface,and as the further breakdown occurs,the tree-like breakages develop from the surface into the inside of a material.