【作者】 王亮；

【导师】 曹金祥；

【作者基本信息】 中国科学技术大学 ， 等离子体物理， 2009， 博士

【摘要】 随着人们对等离子体研究的不断深入,等离子体科学和技术不仅在工业、农业、生命科学和空间技术中得到了广泛的发展和应用,而且近年来这一学科在国外军事技术中也有了重要的发展和应用。等离子体隐身作为飞行器隐形的发展趋势,受到了各国的重视,许多国家都不遗余力的进行该项目研究,天线罩等离子体的研究便是其中的一个研究方向。天线是雷达系统中必不可少的重要组成部分,其隐身是一个长期困扰着工程技术人员的问题,飞行器再入大气层时需要靠雷达天线来搜寻目标,雷达天线则需要天线罩来保护。雷达天线的RCS又是飞行器的强反射区,如何缩减飞行器飞行状态的RCS,提高飞行器的生存能力有效打击来袭目标,是我们国家安全领域的瓶颈技术难题之一。基于此因,本文开展了薄层等离子体天线罩的研究工作。除等离子体隐身外,表面等离子体激元的激发亦能够实现对特定频段入射电磁波能量的完全吸收。表面等离子体激元(Surface plasmons,SPs)是一种高度局域的电磁表面模,它沿着两种介质的分界面传播,而在垂直于界面方向则以指数形式向两侧的介质内衰减。表面等离子体激元的一个重要特性就是,它能与满足一定耦合条件的电磁波发生耦合,使电磁波能量转化为表面等离子体激元的能量;也能通过适当的条件,使表面等离子体子激元转化为普通电磁波。因此表面等离子体激元可以融入一系列电磁波现象的研究中,例如通过激发表面等离子体激元来控制电磁波的传输,通过激发表面等离子体激元实现对入射电磁波能量的完全吸收。除此之外,表面等离子体激元在亚波长光学(Plamonics)、SPs纳米刻蚀技术、SPs新型光源等领域均有重要的应用。在微波领域,电磁波在金属铝中与在等离子体中具有类似的色散模型,金属可以看作是电子密度远大于入射微波截止密度的过密等离子体。因此金属边界的表面等离子体激元应和过密等离子体边界的表面等离子体激元具有相同的性质。基于此,本论文除研究天线罩等离子体外,还对表面等离子体激元的激发和应用技术作了研究。从等离子体的广义定义来讲,这两部分工作都属于电磁波与等离子体的相互作用,后者所引起的对入射电磁波能量的显著衰减为雷达天线的隐身研究提供了一种新的物理机制。本论文主要内容和创新之处如下:1.根据低气压电容耦合放电的原理,设计了一个用于规避电磁波的等离子体夹层天线罩,建立了一套天线罩等离子体发生系统,并进行了一系列旨在提高天线罩等离子体电子密度的实验,详细研究了Ar、Xe和Ar+Hg在不同配比条件下的放电对提高天线罩等离子体电子密度的影响。2.通过控制等离子体的电子密度,研究了该天线罩薄层等离子体在我们所能控制的电子密度范围内对5.09-6.8GHz微波反射的影响。实验发现,该等离子体天线罩在可控的电子密度范围内,可实现对特定频率范围内入射电磁波能量的显著衰减,该实验结果对雷达天线的隐身设计具有一定的参考价值。3.利用表面衍射光栅耦合技术和表面等离子体激元的基本理论,成功地在金属铝的表面上耦合激发了表面等离子体激元,首次在微波的X波段发现了电磁波通过亚波长金属狭缝的超强透射和聚束效应。我们的实验证实,该超强透射和聚束效应都与表面等离子体激元的耦合激发有着密切的联系,出射面具有周期结构是决定聚束效应产生的条件。我们在该频段耦合激发的表面等离子体激元,是目前国际上报道的在金属表面上实验耦合出的波长最长的表面等离子体激元,为表面等离子体激元在微波X波段的技术应用奠定了基础。4.在研究微波通过亚波长金属狭缝的超强透射实验中,我们还详细研究了表面周期结构数目和表面衍射光栅结构的几何参数对超强透射强度之影响。该研究成果为设计微波领域的金属透镜和表面等离子体激元耦合器的最佳参数奠定了实验基础,同时对光波领域和其它电磁波频域表面等离子体激元的研究也具有一定的参考价值和借鉴意义。5.实验研究了金属表面等离子体激元和过密等离子体边界上的表面等离子体激元对微波反射的影响。通过在金属或过密等离子体边界上耦合激发表面等离子体激元,能够使入射电磁波的能量转化为表面等离子体激元的能量。金属表面等离子体激元对10.6GHz微波的最大衰减约为30dB(0.1%),衰减15dB对应带宽约为0.4GHz,衰减10dB的带宽约为0.8GHz;过密等离子体边界的表面等离子体激元对5GHz微波的最大衰减约为23dB(0.5%),反射率R=0.5对应带宽约为0.1GHz。表面等离子体激元所引起的对入射微波能量的全吸收机制,为实现对电磁波能量的吸收提高了一种新的有效途径。更多还原

【Abstract】 With the study of plasma physics going deeper and deeper,plasma science and technology has been developed and applied more and more widely.Not only in the area of industry,agriculture,biology and space technology,but also in the region of military applications of several foreign countries in recent years.Plasma stealth,the developing trend of the stealth of flight vehicles,has attracted great attention from the world.And the investigation into plasma radome is one of the directions among them. The antenna is a necessarily important component in Radar system,whose stealth is a problem that puzzled the technology researchers all the while.The flight vehicle needs antenna to find its aim when reentering the aerosphere,and it also needs the protection by radome at the same time.The RCS of Radar Antennas is the region of strong reflelection,and how to reduce RCS is a difficult problem of the country’s security.Based on this subject,the dissertation carried out the work on plasma layer radome.Besides the plasma stealth,the excitation of surface plasmons(SPs) can also realize the total absorption of the incident electromagnetic waves(EMW) in special frequency band.Surface plasmon is a kind of surface waves that propagate along the interface but decay exponentially from the interface into both mediums.One characteristic of surface plasmons is that it can be excited by the EMW in free space under special coupling conditions,which renders the energy of incident EMW converting into that of SPs.Reversely,SPs could also couple out into free-space EMW under suitable coupling conditions.Therefore,SPs can be applied in a great deal of research on EMW phenomenon,such as via exciting SPs to control the propagation of EMW,via the excitation of SPs to achieve total absorption of incident EMW.Moreover,SPs also has important applications in the area of Plasmonics,SP etching on nanometer scale,SP novel light source and so on.In the microwave region,the dispersion models of EMW in metal aluminium and plasma have the same format,and metal can be regarded as an overdense plasma whose electron density is much greater than the critical density of the incident microwaves.Therefore,SPs at A1 surface and the boundary of overdense plasma have properties in common.So in this dissertation,besides the research on radome plasma, we also studied the excitation and applied technology of SPs.In the broad sense of plasma definition,the work on radome plasma and the coupling between EMW and SPs are both the interaction between plasma and EMW.And the surface-plasmon-induced total absorption of EMW energy provides a new physical mechanism for the stealth of Radar antennas.The main contents and highlights in this dissertation are as following.1.Based on the principle of low pressure capacitively coupled discharge,we designed a plasma layer radome,built a radome plasma generation system,and carried out a series of experiments to highten the electron density of the radome plasma layer.We studied the discharge of Argon,Xenon,and the discharge of Ar+Hg at different mixed ratio in detail.2.By controlling the density of the radome plasma,we studied the influence of the plasma radome on the microwave reflection in the frequency region 5.09-6.8GHz. The experiment results show that the radome plasma can greatly attenuate energy of the incident EMW in special frequencie band when the plasma density is proper. These results will be of use to the plasma stealth of Radar antennas.3.By employing the diffraction grating coupling technology and the basic theory of surface plasmons,we successfully excited the SPs along Al/air interface,and first observed the extraordinary enhancement and beaming effect of EMW transmission through a single subwavelength metallic slit in X-band microwaves. Our experiments demonstrated that the extraordinary enhancement and beaming effect results from the excitation of surface plasmons,and the period corrugations in the output surface results in the beaming effect.The SPs we excited in the X-band microwaves have the longest wavelength that has been experimentally achieved so far.It is of fundamental importance to the applications of SPs in the X-band microwaves.4.In studying the extraordinary enhancement of microwave transmission through single subwavelength slit,we also examined the influences of the groove number and the periodical parameters on the enhancement factor in detail.These works provide an experimental premise to the design of metallic lens and SP coupler in the microwave region.At the same time,our results are also of reference value to the SP study in the optical regime and other EMW frequency regions.5.We experimentally investigated the influences of SPs at boundary of overdense plasma and that at Al surface on microwave reflection.By coupling the incident microwaves into SPs at metal surface or the boundary of overdense plasma,we can convert the incident EMW energy into that of SPs.SPs at Al surface can attenuate the microwave of 10.6GHz to about 30dB(0.1%) at the most,and the band-width at the attenuated value of 15dB is about 0.4GHz,with that of 10dB being about 0.8GHz.At boundary of overdense plasma,SPs can attenuate the microwave of 5GHz to about 23dB(0.5%) at the most,and the band-width at R=0.5 is about 0.1GHz(R:reflection coefficient).The mechanism of surface-plasmon-assisted total absorption of incident EMW energy provides a new effective mean to the absorption of EMW energy.更多还原