【作者】 徐欣欣；

【导师】 江建军；

【作者基本信息】 华中科技大学 ， 微电子学与固体电子学， 2013， 博士

【摘要】 电磁性能可调的有耗频率选择表面电磁吸波结构是宽频微波吸波结构候选体系,已成为微波吸收结构研究热点之一,备受关注。本文提出适用于宽频吸波结构体系分析与优化的直接图解法。应用直接图解法来研究Salisbury屏和Jaumann吸收体的电磁响应特性和吸波机制。并建立了典型单谐振点频率选择表面图形单层与双层吸波结构的理想阻抗匹配模型,用于指导宽频吸波结构设计。进一步,采用直接图解法研究了基于有源频率选择表面的智能吸波结构的吸波特性,来指导智能吸波结构优化设计和分析。采用Smith圆图和等效电路直接图解法分析了Salisbury屏的工作原理,同时考察了Salisbury屏各结构参数对吸波带宽的影响。研究结果表明,Salisbury屏的设计厚度可以通过介质板的介电常数来调整。当介质板的介电常数增大时可以相应减小Salisbury屏的设计厚度,但是伴随吸收峰变窄,带宽变小采用Smith圆图和等效电路直接图解法优化设计了Jaumann吸收体,同时考察了Jaumann吸收体各结构参数对吸波带宽的影响。研究结果表明,通过合理添加Jaumann吸波体的层数,可以使吸波体导纳曲线更加集中,从而获得更宽带的吸波效果。10mm厚度的Jaumann吸收体在4-16GHz范围内反射率低于-8dB,其吸波性能明显优于同厚度的Salisbury屏。设计了由方环和圆环单谐振点频率选择表面图形构成的单层宽带吸波体。借助Smith圆图和等效电路直接图解法发现其阻抗匹配遵循以下规律：当接地介质板电纳的零点中心频率与频率选择表面图形的谐振点相接近；频率选择表面图形的谐振点电导在合理范围之间；端点频率电纳与接地介质板电纳相接近时,可以通过接地介质板和频率选择表面图形的电纳部分相互抵消来得到宽频吸波效果。5mm厚的单层吸波体反射率低于-8db的频带为4GHz～18GHz,远远大于相同厚度下的Salisbury屏,优化Jaumann屏和商用非磁性单层结构吸波体。对于由方环和圆环单谐振点频率选择表面图形构成的双层宽带吸波体来说,其阻抗匹配应当遵循以下规律：当接地介质板电纳的零点中心频率与两组频率选择表面图形的谐振点相接近；上、下层频率选择表面图形谐振点电导控制在合理范围之间；上层介质隔离板能够旋转合适的角度到达上层频率选择表面导纳曲线附近半圆并与其匹配最终到达Smith圆图的中心位置时,可以得到宽频吸波效果。10mm厚双层吸波体从3.3GHz频点开始可以获得低于-8dB的吸波带宽,远远大于相同厚度下的Salisbury屏,优化Jaumann屏和商用非磁性双层结构吸波体。研究表明,智能吸波结构可以通过有源频率选择表面的加载来实现。利用这个特点,在组合型频率选择表面中集成PIN二极管形成阵列,通过改变激励PIN二极管的偏置电压,即可以实现吸波体反射特性的动态改变。借助等效电路直接图解法的优化设计,通过改变有源频率选择表面的等效参数,进一步调节吸波体阻抗匹配状况,实现了在2-18GHz频段宽频可调的智能吸波结构。更多还原

【Abstract】 The adjustable electromagnetic absorbing structure has made considerable progress in the last years. In particular, attention is paid to the lossy frequency selective suface (FSS) to chose it one of candidate systems to realize broadband wave absorbing structure. At first the graphical method for analysis and optimization design of broadband wave absorbing structure is presented. The graphical method is employed to analyse the electromegnetic properties and absorbing principle of Salisbury screen and Jaumann absorber. And then a single and double layer optimal broadband impedance match model based on the single resonance FSSs has been established for the design of broadband wave absorbing structure. Futhermore. the absorbing principle of smart absorbing materials based on active FSSs have been extensively analysised by graphical method for analysis and optimization design of smart absorbing structure.The principles of the Salisbury screen and the influences of the structure parameters to the wave absorbing performance has been studied by Smith chart method and equivalent circuit method. The results indicated that the thickness of the Salisbury screen could be adjusted by the permittivity of the dielectric substrates. If the permittivity of the dielectric substrates increased, the thickness of the Salisbury screen would decrease and the absorption peak would narrow, the bandwidth would decrease.The Jaumann absorber was analysised by Smith chart method and equivalent circuit method. The results revealed that the Jaumann absorber could be designed to produce a larger bandwidth, particularly as more layers were added. A further compression of the final curve was seen because more layers were added. The Jaumann absorber allow obtaining remarkable performance (-8dB in the band from4GHz to16GHz) with an overall thickness of10mm. This performance is superior to Salisbury screen with the same thickness.A single layer broadband electromagnetic absorbers using square loop and circular loop shaped FSSs were designed by Smith chart method and equivalent circuit method. The impedance match law was found as follows:When the null center frequency susceptance of the ground plane is nearly equal to the resonance of the FSSs; resonance conductance of the FSSs remain within a fairly reasonable range; the endpoint frequency susceptance of the FSSs is nearly equal to the susceptance of the ground dielectric plane, the susceptance of the FSSs and the ground dielectric plane to a large degree cancel each other leading to a small reflection. The single layer absorber allow obtaining remarkable performance (-8dB in the band from4GHz to18GHz) with an overall thickness of5mm. This performance is superior to Salisbury screen, optimized Jaumann screen and the available commercially non-magnetic single layer structures with the same thickness.For the double layer broadband electromagnetic absorbers using square loop and circular loop shaped FSSs, the impedance match law was found as follows; When the null center frequency susceptance of the ground plane is nearly equal to the resonance of the two sets of FSSs; resonance conductance of the up-down layer FSSs remain within a fairly reasonable range;The process curve transform through the up layer dielectric slab and obtain the next curve near the admittance curve of the up FSSs. The final match between the curve and admittance of the up layer FSSs yeilding to a broadband absorbing property. The double layer absorber allow obtaining remarkable performance (-8dB in the band greater than3.3GHz) with an overall thickness of10mm. This performance is superior to Salisbury screen, optimized Jaumann screen and the available commercially non-magnetic double layer structures with the same thickness.The research indicated that the smart absorbing materials could be designed by loading the active FSSs. A tunable absorbers comprised of a new combination shaped FSSs printed on a dielectric substrate loaded with PIN diodes were demonstrated. Through at different voltages to control the diodes, the reflectivity characteristics of the structure can be varied. A qualitative analysis by the equivalent circuit method is carried out on the parameters of the tunable absorbers. Though the impedance match, the structure can be turned to provide a variable reflectivity response over a band of frequencies from2GHz to18GHz.更多还原