有耗介质覆盖平面导体表面波传播特性的计算

本文推导了圆柱坐标系下有耗介质涂覆平面导体表面波的场函数和本征方程、每波长径向衰减常数α；分析了介质特性参数、介质层厚度与α的关系；指出磁损耗介质比电损耗介质有更好的抑制表面波的效果。     

光敏型聚酰亚胺对声表面波传输损耗的研究

采用扰动理论推导了聚酰亚胺薄膜作为声表面波的吸声材料时,声表面波的传输损耗模型。利用网络分析仪对表面涂覆厚5μm光敏型聚酰亚胺薄膜的双声路SAW传感器(中心频率165 MH z)的插入损耗进行测试,对理论模型进行了实验验证。理论结果表明,聚酰亚胺薄膜造成SAW的传输损耗和传感器的中心频率的高低、聚酰亚胺薄膜的厚度以及聚酰亚胺薄膜的宽度成正比。实验测试也证明,聚酰亚胺薄膜对声表面波造成的传输损耗和宽度成正比关系,测得传输损耗为9.5 dB/mm。     

改性PbTiO_3压电陶瓷及其在SAW中的应用

本文介绍了采用一般工艺研制的以Nd、Mn、In改性的PbTiO_3压电陶瓷的性能及其测试方法;并探讨了In含量与瓷料的晶粒尺寸、表面波延迟温度系数及传输损耗的关系。以化学分子式为(Pb_(0.88)Nd_(0.1))(Ti__(0.92)Mn_(0.02)In_(0.06))O_3的配方获得了晶粒尺寸为0.5～1.8μm; 抛光表面气孔小于1.5μm;表面波传输损耗为4dB/cm(30MHz);相对介电常数为210;机械品质因数为1800;表面波延迟温度系数为20ppm/℃(0～80℃)优良压电陶瓷材料。本文研究了这种陶瓷材料在SAW中的应用。     

Kerr型介质界面上弱非线性TM表面波的传播特性

本文研究Ｋｅｒｒ型介质界面上弱非线性ＴＭ表面波的性质。数值计算表明了沿线性与非线性介质界面传播的ＴＭ表面波的自散焦特性。     

光声方法测量粘弹介质声衰减的研究

衰减是材料的一项重要参数,测量衰减将有助于评估材料的空隙率、微观裂纹分布、颗粒尺度、材料强度及软体组织结构等。该文利用光声手段对介质的表面波衰减进行了测量研究。由激光激发表面波,换能器检测。对连续采样所获得的表面波信号进行加窗、滤波、FFT处理及相干分析,得出介质衰减与频率的关系。实验结果表明,利用光声手段及表面波方法是对固体材料衰减测量的有效手段之一。     

渐变表面左手介质表面波天线散射特性分析

利用严格的模匹配与多模网络相结合的方法以及阶梯近似和阻抗转移技术分析了不同渐变曲线形状的左手介质表面波天线的反射与辐射特性,着重研究了不同渐变形状对天线反射与辐射特性的影响.从电磁波散射的角度将辐射问题转化为表面波和空间波的传输问题,从而使分析过程得到了极大的简化.分析表明左手介质表面波天线的辐射特性与传统右手情形有很多不同,说明了产生这种不同的原因.所给出的计算结果对左手介质表面波天线的设计有实际参考意义.     

电容加载共面波导移相器的损耗特性

借助仿真软件Sonnet研究了金属导电层厚度、电导率和铁电薄膜介质损耗对移相器传输损耗和反射损耗的影响。结果显示:导电层的厚度超过2.0μm后,移相器的传输损耗不再随导电层厚度的增加而改变;随着导电层电导率的增加,移相器的传输损耗在高频段迅速减小;随着铁电薄膜介质损耗的减小,移相器的传输损耗在高频段下降很快;当介质损耗小于0.001时,移相器的传输损耗几乎不再减小。前述三种因素对反射损耗基本无影响。     

厚介质防护层下天线方向图恶化机理分析及解决办法

定性的讨论了厚介质防护层下天线方向图的恶化机理,并结合电磁软表面提出了改善天线辐射性能的方法。将厚介质防护层等效为多层不同数值的阻抗层。通过分析电磁波和表面波的传播路径,解释了厚介质防护层下天线方向图恶化的原因。通过增加电磁软表面,扼制了表面波的传播及其引起的辐射,降低了厚介质防护层对天线方向图的影响。方向图测试结果显示,利用电磁软表面抑制表面波的传播,可以有效改善厚介质防护层下天线的方向图,在高超音速飞行器通信领域具有一定的应用前景。     

垂直电偶极子在有介质导电平面上激起的场

分析研究了垂直电偶极子在介质涂敷的理想导电平面上激起的电磁场 ,获得了场分量的解析表达式。分析表明 ,垂直电偶极子在介质涂敷的导电平面上激起的电磁场可分解为直达波、反射波、侧面波和吸附表面波。其中吸附表面波在沿介质表面传播的波数介于在空气层和介质层中传播波数 k0 与 k1之间 ,其幅度按ρ-1/ 2 规律衰减 ,在垂直于介质层方向则以指数规律衰减。文中导出的直达波、反射波、侧面波项则与文献 [1 ]中的结果完全一致。当介质层较厚时 ,由于表面波与侧面波相加的结果 ,总场将发生明显的干涉现象。     

微带结构Sommerfeld 积分奇异性分析和表面波极点有效提取

提取表面波的DCIM能够准确计算无耗分层媒质中的空域格林函数。然而,多层媒质表面波极点的提取比较困难,并且此方法没有考虑侧面波在远区的作用。本文基于复变函数理论,严格分析了Sommerfeld积分极点和支点奇异性对远场的影响;将PSO(particle swarm optimization)与Newton-Raphson算法相结合,提出一种快速精确定位表面波极点的方法,并将其应用到提取表面波的三级DCIM,实现了分层媒质空域格林函数的准确计算。通过单层无耗介质和四层有耗介质微带结构空域格林函数的计算实例,证明了该方法的正确性和有效性。     

Scattering of electromagnetic waves by a perfectly conductingcylinder with a thin lossy magnetic coating

We study the scattering interaction of electromagnetic (EM) waves with an infinite cylinder coated with a lossy dielectric material with frequency-dependent material properties. These properties are hypothetical, yet representative of a wide class of available materials. The monostatic and bistatic scattered widths (SW) are evaluated for the TM or TE polarization cases. These calculations require the use of algorithms to evaluate Bessel-Hankel functions of complex arguments. These algorithms are based on a continued fraction approach, which ensures stability of the recursion relations. The bistatic plots of the TM and TE scattering widths for the coated body are displayed in a convenient color-graded scale. The reductions in the scattering widths produced by this type of coating are determined in selected frequency bands and angular sectors, in both polarization cases. It is quantitatively shown how curvature and polarization shift the effectiveness band of the coating. The determined regions in which the SW are minimally affected are the most suitable for target identification purposes     

Surface waves on the interface between a left-handed and a right-handed medium

The frequency regions where a surface wave (SW) exists on a dielectric/metamaterial interface are determined for the case when the metamaterial??s refractive index is negative. With allowance for the conditions of TE and TM SW existence in the structure, the characteristic frequencies that can be controlled with the help of the external magnetic field are calculated. On the basis of dispersion dependences for SWs, it is shown that the TM (TE) wave is forward (backward), and the backward wave is substantially slowed in the structure.     

Surface-Wave Launchers for Beam Steering and Application to Planar Leaky-Wave Antennas

A linear array of surface-wave launchers (SWLs) is presented for surface-wave (SW) beam steering on a grounded dielectric slab (GDS). Specifically, a two-element array of directive Yagi-Uda like SWL antennas (operating between 21–24 GHz) is investigated. By varying the relative phase difference between SWL elements, the excited SW field distribution can be steered. In addition, a six-element linear array of SWLs with nonuniform weighting is also presented. If metallic gratings are placed on top of the GDS, the bound SW mode can be transformed into a radiated leaky-wave (LW) mode and directive beam patterns can be generated in the far field. A specific elliptical grating configuration is also investigated demonstrating single frequency cylindrical-sector LW beam steering. These slotted SWL arrays can be useful for novel SW beam scanning designs, millimeter wave power distribution systems and new LW antennas.      

Reducing losses in dielectric waveguide discontinuities

Rectangular dielectric waveguides are used in millimeter-wave applications. They have low loss and wide bandwidth at high frequencies. Another major advantage to dielectric waveguides is that they are inexpensive to design and manufacture. However, a major disadvantage to the dielectric waveguide is that they experience relatively high losses at bends and T-junctions. This paper looks at a novel approach in reducing the insertion loss in dielectric waveguide bends and T-junctions. A high dielectric material is inserted at the discontinuity, causing the electromagnetic energy to be coupled and launched toward the output. The dielectric constant of the material, position of the material, and shape of the material are instrumental in reducing the insertion loss. A transition discontinuity in the form of a 45° bend has also been found to reduce insertion loss when properly designed. The size, shape, and location of the discontinuity and the high dielectric material are optimized and compared to the results without a high dielectric material. The 90°- and 45°-bend simulations were verified by building test structures and comparing predictions of the insertion loss to measurements     

短/中波双色碲镉汞红外探测器制备研究

报道了基于分子束外延的短/中波双色碲镉汞材料及器件的最新研究进展。采用分子束外延方法制备出了高质量的短/中波双色碲镉汞材料,并通过提高材料质量将其表面缺陷密度控制在300 cm-2以内。在此基础上进一步优化了芯片制备工艺,尤其是在减小像元中心距方面作了优化。基于上述多项材料及器件工艺制备出了320×256短/中波双色碲镉汞红外探测器组件。结果表明,该组件的测试性能及成像效果良好。     

Millimeter wave twist reflector design aspects

A millimeter-wave twist reflector design procedure is described. An effective dielectric constant for capacitive susceptance correction for a unidirectional planar grating at the interface of free space and dielectric material in the twist reflector environment is introduced. The loss factor of the dielectric material is taken into account for the prediction of twist reflector performance. With the introduction of these corrections experimental results are found to be in close agreement with the theory. Normalized curves for the design of twist reflectors in terms of grating parameters, dielectric substrate relative permittivity, and dielectric material thickness are presented. Experimental results are given     

Microwave Measurement of Dielectric Constant of Liquids and Solids Using Partially Loaded Slotted Waveguide (Short Papers)

An accurate method is described for the measurement of the dielectric constant of liquids and solids. The dielectric material partially loads a slotted rectangular waveguide and the guide wavelength is measured for two different thicknesses of the dielectric. The guide wavelengths are related to the dielectric constant of the material through a characteristic equation which can be solved graphically or numerically. Some experimental results are obtained and found to be in close agreement with the values of the dielectric constant available in the literature.     

氧化镉掺杂对钛酸钡基陶瓷材料改性

对ＢａＴｉＯ３－ＺｎＮｂ２Ｏ６－ＣｄＯ系陶瓷介质材料的介电性质进行了研究，并对ＢａＴｉＯ３，ＢａＴｉＯ３－ＺｎＮｂ２Ｏ６，ＢａＴｉＯ３－ＺｎＮｂ２Ｏ６－ＣｄＯ三种材料介电常数，温度稳定性，介电损耗，显微结构进行了比较，得出结论是ＢａＴｉＯ３－ＺｎＮｂ２Ｏ６－ＣｄＯ系陶瓷材料，介电常数高，损耗小，介电常数随温度变化小，是较理想的电容器陶瓷介质材料     

铜互连结构热应力分析及介电材料选择优化

基于Ansys有限元软件,采用三级子模型技术对多层铜互连结构芯片进行了三维建模。研究了10层铜互连结构总体互连线介电材料的弹性模量和热膨胀系数对铜互连结构热应力的影响,在此基础上对总体互连线介电材料的选择进行优化。结果表明,总体互连线介电材料的热膨胀系数对铜互连结构的热应力影响较小,而弹性模量对其影响较大;各层介电材料热应力与弹性模量成正比,SiN界面热应力与弹性模量成反比。最后,为了降低铜互连结构关键位置热应力,通过选用不同参数材料组合对总体互连线介电材料的选取进行优化,提高了铜互连结构可靠性。     

2维各向异性正方介质柱的带隙研究

因各向同性介质组成的正方晶格方形介质柱不能产生绝对带隙,而三角晶格正方介质柱可以产生很小的带隙,为了得到更大带隙,引入各向异性介质来代替各向同性介质,由于各向异性介质在不同方向上的介电常数不同,可以产生较大的绝对带隙,利用平面波展开法分别计算了正方晶格各向异性介质柱产生的绝对带隙宽度为0.03095ωe(ωe为中心频率),三角晶格各向异性正方介质柱产生的完全禁带宽度为0.03831ωe,是各向同性介质所产生带宽的3.6倍。这一结果对光子晶体带隙的研究是很有帮助的。