一种新型复合左右手负阶谐振天线的设计

为了获得高增益小尺寸天线,通过在基片集成波导上引入二阶Hilbert分形缝隙,提出了一种新型复合左右手传输线.在等效电路模型的基础上,利用HFSS和Serenade软件对该传输线的电路参数进行了提取;利用MATLAB语言给出了该传输线的色散曲线;最后,由该传输线设计了终端短路的缝隙天线.实验结果表明：该天线馈电网络简单,工作在复合左右手传输线的-1阶模式上,比之前报道的复合左右手谐振天线具有更小的电尺寸和更高的增益.由于这些性能,使得该天线可以用于无线通信系统中.     

左手材料在天线中的应用研究进展

从理论上解释了左手材料用于天线设计时实现天线高指向性、高效率、小型化以及大扫描范围的原因,重点介绍了基于金属谐振结构和复合左/右手传输线(CRLH TL)结构的左手材料用于天线设计时的研究进展,指出金属谐振结构在提高天线方向性、增大天线增益、减小天线体积等方面具有很大优势,CRLH TL结构在提高天线带宽、增加天线频带、增大漏波天线扫描范围等方面具有潜在的应用价值。     

左手材料对介质谐振腔谐振参数的影响

"左手材料"是与传统材料性质相悖的另外一种材料。根据"左手材料"的特殊性质,采用理论计算与模拟仿真相结合的方法,对影响谐振腔谐振参数的因素进行分析,得出了填充介质的材料属性与谐振腔品质因数、谐振频率的关系。结果显示,"左手材料"的填充,会影响谐振腔的品质因数,相较于介电常数,材料磁导率的作用效果更明显;"左手材料"可以在不改变谐振腔尺寸的基础上提高谐振频率。这相较于传统理论而言有了进一步的进展,为探索和设计新颖的谐振腔提供了理论依据。     

基于零阶算法的矩形面宽带纵振换能器设计

传统换能器的优化一般采用试算修改的方式进行,这样的方式在待优化参数较多时不仅比较繁琐而且有可能会漏掉各参数组合下较好的设计点,对此提出了利用零阶算法进行换能器多参数联合优化设计的方法。建立了一种带宽评价函数,通过该评价函数和零阶算法尝试了对矩形面纵振换能器带宽的优化设计。经有限元仿真和样机测试表明,两款换能器的性能达到了预期指标要求,实现了宽带工作。得到的两款宽带换能器性能为:1#换能器工作频带为10~21.5 kHz,带内起伏约3 dB,发射电压响应大于134 dB;2#换能器工作频带为7.5~31.5 kHz,带内起伏约6 dB,发射电压响应大于131 dB。该方法可以作为换能器设计的一种新方式。     

基于分段重叠零相位滤波的阶比跟踪滤波法

提出了一种用零相位数字滤波实现旋转机械阶比跟踪滤波的新方法，和传统的以硬件实现阶比跟踪滤波方法相比，该方法有无需跟踪滤波硬件、用纯软件的方法实现和对原始采样信号不产生相位移动等优点。在讨论了这一方法的理论依据和算法后，提出了数据分段重叠滤波方法．有效地抑制了一般分段数字滤波产生的边缘效应。仿真试验验证了此方法的正确性和有效性。     

基于Mulitisim的并联谐振电路特性的研究

本文通过Multisim软件仿真平台,实现了对并联谐振电路的特性研究。通过软件测量了谐振情况下,电源电压与电阻两端电压的特点、,谐振电路的相频和幅频特性曲线。软件仿真在实验课中的应用,大大提高了实验的效率,节约了耗材和实验仪器的损耗,值得推广。     

基于分数阶导数的金属橡胶动态特性建模

金属橡胶材料具有非线性和黏弹性的动态特性.本研究用三次非线性函数描述其非线性特性,用分数阶三元模型描述其黏弹性,即分别用经典三元模型与分数阶三元模型,结合金属橡胶动态试验数据进行模型参数识别,发现分数阶三元模型能更准确地描述金属橡胶黏弹性力.不同振幅下金属橡胶迟滞曲线的拟合结果表明,分数阶模型可以较好地拟合不同工况条件...     

基于对称H型的超宽带低损耗左手材料设计与分析

本研究基于电磁谐振理论和镜像对称原理,提出了一种结构简单的新型左手材料,该结构仅在介质板单面印制。通过理论分析、HFSS仿真软件、NRW(Nicolson-Ross-Weir)等效电磁参数提取以及FOM(figure of merit)系数计算验证了该结构的左手特性。结果表明:该结构在12.65～23.32GHz频率范围内具有等效介电常数和等效磁导率同时为负的特性,其左手频带的绝对带宽达到10.67GHz,相对带宽达到59.33%,最大单元损耗仅为0.29dB,远远优于传统的左手材料。     

基于一阶剪切变形理论的功能梯度球环振动特性

提出一种半解析法分析了一般边界条件下中等厚度功能梯度球环结构的自由振动特性。基于一阶剪切变形理论推导了中等厚度功能梯度球环结构公式,其中位移函数用改进傅里叶级数表示以消除边界的不连续性,并利用弹簧参数法来模拟一般边界条件;利用里兹法求解得到功能梯度球环结构的固有频率;在收敛性分析的基础上,将本文结果与有限元法、试验数据和文献数据进行了对比,并探讨相关参数的影响。研究表明,本文提出的方法收敛性好,求解精度高;功能梯度球环结构频率参数随厚度和剪切修正系数的增大而增大。     

基于分数阶导数的苹果果柱蠕变特性研究

为了给果品减损包装设计提供理论依据,降低果品在运输过程中的损耗,研究了果品的蠕变特性。以水晶红富士为实验材料,基于分数阶导数理论,建立了苹果果柱蠕变的分数导数Kelvin模型。结果表明,分数导数Kelvin模型只需要很少的参数,就能够在较长加载历程中表征苹果果柱的蠕变现象。     

基于分形互补开口环谐振器的复合左右手传输线研究

提出了一种基于Minkowski分形互补开口环谐振器(CSRRs)的电小平衡复合左右手传输线(CRLH TL)(单元尺寸为..074A,).采用理论计算、电磁仿真、等效电路模型计算(电仿真)及有效介质参数提取相结合的方法研究了非平衡CRLH TL传输特性随CSRRs环数、Minkowski环水平迭代因子、垂直迭代因子及...     

Group delay equalised monolithic microwave integrated circuit amplifier for ultra-wideband based on right/left-handed transmission line design approach

A group delay equalised InGaP/GaAs HBT monolithic microwave integrated circuit (MMIC) amplifier with an active balun for ultra-wideband (UWB) application has been developed. The MMIC consists of a broadband amplifier with an active balun and a group delay equaliser. The group delay equaliser was designed based on a theory using a composite right/left-handed (CRLH) transmission line. Adding a right-handed (RH) transmission line to a CRLH transmission line in parallel, a convex group delay characteristic is realised. Since various UWB components have concave group delay characteristics, the group delay equaliser can compensate a concave group delay characteristic of the amplifier in an operation frequency band. In this paper, dispersion, group delay and impedance characteristics for the proposed CRLH/RH circuit have been theoretically analysed. Moreover, a minimised group delay equaliser circuit on an MMIC has been designed and fabricated based on the proposed CRLH/RH circuit. A fabricated group delay equalised InGaP/GaAs HBT MMIC amplifier with an active balun exhibited an improved group delay characteristic compared with the MMIC amplifier without the group delay equaliser. The standard deviations of group delays for a frequency variation in a gain band were decreased from 12.8 to 5.5 ps at S₂₁ and decreased from 10.3 to 7.3 ps at S₃₁.     

Rogue waves generation in a left-handed nonlinear transmission line with series varactor diodes

We investigate the electromagnetic wave behavior and its characterization using collective variables technique. Second-order dispersion, first- and second-order nonlinearities, which strongly act in a left-handed nonlinear transmission line with series varactor diodes, are taken into account. Four frequency ranges have been found. The first one gives the so-called energetic soliton due to a perfect combination of second-order dispersion and first-order nonlinearity. The second frequency range presents a dispersive soliton leading to the collapse of the electromagnetic wave at the third frequency range. But the fourth one shows physical conditions which are able to provoke the appearance of wave trains generation with some particular waves, the rogue waves. Moreover, we demonstrate that the number of rogue waves increases with frequency. The soliton, thereafter, gains a relative stability when second-order nonlinearity comes into play with some specific values in the fourth frequency range. Furthermore, the stability conditions of the electromagnetic wave at high frequencies have been also discussed.     

Linear array arrangement using composite right-/left-handed transmission lines for magnetic resonance imaging

Array coils for magnetic resonance imaging have been used to improve field uniformity, improve signal-to-noise ratios, and increase imaging speed. Alternative radio frequency (RF) coils that use metamaterials, such as loop or microstrip coils, have recently been proposed and are expected to provide better performance than the traditional RF array coils. Transmission lines (TLs) based on metamaterials are known as composite right- and left-handed (CRLH) TLs, which are artificially created by adding inductances and capacitances to a common TL. CRLH TLs have a zero-order resonance mode, wherein wave propagation is independent of the TL's electrical length. Decoupling between array elements is important for obtaining the benefits of parallel imaging. In this study, we analyze the decoupling properties between two CRLH TLs. In addition, we design a linear array of four CRLH TLs to obtain a uniform magnetic (|B₁|)-field in the axial- and longitudinal-direction at 7T for the corresponding frequency of 300 MHz.     

基于新型对偶复合左右手传输线的高性能带阻滤波器设计

 利用交指螺旋线结构和枝节贴片设计了一种新型对偶复合左右手传输线结构.采用电磁全波仿真软件和Bloch-Floquet 理论对其进行研究,计算并提取了其色散曲线,研究结果表明该对偶复合左右手传输线结构具有良好的带阻特性,并且阻带内2个传输零点独立可控．在此基础上采用2个单元结构级联的方式设计了一款具有小型化特性的性能优越的带阻滤波器,进行实物加工并使用适量网络分析仪测试,测量结果与仿真结果吻合较好,表明所设计的带阻滤波器中心频率为3.56 GHz,阻带带宽为39.3%,阻带矩形度为0.85,通带带宽为4.47~8.42 GHz,整体性能优越．此外所设计的带阻滤波器整体尺寸为0.237λ×0.145λ（λ为中心频率在自由空间波长）,小型化优势明显．     

Size reduction of microstrip patch antennas with left-handed transmission line loading

A procedure for designing an electrically small microstrip patch antenna (MPA) is developed, wherein the length of a side of the MPA is reduced to significantly less than a half-wavelength. The MPA is loaded with a resonant circuit equivalent to that of a left-handed transmission line to artificially increase the effective wavelength of the device, thus creating a resonance equivalent to, but at a lower frequency than the unloaded {10} mode. The field distribution in the loaded MPA remains relatively unperturbed, unlike the {0} mode case that attempts to decrease the size by introducing a shorting-post; consequently, very low cross-polarisation behaviour is observed. The theory to predict the full spectrum of resonant frequencies of the antenna is developed, with finite-difference time-domain simulations used to finalise the antenna design. Finally, an electrically small ((lambda/6)times(lambda/4)) and thin (相似文献   

Failure investigation of a downed power transmission line

A single section of transmission line, specified as 336.4 30/7 ACSR, C-Phase, was submitted for analysis after it was found to be failed in a township barn fire in April 1994. Transmission personnel desired to know whether the line had failed and resulted in the structure fire or whether the structure had caught fire and the subsequent conflagration resulted in the failure of the transmission line. Evaluation of the strands and the associated fracture faces indicate that the line failed at a temperature of approximately 650 °C (1200 °F) and that the temperatures did not get significantly higher than that. This supports the hypothesis that the failure of the line occurred as the result of the structure fire. None of the fractures examined showed any characteristics normally associated with arcing, such as occur in short-circuit type failures. Subsequent to this analysis, the structure fire was identified as being the result of arson, and the responsible individual was arrested and convicted. At the time of this investigation, the author was an engineer working for GPU Nuclear Corporation, Reading, PA.     

Nonreciprocal left-handed transmission characteristics of microstriplines on ferrite substrate

In this paper, a nonreciprocal left-handed transmission line has been investigated. It is composed of a normally magnetised ferrite microstripline periodically loaded with lumped capacitances and inductive stubs. Based on the simple equivalent circuit model for a predominant edge guided mode, the dispersion relation of the ferrite left-handed transmission line has been estimated, providing the backward wave characteristic in the positive and negative permeability frequency regions. With the aid of the finite element method, it is confirmed that specific three-dimensional structures do show left-handed characteristics as well as the nonreciprocity. Nonreciprocal transmission characteristics with the isolation of more than 30 dB are obtained numerically and demonstrated experimentally in the positive and negative permeability frequency regions, for the edge guided modes. It is explained that the nonreciprocity of the ferrite left-handed transmission line is caused by the leaky wave phenomenon from the microstrip to the ferrite substrate     

基于傅里叶级数的缠绕复合材料刚度预测方法

采用傅里叶级数有关理论,根据缠绕复合材料内部细观结构的特点,建立了缠绕复合材料刚度预测模型。该模型将缠绕复合材料特征单元的刚度作为一个刚度场,利用二维傅里叶级数展开得到描述该刚度场的函数。算例的结果表明,本文中所建立的模型可以预测缠绕复合材料整体刚度特性,同时通过傅里叶级数各阶展开项的叠加可以反映材料内部细观结构对缠绕复合材料刚度特性的影响。