基于谐振法测试微波介质材料的介电参数

介电常数是介质材料的主要性能参数之一,该文讨论了微波介质的介电参数的理论计算,分析了谐振法的模型,研制了基于谐振法测量微波介质材料介电参数的测量系统.通过对多个样品进行实测,结果表明与参考值比较吻合,评价了该测量系统测量结果不确定度,从而建立了微波频段内微波介质材料介电常数测量平台.     

传输/反射法测量固体复介质材料介电常数

介绍/传输反射法测量固体介质材料复介电常数等关键技术难点,通过建立固体介质材料的介电谱和磁谱测量装置,开展复介电常数、复磁导率、复损耗角正切测量技术研究,在30 MHz～18 GHz采用空气线同轴传输的方法、在18～50 GHz采用三段波导传输的方法,实现了30 MHz～50 GHz全频段固体介质材料电磁参数的测试能力,提出了复介电常数、复磁导率、复损耗角正切测量的数学模型,编制了材料测试软件,实现了同轴和波导的全频段测量。     

微扰法配合网络分析仪测试材料的电磁参数

利用网络分析仪连接矩形谐振腔组成材料电磁参数的微扰法测试系统。并根据谐振腔微扰理论,得到小样品装载在样品托中进行电磁参数测试的复介电常数和复磁导率计算公式。对聚四氟乙烯的电磁参数进行了测试,所得结果较为精确,可重复性好,证明此测试系统测试结果稳定可靠。对本测试装置的误差进行了简要分析,指出该测试装置能够满足一般电介质材料,尤其是吸波材料电磁参数的测试需求。     

尖晶石结构磁介电材料的研究进展

随着通信技术的发展,对无限通信设备的集成度有了更高的要求,天线小型化成为目前重要的研究方向。等磁介电材料是一种既具有磁导率又具有介电常数,且磁导率和介电常数几乎相等的材料,使用等磁介电材料作为天线的基板,能有效的减小天线的尺寸,提高带宽,增加辐射效率。铁氧体是由Fe2O3和一种或多种金属氧化物复合而成,具有较高的磁导率和介电常数,由于其同时具有磁特性和介电特性,是一种潜在的等磁介电材料。综述了近几年尖晶石结构磁介电材料的国内外研究进展,着重讨论了掺杂改性对烧结温度、磁导率、介电常数、直流电阻等电磁特性的影响。最后指出目前研究中存在的问题,并展望了该材料在未来发展的方向。     

双曲超材料及其传感器研究进展

超材料为具有超常电磁性质的人工结构,因拥有自然界材料没有的介电常数、磁导率和折射率等电磁性质而引起人们的关注。双曲超材料是具有强各向异性介电张量或磁导率张量的介质,其介电常数张量或磁导率张量的分量在一个或两个空间方向上为负,与其他类型的超材料相比,双曲超材料具有在光学频率下相对容易制造、宽带非共振和三维体响应以及灵活的波长可调谐性等优点。本文综述了双曲超材料的特性、实现方法、可调谐及活性以及其作为超灵敏传感器的发展,重点讨论了基于金属/介质多层结构及金属纳米线阵列的双曲超材料作为生物传感器的原理及研究进展,并指出双曲超材料传感器发展的长期目标是结构简单、便于制备、宽频带和多元分析。     

应用超常介质设计柱形隐形容器

超常介质是一种纳米尺度的人工复合材料,可以同时设定材料的介电常数和磁导率。利用超常介质的这一特性,能够自由地调整光的传播路径。在此基础上,应用坐标转换的方法,计算出圆柱形和椭圆柱形的介电常数和磁导率分布,让光在介质内沿着特定的轨迹传播,绕过包围的空腔,沿入射的方向出射,从而实现圆柱和椭圆柱形状的隐形。     

微波介质谐振器介电参数的测量

本文讨论了微波介质谐振器介电参数测试技术。用研制的测试装置对多个介质样品进行了实测，结果表明，本文的分析与实际值是吻合的。该测试技术可对微波介质谐振器的复介电常数进行迅速、准确、可靠、宽频带、无损伤、自动化和批量检测，具有较强的实用性。     

薄膜材料的微波复介电常数测量

为了精确测量厚度在以1 μm以下薄膜材料的微波复介电常数,提出一种基于金属谐振腔微扰理论的测量方法和装置,对该方法进行了理论分析和实验验证,实验样品采用0.81μm厚度的MC-91(BaO-(SmNdLa)2O3-Bi2O3-TiO2)介质陶瓷薄膜,测试频率在2.4 GHz左右,对测量结果进行了误差分析,其相对误差＜7%,其中3%的误差是由薄膜厚度的测量误差引起的.     

铁氧体内嵌金属线阵宽带负折射特性研究

采用具有大饱和磁化强度(MS)的铁氧体基片提供宽带负μ、内嵌金属线阵列提供负ε的方法,合成了一种X频段8.5～10.7GHz宽带负折射材料.对采用上述合成材料构成的半无限大异向介质平板的电磁波反射、透射等特性进行了研究,抽取得到该合成材料的有效介电常数、有效磁导率、折射率等系列电磁特性参数;同时对电磁波穿过采用上述合成材料构成的半无限大楔形和平面透镜发生的折射、汇聚等现象进行了研究.结果表明,合成材料的有效介电常数、有效磁导率以及折射率的实部在8.5～10.7GHz频带范围内皆为负值.在该频段上,合成材料具有"负折射效应" "双负效应""平面镜成像效应"等负折射异向介质典型的电磁特性.     

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。     

Optimization Techniques for Permittivity and Permeability Determination

This paper discusses optimization techniques for the determination of complex permittivity and permeability in transmission lines. The traditional theoretical model using scattering parameters is extended into a mathematical regression model that can be solved with widely accepted numerical techniques. This new model produces accurate primary mode results for the samples tested including nonmagnetic and magnetic materials with high dielectric constants. An extension of the model includes responses due to higher order modes. The general model determines parameters to specify the spectral functional form of complex permittivity and permeability and is capable of small corrections to independent variable data including angular frequency, sample length, sample position, and cutoff wavelength. The method provides reliable determination for both low and high permittivity materials.     

A nonlinear least-squares solution with causality constraintsapplied to transmission line permittivity and permeability determination

A technique for the solution of one-port and two-port scattering equations for complex permittivity and permeability determination is presented. Using a nonlinear regression procedure, the model determines parameters for the specification of the spectral functional form of complex permittivity and permeability. The method is based on a nonlinear regression technique and uses the fact that a causal, analytic function can be represented by poles and zeros. The technique allows the accurate determination of many low- and high-permittivity dielectric and magnetic materials in either the low- or high-loss range. The model allows for small adjustments, consistent with the physics of the problem, to independent variable data such as angular frequency, sample length, sample position, and cut-off wavelength. The model can determine permittivity and permeability for samples where sample length, sample position, and sample holder length are not known precisely. The problem of local minima is discussed     

多晶铁纤维吸收剂微波复磁导率和复介电常数的理论计算

由麦克斯韦方程出发,导出了多晶铁纤维吸收剂微波复磁导率和复介电常数的理论计算公式;通过对５ＧＨｚ频率点多晶铁纤维吸收剂的数值计算,分析了多晶铁纤维的直径、长径比及电导率等对其电磁参数的影响。     

具有梯度性质的电磁特异材料对电磁波反射的调控

研究"空气/特异材料/理想金属"组成的三明治体系,将梯度性质加入到电磁特异材料层的介电参量中,发现这类结构可以对电磁波具有奇异的调控性质。如果设计材料介电参量的梯度形式,可以使体系对反射波相位具有线性的调控,体系的反射波可变为单一模式的平面波,甚至在某些情况下反射波完全变为表面波。通过数值计算和模拟验证了理论预言。     

Mueller matrix analysis of infrared ellipsometry

A Mueller analysis has been done of IR ellipsometry performed with imperfect optical components. Equations linking experimental and calculated Fourier coefficients have been derived and consistently solved. Correction routines for permittivity measurements are demonstrated and discussed with gold and SrTiO(3) as examples. It is shown that such effects as interferometer polarization, detector dichroism, transmission, and phase changes in polarizers can be calculated and effectively removed from the spectra. The problems of calibration and multiple reflections between IR polarizers are discussed, and error propagation in permittivity measurements is analyzed.     

Improved calibration of a large open-ended coaxial probe fordielectric measurements

An improved method for calibrating an open-ended coaxial sensor is proposed. The calibration utilizes the measurements of an open, a short, and a short-cavity. These terminations are inexpensive to make and result in a calibration that depends only on the geometry of the sensor. The short-cavity is modeled by waveguide modal techniques and the theoretical reflection coefficient determined to any accuracy. Consequently, an improvement in the accuracy of the measurements is obtained over a large bandwidth. The calibration was tested by comparing theoretical and experimental values of the complex permittivity for common liquids, and the discrepancy was seen to be small     

轴向加荷疲劳试验机动态力校准的研究

研究了电液伺服式和电磁谐振式两类疲劳试验机,在对其力学模型振动分析的基础上,得到了两类试验机动态力值误差的解析表达式。分析了影响惯性力大小的主要因素,如工作频率、连接夹具或试样的质量、刚度等,进行了多组比较试验,对理论分析结果进行了验证。讨论了疲劳试验机动态力误差的修正,并对校准装置和夹具的选择提出了建议。     

Nonlocal effective parameters of a coated sphere medium

An analytical theory has been developed to find the general effective parameters of a nonlocal medium. The medium is nonlocal due to presence of spatial dispersion. The proposed theory is based upon the dipolar scattering model of the inclusions comprising the medium. The bianisotropy stemming from the magnetoelectric coupling at the inclusion and lattice level has been discussed. The developed theory is then applied to a medium which consists of coated spheres with realistic materials. Effects of different values of wavevector upon the effective permittivity, effective permeability, and magnetoelectric coefficient stemming from lattice effects have been studied for a coated sphere medium. It is shown that a coated sphere medium with a weak spatial dispersion gives rise to a broader range of frequencies, where real parts of the effective permittivity and permeability are negative. On the other hand, this range of frequencies becomes smaller when the spatial dispersion of the medium is not weak.     

Pseudo-Fourier modal analysis on dielectric slabs with arbitrary longitudinal permittivity and permeability profiles

A pseudo-Fourier modal analysis method for analyzing finite-sized dielectric slabs with arbitrary longitudinal permittivity and permeability profiles is proposed. In the proposed method, the permittivity and permeability profiles are represented by the Fourier expansion without using the conventional staircase approximation. The total electromagnetic field distribution inside a dielectric slab is a linear superposition of extracted pseudo-Fourier eigenmodes with specific coupling coefficients selected to satisfy given boundary conditions. The proposed pseudo-Fourier modal analysis method shows excellent agreement with the conventional rigorous coupled-wave analysis with the S-matrix method.     

Comparison of two post-calibration correction methods for complex permittivity measurement of biological tissues up to 50 GHz

Two correction methods are discussed in this paper to remove residual errors due to the lack of repeatability of coaxial-to-microstrip launchers as part of the TRL calibration procedure. These methods are applied for accurate insertion loss measurement of biological tissues embedded in a two-port microstrip test fixture, from which the tissues' complex permittivity values are extracted for frequencies between 15 and 50 GHz. In the first method, distilled water is used as a calibration standard as part of a two-port calibration procedure. The second method identifies an error transfer function using the difference between simulated and measured insertion loss for distilled water, and then applies it as a correction factor to the measurement results for biological tissues. Both methods are compared in terms of extracting the accurate complex permittivity of brain matter.