Measurement of dielectric properties of high-absorption materials at microwave frequencies

A method is proposed for measuring the dielectric constant ε′ and dielectric loss ε″ of high-absorption dielectric materials by measuring the reflection of electromagnetic radiation with the aid of an adjustable quarter-wave matching plate of nonabsorbing material close to the dielectric surface. Translated from Izmeritel'naya Tekhnika, No. 5, pp. 45–47, May, 1999.     

Measurement of the permittivity of low-impedance composite materials at microwave frequencies

The measurement of the permittivity of low-impedance composite materials using a waveguide sensor in circular waveguide is considered. Translated from Izmeritel’naya Tekhnika, No. 2, pp. 44–48, February, 2009.     

Measurement of electromagnetic parameters of materials at radio and microwave frequencies

Translated from Izmeritel'naya Tekhnika, No. 9, p. 11, September, 1994.     

About a simulation method of the magnetodielectrical materials properties at high frequency magnetic fields

This paper presents an improved simulation method, which permits to study the influence of the electromagnetic high frequency fields on the properties of magnetodielectrical materials. The original method was published by the first author in [JMMM 234 (2001) 148]. The proposed method can be used, for example, to simulate the dependency on the frequency of bulk magnetic permeability by using the dependence on the frequency of the powder magnetic permeability     

Free-space measurement of complex permittivity and complexpermeability of magnetic materials at microwave frequencies

A free-space measurement system operating in the 8.2-40-GHz frequency range is used to measure the reflection and transmission coefficients, S₁₁ and S₂₁, of planar samples. The complex electric permittivity and the magnetic permeability are calculated from the measured values of S₁₁ and S₂₁. The measurement system consists of transmit and receive horn lens antennas, a network analyzer, mode transitions, and a computer. Diffraction effects at the edges of the sample are minimized by using spot-focusing lens antennas. Errors due to multiple reflections between antennas via the surface of the sample are corrected by using a free-space TRL (thru, reflect, line) calibration technique. For thin, flexible samples, the sample had to be sandwiched between two half-wavelength (at mid-band) quartz plates to eliminate sagging. Results are reported in the frequency range of 8.6-13.4 GHz for materials such as Teflon, sodium borosilicate glass, and microwave-absorbing materials     

Electrical properties of films at microwave frequencies

A technique suitable for the measurement of electrical properties of films/sheets at microwave frequencies has been described. Groups of materials are identified for which the absence of any kind of electrodes in these microwave measurements can be utilised with advantage. Results are presented for a variety of materials such as metal films, superionic conductors, semiconductors and insulating polymers.     

Dielectric measurements on PWB materials at microwave frequencies

In quest of finding new substrate for printed wiring board (PWB) having low dielectric constant, we have made PSF/PMMA blends and evaluated the dielectric parameters at 8.92 GHz frequency and at 35°C temperature. Incorporating PMMA in PSF matrix results in reduced dielectric constant than that of pure PSF. The dielectric parameters of pure PMMA and PSF films of different thicknesses have also been obtained at microwave frequencies. We have used dielectric data at microwave frequencies as a tool to evaluate optical constants, absorption index ‘K’ and refractive index ‘n’. The blends of PSF/PMMA may be used as base materials for PWBs.     

Metal slits and liquid crystals at microwave frequencies

While the use of liquid crystals (LCs) over the visible region is ubiquitous in flat-screen displays, there has been little by the way of applications at other wavelengths. Specifically, notwithstanding the continuing permittivity anisotropy to be found at longer wavelengths, there has been virtually no development in the microwave domain. This is largely due to the fact that scaling up the micrometer-thick LC layers used for visible radiation to millimetre dimensions is seen as impractical. In this study, it is shown how, using thin slits in metal structures, a completely new generation of LC devices for use at microwaves may be realized. Such structures include slatted metal Fabry-Perot resonators, beam-steering devices, thin flexible voltage tunable filters and even cascade structures with strongly enhanced and reshaped microwave fields.     

红外波段铜树枝状结构磁响应特性研究

提出一种可用于实现红外波段负磁导率的树枝状磁谐振模型,采用基于有限差分技术的CST微波工作室软件确定了树枝状结构参数与磁谐振响应之间的关系,实现了红外波段的负磁导率.以碳纤维为阴极,采用化学电沉积的方法制备了铜树枝状结构,利用傅立叶变换红外光谱仪测量了样品的空间红外透射行为,结果表明铜树枝状结构实现了红外波段的磁谐振响应,最大透过率达到-7.95dB,实验结果与数值模拟吻合.研究了铜树枝状结构的分形维数和磁响应波段与沉积电压的关系以及两个铜树枝状结构之间的耦合作用,结果表明随着沉积电压的增大分形维数与磁响应波长随之增加,样品之间的耦合作用导致磁谐振响应的波长和强度发生变化.     

Dielectric properties of conducting polymer composites at microwave frequencies

The dielectric properties of conducting polymer composites containing polypyrrole (PPy) crushed films, PPy powder, polyaniline (PAn) base and acid powders as the dispersants and silicone rubber and vinyl ester as matrix materials have been investigated in the frequency range 2-18 GHz. The dielectric parameters such as the real part, , and imaginary part, , of the permittivity and loss tangent, tan, increase with increasing conductivity and concentration of the dispersant. The geometrical shape of the dispersant governs the ability of conductive network formation which is indicated by a large drop in the resistivity of the composite. Also, dispersant/matrix interactions and physical properties of the matrix influence the agglomeration of the dispersant phase which, in turn, affects the dielectric properties of the composites. Flakes of PPy obtained by crushing highly conductive films and large PAn powder aggregates were unable to form a conducting network. The composites without a network of dispersant exhibit low dielectric parameters. On the other hand, high values of tan ranging from 0.7–1.1 were achieved for the PPy powder (15 parts)/silicone rubber composites where a conducting network was observed.     

纳米晶软磁复合磁粉芯在中高频段性能研究

介绍了利用球磨后的FeCuNbSiB合金粉末冷压制作纳米晶复合磁粉芯的工艺.探讨了粉末粒度为80～200目,绝缘剂量为1%～8%时纳米晶复合磁粉芯的频率特性,直流叠加特性及品质因数Q.制备出的平均粒度为80目的磁粉芯有效磁导率μe在1MHz范围内恒为85,在100kHz时其峰值Q为65,在f=50kHz,Bm=50mT测试条件下其损耗为102mW/cm3.其功率损耗比传统铁粉芯,Fe-Ni粉芯小.     

Certification of normal samples of magnetic materials at high frequencies

Conclusions In measuring the magnetic parameters of samples, primarily in certifying normal samples by using sections of coaxial lines, it is necessary to select the optimum length of the line in relation to the available scales on the admittance (impedance) meter and the values of the measured parameters; introduce corrections for losses in the line either by calculations or graphically for materials with low losses; and allow for the electrical parameters of ferrites or magnetodielectrics (their complex permittivity), especially if the normal samples do not fulfill conditions (19).Translated from Izmeritel'naya Tekhnika, No. 12, pp. 42–45, December, 1970.     

Some properties of nickel-coated carbon fibre-polypropylene composite at microwave frequencies

Some properties of nickel-coated carbon fibre-polypropylene composite are considered at microwave frequencies in the range 8 to 12 GHz. The paper presents the measured values of the insertion and return losses and the equivalent input impedance in the above frequency band. Measurements were performed on composite material for different nickel-coated fibre concentrations of 0, 5, 10, 16 and 28 wt%. The filler effects shows a transition region and identifies the dependency of the electrical properties on these concentrations. Furthermore, shielding effectiveness is calculated for the given concentrations and it is found that its value could reach more than 30 dB over the whole frequency band for a specimen of 2.6 mm thickness and with 28 wt% concentration.     

Measurement of the dielectric constant of highly absorbing polar liquids at microwave frequencies

Nomograms are given for claculating the dielectric constant and dielectric loss of polar liquids by measuring the standing wave ratio for an infinitely thick layer of fluid and the layer thickness at which wave reflection is minimum. Translated from Izmeritel'naya Tekhnika, No. 2, pp. 46–47, February, 1996.     

Bio-inspired artificial cilia with magnetic dynamic properties

Inspired by the structure and properties of natural cilia, we focused on a facile template-free approach to prepare magnetic artificial cilia grown on the substrate (glass, PDMS, or others). In an applied magnetic field, the cilia formed spontaneously and immediately from magnetic nanoparticles and elastomeric polymer in a liquid solvent by bottom-up self-assembly. The length of prepared cilia could be in the scale of millimeter and reach a high aspect ratio of even over 100. We studied the effect of the magnetic strength applied and the size of nanoparticles to get tunable scale of cilia. The cilia show reversibly bending in an external magnetic field and this bending actuation gave some important functions: to transport macroscopic nonmagnetic materials on the cilia and to mix liquids.     

BaMnZnCoTi-W型铁氧体微波吸收剂的制备和特性研究

对用Ｃｏ２＋、Ｔｉ４＋部分置换Ｆｅ３＋的Ｂａ（ＭｎＺｎ）ａＣｏｂＦｅ１６－ｙＣｏ２＋０．５ｙＴｉ４＋０．５ｙＯ２７－Ｗ型平面六角晶系微波铁氧体吸收剂的制备和特性进行了研究,并对其复介电常数的实部ε′和虚部ε″、磁导率的实部μ′和虚部μ″、损耗随微波频率、Ｃｏ２＋、Ｔｉ４＋含量、涂层厚度的变化作了测试和分析,发现当ｙ＝１．０时铁氧体的吸收性能最佳,其最佳厚度为１．４０ｍｍ,吸收衰减最大达２７．５ｄＢ。     

Free-space, broadband measurements of high-temperature, complexdielectric properties at microwave frequencies

A free-space microwave measurement system that is used for the high-temperature measurement of dielectric constants and loss tangents of homogeneous materials and that is applicable to composite materials as well is discussed. The system is capable of operating in the 5.85-40-GHz frequency range and ambient to 850°C temperature range. A computer is used to control and coordinate furnace temperature, network analyzer functions, and data storage. Dielectric constants and loss tangents of the materials are calculated from the measured values of S₂₁. The measurement system, including the high-temperature furnace and the calibration technique, is described. Dielectric constants and loss tangents are presented for fused quartz and boron nitride grade HP in the frequency range 13.0-17.4 GHz and the temperature range from ambient to 850°C     

平面Z-型软磁铁氧体频率特性的研究

研究分析了Co2Z材料显微结构与磁性能的关系,在普通铁氧体工艺中引入预磁化处理方法,并适当控制二次再结晶现象,成功地研制出高性能的Co2Z型宽频材料,Z-型铁氧体材料的共振频率可达1.8GHz以上,截止频率在1GHz附近,起始磁导率在8-13之间,介电常数相对较低(ε'<30)。