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1.
Kenneth Bober Robert H. Giles Jerry Waldman 《International Journal of Infrared and Millimeter Waves》1997,18(1):101-123
The microwave permittivity (ɛr) and permeability (μr) of composite materials are tailored by adding various loading agents to a host plastic and are subsequently modeled using
the Maxwell Garnett theory and second order polynomials. With the addition of manganese zinc ferrite, strontium ferrite, nickel
zinc ferrite, barium tetratitanate and graphite powders, materials with values of ɛ′, e″, μ′, μ″ as high as 22, 5, 2.5 and
1.7 have been obtained. Permittivity and permeability data are calculated at 2.0245 GHz from reflection and transmission measurements
performed in a 7 mm coaxial test line. The Maxwell Garnett (MG) theory successfully models ɛr if the filling factor is less than 0.30 and ratio |ɛ1| (host)/ |ɛ2| (powder) is greater than 0.04. As this ratio decreases, the MG theory is shown to be independent of ɛ2 and second order polynomials are used to effectively model the dielectric constant. Polynomials are also used for the ferrite
composites because it was determined that the MG theory was unable to model μr. This deficiency is attributed to the difference of domain structures that exist in powdered and sintered ferrites. 相似文献
2.
《Comptes Rendus Physique》2014,15(5):448-457
Knowing the electromagnetic characteristics of different materials has become a major topic with the growing of wireless communications. The actual tools to perform this characterization have some limits, either in terms of limited frequency band, or in terms of inconstancy according to the different kinds of materials. On the basis of well-known procedures in the microwave domain, we present a new measurement cell equipped with a sample holder that can contain any kind of materials: solids, semi-solids (granular or powder materials), liquids. This technique can also characterize materials of thin thickness that are also more and more used in the RFID domain or in the realization of antennas on flexible substrates. 相似文献
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V. V. Zagoskin E. A. Zamotrinskaya V. M. Nesterov T. G. Mikhailova 《Russian Physics Journal》1981,24(1):29-33
An analysis is made of the existing waveguide methods (short-circuit, infinite layer, variable reactive load, direct determination of the wavelength and pattern of the electromagnetic field in the investigated material) as applied to disperse materials characterized by high losses. A comparison of the short-circuit method with the direct measurement of the propagation constant is used to show that the latter is preferable when applied to materials with large values of the permittivity (in excess of 10) and a large loss-angle tangent (in excess of 0.1). This method does not require complex mathematical calculations and makes it possible to determine unambiguously the permittivity, whereas the values of the loss-angle tangent are physically more reasonable.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 30–36, January, 1981. 相似文献
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A quasi-optical method for measuring the complex permittivity and permeability of materials at millimeter and submillimeter wavelengths is proposed. In principle, this method is applicable not only to solid samples but also to liquid and composite samples. The theory and experiment are described in this paper. 相似文献
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We present a spectral interferometric method to measure the thickness of an optical plate or a film with a single layer. The system is based on the Michelson interferometer configuration, and the spectral interference signal of a broadband light source is recorded by a spectrometer. The optical path difference (OPD) between two interfering beams can be obtained by Fourier transform from the spectral interferogram. Gaussian fitting is used to find the exact peak of fringe to enhance the precision of the measurements. When the sample is inserted into the sample beam, the film’s thickness can be calculated by comparing the change of OPD, provided that the sample group refractive index is known. Only a single measurement is needed to determine a film’s thickness after the initial OPD of the system is calibrated. As no moving parts are required, the system has good stability. In particular, a large range of thicknesses, from micrometers up to several millimeters, can be measured. Such a large range is valuable for optical measurements. For demonstration, we measured the thicknesses of preservative film, cover glass and carrier glass, which were 9.6 ± 0.55, 156.1 ± 0.75, 1008.44 ± 0.96 μm, respectively. 相似文献
6.
The sensitivity of a reflective single-port strip-line technique is increased by 10-20 times by amplification of a measured reflectivity response at a set of resonance frequencies. The resonant behavior is organized by connecting the strip cell to a network analyzer through a capacitor with a long coaxial cable. The capacitance defines the amplification; the cable length defines the resonance frequencies. S-parameters of the coaxial-to-strip junction and the field inhomogeneity inside the cell are accounted for by a reference measurement of sample with known constitutive parameters. Two methods for permeability calculation are suggested. The fist method is based on the comparison of Lorentzian parameters of resonance reflectivity curves. The second method is based on numerical solution of Fresnel's equation. The enhancement is essential at low-frequency part of the band, where the cell reflectivity is close to unity and the sensitivity of non-resonant technique is poor. The technique sensitivity is estimated by permeability measurements of Al stripes with different cross-section. 相似文献
7.
Complex permittivity, complex permeability and microwave absorption properties of ferrite-paraffin polymer composites 总被引:1,自引:0,他引:1
Harun Bayrakdar 《Journal of magnetism and magnetic materials》2011,323(14):1882-1885
We have investigated the electromagnetic (EM) characteristics of CoxMn1−xFe2O4 spinel ferrite (where x=0.0, 0.5 and 1.0) nanoparticles (NPs)/paraffin nanocomposite material at 8-20 GHz. CoxMn1−xFe2O4 NPs have been synthesized by cetyltrimethylammonium assisted hydrothermal route using NaOH. A variation in complex dielectric permittivity and magnetic permeability at room temperature with frequency in the range 8-20 GHz has been studied. Particles showed phase purity and crystallinity in powder X-ray diffraction (XRD) analysis. At the same time, CoxMn1−xFe2O4 NPs demonstrated a spinel cubic structure from XRD results. A reflection loss of −46.60 dB was found at 10.5 GHz for an absorber thickness of 2 mm. CoxMn1−xFe2O4 may be attractive candidates for EM wave absorption materials. 相似文献
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M. Csatlós A. Krasznahorkay A. M. van den Berg M. N. Harakeh S. Y. van der Werf M. Hagemann M. de Huu H. Akimune H. Fujimura M. Fujiwara K. Hara T. Ishikawa 《Acta Physica Hungarica A》2001,13(1-3):203-205
Dipole resonances have been excited in 121?124Sn isotopes using (3He,t) charge exchange reaction at E 3 He=177 MeV and the cross sections were related to the neutron-skin thicknesses. The well understood correlation may be used to determine the neutron-skin thicknesses in the future. 相似文献
9.
Ping Chen Min LiuLing Wang Yin PooRui-xin Wu 《Journal of magnetism and magnetic materials》2011,323(23):3081-3086
We experimentally studied the frequency dependent complex permittivity ε and permeability μ of composite composed of carbonyl iron powder (CIP) and epoxy resin in the frequency range 1-18 GHz. We found that the intrinsic ε and μ of CIP extracted from the measured ε and μ of composites follow the classical Maxwell equations and the Landau-Lifshitz-Gilbert (LLG) equation, respectively. The dependences of ε and μ of composites on the volume fraction of CIP (vfCIP) were investigated using the two-exponent phenomenological percolation equation (TEPPE). We found that the TEPPE can fit the experimental results very well. Comparing the results of percolation parameters derived by experimental data at different frequencies, we show that the TEPPE is frequency independent for the composites at microwave frequencies. The results also show that the ε and μ spectrums of composites with definite vfCIP can be correctly calculated by combining the TEPPE with the theoretical models of intrinsic ε and μ. 相似文献
10.
The complex permittivity (ε′–jε″), complex permeability (μ′–jμ″) and microwave absorption properties of ferrite–polymer composites prepared with different ferrite ratios of 50%, 60%, 70% and 80% in polyurethane (PU) matrix have been investigated in X-band (8.2–12.4 GHz) frequency range. The M-type hexaferrite composition BaCo+20.9Fe+20.05Si+40.95Fe+310.1O19 was prepared by solid-state reaction technique, whereas commercial PU was used to prepare the composites. At higher GHz frequencies, ferrite's permeabilities are drastically reduced, however, the forced conversion of Fe+3 to Fe+2 ions that involves electron hopping, could have increased the dielectric losses in the chosen composition. We have measured complex permittivity and permeability using a vector network analyzer (HP/Agilent model PNA E8364B) and software module 85071. All the parameters ε′, ε″, μ′ and μ″ are found to increase with increased ferrite contents. Measured values of these parameters were used to determine the reflection loss at various sample thicknesses, based on a model of a single-layered plane wave absorber backed by a perfect conductor. The composite with 80% ferrite content has shown a minimum reflection loss of −24.5 dB (>99% power absorption) at 12 GHz with the −20 dB bandwidth over the extended frequency range of 11–13 GHz for an absorber thickness of 1.6 mm. The prepared composites can fruitfully be utilized for suppression of electromagnetic interference (EMI) and reduction of radar signatures (stealth technology). 相似文献
11.
We present a simple method to obtain the optical and dielectric properties of samples without reference measurement in the reflection-type terahertz time-domain spectroscopy. The dielectric properties of the samples of silicon and gallium arsenide were examined. The optical and dielectric properties of the samples were measured through only simple configuration, without the misplacement error. The obtained dielectric functions of the samples in reflection geometry are in good agreement with that predicated by the theory. The main advantage of this method over other methods is its simplicity and accuracy and ease for application of the reflection systems with different incident angle. 相似文献
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Polycrystalline samples of U-type hexaferrite series: (Ba1−3xLa2x)4Co2Fe36O60 with 0.10≤x≤0.20 in step of 0.05, are prepared by conventional solid state reaction route. Partial substitution of Ba2+ ions with La3+ ions enhances the electron hopping and reduces the magnetic interaction in the samples over the entire X-band frequencies; leading to wide band microwave absorption in all sample. Relative complex permittivity (εr=ε′−jε″) and permeability (μr=μ′−jμ″) of the prepared samples were measured using Vector Network Analyzer (VNA, Agilent PNA-L N5230A) for X-band (8.2-12.4 GHz) frequency range. The maximum absorption of 99.8% was obtained for x=0.10 sample for thickness tm=1.8 mm and all sample showed absorption ≥96%. The reflection loss (RL) calculated using the measured parameter (εr=ε′−jε″ and μr=μ′−jμ″) shows good agreement when compared with the return loss measured directly using VNA for sample x=0.20. The material can be expected to find relevance in suppression of electromagnetic interference (EMI) shielding and reduction of radar signatures. 相似文献
14.
I.IntroductionTomeasurethesound1evelofanundcrwatersoundpulsewithunknownamplitudeisofimportanceinunderwaterapp1ication.Forinstancc,asimu1ationsystemusedtointerfcresomesonarmusthavesuchfunction,whichhastobeabIctomeasurethesoundlcvelatreceivingpointandretransmitasimulatcdsignalwithrequircdsoundlcvelafterpropcrprocessing.Itisdifficultforanorma1peakorthresho1ddetectortocompletethistask.Thereasonforthisisthattherangeofthesignalamp1itudercaches7O-8odBandthereissomedistortionofsignalwaveform,inaddit… 相似文献
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提出了一种测量p-GaN载流子浓度的方法,其主要思想是利用p-n+结构GaN探测器长波和短波量子效率的差值随反向偏压的变化关系,找到p-GaN层刚好完全耗尽时的偏压,从而求出p-GaN层载流子浓度.模拟计算表明,该方法能够准确测量出p-GaN层的载流子浓度,而且受表面复合、欧姆接触影响很小.进一步研究了实际测量中如何选择p-GaN层厚度,计算结果表明,p-GaN层的优化厚度值随着p-GaN层的浓度增加而减小.
关键词:
p-GaN
载流子浓度测量
紫外探测器 相似文献
17.
V. V. Zagoskin V. M. Nesterov E. A. Zamotrinskaya T. G. Mikhailova 《Russian Physics Journal》1981,24(7):644-647
The behavior of the dielectric permittivity of a mixture of disperse materials is investigated for a change in the volume content of the component with a high value of the dielectric permittivity. An analysis is performed from the viewpoint of computing the dielectric permittivity of such mixtures. A formula is proposed for computation of the dielectric permittivity of mixtures of disperse materials with water.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 74–78, July, 1981. 相似文献
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We show that a combined application of Mössbauer spectroscopy and other experimental tools such as X‐ray photoelectron spectroscopy, X‐ray absorption spectroscopy and nuclear magnetic resonance provides a coherent picture of the local electronic structure in chalcogenide materials. In order to develop this idea we propose an analysis of the Sn, Sb and Te local electronic structures for three different systems of materials. The first example concerns the In–Sn–S system. We show that Li insertion in In16Sn4S32 leads to changes of the Sn oxidation states from Sn(IV) to Sn(II). The second example concerns materials of the Tl–Sb–S system. We show that variations of the 121Sb Mössbauer isomer shift and surface of the first peak of the X‐ray absorption spectra at the Sb LIII edge can be linearly correlated because of the main influence of the Sb 5s electrons. This is explained by changes in the local environment of the Sb atoms. The last example concerns the crystalline phases of the Tl–Sn–Te system. The formal oxidation numbers of the Te atoms are determined from 125Te Mössbauer spectroscopy and X‐ray photoelectron spectroscopy. They are related to the different types of bonds involving the Te atoms in the Tl–Sn–Te compounds. 相似文献