BaO Nd2O3 Sm2O3 TiO2薄膜的微波特性

在制作完底电极的LaAlO3(100)衬底上,利用磁控溅射法制备了一层BaO-Nd2O3-Sm2O3-TiO2(BNST)系薄膜,再对薄膜进行退火处理.X线衍射仪(XRD)分析表明,经退火处理的BNST薄膜结晶效果良好.采用薄膜电容结构来实现电容的测量,主要研究了BNST薄膜电容的频率特性.阻抗分析测试和矢量网络分析测试表明,在测试频率为1 MHz时,介电常数为58.3,介电损耗小于2％;在1 GHz的测试频率下,介电常数为57.5,介电损耗小于3％.研究表明,制备的BNST薄膜的频率特性稳定,基本满足微波频率下使用的要求.     

微波辐射峰值吸收频率对原油组分的影响

利用微波辐射降低原油粘度是一种新的高效处理方法,微波降粘效果取决于油样吸收微波的能量,油样对微波的吸收率取决于微波频率,因此油样最大能量吸收率所对应的微波频率定义为峰值吸收频率。基于微波二端口网络模型,利用自行设计的微波辐射实验设备进行研究,精确测量了待测油样的峰值吸收频率,并详细分析了频率对原油组分的影响。结果表明:在3.9 ~6.5 GHz 的扫描频率下,油样在频率为5.8 GHz 时出现第1个吸收频率且能量仅剩69.9%,在6.2 GHz 时出现第2 个吸收频率且能量仅剩36.4%,该频率为峰值吸收频率;运用GCMS分析经过5.8 GHz 和6.2 GHz 微波辐射后,轻组分(C7-C14)分别增加了7.6%、8.7%,重组分(C16 及以上碳数)分别减少12.4%、13.5%,原油组分发生明显的改变。研究结论为微波辐射技术在石油行业运用提供了重要的参考,证明了该技术具有良好的应用前景。     

(Zn_(0.3)Co_(0.7))_2-W型钡铁氧体电磁特性及吸波性能

采用sol-gel法合成了Ba(Zn0.3Co0.7)2Fe16O27六方铁氧体样品。通过XRD、SEM和Agilent8722ET网络分析仪等表征手段,研究了样品的显微结构、电磁特性及吸波性能。结果表明:在1250℃下制得的样品基本为单一相的Ba(Zn0.3Co0.7)2Fe16O27铁氧体。样品在14GHz附近出现介电损耗峰,在8～12GHz和15～17GHz内出现很宽的磁损耗。当吸波涂层厚度为1.85mm时,在15.3GHz左右反射损耗峰值可达到–23dB,并且在9～18GHz内反射损耗RL小于–10dB,具有优异的微波吸收性能。     

无压烧结SiC-AlN复相陶瓷导热和介电性能的研究

添加10%(质量分数)BaO-SiO_2-Y_2O_3烧结助剂在氮气氛下无压烧结制备SiC-AlN复相陶瓷。研究了SiC含量、烧结温度对复相陶瓷烧结性能、显微结构、热导率和高频介电性能的影响。结果表明:样品中主晶相为6H-SiC和AlN,次晶相为Y_3Al_5O_(12)和Y_4Al_2O_9;当SiC质量分数为50%时,1850℃烧结1 h,显气孔率低于0.3%;而Si C含量继续增加,显气孔率显著上升。热导率、介电常数和介电损耗都随着烧结温度的升高而升高。当Si C质量分数为50%时,1900℃下复相材料呈现最好的热扩散系数和热导率,分别为26.3 mm~2·s~(–1)和61.5W·m~(–1)·K~(–1);1850℃下获得的Si C-Al N复相陶瓷在12.4~18 GHz频率范围内获相对介电常数和介电损耗分别为33~37和0.4~0.5,该频段内随频率升高,介电常数和介电损耗下降。     

不同形状特征的碳基复合材料吸波性能分析

基于短切碳纤维、碳纳米纤维、石墨烯及炭黑,分析研究碳基复合材料中吸收剂形状比对电磁特性,尤其是吸波性能的影响。采用矢量网络分析仪测试基于不同形状比吸收剂形成碳基复合材料的电磁参数,并且计算出样品理论反射损耗。结果发现,随着频率的增加,碳基复合材料的介电常数逐渐减小;碳纳米纤维样品厚度为2 mm,在8 GHz时反射损耗达到-8 d B;炭黑与石墨烯质量比为1∶1时,在0. 5~12. 8 GHz频段内损耗角正切tanδ随频率的增大而增大且样品厚度为2mm时,其在12~16. 2 GHz反射损耗小于-10 d B,且在12. 8 GHz时反射损耗达到-22. 5 d B。通过对不同形状比吸收剂形成碳基复合材料的电磁参数分析,发现具有一定长径比或较大比表面积的吸收剂复合有利于提升碳基复合材料的吸波性能。     

(1-x)BiFeO3-xCoFe2O4复合陶瓷介电性能的研究

采用传统的固相烧结工艺制备3种不同摩尔比的(1-x)BiFeO3-xCoFe2O4(简称(1-x)BFO-xCFO,x为摩尔分数,且x=0.1,0.3,0.5)复合陶瓷样品,并分析了其在室温和变温下的介电性能。研究结果表明,室温下陶瓷样品的介电常数和介电损耗均随CFO含量的增加而降低;当频率大于100kHz时,样品的介电常数随CFO含量的增加而变化不大;当x(CFO)=0.1时,样品在高频时介电损耗变小,而当x(CFO)=0.3或0.5时,陶瓷样品的介电损耗明显大于纯BFO陶瓷的介电损耗。在高温情况下,由于CFO的添加使陶瓷样品存在更多的缺陷活化及CFO所造成的漏电流,使样品在低频时的介电常数与介电损耗都变得很大。在100kHz频率下的交流导电率均随着温度的增加而减少;且相同温度下样品中包含的CFO含量越大其交流导电率也越大。当x(CFO)=0.3和0.5时,复合陶瓷样品的交流导电率随温度的变化规律几乎相同,且它们在相同温度下的交流导电率比纯BFO的大5～6个数量级。     

考虑频率波动的微波加热数值模拟模型

家用微波炉内磁控管的频率会有波动,且难以测定。为考查微波频率波动对样品温度分布的影响, 获得更加精确的仿真结果,研究假设家用微波炉的频率以2. 45 GHz 为中心波动,并对不同波动范围的频率(2.44~2.46 GHz,2.43~2.47 GHz,2.41~2.49 GHz)与单个频率(2.45 GHz)的基于有限元模型的仿真结果与实验结果进行了比较分析。实验对象是放置于微波炉内加热60 s 的土豆泥。对于不同的频率范围分布,每隔0. 005 GHz 计算一次电磁功率密度,并根据余弦分布对它们进行加权平均,最后将电磁功率作为热源加热土豆泥。模拟结果分别与用热成像仪和光纤热电偶测定的土豆泥表面温度分布和各部位瞬时温度的实验值进行比较。结果显示频率波动范围在2.44~2.46 GHz 预测的温度场与实验值有较好的一致性;而在2.41~2.49 GHz 范围内,温度分布的均匀性最好。该模型也可为指导微波食品的开发提供理论依据。     

Bi1.5Zn1.0Nb1.5O7/Ba0.5Sr0.5TiO3复合薄膜介电性能的频率特性研究

采用射频磁控溅射法在蓝宝石基片上制备了Bi1.5Zn1.0Nb1.5O7(BZN)/Ba0.5Sr0.5TiO3(BST)双层复合薄膜,并研究了该薄膜在100 kHz~6 GHz频率范围内的介电性能。研究结果表明,BZN/BST复合薄膜的介电性能具有良好的频率稳定性。该复合薄膜的介电常数在研究的频率范围内基本与频率无关;其介电损耗在频率低于1 GHz时与频率无关,在频率高于1 GHz时随频率的上升而略微增大;薄膜在研究的频率范围内具有稳定的介电调谐率。     

Bi_(1.5)Zn_(1.0)Nb_(1.5)O_7/Ba_(0.5)Sr_(0.5)TiO_3复合薄膜介电性能的频率特性研究

采用射频磁控溅射法在蓝宝石基片上制备了Bi1.5Zn1.0Nb1.5O7(BZN)/Ba0.5Sr0.5TiO3(BST)双层复合薄膜,并研究了该薄膜在100 kHz~6 GHz频率范围内的介电性能。研究结果表明,BZN/BST复合薄膜的介电性能具有良好的频率稳定性。该复合薄膜的介电常数在研究的频率范围内基本与频率无关;其介电损耗在频率低于1 GHz时与频率无关,在频率高于1 GHz时随频率的上升而略微增大;薄膜在研究的频率范围内具有稳定的介电调谐率。     

卫星链路降雨衰减的测量及频率换算

利用雨量计、频谱仪、计算机等设备,对武汉地区某时段降雨率和Ku频段卫星下行链路(12GHz)的降雨衰减进行了测量.通过数据处理,得到降雨率与降雨衰减的关系.经频率换算得到了相同条件下Ka频段卫星下行链路(20GHz)的降雨率与降雨衰减的关系.针对ITU - R预测模型的不精确性,根据频率换算值对预测模型进行修正.该换算值可为该链路Ka频段卫星通信抗雨衰方案的设计提供理论依据.     

Microwave dielectric properties of DNA based polymers between 10 and 30 GHz

Deoxyribonucleic acid (DNA) based polymer thin-films were characterized at microwave frequencies for the first time. The dielectric properties of the film were extracted from comparison of the propagation constants of the co-planar waveguide (CPW) lines on bare MgO substrates and the DNA based films on MgO substrates. The insertion loss introduced by the DNA film is only 0.1 dB at 10 GHz and 0.5 dB at 30 GHz. The relative dielectric constant of the DNA based film averages to four at microwave frequencies, and the loss-tangent was below 0.1 up to 30 GHz.     

Structural and Microwave Properties of Silica Xerogel Glass-Ceramic Sintered by Sub-millimeter Wave Heating using a Gyrotron

In this paper, we present and discuss experimental results from a microwave sintering of silica glass-ceramics, produced from amorphous silica xerogel extracted from sago waste ash. As a radiation source for a microwave heating a sub-millimeter wave gyrotron (Gyrotron FU CW I) with an output frequency of 300?GHz has been used. The powders of the amorphous silica xerogel have been dry pressed and then sintered at temperatures ranging from 300?°C to 1200?°C. Microwave absorbing properties of the sintered samples were investigated by measuring the dielectric constant, the dielectric loss, and the reflection loss at different frequencies in the interval from 8.2 to 12.4?GHz. Furthermore, the characteristics of the formation process for producing silica glass-ceramics were studied using a Raman Spectroscopy and a Scanning Electron Microscopy (SEM). The results indicate that the samples sintered at 1200?°C are characterized by lower reflection losses and a better transparency due to the formation of a fully crystallized silica glass- ceramic at sufficiently high temperature.     

(Bi2-xZnx)(Ti2-xNbx)O7陶瓷的结构与介电性能

研究了(Bi2-xZnx)(Ti2-xNbx)O7(0.4≤x≤1.0)陶瓷材料的结构与介电性能.X-射线衍射结果表明,该组分体系在950～1 100 ℃烧结,可得到单相立方焦绿石结构陶瓷.扫描电子显微镜观察样品形貌发现,x越大,晶粒尺寸越大.室温介电性能的测试表明,在1 MHz条件下,随x值的增大,介电常数从218下降到122,损耗为(1～4)×10-4.介电温谱测试发现,该组分体系在低温下出现明显的介电弛豫峰,峰形随x增大逐渐宽化.微波特性的测试表明,在谐振频率2～3 GHz,样品的品质因数与谐振频率之积Q×f为112～158 GHz.     

微波烧结Ba_(6-3x)Sm_(8+2x)Ti_(18)O_(54)陶瓷材料的初步研究

研究了Ba_(6-3x)Sm_(8+2x)Ti_(18)O_(54)(x=0.67,BST)陶瓷材料的微波烧结情况,从烧结特性、微结构与相组成及微波介电性能等方面对微波烧结的样品与传统工艺制得的样品进行了对比.结果表明, 与传统制备工艺相比,微波烧结BST陶瓷缩短了烧结周期,并促进了样品的致密化,其物相组成和传统烧结的样品没有区别,且晶粒细小分布均匀.微波烧结BST陶瓷可获得较优的微波介电性能:介电常数ε_r=82.89,品质因数与频率之积Qf=8 450 GHz(频率f=4.75 GHz),谐振频率温度系数τ_f=22.58×10~(-6)/℃.     

Microwave dielectric properties of dry rocks

The use of a combination of several measurement techniques to investigate the dielectric properties of 80 rock samples in the microwave region is discussed. The real part of the relative dielectric constant ε' was measured in 0.1-GHz steps from 0.5 to 18 GHz, and the imaginary part ε" was measured at five frequencies extending between 1.6 and 16 GHz. In addition to the dielectric measurements, the bulk density was measured for all the samples and the bulk chemical composition was determined for 56 of the samples. This study shows that ε' is frequency-independent over the range of 0.5-18 GHz for all rock samples, and that the bulk density ρ_b accounts for about 50% of the observed variance of ε'. For silicate rocks, as much as 78% of the observed variance of ε' may be explained by the combination of density and the fractional contents of various oxides determined by X-ray fluorescence when the silicates are subgrouped by genesis. In contrast, the loss factor ε" decrease with increasing frequency for most rock samples. It was not possible to establish statistically significant relationships between ε" and the measured density of the rock samples. However, in the case of silicate rocks, 60% of the variance in ε" generally can be explained by the bulk chemical composition when the silicates are subgrouped by genesis     

Radiation-corrected open-ended coax line technique for dielectricmeasurements of liquids up to 20 GHz

An experimental technique and associated analysis are described for the measurement of the dielectric constants of liquids at microwave frequencies using an open-ended coax probe. The analysis includes radiative corrections to the probe-liquid interface impedance. The technique is applicable to liquid and liquid-like (e.g., biological) samples, having dielectric constants comparable to water, at frequencies up to 20 GHz and possibly as high as 40 GHz     

CaWO_4-Mg_2SiO_4陶瓷的微波介电性能与应用

为了使微波介电陶瓷在厘米波段获得应用,采用固相法制备了低εr、高Q·f值的(1–x)CaWO4-xMg2SiO4(x=0～1.0)介电陶瓷,并添加质量分数为5%的TiO2调节其τf。研究了其晶相结构和微波介电性能。结果表明,x≤0.2时,Mg2SiO4和CaWO4形成不完全固溶体;x=0.2时,在1300℃烧结2h所制得的陶瓷具有优良的微波介电性能:εr=9.58,Q·f=56400GHz,τf=–8.2×10–6/℃,并采用该材料制作了f0=5.4909GHz,插入损耗小于1.1dB,外形尺寸为5.0mm×2.5mm×4.0mm的两级片式介质带通滤波器。     

Complex Permittivity of GaAs and CdTe at Microwave Frequencies

The microwave dielectric constant and loss tangent of Cr-doped semi-insulatiug GaAs have been measured in the frequency range 2.5-36.0 GHz and the temperature range 300-400 K. The room temperature dielectric constant is 12.95 and the temperature coefficient alpha ( /spl equiv/ epsilon(0)/sup -1/ d epsilon/dT) is 1.6 x 10/sup -4/ /K. The dielectric constant and loss tangent of CdTe have been measured as functions of temperature at 15.95 GHz. The room temperature dielectric constant is 10.39 /spl plusmn/ 0.04 and the temperature coefficient alpha is 2.5 x 10/sup -4/ /K.     

A 4-, 6-, 20-, and 30-GHz-Band Branching Network Using a Multilayer Dielectric Filter for a Satellite Communication Earth Station

This paper describes a four-frequency broad-band branching network for transferring microwave (4 and 6 GHz)- and millimeter-wave (20 and 30 GHz)-band signals between an antenna and transmitter-receivers in a satellite communication earth station. A filter for separating the microwave band from the millimeter-wave band employs a multilayer dielectric filter with matching layers and is included in the primary antenna feed system. The design method used for the multilayer dielectric filter and the construction and experimental results of the four-frequency broad-band branching network are described. Measurements show that its insertion loss, VSWR, and axial ratio are less than 1.2, 1.2, and 2.1 dB, respectively.