La_(0.8)Sr_(0.2)Mn_(0.98-x)Fe_xCo_(0.02)O_3微波吸收特性研究

用溶胶-凝胶法制备La_(0.8)Sr_(0.2)Mn_(0.98-x)Fe_xCo_(0.02)O_3(x=0.08、0.10、0.12、0.14)晶粉,用场发射扫描电子显微镜和XRD表征其微观形貌和晶体结构,用微波网络矢量分析仪测量样品在2~18 GHz频率范围内的复介电常数和复磁导率,根据测量数据计算微波反射率与频率的关系曲线.研究结果表明:900℃煅烧3 h的La_(0.8)Sr_(0.2)Mn_(0.98-x)Fe_xCo_(0.02)O_3粉晶平均粒径约100 nm,晶体结构为钙钛矿型;在测试范围内,样品都有一个吸收峰,峰高及频率位置随x不同而异;厚度2 mm,x=0.08、0.10、0.14,大于10dB的吸收带宽达到4 GHz以上,样品既有介电损耗又有磁损耗,但介电损耗要大于磁损耗.     

采用谐振腔微扰法的NiZn铁氧体介电常数测量

谐振腔微扰法广泛用于材料微波介电性能的测量,它与常规的测量方法相比,具有样品尺寸小、计算公式简单的优点,在近似计算频率、谐振腔品质因数、材料的介电常数等方面具有较高的应用价值.采用谐振腔微扰法,测量不同配方NiZn铁氧体在微波频段的复介电常数,计算得到介电常数的虚部ε″和实部ε',进而分析Ni和Zn的含量对NiZn铁氧体材料介电常数的影响.     

A novel approach to design microwave medium of negative refractive index and simulation verification

In this paper, a novel approach is presented to synthesize microwave medium of negative refractive index by incorporating metallic wire array with negative effective permittivity into the host media such as ferrimagnet-YIG （yttrium iron garnet） applied by external magnetic field whose permeability is negarive. We have designed the composite medium having negative refractive index in C/X band frequencies, analyzed and simulated its electromagnetic （EM） properties by use of EM EDA package based on time-domain finite integration method. The simulation results show that： ① the effective permittivity of the designed metallic wire array is negative in the frequency range from 7.02 GHz to 9.80 GHz; ② the permeability of YIG substrate immersed into an external magnetic field is negative in the frequency range from 5.22 GHz to 8.14 GHz; ③ EM wave can pass through the composite medium synthesized by the above designed metallic wire array and YIG substrate, and ④ the negative refraction behavior occurs on the interface between the composite medium and the normal material with positive refractive index in 7.51-8.13 GHz frequency range, in which the effective permitUvity of the metallic wire array and the permeability of YIG substrate are negative simultaneously. The full wave simulation has demonstrated that the effective refractive index of the designed composite medium is indeed negative and ascertained that the proposed approach to design microwave medium with negative refractive index is viable.     

基于虚拟仪器技术的薄膜电磁参量测量

基于谐振腔微扰技术,利用先进的矢量网络分析仪,结合虚拟仪器技术研制了一套测量薄膜微波电磁参量的自动测量系统．该系统可以方便、快捷地测量薄膜在微波频率下的复介电常数和复磁导率．图形化编程语言LabVIEW大大缩短了系统开发时间,提高了编程效率．     

高温超导微带线的传输特性及其应用

研究了高温超导微带线的衰减和色散特性。推导了超导体的复电导率和外加直流电流的关系。考虑到实际高温超导材料中分布着约瑟夫逊结并且存在一定的剩余电导率，对复电导率公式作了修正。当微带线的带条厚度和穿透深度相当时，用唯象损耗等效方法分析了电磁场渗人超导体而对微波传输特性产生的影响。     

大功率微波作用下溶液复介电系数测量新方法

化学反应过程中的等效复介电系数测量是微波化学研究的重要内容.传统的复介电系数测量方法一般都需要测量反射系数的相位.而在大功率微波条件下，很难做到对反射系数相位的准确测量.为解决该问题，基于天线模型提出了一种新的测量方法.并对氯化钠水溶液和甲醇/乙醇混合溶液的复介电系数进行了测量.实验结果和相关文献中的公式计算值基本吻合.     

W型Ba_(1-x)La_xCo_2Fe_(16)O_(27)的微波吸收性能

用溶胶-凝胶法制备镧掺杂W型钡铁氧体Ba1-xLaxCo2Fe16O27（x=0,0．1,0．2,0-3）样品。用XRD和SEM对样品的晶体结构、表面形貌、粒径进行表征,用微波矢量网络分析仪测试该样品在2-18GHz微波频率范围的复介电常数、复磁导率,根据测量数据计算电磁损耗角正切及得出微波反射率与频率的关系,探讨该材料的微波吸收性能与电磁损耗机理。研究结果表明：适量稀土镧掺杂能改善微波吸收性能,在x=0．2时,样品微波吸收效果最好;当样品厚度为1．90mm及x=0．2时,吸收峰值为16．2dB,10dB以上频带宽度达4．0GHz样品的微波吸收来自磁损耗和介电损耗的共同作用,磁损耗更为显著。     

PAN和MnZn铁氧体复合基质手性材料电磁性质

以导电聚苯胺与MnZn铁氧体的复合物为基质,以碳纤维螺旋体为手性掺杂体,制备了复合手性材料.用微波圆波导法在8.5～11.0GHz内测量了手性材料的旋波性、圆二色性及电磁参数,分析了MnZn铁氧体浓度对实验结果的影响     

Microwave absorbing properties of polyaniline/montmorillonite doped with dodecylbenzensulfonic acid nanocomposite

In this paper, we reported a new type of high performance microwave-absorbing material, polyaniline/montmorillonite doped with dodecylbenzensulfonic acid (PAni-DBSA/MMT) nanocomposite. The microwave-absorbing properties of this nanocomposite were investigated for the frist time. The nanocomposites were synthesized from emulsion polymerization using dodecylbenzensulfonic acid (DBSA) as dopant and emulsifier. The structure of the nanocomposite was analyzed by X-ray diffraction(XRD) and FT-IR, and its results denoted that PAni-DBSA/MMT is a typical intercalative polymer/layered silicate(PLS) nanocomposite, and the interaction between MMT layers and PAni chains enhances the delocalization of free electrons in PAni chains. The complex permittivity, permeability and reflection loss (R.L.) of microwave of a 2.00 mm thick samples containing 50% by weight of PAni-DBSA/MMT nanocomposite and PANI?DBSA were measured, respectively, in 2?18 GHz range. The results showed that the PANI-DBSA/MMT nanocomposite is capable of absorbing 2.0?18 GHz microwaves, and the reflection loss was less than -10 dB in the frequency range of 9.1?12.5 GHz, while the minimum reflection loss was -15.8 dB at 11 GHz. The microwave absorbing mechanism of nanocomposite is disscused.     

纳米晶Fe85Si1Al6Cr8片状颗粒材料微波吸收特性

采用快淬工艺和高能球磨处理技术制备了纳米晶FeSiAlCr片状颗粒材料．研究了高能球磨处理工艺对材料微结构、形貌和微波电磁特性的影响。结果表明高能球磨处理使球形粉粒形状扁平化并细化其晶粒，从而使FeSiAlCr颗粒材料的微波磁导率显著提高，介电常数被有效控制．对用该材料制作的涂层吸波性能进行了计算模拟，结果表明在4GHz附近微波段具有良好吸波性能．     

薄膜材料复介电常数与复磁导率测试研究

采用谐振腔法对薄膜材料复介电常数和复磁导率进行了测试研究。依据腔内电磁场的特性及薄膜材料体积小的特点,采取了较大的模指数、高品质因数、小耦合系数等措施,设计了在2GHz频率下工作模式为TE105的矩形谐振腔。使用Agilent 8722ES络分析仪进行扫频反射测量,由放置试样前后腔的谐振频率和品质因数以及试样的体积等计算出薄膜材料复介电常数和复磁导率,该方法操作简便,准确性较高。     

利用单纯形法对土壤复介电常数的测试研究

作者以数值计算为基础,对单纯形算法的思想、构建和迭代运算过程作了简单的介绍．通过传输线理论,分析得出对土壤复介电常数测试中所满足的复数超越方程,进而对该复数超越方程进行了单纯形迭代求解．结果表明,单纯形法所得到的数值解与文献给定的范围值相吻合．     

冷却速率对高碳铬铁粉电磁性能的影响

采用矢量网络参数法在1~18 GНz频段内分别对电阻炉、空气和水浴中冷却的高碳铬铁粉的电磁性能进行研究.随着冷却速率的提高,高碳铬铁粉的相对复介电常数实部和虚部在大多数频率下均增大.空冷和水冷粉料的相对复介电常数虚部在12~18 GНz频率范围内因极化弛豫而产生较大的峰值.同一频率下相对复磁导率实部随冷却速率变化的趋势与相对复介电常数相反.水冷粉料的相对复磁导率虚部在3~5GНz以外的频段内均大于另两组冷却粉料,且三组粉料的虚部在低频及高频条件下均具有峰值.在2.45 GНz的微波加热频率下,炉冷、空冷及水冷粉料的反射损耗分别为-2.30、-2.15和-2.07 dB.水冷粉料的介电损耗因子及磁损耗因子最大,微波场下具有最佳的升温速率与反应效果.     

ZIF-8衍生的ZnO与RGO复合材料的制备及其电磁波吸收性能

以ZIF-8与氧化石墨烯(GO)为前驱体,采用溶剂热法和碳化法得到ZnO/RGO复合材料.用X射线衍射、扫描电镜和透射电镜测试手段,对制备的ZnO/RGO复合材料的结构与物相进行表征,用矢量网络分析仪测量复合材料的电磁参数(复介电常数和复磁导率),通过反射损耗(RL)公式得到不同厚度样品的RL值.结果表明:煅烧温度为700℃的样品在2~18GHz具有良好的吸波性能;吸波层厚度为4mm、频率为17.2GHz时,RL小于等于-10dB的频率宽为1.0GHz(16.8~17.8GHz),此时的RL达到最小值-22.9dB.     

复合左/右手传输线的电磁特性及其潜在应用

复合左/右手传输线是右手材料和左手材料复合而成的新型传输线,它较一般传输线可以在不同的频率范围内表现出不同的电磁特性.当等效介电常数和等效磁导率同时为负值时表现出"左手特性",而在其它频率范围内表现出"右手特性",同时,复合左/右手传输线还可以进行相位调整.分析了复合左/右手传输线的电磁特性,并指出复合传输线的潜在应用.     

Microwave absorption properties of SiC@SiO_2@Fe_3O_4 hybrids in the 2–18 GHz range

To enhance the microwave absorption performance of silicon carbide nanowires(SiCNWs), SiO_2 nanoshells with a thickness of approximately 2 nm and Fe_3O_4 nanoparticles were grown on the surface of SiCNWs to form SiC@SiO_2@Fe_3O_4 hybrids. The microwave absorption performance of the SiC@SiO_2@Fe_3O_4 hybrids with different thicknesses was investigated in the frequency range from 2 to 18 GHz using a free-space antenna-based system. The results indicate that SiC@SiO_2@Fe_3O_4 hybrids exhibit improved microwave absorption. In particular, in the case of an SiC@SiO_2 to iron(III) acetylacetonate mass ratio of 1:3, the microwave absorption with an absorber of 2-mm thickness exhibited a minimum reflection loss of-39.58 d B at 12.24 GHz. With respect to the enhanced microwave absorption mechanism, the Fe_3O_4 nanoparticles coated on SiC@SiO_2 nanowires are proposed to balance the permeability and permittivity of the materials, contributing to the microwave attenuation.     

Microwave absorption properties of SiC@SiO2@Fe3O4 hybrids in the 2–18 GHz range

To enhance the microwave absorption performance of silicon carbide nanowires (SiCNWs), SiO2 nanoshells with a thickness of approximately 2 nm and Fe3O4 nanoparticles were grown on the surface of SiCNWs to form SiC@SiO2@Fe3O4 hybrids. The microwave absorption performance of the SiC@SiO2@Fe3O4 hybrids with different thicknesses was investigated in the frequency range from 2 to 18 GHz using a free-space antenna-based system. The results indicate that SiC@SiO2@Fe3O4 hybrids exhibit improved microwave absorption. In particular, in the case of an SiC@SiO2 to iron(III) acetylacetonate mass ratio of 1:3,themicrowave absorption with an absorber of 2-mm thickness exhibited a minimum reflection loss of?39.58 dB at 12.24 GHz. With respect to the enhanced microwave absorption mechanism, the Fe3O4 nanoparticles coated on SiC@SiO2 nanowires are proposed to balance the permeability and permittivity of the materials, contributing to the microwave attenuation.     

La0.8Sr0.2Mn0.86Fe0.14-xCoxO3微波吸收性能研究

用溶胶-凝胶法制备了La0.8Sr0.2Mn0.86Fe0.14-xCoxO3（x=0.01,0.02,0.03）粉晶, 用XRD表征了其晶体结构,用微波网络矢量分析仪测量了样品在2-18GHz频率范围内的复介电常数和复磁导率,根据测量数据计算了微波反射率与频率的关系曲线。研究结果表明,样品都有一个吸收峰,峰高及位置随x不同而异,其中样品La0.8Sr0.2Mn0.86Fe0.13Co0.01O3,厚度为1.80mm时,吸收峰高27.9dB,2-18GHz吸收带宽5.3GHz;厚度为2.00mm时,吸收峰高26dB, 2-18GHz吸收带宽4.9GHz。从电、磁损耗角正切看,样品既有介电损耗又有磁损耗,但介电损耗要大于磁损耗。     

高频电磁波测量土水系统环保传感器的设计与制造

提出了一种通过利用微波方法测量物质复介电常数来分析土水系统特性的方法,并设计了一种环保传感器.该传感器采用较简单的单端微波反射系数法,并利用多孔陶瓷材料制成渗透室.本文论述了此种传感器的设计、制造以及实现测量的方法.