Impact of Co doping on physical,structural, microstructural and magnetic features of MgZn nanoferrites for high frequency applications

Cobalt (Co) doped MgZn spinel nanoferrites with composition Mg_0.5Zn_0.5Co_x Fe_2-xO₄ at x = 0.0, 0.10, 0.20, 0.30, 0.40, 0.50 were prepared using sol-gel auto ignition method. The characterizations techniques such as FESEM, FTIR, XRD and VSM were used to determine the morphology, force constants, phase, structure and magnetic features of the samples. Lattice parameters, FWHM, d-spacing, crystallite size, micro strains and volume were investigated using high score plus software. Materials analysis using diffraction (MAUD) software was also used to study the Rietveld refinement properties of the Co doped MgZn ferrites. Physical properties such as porosity, X-ray and bulk density were also determined. Force constants of their respective absorption bands were calculated from FTIR of the Co doped MgZn nanoferrites. Single phase structure with cubic phase were observed for MgZn and Co doped MgZn at x = 0.0 whereas second phase was observed at higher Co concentrations respectively. FESEM show regular shape of the particles at low Co concentrations whereas agglomerations were observed at higher Co concentrations respectively. The magnetic properties of the Co doped MgZn ferrites were also investigated from VSM study. Magnetic remanence, coercivity, initial permeability, saturation magnetization, Bohr magneton and anisotropy constant were determined from VSM analysis. The coercivity, saturation magnetization, remanence, anisotropy constant and initial permeability were enhanced with the doping of ‘Co’ in MgZn nanoferrites. Response of the Co doped MgZn nanoferrites at high frequency regime was also evaluated. It can be seen that the response from all the Co doped MgZn nanoferrites was 2.84 GHz–5.96 GHz respectively and suggested the use of these nanoferrites for the operation of nanodevices in the X-band high frequency regime.     

2.5 GHz城市环境电磁态势的计算与补偿

复杂城市空间的电磁态势分布可以通过电磁场数值计算的方法进行预测。文章使用矩量法(MOM)结合一致性几何绕射理论(UTD)的方法对2.5 GHz频率下某小区环境中的电磁态势进行了仿真计算以及实际测量。场景中的树木结构在此频率下显示出比较强烈的波动性,对电磁仿真计算结果产生了不可忽略的影响,文中将其对仿真计算结果的影响进行了单独建模仿真,给出其产生影响的经验值,对仿真结果进行修正。修正结果与测量结果对比证明该经验值在该频率下可以有效补偿计算结果的缺失。     

Susceptor-assisted fast microwave sintering of TiN reinforced SiAlON composites in a single mode cavity

In the present study, 17 wt % TiN reinforced α-β SiAlON composites were sintered at low temperature by susceptor-assisted microwave heating. The effect of TiN addition on dielectrical properties of starting powders, as well as the influence of sintering temperature on phase evolution, microstructure development and mechanical properties of α/β-SiAlON-TiN composites were investigated. The obtained results showed that TiN addition increased the microwave absorbing properties which is reflected in the peak sintering temperature. Thus, the α:β ratio decreased and mechanical properties were improved, especially the fracture toughness of the composites. Furthermore, an estimate of energy consumption during microwave assisted sintering at the laboratory scale is presented. As a result, the highest values for relative density (97.1%), Vickers hardness (13.35 ± 0.47 GPa), and fracture toughness (7.52 ± 0.54 MPa m^1/2) were obtained by microwave sintering for 30 min at 1300 °C.     

Wi-Fi无线网络2.4GHz频率规划研究

近年来,Wi-Fi技术以其低成本、高速率的优点得到了迅速普及,在教育、金融、酒店以及零售业、制造业等各领域有了广泛的应用。Wi-Fi网络运行在2.4GHz开放频段上,可用频点数较少、干扰较大。需要进行合理的频率配置,以提高Wi-Fi网络覆盖质量,提升用户业务感知。     

采用balun低噪声放大器的5GHz 7.2-dB NF低功耗直接转换接收机前端电路

A 5GHz low power direct conversion receiver radio frequency front-end with balun LNA is presented. A hybrid common gate and common source structure balun LNA is adopted, and the capacitive cross-coupling technique is used to reduce the noise contribution of the common source transistor. To obtain low 1/f noise and high linearity, a current mode passive mixer is preferred and realized. A current mode switching scheme can switch between high and low gain modes, and meanwhile it can not only perform good linearity but save power consumption at low gain mode. The front-end chip is manufactured on a 0.13-μm CMOS process and occupies an active chip area of 1.2 mm². It achieves 35 dB conversion gain across 4.9-5.1 GHz, a noise figure of 7.2 dB and an IIP3 of -16.8 dBm, while consuming 28.4 mA from a 1.2 V power supply at high gain mode. Its conversion gain is 13 dB with an IIP3 of 5.2 dBm and consumes 21.5 mA at low gain mode.     

SWP/HCI协议栈测试研究

本文对NFC产品介绍了系统分层概念,并在此基础上从SWP/HCI协议栈一致性测试、外场测试、兼容性测试的角度对NFC产品测试进行了系统介绍。     

140 GHz关键射频组件研究

在基于超外差体制的太赫兹无线通信系统接收机和发射机中,混频器、滤波器和本振源是决定系统性能的关键器件。本文分别针对基于肖特基二极管技术的140 GHz次谐波混频器、基于微机电系统（MEMS）体硅工艺的140 GHz带通滤波器和V波段毫米波本振倍频源的仿真设计和关键工艺开展了研究。测试结果表明：140 GHz次谐波混频器单边带转换损耗为26 dB,140 GHz带通滤波器的带内插损为8 dB,V波段毫米波本振倍频源最大输出功率大于50 mW（63.2 GHz~67.2 GHz）。     

60 GHz无线通信技术发展现状及趋势研究

60 GHz无线通信技术以其丰富的频谱资源和高速的数据传输速率,成为目前无线通信领域的研究热点之一。首先介绍了60 GHz无线通信技术的概念内涵、特点优势和应用场景;接着重点阐述了60 GHz无线通信技术形成的产业联盟和通信标准;然后分析了60 GHz无线通信技术发展面临的问题;最后根据信息技术的发展形势,展望了60 GHz无线通信技术的发展趋势。     

室外微蜂窝小区3.5GHz 电波传播特性仿真和分析

射线跟踪方法是研究室外微蜂窝小区电波传播的有效方法。基于入射及反弹射线法/ 镜像法对室外微小区环境中3. 5GHz 电波传播的路径损耗进行了仿真和分析,仿真结果与文献所给的结果一致性良好,验证了该 方法的正确性。提出了一种新型的射线管判收方法,可有效判断到达接收机的所有射线管。分析了仿真中得到的接收功率、均方根时延扩展、波达方向等传播参数,并比较了视距传播(LOS)和非视距传播(NLOS)的传播特性,这些分析结果可为3. 5GHz 频段无线通信系统的覆盖提供相应的理论依据。     

60GHz无线通信系统在PPM调制下的信道容量分析

本文主要研究60GHz无线通信系统在高斯信道下的香农信道容量及在脉冲位置调制(MPPM)下的信道容量。理论分析与推导得到香农信道容量与传输距离的关系函数,由MPPM调制原理及高斯信道的数学模型推导系统在MPPM调制下信道容量与信噪比、信道容量与通信距离间的函数关系,利用Matlab仿真,得到不同条件下的关系曲线。研究结果表明,60GHz无线通信系统在高斯信道下的信道容量是通信距离和信噪比的函数,该系统更适合于短距离无线通信。高进制的PPM调制能够显著的提高系统数据传输速率,当数据率相同时,高进制调制的PPM能够提供的可靠通信距离更远。