一种手持式超高频RFID读写器检测仪的设计

射频识别（RFID）技术随着物联网的兴起而得到迅速发展,超高频RFID技术因其识别距离远、识别速度快、有较强的防碰撞能力而被广泛应用。与RFID技术相比,RFID测试技术相对比较滞后,RFID测试还主要是基于参考标签或参考读写器的定性测试。为了实现RFID读写器的射频参数和协议一致性的定量测试,设计了一种基于射频处理和软件无线电（SDR）的超高频RFID读写器检测仪。该检测仪属于手持式设备,体积小、功耗低、重量轻、功能强大、且操作简便,满足超高频RFID读写器批量生产和现场保障的测试需求。     

基于软件无线电的无源超高频RFID标签性能测试

讨论了无源超高频射频识别(UHF RFID)系统的信号传输过程及性能测试方法,以软件定义无线电方式实现了符合ISO/IEC18000-6C标准的无源标签的部分性能测试,研究了部分通信参数动态变化时标签应答功率的变化,并对不同标签的灵敏度进行了测试.所有实验在常规条件下完成,测试研究表明在基带编码采用较小的Tari值、PW为50％以及较高的调制系数时,阅读器能够接收到标签反射回来的最大功率,系统的识别距离最远. 关键词： 射频识别 无源电子标签 标签灵敏度 性能测试     

反应窗理论的适用性研究

基于低能离子与原子碰撞的分子库仑过垒模型，简要描述了与入射离子速度相关的反应窗理论.根据这一理论，计算了不同碰撞速度时O⁸⁺-H，Ar⁸⁺-H，Ar⁸⁺-He，Ne¹⁰⁺-He及Ar¹⁸⁺-He等碰撞体系单电子俘获过程的微分截面，还计算了碰撞速度为0.53 a.u.时¹⁵N⁷⁺-Ne碰撞体系单电子、双电子及三电子俘获过程的微分截面，并与他人的实验结果作了比较.研究发现，反应窗理论预言的末态电子分布与实验结果符合较好.理论和实验研究表明，随着碰撞速度的增加反应窗变宽；反应窗理论所预言的微分截面，当Q值较小时比实验结果偏大，当Q值较大时比实验结果偏小. 关键词： 反应窗理论 态选择微分截面 分子库仑过垒模型 离子与原子碰撞     

无源超高频射频识别系统路径损耗研究

基于射频识别技术原理及Friis传输方程, 导出了自由空间下无源超高频射频识别(RFID) 系统路径损耗表达式. 结合菲涅耳区理论, 分析了菲涅耳余隙及阅读器天线至标签间距两因变量条件下 第一菲涅耳区受阻隔对RFID系统路径损耗的影响, 并提出了双斜率对数距离路径损耗模型. 在开阔室内环境下, 测试了菲涅耳余隙及阅读器天线至标签间距变化时的系统路径损耗. 测试结果表明: 菲涅耳余隙大于第一菲涅耳区半径1.5倍时, 刃形障碍物对系统路径损耗影响较小; 相比传统对数距离路径损耗模型, 双斜率模型标准差减小10%. 关键词： 射频识别 路径损耗 菲涅耳区 线性回归     

低场核磁共振仪器振铃抑制新方法及其电路实现

加快天线残余能量释放以减弱天线振铃信号有利于缩短低场核磁共振仪器的回波间隔（TE）,从而提高快弛豫组分的测量分辨率和信噪比（SNR）．而天线Q值对能量的发射效率和泄放速度起着相反的作用．为此,我们首先设计了一种新型Q转换电路,在保证发射效率的同时,可以大大缩短能量泄放时间．在此基础上,应用了一种优化的脉冲序列以弥补传统相位交替对脉冲序列（PAPs）不能消除90°脉冲振铃的缺陷,通过相位循环的方法进一步提高了信噪比．最后,在2 MHz岩心分析仪上测试了新型Q转换电路,当天线Q值降为发射期间的约1/5时,天线恢复时间由280.0 μs降为18.2 μs;而且,使用新型Q转换电路和优化的脉冲序列后,TE=60 μs时,可以有效获得快弛豫组分的T₂信号．     

平板型感应耦合等离子体源的线圈配置对功率耦合效率的影响

基于感应耦合等离子体的变压器模型，分析了感应耦合等离子体的功率耦合效率与线圈配置(几何尺寸、电学参量)及等离子体基本参量(等离子体电子密度、电子-中性粒子有效碰撞频率)之间的关系；然后，改变平板型线圈的匝数从而改变了线圈的几何尺寸、电学参量，并且测量出了不同的线圈所对应的功率耦合效率.实验结果表明，线圈的电感量是能否实现放电的决定性因素；而功率耦合效率则与感应线圈的Q值、放电参量(气压、功率)等密切相关，射频输入功率的增加、放电气压的上升都会导致感应耦合等离子体耦合效率的提高，这与感应耦合等离子体的变压器模型预测结果是符合的. 然而，变压器模型给出的提高线圈Q值可导致耦合效率增强的预测结果仅适用于同等电感量的线圈条件. 本文对于单线圈的感应耦合等离子体源的研究为线圈的优化设计甚至大面积的多线圈感应耦合等离子体源研制提供了理论依据. 关键词： 感应耦合等离子体 功率耦合效率 变压器模型     

基于分组动态帧时隙的射频识别防碰撞算法

提出了动态调整帧长度原则和标签分组方法, 在此基础上结合二者设计了一种新型的分组动态帧时隙防碰撞算法, 首先对未识别的标签进行数量估计, 如果标签数量超过临界值, 则对标签进行分组, 通过动态调整识别帧长适应每组标签数量进行高效识别. 仿真结果表明: 系统吞吐率稳定在34.6%–36.8% 之间, 识别过程所需要的时隙数也保持了线性增加, 在待识别标签数量大于2000的情况下, 与传统的防碰撞算法相比, 时隙效率提高了30%以上, 极大优化了系统的吞吐率, 节约系统资源. 关键词： 防碰撞 分组 动态帧时隙 吞吐率     

基于半导体光放大器的一阶IIR微波光子学滤波器及其品质因素分析

对基于半导体光放大器(SOA)环形腔结构的一阶无限冲击响应(IIR)微波光子学滤波器的品质因数(Q值)进行了实验和理论研究. 通过在有源环内置入窄带光滤波器,并调节有源环的输入光功率、SOA抽运电流、实验得到的最高Q值接近200. 理论分析表明为了得到较高的Q值,应尽可能提高信噪比和信号光的环路增益. 在考虑了 SOA中放大的自发辐射(ASE)噪声的基础上,计算了输入光功率、SOA抽运电流、环内光滤波器的带宽对Q值的影响. 数值计算的结果与实验现象基 关键词： 微波光子学滤波器 Q值')" href="#">Q值 半导体光放大器 放大的自发辐射     

具有时滞反馈的非对称双稳系统中的振动共振研究

研究了具有时滞反馈的非对称双稳系统中的振动共振现象. 在绝热近似条件下, 应用快慢变量分离法得到系统响应振幅的解析表达式Q, 分析了时滞参数α和不对称参数r对振动共振现象的影响. 结果表明: 在Q-α平台上, α可以诱导响应幅值的极大值以输入高频信号和低频信号的周期出现. 不对称参数并不影响共振发生的位置, 但是能够增强响应幅值. 在Q-B (B为高频信号振幅)平台上, 共振发生的位置B_VR随着α呈现两种不同的周期关系, 且周期分别为输入高频信号和低频信号的周期. 在Q-Ω (Ω高频信号频率)平台上, 随着时滞参数的增大, 当B较小时, 在Ω的小值区间内, Q呈现出多重共振现象, 在Ω的大值区间, Q趋于定值.     

重频Yb:YAG片状激光器电光调$lt;i$gt;Q$lt;/i$gt;时空演化模拟计算和实验研究

基于Yb³⁺抽运动力学,结合光线追迹的方法,建立了抽运过程中的放大自发辐射模型,得到激光介质中三维含时储能分布.将速率方程理论和角谱传播理论结合,对谐振腔内调Q脉冲的形成、传播过程进行建模计算,得到激光脉冲的时间-空间分布和光束质量因子变化规律.同时进行了激光二极管抽运重频Yb：YAG片状激光器电光调Q实验,并与模拟计算的结果进行了对比校核,印证了计算模型的正确性.这为主动调Q固体激光器的设计提供了参考. 关键词： Yb：YAG激光器 Q')" href="#">调Q 时空演化     

Scattering of light by a periodic structure in the presence of randomness VII: Application of statistical detection test

Detection of periodic structures, hidden in random surfaces has been addressed by us for some time and the ‘extended matched filter’ method, developed by us, has been shown to be effective in detecting the hidden periodic part from the light scattering data in circumstances where conventional data analysis methods cannot reveal the successive peaks due to scattering by the periodic part of the surface. It has been shown that if r ₀ is the coherence length of light on scattering from the rough part and Λ is the wavelength of the periodic part of the surface, the extended matched filter method can detect hidden periodic structures for (r ₀/Λ) ≥ 0.11, while conventional methods are limited to much higher values ((r ₀/Λ) ≥ 0.33). In the method developed till now, the detection of periodic structures involves the detection of the central peak, first peak and second peak in the scattered intensity of light, located at scattering wave vectors v _x = 0, Q, 2Q, respectively, where Q = 2Gp/Λ, their distinct identities being obfuscated by the fact that the peaks have width Δv _x = 2Gp/r ₀ ≫ Q. The relative magnitudes of these peaks and the consequent problems associated in identifying them is discussed. The Kolmogorov-Smirnov statistical goodness test is used to justify the identification of the peaks. This test is used to ‘reject’ or ‘not reject’ the null hypothesis which states that the successive peaks do exist. This test is repeated for various values of r ₀/Λ, which leads to the conclusion that there is really a periodic structure hidden behind the random surface.      

A Simple Method for Measuring the Q Value of an NMR Sample Coil

A simple method for measuring the Q (quality factor) value of an NMR sample coil based on an impedance matching principle is described. This method has the advantage of utilizing a signal generator and reflection coefficient bridge rather than an expensive high-frequency Q meter and offers an alternative means of measuring the Q value of an NMR sample coil or any other radio frequency coil.     

Structure and phase transformation of alkali silicate melts analysed by Raman spectroscopy

Raman spectra of binary alkali silicates were measured at various temperatures from 1300°C to room temperature to investigate the relation between structural change and phase transformation phenomena. Distribution of structural units of Q ⁿ was estimated at each temperature by the deconvolution of spectra based on the equilibrium 2Q³ ? Q² + Q⁴. The Q ⁿ distributions of sodium and potassium silicate systems strongly depend on temperature and the equilibrium shifts to the left-hand side with decreasing temperature, but those of lithium silicate system were less sensitive to the temperature variation. In alkali disilicates (33?mol%?R₂O–67?mol%?SiO₂, where R=Li, Na or K), the Q ⁿ distributions near the melting point were independent of alkali ion species, and they held the relation [Q²]?=?[Q⁴]?≈?[Q³]/4. This means that two of 6Q³ units (six-memberd ring) in crystals are transformed into a pair of Q² and Q⁴ in the melting process. Below the melting point, the Q ⁿ distribution in lithium disilicate melt remained while, in sodium and potassium disilicate melts, [Q³] increased with decreasing temperature. Crystallization of the alkali disilicate melts is discussed considering the configuration entropy of Q ⁿ units. In 25?mol%?Li₂O–75?mol%?SiO₂, which is in the range of the immiscibility dome, the Q ⁿ distribution was maintained even when phase separation occurs in the cooling process.     

Minimum-wear characteristics for boundary friction between solids

A new parameter is proposed for characterizing boundary friction between solids—the probability Q that some contact spot will be converted to a wear particle as the real contact area shifts by one mean contact-spot diameter. A method is proposed for the phenomenological detection of optimum regimes of boundary friction, which are characterized by the minimum wear intensity of the sample material, and for measuring the corresponding quantity Q=Q ^opt. For babbitt, one of the most frictionless materials, the value of Q ^opt is found to be ≈2×10⁻¹⁰. When data on the linear wear intensity I _h , the contact pressure p _n , and the hardness H are available, Q can be calculated for the given test conditions. Deviations of Q from the value Q ^opt (for a given material) can serve as a criterion for how closely a prepared surface structure approaches the optimal. Zh. Tekh. Fiz. 68, 48–52 (April 1998)     

Creep behaviour in a discontinuous SiC–Zn-22% Al composite

Creep experiments were conducted on Zn-22%?Al in which SiC particulates were introduced by variable co-deposition of multi-phase materials (VCM). The objective of the investigation is to determine the effect of SiC particulates on the creep behaviour in region I (the low-stress region) and region II (the intermediate-stress or superplastic region) of the sigmoidal plot between stress and strain rate, which was previously reported for the reinforcement-free Zn-22%?Al. The creep data show that the presence of SiC particulates has no effect on the sigmoidal trend between stress and strain rate; and that in region II, the stress exponent, n, and the activation energy for creep, Q, agree well with those reported for SiC-free grades of Zn-22%?Al; n?=?2.5 and Q?～?Q _gb, where Q _gb is energy for grain boundary diffusion in the alloy. However, the data indicate that the presence of the particulates results in narrowing region II and reducing maximum ductility. An analysis of the creep data reveals the presence of a threshold stress that depends strongly on temperature. The microstructural data inferred from an examination of the crept specimens by the means of transmission electron microscopy (TEM) suggest that the origin of τ ₀ may be related to the interaction between moving dislocations and dispersion particles. These particles are introduced in the material as a result of processing the material by thermal spray and deposition.     

High-gradient operators of the unitary matrix-model

A complete classification of all rotationally invariant operators of the two-dimensional unitary matrix model composed of gradients of the fieldQ and their anomalous dimensions are given in one-loop order. Similarly as in the orthogonal case and for then-vector model the leading correction of operators with2n factors Q grows withn(n–1).Work supported in part by the Deutsche Forschungsgemeinschaft through Sonderforschungsbereich 123 Stochastic Mathematical Models     

基于RFID标签的分布式温度测量系统设计

射频识别（RFID）技术是一种低成本且高效的非接触式自动识别技术,其具有的识别速度快,识别距离远等优点,使其具有非常广泛的应用前景。设计一种基于RFID的分布式多点温度测量系统,系统由RFID电子标签、读写器、主接收机和PC组成,实现各节点温度的实时采集功能。为了提高各节点的温度测量精度,提出了一种测温补偿算法,采用最小二乘拟合的方案,克服由于器件的不准确而引入的测量误差。结果表明,该系统可以有效完成多点温度测量采集的功能,同时具有非常高的精确性。     

云计算环境下智能图书借还终端系统设计与实现

针对传统的图书借还系统只能通过条码扫描,获取信息,一直存在工作效率低、用户信任度下降的问题。提出并设计了一种基于RFID技术的智能图书借还终端系统,该系统利用RFID无线射频识别技术采集馆内图书、读者以及书架等信息,采用天线条码标签对智能图书馆内的图书进行监控,实现对图书借还信息进行终端操作,设计了系统软件,并通过实验进行了对比分析,实验表明对RFID系统的硬件和软件测试对传统条码技术的问题有了相对应的解决,从而达到提高智能图书馆借还书和借还终端系统效率的目的。     

Investigation of the Mesostructure of Transition-Metal Monogermanides Synthesized under Pressure

The mesostructure of transition-metal monogermanides Mn_{1 – x}Co _x Ge is studied by small-angle neutron scattering in a wide range of concentrations x = 0–0.95. These compounds were synthesized under high pressure and are metastable under normal conditions. The experimental dependences I(Q) obtained for the whole series of samples in the range of transferred momenta (6 × 10^–2 nm^–1 < Q< 2.5 nm^–1) are described by the power dependence Q^–n with an exponent n = 2.99 ± 0.02, uniquely related to the fractal properties of the system under study. The dependence obtained indicates that the superatomic structure of the samples is characterized by the presence of defects with a spatial organization described by a fractal model with a logarithmic dependence of the correlation function of the defect density. It is interesting to note that such defects are absent in the isostructural FeGe compound, i.e., the experimental dependences of the intensity are described well by the expression Q^–n with an exponent n = 4.1 ± 0.1, which demonstrates the presence of crystallites with a uniform density distribution inside and a sharp boundary characterizing the surface.