高频电磁波的能流密度

高频电磁波的能流密度甘肃景泰二中梁衡山高频电磁波的能流密度不仅是一个重要的物理概念，也是一个必须研究的问题。对于提高远距离通信的效率具有深远意义，涉及卫星直播和卫星通信，地面广播和地面通信等领域。笔者根据场论，以能流密度为论点，对其物理含义给予论述。...     

高频电磁波在有损地面上的传播特性

对于架设在复杂环境的高频天线,用矩量法等算法计算环境对电磁波传播特性的影响非常困难,而了胡着高频技术的发展,这一现实问题迫切需要得到解决,本文利用时域有限差分法（FDTD）对这类问题进行了分析计算,文章计算了架设在海岸边的天线,其辐射的电磁波经过一段有损陆地后,远区电磁场的变化特性,由于存在不同介质的界面,在计算中引入了表面阻抗法概念,提高了运算程度。     

电磁波吸收材料的开发

电波吸收材料的动向电波吸收材料在实际使用时必须根据其使用情况选择合适的最佳吸收频带的材料，一些典型的常用材料有①电阻薄膜、电阻纤维以及导电涂料等电阻型材料，②橡皮、碳素和纤维增强塑料（ERP）等感应型材料，以及③以铁氧体为代表的磁性材料。近年来为了适应对于薄型化、宽频带化、低廉化以及增加附加价值等要求的日益高涨，新材料不断开发成功。Fe3Si扁平磁粉填充的橡胶薄板，是一种吸波特性优异的新材料，通常软磁金属材料由于导电性高形成涡电流而不能低于高频电磁波领域，但这一缺点通过扁平粉末和薄膜化而抑制了涡电流，从而使其可以用于10GHZ这样高的高频波段。粉末扁平化使得磁导率提高也增加了退磁因数，同时以像胶作粘结剂使得金属粉末绝缘从而提高了电阻。在电介质材料之中近年来特别受到关注的有一种碳精微型卷材（CMC），它是节距大约为1／1000mm的微卷状非晶态碳纤维，是由含有微量硫化物的乙炔气体热分解获得的材料。因为传统气相成长的碳纤维其石墨构造沿纤维轴向非常发达，而CMC却形成了非晶态结构，其表面积特别大，能够与所有的波动相互作用，可望在GHz频带等领域中作为电波吸收材料实用化。另外以多层碳纳米管以及短碳纤维主要组分的电波吸收材料，还有以钢铁工业废弃物为原料制备的吸波材料，都是近年来电磁吸收材料开发的重点。     

对高频电压标准装置不确定度的评定

超高频电压毫伏表主要是在高频端对小电压的测量，它在我厂军品调试中起到很重要的作用，因此对高频电压标准装置不确定的正确评定就显得尤为重要，现以我厂经常使用的超高频电压毫伏表DA22A为测试表来对我厂的高频电压标准装置进行全面的不确定度的评定。     

常用塑料透波性能的试验研究

塑料的应用日益广泛,通信领域亦是如此。为了考察市面上常见塑料的透波效果,作者从反向出发,运用简化 的屏蔽室测试法来测试金属材料铁以及常用的近10 种塑料对400MHz～2.4GHz 波段内常用频率电磁波的电磁屏蔽效能进 而达到研究透波性能的目的。试验结果显示,不同种材料对同频率电磁波的衰减作用不同,而同种塑料对不同频率电磁 波的影响也存在很大差别。     

脉冲电磁波波形的变化规律＊

本文研究脉冲电流激励的电磁波波形及其随轴向距离的变化规律。     

利用辛几何理论求解电磁波在非均匀媒质中的传播

提出了一种基于辛几何的高频近似的新方法，并用此方法求解了电磁波在一非均匀媒质中的传播问题。通过辛空间上的坐标变换，使电磁波传播中的焦散问题转化为非焦散的问题，并结合几何光学的方法，求得了包括焦散区在内的高频近似解。解决了几何光学法无法在焦散区求解的问题，还可以推广到二维及三维的情况。     

时钟电路的电磁波干扰

所有会产生电压频率信号的电子组件都是潜在的电磁波干扰(EMI)的来源，这些电磁波信号将会影响如收音机、电视或移动电话等电子产品的正常运作。大多数系统中产生电磁波噪声的主要来源是系统时钟的产生与分配电路，本文将探讨电磁波干扰产生的原因、如何测量电磁波干扰及如何降低电磁波干扰带来的影响。     

基于对数行列式散度与对称对数行列式散度的高频地波雷达目标检测器

高频地波雷达(HFSWR)利用电磁波绕射原理进行目标探测,具有超视距的特性。然而,探测距离的增加会使得雷达目标回波能量减弱,进而使得雷达探测能力下降。为了改善高频地波雷达的探测性能,该文提出了一种基于信息几何理论的局域联合矩阵恒虚警率(CFAR)检测器,利用信号在角度、多普勒速度和距离的多维信息进行检测;并使用对数行列式散度(LDD)和对称对数行列式散度(SLDD)代替黎曼距离(RD)作为距离度量。最后,实验结果验证了该文提出的检测器能够有效地改善雷达对目标的检测性能。     

开槽深度和坡度对高频高阶模带宽和中心频移的影响

为对构建太赫兹频率下高阶单模工作的同轴布喇格谐振腔提供理论依据,基于模式耦合理论,比较研究了不同开槽深度和不同开槽坡度形状及坡度角对工作在太赫兹频率高频高阶耦合模式下工作模式和竞争模式带宽、中心频率偏移特性的影响. 结果表明:工作模式和竞争模式的带宽随着开槽深度的加深都变宽,但中心谐振频率点几乎没有偏移,槽深加深,带隙重叠现象会恶化,不利于模式选择;正圆锥形坡度方式时随着坡度角的增加,工作模式的中心频率点没有发生偏移,竞争模式中心频率点靠近工作模式中心频率点,不利于带隙重叠现象的抑制;倒圆锥形坡度方式时,随着坡度角的增大,竞争模式的中心频率点远离工作模式中心频率点,很好地抑制了带隙重叠;正圆锥形坡度和倒圆锥形坡度对带宽的影响都不大. 这些特性有利于拓展同轴布喇格结构作为反射器和滤波器的性能.     

An analytical treatment of the effect of axial inhomogeneity onfemtosecond solitary waves near the zero dispersion point

A perturbed nonlinear Schrodinger equation, valid for femtosecond pulse propagation in axially inhomogeneous optical fibers near the zero dispersion point, is considered. It is found that for a weak axial nonuniformity, and under certain conditions, this equation can be treated analytically. Exact bright and dark solitary wave solutions are derived and their behavior in the presence of the inhomogeneity is analyzed. The nonuniformity induced time shift of the solitary waves is also obtained. The potential use of this parameter as a diagnostic tool for estimating characteristic parameters of the axial variations is discussed and its range of values is investigated     

高重频大能量亚纳秒板条激光放大器研究北大核心CSCD

高重频大能量亚纳秒固体激光器具有重复频率高、单脉冲能量大、峰值功率高等特点,在国防军事工业加工等领域具有广泛的应用前景。本文报道了一种基于板条多程放大的亚纳秒激光放大器。种子光为重复频率1 kHz、平均功率4.5 W、脉冲宽度700 ps、波长1064 nm的基模激光,经过光束整形以匹配板条放大器口径,放大级采用角度复用及偏振变换实现四程放大,最终实现了重频1 kHz、单脉冲能量189 mJ、脉冲宽度720 ps、光束质量2倍衍射极限的亚纳秒激光输出。     

Sensorless control of induction Machines at zero and low frequency using zero sequence currents

This paper considers both flux and rotor position estimations for sensorless control of delta-connected cage induction machines (IMs) at low and zero frequency operation. The variation of leakage inductance due to either saturation or rotor slotting is tracked by measuring the derivative of the zero sequence current in response to the application of appropriate voltage test vectors. The method requires only a single extra sensor. It requires access to machine phase windings and is appropriate for integrated-type induction motor drives. Both a closed-slot and an open-slot machine is used to demonstrate rotor flux and rotor position tracking, respectively. Experimental results are presented showing sensorless torque control and sensorless speed and position control at low and zero frequencies.     

A novel method of high speed frequency shift keying modulation in mm waves

To place a high speed switching diode in the cavity of the mm wave scillator has the behavior equivalent to an inductive post. The on-and-off switching of the diode will give rise to the change of inductance, hence the change of parameters of the cavity, and the osaillating frequency. In this article, the basic principle and the measured result are given. It is found that this is an efficient method in high speed frequency shift keying (FSK) modulation for a mm wave transmitter in communication.     

Continuous wave frequency doubling of a high energy 1315 nm laser

A series of extracavity frequency doubling tests was performed using the 1315-nm output from RotoCOIL, a chemical oxygen-iodine laser (COIL). LiIO₃ was selected for the doubling medium due to its large nonlinear optical coefficient, its low absorption, and the availability of large crystals. Tests were performed for a variety of beam sizes using 1.1-cm and 2.2-cm crystals. Conversion efficiencies of 8% were achieved resulting in visible (657-nm) CW power levels of nearly 700 W. Catastrophic crystal failure occurred after a 1-s exposure to a focused beam of 6770 W     

高帧频宽温度范围红外点源干扰装置设计

针对机动性能好、突防能力强的红外成像制导系统,利用极薄金属片可以快速加热升温与自然降温的特性,提出了一种适用于末制导阶段的新型红外干扰方法。建立了金属片加热升温及自然降温过程的数学模型,确定了金属片结构形式及材料特性;设计了结构简单、密封环境良好的红外点源干扰装置。试验结果表明:金属片优选2 μm厚的镍片,其加热时间为50 ms （500~1 000 ℃）,自然降温时间为75 ms （1 000~500 ℃）,可以满足帧频要求（10 Hz）;并实现了温度规律性的周期变化。分析与试验结果证实了红外点源干扰装置能够模拟红外辐射特性的快速变化,可为末制导阶段干扰提供一种新思路。     

Speed-sensorless induction Machine control for zero speed and frequency

A recently introduced speed-sensorless controller structure for tracking the rotor-flux orientation of an induction motor was implemented in a laboratory setup. The controller is based on superimposing a low-frequency ac test signal on the stator current of the motor. The response in the stator voltage to the signal depends on the orientation of the signal relative to that of the rotor flux. The dependency is due to the reaction of the mechanical system, and it is used to control the orientation error to zero. In the experiments, the controller operated successfully under nominal torque both at zero speed and at zero frequency. Slow and fast speed reversals under nominal torque were also successful. In addition, the system was capable of withstanding both motoring and generating load torque steps up to 50% of nominal torque.     

Penetration depth as a DInSAR observable and proxy for soil moisture

We use prior theory and experimental results to construct a quantitative relationship between soil moisture and the penetration depth of synthetic aperture radar (SAR) microwaves at L-, C-, and X-bands. This relationship is nonlinear and indicates that a change of 5% volumetric water content (VWC) can cause between 1 and 50 mm of change in C-band penetration depth depending on initial VWC. Because these depths are within the range of differential interferogram SAR (DInSAR) measurement capability, penetration depth may be a viable proxy for measuring soil moisture. DInSAR is unlikely to detect a measurable change in penetration depth above 30% VWC, though certain clay rich soils may continue to cause surface deformation above that level. The possibility of using clay swelling as a proxy for soil moisture was found to be less feasible than penetration depth. Soil moisture may also be a significant, and previously unrecognized, source of noise in the measurement of subtle deformation signals or the creation of digital elevation models using repeat-pass DInSAR.     

采用高频能量的CT几何参数自标定方法

针对锥束CT系统中几何参数失配引起几何伪影的问题,提出了一种采用空域高频能量的几何伪影自校正算法。该算法以重建图像的空域高频能量为目标函数建立优化模型,通过单纯形法迭代求解使空域高频能量最大的几何参数最优解。利用投影图像的特性提取部分参数作为输入初值,减小算法搜索范围。并采用图形处理器（Graphic Processing Unit,GPU）对自校正过程中的图像重建并行加速,减少重建时间,提高校正速度。实验结果表明:该算法具有较高的求解精度,最大相对误差不超过5%,对重建图像中的几何伪影有较好的校正效果。同时,在不影响精度的情况下减少了迭代次数,算法执行效率提高了18.8%。