Absorption and Transmission Power Coefficients for Millimeter Waves in a Weakly Ionised Vegetation Fire

A vegetation fire plume is a weakly ionised gaseous medium. Electrons in the plume are mainly due to thermal ionisation of incumbent alkali impurities. The medium is highly collisional with free electron - neutral particle been the dominant particle interaction mechanism. Signal strength of an incident millimetre wave (MM-Wave) may be significantly attenuated in the plume depending on the extent of ionisation. A numerical experiment was set to investigate signal power loss of a MM-Wave incident on a simulated weakly ionised fire plume with flame maximum (seat) temperature ranging from 1000–1150 K. The simulated fire plume had alkali impurities (potassium) content of 1.0% per unit volume. MM-Wave frequency range investigated in the experiment is from 30–60 GHz. The simulation has application in the prediction of MM-Wave propagation in a crown forest fire and may also be applied in remote sensing studies of forest fire environments. Simulated attenuation per unit path length for the MM-Wave frequencies ranged from 0.06–24.00 dBm^?1. Phase change per unit path length was simulated to range from 2.97–306.17°m^?1 while transmission power coefficients ranged from maximum of 0.9996 for a fire plume at 1000 K to a minimum value of 0.8265 for a plume at a temperature of 1150 K over a plume depth of 1.20 m. Absorption power coefficient ranged from a minimum value of 0.0004 to maximum value of 0.1585 at a seat temperature of 1150 K over the plume depth.     

Measurement of an Electron Density Disturbance in a Positive Column with Magnetic Field

It is found that two columns of different luminosity which are separated by an intervened disc appear along a magnetic field, when a certain disc is inserted in a positive column with an axial magnetic field. These are a luminous column and a dark column which are extended from the disc toward the cathode and the anode side respectively. These deviations in luminosity decay from it in the direction of each side. Change in luminosity along the axis is confirmed by measurements of electron density distribution with movable probes.

An attempt to attribute this recovery toward the normal distribution to ambipolar diffusion of charged particles across the magnetic field is given.     

Frequency Selective Characteristics of a Plasma Layer with Sinusoidally Varying Electron Density Profile

In this study reflection, absorbtion and transmission characteristics of a plasma layer having sinusoidally varying electron number density are analysed. In the analysis, plasma layer is divided into thin subslabs with constant electron number densities. The general frequency selective behavior of the plasma is investigated by varying the plasma parameters, external magnetic field excitation and sinusoidal electron distribution in order to be used in recent plasma applications.     

CPLD和多周期同步测频法在多普勒频率测量系统中的应用

在某相位编码毫米波雷达系统中,要求很高的目标速度测量精度,因而目标多普勒频率测量电路的设计比较重要.多周期同步测量方法作为在直接测频基础上发展起来的新方法,在测频系统中得到越来越广泛的应用.文中介绍了利用复杂可编程逻辑器件(CPLD)以及多周期同步测频方法实现目标多普勒频率的测量.实际使用表明,该设计具有系统集成度高、精度高、可靠等优点.     

短波天波频率的预测与分析

短波通信由于具有建设成本低、通信距离远和抗毁能力强等特点,是唯一不受网络枢纽和中继制约的远程通信手段,特别在发生战争或重大突发自然灾害等紧急情况可发挥其重要的作用.短波天波链路的预测在设计高质量短波通信链路的工作中显得尤为重要.本文介绍了短波天波传播预测的不同方法,利用短波仿真软件ITS对天波链路的频率进行预测和仿真,然后利用通信电台进行预测的验证与分析.     

一种高精度频率测量系统设计

提出了一种高精度频率测量系统的设计方法,应用单片机技术将多周期同步法和量化时延法相结合,实现了频率的高精度快速测量。应用该方法设计出来的测量系统不仅体积小、成本低,而且在不需要复杂的传统等精度频率测量控制的情况下,利用其单片机的自身特性,实现宽范围内实用、简单而且精度较高的等精度频率测量,具有较好的实用价值。     

激光诱导Al等离子体中电子密度和温度的实验研究

激光烧蚀等离子体在微量元素分析方面有着重要的应用背景，而缓冲气体的种类及压力对激光等离子体的特性有重要影响。报道了以氦气、氩气、氮气和空气作为缓冲气体，实验测定了不同气压下Nd：YAG激光烧蚀Al靶产生的等离子体中的时间分辨发射光谱，利用发射谱线的Stark展宽和相对强度计算了等离子体中的电子密度和温度，得到了在不同缓冲气体中激光诱导Al等离子体的电子密度随延时、气压的演化规律，同时得到了电子温度的时间演化特性。实验结果表明，电子密度的数量级约为10^17cm^-3，电子温度测量值约为10000K，二者都是在激光脉冲后随时间快速衰减，直到4μs以后达到一个较低的水平并缓慢变化，其中以氩气作为缓冲气体时等离子体中的电子密度最大。     

低频相位测量系统的研究与实现

文章介绍了低频相位测量系统的设计与实现方法,提出了以单片机最小系统和复杂可编程逻辑芯片为核心的电路设计模型。系统由相位测量仪和数字式移相信号发生器组成:相位测量仪基于相关计数法测量原理,实现对双路同频信号的相位差、频率测量;数字式移相信号发生器基于DDS频率合成技术,产生相位差、频率可程控的双路同频信号。低频相位测量系统实现双路信号的产生和测量功能,并可实时显示测量值,整个系统达到很高的精度指标。     

激光诱导等离子体中电子密度随时间演化的实验研究

通过测定激光等离子体中镁原子和离子谱线Ｓｔａｒｋ展宽的时间演化特性．得到了激光诱导等离子体中电子密度的时间演化行为及其机理。     

Quantum Measurement of Single Electron State by a Mesoscopic Detector

对于一个实际的测量装置,即被介观测量仪器所测量的两态(量子比特)或多态量子系统做了理论研究.为了正确描述测量引起的反作用,发展了一个保持细致平衡条件的量子主方程的方法,建立的这套方案适用于任意电压和任意温度.     

激光诱导Co等离子体电子密度的时间空间演化特性

测定了激光烧蚀Co等离子体中Co原子389.408 nm发射谱线的时间空间分辨发射光谱.由发射光谱线的强度和斯塔克(Stark)展宽计算了等离子体电子密度,并由实验结果讨论了激光等离子体中电子密度的时间空间演化特性.实验结果表明,当延时在100～1000 ns变化时,等离子体中的电子密度变化范围为0.02×1017～0.73×1017 cm-3,在沿激光束方向上,当距离靶表面0～1.8 mm范围内变化时,相应的电子密度ne范围为0.3×1017～0.8×1017cm-3,等离子体电子密度在激光束方向上具有很好的对称性.     

基于一种新型RBF网络的捷变频雷达频率预测技术

针对捷变频雷达的频率预测问题,提出了基于一种新型RBF网络的频率预测方法。该方法将频率预测问题等效为伪随机序列预测问题,并采用结合人工免疫聚类和进化规划的混合算法确定RBF网络的隐层参数。计算机仿真表明,采用这种方法设计的RBF网络预测器可以准确地预测捷变频码,是一种对抗捷变频雷达的有效方式。     

A Recursive Frequency Estimator Using Linear Prediction and a Kalman-Filter-Based Iterative Algorithm

This paper proposes a new Kalman-filter-based recursive frequency estimator for discrete-time multicomponent sinusoidal signals whose frequencies may be time-varying. The frequency estimator is based on the linear prediction approach and it employs the Kalman filter to track the linear prediction coefficients (LPCs) recursively. Frequencies of the sinusoids can then be computed using the estimated LPCs. Due to the coloredness of the linear prediction error, an iterative algorithm is employed to estimate the covariance matrix of the prediction error and the LPCs alternately in the Kalman filter in order to improve the tracking performance. Simulation results show that the proposed Kalman-filter-based iterative frequency estimator can achieve better tracking results than the conventional recursive least-squares-based estimators.     

混响室中低频测量的改进

针对混响室低频混响时间测量的偏差大这一问题,提出对随机噪声信号进行限幅或改用一系列单频信号发生器作稳定激发可显著改善测量结果的偏差。     

基于MEMS技术的微桥制备与共振频率测量

基于扫描探针显微镜(SPM)微机械性能测试的需求,设计了一种可用电容力驱动微桥面振动的新型微桥.通过实验选材和单晶Si的刻蚀研究,提出了一种新的正面刻蚀成桥方法,获得了一种基于湿法刻蚀的低成本、易加工的实用微桥加工技术.利用SEM和AFM观察了微桥,证实微桥已制备成功且微桥桥面形貌比较平整.最后用改进的扫描隧道显微镜(STM)测量了微桥振动的频率响应,测得的共振频率与理论估算值基本一致.     

一种高精度快速频率测量方法

文中研究了一种基于多重自相关的的Hibert变换频率估计算法,利用正弦信号的特性,进行多重自相关运算,有效的提高信噪比,结合Hibert变换对信号的频率进行估计,从而提高了频率测量的准确度,实验结果表明了该方法具有很好的抗噪能力,能有效的对信号的频率进行估计,比传统的直接Hilbert估计算法精度要高2-3个数量级。     

扫频测量的频率偏移与动态带宽

本文通过理论分析揭示并探讨了滤波网络扫频测量时幅频特性的频率偏移和动态带宽现象的成因.并通过数字仿真对理论分析进行了验证,说明和探究了扫频速度与频率偏移和动态带宽展宽的程度之间的关系.该研究有助于扫频测量偏差的分析和特殊通信滤波器的设计.     

机载火控雷达的射频隐身与电磁机动

借鉴电磁机动战思想,从电磁作战环境中机载有源相控阵火控雷达与对方电子侦察系统机动对抗的视角,分析了机载雷达射频隐身与电磁机动的含义,探讨了机载雷达射频隐身的电磁机动敏捷性、电磁机动信息熵.在此基础上,总结了空战电磁环境中,机载雷达射频隐身的最小时间、最小功率和最大信号不确定性3种电磁机动策略,以及对应的电磁机动工作方式.运用电磁机动战研究机载雷达射频隐身问题,拓展了机载雷达电磁作战研究的视野及思路,提出了有应用价值的机载雷达电磁机动策略和工作方式.     

高精度测量电子全息中的位相变化

本文好一种能够高精度测量电子全处民位相变化的新方法。     

Surface-Photovoltage Measurement of Volume Electron Lifetime in p-Si Wafers

The problem of estimating the volume lifetime _v of minority carriers in p-type Si wafers by surface-photovoltage measurements is addressed. An experiment is conducted in order to ascertain the relationship between measured and actual values of _v. The measurements are carried out on circular specimens whose thickness is reduced from about 2000 to 450 m by stepwise etching. The specimens are cut from a Czochralski-grown rod, their actual values of _v ranging from 10 to 300 s. The surface recombination rate of minority carriers is determined on both sides of the specimens covered with native oxide, the sides differing in surface finish. The results of the experiment allow one to determine _v up to about 400 s.