Optimization of spectrum utilization in cognitive radio system

In Cognitive Radio (CR) networks, CR user has to detect the spectrum channel periodically to make sure that the channel is idle during data transmission frame in order to avoid the collisions to the primary users. Hence recent research has been focused on the interference avoidance problem. Quality of Service (QoS) requirement of CR user will affect the time of data transmission in each frame. In this paper, in order to solve the interference avoidance and spectrum utilization problems without cooperation among CR users, a new scheme to obtain the optimal duration of data transmission frame is proposed to maximize the spectrum utilization and guarantee the protection to the primary users. The main advantages of our proposed scheme include the followings: (1) QoS requirement of CR user is concerned; (2) p-persistent Media Access Control (MAC) random access is used to avoid the collisions among CR users; (3) CR network system capacity is considered. We develop a Markov chain of the primary spectrum channel states and an exponential distribution of the CR user??s traffic model to analyze the performance of our proposed scheme. Computer simulation shows that there is an optimal data transmission time to maximize the spectrum utilization. However, the regulatory constraint of the collision rate to the primary users has to be satisfied at the expense of spectrum utilization. And also the tradeoff between the spectrum utilization and the capacity of the CR system is taken into account.     

Basic kinetic processes in neon gas discharge displays

Sahni, Lanza, and Howard have carried out a numerical simulation of ac discharges in high pressure neon Penning mixtures for conditions typical of plasma panel displays [1]. Their work has provided valuable insight regarding the electrical characteristics of such devices. However, relatively little is known about the specific factors affecting the radiative properties of neon plasma displays. The present work focuses on this aspect of the problem by analyzing the production and loss processes controlling the populations of the ten levels of the Ne(2pj) manifold, which are the primary source of radiation in the visible region of the spectrum. Time integrated radiative intensities of the thirty Ne 2pj-1sjtransitions in the 5400-8082-Å range were computed and were found to be in good agreement with measured values obtained using, several plasma panel displays.     

等离子体刻蚀过程中的FTIR监控技术

采用傅里叶红外光谱仪(FHR)和MCT红外探测器可以构成原位的FTIR测量系统,可应用于在电感耦合等离子体刻蚀机中进行的硅刻蚀工艺.文中对反应腔室腔壁状态对刻蚀过程的影响,以及在硅晶片表面反应层的变化进行了详细的研究.实验表明:采用含F化合物对反应腔室进行清洗会改变反应腔室的状态,在腔室内壁状态达到稳定之前会对刻蚀速率的一致性造成扰动.硅片表面反应层中的化学组成变成了以CF为主的薄膜层,对刻蚀过程的有一定的抑制作用.     

Monitoring and diagnosis of plasma etch processes

Plasma etching removes material from a silicon wafer by applying power and gases in a chamber. As material is removed from a wafer, the amount of particular chemicals given off can be measured; this technique is called emission spectroscopy and the measurements are called endpoint traces. An expert system that automatically interprets the traces has been designed and built. The system combines signal-to-symbol transformations for data abstraction and rule-based reasoning for diagnosis. The system detects problems as soon as they occur and also determines their causes     

Measurement of electron attachment processes in a high-temperature plasma

An experimental technique has been developed for measuring rate constants of electron attaching reactions as well as ion-molecule reactions in plasma at 2000-3000°K. Reaction product ions are mass analyzed and rate constants are obtained from plots of the collected ion current. The rate constant for O^-formation from N2O varies from about 3 to 9×10^-9cm³/s over the temperature range of 2400-3000°K while the rate constant for F^-formation from SF6varies from 2.8 to 4×10^-10cm³/s for temperatures from 2775 to 3000°K. A brief survey of experimental techniques for measuring electron attachment rate constants at lower temperatures is also given, together with a comparison of these rate constants and present high-temperature values.     

A gate-charging model for ILD related plasma processes in MOSFETs

A model explaining gate-charging damage in MOSFETs observed during inter-layer-dielectric (ILD)-related plasma processes is reported. It indicates that the charging damage associated with the ILD plasma process can be related to the effect of photoconduction and/or capacitive impedance coupling of plasma potential through the multiple ILD layers. The model leads to a conclusion that by placing a larger-area lower-layer metal (such as Metal-1) plate or polysilicon plate at the gate terminal of MOSFETs, this ILD process-related charging damage can be eliminated or significantly reduced due to a substantial reduction in the gate-to-substrate impedance of the transistors.     

碟片式激光烧蚀微推力器靶盘利用率优化

碟片式激光烧蚀推力器的总冲与靶盘上烧蚀点数量线性相关,提高靶盘利用率有利于在有限的靶面上得到更多的烧蚀点。为了优化靶盘利用率,文中首先对激光烧蚀微推力器进行了结构设计和分析,对靶盘上的烧蚀点分布问题进行了理论建模,提出了串珠法和套圈法两种分析方法,分别设计了圆圈路径、螺旋路径和六角密排三种实际烧蚀点分布方式。通过计算,分析比较了三种分布方式下,靶盘尺寸和烧蚀点尺寸对靶盘利用率的影响规律。结果表明,六角密排的靶盘利用率理论最高可达90.64%,圆圈路径和螺旋路径的靶盘利用率理论最高可达78.54%;靶盘利用率受到靶盘尺寸和烧蚀点尺寸的影响,靶盘尺寸较小时,圆圈路径的靶盘利用率相对较大,靶盘尺寸较大时,六角密排的靶盘利用率较大;三种分布方式各有特点,在应用上各有侧重。该研究为充分利用碟片式激光烧蚀推力器的靶盘提供了理论指导和设计参考,对推力器的工程化设计有一定借鉴意义。     

Etching characteristics of SiO2 in CHF3 gas plasma

The etching characteristics of SiO₂} have been investigated in the CHF₃} gas plasma using the planar type reactor with the 400 kHz rf power. The etch rate of SiO₂}, the SiO₂} /Si and SiO₂}/resist etch rate ratios, and the deterioration of photoresist films are studied with a variety of etching parameters. The etching characteristics depend strongly on the coupling mode. With the cathode coupling mode, the values of 300å/min and of larger than 100 are obtained for the etch rate of SiO₂} and the SiO₂}/Si etch rate ratio, respectively. Only 8 is given for the SiO₂} /Si etch rate ratio with the anode one. The deterioration of photoresist films less occurs with the cathode coupling mode than with the anode one. The dependences of the etching characteristics on the rf current, gas pressure, gas flow rate, and the electrode separations are also studied some in detail with the cathode coupling mode. Possible explanations for some of the experimental results are discussed.     

Wafer-grown heat flux sensor arrays for plasma etch processes

This work treats the design, fabrication, and testing of a wafer-grown thermal flux sensor for use in plasma etch processes. This sensor is capable of separately resolving the heating due to ion flux from that due to surface chemical reactions. The sensor is constructed using a modified Gardon gauge structure with an added antenna structure. This addition allows the exposed portion of the gauge to be formed from any plasma etchable material while still retaining the high sensitivity inherent in a Gargon-type heat flux sensor. The fabrication process for the sensor uses standard MEMS process steps, with an XeF/sub 2/ postprocess structure release. Bench-top experimental results showing the sensitivity (0.25 /spl mu/V/W/m/sup 2/) and repeatibility (8.3 W/m/sup 2/) are presented and discussed, and preliminary efforts at in situ etch monitoring are discussed.     

Electrical charging of liquid sprays in high-pressure gas flows for electrofluid dynamic processes

To produce charged aerosols for electrofluid dynamic processes, various liquids were sprayed through a metal capillary at very high electric field strengths into high pressure air flows. The current produced as the charged liquid spray ruptures is a function of electrical, gas, and liquid properties. Of these parameters the effects of liquid properties, such as surface tension, electrical conductivity, mass flow rate, and air properties such as pressure and velocity on the current production are experimentally investigated. A semi-empirical relation of the current output with the indicated variables is obtained using dimensional analysis.     

A mechanism of low-temperature stimulated processes in plasma anodization of metals and semiconductors

A mechanism of stimulation of low-temperature plasma anodization using a catalyst or ultraviolet radiation in the case of the formation of oxide films of metals and semiconductors is suggested. The stimulating effect of a catalyst or ultraviolet radiation on the process of plasma anodization is attributed to the appearance of an additional concentration of antibonding quasiparticles (electrons and holes) that weaken the chemical bonds in the anodized material. The conditions for implementing the stimulated processes are reported.     

Influence of external conditions on physical processes and plasma parameters in a model of a high-frequency hybrid plasma system

The results of the experimental investigation into parameters of the helicon discharge plasma in a model of high-frequency hybrid plasma system equipped with a solenoidal antenna are presented. It is shown that an increase in the external magnetic field causes the formation of the plasma column and the displacement of the ion current over the discharge axis towards the lower model flange. The variation in the magnetic field configuration makes it possible to control the shape of the plasma column.     

气体等离子体辐射光声信号检测与分析

气体等离子体做为一种新的辐射源,因具有辐射范围宽等优点而备受关注。本文对强飞秒激光脉冲诱导大气等离子体辐射光声信号现象进行了探究,用实验的方法探测和分析了激光脉冲能量、偏振方向以及声传输的径向距离对光声信号强度的影响。     

Optimization of the optical output in a C-to-C pulsed gas laser

An investigation of the optimum condition for maximum optical output in a C-to-C pulsed gas laser (N₂ laser) showed that this condition does not happen when the two capacitances are equal (C ₁=C₂) as this happens in the “Doubling circuit” case, but when the peaking capacitance obtains a critical value. This behavior is attributed to the electric pumping pulse formed by the temporary loading of the peaking capacitor. This electric pumping pulse increases as the peaking capacitor increases. However, for low values of the peaking capacitor the optical output follows the rise of the electric pumping pulse. On the other hand, for higher values of the peaking capacitor than a critical one, a part of the electric energy arrives at the laser channel after the laser output, while the exploitable electric energy decreases causing reduction of the optical output     

小型化准分子激光器气体性能的优化

对于新研制的准分子激光系统而言,激光气体的性能具有非常重要的作用,激光系统的混合气体配比与单脉冲能量、放电稳定性和寿命等性能参量有密切关系。为了获得最佳气体配比,在自行研制的小型化Xecl准分子激光器的基础上进行了激光气体性能优化实验,分析了Xe,HCl气体比例对激光性能的影响,通过理论分析和实验结果给出了Ne和He两种不同缓冲气体下的激光性能差异,并给出了该激光系统的优化气体成分和有效提高激光效率方法。实验结果为研制商业化小型准分子激光器件提供了支持和依据。     

Formation of PNx/lnP structure byIn Situ remote plasma processes

In situ remote plasma processes consisting of removal of native oxide due to hydrogen (H₂) plasma, surface modification due to phosphine (PH₃) plasma and deposition of phosphorus nitride (PN_x) films due to decomposition of PH₃ by nitrogen (N₂) plasma have been developed. The insulating PN_x film with optical bandgap of 5.3 eV and electrical resistivity of 3.7× 10¹⁴ Ωcm is obtained by remote plasma chemical vapor deposition. Au/PN_x/InP tunneling metal-insulator-semiconductor (MIS) type Schottky junction is formed by thein situ multiprocess. The effective barrier height is estimated to be as high as 0.83 eV. Enhancement of the effective barrier height is due to both effects of the MIS structure and unpinning of the surface Fermi level.     

优化电力负荷侧管理，提升能源利用效率

随着宽厚板市场销路的打开,工序成本的降低迫在眉睫。作为占比超过20%的电耗管理成为机动设备专业的头号需待解决的问题。资源综合利用以及节能减排的要求逐渐和设备管理挂钩,对于电耗和电力供应的管理,一方面要保证稳定不断供的基本需求,另一方面对于提高用电效率,优化用电方式,由此带来的电力消耗降低将成为需要研究和深入开展的工作。     

Display devices based on low-voltage excitation of ZnO in a gas plasma

Using a gas plasma as a source of free electrons, a brightness of 60 fL is obtained from an extended layer of ZnO phosphor with about 5 V applied to it. The phosphor efficiency, >10 lm/W, shows little change during 5000 h of operation. For display purposes devices have been constructed incorporating multiple phosphor-coated anodes whose potentials are controlled by low-voltage semiconductor circuits.     

VOCs在线监测气体吸收池的传输效率优化设计

为了满足环境监测需求,需要研制一种能够对挥发性有机化合物（VOCs）成分进行在线高灵敏度、高保真监测,并适用于傅里叶变换红外光谱探测配备的气体吸收池,采用光学追迹结合有限元分析的方法,分别对气体池物镜夹持调节机构与光学整体结构固定方式进行优化设计,较为有效地解决了在VOCs监测中气体池工作温度要求下光学器件形变校正的问题,可优化80℃~180℃工作范围内的光能传输效率。给出了一种适用于VOCs气体特定温度条件下吸收池出射能量优化设计的方法,并以此方法为基础,设计加工了一型气体吸收池,进行了热环境测试。结果表明,该吸收池具备在80℃~180℃工作范围内稳定的传输效率,能够应用到VOCs在线监测系统中进行测量。