基于碳纳米管 X 射线源的静态扫描系统设计

相比传统热阴极 X射线源而言,碳纳米管 X射线源具有结构紧凑、高时间分辨率、可编程式发射等优势,因此可以采用电子式的扫描方式取代传统扫描方式,提高采集图像的时间分辨率,减少运动伪影,降低辐射剂量。文章针对该新型 X射线源静态扫描系统进行软硬件平台设计。其中,硬件平台集成了多光束 X射线源及其驱动电路、高压发生器、复合真空计和数字平板探测器;下位机软件采用 Quartus II开发平台,Verilog硬件描述语言,实现多路脉冲及触发信号的产生;上位机软件平台采用 LabVIEW图形化编程工具,实现多台仪器的集成控制,完成多光束 X射线源静态扫描、高压控制、真空度监测和图像采集功能。本系统设计通过实验验证,可实现多光束碳纳米管 X射线源脉冲式静态扫描成像,为碳纳米管静态 CT的研制提供了实验和测试平台。     

单源双能量X射线物质辨别方法研究

利用X射线双能量进行物质属性的判别,是机场、车站行李安全检查的一项基本技术.未经滤波的单个140KV的X射线源,发射的是连续能谱的X射线,采用两种不同能谱响应的探测器分别得到高低能量的透射信号.综合考虑连续能谱效应和探测器效率的影响,推导出高低能量的线性衰减系数比值的逼近多项式,对于固定的射线源和探测器这个多项式的各个系数是不变的.利用这种方法对物质属性进行判别,并给出了实验结果.     

提高矿用X射线核子秤计量稳定性的研究

为提高矿用X射线核子秤的计量稳定性,从防爆型X射线源和计量零点2个方面给出了具体方法:利用X射线探测器监测X射线源输出的X射线能量和强度,通过在X射线源内加装监控网络模块接收X射线探测器监测的X射线参数,并与设定的X射线参数进行比较,从而反馈控制防爆型X射线源的管电压和管电流,保持X射线源输出的X射线参数稳定;用防爆型X射线源的管电压、管电流的平均值来定义源强零点,通过X射线探测器实时采集X射线参数并与计量零点、源强零点进行比较,从而反馈调整计量零点和源强零点,克服输送机工况变化及X射线管老化对矿用X射线核子秤计量零点的影响。测试结果表明,该方法能有效提高X射线的稳定性,保证矿用X射线核子秤的计量稳定性。     

Reveallmaging Technologies获得250万美元机场安全检测合同

近日,先进的安全检查系统开发商Reveal lmaging Technologies公司宣布，该公司用于图像质量增强和用于基于计算机断层（CT）爆炸物检测系统的新型碳纳米管X射线源的技术已经从技术支持工作组赢得一份科研合同．用以鉴定基于CT的爆炸物检测系统（EDS）的最优设计并根据这些研究结果开发硬件和软件平台。EDS是TSA认证的技术,现在用于机场筛选托运行李。     

奥泰斯（OPTEX）AB-20NV智能光幕探测器

产品特色：1，技术原理：发射与接收一体化设计．探测器利用向监控区域发射并接收反射回来的红外光束，通过分析其信号强度变化来判断监控空间内是否有状态变化．并利用光学透镜分割技术以形成多路光束组合，实现立体监控。     

一种数字化X射线介质识别系统的研究

数字化X射线探测系统是由X射线发生器,准直器,非晶硅平板探测器,多道分析器,接口电路以及上位机能量谱识别系统构成。该系统的创新点在于通过对X射线源加入STM32F103控制电路,实现射线源电压,电流以及曝光时间的可控,从而依据待检物体的情况把X射线的辐射剂量做到最小,而且通过基于LABVIEW环境编写上位机系统,从而远程调控射线发生的参数,最大限度的减小对人的辐射危害;在接受部分使用非晶硅平板探测器以及数字化处理芯片使得所处理信号为数字信号,从而大大的增加了信号的精度以及探测的准确度。     

激光光束质量M2因子测量系统的设计

为了实现对激光器发射激光光束质量的自动化测量,提出了一种激光光束质量M2因子测量系统.该系统选择混合式步进电机作为执行机构来确定多个采样位置;同时系统采用面阵电荷耦合器件(CCD)多点探测激光光斑的图像信息,实时计算不同采样位置激光光斑的质心和光强,并根据M2因子理论计算出激光光束的束腰宽度和束散角等参数,最后由上位机显示激光光斑的二维/三维光强分布及处理结果.实验结果表明,系统能够对400～1100 nm连续激光器发射激光光束质量进行自动化测量,测量精度达±6%,测量时间小于3 min.     

MEMS结构中碳纳米管的电泳沉积及其场发射特性研究

利用电泳沉积的方法在MEMS结构特定位置上组装碳纳米管薄膜,以此作为发射体研制基于碳纳米管场发射的传感器,并对其场发射进行了测试和分析.电镜观测与场发射实验结果表明,利用电泳沉积方法可以只在MEMS结构的特定位置沉积碳纳米管薄膜,对于4μm的发射间隙、该薄膜的场发射开启电压约为3.6V～4V,发射电压20V时的发射电流可至28μA.这种“post-MEMS“的碳纳米管薄膜组装方法具有工艺简单的特点,同时避免了碳纳米管生长对MEMS工艺环境以及器件的污染、破坏,实现了纳米材料组装与MEMS工艺的兼容.     

基于非晶硒平板探测器的乳腺CT图像采集软件设计

针对非晶硒数字平板探测器设计了一个用于乳腺CT成像的图像采集软件,该软件可以实现对CT图像的采集、存储和实时显示。根据非晶硒平板探测器的工作原理和乳腺CT的成像原理,在VS 2010开发环境下,基于MFC和Open CV完成了乳腺CT图像采集软件的设计与测试,该软件实现了图像的快速采集,达到了实时成像的目的。针对设计的图像采集软件,利用碳纳米管X射线源进行了亮暗场及乳腺模体成像实验,结果表明,设计的软件达到了设计需求和目的。     

一种新型显微 CT 系统设计

传统的CT设备由于受到系统架构的物理限制,导致最终扫描结果中运动伪影影响很大,文章依据碳纳米管的场致发射原理设计出一套工作在准静态模式下的显微CT.该系统采用35个碳纳米管X射线光源和5个探测器,相对于传统CT,通过外部时序控制减少了机架的机械旋转次数和行程,大大降低了运动伪影的影响.由于重建角度是稀疏的,因此通过采用迭代重建算法模拟仿真验证了该系统的有效性.     

Improved field emission characteristics of screen-printed CNT-FED cathode by interfusing Fe/Ni nano-grains

Carbon nanotube (CNT) cathode with and without interfusing nano-metal particles was prepared using screen-printing technology. For the good electric conductivity of metal, the turn-on electric field of the Fe/Ni and CNT composite film (Fe/CNT film) decreases to 1.42 V/μm comparing with the usual CNT film of 2.45 V/μm, and the emission current increases from 60 μA to 440 μA at an applied electric field of 2.3 V/μm. Furthermore, the field enhancement factor β increases from 1721 to 3242. By characterizing the prepared samples via X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), it is found that carbide Fe₃C phase is formed in Fe/CNT film, and the metal particles are filled in the interspaces of CNTs. It is evaluated that benefiting from good electrical conductivity and chemical inertness of metal carbide, Fe/CNT film achieves high emission characteristics and emission uniformity.     

Film surface morphology and field‐emission characteristics of a carbon‐nanotube array pattern fabricated under a magnetic field

Abstract— This study focuses on the influence of sodium metasilicate binder on CNT paste and the arrangment of Mg‐Ni alloy multi‐walled carbon nanotubes on the surface of CNT film under the influence of a magnetic field. The CNT paste was prepared by mixing CNTs with silver epoxy resin and sodium metasilicate solution and coating them onto the surface of indium tin oxide (ITO) glass. The impact of sodium metasilicate solution and magnetic strength on the morphology of the paste film's surface and on the field‐emission (FE) characterics of the cathode was examined. The experimental results showed that the CNT paste provided good adhesion between the CNT array and silver epoxy resin when sodium metasilicate solution was presented. CNT paste containing sodium metasilicate showed a better dispersion with silver epoxy resin and a better CNT‐array pattern, and better vertical alignment of the CNT was obtained when the magnetic field and grid were both appied. An optimal condition for a better CNT‐array pattern for both the morphology and FE characteristics had a magnetic strength of 1 89 mT, magnetization time of 30 min, and a grid above the cathode.     

Active‐matrix field‐emission display based on a CNT emitter and a‐Si TFTs

Abstract— An active‐matrix field‐emission display (AMFED), based on carbon‐nanotube (CNT) emitters and amorphous‐silicon thin‐film transistors (a‐Si TFTs), was developed. The AMFED pixels consisted of a high‐voltage a‐Si TFT and mesh‐gated CNT emitters. The AMFED panel demonstrated high performance for a driving voltage less than 15 V. The low‐cost large‐area AMFED approach using a metal‐mesh technology is proposed.     

Growth of uniform carbon‐nanotube arrays with sandwich technology

Abstract— In this work, a novel approach to grow structured, highly oriented carbon nanotubes (CNTs), which are vertically aligned to the substrate and show large field emission is reported. Growth is performed on lithographically defined dots of catalysts, which can be deposited on metallic, semiconducting, and glass substrates. A sandwiched catalyst structure and microwave plasma chemical vapor deposition enables the formation of uniform CNT arrays of 1.6 × 1.6 μm². The method is easily scalable to large areas. The CNT arrays exhibit a stable field emission of 20 mA and a macroscopic current density of 50 mA/cm² at a rather low electric field of 5.33 V/μm. Modeling of space charge indicates that space charge reduces the magnitude of the CNT emission at high field strength: this agrees satisfactorily with the measurements.     

Gas desorption electron stimulated during operation of field emitter-phosphor screen pairs

Gas desorption from a field emitter array (FEA) cathode and phosphor screen anode in a flat panel display during a lifetime operation can affect cathode electron emission and degrade display performance and uniformity. We have measured the outgassing products from selected FEA-phosphor pairs in an ultrahigh vacuum system equipped with a calibrated quadrupole rresidual gas analyzer. Different low voltage phosphors and blank anodes were studied. A Spindt-type FEA was used as the electron source. A unique carousel was used so the desorption from all these different anodes could be measured without intervening vacuum breaks; this allowed the desorption from the different anodes to be directly compared with each other. Quantitative outgassing rates are given and the implications of the results for the pumping of the flat panel and emission from the FEAs are discussed.     

基于机器视觉的全自动电池检测系统的研究

给出了一种基于机器视觉和X射线的全自动电池检测系统.利用X射线的穿透性和计算机对数据的快速处理能力,相机可以采集到成型电池的内部结构图像并对图像数据进行快速处理.通过对图像进行滤波、锐化、边缘提取等过程得到阴极和阳极的精确位置.运用软件来测量各个特征问的距离并与标准值进行比较来判断电池的好坏,从而实现电池检测过程的完全自动化操作.     

Growth and characterization of carbon nanotubes for field‐emission‐display applications

Abstract— This paper will report on the production, dimensional control, and characterization of arrays of cold‐cathode field emitters based on multiwall carbon nanotubes, suitable for use in large‐area field‐emission‐based displays.     

Electron emission from polymer films under electric‐field influence

Abstract— This paper presents the field‐emission characteristics of a polymer‐covered tungsten‐spike cathode. The emission images obtained from a field‐emission microscope together with the electron energy distribution and Fowler‐Nordheim curves compared with those of a typical tungsten cathode are presented.     

频域加权陷波多声发射源定位与伪源辨识方法

针对信号处理中的稀疏阵列有时会出现栅瓣和伪峰的现象,进而影响波束形成法在结构损伤定位中应用的问题,提出了基于频域加权波束零陷的未知真实声发射源数量的声发射定位与伪源辨识方法。首先,推导研究了波束零陷思想在二维频域加权波束形成方法中的作用机理;然后,基于频域加权陷波的波束形成方法,提出了在未知真实声发射源数量情况下的伪声发射源的辨识和真实声发射源的定位流程;最后,在存在较多伪声发射源干扰情况下进行了单声发射源和同时多声发射源的定位试验,验证了所提出方法的准确性。研究结果表明,所提出的方法对于推广波束形成法在结构健康监测领域的应用具有价值。     

Large‐area FEDs with carbon‐nanotube field emitter

Abstract— Application of carbon nanotubes (CNTs) as field emitters for large‐area FED panels is described. In 1998, we presented the first experimental devices: light‐source tubes for outdoor large‐area displays and a diode‐type flat‐panel display, both with screen‐printed CNT cathodes. The fisrt practical high‐luminance color CNT‐FED panel was built in 1999. It employed the new triode‐structure panel was x‐y addressable. The CNT‐FED structure was further optimized for large‐area display panels by improving the luminous uniformity. This paper also describes the design and performance of a new, experimental, 40‐in.‐diagonal panel, which showed that the CNT‐FED technology is suitable for use in large‐area displays.