多倍直流偏置电压对碳纳米管薄膜声源的影响

针对碳纳米管薄膜声源系统的输出声信号频率失真问题,提出在交流信号上施加多倍直流偏置电压的方法。从热致发声原理入手,利用碳纳米管薄膜声压理论,分析出增加多倍直流偏置电压后,输出信号中的一倍频与二倍频声压幅值,并探究两者幅值比变化规律。实验结果表明,随着输入频率和直流偏置电压增加,输出声信号中两者幅值之比亦增加,当直流偏置电压是交流电压的两倍后,输出声信号波形与输入电信号近似一致,较好地解决了频率失真问题;同时,输出声压级也有较大幅度提升。     

偏置电压对PECVD法沉积TiO2薄膜的结构和性能影响

该文采用射频等离子体增强化学气相沉积法制备了TiO<,2>薄膜样品,并通过椭圆偏振仪、红外光谱仪和扫描电子显微镜测量了薄膜厚度、组织结构和光学特性.结果表明:沉积速率随偏置电压升高而增大,在偏置电乐为10V时,沉积速率达到最大值为3.9nm/min,然后沉积速率下降,偏置电压在20V以后,沉积速率基本不变为3.0nm/...     

模拟多路转换器产生可变负偏置电压

从正方波信号产生负电压的常用简单方法是电容器──二极管电荷泵（见图1）。但这种方法存在以下几个问题：第一个问题是二极管的压降会使输出电压Vo值比起Vin峰值幅度总有几百毫伏的损失。即使用高性能肖特基二极管,聂1不同负羹电阻的电E和设些担其输入和输出电压差值甚至在VO轻负载（5PA负载）时也可达到400mV。第二个问题是两个二极管的组合温度系数可引起不希望的V。随温度漂移,若电路工作在宽温度范围内,则温漂是显著的。第三个问题是如输入正弦波的幅度不能变化,则此电路就不能为V。调节提供简单的方法。图2示出另一种方法,…     

碳纳米管薄膜扬声器的声场特性研究

碳纳米管薄膜是基于热声效应产生声场的一种新型声源.文中搭建了碳纳米管薄膜扬声器系统,对其进行了声场测试和特性分析;根据已有的理论公式计算声压和频率响应,与测试结果对比,对碳纳米管薄膜声压公式进行了验证和讨论,分析了导致误差的原因.研究结果表明:碳纳米管薄膜扬声器的声压随着频率升高而增大,在低中频上升迅速,3000Hz以后趋于平缓;在远场,随着测点到薄膜的距离增大,声压逐渐减小;在近场,并非严格的平面波,计算值与测试值误差较大,已有的理论公式需要修正.     

有精准偏置电压输出的霍尔电流传感器

通过介绍开环式霍尔电流传感器的工作原理,在此基础上提出了一种可以输出精准直流偏置电压的直流霍尔电流传感器电路,并通过试验进行了验证.     

电泳电压对碳纳米管沉积薄膜及阴极场发射特性影响

电泳法是制作碳纳米管冷阴极的重要方法.电泳电压是电泳过程中的重要参数,不同电压会影响阴极沉积的厚度和效率、形貌结构及场发射特性.实验对比研究和机理分析认为,电压在20～30 V区间内较易获得良好的碳纳米管场发射冷阴极.针对电泳边缘增厚效应,提出减小电场强度边缘效应方法.     

直流偏置下高频磁性材料铁芯损耗的研究

对具有直流偏置、正弦电压激磁的功率铁氧体铁芯损耗进行有效测量的基础上,分析了直流偏置对铁氧体材料的性能的影响和磁损与交直流磁感应强度的关系,在一定的交流激磁范围内,为磁性元件的设计提供了一定的参考。     

基于数字电位器的直流偏置技术

针对基于数字电位器的直流偏置技术进行了研究,从理论上进行了噪声对直流偏置源影响的分析,重点讨论了利用微控制器、数字电位器等相关器件,实现了直流偏置源的关键技术方法,对电路算法进行了仿真分析证明,此方法噪声低、步行调节灵活、精度高。在实际应用中工作可靠、稳定,符合技术人员工作指标要求。     

多壁碳纳米管薄膜在THz波段的传输与偏振特性

利用化学气相沉积法制备了三种类型多个超有序排列的多壁碳纳米管薄膜样品,通过太赫兹时域光谱技术,获取相位和振幅信息,详细研究了薄膜在太赫兹波段的传输特性。结果表明:超有序多壁碳纳米管薄膜在纳米管轴向方向与垂直于轴向方向表现出明显的光、电各向异性特性;测试的介电常数实部为负,虚部为正,证实了制备的薄膜具有金属性;薄膜具有的各向异性为研究其偏振特性提供了直接证据,随着薄膜厚度的增加,偏振度和消光比增加,其9 m厚的自由薄膜度可以获得99%的偏振度。研究结果对开展超有序多壁碳纳米管薄膜在太赫兹偏振器、调制器与光开关等领域的研究有重要指导意义。     

有序碳纳米管的光电响应实验

通过实验,研究了720℃时通过化学气相沉积(CVD)法在Si基板上得到的大面积垂直排列的有序多壁碳纳米管(MWNTs)的光电响应特性。实验表明,激光诱导所产生的光电流是光强度和偏置电压的线性函数,其大小取决于所产生的光子载体的漂移速度。     

单壁碳纳米管薄膜制备及其光学特性研究

为了将单壁碳纳米管制成实际可用的光电子器件,采用一种新的梯度升温热亚胺化法来制备单壁碳纳米管/聚酰亚胺薄膜。利用分光光度计测得单壁碳纳米管的质量分数为0.02的单壁碳纳米管/聚酰亚胺薄膜的反射谱、透射谱和吸收谱,得到薄膜线性折射率随波长的变化;拟合Sellmeyer公式,得到单壁碳纳米管/聚酰亚胺薄膜的Sellmeyer参量。利用z扫描技术研究了单壁碳纳米管/聚酰亚胺薄膜的3阶非线性特性。结果表明,单壁碳纳米管/聚酰亚胺薄膜具有很强的饱和吸收特性,其非线性吸收系数为β=-5.3×10-10 cm/W;并且具有较强的自散焦效应,对应的非线性折射系数为γ=-4.1×10-13 cm2/W。单壁碳纳米管/聚酰亚胺薄膜具有较强的非线性光学特性。     

采用碳纳米管导电薄膜作为OLED的阳极

采用碳纳米管(CNT)替代ITO作为OLED阳极可以 解决ITO薄膜存在的可弯曲性能差,可靠性低等缺 点,使得柔性显示成为可能。本文采用混合型CNT导电薄膜作为阳极,探讨了CNT薄膜的制备 工艺、掺 杂方式及表面修饰等因素对绿光OLED性能的影响。实验结果表明,P型掺杂对CNT薄 膜的导电性能影响 有限;而PEDOT修饰层可以很好的提高CNT导电薄膜的平整度;此外,采用“十字交叉 ”的阳极形状有助于降低 阳极拐角处毛刺。通过优化器件各参数,制备的PET/CNTs/PEDOT/NPB/ALq₃/LiF/Al绿光OL ED发光效率达 到了195 cd/m²,结果表明采用混合型CNT作为OLED阳极是可行的。     

Improving the emission characteristics of a carbon nanotube film in NaCl electrolyte

Screen printing is undoubtedly the most cost-effective process for the fabrication of large-sized carbon nanotube field emission display (CNT-FED). A novel post-treatment method in NaCl electrolyte was presented to solve the problem of poor field emission characteristics of printed CNT films. Compared to those of untreated films, the turn-on electric field of the treated film decreased from 2.4 to 1.4 V/μm and the total emission current of the treated film that has the same printing area as the untreated one increased from ∼100 to ∼1800 μA. Scanning electron microscope (SEM) and Raman spectrum study revealed that field emission characteristics are enhanced by two factors. Firstly, the NaCl electrolyte treatment appeared to render the CNT surfaces more activey by exposing more CNTs from the CNT film. Secondly, the numerous defects of CNTs of the CNT film were increased by electrical current energy.     

碳纳米管应用研究

随着对碳纳米管研究的不断深入,对碳纳米管的应用研究越来越受到人们的重视。通过分析碳纳米管的物理特性,对碳纳米管的应用前景进行了广泛的探索。着重分析了碳纳米管的电学特性,如导电特性、通流能力、电流特性及其场发射特性。在此基础上,讨论了碳纳米管在纳米电子学和电子场致发射等方面的应用。同时分析了碳纳米管的磁学特性、力学特性及敏感特性等并讨论了其在纳米机械系统、电磁吸收、传感器及其他领域中的应用。研究表明,碳纳米管在众多的领域具有广泛的应用前景。     

Inductance of mixed carbon nanotube bundles

The carbon nanotube (CNT) bundle is a promising candidate for next-generation interconnect/via applications. A realistic CNT bundle is a mixture of single-wall and multi-wall CNTs and its performance analysis needs to consider both kinds of CNTs. The inductances of the mixed CNT bundles are estimated, which are in agreement with the recent experimental results. Impacts of different parameters such as tube density, tube distribution, metallic tube ratio and bundle dimensions are discussed, providing an important guideline to design and fabricate a CNT bundle with a desirable inductance performance.     

Effect of the radius on the resonance properties of carbon nanotube dipole antennas

The resonance characteristics of dipole antennas based on armchair carbon nanotube are numerically investigated. The analysis takes into account the interaction of electrons with acoustic phonons which leads to the dependence of the electron relaxation time on the radius of the nanotube. The input impedance of the nanoantena as a function of the frequency of an incident electromagnetic field in the GHz range is obtained by the numerical solution of the Hallén’s integral equation. The dynamic quantum mechanical conductivity of armchair carbon nanotubes is used including the explicit dependence of the relaxation frequency on the radius. In this way, it is adequately described the resonant activity of the nanoantenna depending on the radius and length of the carbon nanotube. Current distributions are presented.     

多电飞机直流负载系统稳定性分析

多电飞机中存在大量直流负载,这些负载主要可分为恒功率负载与恒压负载。恒功率负载具有负阻抗特性,且因多采用高频电子开关,会产生高频谐波,危害系统的稳定性和安全。首先,研究具有双级LC滤波器的恒功率负载与恒压负载并联系统运行的稳定性,得到系统的稳定平衡工作点;接着,建立基于混合势函数理论的数学模型,利用Brayton-moser定理得到系统在大扰动条件下的稳定性条件;最后,用Matlab/Simulink对系统平稳运行与遭受大扰动的场景进行仿真,并观察输出参数的动态特性。仿真结果显示,满足该条件的系统在大扰动下能保持稳定,且与仅具有单级LC滤波器的直流负载系统相比,其不但对滤波电容需求更低,还有着更强的抑制高频谐波能力。     

An empirical study of dynamic properties of an individual carbon nanotube electron source system

In this paper we present an empirical study of some dynamic properties of an individual carbon nanotube (CNT) field emission electron source system. We propose a circuit model that represents the CNT cathode to anode diode as a capacitor in parallel with a voltage-controlled variable resistor. The transient response of the CNT electron source system to the falling edge of a voltage step input was evaluated. For input voltages below the threshold voltage for field emission, the nanotube loop is effectively open and the circuit response is consistent with a discharging capacitor. On the other hand, for input voltages above field emission threshold, the nanotube loop conducts and now the capacitor discharges to a certain extent through the nanotube loop as well. Field emission current versus voltage data also shows that the resistance across the CNT cathode to anode diode varies as a function of applied voltage. Below turn-on voltage, the diode behaves as an open circuit (4 TΩ at the ammeter noise floor). Above turn-on voltage, resistance falls exponentially, as expected from the Fowler–Nordheim equation for cold field emission current. Experimental current–voltage data is presented for a simple emitter array consisting of two CNTs with equal lengths. Despite the similarity in their lengths the turn-on voltages of the nanotubes varied significantly, viz. 26 V versus 109 V. This large difference in the turn-on voltages can be attributed to tip imperfections. For advanced array applications such as high-throughput parallel e-beam lithography, in which precise dose control is necessary, the diode circuit model will be useful for controlling individually addressed nanotubes to account for dissimilar field emission properties. The model may also be applied to optimize the design of a SEM incorporating a single CNT electron source.     

网络状碳纳米管薄膜应变传感器的机理研究

计算并评估了应力对网络状碳纳米管薄膜力学和本征电阻各参数的影响,结合逾渗理论分析了碳纳米管薄膜的应变传导机理,建立了模型并推导了碳纳米管薄膜在应力下整体电阻变化率的计算公式,最后将理论计算结果与实验数据进行了比较验证,发现碳纳米管含量变化是引起薄膜电阻变化的关键因素。