探究如何利用谐振电路准确测量电容和电感

当正弦波信号源的输出达到某一频率时,RLC电路的电流达到最大值,即产生谐振现象.目前大多数实验主要是通过描绘RLC串并联电路的相频特性、幅频特性曲线来研究RLC电路的谐振现象,进一步测定谐振曲线、电路品质因数Q值等.那么,能不能利用RLC电路的谐振特性反过来测量电路中的电容和电感呢?为此,本文首先通过谐振电路理论推导得出测量电容及电感的实验原理,然后进行大量的实验探究和数据分析,得出了准确测量电容和电感的条件.     

利用数字万用表实现放电法测电容

利用数字万用表自动定时记录数据的功能,提出了一种测量电容值的实验方法.     

双电层电容的测量

根据南开大学基础物理实验教学中心的教学与设备状况,开设了设计性实验"双电层电容的测量".本文包括实验原理、实验设计和数据处理,得到双电层电容的基本现象.     

示波谐振法测电容的研究

示波谐振法测量电容就是用示波器观察RLC串联电路的谐振现象来确定待测电容的值,是测量电容的一种简便方法.理论和实验研究表明,测量灵敏度对测量结果影响较大,电路中标准电感L和标准电阻R的取值对电路灵敏度有较大影响,而电路灵敏度引入的测量不确定度,对测量结果总不确定度影响较大.当L和R的取值使Q≥3时,电路灵敏度已足够高,一般已满足测量的要求.     

计算电容中Fabry-Perot干涉仪测量位移的相位修正方法

计算电容是复现电学阻抗单位的基准装置, 利用计算电容值和量子霍尔电阻值可以准确计算出精细结构常数α. 计算电容的本质是通过高准确度地测量屏蔽电极的位移, 实现对电容量值的测量. 因此, 基于Fabry-Perot干涉仪的精密电极位移测量系统是计算电容装置中最为核心和关键的部分. 在Fabry-Perot干涉仪测位移过程中, 由于高斯激光束存在轴向Gouy相位, 该附加相位将会引起相邻干涉条纹对应位移的变化(大于或者小于λ/2), 导致位移的测量值与实际值存在偏差. 本文阐述了高斯激光场的传播特性, 利用高斯激光束在自由空间和透过薄透镜复振幅的变换关系, 建立了计算电容装置中Fabry-Perot干涉仪透射光束的传输模型; 通过对不同腔长的Fabry-Perot干涉仪透射光场相位的分析, 获得了高斯激光束轴向Gouy相位修正与传输距离的关系. 结果表明, 当腔长从111.3 mm移动至316.3 mm时, 在接收距离为560 mm的情况下, 高斯光束轴向Gouy 相位引起的位移修正的绝对值最小为0.7 nm, 其相对相位修正量|δL|/|ΔL| = 3.4×10^-9.     

杨氏模量实验的改进

杨氏模量测定实验的关键是对钢丝微小伸长量的测量,利用差动电容传感器将微小伸长量变换为电量,研究得出,微小伸长量与电路输出的电压成线性关系,利用模拟实验,测出理论计算与实验数据之间符合的非常好,这种测量方法还可以利用计算机对数据进行处理。     

用于直流回复退磁的脉冲装置电容电压选择研究

脉冲装置用于直流回复退磁时其电容电压值不易把握.利用试验法得到使铁磁体剩磁方向翻转的临界电压为最佳退磁电压,通过计算反向峰值磁场和脉冲电路参数得到电容电压公式,结合公式与实验规律能够快速获得退磁需要的电容电压.     

紧凑型Tesla变压器次级电容的计算

给出了紧凑型Tesla变压器次级电容的近似解析表达式,计算结果表明,紧凑型Tesla变压器的次级电容主要由内外筒之间的电容和次级线圈引入的附加电容组成。附加电容的值约等于一段与次级线圈长度相同的同轴线电容,该同轴线的内外径与变压器内外筒直径相同。建立了一个分析Tesla变压器的电路模型,利用数值方法验证了解析计算方法的正确性。研制了一个小型Tesla变压器,进行了相关实验,实验结果与计算结果一致。     

基于单纯形优化法的准方波脉冲形成网络设计

脉冲形成网络常用于大功率固态调制器、微波驱动源以及激光激励源中,以便获取宽平顶的高压长脉冲输出。针对常用的雷利网络,根据宽平顶低纹波的应用需求,开展了优化设计技术研究,提出了基于单纯形优化法的设计算法。主要针对两种情形进行了优化设计及计算:一是电容值相等,通过优化电感值以获取最优的输出波形;二是约定电容值(电容值不完全相等),通过优化计算不同电容排列下的输出结果,寻求最优的电容排列组合及相应的优化电感值。上述优化算法结果表明,在两种情形下均可以获得较优的准方波脉冲输出,可以为准方波脉冲形成网络的工程实现提供一种新的方法。理论计算和电路仿真结果表明,所提出的方法合理可行。     

共焦椭圆柱等值坐标电容器的电容

利用共焦椭圆柱坐标给出共焦椭圆柱电容器电容的一般表示,求解椭圆柱形电容器和双曲柱形电容器的电容,丰富了此类电容器电容值计算的结果.     

Capacitance extraction method for a gate-induced quantum dot in silicon nanowire metal-oxide-semiconductor field-effect transistors

An improved method of extracting the coupling capacitances of quantum dot structure is reported. This method is based on measuring the charge transfer current in the silicon nanowire metal–oxide–semiconductor field-effect transistor(MOSFET), in which the channel closing and opening are controlled by applying alternating-current biases with a half period phase shift to the dual lower gates. The capacitances around the dot, including fringing capacitances and barrier capacitances, are obtained by analyzing the relation between the transfer current and the applied voltage. This technique could be used to extract the capacitance parameters not only from the bulk silicon devices, but also from the silicon-oninsulator(SOI) MOSFETs.     

Marx发生器等效对地分布电容估算方法

介绍了两种估算Marx发生器等效对地分布电容的方法:逐级累积法和能量守恒法。逐级累积法通过近似求出各级对地电容对Marx发生器等效对地分布电容的贡献,并将之累加得到发生器等效对地分布电容;能量守恒法认为各级对地电容存储的能量之和与发生器等效对地分布电容存储能量相同,从而推导出发生器的等效对地分布电容。采用两种方法计算了闪光二号加速器发生器的对地等效分布电容,并与实测值进行了对比。两种方法计算结果均为114pF,实测值为109pF,二者相差4.6%。     

Ultrafast characterization of in-plane-gate field-effect transistors: parasitics in laterally gated transistors

In-plane-gate field-effect transistors are probed by femtosecond electrooptic sampling. Ultrafast response of the transistors is dominated by a displacement current induced by parasitic gate-drain capacitance. Intrinsic and parasitic gate-drain capacitances of various transistor structures are obtained from displacement-current characteristics and are in quantitative agreement with the calculation of planar capacitances. Intrinsic gate-drain capacitances are in the order of 100 aF, while parasitic gate-drain capacitances are between 1.7 and 4.8 fF, more than ten times that of intrinsic gate-drain capacitances. Reduction in parasitic capacitance by a factor of two is achieved by means of grounded shields and is confirmed by calculation. The grounded-shields screen parasitic electric fields and transform parasitic coupling into a part of the waveguide coupling. This reduction in parasitic capacitance is the first demonstration that the parasitic field effect is controlled artificially by nanometre-scale device technology.     

Quantum capacitances of molecules, fullerenes and carbon nanotubes by the partitioned real-space density functional method

Capacitances of molecules, fullerenes and carbon nanotubes under the condition of no electron-tunneling are calculated by the partitioned real-space density functional method that has been recently developed. We found that a quantum capacitance of a spherical jellium bielectrode decreases and approaches the classical value as the electron density increases. The capacitances of fullerenes and carbon nanotubes do not depend on the detailed atomic geometry but on the overall shapes. The values of the capacitances of these nanostructures are found to be a few 10^-20 F and are compatible with the experimental ones determined by the scanning tunneling microscopy studies.     

薄膜SOI上SiGe HBT集电结耗尽电荷和电容改进模型

文章研究了SOI衬底上SiGe npn异质结晶体管集电结耗尽电荷和电容.根据器件实际工作情况,基于课题组前面的工作,对耗尽电荷和电容模型进行扩展和优化.研究结果表明,耗尽电荷模型具有更好的光滑性;耗尽电容模型为纵向耗尽与横向耗尽电容的串联,考虑了不同电流流动面积,与常规器件相比,SOI器件全耗尽工作模式下表现出更小的集电结耗尽电容,因此更大的正向Early电压;在纵向工作模式到横向工作模式转变的电压偏置点,耗尽电荷和电容的变化趋势发生改变.SOI薄膜上纵向SiGe HBT集电结耗尽电荷和电容模型的建立和扩展为毫米波SOI BiCMOS工艺中双极器件核心参数如Early电压、特征频率等的设计提供了有价值的参考. 关键词： 耗尽电容 SiGe HBT SOI     

Finger capacitance of a terahertz photomixer in low-temperature-grown GaAs using the finite element method

Interdigitated finger capacitance of a continuous-wave terahertz photomixer is calculated using the finite element method.For the frequently used electrode width(0.2 μm) and gap width(1.8 μm),the finger capacitance increases quasi-quadratically with the number of electrodes increasing.The quasi-quadratic dependence can be explained by a sequence of lumped capacitors connected in parallel.For a photomixer composed of 10 electrodes and 9 photoconductive gaps,the finger capacitance increases as the gap width increases at a small electrode width,and follows the reverse trend at a large electrode width.For a constant electrode width,the finger capacitance first decreases and then slightly increases as the gap broadens until the smallest finger capacitance is formed.We also investigate the finger capacitances at different electrode and gap configurations with the 8 μm× 8 μm photomixer commonly used in previous studies.These calculations lead to a better understanding of the finger capacitance affected by the finger parameters,and should lead to terahertz photomixer optimization.     

Nanowire and nanocable junction capacitances: Results for metal and semiconducting oxides

Formulas are derived for Schottky junction and p-n junction capacitances of nanowires and nanocables (which includes the hollow case of nanotubes). Evaluation of these expressions for the very unusual metal oxide, metallic conductor RuO₂, demonstrates that capacitance values occur in the aF range. Furthermore, for recently fabricated conductor RuO₂/SiO₂ nanocables as reported in the literature, we show that the junction capacitances are significantly lower than the intrinsic quantum capacitance. These formulas are of great interest for device applications, and the capacitance findings could also have huge implications for charge storage and energy conversion applications.     

Differential capacitance between circular stacked quantum dots

We have investigated the differential capacitance between two stacked, circular quantum dots. An expression defining such differential capacitance has been derived on the basis of that for the self-capacitance of a single quantum dot. By means of a self-consistent simulation we have obtained numerical results showing that the differential capacitance between the two dots is strongly influenced by shell-filling effects, and that the classical limit of the parallel-plate capacitor is retrieved when the two dots are in close proximity. Our results represent a contribution to the effort for the definition of a capacitance matrix for a complex system of quantum dots.     

加速器电容耦合的研究

首先从腔体的等效集总参数电路出发, 推导出了腔体等效输入阻抗和腔体特性参数, 如谐振频率、并联阻抗及耦合电容的关系. 以此为出发点, 得到了理想耦合所需要的耦合电容大小和腔体参数的关系, 总结出了高频腔体电容耦合系统设计的一般方法. 以一台质子回旋加速器模型腔体为例, 对计算结果和测量结果进行对比分析, 讨论了其结果的可靠性及使用范围.     

GaN发光二极管表观电容极值分析

利用正向交流(ac)小信号方法对GaN发光二极管的电容-电压特性进行测量,可以观察到GaN发光二极管中的负电容现象。正向偏压越大,测试频率越低,负电容现象越明显。测量到的负电容现象是表象,不存在负电容;提出GaN发光二极管p-n结的结电容在特定的正向电压范围内等效于可变电容。分析可变电容对正向交流小信号响应得到:特定参数的可变电容使结电容电流相位落后于交流小信号电压相位π/2,使得在测量中表现为负电容。发现表观电容-正向电压曲线的极值点与理论模型相吻合,证明了该理论模型的正确性。