超高感度CCD摄像传感器的特性分析

介绍了超高感度 CCD(EXview HAD CCD)摄像传感器的概念、结构特点和性能特征。比较了常规的基底为 Nsub、Psub的 CCD传感器和超高动态 CCD传感器各自的灵敏度、饱和信号和暗电流 ,给出了量子转化效率与光波长的关系曲线。结果表明 :超高感度 CCD摄像传感器在减小拖影方面具有突出的优点。     

激光光源粒子计数器响应曲线对粒子折射率敏感度及多值性的分析

采用激光作光源的光学粒子计数器(L_OPC)克服了白炽灯作光源时使用寿命短、发光强度不稳定、需要经常标定的缺点,但激光波长的单一也带来了一些问题,如响应曲线对折射率敏感度的变化和多值性等问题。利用Mie散射理论,通过数值模拟实验,对L_OPC的这些问题进行了分析,提出了L_OPC实验样机的设计参数。     

The Role of a Specific Response of Media in the Vavilov-Cherenkov Effect

It is shown that the condition υ > υ_p (ω), which is necessary in order to trigger the Vavilov-Cherenkov effect, determines the interval of radiated frequencies and it alone cannot establish a strong restriction to the velocity of the particle. It is exhibited that it is possible to define a general lower bound for the velocity of the particle, which does not depend on the frequency when both, a specific response of the medium is taken into account and the mentioned condition is considered. The minimum value of the phase velocity of light in the medium determines the existence of such general lower bound.     

The dynamic behavior of magnetic fluid adsorbed to small permanent magnet in alternating magnetic field

The dynamic behavior of a magnetic fluid adsorbed to a small NdFeB permanent magnet subjected to an alternating magnetic field was studied with a high speed video camera system. The directions of alternating magnetic field are parallel and opposite to that of the permanent magnet. It was found that the surface of magnetic fluid responds to the external alternating magnetic field in elongation and contraction with a lot of spikes. Generation of a capillary magnetic fluid jet was observed in the neighbourhood of a specific frequency of alternating field. The effect of gravitational force on surface phenomena of magnetic fluid adsorbed to the permanent magnet was revealed.     

Early transient responses of multi-span stepped single-walled carbon nanotubes using the method of reverberation ray matrix

The early transient responses of multi-span stepped single walled carbon nanotubes (SWCNTs) under impact loadings are studied by the method of reverberation ray matrix (MRRM). The dynamics model of the carbon nanotubes is established in the Fourier phase space on the basis of the nonlocal Timoshenko beam model. The wave solutions of SWCNTs with arbitrary boundary conditions are obtained by the wave method. The reverberation ray matrix of the multi-span stepped SWCNTs is the product of scattering, phase and permutation matrices, which can be determined by the impact loadings, continuous conditions and boundary conditions. The early transient responses can be calculated by the inverse Fourier transform of the sum of initial ray groups. It can be found that the early transient displacement response in the very short time subjected to the impact loading is very small, while the transient transverse shear strain becomes large in the very short time. The influences of nanotubes span number, nanotubes type and boundary conditions on the early transient responses of multi-span stepped SWCNTs are investigated.     

SERS signal response and SERS/SERDS spectra of fluoranthene in water on naturally grown Ag nanoparticle ensembles

We present experimental results of the time‐dependent Raman signal response of fluoranthene adsorbed on a naturally grown Ag nanoparticle ensemble, which serves as surface enhanced Raman scattering (SERS) substrate. In addition, SERS characteristics such as the concentration‐dependent calibration curves and the limit of detection (LOD) for fluoranthene in distilled water will be shown. The SERS substrate was prepared by Volmer–Weber growth under ultrahigh vacuum condition and exhibits a plasmon resonance wavelength at 491 nm. For the measurement of SERS signal response and SERS/shifted excitation Raman difference spectroscopy spectra of fluoranthene in water, experimental Raman setup containing a microsystem light source with two emission wavelengths (487.61 nm and 487.91 nm) was used. We experimentally demonstrate that the maximum SERS intensity is achieved 9 min after changing the analyte concentration from 0 nmol/l to 600 nmol/l. This response time is explained by a time‐dependent adsorption of the probe molecules onto the nanoparticles. The LOD for fluoranthene in water was evaluated applying shifted excitation Raman difference spectroscopy (SERDS) at different molecule concentrations. For SERDS, two emission wavelengths of a prototype microsystem light source have been used for Raman excitation. The experimental results reveal that the LOD for the probe molecules is very low. Experimentally, we have detected a fluoranthene concentration of only 4 nmol/l, which is very close to our estimated LOD of 2 nmol/l. Thus, the presented Raman setup, with a SERS substrate, whose plasmon resonance coincides with the excitation wavelength for SERS measurements, is well suited for in‐situ trace detection of pollutant chemicals in water. Copyright © 2013 John Wiley & Sons, Ltd.     

三维RC网络仿真异质材料的通用介质响应

提出了一种三维RC网络模型,并采用MATLAB及C语言对该模型进行编码、建模和仿真,得到了该网络的归一化复介电常数.分别计算了元件数为54,144,300,540和882的三维RC网络,结果表明,元件数为300及其以上的网络,其通用介质响应(UDR)特性趋于稳定;获得了电容分别为100nF,10nF,1nF和100pF时,540个元件RC网络的归一化复介电常数与频率关系的仿真结果;仿真了540个元件的RC网络中,电阻比例分别为4％,7％,10％,16％和33％时,归一化复介电常数与角频率ω的 关键词： 三维RC网络 异质材料 介电常数 通用介质响应     

高动态范围图像合成中相机响应函数的快速标定

针对高动态范围图像合成过程中相机响应函数标定速度低的问题,提出了一种快速有效的相机响应函数标定的方法.首先根据不同曝光度的图像在成像过程中场景照度保持一致的特性,提出构建一种新的最小平方代价函数,以降低相机响应函数标定方程组的维数;然后在保证标定方程组求解效率的前提下,根据不同曝光度图像的噪音分布,引入高斯加权函数,有效减小多曝光图像在高亮或过暗区域成像过程中引入的噪音,并利用稳健的QR分解算法提高标定方程组的求解速度;最后采用查表的方法,利用高斯加权函数完成场景照度的合成及相应的色调映射,得到能表现整个场景亮区和暗区细节的可视化图像.实验结果表明,与传统方法相比,本文算法在保证相机响应函数标定准确度的同时,具有计算量小、速度快的优点,可实现相机响应函数的快速标定,而且所获得的可视化图像主观效果有所提高,在便携式摄像设备上具有广泛的应用前景.     

Simulation of near-infrared photodiode detectors based on β-FeSi_2/4H-SiC heterojunctions

In this paper,we propose a near-infrared p-type β-FeSi2/n-type 4H-SiC heterojunction photodetector with semiconducting silicide(β-FeSi2) as the active region for the first time.The optoelectronic characteristics of the photodetector are simulated using a commercial simulator at room temperature.The results show that the photodetector has a good rectifying character and a good response to near-infrared light.Interface states should be minimized to obtain a lower reverse leakage current.The response spectrum of the β-FeSi2/4H-SiC detector,which consists of a p-type β-FeSi2 absorption layer with a doping concentration of 1×1015cm-3 and a thickness of 2.5 μm,has a peak of 755 mA/W at 1.42 μm.The illumination of the SiC side obtains a higher responsivity than that of the β-FeSi2 side.The results illustrate that the β-FeSi2/4H-SiC heterojunction can be used as a near-infrared photodetector compatible with near-infrared optically-activated SiC-based power switching devices.     

振动声成像系统分辨率研究

本文从振动声成像的基本原理出发，通过引入点扩展函数PSF和定义轴向响应函数ARF，研究了由凹球面聚焦换能器分割而成的一种典型共焦换能器参数对振动声成像系统侧向分辨率和轴向分辨率的影响。计算研究表明：增大凹球面换能器的口径、减小几何焦距和提高中心频率均可以提高系统的侧向分辨率和轴向分辨率；但改变凹球面换能器的分割比例对两种分辨率影响不尽相同。综合考虑超声换能器激励、聚焦性能以及产生的辐射力效果等因素，则换能器应按等辐射面积原则分割为宜。文中还分析了介质的声衰减系数对实际轴向分辨率的影响。