二极管负载电缆X射线辐照瞬态响应数值模拟

将时域传输线模型与漂移-扩散模型相结合,提出一种耦合数值计算方法,研究计算了带二极管负载的电缆在X射线辐照下的瞬态响应。该耦合数值计算方法首先利用时域传输线模型计算电缆在X射线辐照下的各节点电参数,然后将得到的终端节点的电压代入漂移-扩散模型中求解二极管的内部参数与偏置电流,最后将得到的偏置电流代入到下一时间步的传输线模型中继续进行计算。该方法能够直接反映出电缆在X射线辐照下的瞬态响应与所连接的负载状态改变之间的耦合关系,利用该方法求解X射线辐照简单电子系统的典型算例,计算结果表明,X射线辐照下,同轴电缆上各处的响应电流会随着PIN二极管状态的改变而发生明显变化,与理论分析相符合,耦合模型适用于此类问题。     

Fast relaxation of carbon nanotubes in polymer composite actuators

Silicone elastomer composites containing multiwalled carbon nanotubes have been irradiated with near-infrared light to study their mechanical actuation response. We show that the speed of the stimulated response is faster than Debye relaxation, instead following a compressed-exponential law. However, the relaxation after switching off the light source follows the simple-exponential relaxation, as does the stimulated response at very low nanotube concentration. We discuss possible models and explanations to account for the fast photomechanical response.     

Second-order filtering and sensing with partially coupled traveling waves in a single resonator

The counterpropagating waves in a single traveling-wave cavity can be partially coupled by means of a small perturbation such as a notch. When it is side coupled to a waveguide, this single cavity yields a general second-order (Chebyshev) reflection response in the waveguide, which is useful for narrow-bandwidth reflecting applications. In a different application, the cavity amplifies small reflections induced by external perturbations, thus finding use in ultrafine sensing. Amplification factors as great as 10(12) are predicted for the highest-Q microsphere resonators. The analytic theory of these devices is presented.     

Role of polarization and alignment in photoactuation of nematic elastomers

Changing the orientational order in liquid-crystal elastomers leads to internal stresses and changes of the sample shape. When this effect is induced by light, due to photoisomerization of constituent molecular moieties, the photomechanical actuation results. We investigate quantitatively how the intensity and the polarization of light affect photoactuation. By studying dissolved, as well as covalently bonded azo-dyes, we determine the changes in absorption and the response kinetics. For the first time we compare the response of aligned monodomain, and randomly disordered polydomain nematic elastomers, and demonstrate that both have a comparable photoresponse, strongly dependent on the polarization of light. Polarization-dependent photoactuation in polydomain elastomers gives an unambiguous proof of its mechanism since it is the only experiment that distinguishes from the associated thermal effects.     

Plasmonic couplers with metal nonlinearities

Usually nonlinear response of metals is neglected in the study of plasmonic waveguiding structures. Recent prediction of strong third-order optical response of metals due to ponderomotive forces opens up novel possibilities for utilizing this effect in the design of active plasmonic devices. We discuss the possibility of implementation of nonlinear response of metals in the design of plasmonic coupler. We analyze the structure and dispersions of linear and nonlinear guided plasmonic modes of two coupled thin metallic films and predict bifurcations of symmetry breaking.     

Analysis of an ultra-compact wavelength filter based on hybrid plasmonic waveguide structure

In this letter, we propose and analyze an ultra-compact wavelength filter on silicon-based hybrid plasmonic waveguides, which confines light in a nanometeric silica dioxide layer between the silicon substrate and metal cap. The filter consists of a stub structure coupled to a straight waveguide. The three-dimensional finite-difference time-domain (FDTD) method is applied to calculate the spectral responses of such devices. Similar resonant behaviors are obtained since those devices are based on two-dimensional Metal-Insulator-Metal waveguide structure. Results also show that by adding stubs and tuning the distance between stubs can further improve the device's performance and shape the spectral response to some extent.     

A novel multiple blade ultrasonic cutting device

In ultrasonic devices consisting of serially coupled tuned components, components whose tuned length dimension is large compared to other dimensions, or components with profiles designed for high gain, the response of the device during operation is often characterised by modal interactions, and especially the excitation of combination resonances. The effects on ultrasonic devices are high noise levels, component failures and poor operating performance. In this paper, energy exchanges between modes are characterised to illustrate the adverse effects of combination resonances. Design solutions are proposed to eliminate these effects which concentrate on reducing the number of modes. In particular, a novel half-wavelength three-blade cutting system tuned to the first longitudinal mode has been designed by finite element modelling. An experimental investigation demonstrates that the measured response does not show evidence of modal interactions.     

Optical fiber-based photomechanical gene transfer system for in vivo application

We developed an optical-fiber-based photomechanical gene transfer system for endoscopic or catheter-based application. A fiber tip with a laser-absorbing film covered with a transparent plastic disk for plasma confinement was attached to a quartz fiber; the film was irradiated with nanosecond laser pulses transmitted through the fiber to generate photomechanical waves (PMWs). Characteristics of PMWs emitted from the fiber tip were examined to confirm the necessary conditions for gene transfer. We then attempted to transfer reporter genes to the rat skin as a test tissue in vivo with the fiber system, and the results showed significantly high protein levels and spatially selective pinpoint gene expressions in the tissue.     

On the mechanism of residual photomechanical effect

The results of investigation of the residual photomechanical effect (PME) in a monocrystalline n-Si sample at various temperatures by the method of microindentation following exposure to light are considered. It is shown that a decrease in the residual PME is an exponential function of time and temperature.     

Track changing by use of the phase response of microspheres and resonators

A microsphere or resonator that is side coupled to an incident optical beam induces a phase response in the beam. In the so-called overcoupled regime, the amplitude of the incident beam remains unmodulated, whereas the phase goes through a shift of p at resonance. This shift is insensitive to the details of the coupling geometry or the resonant mode. In conjunction with an interferometer, the phase response can be used to switch the beam between two well-defined outputs, thus offering a robust means of deploying microspheres and other microresonators in practical photonic devices.     

Reversible photomechanical switching of individual engineered molecules at a metallic surface

We have observed reversible light-induced mechanical switching for individual organic molecules bound to a metal surface. Scanning tunneling microscopy (STM) was used to image the features of individual azobenzene molecules on Au(111) before and after reversibly cycling their mechanical structure between trans and cis states using light. Azobenzene molecules were engineered to increase their surface photomechanical activity by attaching varying numbers of tert-butyl (TB) ligands ("legs") to the azobenzene phenyl rings. STM images show that increasing the number of TB legs "lifts" the azobenzene molecules from the substrate, thereby increasing molecular photomechanical activity by decreasing molecule-surface coupling.     

CCD器件相对光谱响应测试仪

设计并实现了一种涵盖400~950 nm的全自动CCD器件相对光谱响应测试仪。分析了成像器件的相对光谱响应测试原理,采用宽光谱、高灵敏度响应的科学级光纤光谱仪QE65000作为参考探测器,基于单光路直接比较法,构建了CCD器件相对光谱响应测试仪器。该装置可全自动完成CCD器件的相对光谱响应测量,不确定度分析结果表明,该装置对CCD器件开展相对光谱响应测试的最大不确定度为6.21%,满足应用需求,可为CCD等图像传感器甄选、参数性能评价及后续整机测试提供关键数据支撑。     

光纤-手征光纤耦合光波导偏振响应特性的实验研究

在 D形微孔光纤中注入手征液体 ,制作出了光纤 -手征光纤耦合光波导。对其输出端的偏振响应特性进行测试发现 ,与未注入手征液体的 D形微孔光纤相比 ,传播的光矢量方向发生了旋转。这种效应是由光纤与手征光纤相互耦合而引起的 ,将有可能应用到许多新器件的制作中     

基于石墨烯复合材料的近红外光驱动的柔性可调光栅

针对现有柔性可调光栅响应速度慢、功耗高而无法广泛应用的现状,提出一种基于石墨烯纳米片(graphene nanoplatelet, GNP)/聚二甲基硅氧烷(polydimethylsiloxane, PDMS)复合材料的近红外(near-infrared, NIR)光驱动可调谐柔性透射光栅结构。利用紫外线光刻技术制备出的光栅结构,实现了柔性透射光栅与石墨烯复合材料薄膜的一体化。在光功率密度为220 mW·cm-2的近红外光驱动下,GNP/PDMS薄膜的温度变化约为120℃,而且光栅在3 s内可实现2.7%的连续周期调谐。不同驱动频率下,光栅栅距变化规律基本相同,即光栅的光机械效应无显著的时间依赖性。     

Nanoscale defect-deformation solitons in solids with a constant strain gradient and the long-range photomechanical effect

The possibility of a cooperative (soliton) gettering of point defects is analyzed based on the model of a slow nanoscale defect-deformation soliton. It is demonstrated that the soliton model makes it possible to interpret the main experimental data on the long-range photomechanical effect upon the beam irradiation of thin films and plates.     

Suppressing vibrations in a sheet with a Fabry-Perot photomechanical device

We report what we believe to be the first demonstration that the vibration amplitude in a stretched plastic sheet can be reduced by as much as 10 dB with a monolithic all-optical mesoscale photomechanical device.     

随机生长误差对双腔型平顶法布里-珀罗滤波器的影响

在光网络中平顶滤波器可以有效地提高信道光检测的快速性和准确性。利用两个法布里珀罗腔间的串联耦合,可以构建出具有平顶透射特性的双腔型法布里珀罗滤波器。采用传输矩阵的方法,研究了随机生长误差对双腔型平顶滤波器透射特性的影响。模拟分析表明,当两个法布里珀罗腔的物理厚度差超过一个纳米时,在透射谱中就会出现两个高度不同的透射峰;解释了实测器件的透射谱中的双峰不对称性;用界面起伏的概念解释了实测滤波器带宽大于理论值的原因。理论分析与实验结果取得了较好的一致。     

车辆线缆瞬态电磁脉冲耦合仿真与抑制技术

瞬态电磁脉冲可通过车辆互联线缆耦合至电子系统内部，造成电子设备受扰甚至损毁，研究瞬态防护器件对电磁脉冲的抑制特性可为车辆电磁防护设计与实施提供有力支撑。本文以发动机电控系统为研究对象，考虑关键金属结构、线缆与电子设备，建立发动机电磁仿真模型，计算获取了瞬态电磁脉冲作用下线缆端口耦合干扰特性；基于电磁脉冲注入方法设计并搭建了瞬态防护器件测试平台，获取了瞬态电压抑制器与压敏电阻两类典型瞬态防护器件的响应时间、钳位电压、尖峰泄露等响应特性；在仿真与测试结果的基础上，选取一型瞬态电压抑制器应用于凸轮轴位置传感器信号线的电磁防护。研究结果表明，该型瞬态电压抑制器对线缆瞬态电磁脉冲耦合干扰抑制能力接近20 dB，置于滤波器前端可有效抑制线缆耦合干扰，保护终端设备。     

Entrainment and stimulated emission of ultrasonic piezoelectric auto-oscillators

Theoretical modeling and laboratory tests are conducted for nonlinear auto-oscillating piezoelectric ultrasonic devices coupled to reverberant elastic bodies. The devices are shown to exhibit behavior familiar from the theory of coupled auto-oscillators. In particular, these spontaneously emitting devices adjust their limit-cycle frequency to the spectrum of the body. It is further shown that the auto-oscillations can be entrained by an applied field; an incident wave at a frequency close to the frequency of the natural limit cycle entrains the oscillator. Special attention is paid to the phase of entrainment. Depending on details, the phase is such that the oscillator can be in a state of stimulated emission: the incident field amplifies the ultrasonic power emitted by the oscillator. These behaviors are essential to eventual design of an ultrasonic system that would consist of a number of such devices all synchronized to their mutual field, a system that would be an analog to a laser. A prototype uaser is constructed.     

Effect of coupling between passenger compartment and trunk of a car on coupled system natural frequencies using acoustic frequency response function

Conventional numerical techniques, used to study the acoustics of a car passenger cabin, treat the cabin as an isolated cavity excited by the cavity boundaries. Realistically, other cavity volumes such as the trunk communicate with the cabin through the holes in the parcel shelf of the car. An extended acoustic model of a car is formed by the cavity volumes of the passenger compartment and the trunk as well as air leakages through the holes provided for electrical devices and ventilation on the parcel shelf. In this study, the dynamic influence of air leakages between the passenger and trunk compartments on the first and second coupled system modes was investigated experimentally using acoustic frequency response function. The response to the acoustic excitation was measured for four different configurations of trim and holes of the parcel shelf. The natural frequencies of the first and second coupled system modes increased with increasing holes size with and without the trim of the parcel shelf. The experimental results were in good agreement with the reported results of coupling effects of double cavities connected by a neck. In the low frequency region since the wavelength is longer compared to the holes dimension, these holes act as point sources.