Resonant waveguide-grating switching device with nonlinear optical material

The design and analysis of a dielectric guided-mode resonance filter (GMRF) utilizing a nonlinear material for the waveguide is presented. Small changes to the parameters of a GMRF have a large impact on its resonance. A nonlinear material can provide a small change in the refractive index of the waveguide, altering the resonance of the device and resulting in modulation of the transmitted and reflected output of the filter. Numerical results show that nonlinear switching from 100% transmission to 100% reflection can be accomplished with less than 100 kW/cm(2) using a simple design.     

基于SPR的多层金属膜厚在线纳米测量

通过对于首层金属膜的SPR反射光强曲线的分析利用两峰值点标记角度,同时用柱面光与CCD测量系统建立无机械测角转台的反射光强角度分布测量系统。根据CCD接收的光强与位置对应信息经计算机处理换算为光强角度分布曲线,并通过与库内的曲线数据进行匹配而获得膜厚数值。利用该系统对铬钛银铝等常用金属薄膜进行了在线测控研究,得到了纳米级金属薄膜的膜层蒸镀顺序与相应的膜厚测量范围。     

MTL代数的蕴涵滤子与正蕴涵滤子

在MTL代数M上引入了蕴涵滤子、正蕴涵滤子的概念,研究了它们的性质,给出了M的非空子集成为蕴涵滤子及正蕴涵滤子的充要条件和M的蕴涵滤子成为正蕴涵滤子的充要条件.讨论了蕴涵滤子与正蕴涵滤子的关系,得到了M的每一个正蕴涵滤子都是蕴涵滤子,但反之不真.     

Multilayer optics provides laser-plasma-coupling insight

The Herpin theorem permits the reflectance of an arbitrary medium to be reproduced with a substrate of one complex refractive index overlaid with a coating film of a second complex refractive index and an appropriate thickness. The reflectances of a variety of laser-plasma-coupling experiments can be matched with a simple and physically meaningful procedure for choosing the fitting parameters. For short-pulse experiments, s-light coupling is dominated by substrate interactions at electron densities above critical and p-light coupling is dominated by resonance at the critical density. The weak dependence of resonance absorption on damping is the result of the harmonic-oscillator resonance form. As the plasma scale length becomes vanishingly small, the reflectance is that of the Fresnel equations, but surprisingly small plasma scale lengths have dramatic effects on the p-light reflectance. Film-substrate and WKB models predict similar resonance absorption, where both models are valid approximations and both should agree with multilayer and Helmholtz wave-optics calculations. For plasma scale lengths well below a wavelength, the film-substrate and the vacuum-heating models are closely related.     

Multilayer adsorption on heterogeneous surfaces

Although adsorption forces are usually short range in character, multilayer adsorption also concerns the energetic heterogeneity of the adsorbing surface. In this paper we assume that each energetically homogeneous patch forming the heterogeneous surface follows the Brunauer, Emmett, and Teller (BET) adsorption isotherm, while in the submonolayer range the whole surface follows the Dubinin and Radushkevich (DR) isotherm. By so assuming we are able to obtain the multilayer adsorption isotherm for the whole heterogeneous surface, and to compare BET and DR surface areas.     

Wiener-like correlation filters

We introduce a new, to our knowledge, design for a Wiener-like correlation filter, which consists of cascading a phase-only filter (POF) with a photorefractive Wiener-like filter. Its performance is compared with that of the POF and the Wiener correlation filter (WCF). Correlation results show that for intermediate and higher levels of noise this correlation filter has a peak-to-noise ratio that is larger than that of either the POF or the WCF while still preserving a correlation peak that is almost as high as that of the POF.     

Algebraic wavelet filters

A method to compute the discrete wavelet transform for certain wavelet filters is proposed that takes advantage of conjugacy properties in number fields. It is shown that wavelet filters derived from compactly supported orthonormal wavelets can be approximated with arbitrary precision by the proposed wavelet filters. © 1996 John Wiley & Sons, Inc.     

Multilayer transducer transfer matrix formalism

A complete formulation of direct and inverse 4 /spl times/ 4 transfer matrices for parallel and series, electrically connected, mechanically stacked, 1-D thickness mode multilayer piezoelectric transducers is presented. Complex coefficients account for the mechanical, dielectric, and piezoelectric losses. The direct or inverse 4 /spl times/ 4 transfer matrix transfers quantities at the top surface into their values at the bottom surface or vice versa, respectively. The 4 /spl times/ 4 transfer matrices derive from the 3 /spl times/ 3 transfer matrices, which follow from the 3 /spl times/ 3 matrix for the general three-port. For both parallel and series connections, the 3 /spl times/ 3 and 4 /spl times/ 4 direct and inverse transfer matrices are interrelated through transformation symmetries; also, the inverse matrix can be obtained from the direct matrix by changing the sign of both the piezoelectric coefficient and the explicitly occurring complex variable, j. For the electrically parallel connected case, explicit voltage orientation reversals occur at successive piezoelectric layers. Cascading the 4 /spl times/ 4 matrices yields the sum of the currents through the piezoelectric layers for the electrically parallel-connected case and the sum of the voltage differences across the layers for the electrically series-connected case. The resultant matrices are calculated for the cascading of n identical piezoelectric layers connected in parallel and series.     

Multilayer modal actuator-based piezoelectric transformers

An innovative, multilayer piezoelectric transformer equipped with a full modal filtering input electrode is reported herein. This modal-shaped electrode, based on the orthogonal property of structural vibration modes, is characterized by full modal filtering to ensure that only the desired vibration mode is excited during operation. The newly developed piezoelectric transformer is comprised of three layers: a multilayered input layer, an insulation layer, and a single output layer. The electrode shape of the input layer is derived from its structural vibration modal shape, which takes advantage of the orthogonal property of the vibration modes to achieve a full modal filtering effect. The insulation layer possesses two functions: first, to couple the mechanical vibration energy between the input and output, and second, to provide electrical insulation between the two layers. To meet the two functions, a low temperature, co-fired ceramic (LTCC) was used to provide the high mechanical rigidity and high electrical insulation. It can be shown that this newly developed piezoelectric transformer has the advantage of possessing a more efficient energy transfer and a wider optimal working frequency range when compared to traditional piezoelectric transformers. A multilayer piezoelectric, transformer-based inverter applicable for use in LCD monitors or portable displays is presented as well.     

Carbon nanotube filters

Over the past decade of nanotube research, a variety of organized nanotube architectures have been fabricated using chemical vapour deposition. The idea of using nanotube structures in separation technology has been proposed, but building macroscopic structures that have controlled geometric shapes, density and dimensions for specific applications still remains a challenge. Here we report the fabrication of freestanding monolithic uniform macroscopic hollow cylinders having radially aligned carbon nanotube walls, with diameters and lengths up to several centimetres. These cylindrical membranes are used as filters to demonstrate their utility in two important settings: the elimination of multiple components of heavy hydrocarbons from petroleum-a crucial step in post-distillation of crude oil-with a single-step filtering process, and the filtration of bacterial contaminants such as Escherichia coli or the nanometre-sized poliovirus ( approximately 25 nm) from water. These macro filters can be cleaned for repeated filtration through ultrasonication and autoclaving. The exceptional thermal and mechanical stability of nanotubes, and the high surface area, ease and cost-effective fabrication of the nanotube membranes may allow them to compete with ceramic- and polymer-based separation membranes used commercially.     

Dichroic rugate filters

We reduce the sidelobes that are present in the bandpass zones of rugate filters, using antireflection coatings to design dichroic rugate filters. Our designs are based on the formalism of equivalent systems that allow us to consider a rugate filter a simple equivalent layer with equivalent optical admittance and equivalent phase thickness functions. Rugate filters with apodization were considered.     

Unconstrained correlation filters

A mathematical analysis of the distortion tolerance in correlation filters is presented. A good measure for distortion performance is shown to be a generalization of the minimum average correlation energy criterion. To optimize the filter's performance, we remove the usual hard constraints on the outputs in the synthetic discriminant function formulation. The resulting filters exhibit superior distortion tolerance while retaining the attractive features of their predecessors such as the minimum average correlation energy filter and the minimum variance synthetic discriminant function filter. The proposed theory also unifies several existing approaches and examines the relationship between different formulations. The proposed filter design algorithm requires only simple statistical parameters and the inversion of diagonal matrices, which makes it attractive from a computational standpoint. Several properties of these filters are discussed with illustrative examples.     

石墨烯纳米片改性PBT研究

目的采用石墨烯纳米片对聚对苯二甲酸丁二醇酯(PBT)进行改性,以提高其耐热性能和力学性能。方法采用熔融共混法制备PBT/石墨烯纳米片(MLGN)纳米复合材料,通过DSC、SEM、DMA、耐热性能及力学性能测试,研究石墨烯纳米片对PBT性能的影响。结果石墨烯纳米片具有明显的异相成核效果,显著降低了PBT的结晶活化能,加入质量分数为1%的石墨烯纳米片后,结晶活化能降低了66.2%,加入2%后降低了72.8%;石墨烯纳米片与PBT分子链间具有较强的相互作用,有利于提高PBT的结晶峰值温度、玻璃化转变温度、维卡软化温度和拉伸强度。当MLGN质量分数为2%时,玻璃化转变温度提高了1.7℃,维卡软化温度提高了8.8℃,拉伸强度提高了17%左右。MLGN的质量分数在2%以内对冲击强度没有影响。结论石墨烯纳米片能明显改善PBT的耐热性能和力学性能。