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Waveguide
Kinds of Waveguide Terms modified by Waveguide Selected AbstractsOrganic Electronic Interface Devices: Light- and Touch-Point Localization using Flexible Large Area Organic Photodiodes and Elastomer Waveguides (Adv. Mater.ADVANCED MATERIALS, Issue 34 200934/2009) The inside cover shows a flexible, large-area, position-sensitive organic photodetector used as an input device for a desktop computer. R. Koeppe et al. show the assembly of such a device with a photodiode based on a blend of Zn-phthalocyanine and C60 with low conductivity electrodes on p. 3510. The current drop across the electrodes easily allows for the calculation of the position of a localized light signal impinging on the position-sensitive photodetector. By adding an additional elastomer layer with embedded LEDs, the device can also be used as flexible touchpad. [source] Light- and Touch-Point Localization using Flexible Large Area Organic Photodiodes and Elastomer WaveguidesADVANCED MATERIALS, Issue 34 2009Robert Koeppe A homogeneous large area photodiode with high resistance electrodes can be used to trace the position of a localized light signal, thus allowing the easy fabrication of large area light- and touch-point sensors. A readout scheme is presented that allows a direct and simple recalculation of the coordinates from four current signals picked up at the edges of the device. [source] Silk Fibroin Waveguides: Biocompatible Silk Printed Optical Waveguides (Adv. Mater.ADVANCED MATERIALS, Issue 23 200923/2009) The cover shows an artistic rendition that merges silk and fiber optics. Supercontinuum white light is guided through a glass optical fiber that surrounds and illuminates silkworm cocoons. The silkworm cocoons shown here are used as the starting point of an extraction process to isolate pure silk fibroin protein in an aqueous solution. The silk is then reconstituted in the form of optical waveguides, as described by Fiorenzo Omenetto and co-workers on p. 2411, opening new opportunities to guide light in an entirely organic and biocompatible material. [source] Biocompatible Silk Printed Optical WaveguidesADVANCED MATERIALS, Issue 23 2009Sara T. Parker Biocompatible silk optical waveguides are fabricated by direct-write assembly and demonstrated to guide light in both straight and curved architectures. These waveguides can easily be doped or functionalized with bioactive molecules, and are promising materials for biophotonic devices. [source] Single-Crystalline V2O5 Ultralong Nanoribbon WaveguidesADVANCED MATERIALS, Issue 23 2009Bin Yan High-aspect-ratio V2O5 nanoribbons are synthesized by thermal vapor deposition technique. Our results reveal that the nanoribbons can serve as effective active optical waveguides. In addition, the observation of strong Raman signals collected at the end of the ribbon indicate that the unique nanostructure could play a vital role in Raman amplifers and other nonlinear photonic components. [source] Improvement of the Optical Transmission of Polymer Planar Waveguides by Plasma TreatmentPLASMA PROCESSES AND POLYMERS, Issue 3 2008Aissam Airoudj Abstract The aim of the present work is to reduce the optical losses of glycidyl ether of bisphenol A (SU-8) polymer planar waveguides using cold plasmas, which allow the substitution of H atoms by F. CF4 and mixtures of CF4/H2 RF plasma treatments were carried out for the surface fluorination of the SU-8 waveguide. The observed decrease in the optical losses due to propagation in the Si/SiO2/fluorinated SU-8 planar waveguides has been correlated with the surface fluorination as measured by XPS and CA measurements. In order to understand and to optimize the fluorination process, the plasma phase was analyzed by OES. Finally, the thickness of the fluorinated layer was estimated using modulated incident-angle XPS. [source] Trivelpiece-Gould mode produced gas-discharges in a diffusion-controlled regimeCONTRIBUTIONS TO PLASMA PHYSICS, Issue 3-4 2003H. Schlüter Abstract The study presents a numerical fluid-plasma model of waveguide discharges sustained by travelling azimuthallysymmetric Trivelpiece-Gould modes. The results describe weakly-magnetized (, , ,e) plasma production in a diffusion-controlled regime (, being the wave frequency, ,e the electron gyro-frequency). However, with respect to the influence of the external magnetic field on the transverse ambipolar-diffusion coefficient, cases of both weak and strong impact of the magnetic field are covered. In its electrodynamical part, the model involves detailed description of the behaviour of the Trivelpiece-Gould waves in radially-inhomogeneous collisional plasmas. The gas-discharge part of the model specifies plasma production in an argon gas. The results are for the self-consistent structure of the discharge composed out of the interrelated variations of wavenumber, space damping rate, plasma density, electron temperature and power absorbed on average by an electron. The analysis is in terms of influence of gas-pressure and magnetic-field changes. [source] Dielectrophoresis microsystem with integrated flow cytometers for on-line monitoring of sorting efficiencyELECTROPHORESIS, Issue 24 2006Zhenyu Wang Abstract Dielectrophoresis (DEP) and flow cytometry are powerful technologies and widely applied in microfluidic systems for handling and measuring cells and particles. Here, we present a novel microchip with a DEP selective filter integrated with two microchip flow cytometers (FCs) for on-line monitoring of cell sorting processes. On the microchip, the DEP filter is integrated in a microfluidic channel network to sort yeast cells by positive DEP. The two FCs detection windows are set upstream and downstream of the DEP filter. When a cell passes through the detection windows, the light scattered by the cell is measured by integrated polymer optical elements (waveguide, lens, and fiber coupler). By comparing the cell counting rates measured by the two FCs, the collection efficiency of the DEP filter can be determined. The chips were used for quantitative determination of the effect of flow rate, applied voltage, conductivity of the sample, and frequency of the electric field on the sorting efficiency. A theoretical model for the capture efficiency was developed and a reasonable agreement with the experimental results observed. Viable and non-viable yeast cells showed different frequency dependencies and were sorted with high efficiency. At 2,MHz, more than 90% of the viable and less than 10% of the non-viable cells were captured on the DEP filter. The presented approach provides quantitative real-time data for sorting a large number of cells and will allow optimization of the conditions for, e.g., collecting cancer cells on a DEP filter while normal cells pass through the system. Furthermore, the microstructure is simple to fabricate and can easily be integrated with other microstructures for lab-on-a-chip applications. [source] A simple light-emitted diode-induced fluorescence detector using optical fibers and a charged coupled device for direct and indirect capillary electrophoresis methodsELECTROPHORESIS, Issue 9 2006David Arráez-Román Abstract We constructed a simple fluorescence detector for both direct and indirect CE methods using a blue light-emitted diode (470,nm) as excitation source, a bifurcated optical fiber as a waveguide, and a CCD camera as a detector. The connection of all the components is fairly easy even for nonexperts and the use of a CCD camera improves the applicability of this detector compared to the others using PMTs because it permits the recording of 2-D electropherograms or phosphorescence measurements. This detector provides a compact, low cost, and rapid system for the determination of native fluorescence compounds which have high quantum yields by CE with direct fluorescence detection, showing an LOD of 2.6×10,6,M for fluorescein; the determination of fluorescence derivative compounds by CE with direct fluorescence detection, showing an LOD of 1.6×10,7,M for FITC-labeled 1,6-diaminohexane; and nonfluorescence compounds by CE with indirect fluorescence detection with an LOD of 2.7×10,6,M for gallic acid. [source] Waveguide Sensors: Use of Reversal Nanoimprinting of Nanoparticles to Prepare Flexible Waveguide Sensors Exhibiting Enhanced Scattering of the Surface Plasmon Resonance (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 11 2010Mater. The image displays a flexible surface plasmon resonance (SPR)-based waveguide sensor prepared by directly imprinting metal nanoparticles onto flexible plates, as presented by H.-L. Chen et al. on page 1742. The metal nanoparticles could scatter the evanescent wave and the guiding mode waves from the SPR-based waveguide simultaneously. The scattering signal underwent a distinguishable red-shift when the target molecules bound to the particles. [source] Use of Reversal Nanoimprinting of Nanoparticles to Prepare Flexible Waveguide Sensors Exhibiting Enhanced Scattering of the Surface Plasmon ResonanceADVANCED FUNCTIONAL MATERIALS, Issue 11 2010Dehui Wan Abstract A flexible surface plasmon resonance (SPR)-based scattering waveguide sensor is prepared by directly imprinting hollow gold nanoparticles (NPs) and solid gold NPs onto flexible polycarbonate (PC) plates,without any surface modification,using a modified reversal nanoimprint lithography technology. Controlling the imprinting conditions, including temperature and pressure, allows for the fine adjustment of the depths of the embedded metal NPs and their SPR properties. This patterning approach exhibits a resolution down to the submicrometer level. A 3D finite-difference time domain simulation is used to examine the optical behavior of light propagating parallel to the air/substrate interface within the near-field regime. Consistent with the simulations, almost an order of magnitude enhancement in the scattering signal after transferring the metal NPs from the glass mold to the PC substrate is obtained experimentally. The enhanced signal is attributed to the particles' strong scattering of the guiding-mode waves (within the waveguide) and the evanescent wave (above the waveguide) simultaneously. Finally, the imprinting conditions are optimized to obtain a strongly scattering bio/chemical waveguide sensor. [source] Controlling Light Emission in Luminescent Solar Concentrators Through Use of Dye Molecules Aligned in a Planar Manner by Liquid CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 17 2009Paul P. C. Verbunt Abstract A luminescent solar concentrator (LSC) is a potential low-cost enhancement of the standard large-area silicon photovoltaic panels for the generation of electricity from sunlight. In this work, guest,host systems are investigated using anisotropic fluorescent dyes and liquid crystal mesogens to control the direction of emitted light in the LSC. It is determined that up to 30% more light is emitted from the edge of an LSC waveguide with planar dye alignment parallel to the alignment direction than from any edge of an LSC with no alignment (isotropic). The aligned samples continue to show dichroic performance after additions of both edge mirrors and rear scattering layer. [source] Integration of a Rib Waveguide Distributed Feedback Structure into a Light-Emitting Polymer Field-Effect TransistorADVANCED FUNCTIONAL MATERIALS, Issue 9 2009Michael C. Gwinner Abstract Ambipolar light-emitting organic field-effect transistors (LEFETs) possess the ability to efficiently emit light due to charge recombination in the channel. Since the emission can be made to occur far from the metal electrodes, the LEFET structure has been proposed as a potential architecture for electrically pumped organic lasers. Here, a rib waveguide distributed feedback structure consisting of tantalum pentoxide (Ta2O5) integrated within the channel of a top gate/bottom contact LEFET based on poly(9,9-dioctylfluorene- alt -benzothiadiazole) (F8BT) is demonstrated. The emitted light is coupled efficiently into the resonant mode of the DFB waveguide when the recombination zone of the LEFET is placed directly above the waveguide ridge. This architecture provides strong mode confinement in two dimensions. Mode simulations are used to optimize the dielectric thickness and gate electrode material. It is shown that electrode absorption losses within the device can be eliminated and that the lasing threshold for optical pumping of the LEFET structure with all electrodes (4.5,µJ cm,2) is as low as that of reference devices without electrodes. These results enable quantitative judgement of the prospects for realizing an electrically pumped organic laser based on ambipolar LEFETs. The proposed device provides a powerful, low-loss architecture for integrating high-performance ambipolar organic semiconductor materials into electrically pumped lasing structures. [source] A linear finite element acoustic fluid,structure model of ultrasonic angioplasty in vivoINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 7 2010Mark P. Wylie Abstract The delivery of high-power ultrasonic energy via small diameter wire waveguides represents a new alternative therapy for the treatment of chronic totally occluded arteries (CTOs). This type of energy manifests itself as a mechanical vibration at the distal-tip of the waveguide with amplitudes of vibration up to 60,µm and at frequencies of 20,50,kHz. Disruption of diseased tissue is reported to be a result of direct mechanical ablation, cavitation, pressure components and acoustic streaming and that ablation was only evident above the cavitation threshold. This work presents a linear finite element acoustic fluid,structure model of an ultrasonic angioplasty waveguide in vivo. The model was first verified against a reported analytical solution for an oscillating sphere. It was determined that 140 elements per wavelength (EPW) were required to predict the pressure profile generated by the wire waveguide distal-tip. Implementing this EPW count, the pressure field surrounding a range of distal-tip geometries was modelled. For validation, a model was developed with parameters based on a bench-top experiment from the literature of an ultrasonic wire waveguide in a phantom leg. This model showed good correlation with the experimental measurements. These models may aid in the further development of this technology. Copyright © 2010 John Wiley & Sons, Ltd. [source] Improved accuracy for the Helmholtz equation in unbounded domainsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 15 2004Eli Turkel Abstract Based on properties of the Helmholtz equation, we derive a new equation for an auxiliary variable. This reduces much of the oscillations of the solution leading to more accurate numerical approximations to the original unknown. Computations confirm the improved accuracy of the new models in both two and three dimensions. This also improves the accuracy when one wants the solution at neighbouring wavenumbers by using an expansion in k. We examine the accuracy for both waveguide and scattering problems as a function of k, h and the forcing mode l. The use of local absorbing boundary conditions is also examined as well as the location of the outer surface as functions of k. Connections with parabolic approximations are analysed. Copyright © 2004 John Wiley & Sons, Ltd. [source] An extended Huygens' principle for modelling scattering from general discontinuities within hollow waveguidesINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 5 2001Ronald L. Ferrari Abstract The modal fields, generalized scattering matrix (GSM) theory and dyadic Green's functions relating to a general uniform hollow waveguide are briefly reviewed in a mutually consistent normalization. By means of an analysis linking these three concepts, an extended version of the mathematical expression of Huygens' principle is derived, applying to scattering from an arbitrary object within a hollow waveguide. The integral-equation result expresses the total field in terms of the incident waveguide modal fields, the dyadic Green's functions and the tangential electromagnetic field on the surface of the object. It is shown how the extended principle may be applied in turn to perfect conductor, uniform material and inhomogeneous material objects using a quasi method of moments (MM) approach, coupled in the last case with the finite element method. The work reported, which indicates how the GSM of the object may be recovered, is entirely theoretical but displays a close similarity with established MM procedures. Copyright © 2001 John Wiley & Sons, Ltd. [source] Accurate closed-form model for computation of conductor loss of coplanar waveguideINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 1 2010Payal Majumdar Abstract This study estimates the accuracy of HFSS and Sonnet and other models against the experimental results from three sources. A closed-form model for experiment based stopping distance is developed to calculate accurately conductor loss of CPW. The present improved Holloway and Kuester (IHK) model has an average accuracy of 3.7% against the experimental results from different sources in the frequency range 1,120 GHz with conductor thickness of 0.25,1.58 ,m. The original Holloway and Kuester model has an average accuracy of 13.7% and model of Ponchak et al. 17.1 % against same set of experimental results. HFSS and Sonnet have average accuracy of 7.86% and 10.33% against same set of experimental data. The accuracy of IHK model is also examined against HFSS and Sonnet for the conductor thickness up to 9 ,m and substrate relative permittivity in the range of 3.8,20. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010. [source] Miniaturized planar ferrite junction circulator in the form of substrate-integrated waveguideINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 1 2008Wenquan Che Abstract The theoretical analysis and engineering implementation of the planar substrate-integrated waveguide (SIW) ferrite junction circulator have been proposed in this article. The ferrite junction circulator is implemented in the form of SIW, taking the features of low profile, small volume and easy integration with other planar circuits. The design strategies of the device have been introduced, including the design consideration of the microstrip transition. One C-band prototype of SIW ferrite junction circulator has been fabricated and measured. The experimental results indicate the bandwidth is about 33% at ,15 dB isolation and the maximum isolation is near 40 dB. However, the insertion loss is a little big, owing to the imperfect dielectric material and fabrication inaccuracy. The SIW ferrite junction circulator and the microstrip transition are integrated into a same substrate, resulting in a very compact planar ferrite junction circulator and indicating potential applications in integrated communication and radar systems. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008. [source] A compact substrate integrated waveguide H-plane horn antenna with dielectric arc lensINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 5 2007Wenquan Che Abstract An H-plane horn antenna constructed into SIW (substrate integrated waveguide) is proposed. It has a dielectric arc lens for better directivity and a simple microstrip transition as feed. The horn, the lens and the transition share the same substrate. The resulting formula from optical principles shows that the suitable dielectric lens can improve the directivity of the antenna significantly. A prototype was fabricated; the antenna size is 39.175 × 14 × 2 mm3. The frequency band is from 25.5 to 28.5 GHz. The measured gain of this antenna is about 9 dB; the bandwidth, at 10 dB return loss, is over 12%. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007. [source] Miniaturized rectangular waveguide filtersINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 4 2007Alexander Shelkovnikov Abstract Two types of miniaturized rectangular waveguide filters are presented. Miniaturization is achieved using the slow-wave effect of electromagnetic bandgap (EBG) surfaces and the left-handed properties of split ring resonators (SRRs). The proposed EBG waveguide bandpass filter performs passband in the frequency range, which corresponds to the waveguide with the lower recommended operating band consequently enabling significant miniaturization of the structure. The SRR-loaded bandstop filter makes use of the effect imposed by left-handed medium (LHM), which is created by a combination of SRRs and wireline on the dielectric slab. Both filters are designed, simulated, and tested. Experimental results of the SRR-loaded bandstop filter are presented to demonstrate feasibility of the proposed structures. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007. [source] Synthesis of interdigital capacitors based on particle swarm optimization and artificial neural networksINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 4 2006Jehad Ababneh Abstract This article reports on the use of the particle swarm optimization (PSO) algorithm in the synthesis of the planar interdigital capacitor (IDC). The PSO algorithm is used to optimize the geometry parameters of the IDC in order to obtain a certain capacitance value. The capacitance value of the IDC is evaluated using an artificial neural network (ANN) model with the geometry parameters of the IDC as its inputs. Several design examples are presented that illustrate the use of the PSO algorithm, and the design goal in each example is easily achieved. Full-wave electromagnetic simulations are also performed for some of the studied IDC structures implemented using coplanar waveguide (CPW) technology. The simulation results are in good agreement with those obtained using the ANN/PSO algorithm. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006. [source] CAD modeling of coplanar waveguide cross-over air-bridgeINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 3 2005Nihad Dib Abstract In this article, a new CAD model for the coplanar waveguide (CPW) cross-over air-bridge is proposed. The model takes into account the CPW open-end capacitance and the vertical strips of the bridge. The section directly underneath the bridge is modeled as a small section of a microstrip line. Our results are in good agreement with the published full-wave results. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005. [source] Propagation characteristic analysis of ridged circular waveguide using 2D finite-difference frequency-domain methodINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 3 2005Qi Zhang Abstract The propagation characteristics of ridged circular waveguides are analyzed by using 2D finite-difference frequency-domain (2D FDFD). Based on the 2D FDFD method in a cylindrical coordinate system, general difference formulas for the ridged circular waveguide are deduced, and modified difference formulas are built at some special points of the ridged circular waveguides. To verify the proposed method, three ridged circular waveguide structures are investigated and the numerical results are compared with available ones obtained by other research methods. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE 15, 2005. [source] Equivalent network for H-plane rectangular-waveguide circuits and its practical application for analysis of circuit performance and field behaviorINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 3 2004Takaharu Hiraoka Abstract An equivalent network of H-plane rectangular-waveguide circuits, consisting of straight waveguide and step discontinuity, is rigorously given by a cascade connection of the corresponding equivalent network, that is, a multitransmission line and multiport ideal transformer. Thus the entire equivalent network obtained for H-plane rectangular-waveguide inline circuits is useful for the systematic analysis of circuit performance and field behavior. © 2004 Wiley Periodicals, Inc. Int J RF and Microwave CAE 14: 210,226, 2004. [source] Distributed MEMS transmission lines for tunable filter applicationsINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 5 2001Yu Liu Abstract This paper describes the design and fabrication of a distributed MEMS transmission line (DMTL), used to realize a transmission-line with a voltage-variable electrical length for microwave circuits. The DMTL is a coplanar waveguide periodically loaded with continuously-variable MEMS capacitors. A tunable bandpass filter was designed and fabricated on 700 ,m thick glass substrates using three capacitively coupled DMTL sections as variable shunt resonators. The measured results demonstrate a 3.8% tuning range at 20 GHz with 3.6 dB minimum insertion loss. Issues for future improvement are discussed. © 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE 11: 254,260, 2001. [source] Analysis and modeling of microstrip-to-coplanar flip chip package interconnectsINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 4 2001Hussein H. M. Ghouz Abstract In this paper, the discontinuity of a flip chip transition between a microstrip line and a coplanar waveguide is investigated and modeled using the finite-difference time-domain method (FDTD) to predict the overall S -parameters of the package. Effects of the bump and via interconnects on the package performance are investigated and discussed. This includes the effects of different staggered transitions and ground connects on the package performance. A reduction of about 10 dB in the bump and via reflections can be achieved by staggering the signal (bump) and the ground connects (bump/via). A staggering distance of about twice the slot width gave minimum reflection over a wide band of frequencies. Moreover, the larger the relative distance between the ground and the center connects the less the reflection due to the discontinuity. Finally, the computed S -parameters of the flip chip package using the FDTD solution are used to develop an equivalent circuit model for the transition discontinuity over a wide frequency band. The equivalent circuit model of the microstrip to coplanar waveguide discontinuity includes more elements and is more complex than other types of transitions. A TEE or PI circuit model has been used to approximate the general circuit model of the discontinuity. Good agreement has been obtained between the S -parameters of the FDTD model and the equivalent circuit models over a wide frequency band. © 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE 11: 202,211, 2001. [source] Numerical analysis of sleeve monopole in parallel-plate waveguideINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 2 2001Zhi Ning Chen Abstract A monopole with double sleeves, which consists of a resonant loading and a conventional sleeve monopole, is experimentally investigated. The loaded monopole is put vertically in a parallel-plate waveguide and driven by a coaxial feeder. The new structure exhibits a remarkably broad impedance bandwidth. In this paper, a modal expansion technique is used to numerically evaluate the impedance characteristics of the monopole by modeling the fields between the plates using cylindrical harmonic functions. A Fourier least-square integration is applied to finding the expansion coefficients by the boundary and continuity conditions. Prior to modeling the proposed sleeve monopole, the developed analysis scheme is examined for its convergence and accuracy. Calculated results are validated by the measurements. For the optimum design at 5.8 Ghz, we investigate the effects of the structure parameters on the impedance characteristics. © 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE 11: 86,98, 2001. [source] Potential Modulated Attenuated Total Reflectance Spectroscopy of Prussian Blue Films on ITOISRAEL JOURNAL OF CHEMISTRY, Issue 3 2006Zeynep Ozkan Araci Potential modulated attenuated total reflectance (PM-ATR) spectroscopy has been employed to study charge transfer processes in Prussian blue (PB) films deposited on indium tin oxide (ITO) electrodes. PM-ATR is a planar waveguide-based spectroelectrochemical technique in which the optical response of an electroactive film is measured as a function of applied potential and modulation frequency. The multiple internal reflection geometry of PM-ATR provides a significant sensitivity advantage over the single external reflectance geometry that has been employed in most prior electroreflectance studies. The apparent electron transfer rate of PB on ITO obtained using PM-ATR was compared to that obtained with conventional cyclic voltammetry; the respective rates, 0.33 ± 0.15 s,1 (n = 3) and 0.71 ± 0.37 s,1 (n = 10), are in good agreement. [source] Early stages of protein crystallization as revealed by emerging optical waveguide technologyJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2008Attia Boudjemline A highly sensitive method for studying the onset of protein crystallization in real time using an optical-waveguide-based technique is reported. Dual polarization interferometry uses light from sensing and reference waveguides to produce an interference pattern, which when the sensing waveguide is immersed in a protein solution supplies information on the thickness and density of any protein adlayer on the sensing waveguide's surface. This technique provides evidence that crystallization proceeds via large protein aggregates but, more strikingly, shows dramatic light loss from the sensing waveguide at a very early stage during crystallization. The technique proves relatively insensitive to the crystallization of small molecules or poorly formed protein crystals and affords a method of distinguishing crystal formation from the formation of other protein aggregates or salt crystals. The experimental setup currently necessitates crystallization using the batch method, and precipitant mixing at high supersaturation is known to introduce a greater variability compared with methods such as vapour diffusion or dialysis, but first results promise to bridge the paucity of real-time methods available to distinguish the onset of protein crystallization from other forms of aggregation. [source] Comparison of fluoride and sapphire optical fibers for Er: YAG laser lithotripsyJOURNAL OF BIOPHOTONICS, Issue 5-6 2010Jinze Qiu Abstract The long-pulse (200,350 ,s) Holmium: YAG (Ho: YAG) laser (, = 2.12 ,m) is used extensively in urology for laser lithotripsy. The long-pulse Erbium: YAG (Er: YAG) laser (, = 2.94 ,m) fragments urinary calculi up to 5 times more efficiently than the Ho: YAG laser, however, no optical fibers are available to transmit efficiently 2.94 ,m laser light for laser lithotripsy. We report results of a study evaluating a fluoride glass fiber to transmit Er: YAG laser light for laser lithotripsy and compare to a sapphire fiber that provides good transmission of Er: YAG light at low irradiance. The fluoride fiber provides superior light transmission efficiency over the sapphire fiber at an Er: YAG wavelength (2.94 ,m). The sapphire fiber provides a more durable and robust delivery waveguide than the fluoride fiber when ablating urinary calculi in contact mode. Results of our study suggest that further development to improve performance of fluoride fibers for laser lithotripsy is warranted. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||||||||||||||||||||||||||