Frequency- and time-varying scattering parameters of a photo-excited superconducting microbridge

The extended scattering parameters for linear time varying devices are used to model a high-temperature superconducting (HTS) bridge under time-harmonic optical irradiation. It is shown that this structure acts as a time-varying low-pass filter, which its transfer function characteristic changes periodically with time. This behavior makes this configuration ideal for applications where a time-varying filter is on demand.     

Analysis of photo-excited thin superconducting films for optoelectronic device applications

This paper introduces a steady state photoresponse analysis in superconducting thin films. A model is developed for investigating the capability of superconductors for potential optoelectronic applications. First, we consider the thermodynamical variation under the application of continuous optical radiation in superconducting state. Then, the photo-induced changes in electrical parameters are evaluated from thermodynamical variations using the electrodynamics based on the BCS theory. All variations are considered as a function of optical characteristics along with the material properties. The numerical simulation gives us the optimum range of applied optical frequency and absorbed radiation intensity required for sensitive control of superconducting properties for optoelectronic and microwave applications.     

Superconductive Traveling-Wave Photodetectors: Fundamentals and Optical Propagation

This paper studies the theory of superconductive traveling-wave photodector devices (STWPDs), as a general platform for ultrafast, ultrasensitive, and ultralow-noise optoelectronic functions such as detection, modulation, photomixing, high-frequency electrical signal generation and amplification. Principles of operation of STWPDs are discussed based on the kinetic-inductance theory of superconductive thin films and a thorough investigation of the guiding mechanism of light within this class of devices is presented. The transfer matrix method is introduced to model the superconductive optical waveguide in TWDs and an efficient numerical method based on the Cauchy integral method and the argument principle method are developed for the analysis and design of the waveguides. Moreover, several regimes of device operation will be distinguished in terms of the modal characteristics of the optical waveguide and their effects on the overall performance of the device will be highlighted.     

Polyvinyl alcohol thin film reinforced by green synthesized zirconia nanoparticles

The focus of this work is to prepare polyvinyl alcohol (PVA) thin film reinforced by green synthesized zirconia nanoparticles. In order to do so, firstly, zirconia nanoparticles were synthesized by the rosemary extract-assisted sol-gel process as both template and stabilizing agents. The results showed that the as-obtained sample with zirconium salt to rosemary extract ratio of 1:4 had a semi-spherical morphology with the mean particle size of 12–17?nm. This nanoparticle was added as reinforcement with different ratios to the polyvinyl alcohol matrix. The mechanical property of the as-prepared nanocomposites revealed that the elastic modulus of 1?wt% ZrO2-PVA sample was about 5.5 times higher than pure PVA thin film.     

Triple-layer proton exchange membranes based on chitosan biopolymer with reduced methanol crossover for high-performance direct methanol fuel cells application

A novel triple-layer proton exchange membrane comprising two thin layers of structurally modified chitosan, as methanol barrier layers, both sides coated with Nafion^®105 is prepared and tested for high-performance direct methanol fuel cell applications. A tight adherence is detected between layers from SEM and EDX data for the cross-sectional area of the newly designed membrane, which are attributed to high affinity of opposite charged polyelectrolyte layers. Proton conductivity and methanol permeability measurements show improved transport properties for the multi-layer membrane compared to Nafion^®117 with approximately the same thickness. Moreover, direct methanol fuel cell tests reveal higher open circuit voltage, power density output, and overall fuel cell efficiency for the triple-layer membrane than Nafion^®117, especially at concentrated methanol solutions. A power output of 68.10 mW cm^?2 at 5 M methanol feed is supplied using multi-layer membrane, which is found to be about 72% more than that of for Nafion^®117. In addition, fuel cell efficiency for multi-layer membrane is measured about 19.55% and 18.45% at 1 and 5 M methanol concentrations, respectively. Owing to the ability to provide high power output, significantly reduced methanol crossover, ease of preparation and low cost, the triple-layer membrane under study could be considered as a promising polyelectrolyte for high-performance direct methanol fuel cell applications.     

Green Synthesis of ZnO Nanoparticles and Its Application in the Degradation of Some Dyes

A novel ZnO photocatalyst was synthesized by a green method using lemon juice and zinc acetate as precursors, and then the effect of sucrose addition on the initial precursors was investigated. The samples were characterized by field‐emission scanning electron microscopy, X‐ray diffraction, Fourier transform infrared, UV‐visible, and photoluminescence analysis. The result showed that the as‐obtained products with the mix of lemon juice (30 mL) and sucrose had a spherical morphology with the mean particle size of about 21.5 nm. The photocatalytic activity of this sample was tested for the degradation of methyl orange, methyl red and methylene blue solutions. The results also revealed the good photocatalytic activity for the degradation of these three organic dyes. Furthermore, as‐synthesized sample was used in decolorization processes and the treatment of textile dyes (reactive blue 21).     

Analysis and design of a photoconductive integrated photomixer/antenna for terahertz applications

A new terahertz (THz) photoconductive photomixer/antenna device is presented. A continuous-wave THz signal is generated in a dc-biased photoconductive film by employing optical heterodyne scheme, and at the same time, the size of the film on the grounded dielectric substrate is designed to have an efficient broadside radiation. Incorporating the photoconductive film as the photomixing media and the radiation element not only eliminates source to antenna coupling problem but also makes the proposed device attractive for THz array source configurations. Analytical expressions for the photocurrent and the radiation power are derived under high dc bias condition, and the effects of the device configuration on its performance is studied. Two possible photomixer configurations, namely longitudinal and transversal, are introduced and their photomixing efficiencies and radiation power are compared. The typical nW output power is achievable by mW laser pump power for frequencies up to 10 THz.     

Experimental Investigations on Nonlinear Properties of Superconducting Nanowire Meanderline in RF and Microwave Frequencies

We report our experimental investigations on the radio frequency (RF) and microwave nonlinear behavior of the NbN nanowire meanderline. We construct a lumped element model of the NbN nanowire meanderline, which consists of a kinetic inductance, a normal resistance, and a parasitic capacitance that is a load of a transmission line. Two complementary measurements, which are based on the one-port scattering (S)-parameter technique, are used to explore the nonlinearity in the kinetic inductance and the normal resistance of the NbN nanowire meanderline under dc current and voltage bias conditions. In the first series of experiments, the kinetic inductance has directly been measured from zero up to 99% of the critical current and to the voltage bias, where the hotspot plateau occurs. The Ginsburg-Landau (G-L) theory has been employed to justify the results. The technical procedures required to achieve our desired level of accuracy have been described in detail. In the second series of experiments, the quality factor of the NbN nanowire meanderline has been measured, providing an alternative justification to the first experimental results.