Metal Disk Research Articles

Electrochemical Biosensors with Cross-Linked Hydrogels

Leland C. Clark Jr. and Champ Lyons introduced in 1962 the principle of the first electrochemical biosensor with immobilized glucose oxidase (GOx) [1]. This device was specifically designed and used for fast glucose analysis in blood samples from diabetics. Since then, the biosensor field has experienced important growth. In last few decades, this field has been widely explored in many different environments, such as clinical, biotechnological, food and pharmaceutical. This type of device is object of attention because it allows analysis with high specificity, sensitivity, selectivity and low response time.A key parameter for the proper functioning of electrochemical biosensors is the enzyme immobilization onto the electrochemical interface [2]. Immobilization must be performed in a way that the selected enzyme maintains either structure and spatial orientation. In addition, substrate and product have to be able to diffuse to/from the active site, where the biological reaction takes place. One of the simplest and cost effective immobilization method is the polymer entrapment using natural origin polysaccharides. In that frame, chitosan is currently receiving a great deal of interest because of its intrinsic properties: biocompatible, biodegradable, high abundance, low cost of production and it easily forms hydrogels. However, the poor stability of the hydrogel is of major concern [3] when used as an immobilization strategy in the construction of electrochemical biosensors, since it affects the biosensor lifespan.In the present work, amperometric glucose biosensors based on glucose oxidase (GOx) immobilization onto highly ordered titanium dioxide nanotube arrays (TiO2NTAs) was used to determine the long term stability of the constructed probes. TiO2NTAs were grown by electrochemical anodization of a titanium metal disc in ethylene glycol containing ammonium fluoride (0.3%w/w) and water (2%w/w). The electrochemical synthesis was performed at 30 V for 17 hours. This anodization time yields the maximum sensitivity of the sensor. Higher times result in the nanotube walls collapse. Finally, a thermal annealing was performed at 500 ⁰C for 3 h in air to crystallize TiO2 nanotubes from amorphous to anatase phase.In the sensor architecture chitosan was used as a base material for enzyme immobilization in the hydrogel matrix: Ti/TiO2NTAs/GOx–Chitosan. In order to increase the stability of the immobilization matrix, different crosslinking agents were evaluated onto the chitosan matrix: glutaraldehyde, hypochlorous acid and poly(ethylene glycol) diacrylate. Non-modified chitosan provided a biosensor lifespan around 30 days. In contrast, the used of modified chitosan either increases the long-term stability even the sensitivity of the biosensor.

Ti/TiO2ntas/RuO2 Probe for Amperometric Detection of Hypochlorite in Solution

Tool to help provide a healthy environment. Disinfection is a process that is designed to kill actively growing and vegetative microbial microorganisms to a certain level. Generally, there are two methods of disinfection: chemical and physical1. The physical agents of disinfection that have been used include ultraviolet light (UV), electron beam, gamma-ray irradiation, sonication, and heat. Considering the chemical methods, there is a great variety of compounds such as chlorine, ozone, the metals copper and silver, phenolic compounds, quaternary ammonium salts, alcohols and hydrogen peroxide among others. Historically, the most widely used chemical disinfection procedure is chlorination because of its low cost, ease of application, and ability to inactivate a wide variety of pathogenic microorganisms.Hypochlorite ion (ClO-) is widely used in daily life applications such as household bleach, disinfection of drinking water and cooling-water treatment among others. Nevertheless, it has been reported that the abnormal production or the excessive intake of ClO- can lead to numerous diseases, including cardiovascular disorders, neuron degeneration, arthritis or even cancer2. Hence, it is of utmost importance to develop rapid and sensitive methods for the determination of ClO-. So far, iodometric titration and colorimetric methods based on the reaction of ClO- with organic reagents have been widely used so as to determine hypochlorite concentration. These methodologies usually require tedious procedures.In the present work, we propose the design of an amperometric sensor for fast hypochlorite analysis. The architecture of the sensor is a RuO2 coating onto a highly ordered titanium dioxide nanotube array (Ti/TiO2NTAs/RuO2). TiO2NTAs were grown by electrochemical anodization of a titanium metal disc in ethylene glycol containing ammonium fluoride (0.3%w/w) and water (2%w/w). The electrochemical synthesis was performed at 30V. Afterwards, RuO2 was deposited layer by layer onto the TiO2NTAs substrate and a final annealing process was performed at 500 oC in order to fix it to the nanostructure.The fundamental analytical parameters (linear range, limit of detection and sensitivity) of the probe were characterized in the presence of hypochlorite. The sensor working potential was also optimized and then fixed at 0.6 V. Finally, the hypochlorite content of different samples was measured using the sensor and compared with the DPD-method value (Standard Methods: 4500-Cl G)3. The proposed amperometric sensor offers an alternative tool to the classical DPD-method, with higher sensitivity, lower limit of quantification and analysis time.

Tribological characterization of a bearing coated with UHMWPE/GNPs nanocomposite coating

ABSTRACT Polymer nanocomposite coatings with low friction and high wear resistance are being developed to protect aluminium surfaces against wear and tear during dry and boundary lubrication. In the present study, pure and graphene nanoplatelets (GNPs) reinforced ultra-high molecular weight polyethylene (UHMWPE) nanocomposite coatings are deposited on aluminium thrust bearings. Each bearing makes an ROD contact with a metallic disc counterface to simulate the contact configuration in an actual bearing. A set of tests involving pure and reinforced UHMWPE coatings under dry and liquid contact lubrication is conducted. The wear test results reveal that UHMWPE/1 wt-% GNPs performs better than the reference sample significantly. It reduces the friction and wear of aluminium both in the dry and boundary lubrication conditions at different conditions. The 1 wt-% GNPs reinforcement increases the load-bearing capacity of UHMWPE by 440% in the presence of base oil.

Calculating loads and life-time reduction of wind turbine gearbox and generator bearings due to shaft misalignment

During the last two decades, wind turbine industries have faced high failure rates, downtimes and costly repairs. Gearbox and generator have contributed to this, especially, because their high speed shaft bearings have often failed. In this article, an analytical method is proposed to calculate the reaction loads of flexible connecting couplings installed between wind turbine gearbox and generator. Raction loads are determined from joint kinematics and metal disk pack deformations as well as axial and angular shaft misalignment. The calculations are executed for both flexible connecting couplings and a universal joint shaft and applied to the gearbox high speed shaft. The performance of flexible connecting couplings and universal joint shaft is compared with respect to the bearing loads and life-time of the gearbox high speed shaft. It is shown that the early, unplanned bearing failures of gearbox and generator high speed shaft can often be attributed to the flexible connecting couplings installed between gearbox and generator.

Coupling between plasmonic and photonic crystal modes in suspended three-dimensional meta-films.

A complementary metal oxide semiconductor (CMOS) compatible fabrication method for creating three-dimensional (3D) meta-films is presented. In contrast to metasurfaces, meta-films possess structural variation throughout the thickness of the film and can possess a sub-wavelength scale structure in all three dimensions. Here we use this approach to create 2D arrays of cubic silicon nitride unit cells with plasmonic inclusions of elliptical metallic disks in horizontal and vertical orientations with lateral array-dimensions on the order of millimeters. Fourier transform infrared (FTIR) spectroscopy is used to measure the infrared transmission of meta-films with either horizontally or vertically oriented ellipses with varying eccentricity. Shape effects due to the ellipse eccentricity, as well as localized surface plasmon resonance (LSPR) effects due to the effective plasmonic wavelength are observed in the scattering response. The structures were modeled using rigorous coupled wave analysis (RCWA), finite difference time domain (Lumerical), and frequency domain finite element (COMSOL). The silicon nitride support structure possesses a complex in-plane photonic crystal slab band structure due to the periodicity of the unit cells. We show that adjustments to the physical dimensions of the ellipses can be used to control the coupling to this band structure. The horizontally oriented ellipses show narrow, distinct plasmonic resonances while the vertically oriented ellipses possess broader resonances, with lower overall transmission amplitude for a given ellipse geometry. We attribute this difference in resonance behavior to retardation effects. The ability to couple photonic slab modes with plasmonic inclusions enables a richer space of optical functionality for design of metamaterial-inspired optical components.

Infrared localized surface plasmon dark multipole modes generated on subwavelength corrugated metal disks

Terahertz (THz) radiation is very promising for chemical and biological sensing. One of the ways to realize a THz sensor is exciting multipole localized surface plasmon resonances (LSPRs) on subwavelength corrugated metal disks. In this paper, numerical modeling and analysis of LSPRs on a periodic array of such structures were made. At normal incidence of the incoming wave, only dipole resonances can be excited. An additional C-shaped resonator placed in the vicinity of the disk produces dark multipole modes (quadrupole, hexapole, octupole, and decapole ones) due to hybridization of these modes with the brigth dipole mode of the C resonator. Besides, multipole modes can be excited at oblique illumination of the structure. With increase in the incident angle, the multipole resonances become stronger. The high Q-factor resonance modes observed for PEC disks are wider or disappeared in case of Drude gold permittivity.

Unveiling breathing plasmon modes in aluminum metal–insulator–metal cavities by cathodoluminescence

Aluminum (Al) processes excellent plasmon response from the ultraviolet (UV) to visible spectrum. Understanding of the deep sub-wavelength plasmon response of Al nanostructures is essential for the Al-based plasmon device design, such as UV surface-enhanced resonance Raman scattering and emission control of emitters. In this work, by using cathodoluminescence, the plasmonic properties of Al metal–insulator–metal (MIM) disk nanocavities are investigated. The resonant breathing modes rather than edge modes are resolved by the CL spectra and real-space mode patterns, which are in good agreement with the electromagnetic calculations. Moreover, the dispersion behavior of plasmon modes of the MIM cavity can be traced back to the propagating plasmon modes in an Al MIM slab, which shows that the electromagnetic fields are strongly confined in the cavities. Furthermore, a mode volume as small as 1.1 × 105 nm3 is obtained for the 240 nm diameter cavity, demonstrating these MIM resonators to be ideal candidates for studies of strong plasmon-matter interactions.

Investigation on Vibration Response for Misaligned Rotor-Bearing-Flexible Disc Coupling System—Theory and Experiment

AbstractModeling of the dynamic behavior of the rotating system when subject to misaligned shafts is an interesting subject, aiming either the selection of appropriate couplings from early stages of project or the monitoring and model-based diagnosis of such machines. This research is focused on the dynamics of the system when angular misalignment is induced. The methodology to take into account this fault is based on the structural analysis of the flexible coupling, with the consequent use of cyclic restoring forces and moments exerted by this component on the coupled shafts. Structural analysis of metallic disc coupling is conducted by means of the finite element method, in which the flexible disc component is modeled using thin shell formulation. Once misalignments are applied, the cyclic nature of coupling efforts is captured by the application of consecutive shaft spin angles. Steady-state response is simulated and then displacements spectrum are analyzed in order to highlight harmonic components rising due to misalignment. Test rig measurements are performed, and the theoretical model is discussed in terms of locus, frequency response function (FRF), orbit shape, and spectrum information. Disc coupling is regarded, as limited literature in vibration spectrums is available for this type of coupling.

Prediction of thermally induced postbuckling of clutch disks using the finite element method

Buckling and postbuckling of automotive clutch disks can be excited by the temperature fields caused by frictional heat generation during engagement of clutch systems. Linear and nonlinear buckling finite element analyses are performed to evaluate the thermal postbuckling of clutch metal disks. The dominant buckling modes are first obtained through performing linear buckling finite element analysis (FEA) analyses. The scaled displacement fields obtained from the linear buckling FEA analyses are added to the original geometries to generate the perturbed meshes. The postbuckling is then investigated by performing nonlinear buckling FEA analyses. The commercial FEA software ABAQUS is used in the current study. The effects of the temperature-dependent material properties are studied. It is concluded that the temperature dependence of material properties affects the postbuckling behaviors significantly.

Determining the tribological properties of different 3D printing filaments

The paper aims to determine the friction coefficient and wear behaviour of different 3D filaments in contact with a metallic disc. The method used for testing was the pin-on-disc method, where 3D half inch diameter pins with a half sphere end were printed out of the different filaments and rotated on the disc. The optimal time for measuring the friction coefficient was determined by observing when a sudden change in friction was recorded by the sensor as a result of material deposition on the disc. All filaments were tested for the same amount of time using the same normal loads. The friction behaviour was monitored and the mass wear was determined by weighting the spheres before and after each test. The research work of this paper was orientated to determine which 3D printing filament is most suitable for building different parts that come in contact with one another such as parts for creating an innovative 3D printed smart shoes sole.

Interaction between spoof localized surface plasmon and terahertz vortex beam

We theoretically and experimentally investigate a method of exciting multipole plasmons, including terahertz dark spoof localized surface plasmon (Spoof-LSP) modes, by using normally incident terahertz vortex beam. The vortex beam with angular intensity profile and phase singularities, has well-defined angular momentum which can be decomposed into the polarization-state-related spin angular momentum (SAM) for characterizing the spin feature of photon, and the helical-wavefront-related orbital angular momentum (OAM) that is characterized by an integer <inline-formula><tex-math id="Z-20200915102424-1">\begin{document}$ (l) $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20200695_Z-20200915102424-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20200695_Z-20200915102424-1.png"/></alternatives></inline-formula>, called the topological charge. By illuminating terahertz vortex beam on the metallic disk with periodic subwavelength grooves normally, we find that the terahertz dark multipole plasmons can be excited by the terahertz vortex beam carrying different OAM and SAM. We analyze the correspondence between the spin and orbital angular momentum of vortex beam and the excited dark multipolar plasmon modes. In the experiment, a terahertz stepped spiral phase plate (SPP) with high transmission and low dispersion based on the Tsurupica olefin polymer is developed and the stepped SPP can generate a terahertz vortex beam having a topological charge of 1. Then, we further study the excitation of dark multipolar Spoof-LSPs by utilizing the stepped SPP in combination with the near-field scanning terahertz microscopy. The collimated terahertz wave, which is radiated from a 100 fs (<i>λ</i> = 780 nm) laser pulse pumped photoconductive antenna emitter, is converted into terahertz circular polarized light (CPL) which can carry SAM by the combination of the quarter wave plate and the polarizer, and then terahertz CPL impinges on the stepped SPP, producing the terahertz vortex beam which can carry OAM. The spatial two-dimensional electric field distribution is collected in steps of 0.02 mm along the <i>x</i>-direction and <i>y</i>-direction by a commercial terahertz near-field probe which is located close (≈ 10 μm) to the one side of polyimide film by three-dimensional electric translation stage and a microscope (FORTUNE TECHPLOGY FT-FH1080). The experimental results are in good agreement with simulations. We believe that our method will open the way for detailed research on the terahertz physics, plasma and imaging fields.

Oscillation and self-propulsion of Leidenfrost droplets enclosed in cylindrical cavities.

Leidenfrost droplets can be considered as soft engines capable of directly transforming heat into mechanical energy. Despite remarkable advancements in understanding the propulsion of Leidenfrost droplets on asymmetric structures, the complex dynamics of droplets in enclosed structures is not fully understood. To address this fundamental gap, we investigated the dynamics of Leidenfrost droplets restricted by metal disks. The disk alters the accumulation and release of the vapour generated by the droplet, and substantially changes its dynamic characteristics. Our experiments reveal the formation of oscillating multi-lobed structures when restricting the droplet within a disk. In comparison, patterning offset radial grooves on the surface of the disk rectifies the vapour flow and facilitates the self-propulsion of the droplet along the edge of the disk. Our work offers opportunities for developing soft and short-living actuators, which can operate at high temperatures.

Simulation modelling of dynamic processes due discontinuous frictional treatment of the flat surfaces

Friction treatment refers to surface strengthening (hardening) methods using highly concentrated energy sources. In the course of this processing in the surface layers of the processed surfaces of parts the strengthened layer with nanocrystalline structure is formed. The formed layer has specific physical, mechanical, chemical properties, as well as improved performance properties, which are significantly different from the base metal. A highly concentrated energy source is formed in the contact area of the tool-part due to the high-speed friction (60–90 m/s) of the tool on the treatment surface. Frictional treatment of flat parts according to the kinematics of the process is similar to grinding. The strengthening process was carried out on an upgraded surface grinder. The tool is a metal disk made of stainless-steel. Transverse grooves are formed on the working surface of the tool to intensify the process of forming a strengthened (reinforced) layer with a nanocrystalline structure. The grooves form additional shock loads in the contact area of the tool-treatment surface of the part. These shock loads increase the shear deformation of the metal of the parts’ surface during treatment, which affects into formation the quality parameters of the parts’ surface and surface layer. To study the friction treatment process, the calculation scheme of the elastic system of the machine was developed. A simulation model for the study of dynamic processes that take place during the friction treatment of flat surfaces was built. This model gives possibility to determine the displacements and velocities of the machine table on which the part is fixed and the tool, and to determine their mutual displacement and also calculate the reaction of the machine table.

Improving Clamping Accuracy of Thin-walled Workpiece in Turning Operation

This study presents theoretical and experimental error analysis and avoidance which results from the fixation of a thin-walled metal disk workpiece on a duplex turning machine. The distance between the rotating workpiece surface and a fixed datum point is measured using a laser displacement sensor (LDS). The measured data are analyzed numerically to get the error in the fixation system in terms of Euler angles. Then the workpiece clamping points are axially adjusted according to the calculated angles. Moreover, the problem formulation and the solution procedures are presented in details. Finally, a case study has been used to verify the proposed approach. The results indicate that the proposed technique can be used to decrease the fixation error to a reasonable range.

A Fano-Reflection Metafilm Composed of Metamaterial-Lined Discs

This work presents a compact metafilm, which provides frequency-selective reflection and is based on subwavelength metallic discs lined using μ -negative and near-zero (MNNZ) metamaterial liners. It is shown that such particles undergo resonance at sizes of λ/7 or smaller and exhibit interesting transmission/reflection behaviour. It is further demonstrated that when an array of these resonators is illuminated using a normally or obliquely incident plane wave, a Fano-shape reflection profile is obtained, exhibiting a high degree of reflection at resonance followed by strong transmission. These resonators may be closely packed since the resonance mechanism does not rely on diffraction effects. We present simulation data and experimental results demonstrating 98.4% (18-dB) decreased transmission at resonance using a polarization-insensitive compact metafilm measuring 1.7λ by 2.3λ, as well as near-transparency at other frequencies. This novel unit cell provides compact solutions for applications such as switching owing to its miniaturized size and Fano-shape reflection response.

Darkfield colors from multi-periodic arrays of gap plasmon resonators

Abstract We present results on colors of metal disk arrays viewed under a darkfield microscope and show that the darkfield colors can be manipulated independently of the brightfield colors. We investigate the appearance of colors as disks are clustered to form a new array with double the pitch and a basis of four disks. These structures of aluminum disks on aluminum oxide on aluminum have resonances in the visible spectrum, so by arranging them in small tight clusters, a coupled plasmon resonant mode is produced at shorter wavelengths. This feature causes a reflectance minimum and leads to an increase in the gamut of darkfield colors produced. These colors are tuned by changing the size of the disk and the inter-disk gap within the clusters. Interestingly, the intensities of the reflectance peaks also demonstrate good agreement with the Fourier series coefficients for square waves. Polarization-tunable colors are also demonstrated by designing rectangular arrays that have dissimilar periods along the two orthogonal axes of the array, and a four-level security tag is fabricated that encodes images for viewing under brightfield, darkfield (both x and y polarization), and infrared illumination.

Identificadores de cota de malla califales. Un nuevo ejemplar

El trabajo está dedicado a una nueva pequeña chapa circular de metal con inscripción incisa en árabe. Aporta la lectura y traducción de su texto y sitúa el objeto en un grupo especial dentro de la metalística medieval islámica. Es el quinto ejemplo que se conoce. Eran piezas que iban sujetas a cotas de malla del ejército cordobés con la función de identificarlas para reintegrarlas al arsenal después de que fueran usadas. Es de la época del califato de Hiša–m II.

Stochastic resonance via parametric adaptation: Experiments and numerics.

In contrast with the conventionally observed mechanism of stochastic resonance (SR) wherein the level of additive noise is systematically varied with a fixed set-point parameter, in this work we report the emergence of the SR phenomena in an electrochemical system maintaining the same level of noise and varying the parametric distance from a homoclinic bifurcation inherent to the system. The experimental system involves the corrosion of a metal disk in an acidic medium under potentiostatic conditions. The applied potential is used as a control parameter and the anodic current generated during the electrodissolution of the metal is the accessible system variable. In the presence of noise, it was observed that the system was able to enhance its output's fidelity with a weak subthreshold input signal when the set point was kept at an optimal parametric distance from the bifurcation. Numerical simulations were performed on a model for this system to corroborate the experimental observations. This type of SR may be critical in scenarios where a biological entity has control only on its sensory parameters and not on the environmental noise amplitude.

Dual-band isotropic metamaterial absorber based on near-field interaction in the Ku band

We numerically and experimentally investigate single-band and dual-band isotropic metamaterial absorbers (IMAs) based on metallic disks. By optimizing the diameter of the metallic disks and the thickness of the dielectric substrate, the single-band IMA is observed at 16.2 GHz with absorptivity of 97%. When adding one disk-pair to the structure, the dual-band IMA is obtained at 12.8 and 15.5 GHz due to the symmetry breaking. The physical mechanics is explained by near-field coupling effect and equivalent LC circuit model. The measurement results performed in the range 12–18 GHz show a good agreement with simulation and theoretical analysis. Our findings demonstrate a new approach to achieve dual-band and multi-band IMAs.

Plasmons in Infinite 2D Electron System Screened by the Disk-Shaped Metallic Gate

We have examined the plasmon modes in infinite two-dimensional (2D) electron system (ES) with the finite-sized gate formed by a metallic disk over a 2D electron plane. Heretofore, such a problem has never been analytically considered. We have predicted that discrete plasmon modes exist in such a partly-gated system even though no voltage was applied to the gate. The plasmon spectrum has been characterized by the radial and azimuthal mode numbers. We used an analytical approach recently developed for the gate in the form of a metallic stripe [A.A. Zabolotnykh and V.A. Volkov, Phys. Rev. B 99, 165304 (2019)]. Under several reasonable assumptions, we analytically find plasmon frequencies and charge density distributions.