Array Of Grooves Research Articles

Phase Transforming Based on Asymmetric Spoof Surface Plasmon Polariton for Endfire Antenna With Sum and Difference Beams

An endfire antenna with sum and difference beams is designed based on phase transforming of a proposed asymmetric spoof surface plasmon polariton (SSPP) structure. The asymmetric arrays of grooves, with different groove depths, periods, and/or duty ratios, serve as transmission structure and transmit electromagnetic (EM) waves in SSPP modes. Due to the distinct phase constants for the EM fields on the two sides of the asymmetric structures, the transformation of phase difference for the EM waves is realized. Superposition in the endfire direction for the in-phase and out-of-phase EM fields forms the endfire radiations with sum and difference beams. A design procedure is proposed where operating frequencies of the endfire antenna are predicted with the dispersion curves of the asymmetric SSPP structures and allocated by phase transformation. A prototype is implemented to validate the proposed design principle. Sum beam operating frequencies of the endfire antenna are at 5.50, 6.60, and 7.09 GHz, while difference beams appear at 6.10 and 6.90 GHz. Good agreement of the results validates the feasibility of the proposed mechanism and design procedure. The proposed endfire antenna with sum and difference beams has broad prospect in direction finding, tracking, and anti-interference applications.

Directional Droplet Transport Mediated by Circular Groove Arrays. Part I: Experimental Findings.

Directional transport of liquid droplets is crucial for various applications including water harvesting, anti-icing, and condensation heat transfer. Here, bouncing of water droplets with patterned superhydrophobic surfaces composed of circular equidistant grooves was studied. The directional transport of droplets toward the pole of the grooves was observed. The impact of the Weber number, initial polar distance r, and geometrical parameters of the surface on the directional droplet bouncing was experimentally explored. The nature of bouncing was switched when the Weber numbers exceeded We ≅ 20-25. The rebouncing height was slightly dependent on the initial polar coordinate of the impact point for a fixed We, whereas it grew for We > 20. The weak dependence of the droplet spreading time on the Weber number was close to the dependence predicted by the Hertz bouncing, thus evidencing the negligible influence of viscosity in the process. Change in the scaling exponent describing the dependence of the normalized spreading time on the Weber number was registered for We ≅ 25. The universal dependence of the offset distance ΔL of the droplets on the Weber number ΔL/D0 ∼ We1.5 was established. The normalized offset distance decreased with the normalized initial polar distance as ΔL/D0 ∼ (r/S)-1, where D0 and S are the droplet diameter and groove width, respectively. This research may yield more insights into droplet bouncing on patterned surfaces and offer more options in directed droplet transportation.

Thermally Controllable Infrared Absorption in Cylindrical Groove Array Covered by Phase Change Material

A perfect infrared spectrum absorber in a cylindrical groove array perforated in a metallic layer and followed by vanadium dioxide (VO2), a phase-change material, is introduced and analytically investigated. The phase-change material can change from insulator to metallic phase if proper stimuli, such as heat, voltage, and current, are applied, herein the phase change initiated by heating beyond the phase-transition temperature of VO2. The large refractive index variations between two phases enable the manipulation of optical properties. Simulation results reveal that in the metallic phase, the absorption is suppressed to one third, while VO2 works as a transparent medium for impinging light, and perfect absorption is observed in the insulation phase. The process is reversible in a picosecond time scale. Given the structure symmetry, the absorption is irreverent to impinging light polarization. The thermally controlled infrared absorber may have applications in various optical systems, like imaging and sensing, due to its simple and easy fabrication process.

Study of disordered metallic groove arrays with a one-mode analytical model.

Sub-wavelength metallic grooves behave as Fabry-Perot nanocavities able to resonantly enhance the absorption of light as well as the intensity of the electromagnetic field. Here, with a one-mode analytical model, we investigate the effect of a correlated disorder on 1D groove arrays i.e., randomly shaped and positioned grooves on a metallic layer. We show that a jitter-based disorder leads to a redistribution of energy compared to the periodic case. In an extreme case, a periodic diffracting array can be converted into a highly scattering array (98% at λ = 2.8 µm with a 1 µm full width at half maximum). Eventually, we show that the optical response of combinations of variously shaped grooves can be well described by the individual sub-set behaviors.

Effect of different micro-texture shape on corrosion resistance of metal surface

The 304 stainless steel is widely used in daily life. In this paper, the 304 stainless steel was taken as the substrate material and then the five different micro texture shapes were carved on them by nanosecond laser engraving machine under the same parameters. These shapes are the groove array, the square column array, the circular pit array, the regular hexagon column array and the trapezoid column array. Then these samples were immersed in 0.5mol/l perfluorodecyl trimethoxysilane ethanol solution at 45 °C for 5 hours. Five type super-hydrophobic surfaces were obtained. A series of corrosion experiments were conducted out and the influence of different micro texture on the corrosion resistance to the 304 stainless steel surface was analyzed. The results show that the square column array has the best corrosion resistance, and its corrosion rate is4.20mm.a−1, which is the lowest in all other micro texture shapes. It can be used as a reference for improving the corrosion resistance of metal surface.

Absorption enhancement by a period array of nano-grooves in gold substrate.

Comprehensive investigations of absorption enhancement by a period array of nano-grooves in gold substrate are provided. A simple Fabry-Perot model is presented to explore impact factors on absorption enhancement. The impacts of structural parameters on absorption enhancement for an array of nano-grooves are explored and discussed. Our calculations show that complete absorption (about 1) can be obtained with the groove depth fulfilling the Fabry-Perot resonance condition. The effect of groove width on absorption for a trapezoidal groove array is slightly different from that for a rectangular groove array, because of the impact of single-pass loss in the grooves. Surface plasmon resonance that can carry most of the energy away from grooves and propagate along the metal surface could lead to extremely low absorption for a period array of nano-grooves. Our discussions identify two key roles in absorption enhancement for a nano-groove array: the fundamental groove mode resonance and the generation of surface plasma polaritons. In addition, the analysis of absorption enhancement for an array of trapezoidal grooves can also provide a comprehensive contribution of Fabry-Perot resonance and electromagnetic interaction along the bevel edges of the trapezoidal grooves.

Water assisted pulsed laser machining of micro-structured surface on CVD diamond coating tools

In this paper, a water assisted pulsed laser machining with mist spray was investigated for machining the micro-structures on chemical vapor deposition (CVD) diamond coating tools. Firstly, the effect of water assisted condition on the machining quality and the transformation of Gauusian laser beam was analyzed. The theoretical calculation method of the shifted value of laser beam spot radius and defocusing quantity in the water assisted laser machining was presented. And then the effects of laser machining parameters included the laser power, the scanning speed, the scanning times and the scanning pitch were discussed in view of the ablation width, ablation depth, material removal rate and machined surface topography. Finally, three kind of micro-structures included micro groove array and cross-scale composite micro-structures were machined successfully on the CVD diamond coating tools by the developed water assisted pulsed laser machining method.

Ultra-multiband terahertz perfect absorber via a metal groove structure

An ultra-multiband terahertz absorber formed by a periodic metallic groove array filled with high-dielectric-constant material is presented. Simulation results show that since multiple Fabry–Pérot cavity modes are excited in the metal groove, the absorber can obtain 15 narrow-band absorption peaks with an average absorptivity over 99.5% at normal incidence. At oblique incidence, all absorption bands still maintain the high absorption above 90% for angles up to 50°. Due to its structural symmetry, the absorber is polarization insensitive. The frequencies and number of the absorption bands can be controlled by turning the depth of the metal groove. In addition, the proposed absorber can be operated as a highly sensitive refractive index sensor. Such an ultra-multiband, polarization-insensitive, and wide-angle absorber structure can be applied in terahertz-related absorption filters, biochemical sensors, or thermal images.

Producing anomalous uniform periodic nanostructures on Cr thin films by femtosecond laser irradiation in vacuum.

We report on producing unprecedentedly uniform periodic structures on chromium thin films in vacuum conditions with irradiation of femtosecond laser pulses. In sharp contrast to the observations in air, the achieved surface structures of the ablated groove arrays are surprisingly found to have not only an extraordinarily uniform distribution but also a deep-subwavelength period of 360 nm. The measured both width and depth of the ablated periodic grooves are 150 and 120 nm, respectively, showing a large depth-to-width ratio and sharp-edge profiles. Remarkably, such well-organized nanostructures can be enabled to robustly extend into an infinitely long range via the sample scanning and even have a large-area production with a cylindrical lens. Raman spectral analyses reveal that the regular formation of such nanostructures benefits from avoiding the material oxidation and thermal disturbance of the air plasma on the sample surface.

Fluorescent paper-based sensor based on carbon dots for detection of folic acid.

Paper-based devices have been very much in the foreground of analytical science recently. This work innovatively proposed a fluorescent paper-based sensor (FPS) constructed on a hybrid polydimethylsiloxane (PDMS)/paper platform where cellulose papers functionalized with carbon dots (CDs) as fluorophores by Schiff base chemistry were loaded on the grooves array of a designed PDMS plate. As a proof of concept, the performance of FPS was investigated with folic acid (FA) as the target analyte. Under optimal conditions, FPS enabled a rapid fluorescence quenching response to FA via inner filter effect in a wide range of 1-300μmolL-1 with the limit of detection of 0.28μmolL-1. The feasibility of FPS was further verified by the detection of FA in orange juice and urine samples with satisfactory results. The covalent modification of CDs on paper endowed the FPS with good assay reproducibility and stability. Interestingly, FPS achieved a more sensitive assay of FA than the conventional strategy, by which the same CDs were directly used to detect FA in a solution-based system. The FPS illuminated a novel strategy for construction of reliable and sensitive assays based on paper-based devices. It is of paramount importance for its practical application in biosensing and clinical diagnosis. Graphical abstract.

Broadband liquid sensing with a spoof plasmon transmission line

One of the most remarkable features of surface plasmon polaritons (SPPs) is their usefulness for sensing. In this paper, we introduce a spoof SPP sensor consisting of a transmission line with a rectangular groove array. We investigated its dispersion relation and verified the broadband transmission characteristics of its SPP mode. A sensing model with spoof SPPs has been developed and a prototype fabricated. Three analytes with different permittivity were introduced into the model and prototype — edible oil, glycerol, and water — and the results compared to those obtained with air. The results of simulation and measurement show that the sensor is extremely sensitive to the permittivity of a liquid. The results indicate that spoof SPP sensors have important potential applications in industrial processing, food safety, and environmental monitoring.

Broadband Frequency Scanning Spoof Surface Plasmon Polariton Design with Highly Confined Endfire Radiations

This paper proposes a compact broadband frequency scanning spoof surface plasmon polariton (SSPP) based design for efficient endfire radiations with high field confinement. Through the dispersion engineering, highly confined field distribution has been obtained in the operating frequency region. The proposed SSPP antenna has achieved a continuous through endfire scanning in the X-band at other operating frequencies which is in general difficult to obtain for SSPP based antennas. In the proposed design methodology, the swore-shaped surface plasmon antenna has both edges corrugated with an array of rectangular grooves which effectively confines the electromagnetic field into a slow travelling wave. The surface impedances along both edges were engineered to be different at operating frequencies as to force the surface current to preferentially flow along either edge of the antenna to a different extent. The design with overall dimensions of (55 × 30) mm2 has achieved a broadband of 4 GHz with high peak measured gain of 9.8 dBi and peak efficiency of about 95 percent in the X-band. The antenna has been further tested experimentally for scanning application of target location also.

Use of a spoof plasmon to optimize the coupling of infrared radiation to Josephson-junction fluxon oscillations

We show that Infrared radiation impinging onto a 1-d array of grooves drilled in the superconductor electrode of a long overlap junction can improve matching between fluxon oscillations at THz frequencies and a spoof plasmon of comparable wavelength. This example proves that metamaterials can be very helpful in integrating superconductive and subwavelength optical circuits with optimized matching bridging the gap between infrared and microwave radiation.

Approximate impedance models for point-to-point sound propagation over acoustically-hard ground containing rectangular grooves.

A modal model for diffraction by a contiguous array of rectangular grooves in an acoustically-hard plane is extended to predict the free space acoustic field from a point source above such a structure. Subsequently, an approximate effective impedance model for grooved surfaces is presented. Measurements have shown that these ground surfaces can be used for outdoor noise reduction but accurate modelling has required the use of computationally expensive numerical methods. The extended modal model and approximate impedance model inspired by it yield equivalent results in a fraction of the time taken by the boundary element method, for example, and could be used when designing grooved surfaces to reduce noise from road traffic.

Investigation of Enhanced Transmission and Beaming Effect Through an InSb Subwavelength Grating With a Slit at the Terahertz Range

In this paper, we demonstrate the feasibility of realizing the extraordinary optical transmission (EOT) and the collimated beaming effect through InSb grating, which has a subwavelength slit surrounded by a finite array of grooves at both sides of the surface. Firstly, we investigate the transmission properties of the structure by changing the temperature and doping concentration of InSb, and the optimized transmission can reach almost 95%. Besides, it is verified that the transmission is mainly controlled by the pattern on the input corrugation with the variable dimension parameters. At last, the properties of the beaming intensity and focal length are thoroughly analyzed with the variation of the number and depth of the grooves on the output corrugation. These results provide a new plasmonic solution for controlling light in a variety of integrated optical components in the terahertz range.

Fretting friction properties of laser surface texture microfilaments

PurposeThis paper aims to improve the wear resistance of metal rubber microfilaments and the service life. The effect of surface texture by laser processing on the fretting friction properties of metal rubber microfilaments was studied.Design/methodology/approachThe LQL-F20A laser marking machine was used to fabricate a ring groove array with equal spacing and dense arrangement on the surface of metal rubber microfilaments. The test was carried out with a self-made micro-dynamic frictional tester. The topography of the microfilaments was observed by scanning electron microscopy and analyzed.FindingsIt has shown that laser surface texturing can improve the wear performance of microfilaments. Under the same experimental conditions, the microfilaments of textured surface has a smaller depth of wear than un-textured specimen. The wear resistance increases with the increase of texture density. The friction coefficient of textured specimen is significantly reduced compared with un-textured specimen, and the surface texture density of microfilaments has little influence on the friction coefficient after stabilization. In the stage of stable fretting wear, the wear depth will be more with the increase of the load.Originality/valueThere is little research on metal rubber microfilaments tribological properties. In this paper, the effect of laser texturing of microfilaments on micro-dynamic friction properties was studied by friction machine to provide a reference for the application of metal rubber in aerospace, medical and other fields.

Coupling of plasmon and grating resonances for SERS enhancement

We used thermal poling structuring of glass samples followed by chemical etching and subsequent out-diffusion growth of silver nanoparticles to fabricate periodic arrays of grooves etched in the glass with silver nanoparticles at their bottom. A numerical modeling of optical properties of these periodic structures was performed. We demonstrated that they support both plasmon and grating resonances, which interaction provides additional enhancement of an incident electric field. This can increase surface-enhanced Raman scattering by such biresonant structure.

Picosecond laser texturing on titanium alloy for biomedical implants in cell proliferation and vascularization.

Introducing specific textures to titanium alloy implant surface is helpful to modify the surface properties of materials. In this article, biomedical TC4 (Ti-6Al-4V) alloy was textured by a 10-ps infrared laser. Laser parameters that directly affected the detailed dimension of textures and its characteristics were optimized within laser power, defocusing amount, and scanning parameters via response surface methodology. These textures consisted of groove array about 30-90 μm in depth and 100 μm in width were prepared and their surface property (including surface morphology, element composition, wetting behavior, and biocompatibility) was analyzed. Surface characteristic analysis indicated that picosecond laser texturing improved surface properties and biocompatibility mainly by altering the microstructure and morphology of materials. In addition, laser textured groove array promoted contact area and hydrophobicity of material surface. Cell culture experiments and animal studies showed that titanium alloy implants with 30- and 60-μm-deep groove arrays on the surface-enhanced cell proliferation and adhesion. Meanwhile, compared to the polished samples, these groove arrays promoted the growth of new blood vessels and enhanced the combination of blood vessel and implants in vivo. That is, the deeper groove array was, and the better vascularizing effect the blood vessel exhibited.

Spin-wave excitations in YIG films grown on corrugated substrates

Yttrium-iron garnet (YIG) film was deposited by ion-beam sputtering on gadolinium gallium garnet (GGG) substrate with the periodical array of grooves ion-etched in its surface. Spin-wave excitations in the fabricated structure were studied by the ferromagnetic resonance (FMR) method and by the spin-wave spectroscopy. Results were compared with ones for the YIG film deposited on GGG substrate without the periodical relief.

Dual-Band Infrared Perfect Absorber Based on a Ag-Dielectric-Ag Multilayer Films with Nanoring Grooves Arrays

In this paper, we demonstrate a dual-band metamaterial perfect absorber based on a Ag-dielectric-Ag multilayer nanostructure. The structure of top metal film covers nanoring grooves array. A dielectric layer has a function of confining electromagnetic fields. Theoretical analysis shows that two absorption peaks (1059 nm and 1304 nm) with the absorption of 99.2% and 99.9% have been achieved, respectively. The physical origin of perfect absorption peaks are related to the Fabry-Perot resonance effect and localized surface plasmon resonance (LSPR) of the nanoring grooves. Its perfect absorption and resonance wavelength can be well regulated by adjusting the relevant structural parameters. Additionally, the absorber demonstrates good operation angle-polarization-tolerance at wide incident angles (0–60°). We believe that our design has a promising application in plasmon-enhanced photovoltaic, optical absorption switching, and modulator optical communications in the infrared regime.