Array Of Holes Research Articles

Enhanced chirality of TDBC based on gap modes of surface plasmons in metal-air hole array structure

Enhanced chirality of TDBC based on gap modes of surface plasmons in metal-air hole array structure

Thermodynamic performance evaluation of an indoor designed solar air heater duct equipped with V-down baffle blocks having racetrack-shaped staggered openings of varying aspect ratio – an experimental study

ABSTRACT 1This paper presents the thermodynamic performance assessment of an indoor-designed solar air heater (SAH) duct with its absorber affixing the racetrack perforated 45o V-down baffle blocks in staggered holes array. The experimentation work encompasses studying the effect of parameters like – the mass flow rate of air () and the hole aspect ratio (w/d) of baffle blocks on the air temperature rise (), the energy (), the exergy () and the thermohydraulic () efficiencies of the duct under turbulent airflow conditions. The open area ratio (Φ), relative roughness height (e/H) and relative roughness pitch (p/e) of the baffle blocks are maintained constant in this study. The result showed drastic improvement in the performance assessing parameters due to ‘w/d‘ affecting the heat transfer and friction characteristics significantly in the duct. Increasing ‘w/d’ at lower airflow rate results in a uniform downfall of ‘’, and ‘’. At an increased flow rate, the energy and exergy efficiencies decrease. The exergy destruction and pressure drop show non-monotonous variations with the hole-aspect ratio. The smallest hole aspect ratio (w/d of 1.04) baffle blocks outperform in all assessment segments providing maximum values as 14.86oC, 96.81%, 17.46% and 93.95%, respectively, for the air temperature rise, the energy, the exergy and the thermohydraulic efficiency.

Intensification of mixing efficiency and reduction of pressure drop in a millimeter scale T-junction mixer optimized by an elliptical array hole structure

Due to the scale effects, reducing the scale of the channel is conducive to improve the mixing efficiency of the fluid in the T-junction mixer. However, directly reducing the scale to improve the mixing efficiency is accompanied by the sharp increase of pressure drop, resulting in a high energy consumption. The hole structures are proposed and compared to enhance the mixing performance and reduce the pressure drop of millimeter scale mixer. The SHS can enhance the mixing efficiency and mixing cost index of 10 mm T-junction mixer to a level comparable to the 1 mm mixer. The optimal E-90A can enhance the mixing efficiency of 10 mm T-junction mixer to a level comparable to the 0.5 mm mixer, and reduce the mixing cost index to 1.4% of the 0.5 mm mixer. The experimental and simulation results indicate that the optimal EAHS structure achieves a high mixing performance and a low pressure drop. All the findings reported provide useful references for intensification of mixing efficiency and reduction of pressure drop in a millimeter scale mixer.

Effect of Window and Hole Pattern Cut-Outs on Design Optimization of 3D Printed Braces.

BackgroundThere are many different Thoracic Lumbar Sacral Orthosis style brace designs available in the market for the correction of scoliosis deformity. Hole cut out patterns, are commonly used in brace designs. These cut-outs may be subdivided into two groups: hole patterns and windows. Hole patterns are an array of holes which are implemented to lighten the weight of a brace and allow for the skin to breathe. Windows provide space for spinal derotation and/or breathing. From an examination of the literature, it appears that a systematic analysis of the effect of these cut-outs on the structural integrity and functionality of the brace has not been undertaken. Furthermore, there is a lack of understanding on the effect of spacing, size and geometry of the cut-outs on the mechanical behavior of the brace.Method of ApproachIn this study, Finite Element Analysis is employed to examine the mechanical response of the brace to these cut-outs. Geometry for the Thoracic Lumbar Sacral Orthosis was obtained by scanning an existing brace using an optical scan and converted into a Computer Aided Design model. A systematic approach was undertaken where cut-out geometry, spacing and size was varied. The deformation and stress in the thickness of the brace was ascertained from the Finite Element Analysis. An appropriate factor of safety for the structural analysis was determined using a standardized approach and used to quantify the structural integrity of the brace due to the cut-out. Various geometries were analyzed for the hole patterns including circle, triangle, diamond, and hexagon. For the window, the geometries considered were circle, trapezoidal and the “bib” geometry.ResultsIt was found that linear hole patterns where the holes are aligned do not provide a desirable structural factor safety. Furthermore, among all the possible geometries, the hexagonal cut-out was the best structurally while reducing the weight of the brace the most. The optimal spacing was found to be 12 mm, and the optimal hole surface area was found to be 78.54 mm2. For the windows in the abdominal area, the “bib” shape provided the best structural integrity and generated the lowest amount of deformation. An increase in the size of this window had a small effect on the stress but an almost negligible effect on the deformation.ConclusionsA hexagonal hole pattern should be used with a spacing of 12 mm and each hole should have a surface area of 78.54 mm2. Windows in the abdominal area should be of “bib” shape. The size of the window cut-outs does not affect the brace stress and deformation significantly. Thus, the size of these windows should be based on the functional aspects of the brace, i.e., the minimum required size needed to permit the patient to breathe comfortably as in the case of the abdominal window or to allow for proper derotation, as in the case of the derotation window.

Better colloidal lithography: Tilt-rotate evaporation overcomes the limits of plasma etching

Colloidal lithography (CL) is a promising method for large-area fabrication of nanohole and nanodot arrays with applications in optical biosensing, separations, and magnetic data storage. However, reducing the diameter of the polystyrene sphere mask by plasma etching unavoidably increases their coefficient of variation (CV) and deforms their shape, thereby limiting the pitch-to-hole-diameter ratio of the resulting nanohole array to less than 3:1 and the minimum hole size to 200 nm with a 10% or better CV. We show that tilt-rotate evaporation colloidal lithography (TRE-CL) breaks the trade-off between hole diameter and polydispersity by leveraging glancing angle evaporation, not plasma etching, to adjust the hole size. TRE-CL allows pitch-to-hole-diameter ratios as high as 7:1 and nanohole diameters down to 60 nm while maintaining a nearly constant CV below 10% and hole circularity above 91%. We transfer these hole arrays into ultrathin Si3N4 films to form nearly-monodisperse microsieves for separation applications. Furthermore, we extend TRE-CL to fabricate adhesion-layer-free plasmonic Au nanodot arrays down to 70 nm in diameter with 10% CV.

Human 2D Crypt Model for Assaying Intestinal Stem Cell Proliferation and Differentiation.

Intestine is a common site of adverse drug effects in clinical trials; thus, improved in vitro models for preclinical screening of pharmaceutical compounds are sought. A planar, self-renewing human intestinal monolayer platform based on primary adult gastrointestinal stem cells, termed the 2D crypt model, has been developed to screen for the effects of various compounds on the intestinal epithelium. The 2D crypt platform is based on a standard 12-well plate format and consists of cell culture inserts with a collagen film overlaying an impermeable film patterned with an array of micron-scale holes. This two-chamber format enables a gradient of growth factors to be applied such that the tissue self-organizes into spatially segregated stem and differentiated cell compartments. The patterned monolayer mimics a gut epithelium in possessing a stem cell niche, migrating proliferative and differentiated cells. Once established, the 2D crypts replicate many aspects of in vivo physiology, including cell migration, maturation, and apoptotic cell death. The planar geometry of the system simplifies dosing, sampling, and imaging during assay. An immunofluorescence-based assay was established to quantitatively assess cell density, proliferation, migration, viability, and the abundance and localization of postmitotic lineages as a function of time. The model was used to perform a small-scale screen of compounds, including signaling molecules, endogenous hormones/cytokines, and microbial metabolites, on tissue homeostasis. Hit compounds that significantly impacted proliferation and/or differentiation were readily identified. The 2D crypt platform represents a significant innovation in the development of microphysiological systems for emulating the gut epithelium for compound screens.

Absorption Enhancement in a Quantum Dot Thz Detector with a Metal-Semiconductor-Metal Structure

The low absorptivity of quantum dot nano-structures cannot meet the requirements for high-performance next-generation Thz detectors which can be used for environmental pollution detection. In this study, a novel metal-semiconductor-metal (MSM) cavity structure with a square hole array instead of a traditional planar metal electrode was developed to improve and enhance the absorptivity of a quantum dot Thz detector. The possible modes and loss problems in the metal resonant cavity were analyzed using the finite-element transmission matrix, the eigenvector method, and Kirchhoff diffraction theory. The results demonstrate that the MSM cavity structure introduced in the detector can enhance absorption up to 8.666 times higher than that of the conventional counterpart.

The Transformation from Surface Wave into Radiation Wave Using Composite Subwavelength Holes Array

Smith–Purcell radiation (SPR) is a phenomenon in that free electrons moving above a periodic structure deliver a part of their kinetic energies to electromagnetic waves. It plays an important role in the development of radiation sources and beam diagnosis. With the development of nanofabrication technology, various complex micro-nano-metallic periodic or aperiodic structures have been adopted to improve the efficiency and coherence of SPR. In general, when free electrons move above the metallic periodic structure, the localized surface wave and Smith–Purcell radiation wave are excited simultaneously. As the frequency of the surface wave is always lower than the threshold of Smith–Purcell radiation, the surface wave cannot be radiated. Here, the surface wave is transformed into SPR by using a novel composite subwavelength hole array, thus the SPR is enhanced and it becomes coherent and easy to tune. This work provides a competitive approach to achieve a coherent and high-efficiency THz radiation source.

Direct observation of significant hot carrier cooling suppression in a two-dimensional silicon phononic crystal

Finding hot carrier cooling suppression in new material structures is fundamentally important for developing promising technological applications. These phenomenona have not been reported for crystalline silicon phononic crystals. Herein, we experimentally design two-dimensional (2D) silicon samples consisting of airy hole arrays in a crystalline silicon matrix. For reference, the determined hot carrier cooling times were 0.45 ps and 0.37 ps, respectively, at probe wavelengths of 1080 nm and 1100 nm. Surprisingly, when the 2D structured silicon possessed the properties of a phononic crystal, significant suppression of hot carrier cooling was observed. In these cases, the observed hot carrier cooling times were as long as 15.9 ps and 10.7 ps at probe wavelengths of 1080 nm and 1100 nm, respectively, indicating prolongation by orders of magnitude. This remarkable enhancement was also observed with other probe wavelengths. The present work presents experimental evidence for hot carrier cooling suppression in 2D silicon phononic crystals and opens opportunities for promising applications.

Magnetospectroscopy of terahertz surface plasmons in subwavelength perforated superlattice thin-films

Surface plasmons, the resonant oscillations of conducting electrons at the interface of negative and positive permittivity materials, pave the way for enhanced electromagnetic wave–matter interactions at a subwavelength scale. On the other hand, spin-dependent magnetotransport ushers an ingenious technology by inculcating electron spin to realize miniaturized, energy-efficient electromagnetic devices. Generally, magneto-resistive devices (viz., multilayer un-patterned magnetic–non-magnetic thin films) relying on magnetotransport mechanisms are not recognized for supporting surface plasmons toward enhanced electromagnetic interactions. However, an amalgamation of surface plasmons with spin-dependent magnetotransport can exploit magnetic (spintronic) degree of freedom in plasmonic devices. In this work, we propose a patterned superlattice (non-magnetic/ferromagnetic thin films) terahertz (THz) magneto-resistive device for supporting surface plasmons toward enhanced electromagnetic interactions. Magnetotransport dependent enhancement and dynamic magnetic modulation of resonant THz transmissions are experimentally demonstrated in subwavelength superlattice (Al/Ni) hole arrays for varying lattice parameters. Our experiments reveal that typical non-magnetic electromagnetic phenomena like surface plasmon resonances can be tweaked by externally applied low intensity magnetic fields [∼few tens of milli-tesla (0–30 mT)]. Experimental outcomes are explicated by spin-dependent terahertz magnetotransport theory in perforated superlattice metal sheets and, therefore, can stimulate a paragon for spin-based integrated photonic technology.

Quantitative assessment of a beam hole scatter correction in industrial computed tomography

Abstract In industrial Computed Tomography (CT), scattered radiation causes a loss of quality of the reconstructed 3D volume. Scatter is caused by photon-matter interaction, whereby a photon is deflected from its initial propagation direction. The most prominent contributor to scattered radiation in the scope of photon energies occurring in industrial CT is Compton Scattering. With the used Beam Hole Array (BHA) technology for scatter correction, scatter intensities are determined by subtracting the primary intensities, which are gathered behind small apertures from the total intensities, which are gathered in the absence of the apertures. Intensities measured behind the apertures are assumed to be scatter free, since the transversal components of the radiation are strongly reduced. The scatter correction is performed by subtracting scatter intensities from primary intensities in the projection image. Improvements are evaluated for a newly developed test specimen considering image quality metrics and dimensional accuracy. The contrast could be improved especially for small structures. Cupping artifacts that express as systematic offset of grey values rising with the penetration length were reduced. Measurement deviations towards tactile references were decreased.

Multiport Routing of Topologically Optical Transport Based on Merging of Valley-Dependent Edge States and Second-Order Corner States

Topological photonics provide a novel platform to robustly manipulate the flow of light and design high-performance nanophotonic devices. To do this, a fundamental mechanism is the flexible control of optical transport based on topological boundary states on edges or corners. In this work, we design a multiport device to route the topologically optical transport by using both valley-dependent edge states (VDESs) and second-order corner states (SOCSs). The VDESs are derived from sublattice symmetry breaking in a honeycomb lattice, while SOCSs are induced by the lattice deformation of Kagome lattice. In terms of unit cell, we find that both configurations can be reconsidered as the same triangular-lattice photonic crystal, which consists of a hexagon-profile air hole array in silicon background. Therefore, a four-port device is designed based on the two configurations. In simulation, we observe the frequency-dependent routing effect of the topologically optical transport by merging of VDESs and SOCSs. This work not only shows a novel platform to explore various topological phases in the photonic system but also provides guidance in the development of topological photonic integrated circuits with mode division multiplexing.

Preparation of Ordered Nanohole Arrays with High Aspect Ratios by Anodization of Prepatterned 304 Stainless Steel

A nanohole array structure with a regular array of cylindrical holes of a high aspect ratio with a period of 63 nm can be obtained by anodizing 304 stainless steel with a concave pattern. It was shown that matching the concave period to the anodization voltage is important to achieving the fabrication of nanohole arrays with a high aspect ratio. This is because the interhole distance of anodic porous oxide obtained by the anodization of 304 stainless steel in ethylene glycol containing 0.1 M ammonium fluoride depends on the anodization voltage. By optimizing the fabrication conditions, it was possible to fabricate highly ordered nanohole arrays with aspect ratios exceeding 100. The nanohole arrays obtained in this study are promising as key materials for fabricating various functional devices.

Microfabrication of sealable microcell array with ultrathin metal-graphene membrane

A significant challenge in quasi-two dimensional (2D) materials applications is the fabrication of large, suspended layers. This issue is particularly critical when the fabrication of closed cells is required, for example in in-operando x-ray photoemission spectroscopy (XPS) or transmission electron microscopy (TEM), or the design of Golay cell-like detectors. In the quasi-totality of working protocols, the 2D layer transfer is performed in a liquid environment, and the large surface tension forces that are developed during the drying steps often result in the layer damage. This effect becomes dramatic when the fabrication of sealed cells is required. Here we propose an alternative route that involves the sealing in a two-step process, with, first, the fabrication of a large and suspended membrane and then a sealing step performed with the help of a microfabricated self-aligned sealing cork. As a 2D suspended membrane, we choose an ultrathin membrane of single-layer Graphene coupled with a 7.5 nm thick film of evaporated titanium which was transferred over a large array of micrometric holes fabricated on a 30 μm thick silicon membrane. As a cork, we used a silicone structure obtained by pouring liquid silicone in a microfabricated silicon well. The throughput of the whole fabrication process was assessed either by electronic or optical microscopy, to obtain the total yield of integer cells, and by generating a pressure difference within each cell to test the sealing efficiency. A fabrication and sealing yield larger than 95% on arrays as large as 10 mm 2 were demonstrated. • Micro- and nano-meter scale sealed cells are an emerging field for XPS and TEM imaging in-operando. • Graphene and other 2D materials are being studied as suspended membranes for cells sealing. • The freestanding area is limited by defects and the grain size of the 2D crystalline materials. • Graphene-metal nanomembrane and secondary sealing were used to create arrays of sealed cells over more than 10 mm 2 .

Passive control of 3D adaptive shock control bumps using a sealed cavity

This paper presents a Fluid–Structure-Interaction study of a novel passive adaptive shock control bump concept. A flexible plate, clamped on all sides and placed above a sealed cavity, was tested beneath a Mach 1.4 normal shock in the Imperial College London supersonic wind tunnel. The plate was actuated into the shape of a 3D shock control bump by passively controlling the cavity pressure through an array of breather holes. Preliminary experiments were performed with active control of cavity pressure (via a vacuum tank) at Mach 1.4 and 2 to illustrate the potential of this concept. Full-field surface measurement techniques, namely photogrammetry and pressure sensitive paint, were employed in addition to static pressure tappings and schlieren photography. Results confirmed that cavity pressure plays a key role in determining the aerostructural behaviour of the flexible plate. In addition, it was found that carefully placed breather holes allowed the plate to deform into a 3D shock control bump when a shock was on the flexible region and remain flat otherwise. This shows significant potential for improving the off-design behaviour of adaptive shock control bumps.

Simultaneously achieving narrowband and broadband light absorption enhancement in monolayer graphene

We study theoretically how to simultaneously achieve narrowband and broadband light absorption enhancement of monolayer graphene, which is placed on a metallic substrate surface with a periodic array of small holes. By a couple model of double resonances, the narrowband and broadband absorption peaks of monolayer graphene are proven to stem from the hybrid modes of delocalized surface plasmon polartions propagating on the substrate surface and localized magnetic plasmons confined within individual holes. The positions, maxima, and bandwidths of the absorption peaks can be tuned conveniently through changing the hole array period. For an optimized period, the maximum absorption values at the narrowband and broadband peaks are able to reach up to 65% and 85%, respectively. The bandwidth of the narrowband absorption peak can be reduced to only several nanometers, and the bandwidth of the broadband absorption peak can be expanded to tens of nanometers. Our work will be helpful to design graphene-based photoelectric nanodevices whose optical responses are in the visible and near-infrared regions.

Design of thermal lens phononic nanostructure to generate tunable hotspots using quasi-ballistic phonon transport

The direction of the quasi-ballistic thermal flow propagation can be guided using the direct passages between the holes in silicon phononic nanostructures. By designing a radial array of holes where the direct passages converge at the same focal point, we obtain a quasi-ballistic thermal lens nanostructure that creates a hotspot with an ellipse shape away from the holes. We conduct a systematic study of the intensity and size of the hotspot by varying the geometrical features of the thermal lens nanostructure such as the neck size, the number of guiding rows, the diameter of the first row of holes, and the number of direct passages. Our Monte Carlo simulations show a complex interplay between the geometry of the thermal lens nanostructure and hotspot properties through a competition between the guiding effect and the thermal resistance. These results provide guidelines for designing thermal lens nanostructures capable of generating on-demand hotspot properties and shed new light on the possibility of manipulating the quasi-ballistic thermal flow.

Reconfigurable switching between reflecting/absorbing modes in VO2 assisted graphene-coated hemispherical dielectric hole arrays

In this paper, a graphene-coated dielectric hole array is used to design a reconfigurable switchable optical reflector/absorber device. The design benefits from the collective excitation of localized surface plasmon resonances of graphene-coated hole array, providing simpler fabrication fellow and more compact structure with respect to graphene-coated spherical nanoparticle array with similar plasmonic behavior. Geometrical parametric study of the reflecting mode shows that the device has lots of degrees of freedom for spectrum tuning and can highly tolerate fabrication imperfections. Moreover, the reflection rate is slightly affected by the dielectric substrate height, which can be tuned to achieve strong absorption by backing it with a metallic mirror. The designed absorber efficiently captures a wide range of obliquely incident transverse electric (TE) and transverse magnetic (TM) waves. Also, the operating frequency of both reflecting and absorbing modes can be tuned after fabrication, thanks to the two-dimensional nature of graphene material. Finally, using vanadium dioxide (VO2) phase change material, the switchable reflector\\absorber mode of the device is also exhibited.

Quasi-three-dimensional nanopost array integrated Type-II superlattice photodetectors for infrared multispectral filtering

Angle-insensitive and high-transmission infrared spectral filters, comprising periodic quasi-three-dimensional (quasi-3D) nanopost arrays, are fabricated using a nanoimprint lithography technique and directly integrated onto an InAs/GaSb type-II superlattice (T2SL) photodetector. Simulation results of the plasmonic filters reveal that the transmission peak wavelength is linearly adjusted by tuning the filter period as a result of the propagated and localized surface plasmon resonances of the quasi-3D nanopost array structure. Additionally, the transmission peak wavelength of the array structure is measured to increase with decreasing nanopost height owing to stronger field coupling between the Au hole and disk arrays. A tunable bandpass filtering function of the quasi-3D nanopost-integrated T2SL photodetector is successfully demonstrated with narrow bandwidths in the spectral range of 2–6 μm. Our findings offer a significant potential for a scalable low-cost manufacturing method of compact snapshot multispectral infrared imagers for portable-field imaging or airborne-platform-based imaging applications.

Li-Ion Permeability of Holey Graphene in Solid State Batteries: A Particle Dynamics Study.

Lithium (Li)-ion permeability of holey graphene (hG) for use as an electrically conducting scaffold in solid-state battery electrodes is explored through the means of a particle dynamics simulation model. While carbon materials do not typically exhibit Li-ion conductivity, the unique structural motif of hG, which consists of two-dimensional nanosheets with arrays of through-thickness holes, may present an opportunity for Li-ion conductors (i.e., solid electrolyte (SE) particles) to make contacts through the holes. In our model, the SE is presented as a system of hard elastic spheres conductive to Li-ions. The SE spheres are in contact with each other through compression between two plane current collectors. One hG layer is inserted between the current collectors and parallel to them. Randomly distributed circular holes in the hG allow for contact between the SE particles on both sides of the hG layer. By solving the Li-ion conducting network formed between the electrodes through the contact points of all the particles, the overall conductivity of the system was calculated as a function of SE particle size and the size and number of the hG holes (i.e., hG porosity). A critical ratio of around 4 between the SE particle size and the pore size was found. Below this critical value, the hG layer becomes practically transparent for Li-ions. This study helps to guide the design of highly efficient solid-state electrode composition and architectures using hG as a unique electrically conducting scaffold.