Grid Pitch Research Articles

Enhancement of critical heat flux with additive-manufactured heat-transfer surface

In-Vessel Retention (IVR) is a key technology to retain the molten core in the reactor vessel during severe accidents of Pressurized-water reactors (PWRs). In order to gain the safety margin of IVR, it is crucial to enhance the critical heat flux (CHF) of the reactor vessel, which is submerged in a water pool. To enhance the CHF, we have designed and additive-manufactured porous grid plates with a 3-D printer for design flexibility. We measured the CHF for the porous grid plate on the boiling heat transfer surface and found that the CHF was enhanced by 50 % more than that of the bare surface. The CHF enhanced more with a narrower grid pitch and a lower grid height. The visual observation study revealed that the vapor film was formed at the bottom of the grid plate.

Ka-band phased array antenna with waveguide power distributor

Known designs of Ka-band phased array antennas incorporate an optical feed or a radial waveguide feed. Significant disadvantage of an optical feed is microwave energy overflow through antenna aperture, which decreases aperture efficiency and increases a side lobe level. Optical feed requires additional space for feeding antenna location and increases overall antenna dimensions. The design of a phased array with a radial waveguide feed forces placement of the phase shifter control circuits outside the dimensions of the array and increases overall antenna dimensions. The purpose of the article is to design a Ka-band phased antenna array (PAA) with a waveguide feed with smallest overall dimensions and various aperture shapes. The manufactured prototype of PAA with a grid pitch of 6x6 mm and size of 300x40 mm showed acceptable results of the side lobe level, scanning sector ±45° and gain factor. Proposed Ka-band phased array antenna design allows one to construct the extremely compact radar of various types including airborne radars.

A simulation study to evaluate the effect of 2D antiscatter grid primary transmission on flat panel detector based CBCT image quality

Abstact Purpose. Two-dimensional antiscatter grids’ (2D-ASGs) septal shadows and their impact on primary transmission play a critical role in cone-beam computed tomography (CBCT) image noise and artifact characteristics. Therefore, a numerical simulation platform was developed to evaluate the effect of 2D-ASG’s primary transmission on image quality, as a function of grid geometry and CBCT system properties. Methods. To study the effect of 2D-ASG’s septal shadows on primary transmission and CBCT image quality, two new methods were introduced; one to simulate projection signal gradients in septal shadows, and the other to simulate septal shadow variations due to gantry flex. Signal gradients in septal shadows were simulated by generating a system point spread function that was directly extracted from projection images of 2D-ASG prototypes in experiments. Variations in septal shadows due to gantry flex were simulated by generating oversampled shadow profiles extracted from experiments. Subsequently, the effect of 2D-ASG’s septal shadows on primary transmission and image quality was evaluated. Results. For an apparent septal thickness of 0.15 mm, the primary transmission of 2D-ASG varied between 72%–90% for grid pitches 1–3 mm. In low-contrast phantoms, the effect of 2D-ASG’s radiopaque footprint on information loss was subtle. At high spatial frequencies, information loss manifested itself as undersampling artifacts, however, its impact on image quality is subtle when compared to quantum noise. Effects of additive electronic noise and gantry flex induced ring artifacts on image quality varied as a function of grid pitch and septal thickness. Such artifacts were substantially less in lower resolution images. Conclusion. The proposed simulation platform allowed successful evaluation of CBCT image quality variations as a function of 2D-ASG primary transmission properties and CBCT system characteristics. This platform can be potentially used for optimizing 2D-ASG design properties based on the imaging task and properties of the CBCT system.

High Performance Transparent Silver Grid Electrodes for Organic Photovoltaics Fabricated by Selective Metal Condensation.

We report silver grid electrodes on glass and flexible plastic substrates with performance that exceeds that of commercial indium-tin oxide (ITO) coated glass and show their suitability as a drop-in replacement for ITO glass in solution processed organic photovoltaics (OPVs). When supported on flexible plastic substrates these electrodes are stable towards repeated bending through a small radius of curvature over tens of thousands of cycles. The grid electrodes are fabricated by the unconventional approach of condensation coefficient modulation using a perfluorinated polymer shown to be far superior to the other compounds used for this purpose to date. The very narrow line-width and small grid pitch that can be achieved also opens the door to the possibility of using grid electrodes in OPVs without a conducting PEDOT:PSS layer to span the gaps between grid-lines. This article is protected by copyright. All rights reserved.

Minimization of image lag in polycrystalline mercuric iodide converters through incorporation of Frisch grid structures for digital breast tomosynthesis

Objective. Polycrystalline mercuric iodide photoconductive converters fabricated using particle-in-binder techniques (PIB HgI2) provide significantly more detected charge per x-ray interaction than from a-Se and CsI:Tl converters commonly used with active matrix flat-panel imagers (AMFPIs). This enhanced sensitivity makes PIB HgI2 an interesting candidate for applications involving low x-ray exposures—since the relatively high levels of additive electronic noise exhibited by AMFPIs incorporating a-Se and CsI:Tl reduce detective quantum efficiency (DQE) performance under such conditions. A theoretical study is reported on an approach for addressing a major challenge impeding practical use of PIB HgI2 converters—the high lag exhibited by the material (over 10%) which would lead to undesirable image artifacts in applications involving acquisition of consecutive images such as digital breast tomosynthesis. Approach. Charge transport modeling accounting for the trapping and release of holes (thought to be the primary contributor to lag) was used to examine signal properties, including lag, of pillar-supported Frisch grids embedded in the photoconductor for 100 μm pitch AMFPI pixels. Performance was examined as a function of electrode voltage, grid pitch (center-to-center distance between neighboring grid wires) and the ratio of grid wire width to grid pitch. Main results. Optimum grid designs maximizing suppression of signal generated by hole transport, without significantly affecting the total signal due to electron and hole transport, were identified and MTF was determined. For the most favorable designs, additional modeling was used to determine DQE. The results indicate that, through judicious choice of grid design and operational conditions, first frame lag can be significantly reduced to below 1%—less than the low levels exhibited by a-Se. DQE performance is shown to be largely maintained as exposure decreases—which should help to maintain good image quality. Significance. Substantial reduction of lag in PIB HgI2 converters via incorporation of Frisch grids has been demonstrated through modeling.

Selective laser ablation preparation of Ag grid transparent electrodes with fractal-combined structures and optimization of fractal grid pitch

New fractal-structured patterns with different grid period combinations were designed and applied to Ag grid transparent electrodes (TEs). Based on the principle of decreasing or increasing Ag grid line densities in local areas, the optical transmittance or electrical conductivity of the resulting Ag grid TEs could be selectively enhanced, thus effectively improving its comprehensive performance. Fractal-combined Ag grid TEs with different combined periods were firstly prepared by selective laser ablation of sputtered Ag films, and compared with the corresponding regular periodic Ag grid TEs to determine the optimal combined periods. The results indicated that the combined periods of 4 and 9 enabled the Ag grid TE to have a relatively high figure of merit of 4.92 × 10–2 Ω−1. This optimal fractal-combined Ag grid TE was chosen to optimize grid pitch for further comprehensive performance improvement. Using a large grid pitch of 1.1 mm could achieve the best trade-off between optical transmittance and electrical conductivity, and produced the best comprehensive performance with the maximum figure of merit of 5.17 × 10–2 Ω−1. The fractal-combined structure provides a unique scheme for flexibly designing and preparing grid patterns in metal TEs.

Stereo sampling moiré method for three-dimensional deformation mapping with a stereomicroscope.

Three-dimensional (3D) deformation distribution measurement is of great interest in applications of materials evaluation. In this study, we propose a stereo sampling moiré method for full-field 3D deformation measurement based on a stereomicroscope. From the phase analysis on the left and right image planes as well as the relationship between displacements in the world and image coordinate systems, the 3D displacements and the in-plane strains of the specimen can be acquired. We also propose a method to calibrate the microscope convergence angle using the grid pitch variation. The validation experiment shows that the difference between the out-of-plane displacement measured by the proposed method and the movement of the sample stage is less than 0.2 µm. The microscopic 3D displacements and the in-plane strain distributions of a carbon fiber reinforced plastic specimen in a three-point bending test are investigated.

Fabrication and performances of silver grid transparent conducting films and heaters on glass and PET substrates based on fractal periodic grid pattern design

A metal grid transparent conducting film (TCF) requires an excellent trade-off between optical transparency and electrical conductivity, both of which are affected by grid patterns and parameters. In this work, the fractal geometry was introduced to design fractal periodic grid patterns, which were employed to fabricate fractal periodic Ag grid TCFs with different grid periods, pitches and thicknesses on glass substrates by magnetron sputtering Ag films and laser localized removal. By comparing with the corresponding conventional periodic Ag grid, the fractal periodic Ag grid was confirmed to enable a significant improvement in trade-off between optical transparency and electrical conductivity, and thus excellently improving the comprehensive properties of the TCFs. The optimal fractal periodic Ag grid TCF achieved a figure of merit of 15.04 × 10–2 Ω–1, which was higher than that of the optimal conventional periodic Ag grid TCF (11.38 × 10–2 Ω–1). In addition, transparent heaters were prepared by using the optimal fractal periodic Ag grid TCFs on glass and flexible PET substrates, and showed excellent heating performances, good performance stability and deicing availability. This work provides a simple and extendable method for tailoring optical transmittance and electrical conductivity to fabricate high-performance TCFs.

Chebyshev Alternance when Approximating Initial Conditions of the Inverse Cauchy Problem

Purpose of research. The work is devoted to a range of questions related to Cauchy problem on the segment of real axis with the application of the inverse Cauchy problem, in which real constants are initial conditions which are optimally restored according to experimental or tabular values of the solution of the differential equation. The object of the study is an information-measuring system, in which approximate values of initial conditions are calculated from discrete function values of Cauchy problem solving.Methods. The following problems are solved for this purpose: parameters of measuring section placement on the investigated object and approximation grid on measuring section are developed. Characteristics of recovery accuracy of initial conditions of the task are formulated.Results. An experimental-calculated method of determining initial conditions in the inverse Cauchy problem is proposed. It is based on the concept of objective function of regularization of the problem. Task regularization parameter in the form of minimum value by Lebesgue function is proposed.Conclusion. The reaction of uniformly approximating method of the initial conditions of the inverse Cauchy problem to the deviation of the approximation grid coordinates nodes from the coordinates of Chebyshev alternance was described. Graphs of method reaction to deviation of grid pitch from optimal pitch are given.

Numerical simulations of gas explosion using Porosity Distributed Resistance approach Part −1: Validation against small-scale experiments

A new model, PDRFOAM, has been developed for the prediction of gas explosions in congested plant. It uses the PDR approach to model the effect of small-scale obstacles, e.g., pipes and vessels on flame propagation and on explosion overpressure. While the effects of large obstacles i.e., that is the large scales are explicitly resolved. The equations for mass, momentum, enthalpy and Favre-averaged regress variable are solved. In addition, porosity modified standard k-ε turbulence model and the transport equations for the flame wrinkling parameter are solved. The model PDRFOAM, is built as a new application in OpenFOAM, suite of models. OpenFOAM is an open-source CFD package of routines for solution of systems of partial differential equations.In addition, to the PDRFOAM model, the CADPDR program was developed which generates various fields (volume blockage, area blockages, surface area, sub-grid drag and turbulence generation parameters) needed by PDRFOAM. CADPDR needs as input obstacle files that list coordinates and dimension of the obstacles e.g. pipes and vessels. The PDRFOAM code solves porosity-modified momentum and continuity equations with sub-grid source terms. The combustion model in PDRFOAM is based on flame area transport. The turbulent burning velocity correlation used is based on Markstein and Karlowitz number. Flame area generation due to the folding of the flame around obstacles is explicitly modelled.This paper presents the formulation of PDRFOAM and validation of the PDRFOAM code against three series of small- and medium-scale experiments i.e., ERGOS, MERGE and Buxton S-Series experiments. A total of more than 150 experiments were used for validation which includes variation in blockage ratio, grid pitch, size of the congested region, equivalence ratio, confinement, partial fill, obstacle diameter, different obstacle shapes and three different fuels. The model is compared against flame position, flame speed as a function of time and maximum overpressure obtained from experiments. Simulations predict the experimental trends of increase in overpressure with increase in blockage ratio, laminar burning velocity, partial fill of the gas cloud, size of the congested region, confinement, grid pitch and obstacle diameter. It also predicts the trends of increase in overpressure with increase in equivalence ratio, variation of maximum overpressure with ignition location, change in obstacle shape and obstacle configuration. The maximum overpressure predicted by simulations (see Fig. 1) is in general within the uncertainty of a factor of two.

Theoretical investigation of the signal performance of HgI2 x-ray converters incorporating a Frisch grid structure at mammographic energies

Active matrix, flat-panel imagers (AMFPIs) suffer from decreased detective quantum efficiency under conditions of low dose per image frame (such as for digital breast tomosynthesis, fluoroscopy and cone-beam CT) due to low signal compared to the additive electronic noise. One way to address this challenge is to introduce a high-gain x-ray converter called particle-in-binder mercuric iodide (PIB HgI2) which exhibits 3–10 times higher x-ray sensitivity compared to that of a-Se and CsI:Tl converters employed in commercial AMFPI systems. However, a remaining challenge for practical implementation of PIB HgI2 is the high level of image lag, which is believed to largely originate from the trapping of holes. Towards addressing this challenge, this paper reports a theoretical investigation of the use of a Frisch grid structure embedded in the converter to suppress hole signal—which would be expected to reduce image lag. The grid acts as a third electrode sandwiched between a continuous top electrode and pixelated bottom electrodes having a 100 μm pitch. Signal properties of such a detector are investigated as a function of VDR (the ratio of the voltage difference between the electrodes in the region below the grid to that above the grid), grid pitch (the center-to-center distance between two neighboring grid wires) and R GRID (the ratio of grid wire width to grid pitch) for mammographic x-ray energies. The results show that smaller grid pitch suppresses hole signal to a higher degree (up to ∼96%) while a larger gap between grid wires and higher VDR provide minimally impeded electron transport. Examination of the tradeoff between maximizing electron signal and minimizing hole signal indicates that a grid design having a grid pitch of 20 μm with R GRID of 50% and 65% provides hole signal suppression of ∼93% and ∼95% for VDR of 1 and 3, respectively.

Study of the possibility of using strapdown inertial gauges as part of the topographic location and navigation system of own design

Problem statement. During the operation of purchased navigation systems for topographic geodetic referencing and orientation, many shortcomings are revealed, mainly associated with software implementation, the correction of which is not always possible. A way out of this situation is creating own navigation complex from ready-made purchased meters and developed functional software (FSW). In this case, the primary task is to determine the preferable meters as part of the topographic location and navigation system (TLNS).Objective. Conduct a study of strapdown inertial navigation systems (SINS) of various manufacturers for compliance with the declared technical characteristics to determine a suitable meter for TLNS.Results. Information on the practical testing of studies the numerical estimates of standard deviations (SD) of errors in the determination and drift of grid azimuth, roll, and pitch of strapdown inertial meters in various climatic conditions, as well as under the influence of sinusoidal and broadband random vibrations (BRV) is presented. The values deviations of motion parameters from the reference values in autonomous mode as part of the developed navigation complex of mobile land objects of a particular purpose are analyzed. The preferable inertial meter for use in the developed TLNS was determined based on the research carried out.Practical implications. Recommendations are given on the use of SINS as an integral part at the facilities of the proposed base.

High-Performance Transparent Copper Grid Electrodes Fabricated by Microcontact Lithography for Organic Photovoltaics

We report high-performance transparent copper grid electrodes on glass and plastic substrates that offer a higher Haacke figure-of-merit than conventional indium tin oxide electrodes and are well-matched to the requirements for organic photovoltaics (OPVs). The electrode is fabricated using microcontact lithography with a combination of molecular resist and low toxicity etchant, namely, hexadecanethiol and aqueous ammonium persulfate. This approach to electrode fabrication is much faster than conventional lithography because it takes 20 times narrower than is possible using conventional metal printing methods and so a grid pitch <30 μm is easily achieved without increasing metal coverage. The very small grid-line spacing relaxes the requirement to use highly conductive films to span the gaps between grid lines, reducing parasitic absorption losses. This is demonstrated using an extremely thin (10 nm) poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) layer. Additionally, we present evidence that it is not always necessarily to embed the metal grid into the substrate or to planarize with a charge-transport layer, to avoid leakage current across the OPV device.

Second-order moiré method for accurate deformation measurement with a large field of view.

In this study, we propose a second-order moiré method by performing digital sampling at two stages to realize high-accuracy deformation measurement in a wide field of view, where a grid image is recorded at a low magnification. Simulations have verified that this method has high strain measurement accuracy when the grid pitch is close to or even smaller than two pixels for both parallel and oblique grids with random noise. As an application, the two-dimensional microscale strain distributions of a carbon fiber reinforced plastic specimen when the grid pitch was about 2.1 pixels were presented. Shear strain concentration was detected before an interlaminar crack emerged, and tensile strain concentration was found prior to the occurrence of a transverse crack. The proposed method makes the two-step phase-shifting technique achieved indirectly, not only enlarging the field of view, but also maintaining the measurement accuracy.

Effect of grid geometry on the transmission properties of 2D grids for flat detectors in CBCT

To suppress scatter in cone beam computed tomography (CBCT), two-dimensional antiscatter grids (2D grid) have been recently proposed. In this work, we developed several grid prototypes with higher grid ratios and smaller grid pitches than previous designs, and quantified their primary and scatter transmission properties in the context of CBCT for radiation therapy.Three focused 2D grid prototypes were developed with grid ratios at 12 and 16, and grid pitches at 2 and 3 mm. Their scatter transmission properties were measured between 80–140 kVp, and benchmarked against a high performance radiographic grid (1D grid) using a Varian TrueBeam CBCT system. The effect of source–grid misalignment on the primary transmission and the improvement in contrast-to-noise ratio (CNR) were also evaluated.Changing the grid pitch from two to three mm increased the average primary transmission from 84% to 89%. Maximum scatter-to-primary ratio (SPR) with grid ratio of 12 was 0.3, and increasing the grid ratio to 16 reduced SPR by 30%. A 10 mm misalignment in 2D grid position led to a 6%–8% reduction in average primary transmission, and reduction was more pronounced for the higher grid ratio. 2D grids provided up to factor of seven lower SPR and 21% better primary transmission than the 1D grid, and their scatter transmission exhibited lower energy dependence. While 2D grids provided up to factor of 2.3 higher CNR improvement, a significant variation in CNR improvement was not observed among different grid pitch and ratios.In summary, grid ratio of 16 and grid pitch of 2 mm can keep SPRs below 0.2 even in high scatter conditions, while keeping primary transmission fractions above 80%, key benefits of the investigated 2D grids in improving image quality of CBCT. However, such grids require precise alignment in source-grid geometry during CBCT acquisitions. This study also implies that 2D grids can provide substantially better scatter suppression and primary transmission than high-performance 1D grids currently available.

Analysis of grid size and ion temperature effects in retarding field energy analyzers (RFEA)

The self-potential of a high current ion beam may be fairly balanced by a secondary plasma with plasma potential Vp; the retarding field energy analyzer (RFEA) measuring the secondary ion outflow is a promising diagnostic of these plasmas. A detailed analysis of a planar RFEA is here discussed, with a focus on the response (in stationary condition) of the detector to the secondary plasma characteristics, and on the determination of design rules for the parameters of a compact RFEA. First, energy distributions of the secondary ion plasma outflow are discussed, as a function of ion temperature Ti and electron temperature Te. Second, the modulation of grid potential (depending on grid pitch b and wire radius a) is calculated both for 2D and 3D models, reaching a good agreement with accompanying electrostatic simulations. Beam emittance (or temperature) growth and beam diffusion are then discussed, also when input ion energy matches the discrimination voltage Vd; corrections to the usual paraxial dynamics result are then introduced. As regards the response of the whole detector (also called transmission function) and the beam dynamics evolution, systematic 3D multiparticle simulations were performed in order to study the behavior of the detector as a function of Vd and of the secondary plasma parameters Vp, Ti and Te and to determine the design parameter effects on instrumental precision (found to be about 0.1 b |Ez| with Ez the axial field near grids).

Application of generalized equations of the method of finite differences to the calculation of continuous orthotropic plates

The paper considers the calculation of continuous orthotropic plates under various boundary conditions. The numerical solution is constructed using generalized equations of the finite difference method (FDM), which allow solving the problem within the integrable domain, taking into account the discontinuities of the required function, its first derivative and the right-hand side of the original differential equation without special reduction of the grid pitch. The differential equation for the equilibrium of orthotropic plates in fourth-order partial derivatives is written as a second-order differential equation with respect to the second partial derivatives of the deflection function, the difference approximation of which follows from the general difference approximation of the partial differential equation. The second difference equation is obtained by considering the compatibility of deformations. The results of the calculation of continuous slabs for hinged support and for rigid jamming are given. The reliability of the calculation was confirmed by comparing the solutions on several grids, performing static and kinematic checks.

Roll-to-roll sputtered and patterned Cu2-x O/Cu/Cu2-x O multilayer grid electrode for flexible smart windows.

We fabricated cost-effective Cu2−xO/Cu/Cu2−xO multilayer grid electrodes using roll-to-roll (RTR) sputtering and patterning processes for use as transparent and flexible electrodes in flexible smart windows. To optimize the patterned Cu2−xO/Cu/Cu2−xO multilayer grid, the electrical and optical properties of the Cu2−xO/Cu/Cu2−xO multilayer grid electrodes were investigated as a function of grid width and pitch, which directly influence the filling factor of the grid. At the optimized grid width of 16 and pitch of 600 μm, the Cu2−xO/Cu/Cu2−xO multilayer grid had a sheet resistance of 7.17 Ohm per square and an optical transmittance of 87.6%. In addition, the mechanical properties of the optimized Cu2−xO/Cu/Cu2−xO multilayer grid electrode was compared to those of brittle ITO electrodes to demonstrate its outstanding flexibility. To show the potential of the Cu2−xO/Cu/Cu2−xO multilayer grid for smart windows, we fabricated a flexible and transparent thin film heater (TFH) and a flexible electrochromic (EC) device, which are key components of smart windows. The low saturation voltage of the Cu2−xO/Cu/Cu2−xO grid-based TFH and the fast on–off performance of the Cu2−xO/Cu/Cu2−xO grid-based EC device indicates that the RTR-processed Cu2−xO/Cu/Cu2−xO multilayer grid is promising as a low-cost and large-area flexible transparent electrode for high-performance smart windows.

Development of simple high-resolution embedded printing for transparent metal grid conductors

We developed a simple embedded printing method that is capable of forming high-resolution patterns for transparent metal grid conductors. The simple printing method involves embedding conductive ink in a groove structure formed by nanoimprinting. Since this printing utilizes capillary force, conductive ink easily fills groove structures with small widths of several microns to the submicron scale. An embedded pattern with a line width of 300 nm was printed. In addition, a high aspect ratio of 3.1 was achieved with a 1.6 μm embedded pattern. A prototype transparent conductive film was developed with excellent optical and electrical performances: a high transmittance of 82.7% and a low sheet resistance of 5.1 Ω/sq at a grid width of 3.0 μm and a grid pitch of 150 μm. The grid parameters can easily be changed by mold design during the nanoimprint process. The transparent conductive film (TCF) showed excellent bending resistance compared with indium tin oxide.

Numerical simulation of the parameters of terahertz polarizers on a silicon substrate

In this study, single- and multilayer polarizers for terahertz radiation from a metal grid on a silicon substrate are analyzed through numerical simulation. Several variants of the polarizer design and the dependences of the polarizer characteristics on its design are obtained. The effects of the grid pitch, number of layers, and their mutual arrangement on the extinction coefficients and losses of the polarizer are numerically analyzed for the first time for choosing the optimal fabrication technology.