Random Layer Thickness Research Articles

Experimental study and modeling the tensile strength of 3D‐printed aluminium polylactic acid (PLA) parts using artificial neural networks

Background: High quality 3D printed products are in high demand, resulting in an increase in the production of 3D printed parts with precise tolerances, improved surface roughness, and overall durability. The processing parameters of 3D printers have a significant impact on the quality of 3D printed parts. Three-dimensionally printed parts must be durable, especially in terms of tensile strength, and its impact on the printer's process parameters must be investigated. Methods: Tensile test specimens were printed in the Makerbot 3D printer with aluminium polylactic acid (PLA) material. The three controllable input parameters taken into consideration were layer thickness, infill density and number of shells. The three levels for each of the respective parameters were 0.1mm, 0.2mm and 0.3mm for layer thickness; 2,3 and 4 for number of shells; 20% 40% and 60% for Infill density. Tensile testing was carried out on the specimens and data was tabulated. Using these data, an artificial neural network model was created using Matlab R2021b software’s neural network toolbox (alternatively Scilab can be used). Results: A high layer thickness (0.3mm) and a 40% infill density were found to be the most effective among all other parameters. The specimen with the lowest layer thickness of 0.1mm, four shells, and a 20% infill density had the highest tensile strength. With the tensile test data, a Matlab ANN model was developed. Validation was done by comparing the values obtained from the model with the experimental data by using random layer thickness, infill density, and number of shells. Conclusions: In conclusion, higher layer thickness has lower tensile strengths. However, as the number of shells and infill density increases, the tensile strength increases. In summary an ANN model was successfully developed and validated to predict 3D printed aluminium parts.

Design and fabrication of robust broadband extreme ultraviolet multilayers

The robust designs of broadband extreme ultraviolet multilayers based on the multiobjective genetic algorithm are validated experimentally. In order to reduce the influence of random layer thickness fluctuations on the great deformation of the experimental reflection of extreme ultraviolet multilayer with a wide angular band, the multiobjective genetic algorithm has been improved to optimize the multilayer system composed by the layer thicknesses which can be controlled precisely. The robust designs of broadband Mo/Si multilayers were fabricated, and the experimental results were presented and analyzed, and then the advantage of robust multilayer designs was demonstrated.

Double-negative multilayer containing an extrinsic random layer thickness magnetized cold plasma photonic quantum-well defect

Theoretically, the transmission properties of a symmetric double-negative metamaterial one-dimensional photonic crystal containing an extrinsic random layer thickness magnetized cold plasma photonic quantum-well defect structure have been investigated. From the numerical results performed by characteristics matrix method, it is found that, such type of structure possesses a transmission peak within the zero-n¯ gap. To design a tunable microwave filter, the effects of many parameters such as randomness of layer thickness of the multilayer defect in terms of standard deviation (σ), strength of external magnetic field (B) and electron density of magnetized cold plasma (ne) on transmission peak is discussed. Our findings show that the histogram for the central frequency of the transmission peaks becomes wider with respect to smaller values of σ. In addition, in the case of B, our investigations also reveal that the histogram shifts to the higher frequency range and vice versa while considering the case of ne. These findings help to design a tunable filter for different microwave applications.

Scattering of electromagnetic waves from 3D multilayer random rough surfaces based on the second-order small perturbation method: energy conservation, reflectivity, and emissivity.

A theoretical investigation of energy conservation, reflectivity, and emissivity in the scattering of electromagnetic waves from 3D multilayer media with random rough interfaces using the second-order small perturbation method (SPM2) is presented. The approach is based on the extinction theorem and develops integral equations for surface fields in the spectral domain. Using the SPM2, we calculate the scattered and transmitted coherent fields and incoherent fields. Reflected and transmitted powers are then found in the form of 2D integrations over wavenumber in the spectral domain. In the integrand, there is a summation over the spectral densities of each of the rough interfaces with each weighted by a corresponding kernel function. We show in this paper that there exists a "strong" condition of energy conservation in that the kernel functions multiplying the spectral density of each interface obey energy conservation exactly. This means that energy is conserved independent of the roughness spectral densities of the rough surfaces. Results of this strong condition are illustrated numerically for up to 50 rough interfaces without requiring specification of surface roughness properties. Two examples are illustrated. One is a multilayer configuration having weak contrasts between adjacent layers, random layer thicknesses, and randomly generated permittivity profiles. The second example is a photonic crystal of periodically alternating permittivities of larger dielectric contrast. The methodology is applied to study the effect of roughness on the brightness temperatures of the Antarctic ice sheet, which is characterized by layers of ice with permittivity fluctuations in addition to random rough interfaces. The results show that the influence of roughness can significantly increase horizontally polarized thermal emission while leaving vertically polarized emissions relatively unaffected.

Evaluation of Bearing Capacity of Strip Footing Using Random Layers Concept

Abstract The paper deals with evaluation of bearing capacity of strip foundation on random purely cohesive soil. The approach proposed combines random field theory in the form of random layers with classical limit analysis and Monte Carlo simulation. For given realization of random the bearing capacity of strip footing is evaluated by employing the kinematic approach of yield design theory. The results in the form of histograms for both bearing capacity of footing as well as optimal depth of failure mechanism are obtained for different thickness of random layers. For zero and infinite thickness of random layer the values of depth of failure mechanism as well as bearing capacity assessment are derived in a closed form. Finally based on a sequence of Monte Carlo simulations the bearing capacity of strip footing corresponding to a certain probability of failure is estimated. While the mean value of the foundation bearing capacity increases with the thickness of the random layers, the ultimate load corresponding to a certain probability of failure appears to be a decreasing function of random layers thickness.

Disorder in Photonic Structures Induced by Random Layer Thickness

Disorder in Photonic Structures Induced by Random Layer Thickness

Control of the average light transmission in one-dimensional photonic structures by tuning the random layer thickness distribution

In this work we have studied the optical properties of disordered photonic structures, in which we have controlled the distribution of the random layer thickness. Such structures are characterized by the usual alternation of high and low refractive index layers, but the layer thickness follows the aforementioned distribution. We have used two types of distributions: a distribution in which each thickness has the same probability to occur and one in which the thickness follows a Gaussian function. We have simulated the average transmission all over the spectrum for photonic structure characterized by a different width of the distribution. We have found that the choice of the distribution of the layer thickness is a control of the average transmission of a random photonic structure. Photonic structures, fabricated following these distributions, can be interesting for the fabrication of bandpass optical filters.

Constraining complex aquifer geometry with geophysics (2-D ERT and MRS measurements) for stochastic modelling of groundwater flow

Stochastic modelling is a useful way of simulating complex hard-rock aquifers as hydrological properties (permeability, porosity etc.) can be described using random variables with known statistics. However, very few studies have assessed the influence of topological uncertainty (i.e. the variability of thickness of conductive zones in the aquifer), probably because it is not easy to retrieve accurate statistics of the aquifer geometry, especially in hard rock context. In this paper, we assessed the potential of using geophysical surveys to describe the geometry of a hard rock-aquifer in a stochastic modelling framework. The study site was a small experimental watershed in South India, where the aquifer consisted of a clayey to loamy-sandy zone (regolith) underlain by a conductive fissured rock layer (protolith) and the unweathered gneiss (bedrock) at the bottom. The spatial variability of the thickness of the regolith and fissured layers was estimated by electrical resistivity tomography (ERT) profiles, which were performed along a few cross sections in the watershed. For stochastic analysis using Monte Carlo simulation, the generated random layer thickness was made conditional to the available data from the geophysics. In order to simulate steady state flow in the irregular domain with variable geometry, we used an isoparametric finite element method to discretize the flow equation over an unstructured grid with irregular hexahedral elements. The results indicated that the spatial variability of the layer thickness had a significant effect on reducing the simulated effective steady seepage flux and that using the conditional simulations reduced the uncertainty of the simulated seepage flux. As a conclusion, combining information on the aquifer geometry obtained from geophysical surveys with stochastic modelling is a promising methodology to improve the simulation of groundwater flow in complex hard-rock aquifers. (C) 2013 Elsevier B.V. All rights reserved.

Technology-compatible hot carrier solar cell with energy selective hot carrier absorber and carrier-selective contacts

We propose a hot carrier solar cell based on epitaxial growth of a quantum well superlattice and adjacent contact barriers. The concept fulfills required electronic, optical, and several phononic criteria. The first superlattice miniband determines the absorption threshold. The second miniband with appropriate energy width and position provides energy selectivity in situ; contacts are optimized for carrier selectivity exclusively. Electronic transport properties were investigated including elastic random electron–electron scattering, random layer thickness deviation, and illumination as differential absorption per quantum well using a Monte-Carlo code. Carrier extraction probability and energy selectivity strongly suggest a practical implementation of the proposed concept.

Combustion of multilayer systems with random layer thickness distribution: Mathematical modeling

Profile of combustion front in structurally unordered heterogeneous media was found to depend on the character of distribution in scale characteristics of burning media. In case of continuum distribution, dispersion markedly affects a front structure in the vicinity of transition from homogeneous to relay-race combustion. Dispersion also narrows the range of quasi-homogeneous combustion. In case of normal size distribution, oscillations of front amplitude become irregular upon increase in dispersion; this is also accompanied by an increase in the magnitude of forced vibrations caused by system inhomogeneity. Steadiness of combustion was found to depend not only on model parameters but also on the type of size distribution function.

Photonic heterostructures with Lévy-type disorder: Statistics of coherent transmission

We study the electromagnetic transmission $T$ through one-dimensional (1D) photonic heterostructures whose random layer thicknesses follow a long-tailed distribution --L\'evy-type distribution. Based on recent predictions made for 1D coherent transport with L\'evy-type disorder, we show numerically that for a system of length $L$ (i) the average $<-\ln T> \propto L^\alpha$ for $0<\alpha<1$, while $<-\ln T> \propto L$ for $1\le\alpha<2$, $\alpha$ being the exponent of the power-law decay of the layer-thickness probability distribution; and (ii) the transmission distribution $P(T)$ is independent of the angle of incidence and frequency of the electromagnetic wave, but it is fully determined by the values of $\alpha$ and $<\ln T>$.

High performance EUV multilayer structures insensitive to capping layer optical parameters

We have designed and tested a-periodic multilayer structures containing protective capping layers in order to obtain improved stability with respect to any possible changes of the capping layer optical properties (due to oxidation and contamination, for example)-while simultaneously maximizing the EUV reflection efficiency for specific applications, and in particular for EUV lithography. Such coatings may be particularly useful in EUV lithographic apparatus, because they provide both high integrated photon flux and higher stability to the harsh operating environment, which can affect seriously the performance of the multilayer-coated projector system optics. In this work, an evolutive algorithm has been developed in order to design these a-periodic structures, which have been proven to have also the property of stable performance with respect to random layer thickness errors that might occur during coating deposition. Prototypes have been fabricated, and tested with EUV and X-ray reflectometry, and secondary electron spectroscopy. The experimental results clearly show improved performance of our new a-periodic coatings design compared with standard periodic multilayer structures.

Design of aperiodic multilayer structures for attosecond pulses in the extreme ultraviolet

The design of aperiodic reflecting multilayer (ML) structures for attosecond physics in the extreme ultraviolet spectral region is presented. An optimization procedure based on "evolutive strategy" has been developed in order to get coating structures reflecting high photon fluxes in ultrashort duration pulses. The MLs are designed for a specific (75-105 eV) spectral interval with suitable reflectance and phase characteristics, in particular high total spectral reflectivity coupled with very wide bandwidth, spectral phase compensation, and amplitude reshaping. Furthermore, to take into account manufacturing tolerances, solutions stable with respect to random layer thickness variations are selected. To test the reliability of the proposed design procedure, examples of Mo/Si ML structures designed to reflect ultrashort pulses with different amplitude profiles and phase behavior are considered. The performances of the various structures are analyzed.

Sub aerial random wave pressure and layer thickness on impermeable sea walls

Investigations on sub aerial wave pressures and layer thickness on plane impermeable and non-overtopping seawallns were carried out by using physical model studies. Seawalls with slopes of 1:3, 1:4 and 1:6 were used. JONSWAP spectrum with significant wave height, H s from 0.08 to 0.2 m and peak periods, T p from 1.5 to 6.0 s and a constant water depth of 0.7 m is used. Based on extensive measurements, empirical formulas for practical applications are proposed to predict the maximum, significant and mean sub aerial random wave pressure and layer thickness (thickness of water layer perpendicular to the still water level on the run-up zone) by using the surf similarity parameter, significant wave height and elevation on the sub aerial region as inputs. It is found that the maximum layer thickness is 1.11 times the significant layer thickness and maximum sub Arial wave pressure is 1.06 times the significant wave pressures. The predictive equations based on extensive measurements can be used for the design of non-overtopping seawalls.

Nonlinear Optimization Algorithm for Multivariate Optical Element Design

A new algorithm for the design of optical computing filters for chemical analysis, otherwise known as multivariate optical elements (MOEs), is described. The approach is based on the nonlinear optimization of the MOE layer thicknesses to minimize the standard error in sample prediction for the chemical species of interest using a modified version of the Gauss–Newton nonlinear optimization algorithm. The design algorithm can either be initialized with random layer thicknesses or with layer thicknesses derived from spectral matching of a multivariate principal component regression (PCR) vector for the constituent of interest. The algorithm has been successfully tested by using it to design various MOEs for the determination of Bismarck Brown dye in a binary mixture of Crystal Violet and Bismarck Brown.

COMPARATIVE STUDY OF ONE-DIMENSIONAL PHOTONIC BANDGAP STRUCTURES USING MULTILAYER NONLINEAR THIN FILMS

The transmission of electromagnetic radiation through the nonlinear one-dimensional photonic bandgap structure with different configurations are comparatively studied. It is found that the quarter-wavelength thickness arrangement gives rise to a wide window in the visible wavelength range. The modulated superlattice scheme only produces a number of narrow windows. The scheme using random layer thickness is expected to open a very wide window by making use of film nonlinearity when the number of layers is sufficient large. These nonlinear devices can be fabricated by using available materials.

Random and channeled ion-damage distributions in Zn+implanted GaAs by electron microscopy

Abstract Some years ago the Transmission Electron Microscopy of High Resolution Replica (TEMHRR) has been successfully used to show the damage created in Si single crystals by channeled In ions [1]. In the present paper the capacity of the same technique to reproduce the full in-depth damage distribution in 1014 Zn+ /cm2 implanted GaAs is shown. The used replica technique allows us to distinguish three zones in the damaged layer: starting from the implanted surface, the first one connected with the random damage; the second formed by channeled-ion traces; the third showing a damage peak due to the stop of the channeled ions. Comparing the obtained values of the random damaged layer thickness with those already reported in the literature, we found a good agreement.

Tunneling in quantum-wire superlattices with random layer thicknesses.

Tunneling in quantum-wire superlattices with random layer thicknesses.

Mixing of subbands in GaAs/AlAs superlattices with randomly distributed layer thicknesses.

The hole subband structure of GaAs/AlAs superlattices with randomly distributed layer thicknesses is studied with the Luttinger-Kohn Hamiltonian in the Wannier-Bloch mixing representation. By use of Dean's method, the eigenvalues and the subband structure of holes are calculated for several samples with various distributions of the random layer thicknesses. From these results, it is seen that the strong mixing of the hole subbands results in large nonparabolicities in the hole subbands. With an increasing degree of randomness, the effect becomes more and more apparent. It is also found that the introduction of the randomness in the layer thicknesses gives rise to a reduction of the energy gaps and the difference between the hole subbands, and an increase of the total widths of the hole minibands. The effect of the mixing on the optical properties is also qualitatively discussed.

Electronic properties of linear compositions of two binary compounds with random layer thicknesses.

The electronic properties of a one-dimensional (1D) disordered system are studied with a model describing the linear composition of two binary compounds with random layer thicknesses; the model is studied with Dean's method, the transfer-matrix method, and Landauer's formula. For certain degrees of randomness, the energy spectrum, some wave functions, and the average resistivity are obtained. The appearance of some special peaks in the spectrum is due to a particular arrangement of atoms that occurs randomly. Some wave functions remain delocalized with disorder, contrary to the general theorem on the absence of such states in 1D disordered systems.