One-dimensional Absorbing Research Articles

Core-shell structured Co@NC@MoS2 magnetic hierarchical nanotubes: Preparation and microwave absorbing properties

• A novel Co@NC@MoS 2 magnetic hierarchical nanotube is designed and prepared. • The minimum reflection loss (RL min ) exceeds −61.97 dB. • The effective absorption bandwidth (EAB) covers 5.6 GHz. • The electromagnetic parameters can be adjusted by changing the load of MoS 2 . In this study, a new lightweight one-dimensional absorber Co@NC@MoS 2 was designed and prepared. Firstly, polydopamine (PDA) was coated by oxidative self-polymerization with cobalt-nitrilotriacetic acid chelate nanowires (Co-NTAC) as template. Then core-shell structured magnetic hierarchical nanotubes (Co@PDA@MoS 2 ) were prepared by one-step hydrothermal method. After thermal annealing, PDA layer was transformed into nitrogen doped carbon layer (NC) to obtain the efficient microwave absorber Co@NC@MoS 2 . The removal of template and growth of MoS 2 were completed simultaneously, the preparation process was simplified. Because of its good magnetic loss and dielectric loss, Co@NC@MoS 2 shows excellent microwave absorption performance. Under filler content of 15 wt.%, the minimum reflection loss (RL min ) can reach -61.97 dB@9.2 GHz, and the effective absorption bandwidth (EAB) is 5.6 GHz. The electromagnetic parameters of Co@NC@MoS 2 can be further adjusted by changing the load of MoS 2 . Meanwhile, the structure and composition of Co@NC@MoS 2 were systematically analyzed. The influence of the microstructure on the microwave absorbing properties was investigated, and the microwave attenuation mechanism is revealed. As an efficient and lightweight absorber, Co@NC@MoS 2 has potential application value in the construction of new stealth coatings.

Enhanced charge carrier transport via efficient grain conduction mode for Sb2Se3 solar cell applications

The combination of the SnO2 and Sb2Se3 offers an alternative strategy for realizing the n-p heterojunction in Sb2Se3 thin-film solar cells. However, the low conductivity of the SnO2 and the lateral growth of Sb2Se3 grains make carrier extraction more challenging, thereby resulting in unsatisfactory device performance. In this study, the improvement of the Sb2Se3 solar cell performance is achieved by enhancing the conductivity of the SnO2 and rearranging the Sb2Se3 elongated grains simultaneously so that the carriers can be efficiently transmitted through the grain conduction mode instead of the grain boundary conduction mode. Furthermore, the evolution of (Sb4Se6)n ribbons from pure lateral growth to longitudinal growth is observed by adjusting the distribution of doping elements on the SnO2 surface. Finally, under optimal treatment times, the carrier recombination in the heterojunction is effectively inhibited by building an efficient electron-transport channel, and the Sb2Se3 solar cell achieved the highest power conversion efficiency of 5.41%. Our study clarifies the relationship between carrier transport and grain orientation in one-dimensional Sb2Se3 materials and realized the effective adjustment of the (Sb4Se6)n ribbon growth direction. The outcomes of this study provide guidance for the control of carrier behavior in optoelectronic devices with similar one-dimensional absorber materials.

Multi-physics based Simulations of an Oleo-pneumatic Shock Absorber System for PHM

The paper presents multi-physics (Mechanical, Thermal, Hydraulic, and Pneumatic) based modelling and simulation of an Oleo-pneumatic shock absorber with fault capabilities. The fault simulated in this model is leakage due to eccentricity. The one-dimensional shock absorber system models to give loads at different sink velocities. These load values, used in the structural model to do static stress analysis. By using these loads directly from the system model eliminates the error in load computation from the load’s group, thereby eliminating the time and cost involved in this activity. The models and static stress analyses carried out with both 1-D and 3-D elements. The 3-D landing gear model meshed with using both auto and manual mesh generation options. The consequences of both 1-D and 3-D models mesh generation, discussed in this paper. The static stress analysis, compared with the experimental results and it is found that the results are within 5% deviation. Based on the static stress and fatigue analysis computed the life of a landing gear.

One-dimensional Absorbing phase transition in the fermionic parity-conserving particle process with second neighbors branching

By means of Monte Carlo procedure this article analyzes a stochastic process in one-dimensional model. The parity-conserving particle process with infinite annihilation and branching of the two offspring to the second neighbors, each one at each side. The model was firstly considered in Takayasu and Tretyakov (1991) and Jensen (1994) but branching of four offspring to four first neighbors. It has also been solved in Zhong and ben-Avraham (1995) with branching of the two particles to the first neighbors, each one at each side, but with finite annihilation. Now the model has been studied with infinite annihilation in presence of only second neighbors branching of two particles, one to left and the other to the right. Simulations were performed on a regular one dimension lattice in order to determine the threshold of absorbing phase transition. From steady state simulations and finite time scaling analysis, it is shown that the transition exists and critical exponents are obtained. The exponents are found to differ from those of the directed percolation (DP) universality class and are the same found in Takayasu and Tretyakov (1991), Jensen (1994) and Zhong and ben-Avraham (1995). It is also calculated the short-time relaxation dynamical critical exponents and checked the consistence of the related scaling relation.

Polarization-Independent Near-Perfect Absorber in the Visible Regime Based on One-Dimensional Meta-Surface

We present a polarization-independent near-perfect absorber in the visible regime based on one-dimensional meta-surface. In this absorber, the dielectric grating layer with high refractive index is essential, which supports strongly localized electromagnetic modes concentrated in the double-metal regions. The simulation results show that absorption peaks are over 99% at the wavelength of 0.45 μm for both TM and TE polarizations. The near-perfect absorptions are attributed to the lateral plasmon cavity resonance and longitudinal Fabry-Perot-like cavity resonance for TM and TE polarization, respectively. Furthermore, theses absorption peaks can maintain almost unchanged within wide ranges of incident and azimuthal angles. Comparing with those meta-material absorbers with complex two-dimensional array and one-dimensional stacked array, this one-dimensional absorber has a very simple geometrical structure which can be integrated into complex photonic devices expediently.

Chebyshev collocation spectral method for one-dimensional radiative heat transfer in linearly anisotropic-scattering cylindrical medium

In this study, the Chebyshev collocation spectral method (CCSM) is developed to solve the radiative integro-differential transfer equation (RIDTE) for one-dimensional absorbing, emitting and linearly anisotropic-scattering cylindrical medium. The general form of quadrature formulas for Chebyshev collocation points is deduced. These formulas are proved to have the same accuracy as the Gauss-Legendre quadrature formula (GLQF) for the F-function (geometric function) in the RIDTE. The explicit expressions of the Lagrange basis polynomials and the differentiation matrices for Chebyshev collocation points are also given. These expressions are necessary for solving an integro-differential equation by the CCSM. Since the integrand in the RIDTE is continuous but non-smooth, it is treated by the segments integration method (SIM). The derivative terms in the RIDTE are carried out to improve the accuracy near the origin. In this way, a fourth order accuracy is achieved by the CCSM for the RIDTE, whereas it's only a second order one by the finite difference method (FDM). Several benchmark problems (BPs) with various combinations of optical thickness, medium temperature distribution, degree of anisotropy, and scattering albedo are solved. The results show that present CCSM is efficient to obtain high accurate results, especially for the optically thin medium. The solutions rounded to seven significant digits are given in tabular form, and show excellent agreement with the published data. Finally, the solutions of RIDTE are used as benchmarks for the solution of radiative integral transfer equations (RITEs) presented by Sutton and Chen (JQSRT 84 (2004) 65–103). A non-uniform grid refined near the wall is advised to improve the accuracy of RITEs solutions.

Wide-angle and polarization independent perfect absorber based on one-dimensional fabrication-tolerant stacked array.

We propose a wide-angle, polarization independent and fabrication-tolerant perfect absorber, which is based on a one-dimensional stacked array consisted of vertically cascaded two pairs of metal-dielectric bilayers. The results show that the absorption peaks are over 99% at the wavelength of 5.25 μm for different polarization angles, and remain very high within wide ranges of incident and azimuthal angles. We attribute those excellent performances to the excitation of the magnetic resonance (MR) and the guided mode resonance (GMR) for the TM and TE polarization, respectively, and are further expounded by the inductor-capacitor (LC) circuit model and the eigen equation of the GMR, respectively. More importantly, this one-dimensional absorber is very robust to the spacing distance between the neighboring stacks and the metallic strip thickness, which releases degrees of freedom in design and makes the absorber extremely flexible and simple in fabrication, thus it can be a good candidate for many fascinating applications.

Inverse Problem of Absorption Coefficients for One-dimensional Non-uniform Medium

Inverse radiation problem for one-dimensional non-uniform medium has been investigated. A stochastic particle swarm optimization algorithm (SPSO) with a stochastic selection is adopted to estimate the absorption coefficients in a one-dimensional absorbing, emitting medium. The directional radiative intensities simulated by discrete ordinate method are served as input for the inverse problems. The performances of this algorithm on the accuracy of estimation are examined. Numerical results show that the proposed algorithm can guarantee the convergence of the global optimization solution, and is proved to be fast. The absorption coefficients could be estimated accurately.

Design of a wide-band metamaterial absorber based on loaded magnetic resonators

A wide-band, polarization-insensitive and wide-angle metamaterial absorber based on loaded magnetic resonator is proposed. A single unit cell of the absorber is comprised of a magnetic resonator loaded with lumped elements, a substrate and a back metal board. Simulated absorbances of the one-dimensional-array absorber under loading and unloading conditions indicate that compared with under the unloading condition, the one-dimensional absorber under the loading condition can realize a wide-band absorption. Simulated absorbances of the one-dimensional-array absorber with lossy and loss-free substrates indicate that the power loss in the absorber results from lumped resistances in magnetic resonators, and is insensitive to the loss of the substrate. Simulated absorbances of the one-dimensional-array absorber with different lumped resistances and capacitances indicate that there exist optimal values for lumped resistances and capacitances, where the absorbance is highest and the bandwidth is widest. Simulated absorbances of the two-dimensional-array absorber under different polarization angles and different incident angles indicate that the absorber is polarization-insensitive and angle-wide.

Particle Swarm Optimization for Scattering Coefficients in One-Dimensional Non-Uniform Media

Inverse problem of scattering coefficients in one-dimensional non-uniform medium has been investigated. A stochastic particle swarm optimization algorithm (SPSO) with a stochastic selection is adopted to estimate the absorption coefficients in a one-dimensional absorbing, emitting and scattering medium. The directional radiative intensities simulated by discrete ordinate method are served as input for the inverse problems. The performances of this algorithm on the accuracy of estimation are examined. Numerical results show that the proposed algorithm can guarantee the convergence of the global optimization solution, and is proved to be fast. The distribution of scattering coefficients could be estimated accurately.

Inverse radiation problem of temperature distribution in one-dimensional isotropically scattering participating slab with variable refractive index

In this paper, an inverse analysis is performed for estimation of source term distribution from the measured exit radiation intensities at the boundary surfaces in a one-dimensional absorbing, emitting and isotropically scattering medium between two parallel plates with variable refractive index. The variation of refractive index is assumed to be linear. The radiative transfer equation is solved by the constant quadrature discrete ordinate method. The inverse problem is formulated as an optimization problem for minimizing an objective function which is expressed as the sum of square deviations between measured and estimated exit radiation intensities at boundary surfaces. The conjugate gradient method is used to solve the inverse problem through an iterative procedure. The effects of various variables on source estimation are investigated such as type of source function, errors in the measured data and system parameters, gradient of refractive index across the medium, optical thickness, single scattering albedo and boundary emissivities. The results show that in the case of noisy input data, variation of system parameters may affect the inverse solution, especially at high error values in the measured data. The error in measured data plays more important role than the error in radiative system parameters except the refractive index distribution; however the accuracy of source estimation is very sensitive toward error in refractive index distribution. Therefore, refractive index distribution and measured exit intensities should be measured accurately with a limited error bound, in order to have an accurate estimation of source term in a graded index medium.

Chebyshev collocation spectral method for one-dimensional radiative heat transfer in graded index media

Chebyshev spectral collocation method based on discrete ordinates equation is developed to solve radiative transfer problems in a one-dimensional absorbing, emitting and scattering semitransparent slab with spatially variable refractive index. For radiative transfer equation, the angular domain is discretized by discrete ordinates method, and the spatial domain is discretized by Chebyshev collocation spectral method. Due to the exponential convergence of spectral methods, a very high accuracy can be obtained even using few nodes for present problems. Numerical results by the Chebyshev collocation spectral-discrete ordinates method (SP-DOM) are compared with those available data in references. Effects of refractive index gradient on radiative intensity are studied for space dependent scattering media. The results show that SP-DOM has a good accuracy and efficiency for solving radiative heat transfer problems in even spatially varying absorbing, emitting, scattering, and graded index media.

Short-pulsed laser transport in absorbing and scattering media: time-based versus frequency-based approaches

Optical tomography (OT) is a promising non-intrusive characterization technique of absorbing and scattering media that uses transmitted and/or reflected signals of samples irradiated with visible or near-infrared light. The quality of OT techniques is directly related to the accuracy of their forward models due to the use of inversion algorithms. In this paper, forward models for transient OT approaches are investigated. The system under study involves a one-dimensional absorbing and scattering medium illuminated by a short laser pulse; this problem is solved using a discrete ordinates–finite volume (DO–FV) method in both time and frequency domain. Previous works have shown that time-domain approaches coupled with first order spatial interpolation schemes cannot represent the physics of the problem adequately as transmitted fluxes emerge before the minimal physical time required to leave the medium. In this work, the Van Leer and Superbee flux limiters, combined with the second order Lax–Wendroff scheme, are used in an attempt to prevent this. Results show that despite significant improvement, flux limiters fail to completely eliminate the physically unrealistic behaviour. On the other hand, results for transmittance obtained from the frequency-based method are accurate, without physically unrealistic behaviours at early time periods. The frequency-dependent approach is however computationally expensive, since it requires approximately five times more computational time than its temporal counterpart when used as a forward model for transient OT. On the other hand, the great advantages of the frequency-based approach is that limited windows of temporal signals can be calculated efficiently (in transient OT), and it can also be used as a forward model for steady-state, frequency-based and transient OT techniques.

Participating media exposed to collimated short-pulse irradiation – A Laguerre–Galerkin solution

A new method is developed for the solution of radiative transfer in a one-dimensional absorbing and isotropically scattering medium with short-pulse irradiation on one of its boundaries. The time-dependent radiative intensity is expanded in a series of Laguerre polynomials with time as the argument. Moments of the radiative transfer equation, as well as of the boundary conditions, then yield a set of coupled time-independent radiative transfer problems. This set, in turn, is reduced to a set of algebraic equations by the application of the Galerkin method. The transient transmittance and reflectance of the medium are evaluated for various values of the optical thickness, scattering albedo and pulse duration. It is demonstrated that the Laguerre–Galerkin method is not only easier to implement and more efficient but also yields more accurate results compared to the direct application of the Galerkin method. The results are in very good agreement with those available in the literature.

Transient radiative transfer in participating media with pulse-laser irradiation—an approximate Galerkin solution

An assessment is made of the Galerkin technique as an effective method of solution for transient radiative transfer problems in participating media. A one-dimensional absorbing and isotropically scattering plane-parallel gray medium irradiated with a short-pulse laser on one of its boundaries is considered for the application of the method. The medium is non-emitting and the boundaries are non-reflecting and non-refracting. In the integral formulation of the problem for the source function, the time-wise variation of the radiation intensity at any point and in any direction in the medium is assumed to be the same as the time-wise variation of the average intensity at the same point as an approximation for the application of the method. The transient transmittance and reflectance of the medium are evaluated for various values of the optical thickness, scattering albedo and pulse duration. The results are in agreement with those available in the literature. It is demonstrated that the method is relatively simple to implement and yields accurate results.

Radiative transfer in participating media with collimated short-pulse Gaussian irradiation

Radiative transfer in a one-dimensional absorbing and isotropically scattering plane-parallel grey medium with a collimated short-pulse Gaussian irradiation on one of its boundaries is studied. The medium is non-emitting and the boundaries are non-reflecting and non-refracting. The Galerkin method is extended for the solution of the transient radiative transfer problem. The transient transmittance and reflectance of the medium are evaluated for various optical thicknesses, scattering albedos and pulse durations.

Finite element solution of radiative transfer across a slab with variable spatial refractive index

To avoid the complicated computation of ray trajectories, a finite element formulation is developed to solve the radiative transfer problem in a one-dimensional absorbing–emitting–scattering semitransparent slab with variable spatial refractive index. A problem of radiative equilibrium is taken as an example to verify this finite element formulation. The predicted temperature distributions are determined by the proposed method and compared with the data in references. The results show that the finite element formulation presented in this paper has good accuracy in solving the radiative transfer in one-dimensional absorbing–emitting–scattering semitransparent medium with variable spatial refractive index.

Backward Monte Carlo simulation for apparent directional emissivity of non-isothermal semitransparent slab

A backward Monte Carlo method based on radiation distribution factor is extended to compute the apparent directional emissivity of one-dimensional absorbing–emitting–scattering semitransparent slab with specular semitransparent surface and opaque diffuse substrate. A non-isothermal semitransparent slab is taken as an example to examine the efficiency of backward Monte Carlo method. The apparent directional emissivity of the semitransparent slab is determined by backward Monte Carlo simulation and compared with that determined by forward Monte Carlo simulation. The results show that the backward Monte Carlo method is very efficient in solving the apparent directional emissivity of the semitransparent slab. The backward Monte Carlo method converges more quickly than the forward Monte Carlo method.

Temperature distributions in an absorbing–emitting–scattering semitransparent slab with variable spatial refractive index

A Monte Carlo curved ray-tracing method is used to analyze the radiative heat transfer in one-dimensional absorbing–emitting–scattering semitransparent slab with variable spatial refractive index. A problem of radiative equilibrium with linear variable spatial refractive index is taken as an example in this paper. The predicted temperature distributions are determined by the proposed method and compared with the data in references. The results show that influences of refractive index gradient are important and the influences increase with the refractive index gradient, the temperature distribution approaches to the one obtained for a constant refractive index when the slab optical thickness is far greater than 1.0, and the effect of the scattering phase function is similar to that in the medium with constant refractive index.

Discrete curved ray-tracing method for radiative transfer in an absorbing–emitting semitransparent slab with variable spatial refractive index

A discrete curved ray-tracing method is developed to analyze the radiative transfer in one-dimensional absorbing–emitting semitransparent slab with variable spatial refractive index. The curved ray trajectory is locally treated as straight line and the complicated and time-consuming computation of ray trajectory is cut down. A problem of radiative equilibrium with linear variable spatial refractive index is taken as an example to examine the accuracy of the proposed method. The temperature distributions are determined by the proposed method and compared with the data in references, which are obtained by other different methods. The results show that the discrete curved ray-tracing method has a good accuracy in solving the radiative transfer in one-dimensional semitransparent slab with variable spatial refractive index.