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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,657 records · Page 92
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Monoclinic crystal structure of α - RuCl 3 and the zigzag antiferromagnetic ground state

We have proposed the layered honeycomb magnet α - RuCl 3 as a candidate to realize a Kitaev spin model with strongly frustrated, bond-dependent, anisotropic interactions between spin-orbit entangled j eff = 1/2 Ru 3 + magnetic moments. We report a detailed study of the three-dimensional crystal structure using x-ray diffraction on untwinned crystals combined with structural relaxation calculations. We consider several models for the stacking of honeycomb layers and find evidence for a parent crystal structure with a monoclinic unit cell corresponding to a stacking of layers with a unidirectional in-plane offset, with occasional in-plane sliding stacking faults, in contrast with the currently assumed trigonal three-layer stacking periodicity. We also report electronic band-structure calculations for the monoclinic structure, which find support for the applicability of the j eff = 1/2 picture once spin-orbit coupling and electron correlations are included. Of the three nearest-neighbor Ru-Ru bonds that comprise the honeycomb lattice, the monoclinic structure makes the bond parallel to the b axis nonequivalent to the other two, and we propose that the resulting differences in the magnitude of the anisotropic exchange along these bonds could provide a natural mechanism to explain the previously reported spin gap in powder inelastic neutron scattering measurements, in contrast to spin models based on the three-fold symmetric trigonal structure, which predict a gapless spectrum within linear spin wave theory. Our susceptibility measurements on both powders and stacked crystals, as well as magnetic neutron powder diffraction, show a single magnetic transition upon cooling below T N ≈ 13 K. Our analysis of our neutron powder diffraction data provides evidence for zigzag magnetic order in the honeycomb layers with an antiferromagnetic stacking between layers. Magnetization measurements on stacked single crystals in pulsed field up to 60 T show a single transition around 8 T for in-plane fields followed by a gradual, asymptotic approach to magnetization saturation, as characteristic of strongly anisotropic exchange interactions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Stable oscillation in spin torque oscillator excited by a small in-plane magnetic field

Theoretical conditions to excite self-oscillation in a spin torque oscillator consisting of a perpendicularly magnetized free layer and an in-plane magnetized pinned layer are investigated by analytically solving the Landau-Lifshitz-Gilbert equation. The analytical relation between the current and oscillation frequency is derived. It is found that a large amplitude oscillation can be excited by applying a small field pointing to the direction anti-parallel to the magnetization of the pinned layer. The validity of the analytical results is confirmed by comparing with numerical simulation, showing good agreement especially in a low current region.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1989

Microwave field effect transistor

Electrodes of a high power, microwave field effect transistor are substantially matched to external input and output networks. The field effect transistor includes a metal ground plane layer, a dielectric layer on the ground plane layer, a gallium arsenide active region on the dielectric layer, and substantially coplanar spaced source, gate, and drain electrodes having active segments covering the active region. The active segment of the gate electrode is located between edges of the active segments of the source and drain electrodes. The gate and drain electrodes include inactive pads remote from the active segments. The pads are connected directly to the input and output networks. The source electrode is connected to the ground plane layer. The space between the electrodes and the geometry of the electrodes extablish parasitic shunt capacitances and series inductances that provide substantial matches between the input network and the gate electrode and between the output network and the drain electrode. Many of the devices are connected in parallel and share a common active region, so that each pair of adjacent devices shares the same source electrodes and each pair of adjacent devices shares the same drain electrodes. The gate electrodes for the parallel devices are formed by a continuous stripe that extends between adjacent devices and is connected at different points to the common gate pad.

Huang, Ho-Chung↗
NASA NTRS1993

Real-time trajectory optimization on parallel processors

A parallel algorithm has been developed for rapidly solving trajectory optimization problems. The goal of the work has been to develop an algorithm that is suitable to do real-time, on-line optimal guidance through repeated solution of a trajectory optimization problem. The algorithm has been developed on an INTEL iPSC/860 message passing parallel processor. It uses a zero-order-hold discretization of a continuous-time problem and solves the resulting nonlinear programming problem using a custom-designed augmented Lagrangian nonlinear programming algorithm. The algorithm achieves parallelism of function, derivative, and search direction calculations through the principle of domain decomposition applied along the time axis. It has been encoded and tested on 3 example problems, the Goddard problem, the acceleration-limited, planar minimum-time to the origin problem, and a National Aerospace Plane minimum-fuel ascent guidance problem. Execution times as fast as 118 sec of wall clock time have been achieved for a 128-stage Goddard problem solved on 32 processors. A 32-stage minimum-time problem has been solved in 151 sec on 32 processors. A 32-stage National Aerospace Plane problem required 2 hours when solved on 32 processors. A speed-up factor of 7.2 has been achieved by using 32-nodes instead of 1-node to solve a 64-stage Goddard problem.

Psiaki, Mark L.↗
NASA NTRS1993

Approximate optimal guidance for the advanced launch system

A real-time guidance scheme for the problem of maximizing the payload into orbit subject to the equations of motion for a rocket over a spherical, non-rotating earth is presented. An approximate optimal launch guidance law is developed based upon an asymptotic expansion of the Hamilton - Jacobi - Bellman or dynamic programming equation. The expansion is performed in terms of a small parameter, which is used to separate the dynamics of the problem into primary and perturbation dynamics. For the zeroth-order problem the small parameter is set to zero and a closed-form solution to the zeroth-order expansion term of Hamilton - Jacobi - Bellman equation is obtained. Higher-order terms of the expansion include the effects of the neglected perturbation dynamics. These higher-order terms are determined from the solution of first-order linear partial differential equations requiring only the evaluation of quadratures. This technique is preferred as a real-time, on-line guidance scheme to alternative numerical iterative optimization schemes because of the unreliable convergence properties of these iterative guidance schemes and because the quadratures needed for the approximate optimal guidance law can be performed rapidly and by parallel processing. Even if the approximate solution is not nearly optimal, when using this technique the zeroth-order solution always provides a path which satisfies the terminal constraints. Results for two-degree-of-freedom simulations are presented for the simplified problem of flight in the equatorial plane and compared to the guidance scheme generated by the shooting method which is an iterative second-order technique.

Feeley, T. S.↗
DOE OSTI2013

COLD FRONTS AND GAS SLOSHING IN GALAXY CLUSTERS WITH ANISOTROPIC THERMAL CONDUCTION

Cold fronts in cluster cool cores should be erased on short timescales by thermal conduction, unless protected by magnetic fields that are 'draped' parallel to the front surfaces, suppressing conduction perpendicular to the sloshing fronts. We present a series of MHD simulations of cold front formation in the core of a galaxy cluster with anisotropic thermal conduction, exploring a parameter space of conduction strengths parallel and perpendicular to the field lines. Including conduction has a strong effect on the temperature distribution of the core and the appearance of the cold fronts. Though magnetic field lines are draping parallel to the front surfaces, preventing conduction directly across them, the temperature jumps across the fronts are nevertheless reduced. The geometry of the field is such that the cold gas below the front surfaces can be connected to hotter regions outside via field lines along directions perpendicular to the plane of the sloshing motions and along sections of the front that are not perfectly draped. This results in the heating of this gas below the front on a timescale of a Gyr, but the sharpness of the density and temperature jumps may nevertheless be preserved. By modifying the gas density distribution below the front, conduction may indirectly aid in suppressing Kelvin-Helmholtz instabilities. If conduction along the field lines is unsuppressed, we find that the characteristic sharp jumps seen in Chandra observations of cold front clusters do not form. Therefore, the presence of cold fronts in hot clusters is in contradiction with our simulations with full Spitzer conduction. This suggests that the presence of cold fronts in hot clusters could be used to place upper limits on conduction in the bulk of the intracluster medium. Finally, the combination of sloshing and anisotropic thermal conduction can result in a larger flux of heat to the core than either process in isolation. While still not sufficient to prevent a cooling catastrophe in the very central (r {approx} 5 kpc) regions of the cool core (where something else is required, such as active galactic nucleus feedback), it reduces significantly the mass of gas that experiences a cooling catastrophe outside those small radii.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Pinning, rotation, and metastability of BiFeO 3 cycloidal domains in a magnetic field

Earlier models for the room-temperature multiferroic BiFeO 3 implicitly assumed that a very strong anisotropy restricts the domain wave vectors q to the threefold-symmetric axis normal to the static polarization P. However, recent measurements demonstrate that the domain wave vectors q rotate within the hexagonal plane normal to P away from the magnetic field orientation m. In this paper, we show that the previously neglected threefold anisotropy K 3 restricts the wave vectors to lie along the threefold axis in zero field. Taking m to lie along a threefold axis, the domain with q parallel to m remains metastable below B c1 ≈7 T. Due to the pinning of domains by nonmagnetic impurities, the wave vectors of the other two domains start to rotate away from m above 5.6 T, when the component of the torque τ=M×B along P exceeds a threshold value τ pin . Since τ=0 when m⊥q, the wave vectors of those domains never become completely perpendicular to the magnetic field. Our results explain recent measurements of the critical field as a function of field orientation, small-angle neutron scattering measurements of the wave vectors, as well as spectroscopic measurements with m along a threefold axis. Finally, the model developed in this paper also explains how the three multiferroic domains of BiFeO 3 for a fixed P can be manipulated by a magnetic field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Magnetic field induced antiferromagnetic cone structure in multiferroic BiFeO 3

Neutron diffraction measurements were performed under high magnetic fields up to 17 T in a multiferroic BiFeO 3 single crystal, in which an intermediate magnetic (IM) phase has been found between the cycloid and canted antiferromagnetic phases [S. Kawachi et al., Phys. Rev. Mater. 1, 024408 (2017)]. We clearly found that the incommensurate magnetic peaks, which split perpendicular to the magnetic field in the cycloid phase, rotate by 90 deg to align parallel to the field in the IM phase. The magnetic structure in the IM phase can be best described by an antiferromagnetic cone (AF cone) structure. The transition from the cycloid to AF cone is of first order and the direction of the magnetic wave vector and the easy plane of the cycloidal component are rotated by 90 deg without changing the cycloidal modulation period, whereas the transition from the AF cone to canted antiferromagnetic phase is gradual and the cone angle becomes smaller gradually without changing the modulation period. Interestingly, the cycloidal component as well as the cone angle in the IM phase shows a large hysteresis between the field increasing and decreasing processes. Finally, this result, combined with the magnetostriction with a large hysteresis previously reported in the IM phase, suggests a strong magnetoelastic coupling.

36 MATERIALS SCIENCE↗
NASA NTRS2004

Three-Dimensional High-Order Spectral Volume Method for Solving Maxwell's Equations on Unstructured Grids

A three-dimensional, high-order, conservative, and efficient discontinuous spectral volume (SV) method for the solutions of Maxwell's equations on unstructured grids is presented. The concept of discontinuous 2nd high-order loca1 representations to achieve conservation and high accuracy is utilized in a manner similar to the Discontinuous Galerkin (DG) method, but instead of using a Galerkin finite-element formulation, the SV method is based on a finite-volume approach to attain a simpler formulation. Conventional unstructured finite-volume methods require data reconstruction based on the least-squares formulation using neighboring cell data. Since each unknown employs a different stencil, one must repeat the least-squares inversion for every cell at each time step, or to store the inversion coefficients. In a high-order, three-dimensional computation, the former would involve impractically large CPU time, while for the latter the memory requirement becomes prohibitive. In the SV method, one starts with a relatively coarse grid of triangles or tetrahedra, called spectral volumes (SVs), and partition each SV into a number of structured subcells, called control volumes (CVs), that support a polynomial expansion of a desired degree of precision. The unknowns are cell averages over CVs. If all the SVs are partitioned in a geometrically similar manner, the reconstruction becomes universal as a weighted sum of unknowns, and only a few universal coefficients need to be stored for the surface integrals over CV faces. Since the solution is discontinuous across the SV boundaries, a Riemann solver is thus necessary to maintain conservation. In the paper, multi-parameter and symmetric SV partitions, up to quartic for triangle and cubic for tetrahedron, are first presented. The corresponding weight coefficients for CV face integrals in terms of CV cell averages for each partition are analytically determined. These discretization formulas are then applied to the integral form of the Maxwell equations. All numerical procedures for outer boundary, material interface, zonal interface, and interior SV face are unified with a single characteristic formulation. The load balancing in a massive parallel computing environment is therefore easier to achieve. A parameter is introduced in the Riemann solver to control the strength of the smoothing term. Important aspects of the data structure and its effects to communication and the optimum use of cache memory are discussed. Results will be presented for plane TE and TM waves incident on a perfectly conducting cylinder for up to fifth order of accuracy, and a plane wave incident on a perfectly conducting sphere for up to fourth order of accuracy. Comparisons are made with exact solutions for these cases.

Liu, Yen↗
NASA NTRS2000

Performance of the OVERFLOW-MLP and LAURA-MLP CFD Codes on the NASA Ames 512 CPU Origin System

The shared memory Multi-Level Parallelism (MLP) technique, developed last year at NASA Ames has been very successful in dramatically improving the performance of important NASA CFD codes. This new and very simple parallel programming technique was first inserted into the OVERFLOW production CFD code in FY 1998. The OVERFLOW-MLP code's parallel performance scaled linearly to 256 CPUs on the NASA Ames 256 CPU Origin 2000 system (steger). Overall performance exceeded 20.1 GFLOP/s, or about 4.5x the performance of a dedicated 16 CPU C90 system. All of this was achieved without any major modification to the original vector based code. The OVERFLOW-MLP code is now in production on the inhouse Origin systems as well as being used offsite at commercial aerospace companies. Partially as a result of this work, NASA Ames has purchased a new 512 CPU Origin 2000 system to further test the limits of parallel performance for NASA codes of interest. This paper presents the performance obtained from the latest optimization efforts on this machine for the LAURA-MLP and OVERFLOW-MLP codes. The Langley Aerothermodynamics Upwind Relaxation Algorithm (LAURA) code is a key simulation tool in the development of the next generation shuttle, interplanetary reentry vehicles, and nearly all "X" plane development. This code sustains about 4-5 GFLOP/s on a dedicated 16 CPU C90. At this rate, expected workloads would require over 100 C90 CPU years of computing over the next few calendar years. It is not feasible to expect that this would be affordable or available to the user community. Dramatic performance gains on cheaper systems are needed. This code is expected to be perhaps the largest consumer of NASA Ames compute cycles per run in the coming year.The OVERFLOW CFD code is extensively used in the government and commercial aerospace communities to evaluate new aircraft designs. It is one of the largest consumers of NASA supercomputing cycles and large simulations of highly resolved full aircraft are routinely undertaken. Typical large problems might require 100s of Cray C90 CPU hours to complete. The dramatic performance gains with the 256 CPU steger system are exciting. Obtaining results in hours instead of months is revolutionizing the way in which aircraft manufacturers are looking at future aircraft simulation work. Figure 2 below is a current state of the art plot of OVERFLOW-MLP performance on the 512 CPU Lomax system. As can be seen, the chart indicates that OVERFLOW-MLP continues to scale linearly with CPU count up to 512 CPUs on a large 35 million point full aircraft RANS simulation. At this point performance is such that a fully converged simulation of 2500 time steps is completed in less than 2 hours of elapsed time. Further work over the next few weeks will improve the performance of this code even further.The LAURA code has been converted to the MLP format as well. This code is currently being optimized for the 512 CPU system. Performance statistics indicate that the goal of 100 GFLOP/s will be achieved by year's end. This amounts to 20x the 16 CPU C90 result and strongly demonstrates the viability of the new parallel systems rapidly solving very large simulations in a production environment.

Taft, James R.↗
DOE OSTI2018

Spin Transport Investigations in Bilayer Graphene

We study the spin-based electron transport properties in bilayer graphene with half-metallic ferromagnetic (HMF) CrO{sub 2} electrodes. Out-of-plane bilayer graphene has been examined in this paper. A high magneto-resistance ratio (MR) of ∼99% is obtained in the bilayer structure for a potential range of 0 to 0.8 V, after which MR drops because of the increase in spin-up current in the anti-parallel configuration at 1.2 V. High spin filtration of ∼100% is obtained at all bias points. Transmission spectrum studies show that a large number of electronic states are present at the Fermi level in bilayer graphene, which would result in high current.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

A new method for isolating plasma interactions from those of the laser beam during plasma nitriding

Highlights: • Nitriding of titanium was studied using a laser sustained plasma (LSP) reactor, independent of the laser beam. • Nucleation and growth of faceted, dendritic, rectangular and particulate TiN morphologies was observed. • TiN layers up to 300 μm thick formed within 5 s - one of the most rapid TiN growth rates observed for LSP/laser nitriding. • LSP accessed novel microstructures compared to laser nitriding with or without surface-struck plasm plasma. - Abstract: A new method for separating the interactions of a laser plasma from those of a laser beam with a titanium substrate was developed. A laser-sustained plasma (LSP) was generated by striking the plasma on a titanium plate in a flowing nitrogen atmosphere at ambient pressure and subsequently removing the strike plate. The resultant nitrogen plasma was sustained indefinitely around the laser focal plane until the nitrogen gas flow and/or the laser power were switched off. The laser-sustained nitrogen plasma was then used as a “reactor” to study the effects of a nitrogen plasma, independent of the laser beam, when the plasma was brought into close proximity, (2 to 3 mm), parallel to a titanium substrate. There was no interaction of the parallel laser beam with the substrate. Heat, nitrogen and titanium were exchanged between the nitrogen LSP and substrate resulting in melting, nucleation and growth of faceted and dendritic TiN crystals, rectangular hollow TiN morphologies and particulate TiN deposits. Dense TiN layers up to 300 μm thick formed within 5 s. The results demonstrated that compositionally graded layers of nitrogen-enriched titanium, and titanium nitride could be formed very rapidly on model, commercially-pure titanium substrates, with promise for extension to commercial alloys such as Ti-6Al-4V.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Non-thermal electron acceleration from magnetically driven reconnection in a laboratory plasma

Magnetic reconnection rapidly converts magnetic energy into some combination of plasma flow energy, thermal energy and non-thermal energetic particles. Various reconnection acceleration mechanisms have been theoretically proposed and numerically studied in different collisionless and low-β environments, where β refers to the plasma-to-magnetic pressure ratio. These mechanisms include Fermi acceleration, betatron acceleration, parallel electric field acceleration along magnetic fields and direct acceleration by the reconnection electric field. However, none of them have been experimentally confirmed, as the direct observation of non-thermal particle acceleration in laboratory experiments has been difficult due to short Debye lengths for in situ measurements and short mean free paths for ex situ measurements. Here we report the direct measurement of accelerated non-thermal electrons from magnetically driven reconnection at low β in experiments using a laser-powered capacitor coil platform. We use kilojoule lasers to drive parallel currents to reconnect megagauss-level magnetic fields in a quasi-axisymmetric geometry. The angular dependence of the measured electron energy spectrum and the resulting accelerated energies, supported by particle-in-cell simulations, indicate that the mechanism of direct electric field acceleration by the out-of-plane reconnection electric field is at work. Scaled energies using this mechanism show direct relevance to astrophysical observations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Reduction in the interface-states density of metal-oxide-semiconductor field-effect transistors fabricated on high-index Si (114) surfaces by using an external magnetic field

After fabrication of Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) devices on high-index silicon (114) surfaces, their threshold voltage (Vth) and interface-states density (Dit) characteristics were measured under the influence of an externally applied magnetic field of B = 6 μT at room temperature. The electron flow of the MOSFET's channel presents high anisotropy on Si (114), and this effect is enhanced by using an external magnetic field B, applied parallel to the Si (114) surface but perpendicular to the electron flow direction. This special configuration results in the channel electrons experiencing a Lorentzian force which pushes the electrons closer to the Si (114)-SiO{sub 2} interface and therefore to the special morphology of the Si (114) surface. Interestingly, Dit evaluation of n-type MOSFETs fabricated on Si (114) surfaces shows that the Si (114)-SiO{sub 2} interface is of high quality so that Dit as low as ∼10{sup 10 }cm{sup −2}·eV{sup −1} are obtained for MOSFETs with channels aligned at specific orientations. Additionally, using both a small positive Vds ≤ 100 mV and B = 6 μT, the former Dit is reduced by 35% in MOSFETs whose channels are aligned parallel to row-like nanostructures formed atop Si (114) surfaces (channels having a 90° rotation), whereas Dit is increased by 25% in MOSFETs whose channels are aligned perpendicular to these nanostructures (channels having a 0° rotation). From these results, the special morphology of a high-index Si (114) plane having nanochannels on its surface opens the possibility to reduce the electron-trapping characteristics of MOSFET devices having deep-submicron features and operating at very high frequencies.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Study of non-linear Hall effect in nitrogen-grown ZnO microstructure and the effect of H{sup +}-implantation

We report magnetotransport studies on microstructured ZnO film grown by pulsed laser deposition in N{sub 2} atmosphere on a-plane Al{sub 2}O{sub 3} substrates and the effect of low energy H{sup +}-implantation. Non-linearity has been found in the magnetic field dependent Hall resistance, which decreases with temperature. We explain this effect with a two-band model assuming the conduction through two different parallel channels having different types of charge carriers. Reduced non-linearity after H{sup +}-implantation in the grown film is due to the shallow-donor effect of hydrogen giving rise to an increment in the electron density, reducing the effect of the other channel.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Evidence for an interstellar dust filament in the outer heliosheath

A recently discovered filament of polarized starlight that traces a coherent magnetic field is shown to have several properties that are consistent with an origin in the outer heliosheath of the heliosphere: (1) the magnetic field that provides the best fit to the polarization position angles is directed toward ℓ = 357.°3, b = 17.°0 (±11.°2); this direction is within 6.°7 ± 11.°2 of the observed upwind direction of the flow of interstellar neutral helium gas through the heliosphere. (2) The magnetic field is ordered; the component of the variation of the polarization position angles that can be attributed to magnetic turbulence is ±9.°6. (3) The axis of the elongated filament can be approximated by a line that defines an angle of 80° ± 14° with the plane that is formed by the interstellar magnetic field (ISMF) vector and the vector of the inflowing neutral gas (the BV plane). We propose that this polarization feature arises from aligned interstellar dust grains in the outer heliosheath where the interstellar plasma and magnetic field are deflected around the heliosphere. This interpretation suggests that the polarization is seen where stream lines of the flow and the draped ISMF lines are approximately parallel to each other and perpendicular to the sightline. An ordered magnetic field is required so that grain alignment is not disrupted during the interaction. The filament location is consistent with dust plumes previously predicted to form around the heliosphere. The proposed outer heliosheath location of the polarizing grains can be tested with three-dimensional models that track torques on asymmetric dust grains as they propagate through the heliosheath plasma, and using these models to evaluate grain alignment and the asymmetric extinction of the grains.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1981

Suspension system for a wheel rolling on a flat track

An improved suspension system for an uncrowned wheel rolling on a flat track is presented. It is characterized by a wheel frame assembly including a wheel frame and at least one uncrowned wheel connected in supporting relation with the frame. It is adapted to be seated in rolling engagement with a flat track, a load supporting bed, and a plurality of flexural struts interconnecting the bed in supported relation with the frame. Each of said struts is disposed in a plane passing through the center of the uncrowned wheel surface along a line substantially bisecting the line of contact established between the wheel surface and the flat surface of the truck and characterized by a modulus of elasticity sufficient for maintaining the axis of rotation for the wheel in substantial parallelism with the line of contact established between the surfaces of the wheel and track.

Mcginness, H. D.↗
NASA NTRS1990

Scattering properties of woven fibrous insulations - Effects of interference for normal incidence

This paper examines the scattering properties of woven fibrous materials in order to model the interactions between the scattered radiation from individual fibers. A normally incident plane electromagnetic wave is considered and different representative geometries are analyzed theoretically. Experimental results are presented for specific woven thermal insulation fabrics. Previous studies in the literature have mostly ignored the effect of constructive or destructive addition of scattered waves from individual fibers with the exception of the case of parallel fibers. Whereas the light-scattering characteristics of a single long fiber depend only on the size parameter and on the material optical constants, the additional mechanism of interference between the scattered waves from fibers of parallel or perpendicular orientation introduces an additional dependence on fiber locations. In this study, analytical models are developed for obtaining the radiative scattering characteristics of woven fibrous media taking into account the mechanism of interference. Experimental measurements of forward- and backward-scattered light from a woven silica cloth over a broad range of wavelengths in the infrared are obtained and compared with the predicted results for a system of two orthogonal families of infinite parallel fibers.

Kumar, Sunil↗