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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Theory of electromagnetic wave frequency upconversion in dynamic media

Frequency upconversion of an electromagnetic wave can occur in ionized plasma with decreasing electric permittivity and in split-ring resonator-structure metamaterials with decreasing magnetic permeability. We develop a general theory to describe the evolution of the wave frequency, amplitude, and energy density in homogeneous media with a temporally decreasing refractive index. We find that upconversion of the wave frequency is necessarily accompanied by partitioning of the wave energy into low-frequency modes, which sets an upper limit on the energy conversion efficiency. In conclusion, the efficiency limits are obtained for both varying permittivity and varying permeability.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1983

Reflection of electromagnetic waves at a biaxial-isotropic interface

The reflection of electromagnetic waves at a plane boundary between isotropic and biaxial media has been investigated using the kDB approach. The general case has been considered in which the principal dielectric axes of the biaxial medium are oriented at an arbitrary angle to the normal of the plane boundary. In general, two characteristic waves propagate in the biaxial medium, leading to coupling of vertical and horizontal polarizations in the reflected waves. Some special cases are illustrated. The results have applications to problems in remote sensing and integrated optics.

Njoku, E. G.↗
DOE OSTI2015

Electromagnetic wave attenuation measurements in a ring-shaped inductively coupled air plasma

An aerocraft with the surface, inlet and radome covered large-area inductive coupled plasma (ICP) can attenuate its radar echo effectively. The shape, thickness, and electron density (N{sub e}) distribution of ICP are critical to electromagnetic wave attenuation. In the paper, an air all-quartz ICP generator in size of 20 × 20 × 7 cm{sup 3} without magnetic confinement is designed. The discharge results show that the ICP is amorphous in E-mode and ring-shaped in H-mode. The structure of ICP stratifies into core region and edge halo in H-mode, and its width and thickness changes from power and pressure. Such phenomena are explained by the distribution of RF magnetic field, the diffusion of negative ions plasma and the variation of skin depth. In addition, the theoretical analysis shows that the N{sub e} achieves nearly uniform within the electronegative core and sharply steepens in the edge. The N{sub e} of core region is diagnosed by microwave interferometer under varied conditions (pressure in range of 10–50 Pa, power in 300–700 W). Furthermore, the electromagnetic wave attenuation measurements were carried out with the air ICP in the frequencies of 4–5 GHz. The results show that the interspaced ICP is still effective to wave attenuation, and the wave attenuation increases with the power and pressure. The measured attenuation is approximately in accordance with the calculation data of finite-different time-domain simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Electromagnetic waves in a polydisperse dusty plasma

The properties of low-frequency electromagnetic waves in a polydisperse dusty plasma are studied. The dispersion relation for the waves propagating at an arbitrary angle to the external magnetic field is derived, with the coefficients explicitly determined by the dust-size distribution function. The dependence of wave dispersion on properties of the dust-size distribution function is analysed. It is shown that the cutoff for an oblique propagation in plasma with a wide scatter of dust sizes takes place at a much lower frequency than in a plasma with monosized dust particles. It is found that dispersion properties of a transversal magnetosonic wave mode around dust–cyclotron frequencies considerably differ from those in a plasma with monosized dust. In a plasma with low mass fraction of dust particles, the dispersion is smooth without the cutoff and the resonance intrinsic for a plasma with monosized dust. Increase of the dust fraction results in splitting of the dispersion curve on to two branches. Further increase of the dust fraction leads to emergence of the third branch located between the cutoffs and restricted from the lower and higher frequencies by two resonances. The dependence of the frequencies of cutoffs and resonances on the width of the dust-size distribution, its slope and the dust mass fraction are analysed. It is shown that the transparency frequency windows in a plasma with polydisperse dust are wider for transversal elecromagnetic waves, but narrower for longitudinal or oblique waves.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

On the Possibility of the Existence of a Surface Electromagnetic Wave in the Permafrost Area

The results of measurements of the vertical component of electric field at a radio path with the permafrost at a frequency of 255 kHz have been interpreted. An analysis of the results has shown that the considered radio path exhibits the properties of a two-part impedance surface, i.e., it consists of two sections. At a distance of 70 km from a radiation source and at a frequency of 255 kHz of the electromagnetic wave, the field decreases with the distance R according to the power law as R{sup -1.5} and a power index takes an intermediate value between the power indices for decreasing the field in free space R{sup -2} and for the decrease in the field above an ideal conducting surface R{sup -1}. With further propagation at a distance of 70–220 km, the field shows the specific behavior of a surface electromagnetic wave.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

In Situ MOF Pyrolysis Construction of Hierarchical Porous Co‐Nanoparticles/Carbon Cloth Composites for Enhanced Electromagnetic Wave Shielding and Absorption

The development of high-performance electromagnetic protection materials integrating broadband absorption and effective shielding capabilities is hindered by challenges in simultaneously optimizing multiple electromagnetic properties through conventional material designs. This study pioneers a hierarchical porous Co nanoparticle/carbon cloth (Co/CC) composite via controlled annealing of a Co-MOF precursor on carbon cloth. The Co-MOF served a dual role as both magnetic source and pore-forming agent, enabling in situ generation of uniformly dispersed Co nanoparticles and creation of abundant pores/interfaces on the CC fibers during pyrolysis. This unique architecture synergistically enhanced dielectric loss (via interfacial/dipolar polarization) and magnetic loss (via natural resonance, exchange interactions, and eddy currents), significantly improving impedance matching. The hierarchical pores further functioned as integrated “absorption–reflection” units for efficient electromagnetic energy attenuation. Consequently, the Co/CC composite annealed at 800°C (Co/CC-800) achieves minimum reflection loss (−40.69 dB) and 120% effective absorption bandwidth extension (6.16 GHz) as a filler, and exhibits superior electromagnetic interference shielding effectiveness (46.66 dB) as an integrated component. Significantly, Co/CC-800 demonstrated robust photothermal and electrothermal conversion capabilities, ensuring operational stability in ice-covered and humid harsh environments. This work pioneers a pore-structure-mediated strategy to harmonize dielectric–magnetic synergy, providing a new paradigm for designing advanced multifunctional electromagnetic protection materials.

dielectric‐magnetic synergy↗
NASA NTRS1985

Electromagnetic wave scattering in a two-layer anisotropic random medium

For electromagnetic wave propagation and scattering in an anisotropic random medium, the Dyson equation for the mean field and the Bethe-Salpeter equation for the correlation or the covariance of the field were derived. With the random permittivity expressed in a general anisotropic form, the bilocal and the nonlinear approximations are employed to solve the Dyson equation, and the ladder approximation to solve the Bethe-Salpeter equation. The mean dyadic Green's function for a two-layer anisotropic random medium with arbitrary three-dimensional correlation functions has been investigated with the zeroth-order solutions to the Dyson equation under the nonlinear approximation. The effective propagation constants are calculated for the four characteristic waves associated with the coherent vector fields, propagating in an anisotropic random-medium layer, which are the ordinary and extraordinary waves with upward- and downward-propagating vectors.

Lee, J. K.↗