Study on Absorbing Properties of Honeycomb Absorbing Materials

2013 ◽  
Vol 815 ◽  
pp. 645-649
Author(s):  
Hui Min Sun ◽  
Zhao Zhan Gu ◽  
Ran Ran Yang
Keyword(s):  
Layer Thickness ◽  
High Frequency ◽  
Free Space ◽  
Low Frequency ◽  
Resonance Peak ◽  
Test Method ◽  
Electromagnetic Parameters ◽  
Frequency Wave ◽  
Absorbing Materials

Honeycomb absorbing materials were measured using the method of free space in this paper. The reflectance of honeycomb absorbing materials was calculated and simulated, and it was verified based on the measured results. It was demonstrated that this test method was feasible. Through studying on absorbing properties of honeycomb, the results have showed that the radar absorbing properties of honeycomb are related to electromagnetic parameters, as well as thickness of the dip-coatings. With the increase of thickness of the dipping layer, the radar absorbing capability of high frequency and low frequency wave are significantly increased. It is worth noting that the resonance peak moved to the low frequency with the increase of dipping layer thickness. These results are useful for design of honeycomb absorbing materials.

Characterization and Design of Honeycomb Absorbing Materials

2019 ◽  
Vol 294 ◽  
pp. 51-56
Author(s):  
Hui Min Sun ◽  
Le Chen ◽  
Zhao Zhan Gu
Keyword(s):  
Double Layer ◽  
Low Frequency ◽  
Single Layer ◽  
Electromagnetic Parameters ◽  
Honeycomb Sandwich ◽  
Absorbing Materials ◽  
Absorbing Material ◽  
The Difference ◽  
Free Space Method ◽  
Honeycomb Sandwich Structure

Honeycomb absorbing materials are anisotropic structural materials. Depending on the size of honeycomb lattices, the absorbent content of the impregnated layer is different, the thickness of the impregnated layer is different, and the absorbing function of the impregnated honeycomb absorbing materials is also different. For the characterization of electromagnetic parameters of honeycomb absorbing materials, this paper adopts free space method for testing, uses CST software for modeling, and inverts the electromagnetic parameters of honeycomb absorbing structures. The absorbing performance of single-layer and double-layer honeycomb sandwich structures was simulated by RAM Optimizer software. The research shows that the height of the single-layer honeycomb absorbing material is 22mm. When the absorber content is 65%, 75% and 85% respectively, the harmonic peak moves slightly to the low frequency electromagnetic wave with the increase of the absorber content, but the absorbing strength decreases with the increase of the absorber content. For the double-layer honeycomb sandwich structure, the difference of absorber content in the upper and lower honeycomb absorbing materials is smaller, and the absorbing performance is stronger. When the thickness of the wave-transparent panel is thinner, the harmonic peak of the absorbing curve moves slightly to the high frequency.

Growth of low-frequency waves due to a photon beam in a magnetized electron–positron plasma

1997 ◽  
Vol 58 (2) ◽  
pp. 345-366 ◽  
Author(s):  
QINGHUAN LUO ◽  
D. B. MELROSE
Keyword(s):  
High Frequency ◽  
Random Phase ◽  
Low Frequency ◽  
Photon Beam ◽  
Radio Waves ◽  
Wave Interactions ◽  
Frequency Wave ◽  
Pair Plasma ◽  
Electron Positron ◽  
Low Frequency Waves

The effect of a beam of radio waves of very high brightness passing through a cold, magnetized, electron–positron plasma is discussed. The properties of the natural wave modes in such a plasma are summarized, and approximate forms for the nonlinear response tensor are written down. Photon-beam-induced instabilities of low-frequency waves in the pair plasma are analysed in the random-phase approximation. When three-wave interactions involve two high-frequency waves in the same mode and a low-frequency wave in a different mode, wave–wave interactions are similar to wave–particle interactions in that photons act like particles that emit and absorb low-frequency waves. The absorption coefficients for various low-frequency waves due to a photon beam are evaluated. In a pure electron–positron plasma, photon-beam-induced instabilities can be effective only when either the high-frequency or the low-frequency waves are strongly modified by the magnetic field. The growth of the low-frequency waves is most effective when the high-frequency photon beam has a frequency close to the cyclotron frequency.

scholarly journals Simulation of non-hydrostatic gravity wave propagation in the upper atmosphere

2014 ◽  
Vol 32 (4) ◽  
pp. 443-447 ◽  
Author(s):  
Y. Deng ◽  
A. J. Ridley
Keyword(s):  
Wave Propagation ◽  
Gravity Wave ◽  
High Frequency ◽  
General Circulation ◽  
Low Frequency ◽  
Circulation Model ◽  
Horizontal Resolution ◽  
Upper Atmosphere ◽  
Cutoff Wavelength ◽  
Frequency Wave

Abstract. The high-frequency and small horizontal scale gravity waves may be reflected and ducted in non-hydrostatic simulations, but usually propagate vertically in hydrostatic models. To examine gravity wave propagation, a preliminary study has been conducted with a global ionosphere–thermosphere model (GITM), which is a non-hydrostatic general circulation model for the upper atmosphere. GITM has been run regionally with a horizontal resolution of 0.2° long × 0.2° lat to resolve the gravity wave with wavelength of 250 km. A cosine wave oscillation with amplitude of 30 m s−1 has been applied to the zonal wind at the low boundary, and both high-frequency and low-frequency waves have been tested. In the high-frequency case, the gravity wave stays below 200 km, which indicates that the wave is reflected or ducted in propagation. The results are consistent with the theoretical analysis from the dispersion relationship when the wavelength is larger than the cutoff wavelength for the non-hydrostatic situation. However, the low-frequency wave propagates to the high altitudes during the whole simulation period, and the amplitude increases with height. This study shows that the non-hydrostatic model successfully reproduces the high-frequency gravity wave dissipation.

RADIATION FROM A SOURCE NEAR A PLANE INTERFACE BETWEEN AN ISOTROPIC AND A GYROTROPIC DIELECTRIC

1964 ◽  
Vol 42 (11) ◽  
pp. 2153-2172 ◽  
Author(s):  
S. R. Seshadri ◽  
A. Hessel
Keyword(s):  
Magnetic Field ◽  
Electromagnetic Field ◽  
Surface Waves ◽  
High Frequency ◽  
Free Space ◽  
Line Source ◽  
Low Frequency ◽  
Plane Interface ◽  
Magnetic Current ◽  
Asymptotic Evaluation

The radiation from a line source of magnetic current situated in free space near a plane interface between a semi-infinite free space and a semi-infinite gyrotropic dielectric is investigated for the case in which the gyrotropic axis is parallel to the line source. In addition to the space waves, it is found that in general two unidirectional surface waves are excited along the interface. The dispersion relations for the space and the surface waves are thoroughly examined. Both surface waves have different high-frequency cutoff but no low-frequency cutoff. The characteristics of these surface waves are investigated. An asymptotic evaluation of the total electromagnetic field is carried out for a particularly simple choice of the source frequency. For this frequency, the dependence of the efficiency of excitation of the surface waves on the distance of the source from the interface is determined. The radiation patterns are plotted for various values of the static magnetic field and the position of the source.

High-frequency radiation process during earthquake faulting—envelope inversion of acceleration seismograms from the 1993 Hokkaido-Nansei-Oki, Japan, earthquake

1997 ◽  
Vol 87 (4) ◽  
pp. 904-917 ◽  
Author(s):  
Yasumaro Kakehi ◽  
Kojiro Irikura
Keyword(s):  
High Frequency ◽  
Fault Plane ◽  
Source Region ◽  
Low Frequency ◽  
Strong Motion ◽  
Rupture Process ◽  
Wave Radiation ◽  
Radiation Process ◽  
Frequency Wave ◽  
High Frequency Wave

Abstract We investigate the process of high-frequency (1 to 10 Hz) radiation on the fault plane of the 1993 Hokkaido-Nansei-Oki, Japan, earthquake (MW = 7.5) from the envelope inversion of strong-motion acceleration seismograms. For the analysis, empirical Green's functions are used because theoretical approach is not available for such high frequencies. The source is modeled with two fault planes with different strike angles. The rupture process of this earthquake is very complex in terms of high-frequency wave generation. The rupture, which started on the northern fault plane, had a delay of about 10 sec or propagated very slowly between the northern and southern fault planes. High-frequency wave radiation is large at the northern and southern edges of the source region. Deceleration of rupture is also observed there. This is interpreted to be associated with stopping of rupture. Another high-frequency wave radiation area is found at the center of the northern fault plane, where discontinuity in the depth distribution of aftershocks suggests an existence of a barrier. The areas of high- and low-frequency wave radiation are not correlated. This is considered to result from the complexity of rupture process. We cannot distinguish between westward and eastward dip of the southern fault plane because of one-sided station distribution.

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