Band Electromagnetic Wave Research Articles

Stimulated Raman scattering of beat wave of two counter-propagating X-mode lasers in a magnetized plasma

Effects of transverse static magnetic field on stimulated Raman scattering (SRS) of the beat wave excited by two counter-propagating lasers are studied. Two counter-propagating lasers with frequency difference, ω1∼ω2≥2ωp, drive a non resonant space charge beat mode at wave number k→0≈k→1+k→2 in a plasma, where k→1 and k→2 are wave vectors of lasers having frequencies ω1 and ω2, respectively. The driven beat wave acts as a pump for SRS and excites parametrically a pair of plasma wave (ω,k→) and side band electromagnetic wave (ω3,k→3) propagating in the sideward direction in such a way that momentum remains conserved. The growth rate of Raman process is maximum for side scattering at θs=π/2 for lower values of applied magnetic field (∼1 kG), which can be three fold by applying magnetic field ∼5.0 kG. Thus, optimum value of magnetic field can be utilized to achieve maximum electron acceleration in counter propagating geometry of beat wave acceleration by reducing the growth rate of Raman process.

Design of WLAN Anti-Interference λ / 4 - Absorber's Parameters in 4G Era

The problem of WLAN anti -interference has become an important issue that affects the application. This paper explores the electromagnetic parameters' optimization of λ/ 4 type dielectric absorber in 2.4GHz and 3.6GHz .Studies show that: through the early design of the material's parameters, such as complex permittivity and thickness, the obtained ideal electromagnetic parameters' area can achieve a predetermined reflectivity at the desired frequency , then choose material to get high absorbing preparation , which can provide design basis for the preparation of different frequency band and high performance electromagnetic wave absorber.

Galactic Center origin of a subset of IceCube neutrino events

The center of the Milkyway is a host to energetic phenomena across many electromagnetic wave-bands and now possibly of high-energy neutrinos. We show that 5 out of 21 IceCube shower-like events, including a PeV event, likely originated from the Galactic Center region. Hard spectrum and flux inferred from these events are inconsistent with atmospheric neutrinos. The flux of these neutrinos is consistent with an extrapolation of the gamma-ray flux measured by Fermi-LAT from the inner Galactic region. This indicates a common hadronic origin of both, powered by supernovae. Three other shower-like events are spatially correlated with the Fermi bubbles, originating from the Galactic Center activity, within the uncertainty of reconstructing their arrival directions. Origin of the other neutrino events, including 7 track-like events, is still elusive.

Band structure and reflectance for a nonlinear one-dimensional photonic crystal

We consider a model for a one-dimensional photonic crystal formed by a succession of nonlinear Kerr-type equidistant spaceless interfaces immersed in a linear medium. We calculate analytically the band structure of this system as a function of the incident wave intensity, and find two main tendencies: the appearance of prohibited bands, and the separation and narrowing of these bands. We consider as well a finite version of this photonic crystal for a limited number of alternating linear and non linear set of stacks for which we calculate reflectance as a function of the electromagnetic wave intensity, band index and number of periods. A system with these features can be constructed by alternating very thin slabs of a nonlinear soft matter material with thicker solid films, which can be used to design a device to control light propagation for specific wavelength intervals and light intensities of the same propagating signal.

ChemInform Abstract: Broad Band Electromagnetic Wave Absorbers Designed with Nano‐Metal Films

AbstractReview: 15 refs.

Study on the Electrical Behavior of MWCNTs in GF/Epoxy Composites

The multi-wall nanotubes (MWCNTs) were divisionalized equably by the fabric of glass in composites. Then the electrical properties such as permittivity, conductance and electromagnetic interference (EMI) shielding effectiveness (SE) of MWCNTs in GF/EP composite were studied. The effect of the content and dispersion of MWCNTs were researched in this work. Firstly the permittivity of MWCNTs/GF/EP composites were studied respectively by keeping layers of glass fabric and increasing content of MWCNTs or keeping content of MWCNTs and changing layers of glass fabric in electromagnetic wave band (5.85-18 GHz). Then the conductance of MWCNTs/GF/EP composites with different MWCNTs contents was tested. Furthermore, the EMI SE of composites with different MWCNTs contents in electromagnetic wave band (5.85-18 GHz) were studied. In addition, the morphologies of MWCNTs/GF/EP composites with the different MWCNTs weight percent were observed. The results show that the real part of permittivity of composites can be improved highest up to 75 and the imaginary part increase maximum up to 80. However there is no disciplinarian about effect of layers of glass fabric on dielectric property. The MWCNTs/GF/EP composite can be changed from the insulator to the semiconductor along with increasing the weight percent of MWCNTs. In electromagnetic wave band 5.85-18 GHz, the values of SE are increasing with increasing content of the MWCNTs.

Iron Nanofibers Synthesized by the Electrospinning Method for Use as a GHz Band Electromagnetic Wave Absorber

In this study, we fabricated Fe nanofibers that had a high aspect ratio and were coated by an oxidation protection layer, because electromagnetic properties are affected by the aspect ratio and oxidized layers. PVP/Fe salt nanofibers were prepared by an electrospinning method using an optimized concentration of PVP solution with Iron(lll) nitrate nonahydrate (Fe (NO3)3.9H2O) solution to apply a high voltage. Subsequently, to prepare the Fe nanofibers, the PVP/Fe salt nanofibers were heated up to 600 degrees C in air and reduced to 450 degrees C in H2. The Fe nanofibers were then coated by PVP to prevent re-oxidation. The S-parameter of the prepared Fe nanofibers was measured by a network analyzer, and the power loss was calculated to estimate the EM absorption ability.

Broad band electromagnetic wave absorbers designed with nano‐metal films

AbstractIn the thirties of the last century it was shown that nano‐metal films have a frequency independent absorption in the far infrared regime and below. Moreover, the absorption A of these films is 0.5 and at the same time both reflection R and transmission T are 0.25, complying with the relation A + R + T = 1 at a sheet resistance Z□of 60 πΩ. The latter property of nano‐metal films was shown by Woltersdorff in 1934. Multiple reflections between such films allow the design of low reflecting large scale absorbers for the wave length range from far infrared to low frequency radio waves. Experimental data of the novel absorber device measured in the GHz frequency range are presented. The electrical nano‐metal film properties are also useful for applications in IR‐photonics and IR‐communication systems. The article presents a brief review of the historical studies on free carrier electromagnetic wave absorption and on novel applications.

Broad band electromagnetic wave absorbers designed with nano-metal films

In the thirties of the last century it was shown that nano-metal films have a frequency independent absorption in the far infrared regime and below. Moreover, the absorption A of these films is 0.5 and at the same time both reflection R and transmission T are 0.25, complying with the relation A + R + T = 1 at a sheet resistance Z□of 60 πΩ. The latter property of nano-metal films was shown by Woltersdorff in 1934. Multiple reflections between such films allow the design of low reflecting large scale absorbers for the wave length range from far infrared to low frequency radio waves. Experimental data of the novel absorber device measured in the GHz frequency range are presented. The electrical nano-metal film properties are also useful for applications in IR-photonics and IR-communication systems. The article presents a brief review of the historical studies on free carrier electromagnetic wave absorption and on novel applications.

A knowledge-based system for the non-destructive diagnostics of façade isolation using the information fusion of visual and IR images

This paper describes a knowledge-based system for the non-destructive diagnostics of façade isolation. The system uses the fusion of information extracted from images obtained from two electromagnetic wavebands: from low-resolution IR images (320 × 240 pixels; 7.5–13 μm wavelength), and from high-resolution visual RGB images (3264 × 2448 pixels; 0.39–0.75 μm wavelength). The fusion of the information is a perquisite for the design of an efficient knowledge-based system for non-destructive testing and façade diagnostics. In the paper, special attention is devoted to the following knowledge-based system components: system-core components (the database, the knowledge base, the inference engine, and the user interface) and application-specific components (image acquisition, the resolution pyramid, image pre-processing and feature extraction, image registration, object segmentation, fusion, and data analysis). Examples of the non-destructive testing and the façade diagnostics obtained with the system are presented.

Passive remote sensing of the Earth's plasmasphere using Whistler mode waves

AbstractAs the uses of artificial satellites diversify, investigation of the propagation characteristics of electric waves surrounding the Earth has become an important task. These electric waves are strongly influenced by plasma, a propagation medium, but although on the one hand investigation of plasma in the ionosphere is proceeding with various different methods being used, current investigations into the density profile of plasma in the plasmasphere is not progressing since it is hampered by the fact that satellites produce only single point observations. In this paper we develop a method for estimating the density profile of the global electrical field of the plasmasphere from natural VLF band electromagnetic wave frequency spectra and propagation vector direction information observed by satellite by solving an ill‐posed inverse problem. We confirm the uniqueness of the solution by performing a brute force search using a dictionary and investigate the applicability of our method to actual data by using pseudo‐observation data. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(12): 51–61, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20377

Measurement of scattering coefficients of soil by Ka‐band polarimetric scatterometer—Dependence on soil moisture content and surface roughness

AbstractTo clarify the scattering characteristics of the ground surface for Ka band electromagnetic waves, which is necessary for evaluation of the effect of the Ka band rain radar on board the Global Precipitation Measurement Mission core satellite, the dependence of the normalized radar cross section (backscattering coefficient) σ0 of the soil on the surface roughness and the water content in the soil was measured with a Ka band polarimetric scatterometer. The results show that the dependence of the backscatter coefficient σ0 on the surface roughness, the moisture sensitivity, and the angle of incidence is obtained for the Ka band waves. For an angle of incidence of 10°,σ0 does not depend much on the surface roughness and increases in proportion to the water content. σ0 is calculated by the theoretical equation and the empirical equation, and is found accurate by comparison with the experiment. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(2): 1– 11, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20339

Improved algorithm for electromagnetic scattering of plane waves by a radially stratified tilted cylinder and its application

Abstract An efficient numerical procedure for computing the scattering coefficients of a radially stratified tilted cylinder is discussed. Compared with the previous algorithms, computations for scattering field in our code are extended to fairly large parameters, up to more than 10,000 and a few millions in the number of layers, and computational time is only a few seconds. The capabilities of our code depend also on the memory of the computer. The algorithm can also be used for absorbing or nonabsorbing cylinders in different electromagnetic wave bands. Compared with the known results, the algorithm is validated. At last, the algorithm is used to simulate the intensity distributions of two-layered cylinders with large size parameter and of graded-index polymer optical fiber (GI-POF) at tilted incidence, which supplies information on non-intrusive measurement on-line of refractive index profile by light scattering.

The variability of BL Lac 3C 66A

It is now known that there are supermassive black holes at the centre of a galaxy, surrounded by an accretion disc. The black hole-jet-accretion disc model plays an important role in the explanation of the observational properties of active galactic nuclei. BL Lacertae objects form a subclass of blazars; they are monitored through electromagnetic wave bands. During the OJ-94 project, 3C 66A was observed as a comparison object of OJ287 and found to display a possible 65-day period in the V light curve. In this paper, we show that the instability of an accretion disc surrounding a massive central black hole (2.5×107M⊙) may explain this period in 3C 66A.

Spin dynamics and phase transitions in quasi-2D antiferromagnets R 2CuO4 (R=Pr, Nd, Sm, Eu, Gd)

The spin and lattice dynamics of the R2CuO4 quasi-2D antiferromagnetic crystals (R=Pr, Nd, Sm, Eu, Gd) were studied in the millimeter-range electromagnetic wave band. Strong variations of the absorption coefficient were observed to occur at temperatures T≈T0. Absorption lines of electrical nature due to lattice dynamics were also revealed near the T0 temperatures. The observed anomalies are assumed to originate from phase transitions at T≈T0, which entail changes in the structural and magnetic properties.

The intrinsic relation between envelope solitons and plasma instabilities

A general form of the one-dimensional nonlinear Schrödinger equation is derived; the coefficients depend mainly on the linear dispersion relation, as does the nonlinear term. Envelope solitons may only exist together with some plasma instabilities. An example of solar radio bursts is selected as evidence for envelope solitons in the electromagnetic waveband.

Insulation diagnostic technique to assess the condition of generator winding by measuring microwave associated with dielectric breakdown

A partial discharge (PD) occurring in the insulation of the stator winding of the generator is a symptom of the deterioration of the insulation system, PD is a very short duration current and/or voltage pulse, about 1-5 ns. Generally a PD emits a broad band electromagnetic wave (/spl sim/GHz). We developed a new system for detecting the microwave emitted from a PD. From the point of view of predicting an accident caused by the insulation breakdown of the generator winding, it is important to assess the condition of the winding. We applied our system to a dielectric breakdown test to know the relation between the characteristics of the microwave and the condition of the insulation system of the winding. The dielectric breakdown test is useful for estimating the minimum breakdown voltage which is a criterion of the insulation condition of the winding. Experimental results showed that this system was able to assess the insulation condition by measuring the number of the pulses of microwave frequency per voltage cycle.

Example of self-averaging in three dimensions: Anderson localization of electromagnetic waves in random distributions of pointlike scatterers

A simple yet realistic theoretical model is used to study Anderson localization of electromagnetic waves in three-dimensional disordered dielectric media. The preliminary results presented in our previous paper [M. Rusek, A. Or\l{}owski, and J. Mostowski, Phys. Rev. E 53, 4122 (1996)] are substantially extended and a sound physical interpretation is proposed. Very striking universal properties of the spectra of random matrices describing the scattering from a collection of randomly distributed pointlike scatterers are discovered. The appearance of the band of localized electromagnetic waves, emerging in the limit of an infinite system, is numerically observed.

Band of localized electromagnetic waves in random arrays of dielectric cylinders

Anderson localization of electromagnetic waves in random arrays of dielectric cylinders is studied. An effective theoretical approach based on analysis of probability distributions, not averages, is developed. The disordered dielectric medium is modeled by a system of randomly distributed two-dimensional electric dipoles. Spectra of certain random matrices are investigated and the appearance of the band of localized waves emerging in the limit of an infinite medium is discovered. It suggests deeper insight into the existing experimental results. @S1063-651X~97!00410-8# PACS number~s!: 41.20.Jb, 72.15.Rn, 42.25.Fx, 03.65.Ge Disordered dielectric structures with typical length scale matching the wavelength of electromagnetic radiation are still a subject of intensive experimental and theoretical studies. Electromagnetic waves propagating in these structures mimic, to reasonable extent, the behavior of electrons in disordered semiconductors. Many ideas concerning transport properties of light and microwaves in such media exploit the well-developed theoretical methods and concepts of solidstate physics. Let us mention, e.g., the concept of electron localization in noncrystalline systems such as amorphous semiconductors or disordered insulators. According to Anderson @1#, an entire band of electronic states can be spatially localized in a sufficiently disordered infinite material. Before this discovery, it was believed that electronic states in infinite media are either extended, by analogy with the Bloch picture for crystalline solids, or are localized around isolated

Anderson localization of surface electromagnetic waves on rough, perfectly conducting surfaces that are periodic on average

Based on the integral equation satisfied by the Green's function G( r o , r) for electromagnetic waves on a one-dimensional, randomly rough, perfectly conducting surface that is periodic on average, a numerical simulation approach is developed that yields the function 〈| G( r 0, r)| 2〉 − |〈 G( r 0, r)〉| 2, where the angle brackets den the ensemble of realizations of the surface profile function. The frequency dependence of the localization length, obtained from the exponential decay of this function, is then calculated for frequencies about the edges of the surface electromagnetic wave bands of the underlying periodic system. In the gap, the localization length is very small and fairly independent of the frequency. However, when the frequency enters in the allowed bands, the localization length becomes larger; this increase is found to be steeper the weaker the disorder is.