Transmission Of Electromagnetic Radiation Research Articles

Electrophysical and acoustic properties of magnetic elastomers structured by an external magnetic field

Magnetoactive elastomers are promising for use in designing of magnetically operated devices for signal processing and sensors. The results from studying the electrophysical and acoustic properties of new magnetoactive elastomers structured by a nonuniform magnetic field are presented. It is shown that the prestructuring of the magnetic disperse filler by a magnetic field during composite synthesis substantially improves the coefficient of the transmission of electromagnetic radiation through the sample. The effect gets stronger as the mass fraction of filler increases. As the filler concentration grows, the transmission coefficient falls by 50%, and the ref lection coefficient grows by a factor of 150%. The longitudinal elastic modulus and the density vary within the ranges of 1.4–1.8 GPa and 2485–3362 kg m–3, respectively, depending on the magnetic filler concentration and the sample’s structuring. The obtained results demonstrate the potential of usinf structured magnetoactive elastomers as radar absorbing materials.

Sharpening method of satellite thermal image based on the geographical statistical model

To improve the effectiveness of thermal sharpening in mountainous regions, paying more attention to the laws of land surface energy balance, a thermal sharpening method based on the geographical statistical model (GSM) is proposed. Explanatory variables were selected from the processes of land surface energy budget and thermal infrared electromagnetic radiation transmission, then high spatial resolution (57 m) raster layers were generated for these variables through spatially simulating or using other raster data as proxies. Based on this, the local adaptation statistical relationship between brightness temperature (BT) and the explanatory variables, i.e., the GSM, was built at 1026-m resolution using the method of multivariate adaptive regression splines. Finally, the GSM was applied to the high-resolution (57-m) explanatory variables; thus, the high-resolution (57-m) BT image was obtained. This method produced a sharpening result with low error and good visual effect. The method can avoid the blind choice of explanatory variables and remove the dependence on synchronous imagery at visible and near-infrared bands. The influences of the explanatory variable combination, sampling method, and the residual error correction on sharpening results were analyzed deliberately, and their influence mechanisms are reported herein.

Interaction of electromagnetic radiation in the 20-200 GHz frequency range with arrays of carbon nanotubes with ferromagnetic nanoparticles.

The interaction of electromagnetic radiation with a magnetic nanocomposite based on carbon nanotubes (CNT) is considered within the model of distributed random nanoparticles with a core–shell morphology. The approach is based on a system composed of a CNT conducting resistive matrix, ferromagnetic inductive nanoparticles and the capacitive interface between the CNT matrix and the nanoparticles, which form resonance resistive–inductive–capacitive circuits. It is shown that the influence of the resonant circuits leads to the emergence of specific resonances, namely peaks and valleys in the frequency dependence of the permeability of the nanocomposite, and in the frequency dependence of the reflection and transmission of electromagnetic radiation.

Enhanced resonant transmission of electromagnetic radiation through a pair of subwavelength slits

We show that a pair of subwavelength slits in parallel conducting plates supports a localized electromagnetic mode bound to the slits, whose spatial extent is determined not by the plates' size but by the slit dimensions. This mode occurs for electric fields parallel to the slits and plate separation slightly smaller than half the free-space wavelength. Finite element calculations and experimental results at 10 GHz show that the localized mode gives rise to a strong, narrowband resonant enhancement of the transmission which, while limited by conduction losses in the plates, is a factor of 104 larger than for off-resonant transmission.

3D Imaging of Water Behavior at Millimeter Wavelength

During the transmission of electromagnetic radiation through a medium containing water molecules, portions of the electromagnetic spectrum are absorbed by water molecules. This water absorption occurs preferentially at certain characteristic wavelengths while the balance of the spectrum is transmitted with minimal e ects. This characteristic of water provides advantages but also some disadvantages in science and engineering applications. Especially in remote sensing applications, it may cause to produce incorrect information. So identi cation of behavior of electromagnetic wave in water is signi cantly important. Some of the studies based on electromagnetic wave behavior in water are bio-medical researches, sensors, transmitters, accumulators, organic-inorganic materials, and microwave ovens. In this paper, based on the water's absorption of electronic wave property, a plastic cup as half-full of water is imaged using near eld microwave system. After being processed with 3D-DLL algorithm it is imaged as 3D with IRIS software. A robotic system is used for data collection process. Transmission and re ection measurements of system are done with N5230A network analyzer.

Reflectionless transmission of electromagnetic radiation through a magnetic–dielectric system

The conditions and frequency band of reflectionless transmission of electromagnetic radiation through a plane absorbing layer of a magnet that separates two semi-infinite nonabsorbing dielectric media have been found. The dependence of these conditions on the separating layer thickness, magnetic and dielectric properties of the layer substance, and of the adjacent substrate is investigated.

Dielectric and Radiative Properties of Sea Foam at Microwave Frequencies: Conceptual Understanding of Foam Emissivity

Foam fraction can be retrieved from space-based microwave radiometric data at frequencies from 1 to 37 GHz. The retrievals require modeling of ocean surface emissivity fully covered with sea foam. To model foam emissivity well, knowledge of foam properties, both mechanical and dielectric, is necessary because these control the radiative processes in foam. We present a physical description of foam dielectric properties obtained from the foam dielectric constant including foam skin depth; foam impedance; wavelength variations in foam thickness, roughness of foam layer interfaces with air and seawater; and foam scattering parameters such as size parameter, and refraction index. Using these, we analyze the scattering, absorption, reflection and transmission in foam and gain insights into why volume scattering in foam is weak; why the main absorption losses are confined to the wet portion of the foam; how the foam impedance matching provides the transmission of electromagnetic radiation in foam and maximizes the absorption; and what is the potential for surface scattering at the foam layers boundaries. We put all these elements together and offer a conceptual understanding for the high, black-body-like emissivity of foam floating on the sea surface. We also consider possible scattering regimes in foam.

Measuring the parameters of solid and liquid dielectrics at microwave frequencies with the use of microstrip photonic structures

Features of interaction of microwave electromagnetic radiation with one-dimensional photonic crystals made on the basis of microstrip transmission lines with a variable substrate permittivity and variable width of the upper strip conductor are investigated. A method for determining the parameters of solid and liquid dielectrics from the measured frequency dependences of the coefficient of transmission of electromagnetic radiation interacting with the microstrip photonic structure, in which the samples under investigation act as irregularities, is theoretically substantiated and experimentally implemented. The results of measuring the complex permittivity of a number of liquid dielectrics are presented.

Transformation of electromagnetic radiation by rapidly moving inhomogeneities of a transparent medium

A theory of reflection and transmission of electromagnetic radiation by inhomogeneities of the parameters of a static transparent medium moving at the velocity of light is developed. Expressions are obtained for the Doppler frequency shift of radiation; it turns out that, under the condition of pronounced frequency dispersion, the frequency of incident radiation corresponds to two frequencies of reflected radiation (complementary waves). It is found that, as the velocity of an inhomogeneity tends to the phase velocity of radiation in the medium, the reflection and transmission coefficients of radiation by the inhomogeneity indefinitely increase. It is shown that the electromagnetic radiation frequency may increase severalfold, with a transformation coefficient of about unity, due to the Doppler shift by the inhomogeneities of a nonlinear medium that are induced by pulses (solitons) of intense counterpropagating radiation.

Interactions Between Carbon Nanotubes and Liquid Crystals in Binary Nematic Electro-Optic Cells

AbstractWe studied the effects of multiwalled carbon nanotubes (MWCNTs) on the Freedericksz transition of a liquid crystal (LC) and calibrated the altitudinal angle of CNTs as a function of the electric field. In addition, we directed the azimuthal angle which gave us complete control of the 3D orientation of the CNTs. We constructed anti-parallel electro-optic cells using a nanocomposite at a concentration of 0.01% CNTs with 4-Cyano-4'-pentylbiphenyl (5CB) liquid crystal. This low concentration was necessary to achieve maximum transmission of electromagnetic radiation through the cell and to minimize the Van der Waals attraction between the CNTs responsible for their aggregation. We chose two dimensional microscopic transmission ellipsometry (2D-MTE) to measure the phaseshift of the polarized electromagnetic radiation through the cell and to derive from it the altitudinal angle of the CNTs. Our results show that in the presence of CNTs the Freedericksz transition occurs at 55% of the transitional electric field as compared to the control electro-optic cell without CNTs. The width of the Freedericksz transition narrows by a similar factor. The switching time of the cell decreased in the presence CNTs by 18.5%.

Nanocarbon-Epoxy Composites as Electromagnetic Shielding Materials

We present the results of studies of the electromagnetic radiation (EMR) shielding by epoxy-nanocarbon composites (CMs). The EMR frequency range was 25.5–37.5 GHz. Thermoexfoliated graphite and multiwalled carbon nanotubes (CNT) have been used as fillers in CM (the content of a filler was 0.5–2 wt.%). We examined the effect of carbon filler's type in CM on characteristics of the electromagnetic shielding. It is shown that, even for low contents (∼ 1–2 wt.%) of a nanocarbon filler in CMs, the coefficient of EMR transmission is − (25-27) dB (for h = 1 mm).The real ϵ′ and imaginary ϵ″ parts of dielectric permittivity of the composites under investigation have been determined.

Resonant transmission of electromagnetic fields through subwavelength zero-ϵslits

We theoretically investigate the transmission of electromagnetic radiation through a metal plate with a zero-$ϵ$ metamaterial slit, where the permittivity tends towards zero over a given bandwidth. Our analytic results demonstrate that the transmission coefficient can be substantial for a broad range of slit geometries, including subwavelength widths that are many wavelengths long. This resonant effect has features quite unlike the Fabry-Perot-like resonances that have been observed in conductors with deep channels. We further reveal that ultranarrow zero-$ϵ$ channels can have significantly greater transmission compared to slits with no wave impedance difference across them.

Strongly resonant transmission of electromagnetic radiation in periodic anisotropic layered media

The electromagnetic dispersion in periodic layered media can be tailored and their resonant properties can be considerably improved by utilizing anisotropic materials. Periodic structures with a photonic band edge split into two parts, or so-called split band edge, exhibit superior resonant properties including exceptionally high $Q$ values of transmission resonances and nearly perfect impedance matching at the boundaries, even when the number of unit cells $N$ is not large. A microwave transmission resonance with $Q\ensuremath{\sim}220$ is demonstrated in a periodic stack of form-birefringent layers with $N=12$ realized in a waveguide geometry.

Dynamic control of visible radiation by a liquid crystal filled Fabry-Pérot etalon

A liquid crystal filled Fabry-Pérot etalon has been constructed to control the resonant transmission of electromagnetic radiation over the visible range of the spectrum. This has been achieved through the use of a 1.5μm thick homogeneously aligned liquid crystal layer in the core of a silver-clad etalon structure. Applying an electric field across the core reorientates the liquid crystal director and changes the refractive index for incident light polarized parallel to the rubbing direction. By measuring the transmitted intensity as a function of wavelength for a variety of applied voltages shifts in the positions of the resonant transmission modes of up to 80nm have been observed. In addition, these results have been compared to model data generated using a multilayer optics model to obtain the dispersion of the liquid crystal over the visible range of the electromagnetic spectrum.

Improved performance of amorphous silicon solar cells via scattering from surface plasmon polaritons in nearby metallic nanoparticles

An engineered enhancement in short-circuit current density and energy conversion efficiency in amorphous silicon p-i-n solar cells is achieved via improved transmission of electromagnetic radiation arising from forward scattering by surface plasmon polariton modes in Au nanoparticles deposited above the amorphous silicon film. For a Au nanoparticle density of ∼3.7×108cm−2, an 8.1% increase in short-circuit current density and an 8.3% increase in energy conversion efficiency are observed. Finite-element electromagnetic simulations confirm the expected increase in transmission of electromagnetic radiation at visible wavelengths, and suggest that substantially larger improvements should be attainable for higher nanoparticle densities.

All-optical switching of the transmission of electromagnetic radiation through subwavelength apertures

Unprecedented optical control of the surface plasmon polariton assisted transmission of terahertz radiation through subwavelength apertures is rendered possible by carrier-induced changes to the dielectric properties of a semiconductor grating. Although the study presented is static, the extension of our approach to dynamic switching and tuning is deemed straightforward, opening the way for the realization of ultrafast surface plasmon based devices.

SPATIAL DISTRIBUTION OF SURFACE PLASMON POLARITON FROM METALLIC NANOSTRUCTURES

The spatial distribution of the interference of surface plasmon polariton (SPP) on metallic nanostructures has been studied. The results show that the transmission of electromagnetic radiation is remarkably enhanced for frequencies close to the surface plasmon band and the interference of SPP can redistribute the illumination light into subwavelength-scale spatial distribution with high intensity, which beats the Rayleigh diffraction limit. For an appropriate thickness, the transmission of an unperforated structure can be larger than that of holes or slits systems with the same periodicity and thickness when the coupled surface plasmon wave mode is excited. With the help of the interference of the horizontal plasmon excited by Bragg resonance due to the periodicity in the horizontal direction, the vertical plasmons, excited in z direction via Fabry–Perot cavity resonance in different grooves, are correlated, so the transmission is increased via the tunneling process. The properties of transparency for light but impenetrability for gas and liquid will be of importance for device applications. The information on near-field distribution from perforated metallic structures is important for understanding the underlying physics, as well as for optimizing photonic crystals for possible applications.

Macroporous silicon membranes as electron and x-ray transmissive windows

Macroporous silicon membranes are fabricated whose pores are terminated with 60nm thin silicon dioxide shells. The transmission of electrons with energies of 5kV–25kV through these membranes was investigated reaching a maximum of 22% for 25kV. Furthermore, the transmission of electromagnetic radiation ranging from the far-infrared to the x-ray region was determined. The results suggest the application of the membrane as window material for electron optics and energy dispersive x-ray detectors.

Thermal switching of the enhanced transmission of terahertz radiation through subwavelength apertures.

We demonstrate that the extraordinary transmission of terahertz radiation through semiconductor gratings of subwavelength apertures can be switched completely by varying the temperature. The enhanced transmission, which is due to the resonant tunneling of surface plasmon polaritons that can be excited in semiconductors at terahertz frequencies, is controlled by thermally modifying the density of free carriers. The transmission through metal gratings cannot be switched in the same way since the carrier density is temperature independent. Thus semiconductors offer an interesting alternative to metals in enhancing the transmission of electromagnetic radiation.

Band of selective transmission of electromagnetic radiation by an absorbing dielectric layer

Equations for determining the frequency band near the frequency of selective reflectionless transmission of electromagnetic radiation by a layer of an absorbing dielectric which separates two nonabsorbing media with dissimilar optical densities have been obtained. The absorption band of the wave in the dielectric layer as a function of the dielectric properties and thickness of the layer and of the dielectric properties of the separated media has been evaluated.