Electromagnetic Wave Radiation Research Articles

Characteristic Evaluation of Multiple Layers Microwave Absorber Coated with Biomass Composite

Radiation Absorbing Material (RAM) is used to absorb radiations of electromagnetic wave surrounding us. Thus, the multiple layers’ microwave absorber using biomass composite materials could be one of the solutions to address the problem. In order to effectively absorb the radiation of electromagnetic wave, the multiple layers’ absorber is characterized to optimize the performance of the absorber. The characterization is made by varying biomass composite material contents, thickness and other possible considerations. CST Microwave Studio software is first used to design and simulate the multiple layers’ absorber to estimate its performance. Development of multiple layers’ prototype is carried out to test its performance at free space environment. Free space dielectric measurement method is used to determine the value of multiple layers’ absorber dielectric. The dielectric value is then used in CST software in order to make the simulation more precise. Free space arch which is connected to Agilent Analyzer is used to measure absorption of multiple layers’ microwave absorber.

Radiation from relativistic electrons in "light" and in conventional undulators. Classical and quantum approaches

A photon spectrum of undulator radiation (UR) is calculated in the semi-classical approach. The UR intensity spectrum is determined by an electron trajectory in the undulator neglecting by energy losses for radiation. Using the Planck's law, the UR photon spectrum can be calculated from the classical intensity spectrum both for linear and nonlinear regimes. The radiation of an electron in a field of strong electromagnetic wave (radiation in the "light" undulator) is considered in the quantum electromagnetic frame. Comparison of results obtained by both approaches has been shown that UR spectra in the whole cone coincide with high accuracy for the case x<<1. Characteristics of the collimated UR beam were simulated with taking into account the discrete process of photon emission along an electron trajectory in both kinds of undulators.

Численно-аналитический метод решения задачи об излучении из плоского волновода с конечным числом щелей

Численно-аналитический метод решения задачи об излучении из плоского волновода с конечным числом щелей

Radiation of electromagneticwaves by a spheroidal charged drop oscillating in a uniform electrostatic field

The dispersion relation is derived for a spheroidal charged drop oscillating in a uniform electrostatic field and radiating electromagnetic waves in the first and second orders with respect to the dimensionless oscillation amplitude and the steady-state deformation, respectively. For an individual drop and a model cloud the intensity of the electromagnetic radiation and the frequency bandwidth are estimated as functions of the drop dimensions and charge and the external electric field strength.

Spin-down of Pulsars, and Their Electromagnetic and Gravitational Wave Radiations

Pulsars posses extremely strong magnetic fields, and their magnetic axis does not coincide with their rotation axis, this causes the pulsars to emit electromagnetic radiations. Pulsars rely on their rotational energy to compensate for the energy loss caused by the electromagnetic radiation, which leads to the gradually decelerated spin of pulsars. According to the theoretical deduction, we have calculated the initial period of the Crab Nebula pulsar, and derived the period evolution of the pulsar at any time in the future under the effect of the electromagnetic radiation. Considered the possible existence of quadrupole moment in the mass distribution of a pulsar, the gravitational wave radiation will also make the pulsar spin down, hence the variation of spin period of the Crab pulsar under the effect of gravitational wave radiation is further analyzed. Finally, combining the two kinds of radiation mechanisms, the evolution of spin period of the Crab pulsar under the joint action of these two kinds of radiation mechanisms is analyzed.

Biological Defenses against Ultra-Violet, Visible Light, and Near-Infrared Exposure

Objective: Humans are increasingly exposed to artificial light and electromagnetic wave radiation, in addition to solar radiation. Many studies have shown the biological effects of ultra-violet and near-infrared exposure, but few have extensively investigated the innate biological defenses within human tissues against visible light and near-infrared exposure. Herein, we investigated spectral properties of endogenous human biological defenses against ultra-violet to near-infrared. Methods: A double-beam spectrophotometer (190 - 2700 nm) was used to measure the transmission spectra of a saline solution used to imitate perspiration, and oil to imitate sebum, as well as human skin, blood, adipose tissue, and muscle. Results: Saline (thickness, 0.5 mm) blocked 27.5% - 98.6% of ultra-violet, 13.2% - 34.3% of visible light, and 10.7% - 99.8% of near-infrared. Oil (thickness, 0.5 mm) blocked 50.5% - 100% of ultra-violet, 28.7% - 54.8% of visible light, and 19.0% - 98.3% of near-infrared. Blood thicknesses of 0.05 and 0.5 mm blocked over 97.8%, 100% of ultra-violet, over 94.6%, 99.7% of visible light, and over 75.8%, 99.4% of near-infrared, respectively. Skin thicknesses of 0.25 and 0.5 mm blocked over 99.4%, 100% of ultra-violet and over 94.3%, 99.7% of visible light, and over 74.7%, 93.5% of near-infrared, respectively. Adipose tissue thickness of 0.25 and0.5 mm blocked over 98.3%, 100% of ultra-violet, over 94.7%, 99.7% of visible light, and over 88.1%, 98.6% of near-infrared, respectively. Muscle thickness of 0.25 and0.5 mm blocked over 95.4%, 99.8% of ultra-violet, over 93.1%, 99.5% of visible light, and over 86.9%, 98.3% of near-infrared, respectively. Conclusions: Humans possess endogenous biological protection against ultra-violet, visible light and near-infrared exposure on multiple levels, including through perspiration, sebum, blood, skin, adipose tissue, and muscle. Since solar and artificial radiation affects human tissues, biological defenses made of biological materials may be induced to protect subcutaneous tissues against these wavelengths.

Radiation of electromagnetic waves of an oscillating charged drop

The analytical expressions for the intensity of the electric field are found in the vicinity of an oscillating charged drop of a nonviscous electrically conducting fluid, as well as the intensity of electromagnetic radiation induced by it in a linear approximation of the perturbation amplitude. Estimates in order of size are carried out.

Radiation and Scattering of Electromagnetic Waves by a Multielement Vibrator–Slot Structure in a Rectangular Waveguide

A problem of radiation and scattering of electromagnetic waves by a structure, consisting of a narrow transverse slot cut in the broad wall of a rectangular waveguide and two vibrators with a variable surface impedance located inside the waveguide and interacting with one another, is solved. A solution of integral equations for electric currents at the vibrators and equivalent magnetic current in the slot is derived using the generalized method of induced electro-magneto-motive forces (EMMF). Conditions needed to achieve maximum slot radiation coefficient are defined. Computed and experimental graphs of electrodynamic characteristics of the vibrator–slot structure for different vibrator locations and for the various surface impedance distributions along the vibrators are presented.

Spatial transformation-enabled electromagnetic devices: from radio frequencies to optical wavelengths.

Transformation optics provides scientists and engineers with a new powerful design paradigm to manipulate the flow of electromagnetic waves in a user-defined manner and with unprecedented flexibility, by controlling the spatial distribution of the electromagnetic properties of a medium. Using this approach, over the past decade, various previously undiscovered physical wave phenomena have been revealed and novel electromagnetic devices have been demonstrated throughout the electromagnetic spectrum. In this paper, we present versatile theoretical and experimental investigations on designing transformation optics-enabled devices for shaping electromagnetic wave radiation and guidance, at both radio frequencies and optical wavelengths. Different from conventional coordinate transformations, more advanced and versatile coordinate transformations are exploited here to benefit diverse applications, thereby providing expanded design flexibility, enhanced device performance, as well as reduced implementation complexity. These design examples demonstrate the comprehensive capability of transformation optics in controlling electromagnetic waves, while the associated novel devices will open up new paths towards future integrated electromagnetic component synthesis and design, from microwave to optical spectral regimes.

Bulk Acoustic Wave-Mediated Multiferroic Antennas: Architecture and Performance Bound

Time-varying magnetic flux can be induced from the dynamic mechanical strain of acoustic waves in multiferroic devices that are comprised of piezoelectric and magnetostrictive material. Such devices can be used to create electromagnetic radiation and to alleviate the platform effect associated with low-profile conformal antennas. In this paper, a bulk acoustic wave (BAW)-mediated multiferroic antenna structure is proposed. Its potential for efficient radiation of electromagnetic waves is evaluated by analytically deriving the lower bound of its radiation quality factor (Q factor). A one-dimensional (1-D) multiscale finite-difference time-domain (FDTD) technique is developed to predict the bilateral, dynamic coupling between the acoustic waves and electromagnetic waves. The simulation shows a decaying stress profile in the BAW resonator structure, which implies that the radiation of the electromagnetic waves acts as a damping load to the acoustic resonance. The simulated radiation Q factor matches well with the analytical derivations and the agreement validates both the operating principle of the proposed antenna and the FDTD algorithm developed. The study concludes that efficient antennas may be realized at GHz frequencies with thin film multiferroic material that has thicknesses of the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> wavelength.

Effect of Bias Electrode Position on Terahertz Radiation From Pentagonal Mesas of Superconducting &lt;formula formulatype="inline"&gt;&lt;tex Notation="TeX"&gt;${\hbox{Bi}}_{2}{\hbox{Sr}}_{2}{\hbox{CaCu}}_{2}{\hbox{O}}_{8+\delta}$&lt;/tex&gt; &lt;/formula&gt;

We examined the effect of the bias current position on the radiation of intense and coherent terahertz electromagnetic waves from the intrinsic Josephson junctions (IJJs) in regular pentagonal mesas of single crystalline high- $T_{\rm c}$ superconducting ${\hbox{Bi}}_{2}{\hbox{Sr}}_{2}{\hbox{CaCu}}_{2}{\hbox{O}}_{8+\delta}$ . The emission from Sample 1, a mesa with a current bias feed on its middle, is strong and sharply peaked at 0.47 THz, whereas that from Sample 2, a mesa with its feed along an edge, shows a comparably strong, sharp peak at 0.43 THz. The common backbending in the current-voltage characteristics due to Joule heating was seen for Sample 1 but almost not for Sample 2. The experimental results are in good agreement with numerical simulations and calculations, both for the cavity resonances and the angular emission patterns. The resonance peaks obtained from these pentagonal mesas are both stronger and narrower than those found previously from differently shaped mesas fabricated by focused ion beam milling. The overall devices are small enough to be cooled to their operational temperatures by Stirling refrigerators, so that properly designed devices could be held in one hand as for laser pointers. Therefore, our IJJ-based emitter devices are promising candidates to fill the THz gap with compact, continuous-wave quantum solid-state sources.

Effect of ion compensation of the beam space charge on gyrotron operation

In gyrotrons, the coherent radiation of electromagnetic waves takes place when the cyclotron resonance condition between the wave frequency and the electron cyclotron frequency or its harmonic holds. The voltage depression caused by the beam space charge field changes the relativistic cyclotron frequency and, hence, can play an important role in the beam-wave interaction process. In long pulse and continuous-wave regimes, the beam space charge field can be partially compensated by the ions, which appear due to the beam impact ionization of neutral molecules of residual gases in the interaction space. In the present paper, the role of this ion compensation of the beam space charge on the interaction efficiency is analyzed. We also analyze the effect of the electron velocity spread on the limiting currents and discuss some effects restricting the ion-to-beam electron density ratio in the saturation stage. It is shown that the effect of the ion compensation on the voltage depression caused by the beam space charge field can cause significant changes in the efficiency of gyrotron operation and, in some cases, even result in the break of oscillations.

Effect of cold plasma permittivity on the radiation of the dominant TEM‐wave by an impedance loaded parallel‐plate waveguide radiator

The effects of wall impedances on the radiation of the dominant transverse electromagnetic wave by an impedance loaded parallel‐plate waveguide radiator immersed in a cold plasma have been analyzed. The solution to the governing mathematical model in cold plasma is determined while using the Wiener–Hopf technique. It is observed that the amplitude of the radiated field increases with increasing permittivity of the plasma. The work presented may be of great interest to quantify the effects of ionosphere plasma on the communicating signals between Earth station and an artificial satellite in the Earth's atmosphere. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Radiation of Ultra Low Frequency Electromagnetic Waves from Atmosphere under the Influence of Strong Shock Waves

We present preliminary results from the experimental investigation of the response of the atmosphere due to the impact of powerful shock waves. The response is evidenced as ultra low frequency electromagnetic wave radiation at frequency of 2–5 kHz and in duration of 3–7 s. We hypothesize that this radiation appears due to the following process: the shock wave ionizes the neutral particles in the air and these charged and neutral particles continue their vertical motion, which forms in the trail of the shock wave. Such motion can cause the cyclotron-like radiation measured.

A Novel Technique for Radar Depth Sounding of Fast Outlet Glaciers and Ice-Sheet Margins

The surface clutter simulator and the digital filter technique are developed for sounding and imaging of a subsurface stratified structure with arbitrary ice surface roughness of fast outlet glaciers and ice-sheet margins, which provides a new insight into the strong surface clutter reduction. The radar signal simulation method developed by employing Kirchhoff approximation of rough surface scattering and the ray tracing of geometric optics theory can give clear understanding of electromagnetic (EM) wave radiation and propagation through multilayer stratified media and support the interpretation of radar actual observations for retrieving good information on ice bed and internal layers. The radar sounder echo simulator can calculate the EM scattering from ice internal multilayer rough interfaces and identify whether deeper layers or ice-bed nadir echoes masked by a strong surface off-nadir echo still return to the radar receiver or not, which offers an important tool for designing and optimizing radar system performance. The numerical spline interpolation technique is proposed to discretize the 3-D real ice topography into a suitable triangulated mesh for obtaining higher accurate radar simulation data compared with the facet method. The digital filter technique can be complementary to conventional processing methods in order to distinguish an ice bed from a strong surface clutter with an extremely crevassed rough surface in Antarctica and Greenland. Ice data processing results of certain outlet glaciers' topography are demonstrated. The presented unified data analysis methodology can be also applied to planetary exploration.

Cuboids of Infrared Images Reduction Obtained from Unmanned Aerial Vehicles

Currently, both in practice and in theory, there is an acute contradiction between the current state of scientific, technical, and engineering achievements in the field of aerospace monitoring and lack of sufficient volume of new knowledge (models and methods) about the peculiarities of thermal processes accompanying operation of hidden objects. Removing this contradiction is substantially related to the solution of the problem on the solution of the actual scientific problem on developing thermal tomograms of the Earth's surface, based on the solution of the coefficient inverse problem, in order to find and discover the hidden objects during the monitoring of the Earth's surface using unmanned aerial vehicles (UAV). The paper presents experimental data on the spatial distribution of thermal parameters of the objects. The paper reflects their effective thermal conductivity in the course of daily observations in the infrared wavelength range using unmanned aerial vehicles. The measurement results proved the possibility of obtaining a numerical evaluation of the visibility of objects through research of manifestations of thermal physic properties in the nature of the radiation of electromagnetic waves in the infrared range.

Propagation characteristics of power line harmonic radiation into the stratified anisotropic ionosphere

Power line harmonic radiation (PLHR), which specifically refers to the electromagnetic wave radiation observed in ionosphere or magnetosphere, is radiated by the transmission lines of power systems on the ground. PLHR is shown as a parallel spectrogram between 400 Hz and 5 kHz in frequency-time power spectrogram of electromagnetic field. And the frequency spacing of the parallel spectrogram is 50/100 Hz or 60/120 Hz. As an artificial pollution source in the near earth space, PLHR has attracted more and more attention. However, so far, there have been little proposed quantitative researches on the formation mechanism. This paper studies the propagation model for the electromagnetic waves generated by the electric dipole source above the non-ideal conductive ground in the stratified anisotropic ionosphere. Based on the method by Lehtinen(2008), a new full-wave finite element method is give to solve the problem. By recursively calculating reflection coefficients and mode amplitudes, the method contains no index increasing items. So it can effectively overcome the numerical overflow in programming calculations. In order to verify the correctness of the method, comparison are made between the existing analytical solutions and the solutions obtained from the proposed method, and they are in excellent agreement. Further more, using the present model, the new method and the associated parameters about practical power lines, ground and ionosphere, we have studied the effects of the frequency of dipole source, the bottom boundary height of ionosphere, the earth conductivity, and the geomagnetic field direction on PLHR propagation in the ionosphere. Results show that when the frequency of radiation source equals the cut off frequency of earth-ionosphere waveguide-guided wave modes, the strength of PLHR for penetrating into the ionosphere becomes larger. Keeping the harmonic current constant, a smaller ground conductivity would be accompanied by a larger power of PLHR. PLHR propagates along the direction of the geomagnetic field in the ionosphere. Therefore, it is much easier for a high-order harmonic radiation of transmission lines to penetrate into the ionosphere along the direction of the geomagnetic field in the areas with low ground conductivity under a certain condition. Results obtained in this paper may have important implications to explain the formation mechanism of PLHR.

ELECTRODYNAMIC CHARACTERISTICS OF HORIZONTAL IMPEDANCE VIBRATOR LOCATED OVER A FINITE-DIMENSIONAL PERFECTLY CONDUCTING SCREEN

A problem of electromagnetic waves radiation by an impedance vibrator located over finitedimensional perfectly conducting screen is solved. The vibrator may have surface impedance distributed over its length. The solution is derived using asymptotic expressions for the current in a horizontal impedance vibrator placed over an infinite plane, obtained by averaging method. The problem was solved provided that the diffracted fields from the edges of the screen have little effect on the vibrator current amplitude, i.e., if the screen dimensions are comparable to or larger than the wavelength. Full radiation fields in all observation space in the far zone were found by the uniform geometrical theory of diffraction. The vibrator dimensions, value and type of surface impedance, removing from the screen and screen sizes were used as parameters. The multivariable electrodynamic characteristics of the resonant impedance vibrators placed above an infinite plane and square screen were studied. Characteristics dependences upon the vibrator dimensions, value and type of the surface impedance, removing from the screen, and screen dimensions were obtained.

Single Scattering Albedo derived from Aerosol Optical Thickness Measurement at Ilorin

The seasonal variation of Single Scattering Albedo (SSA) derived from the monthly variations in the Aerosol Optical Thickness (AOT) values obtained from the CIMEL sun photometer in Ilorin (lat. 8032’N; long. 4034’E) is studied. Single Scattering Albedo for the site was found to range from 0.20 to 0.89 for the period under consideration - January 2003 to December 2004. For the Rain-Harmattan transition months (October and November), the SSA for the month of October was found to range approximately from 0.55 to 0.89. For the month of November, SSA was found to range approximately from 0.25 to 0.54. For the Harmattan months (December and January) and the Rainy months (April, August and September), the SSA was found to range from approximately 0.18 to 0.45. Whereas the AOT for the Harmattan months increased that of the Rainy months was decreasing for most of the months. The average monthly SSA in the Harmattan- Rain transition months (February and March) was found to range approximately from 0.20 to 0.38, depicting an increase in the Aerosol Optical Thickness at this period. These ranges show that the effect of aerosols on the direct radiation of electromagnetic waves is not negligible at the site. Therefore, this could be considered significant to atmosphere at the project site (Ilorin) by characterising it as an absorptive atmosphere.

ROLE OF TWO-PHOTON ELECTRONIC TRANSITIONS IN OPERATION OF QUANTUM CASCADE LASERS

The theory of dynamic conductivity of three-barrier resonant tunneling structure in weak electromagnetic field taking into account two-photon electronic transitions with different frequencies is developed within the approximation of effective mass and rectangular potential wells and barriers for the electron using the analytically obtained solutions of complete Schrodinger equation. It is shown that the contribution of two-photon electronic transitions into the total magnitude of dynamic conductivity for some configurations of resonant tunneling structure can approach 40% for the transitions with radiation of electromagnetic wave.