Emission Of Electromagnetic Waves Research Articles

Intense terahertz emission from molecular beam epitaxy-grown GaAs/GaSb(001)

Intense terahertz (THz) electromagnetic wave emission was observed in undoped GaAs thin films deposited on (100) n-GaSb substrates via molecular beam epitaxy. GaAs/n-GaSb heterostructures were found to be viable THz sources having signal amplitude 75% that of bulk p-InAs. The GaAs films were grown by interruption method during the growth initiation and using various metamorphic buffer layers. Reciprocal space maps revealed that the GaAs epilayers are tensile relaxed. Defects at the i-GaAs/n-GaSb interface were confirmed by scanning electron microscope images. Band calculations were performed to infer the depletion region and electric field at the i-GaAs/n-GaSb and the air-GaAs interfaces. However, the resulting band calculations were found to be insufficient to explain the THz emission. The enhanced THz emission is currently attributed to a piezoelectric field induced by incoherent strain and defects.

Simulation on locating Partial Discharge source occurring on distribution line by estimating the DOA of emitted EM waves

AbstractA new method for locating the position of partial discharge (PD), which occurs on distribution line, is presented. The method uses the direction‐of‐arrival (DOA) of electromagnetic (EM) waves emitted from PD source. The DOAs of EM waves in azimuth and elevation angles are estimated by using the two‐dimensional improved coherent signal subspace method (2D I‐CSM). The position of PD can be located as the intersection of DOAs estimated at two points. In this paper, the finite difference time domain (FDTD) method is applied to simulate the propagation of EM waves emitted from PD, which occurs on distribution line. The proposed method is applied to locate the position of PD based on the simulation results. The method is shown to be useful for locating the position of PD in multipath environment. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Continuous gravitational waves from isolated Galactic neutron stars in the advanced detector era

We consider a simulated population of isolated Galactic neutron stars. The rotational frequency of each neutron star evolves through a combination of electromagnetic and gravitational wave emission. The magnetic field strength dictates the dipolar emission, and the ellipticity (a measure of a neutron star's deformation) dictates the gravitational wave emission. Through both analytic and numerical means, we assess the detectability of the Galactic neutron star population and bound the magnetic field strength and ellipticity parameter space of Galactic neutron stars with or without a direct gravitational wave detection. While our simulated population is primitive, this work establishes a framework by which future efforts can be conducted.

Electron dynamics in the reconnection ion diffusion region

We investigate and compare Cluster observations of electron dynamics in different locations of the ion diffusion region for magnetic reconnection in the Earth's magnetotail. On the basis of the 2‐D reconstructed magnetic field map from Cluster 1 (C1), we pinpoint that the observed Hall field is ∼6000 km (∼9 ion inertial lengths) away from the magnetic X‐point, and reveal that C3 was the one in closest proximity to the X‐point at the time when the reconnection jet reversal was simultaneously seen by three spacecraft, namely, C1, C3, and C4. No evidence is found for strong wave emission and energetic electron enhancement near to the X‐point, as compared to that within the diffusion region. We find that (1) the Hall current loop is mainly carried by the low‐energy, field‐aligned counterstreaming electrons; (2) a flat‐top distribution in phase space density is a common feature for Hall‐related electrons; (3) an enhancement of energetic electrons is observed together with the presence of the flat‐top electrons; and (4) electromagnetic wave emission is enhanced within the diffusion region. Two different regions of field‐aligned counterstreaming (FC) electrons are identified: one is associated with the Hall current loop (i.e., the electron flow reversal) while another one stays at the edge of the loop. Interestingly, observations show that at the transition between the two FC regions, the waves seem to suppress the energetic electrons but to promote the flat‐top electrons.

Electromagnetic Wave Emission from Intrinsic Josephson Junction Stacks: A Review of Theory and Simulation

We review theoretical and numerical research developments in intrinsic Josephson junctions in terms of spontaneous THz electromagnetic-wave emission and report our recent multi-scale simulation scheme to further enhance the radiation power. Starting with theoretical treatments on the couplings among the stacked Josephson junctions, we reveal that solitonic excitation is essential for large spontaneous emission. Finally, we propose an experimental setup, in which an intrinsic Josephson junction is enwrapped by the dielectric materials and reveal that radiation power enhancement occurs by tunning the dielectricity.

Terahertz emission from surface-immobilized gold nanospheres

Electromagnetic wave emission based on optical rectification at terahertz (THz) wavelengths was observed from surface-immobilized gold nanospheres (SIGNs) above a gold surface. Although the excitation wavelength is off-resonant with the localized surface plasmons, the THz emission field was observed to be approximately 4.8 times greater than that from a percolated gold thin film of 10 nm thickness. A theoretical calculation predicts that the light electric field is enhanced in the SIGN system, even at off-resonance wavelengths. The observed THz field amplitude was quadratic with the illumination light field, suggesting that the THz generation is due to a second-order nonlinear optical process.

Impact of Electromagnetic Waves Generated by Cellular Phones on Male Fertility: A Review

There has been a manifold increase in the number of mobile phone users throughout the world in the past decade, with the current number of users exceeding 2 billion. However, this advancement in technology like many others is accompanied by a progressive boost in the intensity and frequency of emitted electromagnetic waves without consideration of their health consequences. The detrimental impact of these waves is generally classified into thermal and non-thermal effects. While the thermal effects at the present cell phone radiation level are considered negligible, most of the negative biological effects are attributed to the non-thermal effects. The male reproductive system is a highly compartmentalized and sensitive biological system that requires the interaction of extrinsic and intrinsic factors to function properly. In daily living since most men carry their mobile phones in their trouser pockets or in holders close to their reproductive organs, it is worthwhile to evaluate the effect of mobile phones on male fertility. A number of animal and human studies have been done in recent years suggesting a possible role of cell phone exposure on male infertility, but their mechanism of action remains unclear. The effects on sperm motility, concentration and viability have been evaluated in a number of studies but the results are inconclusive. Sperm motility is the only parameter which has seen to be decreased in most of the studies done on this subject so far. Electromagnetic waves may affect the sperms via an EMW-specific effect, thermal molecular effect or a combination of the two. Studies done on humans are scarce; hence further carefully designed studies are needed to determine the effect of electromagnetic waves emitted by cellular phones on male fertility.

Investigation on spectral character of ELF electromagnetic radiations during Leonid 2009 meteor shower

There are several reports of simultaneous optical flashes as well as audible sounds called electrophonics during the passage of meteors through the Earth’s atmosphere, but the exact physical mechanism behind these phenomena is still poorly understood. Some experiments performed during meteor showers indicate the presence of ELF-VLF electromagnetic waves generated simultaneously with the passage of a meteor, which after suitable transduction are converted into audible sound waves. In this context, the present paper investigates the temporal and spectral character of ELF electromagnetic waves produced during the Leonid meteor shower on 18th November, 2009. A well calibrated broadband GPS locked software receiver was used to perform the experiment at the Department of Physics, Tripura University, India (23.50° N 91.25° E). The analysis of temporal data and dynamic spectrogram reveals distinct electromagnetic pulses in the frequency range of a few Hz to 2 kHz during the predicted time of peak activity of the shower. The spectral character of these pulses is found to be completely different from the spectral signatures originating from lightning discharges. During the peak activity period, the meteor counts using ELF method is found to be around 11,000 meteors hr−1, which is around 137 times more than the worldwide reported visible rate. The observational results are discussed from the viewpoint of deposition of meteoric dust particles and its interaction with ionospheric plasma, leading to emission of electromagnetic waves during the passage of meteors through the Earth’s atmosphere.

EMF controversy in Chigu, Taiwan: contested declarations of risk and scientific knowledge have implications for risk governance

This article examines the controversy concerning the emission of electromagnetic waves at a meteorological radar site in Chigu, Taiwan, as an example of an emerging technologi- cal risk. At the heart of this controversy is a lack of scientific evidence and consensus regarding potential or future effects of the radiation on human health. The Chigu meteorological radar site started operating in 2000, and medical problems have inexplicably increased in one offshore com- munity adjacent to this radar station since 2006. The community residents have long suspected that such disproportionate medical problems are a result of their daily exposure to electromag- netic waves from this meteorological radar site and now they are calling for this station to be dis- mantled. The Central Weather Bureau has responded to local residents' protests by claiming that no scientific evidence of such risk exists, according to the criteria set by the Environmental Protec- tion Administration (EPA) in Taiwan and several documents published by the World Health Orga- nization. Environmental activists and local residents have never agreed with such responses and claims. Controversies between both camps continue to fester. Drawing from arguments presented in studies by Funtowicz and Ravetz and the literature on participatory risk governance, the pre- sent study employs a qualitative approach, with in-depth interviews and analysis of documentary data, to investigate this case. The research delineates conflicting portrayals and framings of scien- tific knowledge and risk by technocrats and by civil society. The 'post-normal science' call for democratizing expertise has a critical role in providing a perspective through which a contempo- rary complex scientific controversy may be better understood in social-political contexts in Taiwan and shed light on better risk governance.

Fluxon dynamics of a long Josephson junction with two-gap superconductors

We investigate the phase dynamics of a long Josephson junction (LJJ) with two-gap superconductors. In this junction, two channels for tunneling between the adjacent superconductor (S) layers as well as one interband channel within each S layer are available for a Cooper pair. Due to the interplay between the conventional and interband Josephson effects, the LJJ can exhibit unusual phase dynamics. Accounting for excitation of a stable 2$\ensuremath{\pi}$-phase texture arising from the interband Josephson effect, we find that the critical current between the S layers may become both spatially and temporally modulated. The spatial critical current modulation behaves as either a potential well or barrier, depending on the symmetry of the superconducting order parameter, and modifies the Josephson vortex trajectories. We find that these changes in phase dynamics result in emission of electromagnetic waves as the Josephson vortex passes through the region of the 2$\ensuremath{\pi}$-phase texture. We discuss the effects of this radiation emission on the current-voltage characteristics of the junction.

Information communication technology (ICT) - its waste and consequences

Information Communication Technology (ICT) growth is important for achieving the millennium development goal. It has the revolutionary actions which create changes in the official processes and invoke tremendous change in this field as people are more dependent on the ICT products and services like mobile phones, computers and laptops. The serious concern which the author tries to highlight in this paper is the improper handling of ICT devices and huge amount of waste generated by electronic companies and other anthropogenic activities. Study is focused on unmanaged ICT-wastes and their related health hazard due to the emission of electromagnetic waves in its manufacturing and disposal process. At the discussion it is highlighted that ICT-waste management practices are now opening new door of employment with specialised logistics for the collection and effective treatment of ICTwastes during recycling, avoids dissemination of the hazardous pollutants to the environment and their effect on health.

METHOD OF ELECTROMAGNETIC PULSE ULTRA WIDEBAND PROBING OF THE UNDERLYING MEDIUM

A method for subsurface EMP UWB probing, using different DSRD (drift step recovery diodes) generators for the emission of electromagnetic waves, is described. More depth of the signal propagation is based on the manifestation of the low-frequency dispersion of the dielectric constant of the medium, which is due to the presence of induced polarization with the dipole relaxation mechanism, describing the behavior of wet soil under the influence of a strong electromagnetic pulse field. The article describes methods for solving the inverse problem of the depth and a comparison of EMP UWB probing predictions ahead of tunnels with the results of direct tunneling

Cell Phones and their Impact on Male Fertility: Fact or Fiction

Today, cell phone technology is an integral part of everyday life and its use is not only restricted to voice conversations but also conveying news, high resolution pictures and internet. However, these advances in technology are accompanied by progressive boost in the intensity and frequency of the emitted electromagnetic waves without consideration of their health consequences. Our bodies act as parasitic antennas that receive these waves and convert them into electric and magnetic fields. While thermal effects at the present level of cell phone radiation are negligible, most of the biological interactions are attributed to non-thermal effects. Male reproductive system is highly compartmentalized and sensitive biological system that requires the integration of intrinsic and extrinsic factors to properly function. The generated electrical currents may alter the hormonal milieu and testicular microenvironment, necessary for sperm production. Additionally, sperm are electrically active cells and their exposure to cell phone electromagnetic waves and currents may affect their motility, morphology and even their count. Leaky plasma membranes, calcium depletion and oxidative stress are the postulated cellular mechanisms mediating the harmful effects of cell phones radiation on sperm and male fertility potentials. Evidences for such impacts come from designed animal and in vitro studies which may be different from in vivo human exposure. Nevertheless, the important advice is to apply strict regulations on further increase in the power density of the emitted cell phone radiation and to conduct in vivo human research to study its negative effects on fertility.

Electrons in a relativistic-intensity laser field: generation of zeptosecond electromagnetic pulses and energy spectrum of the accelerated electrons

We study the motion of an electron and emission of electromagnetic waves by an electron in the field of a relativistically intense laser pulse. The dynamics of the electron is described by the Newton equation with the Lorentz force in the right-hand side. It is shown that the electrons may be ejected from the interaction region with high energy. The energy spectrum of these electrons and the technique of using the spectrum to assess the maximal intensity in the focus are analysed. It is found that electromagnetic radiation of an electron moving in an intense laser field occurs within a small angle around the direction of the electron trajectory tangent. The tangent quickly changes its direction in space; therefore, electromagnetic radiation of the electron in the far-field zone in a certain direction in the vicinity of the tangent is a short pulse with a duration as short as zeptoseconds. The calculation of the temporary and spectral distribution of the radiation field is carried out.

Controlled leaky wave radiation from anisotropic epsilon near zero metamaterials

We investigate the emission of electromagnetic waves from biaxial subwavelength metamaterials. For tunable anisotropic structures that exhibit a vanishing dielectric response along a given axis, we find remarkable variation in the launch angles of energy associated with the emission of leaky wave radiation. We write closed form expressions for the energy transport velocity and corresponding radiation angle $\phi$, defining the cone of radiation emission, both as a functions of frequency, and material and geometrical parameters. Full wave simulations exemplify the broad range of directivity that can be achieved in these structures.

Cherenkov radiation emitted by a vortex into an anisotropic dielectric

The fields produced by a Josephson vortex moving in a sandwich placed into an anisotropic dielectric are investigated. When the vortex velocity exceeds the velocity of light in the direction of the normal to the sandwich surface, Cherenkov emission of electromagnetic waves propagating from the sandwich to the bulk of the dielectric takes place. The Poynting vector of outgoing waves is determined. It is shown that the radiation directivity considerably depends on the degree of anisotropy in the permittivity. The radiation loss power of the vortex is determined, and the relation between the transport current and the vortex velocity is established.

Terahertz electromagnetic radiation from intrinsic Josephson junctions at zero magnetic field via breather-type self-oscillations

I propose a new mechanism of intense high-frequency electromagnetic wave generation by spatially uniform stacked Josephson junctions at zero magnetic field. The ac-Josephson effect converts the dc-bias voltage into ac-supercurrent, however, in the absence of spatial variation of Josephson phase difference, does not provide dc-to-ac power conversion, needed for emission of electromagnetic waves. Here I demonstrate that at geometrical resonance conditions, the spatial homogeneity of phase can be spontaneously broken by appearance of breathers (bound fluxon-antifluxon pairs), facilitating effective dc-to-ac power conversion. The proposed mechanism explains all major features of recently observed THz radiation from large area Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ mesa structures.

Numerical study for electromagnetic wave emission in thin samples of intrinsic Josephson junctions

Emission of THz electromagnetic waves from thin samples of intrinsic Josephson junctions (IJJ’s) is numerically studied, using the xz-model. We show that the spatial symmetry of the electromagnetic excitations corresponding to the π-cavity mode is different from that of the 2π-cavity mode in the IJJ’s where the junction parameters such as the Josephson critical current are weakly inhomogeneous. In such IJJ’s the emission in the [001] direction, which is forbidden in the dipole emission, appears at the π-cavity mode resonance, whereas it is not observed in the 2π-cavity mode resonance. It is also shown that the strong emission occurs when the transition between branches in the I–V characteristics takes place.

An alternative to the plasma emission model: Particle-in-cell, self-consistent electromagnetic wave emission simulations of solar type III radio bursts

High-resolution (sub-Debye length grid size and 10 000 particle species per cell), 1.5D particle-in-cell, relativistic, fully electromagnetic simulations are used to model electromagnetic wave emission generation in the context of solar type III radio bursts. The model studies generation of electromagnetic waves by a super-thermal, hot beam of electrons injected into a plasma thread that contains uniform longitudinal magnetic field and a parabolic density gradient. In effect, a single magnetic line connecting Sun to Earth is considered, for which five cases are studied. (i) We find that the physical system without a beam is stable and only low amplitude level electromagnetic drift waves (noise) are excited. (ii) The beam injection direction is controlled by setting either longitudinal or oblique electron initial drift speed, i.e., by setting the beam pitch angle (the angle between the beam velocity vector and the direction of background magnetic field). In the case of zero pitch angle, i.e., when v→b·E→⊥=0, the beam excites only electrostatic, standing waves, oscillating at local plasma frequency, in the beam injection spatial location, and only low level electromagnetic drift wave noise is also generated. (iii) In the case of oblique beam pitch angles, i.e., when v→b·E→⊥=0, again electrostatic waves with same properties are excited. However, now the beam also generates the electromagnetic waves with the properties commensurate to type III radio bursts. The latter is evidenced by the wavelet analysis of transverse electric field component, which shows that as the beam moves to the regions of lower density and hence lower plasma frequency, frequency of the electromagnetic waves drops accordingly. (iv) When the density gradient is removed, an electron beam with an oblique pitch angle still generates the electromagnetic radiation. However, in the latter case no frequency decrease is seen. (v) Since in most of the presented results, the ratio of electron plasma and cyclotron frequencies is close to unity near the beam injection location, in order to prove that the electromagnetic emission, generated by the non-zero pitch angle beam, oscillates at the plasma frequency, we also consider a case when the magnetic field (and the cyclotron frequency) is ten times smaller. Within the limitations of the model, the study presents the first attempt to produce synthetic (simulated) dynamical spectrum of the type III radio bursts in the fully kinetic plasma model. The latter is based on 1.5D non-zero pitch angle (non-gyrotropic) electron beam that is an alternative to the plasma emission classical mechanism for which two spatial dimensions are needed.

Behavior of polystyrene-based nano- and microcomposites under fast compression

Composites based on polystyrene (PS) and core-shell hybrid nanoparticles of molecular silica sol are studied during fast compression. At a certain critical pressure, PS and the related composites are found to fail instantaneously. This process is accompanied by the emission of electromagnetic and acoustic waves. The sample composition and the filler particle size change both the critical pressure during explosion and the frequency characteristics of the appearing electromagnetic and acoustic waves. The fracture of PS and the related composites is accompanied by the formation of a fibrillar structure.