Emission Of Electromagnetic Waves Research Articles

On the role of longitudinal currents in radiating systems of charges

The time derivative of a charge density is linked to a current density by the continuity equation. However, it features only the longitudinal part of a current density, which is known to produce no radiation. This fact usually remains unnoticed and may appear puzzling at first, suggesting that the temporal variation of a charge density should be also irrelevant to radiation. We alleviate the apparent contradiction by showing that the effective longitudinal currents are not spatially confined, even when the time-dependent radiating charge density that generates them is. This enforces the co-existence of the complementary, i.e. transverse, part of the current, which, in turn, gives rise to radiation. We illustrate the necessarily delocalized nature and relevance of longitudinal currents to the emission of electromagnetic waves by a dynamic electric dipole, discussing the practical implications of that for radation in partially conducting condensed matter. More generally, we show how the connection between the longitudinal and transverse currents shapes the structure of the conventional multipole expansion and fuels the ongoing confusion surrounding the charge and toroidal multipoles.

Driving voltage frequency and electrode material effects on electromagnetic radiation of the surface dielectric barrier discharge in the air

The electrical discharges are, among others, accompanied by the emission of electromagnetic waves of various frequencies. We studied this emission for the surface dielectric barrier discharge in the air. We used the discharge with one strip-driven electrode and a sinusoidal driving voltage of frequencies 5 and 10 kHz. From the spectra of emitted waves in the frequency band up to 3 GHz, we found that this type of discharge emits the radiation of frequencies below 500 MHz. In this frequency band, we focused on the effect of the driving voltage frequency and driven electrode material on the spectra of these waves. It was found that emitted radiation is distributed in several packages of frequencies, and an increase in the driving voltage frequency or voltage increases the power level of emitted radiation. Compared with the radiation spectrum of the discharge with an aluminium-driven electrode in the spectrum of the discharge with the copper-driven electrode, new peaks of various power levels and the shift of certain radiation frequencies to lower values appear. To understand the underlying mechanism of the discharge electromagnetic waves emission, we focused on the correlation between the electric component of emitted EMWs and the discharge electrical parameters as a function of time and discharge voltage.Graphical abstract

A Numerical Consideration on the Correlation Between Magnitude of Earthquakes and Current Intensity Causing ULF Electromagnetic Wave Emission

A Numerical Consideration on the Correlation Between Magnitude of Earthquakes and Current Intensity Causing ULF Electromagnetic Wave Emission

Acceleration of Electrons and Ions by an “Almost” Astrophysical Shock in the Heliosphere

Collisionless shock waves, ubiquitous in the Universe, are crucial for particle acceleration in various astrophysical systems. Currently, the heliosphere is the only natural environment available for their in situ study. In this work, we showcase the collective acceleration of electrons and ions by one of the fastest in situ shocks ever recorded, observed by the pioneering Parker Solar Probe at only 34.5 million km from the Sun. Our analysis of this unprecedented, near-parallel shock shows electron acceleration up to 6 MeV amidst intense multiscale electromagnetic wave emissions. We also present evidence of a variable shock structure capable of injecting and accelerating ions from the solar wind to high energies through a self-consistent process. The exceptional capability of the probe’s instruments to measure electromagnetic fields in a shock traveling at 1% the speed of light has enabled us, for the first time, to confirm that the structure of a strong heliospheric shock aligns with theoretical models of strong shocks observed in astrophysical environments. This alignment offers viable avenues for understanding astrophysical shock processes and the self-consistent acceleration of charged particles.

Atmospheric Noise Measurements in the Garden: Detecting Universalities in Inter-Spheric Waiting Time Statistics

Lightning flashes result in an instantaneous emission of electromagnetic (EM) waves that encompass a broad spectrum of frequencies in the domain of radio waves. The signature of these impulses in the region of the very low frequency (VLF) of radio waves and bellow are called spherics. These impulsive signals traverse great distances in the waveguide between the Earth’s ionosphere and its surface. Due to the abundance of lightnings the lower end of the EM spectrum is dominated by the waveforms of these emission. It is called atmospheric radio noise because of its origin. This article outlines a straightforward approach for capturing spherics activity within the VLF radio wave range. Employing data processing techniques, we pinpoint the timestamps of spherics within time series data. The distribution of inter-spheric times is analyzed across various detection threshold levels. Utilizing recordings spanning two distinct years and seasons, we replicate the established form of the inter-spheric time distribution described in the literature. Notably, we demonstrate that by rescaling the time intervals between spherics with the mean time for a specific recording and given detection threshold, the distributions collapse to a master curve. This universal pattern is accurately characterized by a single-parameter mean-scaled Gamma distribution. Additionally, we note the similarities in the distribution of inter-spheric times with patterns found in earthquake recurrence times.

A Clutter Removal Method Based on the F-K Domain for Ground-Penetrating Radar in Complex Scenarios

Ground-penetrating radar (GPR) is a classic geophysical exploration method that utilizes the emission and reception of electromagnetic waves to non-destructively detect target objects in the target medium. It has been widely applied in various fields such as pipeline detection, cavity detection, and rebar detection. However, GPR systems are susceptible to environmental clutter interference, which poses challenges for data interpretation and subsequent processing. In this paper, the separability of clutter and target signal in the frequency-wavenumber (F-K) domain is validated through modeling, leading to the proposal of a comprehensive clutter removal method based on the F-K domain for complex scenarios. The direct coupling wave is initially eliminated by applying a peak matching mean subtraction filter, which avoids the artifacts. Subsequently, the F-K domain transformation is performed and surface clutter undulations are effectively removed using a method based on singular value decomposition and k-means clustering. Finally, an angle filter with Gaussian tapering at the edges is designed based on physical models to efficiently eliminate linear interference without undesired ringing interference. The commonly used clutter removal algorithms, including mean subtraction (MS), singular value decomposition (SVD), robust principal component analysis (RPCA), and traditional F-K filtering methods, are compared with the proposed algorithm on both the numerical simulated data and actual GPR data. The results from visual and quantitative analysis confirm that our proposed method is more effective than current commonly used clutter suppression algorithms. We have successfully enhanced the Signal-to-Clutter Ratio (SCR) of the GPR data, resulting in an Improvement Factor (IF) of 30.63 dB, 23.59 dB, and 30.60 dB for simulated data, experimental data, and TU1208 public data, respectively. The detection capability of buried targets is enhanced, thereby establishing a solid foundation for subsequent data interpretation and target identification.

Second Harmonic Electromagnetic Wave Emissions from a Turbulent Plasma with Random Density Fluctuations

In the solar wind, electromagnetic waves at the harmonic plasma frequency 2ω p can be generated as a result of coalescence between forward- and backward-propagating Langmuir waves. A new approach to calculate their radiation efficiency in plasmas with external background density fluctuations is developed. The evolution of Langmuir wave turbulence is studied by solving numerically the Zakharov equations in a two-dimensional randomly inhomogeneous plasma. Then, the dynamics of the nonlinear electric currents modulated at frequencies close to 2ω p are calculated, as well as their radiation into harmonic electromagnetic waves. In the frame of this non-self-consistent approach where all transformations of Langmuir waves on density inhomogeneities are taken into account, the electromagnetic wave radiation rate (emissivity) is determined numerically as well as analytically, providing in both cases similar results. Moreover, scaling laws of the harmonic wave emissivity as a function of the ratio of the light velocity to the electron plasma thermal velocity are found. It is also shown how the emissivity depends on the average level of density fluctuations and on the isotropic/anisotropic character of the Langmuir waves’ and density fluctuations’ spectra.

Elaboration of Distance Standards Against the Electromagnetic Effects of High-Voltage B Overhead Lines in the Republic of Benin

The high-voltage overhead lines used to transport electrical energy from production plants to distribution stations constitute a very important link in the chain of providing electrical energy to communities. However, they constitute potential sources of emission of electromagnetic waves whose impacts are harmful to human health (thermal electrical stimulation of tissues and in particular those of the brain causing different forms of cancer) if the safety distance between these lines and users is not respected. In recent years, Benin has experienced, in urban areas crossed by transport lines and particularly among populations living in the vicinity of these lines, an explosion in the rate of people suffering from cancer. This study is carried out not only to check whether the minimum distance according to the voltage levels of these lines is respected in order to ensure the safety of people living in their vicinity but also to develop a standard of minimum distances to be respected. By the numerical simulation method based on Maxwell's equations established in a supposedly empty medium, the Bio-Savart law and the Lorentz transformation, the model of wave intensity as a function of distances, is determined. The results obtained respectively give minimum safety distances of 15 meters, 20 meters and 36 meters for the 63 kV, 161 kV and 330 kV high voltage lines Category B. These distances are, by far, respected by the populations. Furthermore, the results clearly show that electric fields are more decisive in defining the minimum distances obtained.

Study of Conducted Emission Characteristics Induction Stoves on 9 kHz-30 MHz Frequency

The presence of increasingly sophisticated and innovative cooking utensils such as induction cookers has changed the way of cooking by providing a high level of efficiency. Induction cookers are also a breakthrough in reducing carbon emissions and making them an important choice in energy conservation efforts. The use of induction stoves in the community still faces several obstacles such as relatively high prices, significant power consumption, and the need for special cooking containers. In addition, the development of induction stove technology can produce electromagnetic emissions in the form of conduction emissions. Conducted emission is electromagnetic interference caused by electronic devices through conductors which can be interpreted as noise currents that propagate on the conduction path and have the potential to interfere with other electronic equipment through voltage sources. In the same power grid, conducted emissions caused by induction stoves can also interfere with data signals using Power Line Carrier (PLC) at a frequency of 30-500 kHz. This study aims to understand and identify patterns of electromagnetic wave emission, namely conduction emissions produced by induction stoves. The main focus is on conducted emissions, which can affect the performance of such electronic devices. The results of research related to the characteristics of the conducted emission value of this induction stove are expected so that this household device is safer and more comfortable to use by the community and can provide a reference for the further development of induction stove technology. The test method was carried out on 4 (four) brands of induction stoves C, A, M and P under various operating conditions and cooking modes both individually and simultaneously in the frequency range of 9 KHz-30 MHz through Electromagnetic Compatibility (EMC) testing. The measured parameter is a Quasi Peak (QP) value, in accordance with CISPR standard 14.1:2020. Based on measurements in the frequency range of 9 kHz-30 MHz, individual conditions were obtained that some of the induction stoves used in this study were above the threshold values required in CISPR 14.1:2020. Based on measurements with the condition that the induction stove is operated simultaneously, the level of conducted emission decreases and there is a disturbance at a new frequency beyond the disturbance frequency at individual conditions.

POWER SUPPLY OF RING ANTENNA USING DIRECTIONAL COUPLERS

Context. The circular polarization of radio waves is used in various electronic systems. This includes, for example, space communications stations, some radio relay communication systems, radar stations, data transmission systems and others. The characteristics of radio wave propagation are studied by using electromagnetic waves separated by circular orthogonal polarization in radiomonitoring and radiocontrol systems. Compared to other antenna types, circularly polarized antennas, such as rings, have superior design simplicity and excellent electrodynamics properties.
 Objective. The objective of this study is to analyse the characteristics and application of directional microstrip couplers for supplying power to ring antennas.
 Method. To better the performance of microstrip ring antennas, the reasons for their limited operating frequency range are analysed. These causes include the frequency-dependent parameters of the coupler, errors in calculating the directional coupler circuit, and radiation from asymmetric strip lines. To understand how supply lines, affect antenna characteristics, correlations between radiation fields determined in both its coordinate system and that of the primary axis are taken into account.
 Results. An analysis of the dependence graphs of the main characteristics of ring microstrip antennas with intricate power supply circuits for directional couplers and comparison with similar characteristics for simple circuits revealed that the shape of the radiation pattern in the higher radiation hemisphere became symmetrical about the axis, especially when symmetrically supplying the ring with branch-line couplers. The frequency band has also widened, at which there was an acceptable degree of deviation in the ellipticity coefficient from unity.
 Conclusions. The simulation results of microstrip ring antennas with power lines connected to directional couplers of different types showed that supplying the ring antenna with electricity via the directional coupler ensures circular polarization for the emitted electromagnetic waves. Additionally, the range of operating frequencies where there is only a small discrepancy in ellipticity coefficient remains at an acceptable level of –3 dB is quite broad. By utilizing directional branch-line couplers to power a ring antenna, it is possible to simultaneously emit both right and left circularly polarized waves with the same antenna.

Villari effect in FeSe1–xSx

Acoustoelectric transformation (occurrence of electromagnetic radiation under the action of an elastic wave) in a FeSe0.925S0.075 crystal in the presence of an external magnetic field has been studied. It is shown that the application of the magnetic field along the direction of propagation of the elastic wave leads to a rotation of the plane of polarization of the emitted electromagnetic wave. The physical mechanism is that the elastic deformation leads to the appearance of a non-diagonal component of the magnetic susceptibility and to the generation of an additional alternating magnetic moment perpendicular to the external magnetic field and to the elastic displacement. The observed features are interpreted as a manifestation of the Villari effect. A phenomenological description of the experimental results is presented. The observed effect shows that the symmetry of the low-temperature FeSe1–xSx phase belongs to the triclinic syngony.

ON THE EFFECT OF VISCOSITY RELAXATION ON ELECTROMAGNETIC RADIATION INTENSITY OF AN OSCILLATING CHARGED DROPLET

Theoretical asymptotic calculations linear with respect to small dimensionless amplitude of oscillations have been employed to study the influence of the viscoelastic properties of a charged droplet of an electrically conducting viscous liquid on the intensity of its electromagnetic radiation. It has been shown that allowance for the effect of viscosity relaxation leads to a decrease in the damping decrement value, which is determined by energy losses for electromagnetic wave emission, and the intensity of high-frequency electromagnetic radiation; a substantial reduction in the viscous damping decrement of small cloud droplets; and an essential dependence of the viscous damping decrement on the characteristic relaxation time. It has been found that the viscosity relaxation of a liquid has no significant effect on damped capillary oscillations and electromagnetic radiation of rain droplets. Viscoelasticity and viscosity of the liquid do not influence the conditions critical for the realization of the electrostatic instability of a droplet with respect to its own charge.

Radio Wave Energy Harvesting Model of a Maritime Automatic Identification System

Radio waves, the spectrum of the electromagnetic waves, are all around us and in most cases have only one purpose. The maritime Automatic Identification System (AIS) uses Very High Frequency (VHF) radio waves for the purpose of data exchange between ships and shore stations. These data exchanges take place during certain time intervals, resulting in intermittent emission of electromagnetic waves. In the research presented in this paper, the objective was to add a new purpose for the AIS electromagnetic waves, i.e. to act as a power source for the RF energy harvester. After collecting the electromagnetic waves of the AIS system, the signals’ voltage is rectified, amplified and delivered to the load. In this paper, the process of radio wave energy harvesting is simulated in the Multisim software and analyzed in detail. The results of the analysis showed a multiple increase in the voltage value at the output of the RF energy harvester.

Advances in Searching for Galactic Axions with a Dielectric Haloscope (MADMAX)

AbstractAxions are hypothetical particles that could explain the observed dark matter density and, simultaneously, could naturally resolve the strong charge parity (CP) problem in quantum chromodynamics (QCD). Recent theoretical works indicate that axions are expected to have masses in the range of , a range that presently still evades experimental detection. An experimental design is presented to search for QCD axions in this mass range via the magnetized disk and mirror axion experiment (MADMAX). MADMAX will be composed of multiple movable dielectric disks and a stable mirror that are placed inside a strong magnetic field to utilize the axion‐induced coherent electromagnetic wave emissions from each disk surface. In this paper, new R&D milestones achieved will be reported, that is, the updated magnet quench protection system, a closed booster dielectric haloscope system tested in the MORPURGO magnet at (European Organization for Nuclear Research) CERN using a full experimental data acquisition chain. These new main novel accomplishments investigate the feasibility of the experiment.

A Sound Source Localization Method Based on Frequency Divider and Time Difference of Arrival

In recent years, sound source localization, as a passive localization technique with higher safety and convenience compared with other localization techniques such as active emission of electromagnetic waves, has received more and more attention in academia. This paper researches and improves the far-field sound source localization algorithm based on the generalized cross-correlation method (GCC) Time Difference of Arrival (TDOA) estimation algorithm and completes the design and implementation of the microphone array sound source localization system. This paper adds a frequency divider to the traditional generalized correlation time delay estimation algorithm for pre-processing, sampling, and localization of sound source acoustic waves and adopts a low-cost microphone array deployment scheme as far as possible to improve the flexibility and practicality of the localization system; at the same time, the “Minimum Sphere Method” is used at the back end of the algorithm to classify the localization coordinates at different frequencies and, finally, output reasonable sound source coordinates. In the back-end of the algorithm, the “Minimum Sphere Method” is used to classify the localization coordinates at different frequencies and, finally, output the reasonable sound source coordinates. The experimental results show that the sound source localization system designed in this paper has good performance in terms of localization accuracy and cost-effectiveness and overcomes the failure of the generalized mutual correlation algorithm in the original application of high noise environment and multi-source environment localization.

Design of an applied method with graphite structure for suppression of surface electromagnetic waves between array antennas

In this study, a method of combining graphite structure and electromagnetic bandgap to reduce the mutual coupling of electromagnetic waves in array antennas is proposed. This structure is designed according to the special physical properties of graphite for the emission of electromagnetic waves, transmission theory, as well as the inductance and capacitive properties of the electromagnetic bandgap structure to dissipate surface currents. The proposed multi-input and multi-output (MIMO) antenna was designed and measured with two radiating elements on a substrate. The results show that the effects of mutual coupling between radiating elements are reduced by 30 dB at the operating frequency of 3.34 GHz. By placing this structure, all antenna components, including gain, patterns, and radiation efficiency, are improved. Calculations showed that antenna components: gain and antenna radiation efficiency increased by 1.2 dB and nearly 24%, respectively. To confirm the good performance of the graphite structure, all components of the MIMO antenna, including the envelope correlation coefficient, diversity gain, mean effective gain, channel capacity loss, and total active reflection coefficient, were investigated. The results showed the desired values, which indicate the very good performance of the graphite structure on all the basic characteristics of the antenna.

Gypsum and quartz specimens in compression failure: Fracto-emissions and related stoichiometric balances

Extensive experimental investigations were conducted on Gypsum and Quartz compression specimens of different sizes. They were brought to complete failure, showing two different failure modalities: (1) Very brittle loading drop for micro-crystalline Gypsum and Quartz; (2) Stable strain-softening behaviour for macro-crystalline Gypsum. All the tested specimens emitted acoustic and electromagnetic waves and the single events cumulated up to the peak load. On the other hand, neutron emissions were evident only for the largest specimens. The significant chemical composition changes occurring on the fracture surfaces are consistently explained by the assumption of Low-energy Nuclear Reactions (LENR), both fusion and fission. It is the first time that fusion reactions emerge from crushing tests, whereas fission reactions have already consistently explained the results related to other materials like the iron-rich natural rocks. Therefore, a correlation emerges between fusion nuclear reactions and strain-softening mechanical behaviour, as well as between fission nuclear reactions and brittle mechanical behaviour.

Tough polyimide composites synergistically reinforced by carbon nanofiber-grafted carbon fiber and rGO for improved heat dissipation and electromagnetic interference shielding

The rapid miniaturization and a consequent increase in electromagnetic wave (EM) and heat emission in integrated electronic devices are now urgently desiring for multifunctional polymer composites that simultaneously possess high mechanical properties, excellent electromagnetic interference (EMI) shielding ability and heat dissipation capability. Herein, a series of novel polyimide-based composite films were constructed by rationally assembling the carbon nanofiber-grafted carbon fiber (NCF) and reduced graphene oxide (rGO) into a highly electrically and thermally conductive pathway within polyimide matrix via a sequential bidirectional freezing casting and hot-pressing strategy. The combination of high tensile strength and toughness was obtained by incorporating rGO into the NCF-reinforced PI composite, giving rise to a hierarchical reinforcing structure of NCF and crack deflection induced by rGO nanosheets. The high electrical conductivity (7.0 × 103 S m−1) endows the PI/NCF30/rGO3.5 composite film with a good EMI shielding effectiveness of 45 dB. Moreover, the well-aligned thermally conductive NCF and rGO and strong interfacial bonding between the polymer matrix and reinforcing fibers give rise to improved thermal conductivity (λ), particularly along the in-plane direction. Typically, the PI/NCF30/rGO3.5 exhibits an in-plane thermal conductivity of 5.18 W m−1 K−1, ∼4.7 times increment compared to the pure PI (0.91 W m−1 K−1). Besides, the resultant PI/NCF30/rGO3.5 composite film presents a superior Joule heating performance with some features of fast thermal response, ease of regulation and sufficient reliability. Accordingly, the developed multifunctional polyimide-based composite films demonstrate high potential as advanced EMI shielding materials with excellent heat dissipation.

Time-frequency characteristics of microwaves generated by hypervelocity impact

When space debris impinges upon a spacecraft shield structure at an ultra-high speed, part of the debris’ kinetic energy is converted into electromagnetic energy, which radiates outward in the form of electromagnetic waves and can interfere with the spacecraft's normal communication. To investigate the radiation characteristics of the emitted electromagnetic waves, a series of experiments were conducted using a two-stage light gas gun, in which a spherical aluminum alloy (diameter:6.4 mm) projectile impinges on a 23-mm-thick target of the same material at velocities of 3.3–6.3 km/s. A real-time spectrum analyzer and super-heterodyne receiver were used to measure the microwaves in the frequency and time domains, respectively. Then, the time–frequency spectrum of the microwaves was obtained by Hilbert-Huang Transform. Further, two mechanisms of microwave generation—plasma expansion and material destruction—in an aluminum–aluminum impact are proposed, and the radiation powers of the two mechanisms are estimated based on the theoretical analysis and experimental results. Finally, the effect of the plasma cutoff frequency on the microwave propagation is explained, and the relationship between the radiation mechanism and the impact velocity is obtained. When the impact velocity is less than 5.2 km/s, material destruction is the main mechanism of microwave radiation, whereas at impact velocities > 5.2 km/s, plasma expansion dominates.

Ionising Radiation in Non-destructive Testing, Part 1 Types of Radiation used for Radiographic Testing – Basic Properties and Mechanism of Image Recording

Electromagnetic radiation, which is a special example of the electromagnetic field, has been present in the universe since its creation. Examples of radiation include radio waves, X-rays, and visible light. Depending on the frequency of the emitted electromagnetic wave, it can be ionising or non-ionising. Ionising radiation, due to its ability to penetrate matter, is oft en used in many areas of life. In industry, it is used for diagnostic purposes, e.g. in radiography.