Journal articles on the topic 'Low frequency electromagnetic waves, EM waves, Electromagnetic waves, Magnetopshere'

Low-frequency electromagnetic (EM) signal propagation in geophysical applications is sometimes referred to as diffusion and sometimes as waves. In the following we discuss the mathematical and physical approaches behind the use of the different terms. The basic theory of EM wave propagation is reviewed. From a frequency-domain description we show that all of the well-known mathematical tools of wave theory, including an asymptotic ray-series description, can be applied for both nondispersive waves in nonconductive materials and low-frequency waves in conductive materials. We consider the EM field from an electric dipole source and show that a common frequency-domain description yields both the undistorted pulses in nonconductive materials and the strongly distorted pulses in conductive materials. We also show that the diffusion-equation approximation of low-frequency EM fields in conductive materials gives the correct mathematical description, and this equation has wave solutions. Having considered both a wave-picture approach and a diffusion approach to the problem, we discuss the possible confusion that the use of these terms might lead to.

In the era of wireless communication, WiFi becomes an indispensable accessory to most of us. People use WIFI to interact with the wireless Internet, perform commercial and financial transactions, or conducting recreational activities, etc.Though it offers a more convenient life to people, the strong Electromagnetic waves(EMW) resulted from it endangers human health, that has already turned out to be the primary study for medical science. Furthermore, EMW also attracts concern and panic of the inhabitants living in the surroundings which is filled with high-frequency and low-frequency EMwave. EMW today comes from broadcast towers, the system of the wireless communication, GPS, TVs and defense satellites mostly. Enjoying the convenience resulted from communication technology, people nowadays should also concern about whether EM wave would damage people’s health at the same time. Based on the perspective of cognitive neuroscience, this study mainly focuses on how EM wave produced from WiFi affects subject’s brainwaves under a specific physiological situation. The researcher observes different changing of brainwave when human beings expose in various strength of EM wave, and analyses the affection of EMW toward subject’s brainwaves.

In this paper, the detection of the lunar surface soil permittivity with megahertz electromagnetic (EM) waves by spaceborne radar is studied based on the EM scattering theory, the Boltzmann–Shukla equations, and the improved scattering matrix method (ISMM). The reflection characteristics of the lunar surface soil subject to megahertz waves are analyzed through the EM scattering theory and expressed by the lunar surface soil permittivity. Then, the lunar ionosphere is assumed to be composed of dusty plasma, and its EM characteristics are described with the Boltzmann–Shukla equations. Finally, the transmission and reflection characteristics of the propagation of EM waves in the lunar ionosphere are numerically calculated with ISMM. Thus, the complex permittivity of lunar surface soil is obtained. In addition, the effects of detection environment situations, such as the lunar illumination intensity, characteristics of the lunar dust and dust charging process in the lunar ionosphere, on the amplitude and phase of EM waves are also investigated in this study. The simulation results show that an EM wave at a high frequency induces a strong effective wave with a stable phase shift and a significantly small interferential wave. Moreover, the lunar illumination is more effective under EM waves in low frequency bands; the characteristics of the lunar dust have a notable influence on the transmission and absorption coefficients of the effective waves. These conclusions help in real applications involving the detection of the lunar surface soil permittivity by spaceborne radar in various lunar environments.

AbstractThe linear propagation of the low-frequency (compared to the electron gyrofrequency) electromagnetic (EM) waves in a self-gravitating, strongly coupled magnetized plasma with ultra-relativistic degenerate electron fluid is investigated. It is found that the dispersion properties of the EM waves and stability criteria for such a degenerate plasma are significantly modified by the effects of the ultra-relativistic degenerate electron pressure, strong co-relation among extremely dense ion fluid, and the direction of the EM wave propagation relative to the ambient magnetic field direction. The relevance of our investigation to stability of white dwarf stars is briefly discussed. It is particularly seen here that the cores of such stars are stable for the class of gravito-electrodynamic waves that are analyzed for the characteristic ranges of relevant physical parameters.

A new electromagnetic (EM) scattering model of the sea surface with single breaking waves is proposed based on the high-frequency method in this paper. At first, realistic breaking wave sequences are obtained by solving the fluid equations which are simplified. Then, the rough sea surface is established using the linear filtering method. A new wave model is obtained by combining breaking waves with rough sea surface using a 3D coordinate transformation. Finally, the EM scattering features of the sea surface with breaking waves are studied by using shooting and bouncing rays and the physical theory of diffraction (SBR-PTD). It is found that the structure that is similar to a dihedral corner reflector between the breaking wave and rough sea surface exhibits multiple scattering, which leads to the sea-spike phenomenon that the scattering result of horizontal (HH) polarization is larger than that of vertical (VV) polarization, especially at low-grazing-angle (LGA) incidents with upwind. The sea-spike phenomenon is also closely related to the location of strong scattering.

Abstract Because of the unpredictable range of propagation, knowledge of the wave transmission properties of the aquatic environment is needed for efficient underwater electromagnetic (EM) wave activity. Most publications concern low frequencies to achieve long contact distances, and data transmission is widely known to be captivated with one of the critical parameters, frequency. However, there are some new applications that need data in order to be implemented underwater over short distances. This survey provides a detailed overview of current underwater communication techniques, as well as their advantages and disadvantages. Potential future directions and recommendations for enabling next-generation underwater wireless networking systems are discussed. This paper also summarizes radio-frequency communication studies and, as a result, developments in radio-frequency identification technology for data transmission in a variety of aquatic environments, including freshwater and saltwater.

Abstract. The modeling of very low-frequency (VLF) electromagnetic (EM) beam propagation in the Earth–ionosphere waveguide (WGEI) is considered. A new tensor impedance method for modeling the propagation of electromagnetic beams in a multi-layered and inhomogeneous waveguide is presented. The waveguide is assumed to possess the gyrotropy and inhomogeneity with a thick cover layer placed above the waveguide. The influence of geomagnetic field inclination and carrier beam frequency on the characteristics of the polarization transformation in the Earth–ionosphere waveguide is determined. The new method for modeling the propagation of electromagnetic beams allows us to study the (i) propagation of the very low-frequency modes in the Earth–ionosphere waveguide and, in perspective, their excitation by the typical Earth–ionosphere waveguide sources, such as radio wave transmitters and lightning discharges, and (ii) leakage of Earth–ionosphere waveguide waves into the upper ionosphere and magnetosphere. The proposed approach can be applied to the variety of problems related to the analysis of the propagation of electromagnetic waves in layered gyrotropic and anisotropic active media in a wide frequency range, e.g., from the Earth–ionosphere waveguide to the optical waveband, for artificial signal propagation such as metamaterial microwave or optical waveguides.

WHO (World Health Organization) concludes that not much effect is caused by electric field up to 20 kV / m in humans. WHO standard also mentions that humans will not be affected by the magnetic field under 100 micro tesla and that the electric field will affect the human body with a maximum standard of 5,000 volts per meter. In this study did not discuss about the effect of high voltage radiation SUTT (High Voltage Air Channel) with human health. The research will focus on energy utilization of SUTT radiation. The combination of electric field and magnetic field on SUTT (70-150KV) can generate electromagnetic (EM) and radiation waves, which are expected to be converted to turn on street lights around the location of high voltage areas or into other forms.The design of this prototype works like an antenna in general that captures electromagnetic signals and converts them into AC waves. With a capacitor that can store the potential energy of AC and Schottky diode waves created specifically for low frequency waves, make the current into one direction (DC). From the research results obtained the current generated from the radiation is very small even though the voltage is big enough.

Abstract. We have developed a fully kinetic electromagnetic model to study instabilities and waves in planetary plasma environments. In the particle-in-a-cell (PIC) model both ions and electrons are modeled as particles. An important feature of the developed global kinetic model, called HYB-em, compared to other electromagnetic codes is that it is built up on an earlier quasi-neutral hybrid simulation platform called HYB and that it can be used in conjunction with earlier hybrid models. The HYB models have been used during the past ten years to study globally the flowing plasma interaction with various Solar System objects: Mercury, Venus, the Moon, Mars, Saturnian moon Titan and asteroids. The new stand-alone fully kinetic model enables us to (1) study the stability of various planetary plasma regions in three-dimensional space, (2) analyze the propagation of waves in a plasma environment derived from the other global HYB models. All particle processes in a multi-ion plasma which are implemented on the HYB platform (e.g. ion-neutral-collisions, chemical processes, particle loss and production processes) are also automatically included in HYB-em model. In this brief report we study the developed approach by analyzing the propagation of high frequency electromagnetic waves in non-magnetized plasma in two cases: We study (1) expansion of a spherical wave generated from a point source and (2) propagation of a plane wave in plasma. The analysis shows that the HYB-em model is capable of describing these space plasma situations successfully. The analysis also suggests the potential of the developed model to study both high density-high magnetic field plasma environments, such as Mercury, and low density-low magnetic field plasma environments, such as Venus and Mars.

Genotoxic Effects of Radiofrequency-Electromagnetic Fields. IntroductionRadiation is energy emission in the form of electromagnetic waves emitted from the solar system and natural resources on earth. The currents produced by the elementary particles formed by the electric current create the magnetic field. Earth's surface is under the influence of the geomagnetic field emanating from the sun. However, the outer liquid also has a magnetic field created as a result of heat transfer in the core. Therefore, all living organisms on earth live under the influence of electromagnetic fields (EMF). Today, besides these natural energy resources, rapidly developing technological developments provide most of the convenience in our lives and expose people to artificial electromagnetic fields. However, man's magnetic field is also under the influence of other natural and artificial magnetic fields around him. In particular, by ionizing radiation, which carries enough energy to break down the genetic material, die cells as a result of DNA damaging, and other diseases, especially cancer, can develop as a result of tissue damage. Electromagnetic Fields in Our LivesToday, apart from natural geomagnetic fields, radiation is emitted from many technological devices. The spectrum of these fields includes many different types of radiation, from subatomic radiation such as gamma and X-rays to radio waves, depending on their wavelengths. Though, as a result of the rapid increase of technological growth, the duration and amount of exposure to EMF is also steadily increasing. On the other hand, wireless gadgets such as computers, smartphones and medical radiological devices have become a necessity for humans. Almost everyone is exposed to radiofrequency electromagnetic fields (RF-EMF) from cell phone and base station antennas or other sources. Thus, the damage caused by the radiation to the environment affects living organisms even many kilometres away unlimitedly. All organisms in the world live under the influence of these negative environmental changes and a large part of the world population is exposed to radiofrequency (RF) radiation for a long time in their daily lives. So, though we are not aware of it, our organs and tissues are constantly exposed to radiation. Therefore, radiation adversely affects human, animal and plant health and disrupts the environment and ecological balance. An example of negative effects, radiation can cause genetic changes in the body (Figure 1). Radiation is divided into ionizing and non-ionizing. Ionizing radiations cause electron loss or gain in an atom or group of atoms in the medium they pass through. Thus, positively or negatively charged ions are formed. High energy X, gamma, ultraviolet and some visible rays in the ionized region of the electromagnetic spectrum can be counted. Since gamma rays, X rays and ultraviolet rays can ionize the molecules in living things more, they can easily disrupt the chemical structure of tissues, cells and DNA molecules in living organisms. Therefore, they can be very dangerous and deadly to living things. The energy of the waves in the non-ionizing region of the electromagnetic spectrum is low and the energy levels are insufficient for the ionization of molecules. Electricity, radio and TV waves, microwaves, and infrared rays are not ionizing because they have low energy. Waves emitted from electronic devices (cell phones, computers, microwave ovens, etc.) are absorbed by the human and animal body. The amount of energy absorbed by the unit biological tissue mass per unit time is called the specific absorption rate (SAR), and its unit is W/kg. Risks of Electromagnetic Fields on Living ThingsDepending on the structure of the tissues and organs, the radiation must reach a certain threshold dose for the effect to occur. Radiation levels below the threshold dose are not effective. Depending on the structure of the tissues and organs, the radiation must reach a certain threshold dose. The effects of small doses of waves are negligible. However, the clinical effects of waves above a certain threshold may increase. High dose waves can cause cell death in tissues. Damages in the cell may increase the risk of cancer and hereditary damage after a while, and somatic effects in people exposed to radiation may cause cancer to appear years later. There is much research on the effects of RF fields. In vitro and in vivo studies on rats, plants and different tissues of humans; suggests that the RF fields are not genotoxic and the fact that harmful effect is due to the heat effect. The contradictory results on this issue have brought about discussions. Therefore, there are still concerns about the potential adverse effects of RFR on human health. A good understanding of the biological effects of RF radiation will protect against potential damages. Due to these uncertainties, with the electromagnetic field project of the World Health Organization, experimental and modelling studies on the biological effects of RF radiation have been accelerated. In 2011, the International Agency for Research on Cancer decided that RF-EMR waves could be potentially carcinogenic to humans (2). Considering that almost everyone, including young children, uses mobile phones in addition to other technological devices, the danger of electromagnetic waves has increased social interest. Genotoxic Effects of EMFIn addition to stimulating apoptosis and changes in ion channels, RF-EMF waves also have a potential effect on genetic material. The radiation absorbed by organisms causes the ionization of target molecules. In particular, biological damage may occur as a result of stimulation/ionization of atoms and disruption of molecular structures while ionizing radiation passes through tissue. As a result of ionization in the cell, electron increases and free electrons cause damage, especially in macromolecules and DNA. Free electrons move directly or indirectly. Free electrons directly affect the phosphodiester or H-bonds of DNA. As a result, the phosphodiester bonds of DNA in the cell are broken, single or double-stranded breakages and chemical toxins increase. DNA double-strand breaks are the most relevant biologic damage induced by ionizing radiation (3,4). There are no cells that are resistant to radiation. The nucleus of the cell and especially the chromosomes in dividing cells are very sensitive to radiation. One of the most important effects of radiation on the cell is to suppress cell growth. In particular, growth is impaired in cells exposed to radiation during cell division (mitosis). Consequently, cells with a high division rate are more sensitive to radiation. DNA damage in somatic cells can lead to cancer development or cell death. Cell death can occur as a result of breaking down DNA because ionizing radiation has enough energy to break down the cell's genetic material. Thus, tissues are damaged and cancer development may be triggered. DNA damage caused by radiation in cells is repaired by metabolic repair processes. If the breaks in DNA as a result of DNA damage caused by radiation in cells are not too large, they can be repaired by metabolic repair processes. Still, errors may occur during this repair. Chromosomes containing different genetic codes and information may also occur. In the cell, the released electrons interact with water molecules, indirectly causing the water to be reactively divided into two parts. Free radicals carry an electron that is not electrically shared in their orbits. Free radicals can cause genetic damage in DNA such as nucleotide changes, double and single-strand breaks. Radiation can cause chromosomes to break, stick together and rearrange. All these changes can lead to mutations or even further, the death of the cell. However, in addition to ionizing radiation, extracellular genotoxic chemicals and intracellular oxidative metabolic residues can also create stress in cells during DNA replication and cell division. Damage may occur during DNA replication under such environmental stress conditions. To date, conflicting results have been reported regarding the genotoxic effects of RF-EMF waves on genetic material. It has been reported that the energy of low EM fields is not sufficient to break the chemical bonds of DNA, but the increase in exposure time is effective on the formation of oxygen radicals and the disruptions in the DNA repair process. The absorption of microwaves can cause significant local warming in cells. For example, an increase in temperature has been observed in cells in culture media exposed to waves of high SAR levels. However, there is evidence that reactive oxygen species are formed in cells indirectly and experimentally exposed to RF-EMF waves. Free oxygen radicals can create nucleotide entries in DNA as well as bind cellular components to DNA bases (5). The frequency of polymorphisms observed in DNA repair mechanism genes in children with acute leukaemia living close to high energy lines reveals the effect of this energy on the repair process. Significant evidence has been reported that genotoxic effects occur in various cell types when exposed to RF-EMF waves (6-10). Here, it has been reported that cells exposed to RF-EMF waves (1.800 MHz, SAR 2 W/kg) cause oxidative damage in mitochondrial DNA, DNA breaks in neurons and DNA breaks in amniotic cells (6,10). Similarly, the damage has been reported in lymphocytes exposed to various RF-EMF waves (8). However, exposure to RF-EMF waves is known to cause chromosome imbalance, changes in gene expression, and gene mutations. Such deleterious genetic effects have also been reported in neurons, blood lymphocytes, sperm, red blood cells, epithelial cells, hematopoietic tissue, lung cells, and bone marrow (1,11,12). It has been found that exposure to RF-EMF radiation also increases chromosome numerical aberrations (6,13). It has also been reported that increased chromosome separation in mouse oocytes exposed to EM and increased DNA fragmentation and apoptosis in fly egg cells (14,15). However, increased DNA breaks have been reported in the blastomeres of embryos of pregnant mice exposed to a frequency of 50 Hz, and a decrease in the number of blastocysts has been reported (16). Genetic damages to sex cells can lead to persistent genetic diseases in subsequent generations. Today, X-ray devices used for medical diagnosis have become one of the largest sources of radiation. These radiological procedures used for diagnosis constitute an important part of ionizing radiation. During these processes, the human body is visibly or invisibly affected by X-rays. As a matter of fact, X-rays have effects of disrupting the structure and biochemical activities of DNA, RNA, proteins and enzymes that are vital in the organism (17). Many studies on this subject have revealed that radiation has suppressive and mutational effects on DNA synthesis. These effects can cause serious damage to the cell as well as DNA and chromosome damage. In a recent study, chromosome damage was investigated in patients with X-ray angiography and personnel working in radiological procedures (18). Our findings showed that the beams used in interventional radiological procedures caused chromosomal damage and the rate of chromosomal abnormalities (CAs) increased significantly in patients after the procedure and this damage increased with the amount of radiation dose. Therefore, the radiation dose to be given to the patient should be chosen carefully. Besides, our findings showed that the frequency of CA is significantly higher in personnel working in radiological procedures. This reveals that interventional cardiologists are exposed to high radiation exposure. For this reason, we can say that the personnel working in radiological procedures (physician, health technician and nurse) are very likely to get diseases after years because they are exposed to low doses but long-term X-rays. Therefore, both the potential risks and safety of exposure to medical radiological devices must be continuously monitored. Furthermore, the fact that chromatid and chromosome breaks are very common among structural CAs in our findings suggests that they may be the cause of malignancy. Because, there are many cancer genes, tumour suppressor genes, enzyme genes involved in DNA repair and important genes or candidate genes responsible forapoptosis on these chromosomes. All this information shows that patients are more susceptible to DNA damage and inappropriate radiological examinations should be avoided. Therefore, X-ray and other diagnostic imaging techniques should not be applied unless necessary, and physicians and patients should be more careful in this regard. It has been reported that RF-EMR waves emitted from wireless communication device mobile phones have a genotoxic effect on human and mammalian cells (6,19). In a recent study; The effects of 900 and 1800 MHz cell phone frequencies on human chromosomes were investigated in amniotic cell cultures (6). Here, it has been reported that chromosome packing delays, damage and breaks occur in amniotic cells exposed to 900 and 1800 MHz every day at 3, 6 and 12 hours for twelve days. However, it was found that the frequency of 1800 MHz caused more CAs than 900 MHz, and the amount of damage increased with increasing usage time. These results confirm that GSM-like RF-EMR causes direct genotoxic effects in human in vitro cultures and has adverse effects on human chromosomes, and these effects increase in parallel with exposure time. This shows us that the mobile phone carries a risk for human health and these genetic damages can cause cancer. Therefore, necessary precautions should be taken for these harmful effects of mobile phones. Among these measures, the periods of mobile phone use should be kept short, especially the exposure of developing children and infants to mobile phones should be prevented, and avoiding excessive use of mobile phones may be one of the precautions against cancer. However, in order to evaluate it in more detail, the effects of mobile phones with environmental mutagens and/or carcinogens should be considered in subsequent researches. ConclusionToday, in parallel with the increasing technological developments, the demand of the society for electronic devices and phones and the frequency ranges of electronic devices are constantly increasing. Waves emitted from electronic devices are absorbed by human and animal bodies. Especially, the use of phones by contact with our body and the increase in usage time affects not only adults but also young children. Therefore, there is increasing concern in society about the negative biological effects of EM waves emitted from phones and other electronic devices. Results from all studies show that RF-EMF waves may be carcinogenic due to their genotoxic effect. Because cancer is a disease that occurs as a result of genetic damage. Considering these negative and harmful effects, regulations following international standards regarding the use of electronic devices should be made and society should be made aware of the risks.References Kim JH.; Lee K.; Kim HG.; Kim KB.; Kim HR. 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This paper addresses the effect of concrete carbonation on the propagation and dispersion of electromagnetic (EM) waves and the capability of two EM, non-destructive techniques to detect this pathology. A capacitive technique operating at low frequency (around 33 MHz) and a ground penetrating radar (GPR) with a 1.5 GHz antenna were tested for the monitoring of reinforced concrete structures. To better understand the phenomena involved in concrete carbonation, the results of two complementary experimental campaigns were analyzed for saturated concretes. First, the dispersion curves of complex permittivity were measured for both carbonated and non-carbonated samples by a cylindrical coaxial EM cell. Due to carbonation, the permittivity decreased and the level of dispersion reduced slightly. Second, using GPR (coupled at approximately 900 MHz) and capacitive measurements conducted on controlled slabs, it was confirmed that the real part of the relative permittivity decreased within a range of 2 at 33 MHz and a range of 1 to 900 MHz, while the radar signal amplitude increased.

Electromagnetic (EM) waves are able to distinguish between water and hydrocarbons due to their high difference in resistivity value. The method that uses EM technology to explore hydrocarbon is called Seabed Logging (SBL). Due to high demand of hydrocarbons, improvement of this technology is needed. The paper consists of modelling of the prototype of EM transmitter and receiver for hydrocarbons exploration. EM transmitter consists of carbon nanotubes (CNT), aluminium wire with magnetic feeder in toroidal shape. ZnO-CNTs-PVDF composites are used for EM detection. The XRD analysis showed a clear diffraction peak of [101] plane at 36°C of the 2θ. Raman spectra were obtained for ZnO synthesised at 200°C and 300°C temperatures. The initial permeability, Q-factor and relative loss factor were measured using vector network analyser. Results show high value of Q-factor (~43) of the ZnO-CNTs at frequency between 20-30 MHz. The nanoparticles also show low relative loss factor for frequencies above 10 MHz. The grain size, morphology and shape of the particles were characterized using FESEM and revealed rod-like structures. The CNT dipole transmitter system using improved CNT dipole antenna and CNT-ZnO detector record an enhancement of 192% and can be used for hydrocarbon detection.

Before and after earthquakes, abnormal physical and chemical phenomena can be observed by gathering ground-based and satellite data and interpreted by the lithosphere–atmosphere–ionosphere coupling (LAIC) mechanism. In this study, we focused on the mechanism of LAIC electromagnetic radiation and investigated the seismic electromagnetic (EM) wave generated in the lithosphere by earthquakes and its global propagation process from the lithosphere through the atmosphere and into the bottom of ionosphere, in order to analyze the abnormal disturbance of ground-based and space-based observation results. First, analytic formulas of the electrokinetic effect were used to simulate the generation and propagation process of the seismic EM wave in the lithosphere, interpreted as the conversion process of the seismic wave and EM wave in porous media. Second, we constructed a three-dimensional Earth–ionosphere waveguide by applying the finite-difference time-domain (FDTD) algorithm to model the global propagation process of the seismic EM wave into the atmosphere and cavity between the bottom of the ionosphere and the surface of the Earth. By combining the model of the electrokinetic effect in the lithosphere with the numerical model of the Earth–ionosphere waveguide in the atmosphere and ionosphere, we numerically simulated the global transmission process of extremely low-frequency (ELF: 3 Hz–3000 Hz) EM waves which are related to earthquakes. The propagation parameters of coseismic ELF EM waves with different duration times and center frequencies were analyzed and summarized. The simulation results demonstrate that the distribution characteristics of an electric field along longitude, latitude and altitude with time are periodic and the time interval during which an EM wave travels around the whole Earth is approximately 0.155 s when adopting the conductivity of the knee profile. We also compared the observation data with the simulation results and found that the attenuating trends of the ELF electric field are consistent. This proposed ELF EM wave propagation model of lithosphere–atmosphere–ionosphere coupling is very promising for the explanation of abnormal disturbances of ground-based and space-based observation results of ELF EM fields which are associated with earthquakes.

Aims. We studied the properties and occurrence of narrowband whistler waves and their interaction with strahl electrons observed between 0.17 and 0.26 au during the first encounter of Parker Solar Probe. Methods. We used Digital Fields Board band-pass filtered (BPF) data from FIELDS to detect the signatures of whistler waves. Additionally parameters derived from the particle distribution functions measured by the Solar Wind Electrons Alphas and Protons (SWEAP) instrument suite were used to investigate the plasma properties, and FIELDS suite measurements were used to investigate the electromagnetic (EM) fields properties corresponding to the observed whistler signatures. Results. We observe that the occurrence of whistler waves is low, nearly ~1.5% and less than 0.5% in the analyzed peak and average BPF data, respectively. Whistlers occur highly intermittently and 80% of the whistlers appear continuously for less than 3 s. The spacecraft frequencies of the analyzed waves are less than 0.2 electron cyclotron frequency (fce). The occurrence rate of whistler waves was found to be anticorrelated with the solar wind bulk velocity. The study of the duration of the whistler intervals revealed an anticorrelation between the duration and the solar wind velocity, as well as between the duration and the normalized amplitude of magnetic field variations. The pitch-angle widths (PAWs) of the field-aligned electron population referred to as the strahl are broader by at least 12 degrees during the presence of large amplitude narrowband whistler waves. This observation points toward an EM wave electron interaction, resulting in pitch-angle scattering. PAWs of strahl electrons corresponding to the short duration whistlers are higher compared to the long duration whistlers, indicating short duration whistlers scatter the strahl electrons better than the long duration ones. Parallel cuts through the strahl electron velocity distribution function (VDF) observed during the whistler intervals appear to depart from the Maxwellian shape typically found in the near-Sun strahl VDFs. The relative decrease in the parallel electron temperature and the increase in PAW for the electrons in the strahl energy range suggests that the interaction with whistler waves results in a transfer of electron momentum from the parallel to the perpendicular direction.

We propose that the meridian system as a whole is one grand transmission line, excited periodically at a frequency of f50, the frequency of the 50-round circulation (0.578×10-3 Hz). This grand transmission line is analyzed as a 28-leg, uniform, low pass (LP) electromagnetic (EM) birdcage coil, consisting of capacitors and inductors. The second lowest resonant frequency (mode 1) of the birdcage is f50. Each leg represents one channel and is analyzed as a lossless transmission line itself. The amplitude of the Qi standing wave on each channel is periodically amplified at f50. The average number of acupoints on the 28 channels involved in the 50-round circulation and the speed of Qi were used to calculate the resonant frequencies. A mechanical birdcage consisting of mass and spring may co-exist and exchange energy with the EM birdcage. Magnetic resonance imaging (MRI) may be used to map the diffusion coefficient, elastic modulus and electric conductivity of tissues in vivo, as an indirect evidence of the existence of the proposed EM and mechanical standing waves.

ABSTRACT Gravitational-wave (GW) astronomy, together with precise pulsar timing and long baseline interferometry, is changing our ability to perform tests of fundamental physics with astrophysical observations. Some of these tests are based on electromagnetic (EM) probes or electrically charged bodies, and assume an empty Universe. However, the cosmos is filled with plasma, a dilute medium which prevents the propagation of low-frequency, small-amplitude EM waves. We show that the plasma hinders our ability to perform some strong-field gravity tests, in particular: (i) nonlinear plasma effects dramatically quench plasma-driven super-radiant instabilities; (ii) the contribution of EM emission to the inspiral of charged black-hole binaries is strongly suppressed; (iii) EM-driven secondary modes, although present in the spectrum of charged black holes, are excited to negligible amplitude in the GW ringdown signal. The last two effects are relevant also in the case of massive fields that propagate in vacuum and can jeopardize tests of modified theories of gravity containing massive degrees of freedom.

Electromagnetic (EM) signals can only be transmitted through seawater for short distances (<1 m) for frequencies (>1 MHz). Therefore a new technique, the ionic current wave (ICW), has been developed for signal propagation at MHz frequency. This technique uses the conduction current produced in seawater as a result of thermal ionisation releasing H+ and OH– ions. A small voltage (<1.5 V pk) is applied between two metal electrodes submerged in the seawater to avoid ionisation by the input electrical energy.<br/> A detailed theoretical analysis of the ICW process has shown that ionic currents can be transmitted at MHz frequency over distances of 10 m with low signal loss per decade. For longer propagation distances of 100 m the theory predicts a signal loss of –20 dB per decade.<br/> Propagation experiments have been carried out in Liverpool dock seawater for distances of 2 m–28 m between parallel 0.5 m × 0.3 m electrodes placed vertically in the seawater at a depth of 2 m. Signal frequencies within the range of 1 MHz–8 MHz have been investigated. In each experiment the received propa gated signal power was approximately –67 dBm (well above the dock electrical noise of –140 dBm) and only showed a small power loss over the full range of propagation.<br/> The ICW system will be able to measure longer propagation distances in deep seawater conditions suitable for ship and submarine communications. Its performance is comparable to that of sonar systems.

Great attention has been paid to the propagation of electromagnetic (EM) waves across the sea surface due to its important applications. Most of the previous research, however, focuses on the half-space model illustrating the deep sea environment. In this paper, EM field distribution in the extremely low frequency (ELF) near-region under horizontal electric dipole (HED) excitation in homogeneous half-space seawater is analyzed based on the general expression of the Sommerfeld integral using the quasistatic approximation method. The focus is on deriving complete and effective solutions in air and seawater regions under the cylindrical coordinates for the EM near-field, which is generated by an HED in a shallow sea. The resulting formulas can be given by a few summands in closed form as the well-known Fourier–Bessel integrals. The analytical approximate expression of ELF Sommerfeld EM field integral excited by the HED in the homogeneous half-space seawater is deduced under the condition that the propagation distance ρ satisfies kρ << 1. To this end, the EM field distribution in the range close to the HED antenna in seawater is simulated, the results have shown that the minimum attenuation value of the vertical electric component Ez is about 15 dB, and that of the radical magnetic components Hφ is about 30 dB, and these values are found to be of greatest potential for the near-field region propagation among the electric and magnetic components. Finally, the correctness of the proposed method is verified by comparison with Pan’s approximation method and Margetis’s exact expression approximation method, which demonstrated the correctness of the proposed method.

There are various methods being used to model and study behavior of electromagnetic (EM) waves in controlled source electromagnetic (CSEM) environment. Sea Bed logging (SBL) is using CSEM technique in detecting and characterizing hydrocarbon bearing reservoirs in deep water areas. It uses a mobile horizontal electric dipole (HED) source called transmitter that transmits low frequency of 0.1Hz to 10Hz, 30m - 40m above sea bed and an array of seafloor electric field receivers. These signals depend on the resistivity structure beneath the sea bed as hydrocarbon is known to have high resistivity value of 30 500 Ωm in contrast to sea water layer of 0.5 2 Ωm and sediments of 1-2 Ωm. Array of seafloor receivers detect EM energy that propagates through the sea and subsurface. Data collected is used for processing and modeling purposes to predict depth of resistive bodies. In this paper, synthetics data generated from developed simulator that is able to replicate SBL environment is compared to synthetics data generated from Computer Simulation Software (CST) and COMSOL software with same parameter setting to study trends between them. Percentage differences between data with hydrocarbon and without hydrocarbon are calculated and comparisons are made. Overburden thickness is varied from 1000m to 3000m (incremented by 500m) at frequency of 0.125Hz. It was found that all the data generated either from simulator, CST software and COMSOL showing the same trends. From these findings it shall conclude that the simulator is a reliable tool to model any sea bed logging environment and predicting present of hydrocarbon reservoir in SBL environment.

Abstract Short-term earthquake forecasting is impossible due to the seismometer’s limited sensitivity in detecting the generation of micro-fractures prior to an earthquake. Therefore, there is a strong desire for a non-seismological approach, and one of the most established methods is geomagnetic disturbance observation. Previous research shows that disturbances in the ground geomagnetic field serves as a potential precursor for earthquake studies. It was discovered that electromagnetic waves (EM) in the Ultra-Low Frequency (ULF) range are a promising tool for studying the seismomagnetic effect of earthquake precursors. This study used a multiple regression approach to analyse the preliminary study on the relationship between Pc4 (6.7-22 mHz) and Pc5 (1.7-6.7 mHz) ULF magnetic pulsations, solar wind parameters and geomagnetic indices for predicting earthquake precursor signatures in low latitude regions. The ground geomagnetic field was collected from Davao station (7.00° N, 125.40° E), in the Philippines, which experiences nearby earthquake events (Magnitude <5.0, depth <100 km and epicentre distance from magnetometer station <100 km). The Pc5 ULF waves show the highest variance with four solar wind parameters, namely SWS, SWP, IMF-Bz, SIE and geomagnetic indices (SYM/H) prior to an earthquake event based on the regression model value of R2 = 0.1510. Furthermore, the IMF-Bz, SWS, SWP, SWE, and SYM/H were found to be significantly correlated with Pc5 ULF geomagnetic pulsation. This Pc5 ULF magnetic pulsation behaviour in solar winds and geomagnetic storms establishes the possibility of using Pc5 to predict earthquakes.

The physical destruction and fatalities caused by earthquake events compelled scientists to develop Earthquake predictions. Due to limited seismometer sensitivity, it was impossible to detect earthquake events; therefore, non-seismological is established, which in Ultra Low Frequency (ULF). The study of electromagnetic waves (EM) in the Ultra-Low Frequency (ULF) range is a promising tool for investigating seismomagnetic effects that act as an earthquake precursor. This study analysed the ULF frequency range as a short-term earthquake precursor at a depth < 100 km and an epicentral distance < 100 km (distance from Cebu magnetometer station) measured using a ground magnetometer installed in Cebu (10.36oN, 123.91oE), in the Philippines. This study also intended to determine the emission of magnetic pulsation (Pc4 and Pc5), solar wind parameters and near equatorial geomagnetic storms (SYM/H) in low latitude regions prior to an earthquake event. Findings show that the most evident ULF that acts as a potential earthquake precursor was at a frequency range of Pc5 (1.7 - 6.7 mHz) compared to Pc4 (6.7 - 22 mHz). It also shows that high solar wind changes and geomagnetic storms respond to the emission of ULF magnetic pulsations (Pc4 and Pc5) prior to earthquake events at low latitudes. Thus, it can be concluded that magnetic pulsations are signatures that indicate the probability of short-term earthquakes precursor.

Purpose The purpose of this paper is to investigate cotton fabric behavior that is exposed to radar waves between selected operation frequencies as an alternative radar-absorbing material (RAM) response. Cotton fabric biocomposite materials were compared with carbon fabric composite materials, which are good absorbers, in terms of mechanical and electromagnetic (EM) properties for that purpose. Design/methodology/approach The laminated composite plates were manufactured by using a vacuum infusion process. The EM tests were experimentally performed with a vector network analyzer to measure reflection, transmission and absorption ability of cotton fabric, carbon fabric and cotton–carbon fabric (side by side) composite plates between 3 and 18 GHz. The tensile and low-velocity impact tests were carried out to compare the mechanical properties of cotton fabric and carbon fabric composite plates. A scanning electron microscope was used for viewing the topographical features of fracture surfaces. Findings The cotton fabric composite plate exhibits low mechanical values, but it gives higher EM wave absorption values than the carbon fabric composite plate in certain frequency ranges. Comparing the EM absorption properties of the combination of cotton and carbon composites with those of the carbon composite alone, it appears that the cotton–carbon combination can be considered as a better absorber than the carbon composite in a frequency range from 12 to 18 GHz at Ku band. Originality/value This paper shows how cotton, which is a natural and easily supplied low-cost raw material, can be evaluated as a RAM.

This paper aims to investigate the effect of cell phone radiation on human brain. It is known that the cell phone emits electromagnetic (EM) radiation which could be harmful to the human brain. In this research the electroencephalogram (EEG) signal has been acquired from 24 healthy subjects using a 16 channel EEG headset under different experimental conditions. The signal is decomposed into different brain rhythms using Daubechies Discrete Wavelet Transform up to 5th-level of the decomposition. Quantitative analysis has been carried out using two statistical parameters (Energy, Entropy) and Absolute Power. Special attention was focused on Temporal and Frontal lobes as these are near to the ear. Experimental results show higher values (for energy, entropy and absolute power) in the low-frequency bands (delta and theta) compared to the high frequency bands (alpha, beta and gamma) in both lobes. When the phone was placed 5cm away from the head there was less brain activation compared to when the cell phone was placed next to the ear/head on both sides. It was found that there was more effect on the right side compared to the left side from the cell phone’s radio waves.

In the last decades, Radio Frequency Identifiers (RFID) has gained massive popularity.In the last decades, Radio Frequency Identifiers (RFID) have gained massive popularity. RFID technology allows data to be encoded in a small form (tag). The data contained inside the RFID tag can be captured wirelessly by the RFID reader through electromagnetic (EM) waves. On the other hand, localization techniques have achieved significant developments in the last decade. There is a wide range of localization tool variations, including satellite-based localization (i.e., GPSS, GLONASS), Bluetooth Low Energy (BLE), IMU, camera, infrared sensor, and even RF-based localization. In this work, we present an accurate localization technique via battery-less passive RFID tag-UAV integration. We have employed two low-complexity methods: generalized cross-correlation with phase transformation (GCC-PHAT) algorithm and triangulation technique. By simulation, we have validated that an accurate antenna array-based dynamic localization can be realized. For the sake of simplicity, we only demonstrate two-dimensional movement. However, the identical method can also be used in the three-dimensional movement. While this paper considers only two antenna arrays and one RFID tag, the proposed concept can be expanded to a more extensive system with a larger number of antenna arrays and RFID tags.

During hypersonic vehicle flight at high speed, plasma sheath on the vehicle surface will attenuate or even interrupt the communication signal, leading to the “communication blackout” problem. The vehicle probably moves a long distance during the communication blackout due to its high speed, which is a serious threat to the safety of the vehicle. This paper proposes a method to solve the communication blackout problem using high-power microwave (HPM) irradiation. The multicomponent compressible model, finite difference time domain algorithm, and multi-fluid model are used to simulate the interaction between HPM and plasma sheath. The results show that after HPM irradiation, the electromagnetic (EM) wave transmissivity of the plasma sheath will change, and the electric field (E-field) amplitude and irradiation time of HPM significantly influence the change of transmissivity. Thereafter, analyses of the changes of the collision and plasma frequencies of the plasma sheath after HPM irradiation showed the transmissivity of the plasma sheath to low-frequency EM waves is improved by optimizing E-field amplitude and irradiation time of HPM. Therefore, HPM irradiation can be performed to enhance the transmissivity of the plasma sheath to the communication signal, thus alleviating the communication blackout problem.

Geologic noise and background electromagnetic (EM) waves often degrade the quality of very low frequency electromagnetic (VLF-EM) data. To retrieve signals with significant geologic information, we used a new nonlinear decomposition technique called the empirical mode decomposition (EMD) method with the Hilbert transform. We conducted a 2D resistivity model study that included inversion of the synthetic data to test the accuracy and capabilities of this method. Next, we applied this method to real data obtained from a field experiment and a geologic example. The filtering procedure for real data starts with applying the EMD method to decompose the VLF data into a series of intrinsic mode functions that admit a well-behaved Hilbert transform. With the Hilbert transform, the intrinsic mode functions yielded a spectrogram that presents an energy-wavenumber-distance distribution of the VLF data. We then examined the decomposed data and their spectrogram to determine the noise components, which we eliminated to obtain more reliable VLF data. The EMD-filtered data and their associated spectrograms indicated the successful application of this method. Because VLF data are recorded as a complex function of the real variable distance, the in-phase and quadrature parts are complementary components of each other and could be a Hilbert transform pair if the data are analytical and noise free. Therefore, by comparing the original data set with the one obtained from the Hilbert transform, we could evaluate data quality and could even replace the original with its Hilbert transform counterpart with acceptable accuracy. By application of both this technique and conventional methods to real data in this study, we have shown the superiority of this new method and have obtained a more reliable earth model by inverting the EMD-filtered data.

Borehole Radar (BHR) uses ultra-wideband electromagnetic (EM) waves to image discontinuities in formations. It has been a major bottleneck to extend BHR applications to obtain a clear and high-resolution radar profile in a complex and noisy environment, which increases ambiguity in the geology interpretation. To avoid this increased ambiguity in the geology interpretation, we proposed a scheme based on the empirical mode decomposition (EMD) and complex signal analysis theory to process the BHR data with low signal to noise ratio (SNR). The scheme includes four steps. First, the original radar profile is pre-processed to avoid mode confusion and noise interference to the radar echo. Next, the EMD method is used to process a single-channel radar dataset and to analyze the frequency components of the radar signal. Various intrinsic modes of the pre-processing radar profile are also obtained by using EMD. Finally, we reconstruct the intrinsic mode profile, which contains information about the formation, calculate the complex signals of the reconstructed radar profile using the Hilbert transform, extract the three instantaneous attributes (instantaneous amplitude, instantaneous phase, and instantaneous frequency), and draw the separate instantaneous attributes profiles. This processing scheme provides both the conventional time-distance profile also in addition to the three instantaneous attributes. The additional attributes reduce ambiguity when evaluating the original radar profile and avoid the deviation relying solely on a conventional time-distance profile. An actual radar profile, which was obtained by a BHR system in a limestone fracture zone, is used to verify the effectiveness of instantaneous attributes for improving interpretation accuracy. The results demonstrate that the EMD method is superior in processing the BHR signal under a low SNR and has the capability to separate the high-low components of the radar echo effectively.

We have used the radio imaging method (RIM) to delineate attenuating zones in two borehole sections in the area of the Pyhäsalmi volcanogenic massive sulfide (VMS) copper-zinc deposit located in central Finland. The frequency band (312.5–2500 kHz) is higher and thus provides better resolution and sensitivity to conductive targets than traditional ground-level and borehole electromagnetic (EM) methods. When EM waves are assumed to be propagated along straight rays, the simultaneous iterative reconstruction technique can be used and the decayed amplitudes of the electric field are converted to the attenuation coefficient in dB/m. The straight-ray assumption was, however, not met in this study. The reconstruction results of two borehole sections were compared with time-domain EM (TEM) data and electric logging data. Electric logging reveals the nearby conducive mineralizations, and when compared with RIM data, the continuation of attenuating formations can be better predicted. The intersections interpreted from the TEM data were consistent with the RIM data. However, continuation of the attenuating domains could only be established from RIM data. Low ray densities at the upper and lower edges, violation of the straight-ray assumption, and out-of-plane targets may generate artifacts. In addition, the constructions suffer from smearing in the direction of the raypath. According to the results, we can recover the shape and orientation of attenuating targets in the borehole sections, but the physical properties are underestimated due to the straight-ray assumption. The comparison studies confirmed that RIM is well-suited to estimating subsurface conductivity properties and to predicting the continuation of attenuating domains between the boreholes at the Pyhäsalmi VMS deposit.

Abstract In this paper, a metasurface (MS)-based multi-functional electromagnetic (EM) structure is proposed to realize its two different applications, namely absorption and radiation. The proposed structure is based on periodic arrays of disk-shaped metallic patches and split rings with four embedded lumped resistors. The metallic vias are inserted from top to bottom to connect the disk-shaped patches with a feeding network designed on the bottom layer where two p-i-n switches are embedded in the feeding network to alter the different functions of the proposed structure. For free space incident plan wave, the designed structure works as an absorber when the p-i-n switches are switched OFF. The absorber operates over a frequency band from 6.2 GHz to 8.2 GHz and unchanged over an incident angle from 0° to 30° for both TE and TM polarized incident waves. The same structure also works as a low scattering and high gain radiator when the p-i-n switches are turned ON and radiate within absorbing frequency band, i.e. from 7.5 to 8.0 GHz. The designed structure is fabricated and experimentally verified for EM absorption and radiation applications.

How terahertz signals perform in the neural system has attracted widespread interest in the life sciences community. Relevant experimental reveals that in animal nerve cells, the myelin sheath of the nerve axon has a higher refractive index than the intracellular and extracellular fluids in the Terahertz-far-infrared (THz-FIR) frequency band. This makes THz-FIR wave transmission possible in nerve fibers. Based on this premise, this article carries out the following work from the theoretical level to investigate the electromagnetic (EM) characteristics of in vivo nerve fibers at the THz-FIR band. First, the EM transmission model of the nerve fibers is established and studied theoretically. The dispersion curves of THz-FIR wave modals transmission in nerve fibers are calculated, which predict that nerve fibers can act as dielectric waveguides for transmitting THz-FIR waves and the THz-FIR waves can transmit at speeds up to 108 m/s. Second, a mode matching algorithm is proposed, which is named RNMMA, to calculate the transmission characteristics of THz-FIR waves at the nodes of Ranvier. The scattering matrix obtained from the proposed algorithm is in good agreement with the results from EM simulation software, which reveals how THz-FIR signals are transmitted forward through the nodes of Ranvier with low loss.

WHO (World Health Organization) concludes that not much effect is caused by electric field up to 20 kV / m in humans. WHO standard also mentions that humans will not be affected by the magnetic field under 100 micro tesla and that the electric field will affect the human body with a maximum standard of 5,000 volts per meter. In this study did not discuss about the effect of high voltage radiation SUTT (High Voltage Air Channel) with human health. The research will focus on energy utilization of SUTT radiation. The combination of electric field and magnetic field on SUTT (70-150KV) can generate electromagnetic (EM) and radiation waves, which are expected to be converted to turn on street lights around the location of high voltage areas or into other forms. The design of this prototype works like an antenna in general that captures electromagnetic signals and converts them into AC waves. With a capacitor that can store the potential energy of AC and Schottky diode waves created specifically for low frequency waves, make the current into one direction (DC). From the research results obtained the current generated from the radiation is very small even though the voltage is big enough.Keywords : Radiance Energy, Joule Thief, and LED Module.

We will review the history of photonic crystals and overview of the theoretical and experimental efforts in obtaining a photonic bandgap, a frequency band in three-dimensional dielectric structures in which electromagnetic (EM) waves are forbidden, is presented. Many experimental groups all over the world still employ this woodpile structure to fabricate PCs at optical wavelengths, waveguides, enhance nanocavities, and produce nanolasers with a low threshold limit. We have been focused on a new class of materials, the so-called metamaterials (MMs) or negative-index materials, which exhibit highly unusual electromagnetic properties and hold promise for new device applications. Metamaterials can be designed to exhibit both electric and magnetic resonances that can be separately tuned to occur in frequency bands from megahertz to terahertz frequencies, and hope-fully to the visible region of the EM spectrum.

Abstract With a high signal-to-noise ratio and a great depth of exploration, the wireless electromagnetic method (WEM) has wide applications in the exploration of deep mineral resources and oil and gas reservoirs. Extremely low-frequency electromagnetic (ELF) waves emitted from a horizontal antenna are used to achieve synchronous acquisition for different receivers of multi-coverage information in a global region. However, previous research based on a planar model ignored the curvature of the Earth. This work focuses on the electromagnetic fields (EM fields) in the model of a spherical “Earth ionosphere” to extend the coverage of WEM. By transferring the EM fields from a vertical electric dipole (VED) as well as a vertical magnetic dipole (VMD) in the multi-layered medium of the Earth, we obtain the formulae for the EM fields emitted by a horizontal electric dipole (HED) by using a reciprocity theorem. The correctness of the proposed method is verified by comparing it with the approximate analytical formula and previous work. Based on the above results, we have studied the propagation and frequency characteristics of electromagnetic fields in a spherical waveguide consisting of the ionosphere and earth. The results show that the electromagnetic fields under the spherical model produce interference effects that are different from those of the planar model. The electromagnetic response of the layered Earth was then discussed, and its potential as an electromagnetic technique for exploring the deep Earth was demonstrated.

The ultra low frequency (ULF) electromagnetic (EM) wave activity usually recorded on Earth’s ground has been found to depend on various types of space weather. In addition ULF waves observed before an earthquake have been hypothesized to be a result of geotectonic processes. In this study we elaborate for the first time the origin of sub-ULF (&lt;1 msec) magnetic field waves before an earthquake (Chi-Chi/Taiwan, 20.9.1999) by comparing simultaneously obtained measurements in the interplanetary space (ACE satellite) and on the Earth’s ground (Taiwan). The most striking result of our data analysis, during a period of 7 weeks, is that the detection of four groups of sub-ULF waves in Taiwan coincide in time with the quasi-periodic detection of two solar wind streams by the satellite ACE with approximately the solar rotation period (∼28 days). The high speed solar wind streams (HSSs) in the interplanetary space were accompanied by sub-ULF Alfvén wave activity, quasi-periodic southward IMF and solar wind density perturbations, which are known as triggering agents of magnetic storm activity. The four HSSs were followed by long lasting decreases in the magnetic field in Taiwan. The whole data set examined in this study strongly suggest that the subULF magnetic field waves observed in Taiwan before the Chi-Chi 1999 earthquake is a normal consequence of the incident of HSSs to the magnetosphere. We provide some observational evidence that the sub-ULF electromagnetic radiation on the Earth was most probably a partner to (not a result of) geotectonic processes preparing the Taiwan 1999 earthquake.

Background: Electromagnetic imaging (EMI) is an emerging technology that transmits low energy electromagnetic waves from a ring of transceivers around the head, modified as they pass through abnormal tissue, providing unique signatures for brain pathology. It promises to provide portable, non-ionizing, rapid neuroimaging for prehospital and bedside evaluation of stroke, based on the dielectric properties of the tissue. We aimed to assess the clinical utility of EMI in stroke diagnosis in a pilot study. Methods: In a prospective, observational, open, non-interventional pilot study, patients with imaging-proven ischemic (IS) or haemorrhagic stroke (ICH) within the preceding 48 hours were recruited. Using the EMVision scanner, EMI was performed within 1-24 hours of diagnostic CT or MRI. Images were obtained by processing signals from encircling transceiver antennae contained in an instrumented 18 kg helmet which emit and detect low energy non-ionising signals in the microwave frequency spectrum (0.5-2.0 GHz). Localisation was assessed by determining whether fusion images resulted in target detection in the same quadrant as comparable CT or MRI. Electromagnetic (EM) images were reconstructed by creating maps of the EM wave scattering arising from contrast in electrical parameters between IS or ICH lesions and normal brain. A blinded clinician assessed agreement between regional abnormalities on EMI and CT or MRI scans. Algorithms for distinction between IS and ICH were based on differences in EM transmission, reflection and scattering through brain tissue. Results: Thirty patients were studied, 21 IS and 9 ICH. Mean age was 66.7 years (range 37-87), 57% were female. Mean NIHSS at presentation was 5. Mean time to routine imaging was 5.5 hrs (range 1-48) and to EMI 24 hrs (range 6-60). Nineteen patients (63%) had only CT performed; 11 (37%) had both CT and MRI. EMI differentiated ICH from IS with 93% accuracy and localised the stroke to the correct brain quadrant with 87% accuracy. Conclusion: In this early validation pilot study we show the ability to distinguish between IS and ICH and stroke location within a given brain quadrant. Further developments may produce a valuable imaging tool to assist in prehospital and bedside stroke diagnosis and management.

Microstrip patch antennas stand out because of their low cost, smaller size and easy fabrication. The study presents the design of a microstrip rectangular patch antenna operating at 2.6 GHz frequency and the effect of different weather conditions on the antenna. During the antenna design on CST program and manufacturing in the laboratory, it is aimed to perform the measurement at the desired frequency and decibel level. The study includes experiments and results made on different types of snow, apart from the normal measurement with the VNA. A good S11 scattering value was obtained at the desired frequency in the designed microstrip patch antenna as -18.48 dB. This value decreased to around -5 dB when there was wet snow on the antenna due to attenuation and thermal effects. If the snow was removed from the antenna, the old S11 value could not be returned because of the wetness left by the snow, and it remained at approximately -14 dB. Consequently, the attenuation of the electromagnetic waves have been confirmed by the literature under different conditions as wet snow with nano VNA for the first time. Attenuation by wet snow and water is greater than dry snow with voids.

Abstract Surface plasmon polaritons (SPPs) are interactions between incident electromagnetic (EM) waves and free electrons on the metal-dielectric interface in the optical regime. To mimic SPPs in the microwave frequency, spoof SPPs (SSPPs) on ultrathin and flexible corrugated metallic strips were proposed and designed, which also inherit the advantages of lightweight, conformal, low profile, and easy integration with the traditional microwave circuits. In this paper, we review the recent development of SSPPs, including the basic concept, design principle, and applications along with the development from unwieldy waveguides to ultrathin transmission lines. The design schemes from passive and active devices to SSPP systems are presented respectively. For the passive SSPP devices, the related applications including filters, splitters, combiners, couplers, topological SSPPs, and radiations introduced. For the active SSPP devices, from the perspectives of transmission and radiation, we present a series of active SSPP devices with diversity and flexibility, including filtering, amplification, attenuation, nonlinearity, and leaky-wave radiations. Finally, several microwave systems based on SSPPs are reported, showing their unique advantages. The future directions and potential applications of the ultra-thin SSPP structures in the microwave and millimeter-wave regions are discussed.

Abstract Two-dimensional fully coupled EM wave-plasma simulations are used to study the formation, early transient and quasi-steady state of the argon plasma excited by a two-dimensional discontinuous microstrip line. The electromagnetic waves that normally propagate in the microstrip transmission line, radiate and scatter at the position of the gap and the electric field is enhanced primarily at the corner of the gap. The microdischarge is preferentially formed at this position of the EM field hotspot and in low frequencies propagates on the dielectric surface, much like a microwave surface streamer. In longer times, diffusion dominates and the whole gap is filled with plasma of maximum density in the order of $10^{20}$ $m^{-3}$ while it occupies a volume larger than the gap. Mean electron temperatures range from 2.8 to 3.9 eV, while the plasma reaches a quasi-static regime in approximately 2 $\mu$ s having reconfigured the transmission and radiation patterns of the slitted microstrip line. The tunability of the microstrip due to plasma formation provides means for sustaining the discharge in a stable regime. For the same input EM power, the electron temperature increases with increasing excitation frequency while electron densities found to decrease. For the same wave frequency, a decrease of the electron densities with increasing gap is also found in addition to a restriction of the discharge expansion. Finally, thicker dielectrics result to higher electron densities and electron temperatures as well as absorbed power from the plasma. These findings are attributed to the dependence of absorbed EM power and skin depth on the EM wave angular frequency, the critical for shielding electron density as well as the restructuring of the S-parameters due to the changes in operational parameters.

As the core issue in helicon discharge, the physical mechanism behind the high ionization rate phenomenon is still not fully understood. Based on the warm plasma dielectric tensor model which contains both the particle drift velocity and temperature anisotropy effect, by employing the general dispersion relation of electromagnetic waves propagating in magnetized and uniform plasma with typical helicon discharge parameter conditions, wave mode propagation characteristic and collisional, cyclotron and Landua damping induced wave power deposition properties of azimuthally symmetric mode were theoretically investigated. Systematic analysis shows that, under typical helicon plasma parameter conditions, i.e., wave frequency <em>ω/2π</em>=13.56 MHz, ion temperature is one tenth of the electron temperature, for given magnetic field <em>B₀</em> (or wave frequency <em>ω</em>), there exists a critical wave frequency <em>ω_cr</em> (or magnetic field <em>B_0,cr</em> ), above which (or below <em>B_0,cr</em>) the damping of the <em>n=1,2,3 </em>cyclotron harmonics begins to increase sharply; for the electron temperature isotropic case, the attenuation constant of different harmonics starts to increase significantly and monotonically at different threshold of magnetic field, while the phase constant abruptly increases monotonically from the beginning of the parameter interval, on the other hand, for the electron temperature anisotropic case, both the phase constant and attenuation constant have peak phenomenon, i.e., the attenuation constant begins to increase sharply at a certain value of <em>B₀</em> and meanwhile the phase constant appears a maximum value near the same value of magnetic field, the phase constant starts to keep constant at a certain value of <em>B₀</em> and meanwhile the attenuation constant has a maximum value near this same value of magnetic field; for the wave power deposition properties, under electron temperature anisotropy conditions, power deposition due to collisional damping of Trivelpiece-Gould (TG) wave plays a dominant role in low field (<em>B₀</em>=48 Gs), and by considering the electron finite Larmor radius (FLR) effect, the power deposition of TG wave appears a maximum value at a certain point of parallel electron temperature <em>T_e, _//</em> , and with the decrease of <em>T_e,_⊥</em>/<em>T_e, _//</em>, the maximum value of power deposition increases gradually. All these conclusions are very important for us to further reveal the physical mechanism of high ionization rate in helicon plasma.