Low-frequency Electromagnetic Research Articles

Facile fabrication of cellulose-derived flawed graphite carbon with low-frequency minimum reflection loss in the C bands

Developing strong electromagnetic (EM) wave absorbing materials to solve the issue of EM radiation emanating from electronic devices in low-frequency range remains currently a great challenge. The majority of current solutions in low-frequency range are based on magnetic absorbent. However, this approach is constrained by the poor impedance matching, high production cost and limited absorption bandwidth. Herein, the novel reproducible cellulose-derived flawed graphite carbon material (represented as CFGC) was prepared by chemical and following simple carbonization method. Besides, the unique defect structure and the mechanism underlying microwave absorption (MA) are elaborated in detail. By fine-tuning the content of CFGC, the MA property is optimized. The minimum reflection loss (RLmin) of 50wt% filling for CFGC is –42.08dB at 4.08GHz, showing an excellent MA property within the low-frequency range of C bands. Thus, the novel CFGC in this study provides a new and convenient way to solve low-frequency EM pollution.

Atomic Infusion Induced Reconstruction Enhances Multifunctional Thermally Conductive Films for Robust Low-Frequency Electromagnetic Absorption.

Deterministic fabrication of highly thermally conductive composite film with satisfying low-frequency electromagnetic (EM) absorption performance exhibits great potential in advancing the application of 5G smart electric devices but persists challenge. Herein, a multifunctional flexible film combined with hetero-structured Fe6W6C-FeWO4@C (FWC-O@C) as the absorber and aramid nanofibers (ANFs) as the matrix was prepared. Driven by an atomic gradient infusion reduction strategy, the carbon atoms of absorbers can be precisely relocated from carbon shell to core oxometallate lattice, triggering in situ carbothermic reduction for customization of unique oxometallate-carbide heterojunctions and surface geometrical structure. Such an atoms reconstruction process effectively regulates interface electronic structure and magnetic configuration, resulting in enhanced polarization loss from abundant heterointerfaces and crystal defects and magnetic loss from hierarchical structure endowed magnetic coupling interaction, which jointly contributes to the efficient low-frequency EM absorption performance. Eventually, optimized FWC-O@C microplate exhibits a broad absorption bandwidth surpassed the entire C band, and the assembled FWC-O@C/ANFs composite film also performs a high thermal conductivity over 2500 % higher than that of the pure ANFs. These findings provide a new insight into the atomic reconstruction affected EM properties and a generalized methodological guidance for preparing multifunctional thermally conductive composite films.

Seismic Electromagnetic Radiation Simulation Using Finite-Element Time-Domain Method

ABSTRACT Low-frequency electromagnetic (EM) radiation is one of the major observed phenomena during seismogenic and rupture processes, playing a significant role in the study of seismic hazards and early earthquake warning. Previous research has shown that regardless of the specific mechanism, the seismic EM process can be studied through the simulation of dipole source radiation. Currently, these large-scale seismic EM simulations are mainly carried out by the finite-difference time-domain method. In this article, we present the first finite-element time-domain seismic EM simulation with adaptive time step size. The algorithm can guarantee unconditional stability during time iterations and has flexible grid adaptivity. The accuracy of the algorithm is verified by both the analytical solutions and the global Schumann resonance frequencies. To accurately simulate the propagation of low-frequency seismic EM waves, we further establish a realistic multiresolution model of the Earth–ionosphere system. In this model, a normalized excitation function of the seismic dipole source related to the rupture process is proposed to simulate electrokinetic-related EM radiation. Under these settings, simulation results show that the reflection effect of the ionosphere prohibits the seismic EM field from fast disappearance, yet its inner anomalies have slight effects on the resultant field. Meanwhile, the time-domain magnetic field is more sensitive to the source characteristics, for instance, the uplift and decline time of the seismic dipole pulse, than the frequency-domain waveforms. It is also observed that the seismic EM field in the air is higher than that in the Earth’s land. These results suggest the feasibility of air time-domain observation of the seismic EM field.

EFFECT OF EXTREMELY LOW-FREQUENCY ELECTROMAGNETIC FIELDS ON PROMOTING MYOGENESIS IN THE EARLY PROCESS OF DENERVATED MUSCLEATROPHY

Objective: To investigate the effects of extremely low-frequency electromagnetic fields (ELF-EMF) on myogenesis during the early stage of denervated muscle atrophy in Sprague-Dawley (SD) rats. Methods: a total of 36 female SD rats were fed in cages and divided into three groups: the normal control group, the muscle atrophy group and the 10[Formula: see text]Hz/1.5[Formula: see text]mT magnetic field group. The rats in the 10[Formula: see text]Hz/1.5[Formula: see text]mT magnetic field group received a magnetic field intervention for 2[Formula: see text]h per day. The posterior muscle groups of the lower limbs of rats were sampled on the first, second, third and fourth weeks for evaluating the underlying changes. The harvested tissues were stained with hematoxylin–eosin (HE) dye to observe the morphology of the muscle atrophy and to measure the muscle fiber cross-sectional area ratio. A reverse transcription polymerase chain reaction was used to detect the expression of Myf5 mRNA in each group. The myogenesis-related proteins in the harvested muscle tissue were detected by western blot assay. Results: (1) HE staining showed that with the extension of denervation time, the structural disorder of muscle fibers was aggravated, and in the second week of the denervated muscle atrophy, muscle fiber cross-sectional area tended to increase in the 10[Formula: see text]Hz/1.5[Formula: see text]mT magnetic field group. Overall muscle atrophy was inevitable. (2) Results of RT-PCR showed that the expression of Myf5 mRNA in the 10[Formula: see text]Hz/1.5[Formula: see text]mT magnetic field group was significantly high in the second week of denervation, and the difference was statistically significant compared with the muscle atrophy group (*[Formula: see text]). (3) Western blot analysis showed that the expression of MYF5 proteins in the 10[Formula: see text]Hz/1.5[Formula: see text]mT magnetic field group was significantly higher than that in the muscle atrophy group (**[Formula: see text]) in the second week of denervation. Further, the expression of MYOG protein in the 10[Formula: see text]Hz/1.5[Formula: see text]mT magnetic field group was significantly higher than that in the muscle atrophy group (****[Formula: see text]). Conclusions: 10[Formula: see text]Hz/1.5[Formula: see text]mT ELF-EMF can significantly promote myogenesis during early denervated muscle atrophy in SD rats.

Parasitic modulation effect caused by dynamic plasma in low frequency

Abstract-dynamic plasma sheath can severely interfere with the communication of hypersonic vehicles during atmospheric reentry. Theoretical and experimental results show that low-frequency (LF) electromagnetic (EM) waves could penetrate the plasma sheath, building a feasible method to solve the “radio blackout” problem. This paper discovers that the propagation of LF EM waves in plasmas is still influenced by parasitic modulation effects. Compared to microwave frequencies, the impact of parasitic modulation effects on signal modulation patterns is more distinct for LF EM waves. In contrast to the microwave frequency range, where the rotation direction of QPSK signal constellation points changes with the ratio of plasma frequency to electromagnetic wave frequency, in the LF range, the constellation points undergo limited clockwise rotation. This phenomenon can be attributed to the unique magnetic field propagation mechanism of LF EM waves in dynamic plasmas. This paper analyzes the mechanism of this specific parasitic modulation effect and discovers a sinusoidal transformation relationship between amplitude attenuation and phase shift. Meanwhile, the experimental and simulation results proved that the time-varying plasma could cause the parasitic modulation effect of LF EM wave, resulting in a limited clockwise rotation of orthogonal phase-shift keying constellation points, which is consistent with the theoretical analysis.

The effectiveness of very low-frequency electromagnetics (VLF-EM) method in detecting buried targets at a controlled site

The ever-increasing anthropogenic activities that pose a significant threat to environmental security and sustainability have spurred geophysicists to review enhance geophysical techniques for shallow geophysical investigations, especially in identifying illegal buried materials. This article applied very low-frequency electromagnetic (VLF-EM) at an experimental geophysical site (EGS) to examine the geophysical response over various buried targets. The VLF-EM data acquired on the site with and without buried targets demonstrate the nature of the anomalies and the characteristic signals of the buried targets. There are significant variations in the anomalies source-bodied between the site with and without buried targets. The result of the pre-burial investigation shows no major contrast in the equivalent current density values across the site without targets. Minors and major anomalies were encountered after burying the targets corresponding to the buried targets. Some signals become stronger over a large buried target. However, there were a few undetected targets and some cases of unsatisfied results, which were also discussed. The performance of the VLF-EM method in terms of depth estimation was also examined. A significant variation was noted due to the presence of the buried targets and it was noted that the current density seems to always emerge maximally and minimally around the conductor targets and non-conductive targets, respectively. The failure of the VLF-EM to detect the buried pipes in various orientations was examined. The VLF-EM method is more consistent at small spacing and it can be very useful for identifying underground metallic and non-metallic targets. The study successfully provides useful information to complement the complexity of the use of geophysical methods while enhancing the subsurface information and understanding of VLF-EM anomalies or responses generated by various targets such as subsurface geological structures, buried waste contaminants and underground utilities to boost environmental studies and engineering investigations.

Design of broadband gradient resistive film metamaterial absorber based on genetic algorithm

In recent years, electromagnetic (EM) wave absorbing devices based on metamaterials have attracted widespread attention, due to their advantages such as broadband, easy preparation, and flexibility to tailor EM waves. Nevertheless, a review of the existing research reveals that the inherent sub-wavelength characteristics of metamaterials and metasurfaces impose certain constraints on their applications in low-frequency ranges. In order to achieve low detectability that takes into account both low-frequency and broadband absorbing performance, this work, presents a metamaterial absorber based on 5-layer gradient resistance film and dielectric composite structure, as shown in <xref ref-type="fig" rid="FigureAbstract">Fig. (a)</xref>. To begin with, we introduce the structural design of the initial element, and based on this, the transmission line theory and impedance matching principle are used to analyze the strong wave absorption conditions of the absorber element. In terms of the element structure optimization, the genetic algorithm is adopted to globally search for the optimal solution in the multi-variable domain, resulting in the rapid determination of metamaterial elements’ configurations and resistance parameters that meet the design goals. In the simulation, the wave absorption performance and mechanism of the designed absorbing element are also investigated in an in-depth manner. Simulation results show that the designed metamaterial absorber can achieve more than 90% EM wave absorption in a frequency range of 1.62–19.16 GHz (with a relative bandwidth of 168.8%) under normal incidence of linearly polarized plane waves, which effectively expands the absorption bandwidth to the L band and K band. In addition, the simulations for oblique incidence at different polarizations provide strong evidence for the device’s insensitivity to both polarization and angle. The radar cross section (RCS) curves obtained by the time domain (TD) simulation illustrate that the novel structure can achieve more than 10 dB RCS reduction in a frequency range of 1.7–20 GHz. In the device's performance verification process, a metamaterial absorber with 20 × 20 elements and dimensions of 1.566<inline-formula><tex-math id="M1">\begin{document}$ {\lambda }_{l} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="7-20231781_M1.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="7-20231781_M1.png"/></alternatives></inline-formula>×1.566<inline-formula><tex-math id="M2">\begin{document}$ {\lambda }_{l} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="7-20231781_M2.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="7-20231781_M2.png"/></alternatives></inline-formula>× 0.113<inline-formula><tex-math id="M3">\begin{document}$ {\lambda }_{l} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="7-20231781_M3.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="7-20231781_M3.png"/></alternatives></inline-formula> is fabricated and tested by using the bow method reflectivity test system. The absorptivity curves under 5° oblique incidence of different polarizations, show that the proposed metamaterial absorber can realize more than 80% EM absorption in an entire frequency range from 2 to 18 GHz, the test results of different polarizations are basically consistent. The test results at oblique incidence (<i>θ</i> ≥ 30°) show that although the measured and simulated curves exhibit discrepancies in certain frequency bands due to human error or material dispersion characteristics, the overall experimental results are consistent with our expectations, which fully proves that the designed metamaterial absorber has potential application value in the field of low-frequency and broadband EM absorption.

The Geophysical Investigation of Leachate Formation in Mgbuka Obosi, Idemili North Local Government Area of Anambra State, Nigeria

The contamination of leachates (a polluted liquid made up of various toxic substances) from landfills is a significant environmental concern, especially in developing countries.This contaminated fluid is formed when rainwater interacts with refuse and travels through the pore spaces in soil. Constant migration of this fluid poses a significant threat to the quality of both surface and groundwater in and close to the landfill area. To determine the extent of leachate formation, the study used both Very Low-Frequency Electromagnetic (VLF-EM) and Electric Resistivity Tomography (ERT) to locate and define the spatial distribution of the leachate plume migration pathway at Mkpuka Obosi Dumpsite in Idemili North LGA of Anambra, Nigeria. Seven profiles were surveyed for both the VLF-EM and ERT. The VLF-EM survey, with a profile length of 100 to 200m and a 10m interstation spacing, revealed the presence of a conductive pollutant (leachate plume) in the subsurface. The results from the 2D ERT survey that employed a Wenner array with a profile length of 100 to 200m and an electrode spacing of 5m, divided the subsurface into six zones with an unusually low resistivity ranging from 0-250\(\Omega\)m. The leachate plumes were interpreted as the zone with the lowest resistivity of 0 to 25\(\Omega\)m, having an average thickness of approximately 10m and extending beyond the probed depth of 50m. Additionally, the percentage of leachate was found to be concentrated primarily at the center of the landfill and gradually decreasing proportionally from the center. Thus, emphasizing the importance of addressing the issues in landfill management.

New Insights into the Gold Mineralization in the Babaikundi–Birgaon Axis, North Singhbhum Mobile Belt, Eastern Indian Shield Using Magnetic, Very Low-Frequency Electromagnetic (VLF-EM), and Self-Potential Data

The North Singhbhum Mobile Belt (NSMB) in the eastern Indian shield is an excellent example of a diverse lithological domain with multiphase shear/fracture zones. It is a well-acknowledged prospective region known for various mineralizations, e.g., Cu, Au, U, and Fe. The present study was conducted in the Babaikundi–Birgaon Axis (a shear and fracture zone within NSMB) within Babaikundi village. The study suggests that anomalous zones are possibly related to gold-associated sulfide mineralization using photomicrography and geophysical methods such as magnetic, self-potential (SP), and very low-frequency (VLF) electromagnetic (EM) methods. Photomicrography on quartz samples and Scanning Electron Microscope (SEM) Backscattered-Electron (BSE) images show that gold particles are present in the quartz reef vein in Babaikundi. Magnetic data are presented in the total magnetic intensity (TMI), upward continuation, and analytical signal maps. VLF-EM data were analyzed using different processing techniques to delineate anomalous auriferous zones. Furthermore, the SP data were inverted using the Particle Swarm Optimization (PSO), Very Fast Simulated Annealing (VFSA), and Genetic Algorithm (GA) approaches for comparative study of the resultant model parameters and their suitability considering a 2D inverted resistivity section derived using VLF-EM. The photomicrography study indicates the existence of gold/ pyrite/pyrrhotite within the Babaikundi–Birgaon axis, which corresponds to a low magnetic anomaly based on a magnetic study; a high current density, a high Fraser value, and a low resistivity based on the VLF-EM study; and a negative SP value was found based on the SP study. The combined study generally supports mapping auriferous zones and demarcates the Babaikundi–Birgaon axis within the Babaikundi–Birgaon area.

Analysis of Low-Frequency Communication of Hypersonic Vehicles in Thermodynamic and Chemical Non-Equilibrium State

A plasma sheath will be developed surrounding a hypersonic vehicle in flight, which can reflect, absorb, and scatter electromagnetic (EM) waves of lower frequencies than its own, resulting in a communication blackout. This paper focuses on knowing how to limit the absorption and reflection of low-frequency EM waves by plasma sheath in a thermodynamic and chemical non-equilibrium state. According to the temperature increment model, the energy of high-power microwave (HPM) irradiation is translated into the temperature increment of heavy particles in plasma. As a result of this modification process, the transmittance of low-frequency EM waves going through the plasma sheath in a certain time frame rises, potentially easing the communication blackout problem.

A microfabricated lab-on-chip with three-dimensional electrodes for microscopic observation of bioelectromagnetic effects of cells

Electromagnetic (EM) signals are widely used in electronic instruments and biomedical systems and might have affected the human bodies surrounded by them. However, the interaction mechanism of EM signals with biological structures is poorly understood. We propose a micro-fabricated low-frequency EM stimulation lab-on-chip with three-dimensional interdigital electrodes for observation of cell lines with microscope. The field strength between the electrodes at various frequencies is estimated through simulation. An electric field strength of 4.45Vrms/m is reached in the culture medium with a 10Vpp, 10 kHz input signal. According to the simulation results, the high end of the applicable frequency range of the testbench is 3 MHz. A prototype is fabricated using full-wafer microfabrication techniques. The impedance of the prototype between 20 Hz and 30 MHz is characterized. Moreover, human cell line HEK293T is cultured in the testbench for 24 h and observed using microscope to check the biocompatibility of the electrodes. The prototype is thus applicable to long-term microscopic observation of cell lines for study of EM effect on biological structures. The 24-h cell culturing experiment with and without EM stimulation with the proposed prototype shows that the cell growth is obviously affected by a 10 kHz EM signal.

A probability of detection model for a sensor-based monitoring method against local wall thinning

In this study, a multivariable probability of detection (POD) model is developed to quantify the detection capability of a low frequency electromagnetic (LFEM) testing method with permanently installed sensors to monitor the thinning of pipe walls. Numerical simulations are utilized to predict the signal response by modeling LFEM testing against local wall thinning with different profiles. By probabilistically calibrating the simulated signal response with a limited number of experimental samples, signal response distributions due to various flaw profiles are inferred. Subsequently, a model is developed using Monte Carlo simulation to determine the distribution of the signal response affected by sensor placement and to calculate the POD. The resultant POD contours reflect the effect of multiple flaw parameters and sensor placement on the detection capability of the LFEM testing method.

Simulation study of alleviating the communication blackout using high-power microwave irradiating plasma sheaths

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.

Geoelectrical model of geothermal spring in Ie Jue Seulawah deriving from 2D VLF-EM and DC resistivity methods

Seulawah Agam is one of the volcanic areas in Aceh province, Indonesia, which planned for a powerplant constriction with an energy capacity expected to be approximately 230 MWe. This volcano has seven manifestations in the form of craters, hot water, and heated soil. The hydrothermal system in this volcano is controlled by a fault system which acts as a medium for the entry and exit of fluids. Therefore, understanding the local geology is required for geothermal power plant development, especially for the determination area for injection and production wells. In this research, we use the Very Low-Frequency Electromagnetic (VLF-EM) methods combined with electrical resistivity tomography data on the Ie Jue manifestation area to determine the shallow structure related to the manifestation. The VLF was made for 4 profiles with 700 m length for each VLF-EM profile and 300 m for electrical resistivity lines. We utilized the Karous Hjelt filter for qualitative interpretation, while Occam's algorithm was applied for 2D inversion of data for quantitative analysis of VLF-EM data. Based on the current density model, several vertical conductive anomalies can be well demonstrated at a distance of 300-400 m from the four VLF profiles. The conductive anomaly can also be seen in the resistivity data from the electrical resistivity. The results of the Occam model show that the depth of faults and fractures is seen at 30 m depth with low resistivity (below 100 Ωm). This anomaly is generally associated with outcrops in the field, such as fumarole and warm ground on the east side of the manifestation area. In addition, the 2D inversion model of VLF also shows the contrast of several fracture zones as a place for fluid to enter and exit the Seulawah volcano. Therefore, based on our result, it can be summed up that this method is effectively applied to geothermal in high terrain areas such as in Indonesia and can be used to suggest safe locations for injection wells and production of geothermal drilling.

Numerical Study of Global ELF Electromagnetic Wave Propagation with Respect to Lithosphere–Atmosphere–Ionosphere Coupling

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.

Formation and evolution of post-solitons following a high intensity laser-plasma interaction with a low-density foam target

The formation and evolution of post-solitons has been discussed for quite some time both analytically and through the use of particle-in-cell (PIC) codes. It is however only recently that they have been directly observed in laser-plasma experiments. Relativistic electromagnetic (EM) solitons are localised structures that can occur in collisionless plasmas. They consist of a low-frequency EM wave trapped in a low electron number-density cavity surrounded by a shell with a higher electron number-density. Here we describe the results of an experiment in which a 100 TW Ti:sapphire laser (30 fs, 800 nm) irradiates a TMPTA foam target with a focused intensity . A third harmonic ( nm) probe is employed to diagnose plasma motion for 25 ps after the main pulse interaction via Doppler-Spectroscopy. Both radiation-hydrodynamics and 2D PIC simulations are performed to aid in the interpretation of the experimental results. We show that the rapid motion of the probe critical-surface observed in the experiment might be a signature of post-soliton wall motion.

Biomimetic 3D coral reef-like GO@TiO2 composite framework inlaid with TiO2–C for low-frequency electromagnetic wave absorption

Improving the non-magnetic low-frequency electromagnetic (EM) wave performances of common microwave-absorbing materials is yet very difficult and depends on the assistance of structural design to realize tremendous microwave reflectance absorption in a limited space. Herein, a biomimetic three-dimensional coral reef-like graphene oxide (GO)@TiO2 composite framework was prepared with porous TiO2–C inlaid subunits derived from MIL-125 (Ti), which provided an effective platform for concentrating two unusual structures of TiO2 and carbon sources into single particles. The formation mechanism of the material was analyzed in detail. Compared with GO@TiO2/TiO2–C composite materials at varying mass ratios, the minimum RL of GO@TiO2/TiO2–C-15 is −64.4 dB at 7.4 GHz, and the intensity of −25 dB (>99% energy absorption) can be improved at different thickness, which exhibits an excellent low-frequency EM absorption behavior. Simultaneously, GO@TiO2/TiO2–C-15 has obvious extended performances, including antimicrobial activities and low infrared emissivity, which demonstrate the versatility and application potential of non-magnetic low-frequency microwave absorbers in wearable devices and other fields. The new material is beneficial to reducing the EM waves-caused threat to human health in communication band and to attaining the sustainable utilization of EM waves.

Zel'dovich Amplification in a Superconducting Circuit.

Zel'dovich proposed that electromagnetic (EM) waves with angular momentum reflected from a rotating metallic, lossy cylinder will be amplified. However, we are still lacking a direct experimental EM-wave verification of this fifty-year-old prediction due to the challenging conditions in which the phenomenon manifests itself: the mechanical rotation frequency of the cylinder must be comparable with the EM oscillation frequency. Here, we propose an experimental approach that solves this issue and is predicted to lead to a measurable Zel'dovich amplification with existing superconducting circuit technology. We design a superconducting circuit with low frequency EM modes that couple through free space to a magnetically levitated and spinning microsphere placed at the center of the circuit. We theoretically estimate the circuit EM mode gain and show that rotation of the microsphere can lead to experimentally observable amplification, thus paving the way for the first EM-field experimental demonstration of Zel'dovich amplification.

Response of young Nerium oleander plants to long-term non-ionizing radiation.

Although exposure to low frequency electromagnetic radiation is harmful to plants, LF-EM irradiated Nerium oleander seedlings exhibited enhanced development and growth, probably taking advantage of defined structural leaf deformations. Currently, evidence supports the undesirable, often destructive impact of low frequency electromagnetic (LF-EM) radiation on plants. The response of plants to LF-EM radiation often entails induction in the biosynthesis of secondary metabolites, a subject matter that is well documented. Nerium oleander is a Mediterranean plant species, which evolved remarkable resistance to various environmental stress conditions. In the current investigation, cultivated N. oleander plants, following their long-term exposure to LF-EM radiation, exhibited major structural modifications as the flattening of crypts, the elimination of trichomes and the reduction of the layers of the epidermal cells. These changes co-existed with an oxidative stress response manifested by a significant increase in reactive oxygen species at both the roots and the above ground parts, a decline in the absorbance of light by photosynthetic pigments and the substantially increased biosynthesis of L-Dopa decarboxylase (DDC), an enzyme catalyzing the production of secondary metabolites that alleviate stress. The exposed plants exhibited greater primary plant productivity, despite a manifested photosynthetic pigment limitation and the severe oxidative stress. This unique response of N. oleander to severe abiotic stress conditions may be owed to the advantage offered by a structural change consistent to an easier diffusion of CO2 within the leaves. A major plant response to an emerging "pollutant" was documented.

Neuroprotective Effects of Low Intensity and Low Frequency Electromagnetic �in vitro� Stimulation on Glial Cells

Degenerative neurological diseases (senile dementia, Alzheimer`s disease, glaucoma), post-stroke sequelae are increasing as prevalence nowadays, in context of aging in general population, and there are strong evidences that astrocytes may play a significant role in neuroprotection. The study evaluates the effects of low intensity low frequency electromagnetic field (EMF) �in vitro� stimulation (195 mA, 7-8 Hz) on the glial cells, in different conditions, in order to identify the neuroprotective potential. Three cell lines were used for the study: the Clonetics (Lonza) line of normal human astrocytes, U87 glioblastoma tumor cells (ATCC) and L929 murine fibroblasts. The cell cultures were exposed to EMF stimulation for 2 hours/day, for 5 and 10 day, in absence and in the presence of oxidative stress stimuli. Cell viability, apoptotic potential, changes in cell phenotype, stimulation of cell proliferation for normal and malignant transformed cell lines, resilience to oxidative stress were investigated. The viability of the cells was investigated by MTS assay, and the Griess test was used to detect nitrite production as a marker of oxidation and inflammation. Inverted microscopy examination revealed that following exposure to the tested EMF, no morphological changes of the cells were recorded. In none of the cell lines tested, no cytotoxic or cytopathic effects were observed in the cultures exposed under low density conditions. In case of exposure of cell cultures for 10 days to the action of EMF, a viability of 98.2% of glial cells and 97% of exposed fibroblasts is observed, compared to unexposed cells. The viability of the cells exposed to both EMF and oxidative and inflammatory stimuli is increased by 0.96% in the case of H2O2 stimulation and in 3.76% in the case of LPS stimulation, suggesting a possible neuroprotective effect of EMF exposure. Low intensity low frequency EMF �in vitro� stimulation increased viability of the glial cells exposed to oxidative and inflammatory stimuli. No cytotoxic or cytopathic effects were observed in the exposed cultures under conditions of low density. Further tests are needed in order to elucidate the mechanisms of action of EMF on astrocytes, especially on astrocyte-neuron co-cultures to highlight the interactions between these cell types. Confirmation of the neuroprotective effect of low intensity and low frequency EMF opens the way for the development of an innovative, non-invasive therapy.