Low-frequency Electromagnetic Waves Research Articles

Well-Dispersed CoNiO2 Nanosheet/CoNi Nanocrystal Arrays Anchored onto Monolayer MXene for Superior Electromagnetic Absorption at Low Frequencies

Developing microwave absorbers with superior low-frequency electromagnetic wave absorption properties is one of the foremost important factors driving the boom in 5G technology development. In this study, via a simple hydrothermal and pyrolysis strategy, randomly interleaved CoNiO2 nanosheets and uniformly ultrafine CoNi nanocrystals are anchored onto both sides of a single-layered MXene. The absorption mechanism demonstrated that the hierarchical heterostructure prevents the aggregation of MXene nanoflakes and magnetic crystallites. In addition, the introduction of the double-magnetic phase of CoNiO2/CoNi arrays can not only enhance the magnetic loss capacity but also generate larger void spaces and abundant heterogeneous interfaces, collectively promoting impedance-matching and furthering microwave attenuation capabilities at a low frequency. Hence, the reflection loss of the optimal absorber (M–MCNO) is −45.33 dB at 3.24 GHz, which corresponds to a matching thickness of 5.0 mm. Moreover, its EAB can entirely cover the S-band and C-band by tailoring the matching thickness from 2 to 7 mm. Satellite radar cross-section (RCS) simulations demonstrated that the M–MCNO can reduce the RCS value to below −10 dB m2 over a multi-angle range. Thus, the proposed hybrid absorber is of great significance for the development of magnetized MXene composites with superior low-frequency microwave absorption properties.

Piezo‐Turned Magnet Rotation for ELF/SLF Cross‐Medium Communication in Omni‐Direction

AbstractExtremely/super low frequency (ELF/SLF) electromagnetic (EM) waves offer efficient propagation in challenging cross‐medium environments. However, conventional coil antennas, when emitting ELF/SLF EM waves, face constraints related to size, radiation efficiency, and high power consumption. To overcome these limitations, a disc‐rod structured piezoelectric rotating resonator is proposed, which can turn a NdFeB permanent magnet disc into rotation with an impressive high‐speed up to 10 000 r min−1 via wobbling motion of the rod tip, effectively generating ELF/SLF magnetic field radiation via rotational oscillation other than common linear and swinging oscillation of the magnetic dipole moments. The piezo‐turned magnetic rotation (PTMR) method leads to a two to five‐fold enhancement in magnetic field emission compared to existing piezo‐actuated acoustic resonant antennas, and a 370 times higher emitting efficiency compared to the traditional coil antenna with a comparable size. In contrast to unidirectional EM wave radiation at their solely resonant frequencies, the PTMR antenna showcases omnidirectional B‐field radiation with continuous tunability in a dual frequency band spanning from 10 to 100 Hz. Moreover, an air–seawater cross‐medium magnetic field communication is successfully demonstrated. With outstanding performance metrics, the PTMR antenna emerges as a promising solution for efficient long‐distance ELF/SLF cross‐medium communication.

Initial Experimental Results on Ion Cyclotron Resonance Heating Selectively Mixed Low Z Ions to Enhance Production Efficiency of Multicharged Ions on Electron Cyclotron Resonance Ion Source

According to the accessibility conditions of wave propagation in the magnetized plasma of an electron cyclotron resonance (ECR) ion source (ECRIS), it is speculated that the essential factor that determines the limitations in the multiply charged ion currents is the left-hand polarization wave cutoff (L-cutoff). It is necessary to overcome this limitation, we proposed the introduction of ion cyclotron resonance (ICR) or lower hybrid resonance (LHR) by lower frequency waves. We conduct heating low-mass ions selectively in enhanced producing multiply charged ion by mixing low-mass element gas, which has been conventionally performed in ECRIS, or relaxation of the potential well based on the existence of resonant electron particles by ECR. This paper will describe the initial experimental results of ICR application by introducing low-frequency RF electromagnetic waves in the ECRIS.

Initial Experimental Results of Producing Multicharged Ions Efficiently by Lower Hybrid Resonance Heating with Exciting Helicon Waves on Electron Cyclotron Resonance Ion Source

Based on experimental results, we considered the accessibility conditions for wave propagation in the magnetized plasma in an electron cyclotron resonance (ECR) ion source (ECRIS), and proposed introducing electromagnetic waves with frequencies lower than those of ECR. We generate the lower hybrid resonance (LHR) in the ECRIS by the electric field of the extra-ordinary mode (X-mode) on the helicon wave which additionally heat the electrons, and then it was conducted to improve the efficiency of multicharged ion generation successfully in over density condition. The electron energy distribution function obtained by the probe measurement shows an increase in the high-energy region in the corresponding LHR region. In this paper, for the first time we describe the initial experimental results on enhanced production of multicharged ions by the LHR of the low-frequency RF electromagnetic waves into the ECRIS.

Interface-induced dual-pinning mechanism enhances low-frequency electromagnetic wave loss

Improving the absorption of electromagnetic waves at low-frequency bands (2-8 GHz) is crucial for the increasing electromagnetic (EM) pollution brought about by the innovation of the fifth generation (5G) communication technology. However, the poor impedance matching and intrinsic attenuation of material in low-frequency bands hinders the development of low-frequency electromagnetic wave absorbing (EMWA) materials. Here we propose an interface-induced dual-pinning mechanism and establish a magnetoelectric bias interface by constructing bilayer core-shell structures of NiFe2O4 (NFO)@BiFeO3 (BFO)@polypyrrole (PPy). Such heterogeneous interface could induce distinct magnetic pinning of the magnetic moment in the ferromagnetic NFO and dielectric pinning of the dipole rotation in PPy. The establishment of the dual-pinning effect resulted in optimized impedance and enhanced attenuation at low-frequency bands, leading to better EMWA performance. The minimum reflection loss (RLmin) at thickness of 4.43 mm reaches -65.30 dB (the optimal absorption efficiency of 99.99997%), and the effective absorption bandwidth (EAB) can almost cover C-band (4.72 ~ 7.04 GHz) with low filling of 15.0 wt.%. This work proposes a mechanism to optimize low-frequency impedance matching with electromagnetic wave (EMW) loss and pave an avenue for the research of high-performance low-frequency absorbers.

Combustion-Assisted construction of Defect-Enriched hierarchical carbon composites towards efficient Low-Frequency electromagnetic wave absorption

Due to the high intrinsic conductivity of graphitized carbon-based composite materials, it induces a serious skin effect of incident electromagnetic waves, which deteriorates impedance matching and limits the wave absorption performance in the low-frequency regions. The introduction of defects can change the electrical and physical and chemical properties of carbon-based materials, affect the density of skin current, and thereby improve the overall performance of carbon-based absorbers. Therefore, it is important to develop a simple, low-cost, and fast preparation method for defect-rich structures. Herein, the defect-enriched hierarchical composites have been synthesized successfully via the soaking-burning-annealing process. The combustion treatment introduced numerous defects and oxygen vacancies while inducing a non-graphitization transition that reduced conductivity and improved electromagnetic balance in the low-frequency region. As expected, the charred sample exhibited notable enhancements in reflection loss (RL) and the effective absorption bandwidth within the low-frequency range of 2–8 GHz. The value of RL reached −52.2 dB, marking a 199 % increase over the unburned sample, while the effective absorption bandwidth increased by 28 % to 2.70 GHz. Even at a filling rate of only 10 %, the RLmin values of the optimal sample were lower than −30 dB across the S, C, X, and Ku bands. Additionally, the combination-induced defects led to phonon scattering, thereby reducing the thermal conductivity of the material. Thus, combustion can enhance the low-frequency microwave properties and thermal insulation of carbon-layered composites.

Low-frequency whistler waves driven by energetic electrons in plasmas of solely electron cyclotron wave heating

Whistler waves are a type of low-frequency electromagnetic wave common in nature, which is usually associated with energetic electron phenomena. This study presents experimental observations of low-frequency whistler wave instabilities driven by energetic electrons through wave–particle interactions on EXL-50. The energetic electrons are generated by electron cyclotron waves (ECWs) through stochastic heating [Wang et al., J. Plasma Phys. 89, 905890603 (2023)] and do not match the characteristics of the runaway electrons [Shi et al., Nucl. Fusion 62, 086047 (2022)]. In the steady-state plasma of the Energy iNNovation XuanLong-50 (EXL-50), whistler waves within the 30–120 MHz frequency range were observed during electron cyclotron resonance heating. These waves displayed multiple frequency bands, and the frequencies of waves were directly proportional to the Alfvén velocity. Furthermore, it was interesting to find that superposition of lower hybrid wave into ECW resulted in the suppression of these whistler waves. The experimental results may indicate that the whistler waves are driven by energetic electrons (excluding runaway electrons). These discoveries carry significant implications for several areas of research, including the investigation of wave–particle interactions, the development of radio frequency wave current drivers, their potential impact on the electron dynamics in future fusion devices, and even the presence of unusually low-frequency whistler waves in Earth's radiation belts.

Diagnosing ratio of electron density to collision frequency of plasma surrounding scaled model in a shock tube using low-frequency alternating magnetic field phase shift

A non-contact low-frequency (LF) method of diagnosing the plasma surrounding a scaled model in a shock tube is proposed. This method utilizes the phase shift occurring after the transmission of an LF alternating magnetic field through the plasma to directly measure the ratio of the plasma loop average electron density to collision frequency. An equivalent circuit model is used to analyze the relationship of the phase shift of the magnetic field component of LF electromagnetic waves with the plasma electron density and collision frequency. The applicable range of the LF method on a given plasma scale is analyzed. The upper diagnostic limit for the ratio of the electron density (unit: m−3) to collision frequency (unit: Hz) exceeds 1 × 1011, enabling an electron density to exceed 1 × 1020 m−3 and a collision frequency to be less than 1 GHz. In this work, the feasibility of using the LF phase shift to implement the plasma diagnosis is also assessed. Diagnosis experiments on shock tube equipment are conducted by using both the electrostatic probe method and LF method. By comparing the diagnostic results of the two methods, the inversion results are relatively consistent with each other, thereby preliminarily verifying the feasibility of the LF method. The ratio of the electron density to the collision frequency has a relatively uniform distribution during the plasma stabilization. The LF diagnostic path is a loop around the model, which is suitable for diagnosing the plasma that surrounds the model. Finally, the causes of diagnostic discrepancy between the two methods are analyzed. The proposed method provides a new avenue for diagnosing high-density enveloping plasma.

Research on electromagnetic field characteristics of rotating-magnet based mechanical antenna through the earth

Conventional low-frequency electromagnetic wave (LFEM) transmitting antennas are enormous in size, which limits the application of LFEM in underground space. Rotating-magnet Based Mechanical Antennas can realize the miniaturization of low-frequency antennas, which is expected to bring new possibilities for underground electromagnetic detection or ground penetration communication. Firstly, this paper establishes a synthetic field method for solving the electromagnetic field of a rotating permanent magnet in the air-earth cross-domain case. The method equates the magnet as an orthogonal superposition of vertical and horizontal dipole sources, and the phase difference between vertical and horizontal dipole sources is 𝜋/2. Based on the half-space theory of multilayer planar media, the quasi-analytical solution of the electromagnetic field of the magnetic dipole in the case of air-earth trans dimensionality can be found by superposition. Secondly, based on the finite element numerical model, the trans-earth propagation characteristics of the electromagnetic field excited by the rotating permanent magnet across the air-earth dual domain are studied. At the same time, the radiation characteristics in the rotating plane of the permanent magnet are also studied. Again, this paper systematically investigates the influence of parameters such as earth conductivity, emission frequency, and propagation distance on the electromagnetic field propagation. Finally, the principle prototype is developed and experiments are carried out. The results show that the finite element numerical model established in this paper is correct, the experimental results are consistent with the theoretical values, and a field strength signal of 0.9 nT can be received at 20 m. The research work in this paper lays the foundation for the future use of mechanical antennas for electromagnetic detection and ground penetration communication.

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.

A simple co-doping strategy to synthesis of Ni@B/N carbon nanotubes with broadband and low-frequency electromagnetic wave absorption

Development of magnetic composites with rational microstructural design to achieve excellent electromagnetic wave (EMW) absorption in the low-frequency range is necessary and still challenging. Herein, the B/N carbon nanotubes loaded with Ni nanoparticles were successfully synthesized through a homogeneous precursor pyrolysis route. The homogeneity of the micro-magnetic field in the composite architecture is improved by the co-doping of B and N in carbon nanotubes due to the polarization effect, which would enhance the impedance matching and EMW absorption. The Ni@B/N carbon nanotubes exhibit a minimum reflection loss (RLmin) of −56.9 dB at 8.24 GHz with a maximum bandwidth of 7.12 GHz ranging almost all S and C bands (from 3.44 to 10.56 GHz) suggesting that the composite architecture effectively enhances low-frequency EMW absorption properties. The combination of impedance matching and interfacial polarization resulting from the homogeneous Ni nanoparticles and co-doping of B and N in carbon lattice structure is responsible for the enhanced low-frequency EMW absorption properties. This simple co-doping synthesis strategy provides a new design strategy for the preparation of broadband and low-frequency EMW absorbers.

On the possibility of mode coupling for low frequency electromagnetic waves in plasmas with anisotropy of temperature

We study the dispersion relation for low frequency electromagnetic waves propagating along the ambient magnetic field and investigate the possibility of occurrence of coupling between waves in the ion cyclotron branch and waves in the whistler branch. The results obtained show that the coupling may occur in the case of conditions leading to the ion cyclotron instability, for sufficiently high value of the ratio between perpendicular and parallel ion temperature, and does not occur in the case of conditions leading to the ion firehose instability. The results also show that the decrease in the value of the plasma beta may lead to the disappearance of the mode coupling conditions. Regarding the effect of the electron population, it is shown that the change in the shape of the electron velocity distribution, from Maxwellian to bi-Kappa form, does not change the results obtained, as long as the electron temperatures are isotropic, but the increase in anisotropy in the electron temperatures may lead to the disappearance of the coupling between the different waves. The consequences of the frequency dependency of the mode coupling conditions are discussed considering wave propagation in an inhomogeneous medium, leading to the conclusion that the energy of a packet of waves of a given mode can be absorbed or mode converted over an extended region of space. These findings can be of relevance for the analysis and understanding of processes related to the conversion between ion cyclotron waves and whistler waves.

Design of porous SiC/MnO2 bulk composite with improved absorption of low-frequency electromagnetic waves

Silicon carbide (SiC) is expected to be the new-generation electromagnetic wave (EMW) absorber. In this context, the SiC/C composites were first prepared through a hydrothermal method using glucose as the carbon source. Then SiC/MnO2 composites were fabricated by a second hydrothermal reaction using potassium permanganate (KMnO4) as raw material. With glucose content increased to 10 wt%, the composition exhibited outstanding EMW absorption performance with the minimum reflection loss value of − 55.7 dB at the frequency of 2.1 GHz, and effective absorption bandwidth can cover the entire S-band by adjusting sample thickness. Therefore, the SiC/MnO2 composites present a promising EMW-absorbing material for low-frequency applications.

A High-Q Electric-Mechano-Magnetic Coupled Resonator for ELF/SLF Cross-Medium Magnetic Communication.

Extremely/super low frequency (ELF/SLF) electromagnetic wave can effectively propagate in the harsh cross-medium environment where a high-frequency electromagnetic wave cannot pass due to the fast decay. For efficiently transmitting a strong ELF/SLF radiation signal, the traditional electromagnetic antenna requires a super-large loop (>10km). To address this issue, in this work, a piezoelectric ceramic/ferromagnetic heterogeneous structured, cantilever beam-type electric-mechano-magnetic coupled resonator at only centimeter scale for ELF/SLF cross-medium magnetic communication is reported. Through designing hard-soft hybrid step-stiffness elastic beam, the resonator exhibits a much higher quality factor Q (≈240) for ELF/SLF magnetic field transmitting, which is one to five orders of magnitude higher than those of previously reported mechanical antennas and loop coil antennas. Moreover, the resonator exhibits a 5000 times higher magnetic field emitting efficiency compared to a conventional loop coil antenna in ELF/SLF band. It also demonstrates a 200% increase in magnetic field emitting capacity compared to existing piezoelectric-driven antennas. In addition, an ASK+PSK modulation method is proposed for suppressing relaxation time of the resonator, and a reduction in the relaxation time by 80% is observed. Furthermore, an air-seawater cross-medium magnetic field communication is successful demonstrated, indicating its potential as portable, high-efficient antenna for underwater and underground communications.

ANALYSIS OF RESISTANCE OF CASSAVA TAPE BY EXPOSURE TO 1000 μT INTENSITY ELF MAGNETS

Extremely Low Frequency (ELF) electromagnetic waves are electromagnetic waves with a frequency range of 0 to 300 Hz. ELF electromagnetic wave radiation produces non-thermal effects on the biological objects used, meaning that it does not cause temperature changes when interacting with or inducing the system. Electromagnetic waves are waves that arise due to changes in electric fields and strong magnetic fields. This research aims to prove the effect of Extremely low frequency (ELF) magnetic field on the food resilience process. The research method used is experimental research method. This research was carried out in the basic physics laboratory at the University of Jember. Data collection techniques using observation. Based on the research, it can be concluded that ELF magnetic field radiation has the potential as an alternative method in increasing the nutritional value and durability of fermented food ingredients. Exposure to Extremely Low Frequency magnets with an intensity of 1000 μT for 45 minutes resulted in changes in pH value and physical quality that affect food durability in cassava tape.

THE IMPACT OF LOW-FREQUENCY MAGNETIC FIELD ON KETAN TAPE MATURATION: pH, DENSITY, AND TASTE

This study explores the novel effect of Extremely Low Frequency (ELF) electromagnetic waves on the fermentation process of sticky rice tape, a traditional Indonesian food made from glutinous rice. ELF electromagnetic waves are waves consisting of magnetic fields and electric fields that do not require intermediaries in their propagation and have frequencies ranging from 0-300 Hz. The study uses a unique experimental method that exposes 2 kg of sticky rice tape, divided into 10 control and 10 experimental samples, each weighing 100 grams and wrapped in ziplock plastic, to ELF electromagnetic waves for two days. The study uses a device that generates ELF electromagnetic waves with a certain intensity and frequency. The study measures the changes in the pH, density, and taste of the sticky rice tape samples after the exposure. The results show that the experimental group’s sticky rice tape had a higher pH, higher density, and sweeter taste than the control group’s sticky rice tape. The study proves the effect of ELF electromagnetic waves on the fermentation process of sticky rice tape and provides insights for the development of new food processing techniques. The study demonstrates the applicability and innovation of using ELF electromagnetic waves for food fermentation.

Wireless electromagnetic telemetry for metal cased wells: A novel approach with comprehensive channel analysis

Low-frequency electromagnetic telemetry has been widely adopted for downhole data acquisition in the oil and gas industry. However, its application in cased wells has been limited by the high magnetic permeability and low resistivity of the metal casing, which causes the casing to absorb most of the electromagnetic waves transmitted by the downhole transmitter, resulting in inaccurate downhole data acquisition. We propose a novel approach to address this issue by suspending a transmitter (tens of meters in length) in the casing and connecting it electrically to the metal casing through two connectors. By forming a circulation along the transmitter and the casing, low-frequency electromagnetic waves can penetrate through the casing and reach the formation for telemetry. To further enhance the signal received by the ground antenna, we conduct a comprehensive analysis of the complex downhole-to-surface communication channel. Notably, the channel, which consists of the formation, the casing, and the transmitter, is divided into a near field and a far field for separate analysis. Quantitative assessments of four crucial factors on the ground-received signal strength are also conducted, i.e., electromagnetic wave frequency and location of the excitation source in the transmitter, as well as the length and location of the transmitter in the well. An 80-meter telemetry device is designed and optimized for integration into the well test. Experimental results confirm the consistency between the theoretically analyzed and measured attenuation law of the ground-received signal, indicating the effectiveness of our wireless electromagnetic telemetry technique for cased wells.

Pemanfaatan Gelombang Elektromagnet Extremely Low Frequency (Elf) Dalam Ketahanan Pangan

Physics is considered an important subject that is taught as a subject in itself with various considerations. Physics is seen as both a process and a product, so successful physics learning requires attention to effective and efficient learning. The utilization of Extremely Low Frequency (ELF) electromagnetic waves has great potential in the field of food security. ELF waves have low-frequency characteristics that create a unique potential to influence microbial activity and nutrient availability in improving food security productivity. ELF waves can be used to increase the productivity and quality of food crops, as well as extend the shelf life of food products. Thus, the utilization of ELF waves can help in achieving sustainable food security. In an effort to improve food security, it is necessary to innovate and develop technology that can support agricultural productivity. More research is still needed to fully understand the mechanism of action of ELF waves and how best to use them in agricultural and food processing practices.

3D forward modeling and response characteristics of low-resistivity overburden of the CFS-PML absorbing boundary for ground-well transient electromagnetic method

This study used the stable and convergent Dufort-Frankel method to differentially discretize the diffusion equation of the ground-well transient electromagnetic secondary field. The absorption boundary condition of complex frequency-shifted perfectly matched layer (CFS-PML) was used for truncation so that the low-frequency electromagnetic wave can be better absorbed at the model boundary. A typical three-dimensional (3D) homogeneous half-space model was established and a low-resistivity cube model was analyzed under the half-space condition. The response patterns and drivers of the low-resistivity cube model were discussed under the influence of a low-resistivity overburden. The absorption boundary conditions of CFS-PML significantly affected the low-frequency electromagnetic waves. For a low-resistivity cube around the borehole, its response curve exhibited a single-peak, and the extreme point of the curve corresponded to the center of the low-resistivity body. When the low-resistivity cube was directly below the borehole, the response curve showed three extreme values (two high and one low), with the low corresponding to the center of the low-resistivity body. The total field response of the low-resistivity overburden was stronger than that of the uniform half-space model due to the low-resistivity shielding effect of electromagnetic waves. When the receiving-transmitting distance gradually increased, the effect of the low-resistivity overburden was gradually weakened, and the response of the low-resistivity cube was strengthened. It was affected by the ratio of the overburden resistivity to the resistivity of the low-resistivity body.

Turbulent dipolarization regions in the Earth’s magnetotail: ion fluxes and magnetic field changes

In this work, we consider the dynamics of ion fluxes and magnetic field changes in turbulent regions of magnetotail dipolarizations. The data from the Cluster-II mission (magnetic field measurements from fluxgate magnetometers and energetic charged particle observations from RAPID spectrometers) were used for the analysis. We study individual events and investigate statistically the changes of charged particle fluxes during magnetic field dipolarizations observed during 2001–2015. Received changes in the spectral index indicate that CNO+ ions undergo stronger acceleration during dipolarization than protons and helium ions. Before dipolarization front monotonic growth the ions flux is observed (the maximum of flux is observed at 1–1,5 min after the start of dipolarization) in the range of ∼ 92–374 keV for proton; in the energy range ∼ 138–235 keV for He+ and in the energy range of 414–638 keV for CNO+ ions. Flux increase before arriving dipolarization front may result from the reflection of plasma sheet ions at the dipolarization front and the result of the resonant interactions of ions with low-frequency electromagnetic waves.