Low-frequency Electromagnetic Waves Research Articles

Quantifying Heterogeneous Interface Effect of Fe3O4(111)/C for Enhanced Low-Frequency Electromagnetic Wave Absorption

How to tailor electromagnetic parameters of multi-component materials is the fundamental issues for low-frequency electromagnetic wave absorbers (EMA). However, there remains a challenge to accurately elucidate the impact of respective components at heterogeneous interfaces on the EMAs, not to mentioning the further quantitative contribution of the interfacial effect to the electromagnetic loss. In this paper, we for the first time separated the Fe3O4(111)/C heterogeneous interface of Fe3O4@C via a controllable interfacial separation strategy, meanwhile ensuring the consistent microstructure and the ratio of each component, as well as the unchanged macroscopic structure of the particles. Once all potential influences on electromagnetic parameters have been independently studied, the unique difference in heterogeneous interfaces enabled us to quantitatively evaluate the effect of them on electromagnetic parameters. Both experimental and density functional theory (DFT) calculation results consistently demonstrate that the Fe3O4(111)/C heterointerface increases carrier concentration and conductivity, thereby enhancing the imaginary part of the dielectric constant. Very distinguished from traditional interfacial polarisation mechanism presented in previous publications, this study introduces a novel interfacial loss mechanism primarily characterized by conductivity loss, which is rigorously investigated in a quantitative way. This discovery offers a novel approach for designing controllable heterogeneous interfaces and manipulating electromagnetic parameters in multicomponent EMAs.

High anisotropy 2D large-size iron-based coral for C-band ultra-wide microwave absorption

Lightweight microwave-absorbing (MA) materials with broadband absorption in the C-band remain challenging to date. Recent studies have shown that promoting anisotropy in materials is expected to break the Snoek limit and enhance the absorption performance of magnetic materials in the C-band. In this paper, two-dimensional (2D) large-size coral-like iron-based composites (LCIC) were prepared using an NH4NO3-assisted blow molding separation strategy. The special structure with large shape anisotropy realizes a wide and strong natural magnetic resonance, leading to strong magnetic loss. The enhanced natural resonance effectively broadens the effective absorption bandwidth (EAB) of the LCIC in the C-band. The minimum reflection loss (RLmin) of LCIC is −41.64 dB, and the EAB is 5.42 GHz (3.83–9.25 GHz), covering the entire C-band. Strong natural resonance is necessary to improve the dissipation of magnetic losses in low-frequency electromagnetic waves. This work explores the important role of size effect in enhancing the C-band absorption properties of magnetic materials. It provides a feasible reference for the preparation of C-band broadband, strongly absorbing MA materials.

LaFe-MOFs derivatives with different compositions for boosting low-frequency and broadband electromagnetic wave absorption

To achieve low-frequency and broadband electromagnetic wave absorption (EMWA), building excellent metal-organic frameworks (MOFs)-derived EMWA materials is critical but remains challenging. In this research, La2O3/La2O2CN2/Fe/N-doped carbon (LFC) composites with different compositions were synthesized by adjusting the La3+ content to tune the electromagnetic parameters. As the La3+ content increased, the EMWA performance showed a trend of first increasing and then decreasing. As a result, LFC-2 achieved a minimum reflection loss (RLmin) value of −60.82 dB at a thickness of 2.60 mm when the molar ratio of La3+ to Fe3+ was 1: 1, along with an effective absorption bandwidth value of 5.76 GHz (9.84–15.60 GHz) at 2.29 mm. Moreover, the EMWA performance of LFC-3 at low-frequency (4.08 GHz) was enhanced when the La³⁺ to Fe³⁺ molar ratio was 2: 1, with an RLmin value of −47.47 dB. Comprehensive characterizations suggested that the formation of the La2O2CN2 phase played an indispensable role in optimizing impedance matching and enhancing magnetic loss and dielectric loss. In addition, La3+ had a high coordination number, which effectively regulated the electromagnetic parameters. Concurrently, radar cross-section simulation results confirmed the outstanding EMWA capability of the LFC coating. This work proposed a strategy for LaFe-MOFs derivatives, shedding light on the foundation for designing more efficient low-frequency and broadband absorbent materials.

The Impact of Mobile Phone Electromagnetic Waves on the Neurons and Blood Brain Barrier Integrity in the Chick Embryo

The electromagnetic environment surrounding us has dramatically evolved over the past decade, with the proliferation of Wi-Fi, Bluetooth, and other wireless technologies becoming commonplace in our daily lives. Mobile phones emit non-ionizing low-frequency electromagnetic waves (EW). To examine the effects of EW on living cells, this study aims to explore the impact of cell phone EW on the developing brain of chick embryos. The fertilized eggs were allowed to develop under exposure to electromagnetic waves emitted by cell mobile. A cell phone was placed inside the incubator with 20 eggs and was called from outside on a precise schedule. The same number of fertilized eggs were placed in another incubator without a mobile phone and served as the control. Embryos were sacrificed on days 10 and 15, and the cerebral cortex and cerebellum were removed and sent for electron microscopy. In the control group, cerebral neurons appeared healthy, with a large, centrally placed nucleus, visible oligodendrocytes, and a less dense extracellular matrix. In contrast, neurons from the exposed group were smaller, fewer in number, with unclear nuclear margins, signs of shrinkage, and apoptosis and a dense extracellular matrix. In the cerebellum, the exposed group revealed a reduced number of Purkinje neurons and noticeable mitochondrial swelling. The blood-brain barrier remained intact in the control group but was compromised in the exposed group. We conclude that electromagnetic waves emitted by cell phones adversely affect the normal development of the brain in chick embryos.

Rational construction of dicarbonous CB/CNT@PI composites toward low filler loading and low-frequency electromagnetic wave absorption.

With the application of low frequency radar and the demand for stealth of high temperature resistant components, it is increasingly urgent to develop absorbing materials with both low frequency and high temperature resistant properties. Here, we successfully prepared various carbon/polyimide composites as low-frequency electromagnetic wave absorbing materials by simple blending method. The well-designed mesh lap structure introduces a large amount of free space, further optimizing the impedance matching of the material. At the same time, the multiple loss mechanism formed by the combination of carbon black dominated polarization and carbon nanotube dominated conductive loss enhances the loss of incident electromagnetic wave. The results showed that only 10 wt% filler loading of the CB/CNT@PI is achieved in the low frequency range (1-4 GHz) with a minimum RL strength of - 18.3 dB, which has obvious advantages compared with other works in recent years. This study provides a way for the design and preparation of resin-based absorbing materials.

Coherent Inverse Compton Scattering in Fast Radio Bursts Revisited

Growing observations of temporal, spectral, and polarization properties of fast radio bursts (FRBs) indicate that the radio emission of the majority of bursts is likely produced inside the magnetosphere of its central engine, likely a magnetar. We revisit the idea that FRBs are generated via coherent inverse Compton scattering (ICS) off low-frequency X-mode electromagnetic waves (fast magnetosonic waves) by bunches at a distance of a few hundred times the magnetar radius. The following findings are revealed: (1) Crustal oscillations during a flaring event would excite kHz Alfvén waves. Fast magnetosonic waves with essentially the same frequency can be generated directly or be converted from Alfvén waves at a large radius, with an amplitude large enough to power FRBs via the ICS process. (2) The cross section increases rapidly with radius and significant ICS can occur at r ≳ 100R ⋆ with emission power much greater than the curvature radiation power but still in the linear scattering regime. (3) The low-frequency fast magnetosonic waves naturally redistribute a fluctuating relativistic plasma in the charge-depleted region to form bunches with the right size to power FRBs. (4) The required bunch net charge density can be sub-Goldreich–Julian, which allows a strong parallel electric field to accelerate the charges, maintain the bunches, and continuously power FRB emission. (5) This model can account for a wide range of observed properties of repeating FRB bursts, including high degrees of linear and circular polarization and narrow spectra as observed in many bursts from repeating FRB sources.

Research on extremely low frequency electromagnetic wave model and simulation in wellbore communication

Over recent years, as digitalization and intelligence in oil wellbore have increased, so have the stricter requirements for wireless communication technology in terms of distance, accuracy, and portability. As a result, it’s necessary to rely on more advanced and efficient wireless communication technologies to meet the industry’s needs. However, traditional communication technologies such as cables and optical fibers have inherent shortcomings in construction, data interpretation, and cost. ELF electromagnetic waves are an ideal solution for communication in complex wellbore conditions due to long-distance communication and strong penetration capabilities, making it a highly effective option. Based on the theory of network splitting, this paper establishes a polygonal multiple-delays uncertainty coupled complex network model of ELF electromagnetic waves propagating through the casing in layered media and designs a controller, including expressions for the intensity of the magnetic and electric fields in different directions, and the propagation and distribution characteristics in different media. We determined that the optimal transmitting frequency of ELF electromagnetic waves under general conditions is 12.7 Hz. Based on field experiments, we verified that ELF electromagnetic waves can enable wireless wellbore communication within 1500 m without relays. We also analyzed the impact of casing thread deformation on ELF electromagnetic wave propagation due to high-temperature and high-pressure environments. We used simulation experiments to solve the distribution relationship between the electric and magnetic fields of the solenoids through casing and strata, as well as the coupling coefficients between the transmitting and receiving solenoids, and explore how different transmitting frequencies affect the efficiency of signal propagation. Both theories and experiments have verified the correctness of the model, and have also demonstrated the reliability and continuity of using ELF electromagnetic waves to achieve wireless wellbore communication, which provides a theoretical basis and feasibility for subsequent engineering applications.

Low-frequency and broadband electromagnetic wave absorption mechanism of (Hf0.2Zr0.2Ti0.2Ce0.2La0.2)C1-δ/PyC microspheres with hierarchy pores from 4 GHz to 17 GHz

Achieving low-frequency broadband electromagnetic wave absorption in extreme environments over 2000 °C is challenging. Biomimetic hierarchy materials of high entropy lanthanide carbides were designed to optimize electromagnetic wave absorption. Composite microspheres of (Hf0.2Zr0.2Ti0.2Ce0.2La0.2)C1-δ and SiC embedded in pyrolytic carbon (MC/PyC) were prepared by using the electro-spray method followed by heat treatment. The specimens of MC/PyC microspheres with a thickness of 2.5 mm exhibited a minimum reflection loss value of − 48.9 dB, and electromagnetic wave absorption from 4.0 GHz to 17 GHz. The enhanced absorption capability is attributed to the synergistic effect of dielectric losses from conduction and polarization, along with magnetic losses due to eddy currents and natural resonance of the high-entropy carbides within the multiscale pores. The composition and featured microstructure MC/PyC microspheres were noteworthily stable under the 2200 °C oxyacetylene ablation, ensuring consistent high-performance electromagnetic wave absorption even in harsh conditions.

In Situ Exsolution-Prepared Solid-Solution-Type Sulfides with Intracrystal Polarization for Efficient and Selective Absorption of Low-Frequency Electromagnetic Wave.

The excellent dielectric properties and tunable structural design of metal sulfides have attracted considerable interest in realizing electromagnetic wave (EMW) absorption. However, compared with traditional monometallic and bimetallic sulfides that are extensively studied, the unique physical characteristics of solid-solution-type sulfides in response to EMW have not been revealed yet. Herein, a unique method for preparing high-purity solid-solution-type sulfides is proposed based on solid-phase in situ exsolution of different metal ions from hybrid precursors. Utilizing CoAl-LDH/MIL-88A composite as a precursor, Fe0.8Co0.2S single-phase nanoparticles are uniformly in situ formed on an amorphous substrate (denoted as CoAl), forming CoAl/Fe0.8Co0.2S heterostructure. Combing with density functional theory (DFT) calculations and wave absorption simulations, it is revealed that Fe0.8Co0.2S solid solution has stronger intracrystal polarization and electronic conductivity than traditional monometallic and bimetallic sulfides, which lead to higher dielectric properties in EM field. Therefore, CoAl/Fe0.8Co0.2S heterostructure exhibits significantly enhanced EMW absorption ability in the low-frequency region (2-6GHz) and can achieve frequency screening by selectively absorbing EMW of specific frequency. This work not only provides a unique method for preparing high-purity solid-solution-type sulfides but also fundamentally reveals the physical essence of their excellent EMW absorption performance.

A Bionic Flapping Magnetic-Dipole Resonator for ELF Cross-Medium Communication.

Extremely low-frequency (ELF) electromagnetic (EM) waves adeptly propagate in harsh cross-medium environments, overcoming rapid decay that hinders high-frequency counterparts. Traditional antennas, however, encounter challenges concerning size, efficiency, and power. Here, drawing inspiration from nature, we present a groundbreaking piezo-actuated, bionic flapping-wing magnetic-dipole resonator (BFW-MDR), operating in the electro-mechano-magnetic coupling mechanism, designed for efficient ELF EM wave transmission. The unique rigid-flexible hybrid flapping-wing structure magnifies rotation angles of anti-phase magnetic dipoles by tenfold, leading to constructive superposition of emitted magnetic fields. Consequently, the BFW-MDR exhibits a remarkable quality factor of 288 and an enhanced magnetic field emission of 514 fT at 100 meters with only 6.9 mW power consumption, surpassing traditional coil antennas by three orders of magnitude. The communication rate is doubled by the ASK+PSK modulation method. Its robust performance in cross-medium communication, even amidst various interferences, underscores its potential as a highly efficient antenna for underwater and underground applications.

Construction of CoO/Co9S8/NC composites with low-frequency and broadband electromagnetic wave absorption

Low-frequency electromagnetic wave absorption (EMWA) materials were crucial for addressing electromagnetic pollution and radar stealth. However, achieving low-frequency and broadband absorption still faces challenges. In this work, a succession of CoO/Co9S8/N-doped carbon (NC) composites were fabricated via a partial sulfidation strategy of Co-Prussian blue analogue (Co-PBA). The as-prepared CoO/Co9S8/NC composites featured a porous architecture. The electromagnetic parameters were effectively modulated via varying the sulfidation time. When the sulfidation time was 9 h, the minimum reflection loss (RLmin) value was −50.40 dB at 2.93 mm and a maximum effective absorption bandwidth value was 5.76 GHz (12.24–18.00 GHz) at 1.80 mm. Notably, when the sulfidation time was 12 h, the composites exhibited enhanced EMWA capability in the low-frequency S-band (3.52 GHz) with an RLmin value of −28.91 dB. The superior EMWA performance of composites were primarily attributed to appropriate dielectric constants and optimized impedance matching due to magnetic loss. Moreover, the radar cross section simulation consequences further verified that dissipation capability of electromagnetic wave of the CoO/Co9S8/NC composites in the actual far field. This work afforded novel perspectives into the rational develop of PBA-derived carbon-based EMWA materials with the low-frequency and broadband absorption.

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.