Time-varying Electromagnetic Fields Research Articles

Induction of apoptosis in B16-BL6 melanoma cells following exposure to electromagnetic fields modeled after intercellular calcium waves.

Exposure to time-varying electromagnetic fields (EMF) has the capacity to influence biological systems. Our results demonstrate that exposure to time-varying EMF modeled after the physiological firing frequency of intercellular calcium waves can inhibit proliferation and induce apoptosis in malignant cells. Single exposure of B16-BL6 cells to a Ca2+ EMF for 40 min reduced the number of viable cells by 50.3%. Cell imaging with acridine orange and ethidium bromide dye revealed substantial cellular apoptosis, preapoptotic cells, nuclear fragmentation, and large spacing between cells in the Ca2+ EMF condition when compared to the control condition. The ability of Ca2+ EMF to influence the proliferation and survival of malignant cells suggests that exposure to specific EMF may function as a potential anticancer therapy.

4D printed zero Poisson’s ratio metamaterials with vibration isolation properties for magnetic response

Although mechanical metamaterials possess high specific energy absorption, they suffer from drawbacks such as irreversible deformations and non-adjustable mechanical properties. Magnetic excitation is considered to be one of the most promising methods for special working environments; for which uniform incorporation of UV-cured four-dimensional (4D) printed resin is considered to be an effective approach to achieving fine structural features. Our study investigated the impact of soft magnetic particle content on the mechanical and dynamic mechanical properties of a shape memory polymer matrix material. This paper presents a 4D printed metamaterial with a zero Poisson’s ratio that can sense magnetic field intensity and alter its mechanical properties. Its rapid shape recovery, achieved through magnetic excitation, enables multiple energy absorption within a short timeframe. By increasing the curvature radius, the stress concentration in the hexagonal honeycomb structure is reduced, ensuring the metamaterial maintains its zero Poisson’s ratio even under in-plane loading. The study investigates the energy absorption performance and force–displacement curve of metamaterials with different layers and cell sizes, focusing on a four-layer metamaterial for the analysis. Furthermore, the paper explores the tunable energy absorption characteristics of the four-layer metamaterial under time-varying electromagnetic fields, aiming to enhance the stability of a lander’s center of gravity while landing on uneven terrain.

A workflow for predicting radiofrequency-induced heating around bilateral deep brain stimulation electrodes in MRI.

Heating around deep brain stimulation (DBS) in magnetic resonance imaging (MRI) occurs when the time-varying electromagnetic (EM) fields induce currents in the electrodes which can generate heat and potentially cause tissue damage. Predicting the heating around the electrode contacts is important to ensure the safety of patients with DBS implants undergoing an MRI scan. We previously proposed a workflow to predict heating around DBS contacts and introduced a parameter, equivalent transimpedance, that is independent of electrode trajectories, termination, and radiofrequency (RF) excitations. The workflow performance was validated in a unilateral DBS system. To predict RF heating around the contacts of bilateral (DBS) electrodes during an MRI scan in an anthropomorphic head phantom. Bilateral electrodes were fixed in a skull phantom filled with hydroxyethyl cellulose (HEC) gel. The electrode shafts were suspended extracranially, in a head and torso phantom filled with the same gel material. The current induced on the electrode shaft was experimentally measured using an MR-based technique 3cm above the tip. A transimpedance value determined in a previous offline calibration was used to scale the shaft current and calculate the contact voltage. The voltage was assigned as a boundary condition on the electrical contacts of the electrode in a quasi-static (EM) simulation. The resulting specific absorption rate (SAR) distribution became the input for a transient thermal simulation and was used to predict the heating around the contacts. RF heating experiments were performed for eight different lead trajectories using circularly polarized (CP) excitation and two linear excitations for one trajectory. The measured temperatures for all experiments were compared with the simulated temperatures and the root-mean-squared errors (RMSE) were calculated. The RF heating around the contacts of both bilateral electrodes was predicted with ≤ 0.29°C of RMSE for 20 heating scenarios. The workflow successfully predicted the heating for different bilateral DBS trajectories and excitation patterns in an anthropomorphic head phantom.

Effect of time-varying electromagnetic field on Wiedemann-Franz law in a hot hadronic matter

Effect of time-varying electromagnetic field on Wiedemann-Franz law in a hot hadronic matter

Optical analogs of pair production and annihilation in binary waveguide arrays with a linearly shifted straight section

We systematically investigate the optical analogs of the e−e+ pair production and annihilation phenomena which can take place simultaneously in a binary waveguide array having a linearly shifted straight section sandwiched between two straight sections. These two processes can be realized by the beam splitting in the linearly shifted straight section which performs the function of an external vector potential with a rectangular form in time in quantum electrodynamics (QED) which is different from two widely used concepts based on an external time-varying electromagnetic field, or an external ultrastrong time-independent potential barrier in space as in the Schwinger mechanism. We show that the numerical results for annihilation and pair production probabilities based on the simulations of beam propagation in binary waveguide arrays in the low-power regime are in very good agreement with the theoretical results. We also reveal that with certain requirements, the proposed discrete model quantitatively mimics the two processes as well as the continuous model of the genuine Dirac equation in free space in QED. We also show that the nonlinearity in the high-power regime can reduce these two effects.

Simplified damping model of the eddy current damper with a double-annular-plate configuration

The eddy current damper has plenty of advantages, such as non-contact energy dissipation, stable damping performance, and high reliability and durability, which is a novel damping device with great potential to apply in various fields. However, there are still many challenges in the applications of eddy current dampers for vibration suppression, especially in confined installation environments of aerospace structures, such as the insufficient energy dissipation efficiency of miniaturized eddy current dampers and the nonlinear characterization of eddy current damping under high frequency conditions. This study aims to propose a new design scheme for the eddy current damper to achieve high energy dissipation efficiency from lightweight and miniaturized eddy current dampers. By comparing with the composite planar configuration (which provides the highest energy dissipation efficiency in the literature) designed by Chen's group through the finite element analysis, the proposed double-annular-plate configuration achieves much better damping performance in the miniaturized version for the applications in confined installation spaces. To help the future design of the damper and uncover the underlying principle resulting in the nonlinear effect, based on the generation mechanism of eddy current damping, a simplified damping model for the double-annular-plate eddy current damper is established considering the nonlinearity of eddy current damping at high frequencies. The simplified model shows that the nonlinearity of eddy current damping mainly depends on the phase delay between the damping force and the excitation displacement. Moreover, based on the time-varying electromagnetic field theory, a mechanical-magnetic coupling finite element model is established to simulate the damping performance of the proposed damper. After validating the simplified damping model by the finite element analysis, a prototype of the double-annular-plate eddy current damper is manufactured and its dynamic behaviors and damping characteristics are measured by experiments. The results show that there is good agreement among the calculation results by the simplified model, the calculation results by the finite element analysis simulation, and the experiment results. The damping force amplitude of the double-annular-plate damper is approximately proportional to the frequency, and the delayed initial phase is slightly less than -π/2 and decreases with the increase of the frequency. The equivalent linear damping coefficient of the damper also decreases with the increase of the frequency, which shows the nonlinear effect of eddy current damping. Therefore, the proposed simplified theoretical model and the finite element model can efficiently characterize the nonlinearity of eddy current damping and can be well utilized for the mechanical and damping characteristics analysis and optimization design of eddy current dampers, which provides theoretical reference and technical support for the application of the novel damper in the aerospace field.

Logistic stochastic resonance in the Hodgkin–Huxley neuronal system under electromagnetic induction

Hodgkin–Huxley neurons can be used as logic gates to perform reliable logic operations under an optimal noise intensity window. Fluctuations in ion concentrations inside and outside the neuron cell generate time-varying electromagnetic fields regulating neuronal dynamics. In this paper, a modified Hodgkin–Huxley neuron model is used to report the phenomenon of logical stochastic resonance under electromagnetic effects. The results show that electromagnetic induction affects the speed of neuronal response when switching to logic signals. Appropriately reducing the magnitude of the external bias current allows Hodgkin–Huxley neurons to perform reliable logic operations while consuming less energy. However, regulating the signal strength requires a trade-off between the reliability of logic operations and energy consumption. We further extend the logical stochastic resonance effect to neuronal networks. It is found that an appropriate increase in coupling strength has a favorable impact on system logic operations. The dynamical mechanism is explained in terms of bifurcation diagrams and phase space. Finally, we also compare the difference in the reliability of logical operations between small-world and scale-free networks. Small-world networks outperform scale-free networks for logical operations. Our results contribute to the study of neuronal simulation circuits with logic computation functions, and provides important clues for building new neuron-based logic devices with high energy efficiency.

Some considerations on the challenges related to the use of the new ICNIRP restrictions for human exposure to radiofrequency fields.

ICNIRP 2020 guidelines for limiting exposure to radiofrequency fields replace the radiofrequency part of the ICNIRP 1998 guidelines for limiting exposure to time-varying electric, magnetic and electromagnetic fields. Besides setting new restrictions that prevent thermal effect they also took over the 100kHz to 10MHz part of the ICNIRP 2010 guidelines for limiting exposure to low-frequency electromagnetic fields, which provides restrictions that prevent nerve stimulation effect. The latest guidelines brought many changes to the system of protection against exposure to radiofrequency fields starting with the physical quantities used to express restrictions and continuing with specific restrictions and new exposure metrics employed. For the first time, the case of brief local exposure to intense radiofrequency fields was accounted by ICNIRP for setting new types of exposure restrictions. All these changes led to more detailed and complex guidelines, but their provisions are more difficult to apply in practice. Our paper presents some of the challenges related to the use in practice of the new ICNIRP restrictions for human exposure to radiofrequency fields.

Simultaneous inversion for source field and mantle electrical conductivity using the variable projection approach

Time-varying electromagnetic field observed on the ground or at a spacecraft consists of contributions from (i) electric source currents, such as those in the ionosphere and magnetosphere, and (ii) corresponding fields induced by source currents within the conductive Earth’s interior by virtue of electromagnetic induction. Knowledge about the spatio-temporal structure of inducing currents is a key component in ionospheric and magnetospheric studies, and is also needed in space weather hazard evaluation, whereas the induced currents depend on the Earth’s subsurface electrical conductivity distribution and allow us to probe this physical property. In this study, we present an approach that reconstructs the inducing source and subsurface conductivity structures simultaneously, preserving consistency between the two models by exploiting the inherent physical link. To achieve this, we formulate the underlying inverse problem as a separable nonlinear least-squares (SNLS) problem, where inducing current and subsurface conductivity parameters enter as linear and nonlinear model unknowns, respectively. We solve the SNLS problem using the variable projection method and compare it with other conventional approaches. We study the properties of the method and demonstrate its feasibility by simultaneously reconstructing the ionospheric and magnetospheric currents along with a 1-D average mantle conductivity distribution from the ground magnetic observatory data.Graphical

Numerical and experimental studies on the effectiveness of time-varying electromagnetic fields in reducing electron density

When an aircraft or a hypersonic vehicle re-enters the atmosphere, the plasma sheath generated can severely attenuate electromagnetic wave signals, causing the problem of communication blackout. A new method based on time-varying E × B fields is proposed to improve on the existing static E × B fields and mitigate the radio blackout problem. The use of the existing method is limited by the invalid electron density reduction resulting from current density j = 0 A m−2 in plasma beyond the Debye radius. The most remarkable feature is the introduction of a time-varying electric field to increase the current density in the plasma to overcome the Debye shielding effect on static electric field. Meanwhile, a magnetic field with the same frequency and phase as the electric field is applied to ensure that the electromagnetic force is always acting on the plasma in one direction. In order to investigate the effect of time-varying E × B fields on the plasma electron density distribution, two directions of voltage application are considered in numerical simulation. The simulation results indicate that different voltage application methods generate electromagnetic forces in different directions in the plasma, resulting in repulsion and vortex effects in the plasma. A comparison of the vortex effect and repulsion effect reveals that the vortex effect is better at reducing the electron density. The local plasma electron density can be reduced by more than 80% through the vortex effect, and the dimensions of the area of reduced electron density reach approximately 6 cm × 4 cm, meeting the requirements of electromagnetic wave propagation. Besides, the vortex effect of reducing the electron density in RAM-C (radio attenuation measurements for the study of communication blackout) reentry at an altitude of 40 km is analyzed. On the basis of the simulation results, an experiment based on a rectangular-window discharge device is proposed to demonstrate the effectiveness of the vortex effect. Experimental results show that time-varying E × B fields can reduce the electron density in plasma of 3 cm thickness by 80% at B = 0.07 T and U 0 = 1000 V. The investigations confirm the effectiveness of the proposed method in terms of reducing the required strength of the magnetic field and overcoming the Debye shielding effect. Additionally, the method is expected to provide a new way to apply a magnetic window in engineering applications.

Electromagnetic Stirring and Joule Heating in Continuous Casting Mold

"It has been developed a 3-D transient model of in-mold electromagnetic stirring in a continuous casting mold. The magnetohydrodynamics model was used to couple the time-varying electromagnetic field with fluid flow, and the solidification of liquid steel was analyzed using the enthalpy-porosity technique. The fluid flow was modelled with turbulence using a realizable k-ε turbulence model. The effect of Joule heat in steel at different frequencies of the electromagnetic stirrer has been predicted using Joule heating caused by induced current inside the mold. Preliminary research indicates that electromagnetic stirring retards the initial start of solid shell formation at the mold wall and transforms the liquid core present at the strand's center into the mush of the liquid-solid interface. Joule heating is observed to be limited in the stirring zone, with a maximum value observed close to the mold wall. The total Joule heat in the strand is found to be less than 1% of the total heat loss from the strand during the solidification process. An increase in frequency though increases the Joule heat in the strand, it is found to be dominant near the wall in the stirrer zone. The liquid core present above the stirrer position is found to expand marginally along the horizontal direction because of Joule heating.

Thermal and thermoelectric responses of hot QCD medium in time-varying magnetic fields

The thermal response of the hot QCD matter has been studied in the presence of a time-varying magnetic field. The impact of the magnetic field, its time dependence, and the collision aspects of the medium on thermal transport have been studied within the relativistic kinetic theory. The decay time of the magnetic field in the medium seems to have a strong dependence on thermal conductivity. The applicability of the Wiedemann-Franz law for the QCD medium has been investigated in the presence of time-varying external electromagnetic fields. The phenomenological significance of thermal transport in heavy-ion collision experiments has also been investigated by relating the thermal conductivity to the elliptic flow through the Knudsen number. The investigations are extended to study the thermoelectric behavior of hot QCD medium and its dependence on the magnetic field. The time dependent magnetic field is observed to significantly influence the thermoelectric behavior of the medium.

The FPGA-Based Realization of the Electromagnetic Effect Defined FitzHugh-Nagumo Neuron Model

The electrical transmission, which occurs on the surface of the neuron membranes, is based on the flow of charges such as calcium, potassium and sodium. This potential change means a current flow and if there is a variable current flow, a flux change comes into question. Accordingly, recent studies have suggested that these electrophysiological neuronal activities can induce a time-varying electromagnetic field distribution. The electric field is usually defined as an external stimulation variable of the biological neuron models in literature. However, the electric field is included in the biological neuron models as a new state variable in another perspective and it is described the polarization modultion of media. Here, this study focused on that the electric field is a state variable in the biological neuron model. The numerical simulations of the FitzHugh-Nagumo neuron, which is improved by including the electromagnetic effect, are re-executed in this study. Then, the hardware realization of this system is built on the FPGA device. Therefore, it is shown that it is also possible to perform the hardware realizations of the neuronal systems, which have a new state variable for the electric field definition.

Gold nanoparticles as enablers of cell membrane permeabilization by time-varying magnetic field: influence of distance and geometry.

This study is based on the quantification of the influence of the presence of gold nanoparticles (Au NPs), of their geometry and their distance from cell membrane during time-varying electromagnetic fields cell membrane permeabilization on the pores opening dynamics. Results showed that the combined use of Au NPs and time-varying magnetic field can improve significantly the permeabilization of cell membrane. The presence of Au NPs allowed to reach transmembrane potential values enabling the cell membrane permeabilization only when placed at very short distance, equal to 20 nm. Both geometry and variability of the positioning in proximity of the cell membrane showed a strong influence on the probability of enabling pores opening. Clinical Relevance- This study provides a better comprehension about the mechanisms, still not completely understood, underlying cell membrane permeabilization by combining Au NPs and time-varying magnetic fields.

Controlling discharge mode in electrical activities of myocardial cell using mixed frequencies magnetic radiation

Based on the standard Fitzhugh–Nagumo model for myocardial cell excitations and electrical activities, the effect of electromagnetic induction is considered and through which mixed frequencies magnetic radiation is imposed to detect the mode transition. Indeed, time-varying electromagnetic field can be induced when myocardial cell is exposed or surrounded by electromagnetic field and thus the effect of electromagnetic induction should be considered. From the analyzes of sampled series for membrane potentials, the improved model holds many bifurcation parameters and the mode of excitations and electric activities can be detected and observed in larger parameter zones. It is found that apart from exciting a myocardial cell, the mixed frequencies magnetic radiation can promote mode transition to bursting type behavior as the frequency is increased as well as suppress the electrical activities to quiescent state under high intensities magnetic radiations, which are consistent with biological experiments.

Dynamics of entropy and information of time-dependent quantum systems: exact results

Dynamical aspects of information-theoretic and entropic measures of quantum systems are studied. First, we show that for the time-dependent harmonic oscillator, as well as for the charged particle in certain time-varying electromagnetic fields, the increase of the entropy and dynamics of the Fisher information can be directly described and related. To illustrate these results, we have considered several examples for which all the relations take the elementary form. Moreover, we show that the integrals of (geodesic) motion associated with some conformal Killing vectors lead to the Ermakov–Lewis invariants for the considered electromagnetic fields. Next, we explicitly work out the dynamics of the entanglement entropy of the oscillators coupled by a continuous time-dependent parameter as well as we analyse some aspects of quantum-classical transition (in particular decoherence). Finally, we study in some detail the behaviour of quantum quenches (in the presence of the critical points) for the case of mutually non-interacting non-relativistic fermions in a harmonic trap.

Use of Nanoparticles as Nanoelectrodes in Contact-Less Cell Membrane Permeabilization by Time-Varying Magnetic Field: A Computational Study

This paper describes a computational approach for the assessment of electric field enhancement by using highly conductive gold nanoparticles (Au NPs) in time-varying electromagnetic fields cell membrane permeabilization, estimating the influence of the presence of Au NPs on transmembrane potential and on the pore opening dynamics. To account for variability and uncertainty about geometries and relative placement and aggregations of the Au NPs, three different NP configurations were considered: spherical Au NPs equally spaced around the cell; cubic Au NPs, for accounting for the possible edge effect, equally spaced around the cell; and spherical Au NPs grouped in clusters. The results show that the combined use of Au NPs and a time-varying magnetic field can significantly improve the permeabilization of cell membranes. The variability of NPs’ geometries and configurations in proximity of the cell membrane showed to have a strong influence on the pore opening mechanism. The study offers a better comprehension of the mechanisms, still not completely understood, underlying cell membrane permeabilization by time-varying magnetic fields.

Abundant Firing Patterns in a Memristive Morris–Lecar Neuron Model

Improving the neuron model and studying its electrical activities according to the real biophysical environment are significant in human cognitive brain activity and neural behavior. The complex transmembrane motion of ions on the neuronal cell membrane can establish time-varying electromagnetic fields and affect the transition firing patterns of neurons. In this paper, a threshold memristor is used to describe the electromagnetic induction and magnetic field effects of neuron cell membrane ion exchange to improve the neuron model, and a memristive Morris–Lecar (mM–L) neuron model is proposed. Numerical simulation confirms that different intensities of electromagnetic fields can produce distinct pattern transitions in electrical activities of the neuron, such as periodic bursting, periodic spiking, chaotic bursting. From the perspective of neuron’s interspike interval (ISI), the ISIs bifurcation in the multiparameter planes, ISIs firing periods, the variance of ISIs and other methods are used to find the trend of the mM–L neuron firing pattern transition. Finally, based on the 4D nonlinear differential equation of the mM–L neuron model, the complete electronic implementation of the model is designed. The output of the designed circuit is consistent with the theoretical prediction, which is extremely useful for studying the dynamics of a single neuron.

Stochastic analysis of the electromagnetic induction effect on a neuron’s action potential dynamics

The presence of time-varying electromagnetic fields across a neuron cell may cause changes in its electrical characteristics, most notably, in the action potential dynamics. This phenomenon is examined by simulating electrophysiology of a single cortex neuron. Magnetic flux is captured by using a polynomial approximation of a memristor embedded into Hodgkin–Huxley model, equivalent electrical circuit of a neuron cell. Bifurcation analysis is carried out for two different electrical modes associated with the nature of the external neuronal stimulus. Aiming to determine the true influence of the variability of ion channels conductivity, the stochastic sensitivity analysis is undertaken post hoc. Additionally, numerical simulations are enriched with uncertainty quantification, observing values of ion channel conductivity as random variables. The aim of the study is to computationally determine the sensitivity of the action potential dynamics with respect to changes in conductivity of each ion channel so that the future experimental procedures, most often medical treatments, may be adapted to different individuals in various environmental conditions.

Testosterone synthesis in testicular Leydig cells after long-term exposure to a static electric field (SEF)

China’s clean energy and resources are mainly located in the west and north while electric load center is concentrated in the middle and east. Thus, these resources and energy need to be converted into electrical energy in situ and transported to electric load center through ultra-high voltage direct current (UHVDC) transmissions. China has built 25,000 km UHVDC transmission lines of 800 kV and 1100 kV, near which the impact of electric field on health has attracted public attention. Previous studies showed that time-varying electromagnetic field exposure could disturb testosterone secretion. To study the effect of non-time-varying electric field caused by direct current transmission lines on testosterone synthesis, male ICR mice were continually (24 h/d) exposed to static electric field of 56.3 ± 1.4 kV/m. Results showed that on the 3rd day of exposure and on the 7th day after ceasing the exposure of 28 d, serum testosterone level and testicular oxidative stress indicators didn’t change significantly. On the 28th day of exposure, serum testosterone levels, testicular glutathione peroxidase (GSH-Px) activity, the mRNA and protein levels of testicular StAR, PBR, CYP11A1 decreased significantly, and testicular malondialdehyde (MDA) content increased significantly. Meanwhile, electron-dense edges and vacuolation appeared in lipid droplets of Leydig cells. The gap between inner mitochondrial membrane (IMM) and outer mitochondrial membrane (OMM) enlarged, which would cause the swelling of mitochondria, the rupture and deficiency of mitochondrial membranes. Analysis showed that testicular oxidative stress could induce the damage of mitochondrial structure in Leydig cells, which would decrease the rate of cholesterol transport from cytoplasm to mitochondria. Since cholesterol is the necessary precursor of testosterone synthesis, testosterone synthesis was inhibited. The decrease of the mRNA and protein expression levels of StAR and PBR in testes could diminish the cholesterol transported from OMM to IMM. The decrease of the mRNA and protein expression levels of CYP11A1 could reduce the pregnenolone required in testosterone synthesis and inhibit testosterone synthesis consequently.