Low-frequency Electromagnetic Research Articles

Dielectric properties of a novel high absorbing onion-like-carbon based polymer composite

A novel lightweight onion-like carbon (OLC) based Poly(methyl metacrylate) (PMMA) composite with high electromagnetic (EM) absorption capability determined earlier in microwave range is studied in low frequencies from 20 Hz to 1 MHz by dielectric spectroscopy. The investigation of dielectric properties of PMMA films with incorporated OLC in small concentration (0.5–2 wt.%) have been carried out by varying the temperature between 240 and 520 K. The temperature behavior of the complex permittivity at a given frequency is found to be strongly dependent on the OLC concentration. The experimental data are in quantitative agreement with the results of modified effective medium calculations of OLC-based polymer film's permittivity. Both the experimental observations and theoretical simulation demonstrate that small additions of onion-like carbon particles to a polymer matrix can noticeably modify the composite response to low-frequency EM radiation as well as improve its thermal stability (increased glass transition and melting temperatures, correspondingly).

Interaction of Electromagnetic Waves with Two-Dimensional Metal Covered with Radar Absorbing Material and Plasma

A two-dimensional metal model is established to investigate the stealth mechanisms of radar absorbing material (RAM) and plasma when they cover the model together. Using the finite-difference time-domain (FDTD) method, the interaction of electromagnetic (EM) waves with the model can be studied. In this paper, three covering cases are considered: a. RAM or plasma covering the metal solely; b. RAM and plasma covering the metal, while plasma is placed outside; c. RAM and plasma covering the metal, while RAM is placed outside. The calculated results show that the covering order has a great influence on the absorption of EM waves. Compared to case a, case b has an advantage in the absorption of relatively high-frequency EM waves (HFWs), whereas case c has an advantage in the absorption of relatively low-frequency EM waves (LFWs). Through the optimization of the parameters of both plasma and RAM, it is hopeful to obtain a broad absorption band by RAM and plasma covering. Near-field attenuation rate and far-field radar cross section (RCS) are employed to compare the different cases.

Grain Refinement of AZ31 Magnesium Alloy by Titanium and Low-Frequency Electromagnetic Casting

The grain-refinement effects of titanium (Ti) additions and a low-frequency electromagnetic casting (LFEC) process on the AZ31 magnesium alloy have been investigated. It is shown that Ti has no effect on the formation and distribution of secondary phases in the AZ31 alloy. The results suggests that the grain size decreases with an increasing cooling rate for the AZ31 alloy; it decreases first, however, then increases slightly for Ti-containing AZ31 alloys, indicating that the grain-refinement effect of Ti decreases with an increasing cooling rate. However, the grain size decreases first, and then increases with increasing Ti for a given cooling rate. The lowest grain size is obtained at the addition of about 0.01% Ti and the cooling rate of about 6 K/s. The grain refinement effect is explained in terms of the growth restriction factor (GRF) due to the constitutional undercooling generated by the Ti solute elements, which produces grain refinement up to a critical GRF value corresponding to about 0.01% Ti addition. The yield strength of a conventional-cast AZ31 alloy can be improved by grain refinement and expressed as σy = 39.31 + 142.53 d−1/2 according to the Hall−Petch relationship. The combination of the Ti grain refiner and the LFEC process during direct-chill (DC) casting of an AZ31 alloy can produce high-quality magnesium alloy billets with uniform and equiaxed grains of less than 40 μm across the billet section up to at least a 100-mm diameter, which further improves the yield strength of the alloy, resulting in σy = 51.53 + 90.85 d−1/2.

Three-dimensional particle simulation on structure formation and plasma instabilities in collisionless driven reconnection

Structure formation and plasma instabilities in collisionless driven reconnection are investigated by three-dimensional electromagnetic (EM) particle simulation in an open system. In the early period, the lower-hybrid drift instability is excited in tlie periphery of the current layer. In the intermediate period, magnetic islands are created in the downstream due to magnetic reconnection. and they become unstable against a kink instability. In the late period, after the magnetic islands go out through the boundary, a wide, thin current sheet is generated and a low-frequency EM mode is excited in the central region. This mode has a frequency comparable to the ion gyration frequency, and thus it is considered to be the drift kink instability.

Low-frequency electromagnetic fields in applied geophysics: Waves or diffusion?

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

Electric currents streaming out of stressed igneous rocks – A step towards understanding pre-earthquake low frequency EM emissions

Transient electric currents that flow in the Earth’s crust are necessary to account for many non-seismic pre-earthquake signals, in particular for low frequency electromagnetic (EM) emissions. We show that, when we apply stresses to one end of a block of igneous rocks, two currents flow out of the stressed rock volume. One current is carried by electrons and it flows out through a Cu electrode directly attached to the stressed rock volume. The other current is carried by p-holes, i.e., defect electrons on the oxygen anion sublattice, and it flows out through at least 1 m of unstressed rock to meet the electrons that arrive through the outer electric circuit. The two outflow currents are part of a battery current. They are coupled via their respective electric fields and fluctuate. Applying the insight gained from these laboratory experiments to the field, where large volume of rocks must be subjected to ever increasing stress, leads us to suggest transient, fluctuating currents of considerable magnitude that would build up in the Earth’s crust prior to major earthquakes.

Extremely Low-Frequency Electromagnetic Fields do not Affect DNA Damage and Gene Expression Profiles of Yeast and Human Lymphocytes

We studied the effects of extremely low-frequency (50 Hz) electromagnetic fields (EMFs) on peripheral human blood lymphocytes and DBY747 Saccharomyces cerevisiae. Graded exposure to 50 Hz magnetic flux density was obtained with a Helmholtz coil system set at 1, 10 or 100 microT for 18 h. The effects of EMFs on DNA damage were studied with the single-cell gel electrophoresis assay (comet assay) in lymphocytes. Gene expression profiles of EMF-exposed human and yeast cells were evaluated with DNA microarrays containing 13,971 and 6,212 oligonucleotides, respectively. After exposure to the EMF, we did not observe an increase in the amount of strand breaks or oxidated DNA bases relative to controls or a variation in gene expression profiles. The results suggest that extremely low-frequency EMFs do not induce DNA damage or affect gene expression in these two different eukaryotic cell systems.

Comment: A biological guide for electromagnetic safety: the stress response

Questions of safety of electromagnetic (EM) fields should be based on relevant biological properties, i.e., specific cellular reactions to potentially harmful stimuli. The stress response is a well documented protective reaction of plant and animal cells to a variety of environmental threats, and it is stimulated by both extremely low frequency (ELF) and radio frequency (RF) EM fields. It involves activation of DNA to initiate synthesis of stress proteins. Thermal and non-thermal stimuli affect different segments of DNA and utilize different biochemical pathways. However, both ELF and RF stimulate the same non-thermal pathway. Since the same biochemical reactions are stimulated in different frequency ranges with very different specific absorption rates (SARs), SAR level is not a valid basis for safety standards. Studies of EM field interactions with DNA and with model systems provide insight into a plausible mechanism that can be effective in ELF and RF ranges.

Low-Frequency Electromagnetic Stimulation May Lead to Regression of Morris Hepatoma in Buffalo Rats

The influence of low-frequency electromagnetic (LF-EM) waves on the processes of carcinogenesis and tumor growth has been the subject of experimental investigations for more than two decades and the results are promising. In parallel, an interesting method of complementary medicine, biophysical-information therapy (BIT) or bioresonance therapy (BRT), which in principle is based on LF-EM stimulation, has emerged. BRT has been known since the late 1980s but is still poorly studied. The idea of applying BRT to tumors is based on two main premises: (1) endogenous biophotonic emission in the case of tumors is different from that produced by healthy tissues/cells and (2) BRT effects are believed to be primarily manifested at the immune-system level. Consequently, we decided to study the influence of BRT on a dynamic and well-known process: the expansion of transplantable hepatoma in rats. The study was carried out on female Buffalo rats with implanted Morris tumors (three experimental and one control group). Fourteen (14) consecutive in vivo exposures using a BRT device (BICOM B15, REGUMED Regulative Medizintechnik Gmbh, Graefelfing, Germany), were made from the third day after inoculation of the tumors. Biometric observations, intra vitam (tumor volume, growth ratio), were completed with histologic investigation (implantation locus, selected internal organs [lungs]). Thirty-one (31) cases (69%; n = 45) of total tumor regression were observed in experimental groups and these individuals were anesthetized to enable histologic verification to be made. No lung metastases--usually observed in tumor-bearers--could be detected. Moreover, in the inoculation loci, traces of former implantation and tumor absorption were found to be associated with high activity of cell-mediated immune response. No regressions were observed in the control group. We cannot exclude the possibility that LF-EM signals transmitted via BRT into the tumor-bearers may stimulate two separate processes: effective immunological response and/or tumor-cell death. The method appears to be capable of inducing the regression of transplantable hepatoma in vivo, thus is a potential subject of further studies.

Modeling assemblies of biological cells exposed to electric fields.

Gap junctions are channels through the cell membrane that electrically connect the interiors of neighboring cells. Most cells are connected by gap junctions, and gaps play an important role in local intercellular communication by allowing for the exchange of certain substances between cells. Gap communication has been observed to change when cells are exposed to electromagnetic (EM) fields. In this work, we examine the behavior of cells connected by gap junctions when exposed to electric fields, in order to better understand the influence of the presence of gap junctions on cell behavior. This may provide insights into the interactions between biological cells and weak, low-frequency EM fields. Specifically, we model gaps in greater detail than is usually the case, and use the finite element method (FEM) to solve the resulting geometrically complex cell models. The responses of gap-connected cell configurations to both dc and time harmonic fields are investigated and compared with those of similarly shaped (equivalent) cells. To further assess the influence of the gap junctions, properties such as gap size, shape, and conductivity are varied. Our findings indicate that simple models, such as equivalent cells, are sufficient for describing the behavior of small gap-connected cell configurations exposed to dc electric fields. With larger configurations, some adjustments to the simple models are necessary to account for the presence of the gaps. The gap junctions complicate the frequency behavior of gap-connected cell assemblies. An equivalent cell exhibits low-pass behavior. Gaps effectively add a bandstop filter in series with the low-pass behavior, thus lowering the relaxation frequency. The characteristics of this bandstop filter change with changes to gap properties. Comparison of the FEM results to those obtained with simple models indicates that more complex models are required to represent gap-connected cells.

Health and Low-Frequency Electromagnetic Fields

Health and Low-Frequency Electromagnetic Fields

Health and Low-Frequency Electromagnetic Fields

The nature of low-frequency electromagnetic fields sources of low-frequency fields natural sources of exposure the coupling of electromagnetic fields to the body natural sources of noise observed interactions with electromagnetic fields questions for future research.

A Review of In Vitro Studies: Low-Frequency Electromagnetic Fields

In vitro studies of effects of low-frequency (LF) electromagnetic (EM) fields have revealed a variety of sensitive cell-physiologic end-points. Effects have been reported on (1) DNA, RNA, and protein synthesis; (2) cell proliferation; (3) cation fluxes and binding; (4) immune responses; and (5) membrane signal transduction (i.e., hormones, enzymes, and neuro-transmitters). Typically such effects occurred as a result of short-term exposure of cells to EM at frequencies of 100 Hz or less and at low field intensities. The dependency on frequency or modulation, as well as the apparent weak cellular interaction of these LF EM fields, lacks theoretic explanation. It has not been determined whether effects are induced by electric or magnetic fields. Confounding interpretation of the results are phenomena such as (1) transient or time-delayed responses; (2) modulation- and intensity-specific effects, referred to as modulation or intensity “windows;” and (3) general lack of dose- (or dose-rate) response data or EM field thresholds. Consequently, although it is well-established that LF EM fields affect biological systems in vitro, use of these data to assess human health effects is limited. This paper reviews selected published reports of LF EM fields on in vitro systems. Where possible, relevance of the findings to occupational exposures will be assessed, principally by considering the consistency of in vitro and in vivo EM exposure effects and comparison of EM field intensities that affect in vitro systems with occupational EM exposure intensities. Finally, suggestions will be made for the direction of future in vitro research of direct pertinence to potential occupational exposure problems.

A review of in vitro studies: low-frequency electromagnetic fields.

In vitro studies of effects of low-frequency (LF) electromagnetic (EM) fields have revealed a variety of sensitive cell-physiologic end-points. Effects have been reported on (1) DNA, RNA, and protein synthesis; (2) cell proliferation; (3) cation fluxes and binding; (4) immune responses; and (5) membrane signal transduction (i.e., hormones, enzymes, and neuro-transmitters). Typically such effects occurred as a result of short-term exposure of cells to EM at frequencies of 100 Hz or less and at low field intensities. The dependency on frequency or modulation, as well as the apparent weak cellular interaction of these LF EM fields, lacks theoretic explanation. It has not been determined whether effects are induced by electric or magnetic fields. Confounding interpretation of the results are phenomena such as (1) transient or time-delayed responses; (2) modulation- and intensity-specific effects, referred to as modulation or intensity "windows;" and (3) general lack of dose- (or dose-rate) response data or EM field thresholds. Consequently, although it is well-established that LF EM fields affect biological systems in vitro, use of these data to assess human health effects is limited. This paper reviews selected published reports of LF EM fields on in vitro systems. Where possible, relevance of the findings to occupational exposures will be assessed, principally by considering the consistency of in vitro and in vivo EM exposure effects and comparison of EM field intensities that affect in vitro systems with occupational EM exposure intensities. Finally, suggestions will be made for the direction of future in vitro research of direct pertinence to potential occupational exposure problems.

Electrostimulation in Cell Biology by Low-Frequency Electromagnetic Fields

Surprising phenomena have been detected by electric, magnetic, or electromagnetic treatment of various cells or tissues. To estimate the efficacy and possibilities of this new tool in biosciences, a short review will be presented dealing with (1) the current models for the analysis of mechanisms and (2) the experimental outcomes of electrostimulation of cells, which are treated by low-frequency-induced currents (mostly using Helmholtz coils): B > 10 mT, E > 10 mV/cm.The broad view of results on biopolymer syntheses, enzyme activities, membrane transport, proliferation, and other morphological changes is sometimes difficult to compare, because of numerous parameters and different “electrical and biological windows” for efficacy. Nevertheless it could be concluded that cells can react sensitively by manifold metabolic responses. Future research will prove whether such field influence on these processes is universal.

Low-frequency computational electromagnetics for antenna analysis

An overview of computational methods for modeling the low-frequency electromagnetic characteristics of antennas is given. Presented first is a brief analytical background that forms the basis for numerically solving low-frequency antenna problems using the method of moments. Next discussed are extensions to modeling perfectly conducting objects in free space, followed by a consideration of some computational issues that affect model accuracy, efficiency, and utility. A variety of representative applications is given to illustrate various aspects of modeling and capabilities that are currently available. A fairly extensive bibliography is included. >

Prenatal exposure to a low‐frequency electromagnetic field demasculinizes adult scent marking behavior and increases accessory sex organ weights in rats

Pregnant Sprague-Dawley dams were exposed to a low-level, low-frequency pulsed electromagnetic (EM) field (15 Hz, 0.3 msec duration, peak intensity 8 gauss) for 15 min twice a day from day 15 through day 20 of gestation, a period in development that is critical for sexual differentiation of the male rat brain. No differences in litter size, number of stillborns, or body weight were observed in offspring from field-exposed dams. At 120 days of age, field-exposed male offspring exhibited significantly less scent marking behavior than controls. Accessory sex organ weights, including epididymis, seminal vesicles, and prostate, were significantly higher in field-exposed subjects at this age. However, circulating levels of testosterone, luteinizing hormone, and follicle-stimulating hormone, as well as epididymal sperm counts, were normal. These data indicate that brief, intermittent exposure to low-frequency EM fields during the critical prenatal period for neurobehavioral sex differentiation can demasculinize male scent marking behavior and increase accessory sex organ weights in adulthood.