Extremely Low Frequency Range Research Articles

Correction of the electromagnetic monitoring data for tidal variations of apparent resistivity

The use of the ELF (extremely low frequency) radio station “Zevs” for the study of the stress–strain state of geological media is considered. Analysis of prior research on the connection between tidal phenomena and apparent resistivity ρ a variations at earthquake prediction sites are made. In the ELF range experimental measurements of artificial electromagnetic field impedance and the results of calculation of tidal deformations are considered. A high degree of correlation of ρ a values and vertical deformations of the Earth surface Δ H are noted. Diurnal ρ a changes of 7% due to tidal phenomena, were recorded with measurements accuracy of ±0.6%. To increase the reliability of earthquake prediction it is necessary to correct the electromagnetic monitoring data for tidal effects using correlation equations between ρ a and Δ H.

Generation of extremely-low frequency magnetic fields with standard available commercial equipment: Implications for experimental bioelectromagnetics work

Generation of magnetic fields is theoretically very simple. Depending on the size of biological models, we have to design coils and use enough current to get the required field. We chose to study the electrical configuration of Helmholtz coils because of their widely used property of giving a uniform field. Commercial generators produce various current shapes at any frequency up into the MHz range. However they suffer some drastic limitations with output impedances and output voltages. Powerful amplifiers can help overcome this problem by delivering higher current into lower resistances, but limitations appear then in the available frequency which are kept in the extremely-low frequency range (0–300 Hz). We show a relation between the intensity B of the field and its frequency f, depending on the diameter D of the coil, the diameter of the wire used d and the intensity of the current I: Bf=44.2 I/[ Dd 2(ln(8 D/d) -1.36)] for one pair of Helmholtz coils. We show tables of available fields and frequencies taking into account limitations such as voltages, resistances, current density, coil mass and volume. This will help scientists to design better their field generating system.

Extremely‐low‐frequency and very‐low‐frequency magnetic fields emitted by video display units

Extremely-low-frequency (ELF) and very-low-frequency (VLF) magnetic fields as emitted by monochrome and multichrome video display units (VDUs) were measured for their frequency domains. The rms magnetic-flux densities (MFDs) were measured as a function of distance from all six sides of VDUs of four types. The MFDs at a distance of 30 cm from the screen (defined as the operator's position) were between 0.06 and 0.6 microT in the ELF range and between 0.02 and 0.06 microT in the VLF range. The contribution of harmonics to the total MFD was the same for both frequency ranges, less than 6%. For the first three harmonics, the MFD of each higher harmonic was one-half that of the immediately lower harmonic.

Visualization of electric fields around a biological body.

A system was developed that can visualize the spatial distribution of the ELF (extremely low frequency) electric field around an object with a complex shape such as a biological body. A mechanical X-Y scanner controlled by a microcomputer moves an optical sensor, automatically scanning the space around the object. The measured data are processed and the field distribution is represented in a color distribution pattern. Using an object with a simple shape such as a cylinder, the accuracy of the measurement was confirmed by comparison to a numerical calculation. The field distributions around experimental animals (a rat and a cat) were measured and it was shown that a conductor model can be used instead of a living body in the ELF range. The field distribution around a human model was measured in various postures, showing reasonable agreement with measurements for a real human body standing under transmission lines. >

General properties of the interaction between animals and ELF electric fields.

An analysis is given of the interaction between extremely low-frequency (ELF) electric fields and animals of arbitrary body shape. This analysis is based on three approximations which are valid in the ELF range: In living tissues, capacitive (displacement) currents are negligible compared to conduction currents; effects resulting from the finite velocity of propagation of electromagnetic fields are negligible; skin effect in living tissues is negligible. Major conclusions of the analysis are: (a) The electric field outside the body, the induced charge on the surface of the body, and the total current crossing any section through the body (eg, through the neck or limbs) are completely determined by the characteristics of the applied ELF electric field, the shape of the body, its location relative to ground and other conductors, and any conduction currents from the body to ground or other conductors. (b) All of the quantities in (a) can be measured using conducting animal models. (c) The magnitudes of the electric field outside the body and the induced charge density on the surface of the body are independent of frequency, in the ELF range, when the body is either insulated from or shorted to ground (and any other conductors in the system). (d) The only quantities affected by the electrical properties of the tissues comprising the body are the current density and electric field inside the body. (e) The electric field outside and inside a body will be unchanged by a scaled change in its size.