Explore chapters and articles related to this topic
Foundations of electromagnetism
Published in Riadh Habash, BioElectroMagnetics, 2020
The majority of ELF fields and RFR are artificial, however, the rest of frequency is mixed, natural and artificial. ELF fields include power frequency (50/60 Hz) fields associated with electricity supplies while RFR is associated mainly with 3 kHz–300 GHz frequencies which are extensively used in communications, navigation, industrial, and medical applications. Between power frequency and RFR, VLF fields in the kHz range exist. ELF fields and RFR are the commonest EM fields encountered in practice and are the main focus of this book.
Highway plant
Published in Malcolm Copson, Peter Kendrick, Steve Beresford, Roadwork, 2019
Malcolm Copson, Peter Kendrick, Steve Beresford
(b)Radio mode: This enables the tool to detect long conductors even if they do not carry any energy of their own. These conductors include live, but not loaded, power cables, main telephone cables and some continuous metal pipes. The signals originate from distant VLF radio transmitters and these signals are re-radiated by the buried conductors in sufficient strength to be detected by the tool.
Wave Re-emission from a Density Duct
Published in Igor G. Kondrat’ev, Alexander V. Kudrin, Tatyana M. Zaboronkova, Electrodynamics of Density Ducts in Magnetized Plasmas, 2019
Igor G. Kondrat’ev, Alexander V. Kudrin, Tatyana M. Zaboronkova
We saw in Chapter 6 that when the plasma density in the duct is high enough, the wavelength of the VLF/ELF signal excited in the duct core becomes of the same order as the antenna size. This leads to a noticeable increase in the total radiated power due to the effective excitation of guided modes in the duct. We showed in Chapter 7 and the present chapter that these modes can be conveyed by the duct and can re-emit from its end, giving rise to an increase in power that goes to the long-wavelength part of the spectrum of waves excited in the surrounding medium. It is this part that is useful for communication through the ionosphere, enabling a VLF/ELF signal to be received anywhere on the surface of the Earth. In other words, the antenna plus the artificial duct can act as a plasma-waveguide transmitting system (‘plasma antenna’) which excites, as a whole, VLF/ELF signals in the ambient medium. Of course, the radiation characteristics of such plasma-waveguide systems depend on various plasma parameters in a very complicated manner and, for the future, there is much to be done in improving our understanding of both the mechanisms of their formation and the methods of efficient control of wave emissions from them.
Quantitative effects of cyclotron resonance on the coupling of ULF with VLF and langmuir waves
Published in Waves in Random and Complex Media, 2021
Asif Shah, Shahzad Mahmood, Saeed Ur Rehman
The ULF waves are hydromagnetic in nature and occupy a vast band 1 mHz–10 Hz ([1] and references therein). These waves have been classified into two categories, continuous pulsations (Pc) and irregular pulsations (Pi). In Pc there are five sub-bands, Pc1 (oscillation periods fall in the range of 0.5–5 seconds), Pc2 (5–10 seconds), Pc3 (10–45 seconds), Pc4 (45–150 seconds), Pc5 (150–600 seconds). However, the Pi oscillations have only two sub-bands, Pi1 (1-40 seconds), and Pi2 (40–150 seconds) [1,2]. The VLF waves are electromagnetic oscillations at 3–30 kHz [3]. The frequencies of Langmuir oscillations are strongly dependent on the plasma frequency and electron thermal speed [4].
An alternative amelioration of ME-based DZT-PML for truncating FDTD problems
Published in Electromagnetics, 2021
Naixing Feng, Xue-Shi Li, Yuxian Zhang, Yanming Sun
As known to all, the signal in shorter-wavelength radio waves will be weakened to be neglected when propagating farther and farther, and easily prohibited by the rock layer. To solve out this problem, the VLF radio wave is employed because of its advantages of long-distance propagation and strong-power penetration so that it can propagate and span over hundreds of feet in water and earth, and thousands of miles in the air. Therefore, to validate the absorption accuracy of the proposed DZT-ME-PML, we present 3D VLF subsurface sensing cases for the geophysics exploration.