Large-Scale Electromagnetic Modeling for Multiple Inhomogeneous Domains

We present a new formulation of the integral equation (IE) method for models with variable background conductivity. This method overcomes the standard limitation of the conventional IE method related to the use of a horizontally layered background only. The new IE method still employs the Green's functions for a horizontally layered 1‐D model. However, the new method allows us to use an inhomogeneous background with the IE method. The method was carefully tested for modeling the electromagnetic (EM) field for complex structures with known variable background conductivity. It can find wide application in modeling EM data for multiple geological models with some common geoelectrical features. As an example, we consider marine controlled source EM (MCSEM) application for simulating EM response of a petroleum reservoir in the presence of a salt dome structure.

In this paper we present a new approach to the interpretation of the marine controlled‐source electromagnetic (MCSEM) data in areas with rough bathymetry. This approach is based on a new formulation of the integral equation EM modeling method in models with inhomogeneous background conductivity. The developed technique allows us to incorporate known geological structures and bathymetry effects in the method of iterative EM migration/holographic imaging and inversion. This approach provides us with the ability to precompute only once the effect of a known geoelectrical structure (e.g., the bathymetry effect) and keep it unchanged during the entire modeling and migration process. The method is illustrated by numerical examples of modeling and inversion of marine CSEM data in areas with rough bathymetry.

New integral equations are introduced in which the transverse electromagnetic field components are unknown for the two‐dimensional (2‐D) electromagnetic scattering problems and electromagnetic waveguide problems. A numerical analysis by the boundary element method is proposed. The conventional integral equations in which the longitudinal electromagnetic field components are unknown are difficult to determine at certain angular frequencies and at certain longitudinal propagation constants for the electromagnetic scattering problem. In the waveguide problem, the spurious modes may enter as nonphysical solutions.The integral equations proposed in this paper do not have conventional difficulties. Here, the integral equations using the transverse electromagnetic fields are derived and the uniqueness of the solution is proven. Further, for practical examples, the integral equations are analyzed numerically by the boundary element methods so that the validity and effectiveness are investigated.

It has been reported that electromagnetic (EM) fields induce stress proteins in vitro. These proteins have been shown to be important in recovery from ischemia/reperfusion. It was, therefore, hypothesized that EM fields could activate stress responses in vivo and protect myocardial tissue during anoxia. Chick embryos were exposed to 4-, 6-, 8-, and 10- microT and 60-Hz EM fields for 20 minutes followed by a 1-hour rest period before placement in an anoxic chamber. Embryos were reoxygenated when survival of controls dropped to <40%, and final observations were made 30 minutes later. Data from 80 experiments (>500 EM field-exposed embryos) indicated that EM field protection was extremely significant (P<0.0001). Survival rates were 39.6% in controls and 68.7% in field-exposed embryos. In a second set of experiments, embryos were exposed for 20 minutes to several pretreatments: (1) hyperthermia (43 degreesC), (2) 60-Hz, 8- microT EM fields, or (3) 60-Hz, 8- microT EM fields plus a random EM noise field (8 microT). Embryo survival was 37.7% (control), 57.6% (heated), 69% (60-Hz EM field only), and 41.5% (60-Hz EM field plus EM noise). To confirm that heating resulting from field exposures did not occur, thermocouples were placed into several eggs at the site of the embryo during exposure; no increase in temperature was noted. We conclude that athermal EM field exposures induce stress responses that protect chick embryo myocardium from anoxia damage. These results suggest that EM field exposures may be a useful, noninvasive means of minimizing myocardial damage during surgery, transplantation, or heart attack in humans.

In traditional artificial-source electromagnetic exploration, the effects of the ionosphere and displacement current (DC) in the air were neglected, and only the geoelectrical structure of the earth's crust and upper mantle was considered, such as for controlled source audio-frequency magnetotelluric (CSAMT). By employing a transmitter (less than 30 kW) to generate source fields, the CSAMT method overcomes the problems associated with weak natural electromagnetic (EM) fields used in magnetotellurics. However, the transmitter is moved and the source–receiver offset is approximately less than 20 km, because of the limitation of emission energy. We put forward a new idea, that is, a fixed artificial source (greater than 200 kW) is used and the source location selected at a high resistivity region (to ensure a high emission efficiency), so there may be a possibility that as long as the source strength magnitude is strong enough, the artificial EM signal can be easily observed within a distance of several thousand kilometres. Previous studies have provided the evidence to support this idea; they used the ‘earth–ionosphere’ mode in modeling the EM fields with the offset up to a thousand kilometres. Such EM fields still have a signal/noise ratio over 10–20 dB; this means that a new EM method with fixed source is feasible. However, in their calculations, the DC which plays a very important role for large offsets was neglected. This paper pays much attention to derive the formulae of the ‘earth–ionosphere’ mode with a horizontal electric dipole source, and the DC is not neglected. We present some three layers modeling results to illustrate the basic EM field characteristics under the ‘earth–ionosphere’ mode. As the offset increases, the contribution of the conduction current decreases, DC and ionosphere were taken into account, and the EM field attenuation decreases. We also quantitatively compare the predicted and observed data. The comparison of these results with the data reveal the excellent agreement between the experimental and theoretical results. The DC and ionosphere affects the EM fields, however impedances (ratio of E to H) are unaffected, and this means we need to include ionosphere and DC effects to accurately model the EM field amplitudes for optimal setting of measurement parameters, but we do not need to include these complications for the interpretation of the data for the Earth conductivity.

Iterative Solution Method for the Linearized Poisson–Boltzmann Equation: Indirect Boundary Integral Equation Approach

Electromagnetic (EM) field is often referred to diffusion (quasi-static assumption) that displacement currents are neglected during data processing in geophysical application, while the ratio of conduct currents to displacement currents is higher than 10, that is ,we think EM field is diffusion dominated and wave dominate for the ratio less than 0.1. Our simulating with Horizontal Electric Dipole Field indicated that frequency range of wave dominated is that the ratio is less than 0.007, the magnitude curves of EM component and impedance referring to diffusion and wave are different from those of diffusion. And in transform zone () the curves are different from those of wave and diffusion.

Marine controlled-source electromagnetic (CSEM) method has proved to be a powerful tool and found its increasing applications for offshore resource exploration and tectonic studies. However, bathymetric variations and anisotropic structures encountered in practical measurements have posed challenges for reliable interpretation of marine CSEM data collected in increasingly complex geologic settings. In this study, we present a Finite element (FE) based forward algorithm for simulating 3-D marine CSEM responses in geologic settings characterized with rough bathymetry and electrical anisotropy. Unstructured tetrahedral meshes are employed to permit precise descriptions of arbitrary seafloor topography. After validating the accuracy of the algorithm, we investigate the effects of bathymetric variations and complicated electric anisotropy separately and jointly on marine CSEM responses. Numerical results have demonstrated that both the bathymetry and electrical anisotropy can cause significant distortions on marine CSEM responses, but to different extent. The effects of full electrical anisotropy and bathymetry have to be taken into consideration for reliable interpretations of marine CSEM data in practice.

Exploration of hydrocarbons in the sea is particularly expensive because it is best done by supplying a transmitter with a strong current, which is hazardous to the lives of marine life. A steady supply of voltage and current to the transmitter is normally used to determine the strength of electromagnetic waves. The mineral deposition has been detected using different techniques, both offshore and onshore. Detection of minerals by employing a controlled source electromagnetics (CSEM) has recently proved to be extremely effective with yielding promising results. Due to noise, both the transmitted and received signals may differ. The signal received from the subsurface in marine settings is generally limited by a variety of noise. The frequency spectrum of frequency signals and wave-forms change when they interact with physical objects. Understanding how the frequency spectrum is altered allows us to examine how the signal and wave-forms change. To accurately evaluate and eradicate these noises, they must be researched and taken into consideration. One of the most challenging problems employing Marine CSEM (MCSEM) in the detection of hydrocarbon is airwaves. When an electromagnetic (EM) is passed over a conductive surface, the affected signal is frequently influenced by the resistive body with high resistivity distribution. The signal is recorded by some electromagnetic (EM) fields scattered by subsurface with electric and magnetic sensors. Furthermore, the signal recorded is noise, often known as airwaves. This, however, occurs in shallow water. Hence, this work proposes to use Fast Fourier Transform (FFT) to detect and remove the noise from the transmitted signal to reduce misinterpretation in the exploration of hydrocarbon in shallow water environments. Moreover, the simulated results obtained from the CST EM studio shows that when an EM signal is subjected to FFT, airwaves can be detected and removed, which enhances and reduces the uncertainty in the deposition of the hydrocarbon layer in a shallow water environment.

Electromagnetic Environment Associated with Lightning Strikes to Tall Strike Objects

Machine learning-based electro-magnetic field guided localization technique for autonomous underwater vehicle homing

SUMMARY Most of the existing 3-D electromagnetic (EM) modelling solvers based on the integral equation (IE) method exploit fast Fourier transform (FFT) to accelerate the matrix–vector multiplications. This in turn requires a laterally uniform discretization of the modelling domain. However, there is often a need for multiscale modelling and inversion, for instance, to properly account for the effects of non-uniform distant structures and, at the same time, to accurately model the effects from local anomalies. In such scenarios, the usage of laterally uniform grids leads to excessive computational loads, in terms of both memory and time. To alleviate this problem, we developed an efficient 3-D EM modelling tool based on a multinested IE approach. Within this approach, the IE modelling is first performed at a large domain and on a (laterally uniform) coarse grid, and then the results are refined in the region of interest by performing modelling at a smaller domain and on a (laterally uniform) denser grid. At the latter stage, the modelling results obtained at the previous stage are exploited. The lateral uniformity of the grids at each stage allows us to keep using the FFT for the acceleration of matrix–vector multiplications. An important novelty of the paper is the development of a ‘rim domain’ concept that further improves the performance of the multinested IE approach. We verify the developed tool on both idealized and realistic 3-D conductivity models, and demonstrate its efficiency and accuracy.

Where is consciousness? Neurobiological theories of consciousness look primarily to synaptic firing and "spike codes" as the physical substrate of consciousness, although the specific mechanisms of consciousness remain unknown. Synaptic firing results from electrochemical processes in neuron axons and dendrites. All neurons also produce electromagnetic (EM) fields due to various mechanisms, including the electric potential created by transmembrane ion flows, known as "local field potentials," but there are also more meso-scale and macro-scale EM fields present in the brain. The functional role of these EM fields has long been a source of debate. We suggest that these fields, in both their local and global forms, may be the primary seat of consciousness, working as a gestalt with synaptic firing and other aspects of neuroanatomy to produce the marvelous complexity of minds. We call this assertion the "electromagnetic field hypothesis." The neuroanatomy of the brain produces the local and global EM fields but these fields are not identical with the anatomy of the brain. These fields are produced by, but not identical with, the brain, in the same manner that twigs and leaves are produced by a tree's branches and trunk but are not the same as the branches and trunk. As such, the EM fields represent the more granular, both spatially and temporally, aspects of the brain's structure and functioning than the neuroanatomy of the brain. The brain's various EM fields seem to be more sensitive to small changes than the neuroanatomy of the brain. We discuss issues with the spike code approach as well as the various lines of evidence supporting our argument that the brain's EM fields may be the primary seat of consciousness. This evidence (which occupies most of the paper) suggests that oscillating neural EM fields may make firing in neural circuits oscillate, and these oscillating circuits may help unify and guide conscious cognition.

Marine controlled-source electromagnetic (MCSEM) surveys have become an important part of off-shore petroleum exploration. In this paper we discuss new advances in the development of 3D inversion methods for the interpretation of MCSEM data. Our method is based on rigorous integral equation (IE) forward modeling and a new IE representation of the sensitivity (Frechet derivative matrix) of observed data to variations in sea-bottom conductivity. We use quasi-analytical approximation for models with variable background conductivity (QAVB) for more efficient Frechet derivative calculations. In our regularized focusing inversion algorithm we introduce a new stabilizing functional, a minimum vertical support stabilizer. This stabilizer helps generate a focused image of the relatively thin and flat resistive structure of a hydrocarbon (HC) reservoir. The methodology is tested on a 3D inversion of the synthetic EM data and the interpretation of an MCSEM survey conducted in the Troll West Gas Province (TWGP).

The conscious electromagnetic information (cemi) field theory proposes that the seat of consciousness is the brain’s electromagnetic (EM) field that integrates information from trillions of firing neurons. What we call free will is its output. The cemi theory also proposes that the brain has two streams. Most actions are initiated by the first non-conscious stream that is composed of neurons that are insulated from EM field influences. These non-conscious involuntary actions are thereby invisible to our EM field-located thoughts. The theory also proposes that voluntary actions are driven by neurons that receive EM field inputs and are thereby visible to our EM field-located thoughts. I review the extensive evidence for EM field/ephaptic coupling between neurons and the increasing evidence that EM fields in the brain are a cause of behaviour. I conclude by arguing that though this EM field-driven will is not free, in the sense of being acausal, it nevertheless corresponds to the very real experience of our conscious mind being in control of our voluntary actions. Will is not an illusion. It is our experience of control by our EM field-located mind. It is an immaterial, yet physical, will.