3 EM-induction (original) (raw)

The use of electromagnetic induction techniques in soils studies

Geoderma, 2014

Electromagnetic induction (EMI) has been used to characterize the spatial variability of soil properties since the late 1970s. Initially used to assess soil salinity, the use of EMI in soil studies has expanded to include: mapping soil types; characterizing soil water content and flow patterns; assessing variations in soil texture, compaction, organic matter content, and pH; and determining the depth to subsurface horizons, stratigraphic layers or bedrock, among other uses. In all cases the soil property being investigated must influence soil apparent electrical conductivity (EC a) either directly or indirectly for EMI techniques to be effective. An increasing number and diversity of EMI sensors have been developed in response to users' needs and the availability of allied technologies, which have greatly improved the functionality of these tools. EMI investigations provide several benefits for soil studies. The large amount of georeferenced data that can be rapidly and inexpensively collected with EMI provides more complete characterization of the spatial variations in soil properties than traditional sampling techniques. In addition, compared to traditional soil survey methods, EMI can more effectively characterize diffuse soil boundaries and identify areas of dissimilar soils within mapped soil units, giving soil scientists greater confidence when collecting spatial soil information. EMI techniques do have limitations; results are site-specific and can vary depending on the complex interactions among multiple and variable soil properties. Despite this, EMI techniques are increasingly being used to investigate the spatial variability of soil properties at field and landscape scales.

Electromagnetic Induction: An Alternative for Teaching and Understanding

2018

The classical physics treatment of "Electromagnetic Induction" is based on Faraday’s Law and Lorentz Force. This paper presents an alternative approach, based on Wilhelm Weber ́s Fundamental Force Law of Electrodynamics. It covers mutual induction, self-induction, parallel and anti-parallel currents, and currents in the same and opposite direction. The two approaches lead to the same quantitative results, but the conceptual difficulties are quite different. These problems are discussed in this paper, together with some consequences for teaching and classroom activities.

A Proposal for a Curricular Path About Electromagnetic Induction

Research on learning of electromagnetic phenomena has revealed some learning difficulties related to the fact that students often reach a partial understanding of electromagnetic induction, due to an incomplete knowledge of the different situations producing induced currents or, on the contrary, related to an incorrect use of the Lenz law

Electromagnetic induction studies

Reviews of Geophysics, 1983

On a somewhat more regional scale, geomagnetic variation studies by Porath and Gough (1971), compared by Smith (1978) with a summary of seismic refraction studies, indicate a general correlation between depth to anomalous conductivity, regional heat flow and anomalous seismic features in the crust and mantle. It is important to recognize, however, that the interpretation of the geomagnetic variation data does not take into account the contribution from the anomalous crustal conducting zone-a contribution which appears to be substantial. Kaufman and Keller (1981) reviewed magnetotelluric measurements made in the Basin and Range near Milford, Utah. Their results are not atypical for the Basin and Range in general (e.g. Stanley e__[t al., 1976a; Lienert and Bennett 1977; Morrison et al., 1979; Wannamaker, 1978; Wannamaker et al., 1980). They noted however that the distortion of the telluric field due to 3-D lateral heterogeneities in the surface sediments may be the cause of a modulation in the inferred depth to the crustal conductor. This phenomenon, which has been recognized for many years by Soviet workers (e.g. the degree to which the effects of 3-D distortion systematically bias the interpretation of data when simple 1-D models are used. The uncertainty of the depth to conducting layers in the crust is a good case in point. Swift (1979) reports the presence of a widespread conductor beneath the Beowawe geothermal area at a depth of approximately 3 km. Typically, a conductor appears beneath most of the Great Basin at a depth of 10-20 km, while it is reported to be at a depth as great as 35 km beneath the Milford, Utah area (near Roosevelt Hot Springs; Ward (1982); Wannamaker et al., 1980, 1982 a). Wannamaker et al. favor models for the Milford area which rely heavily on the interpretations of TM (transverse magnetic or H-polarization) mode response functions-this mode makes the conductor appear to be somewhat deeper (35 km) than the TE (transverse electric) mode. This interpretation places the anomalous conductor in the mantle, rather than in the crust, which if true has important implications regarding its physical cause and its relation to other tectonic phenomena. The question that many workers have is whether these modulations in the depth to the conductor are real, or are they artifacts introduced by the effects of 3-D lateral heterogeneities, such as the distortion of current due to surficial 3-D features. Most workers concur that one cannot minimize the distortion effects of surficial 3-D heterogeneities on regional electromagnetic studies in the Basin and Range. The effects of current channeling (e.g. visualized by Babour and Mosnier, 1977) may be particularly severe, since strong "edge-effects" on geomagnetic field variations are associated with the eastern and western margins of the Basin and Range (Schmucker, 1970; Porath and Gough, 1971; Gough, 1974). Towle (1980 a,b,c) has inferred the presence of channeled currents beneath the Rio Grande rift, as well as along the western edge of the Basin and Range Province, associated with the eastern front of the Sierra Nevadas. We do not know whether these currents exist elsewhere beneath this tectonic province, nor to what degree their effects lead to distortion of the conventional electromagnetic response functions. But most workers are concerned with the effects of such distortions on interpreting their field data (Morrison et al., 1979; Wannamaker et al., 1980; Wannamaker et al., 1982a). Clearly the phenomena associated with current channeling in distributed conductors merits greater attention than given in the present literature; particularly if we are to separate local channelling effects from the local induction effects usually invoked to explain electromagnetic anomalies. Advances in numerical modelling are rapidly becoming able to cope with the problem of induction and distortions associated with embedded 3-D bodies (F.W.

Electromagnetic induction in the earth due to stationary and moving sources

Pure and Applied Geophysics PAGEOPH, 1990

A new approach to the theory of electromagnetic induction is developed that is applicable to moving as well as stationary sources. The source field is considered to be a standing wave generated by two waves travelling in opposite directions along the surface of the earth. For a stationary source the incident waves have velocities of the same magnitude, however for a moving source the velocities of the two incident waves are respectively increased and decreased by the velocity of the source. Electromagnetic induction in the earth is then considered as refraction of these waves and gives, for both stationary and moving sources, the magnetotelluric relation:-Ey " co/la) where v is the wavenumber of the source,/~ is the permeability (4n 9 10-7) and a is the conductivity of the earth. 09 is the angular frequency of the variation observed on the earth. For a stationary source the observed frequency is the same as the source frequency, however the effect of moving a time-varying source is to make the observed frequency different from the frequency of the source. Failure to recognise this in previous studies led to some erroneous conclusions. This study shows that a moving source is not "electromagnetically broader" than a stationary source as had been suggested.

Electromagnetic induction: physics, historical breakthroughs, epistemological issues and textbooks

2021

The discovery of Electromagnetism by Ørsted (1820) initiated an “extraordinary decennium” ended by the discovery of electromagnetic induction by Faraday (1831). During this decennium, in several experiments, the electromagnetic induction was there, but it was not seen or recognized. In 1873, James Clerk Maxwell, within a Lagrangian description of electric currents, wrote down a ‘general law of electromagnetic induction’ given by, in modern form and with standard symbols:

Fourth Electromagnetic Induction

Fourth Electromagnetic Induction. The Papers of Independent Authors, ISSN 2225-6717, 2022, 55(1), 19–26., 2022

Variants of electromagnetic induction are considered. It is shown that there is also an induction caused by the existence of a flow of electromagnetic energy. The dependence of emf is found. this induction on the electromagnetic energy flux density.

The Fourth Electromagnetic Induction

2014

Different variants of electromagnetic induction are considered. The type of induction caused by changes of electromagnetic induction flow is separated. The dependence of this induction on the flow density of electromagnetic energy emf and on the parameters of the wire is explored. We are discussing the mechanism of occurrence of energy flow, which enters the wire and compensates the heat loss.