3 EM-induction (original) (raw)
Electromagnetic induction studies
Reviews of Geophysics, 1983
This report constitutes an attempt to review the major developments and identify important trends in the broad field of geophysical electromagnetic induction and related phenomena over the past four years. Following in the spirit of previous reports of this type [e.g., Filloux, 1979; Hermance, 1983b], the work of US researchers will be emphasized, although we will cover foreign research when appropriate. Many of the recent theoretical developments and the largest EM field program ever (EMSLAB) are the direct result of' international cooperation, and strict adherence to the concept of national boundaries would result in an uninformative and incomplete review. Due to the fact that readers of this paper have diverse interests ranging from theory through field to laboratory studies, we have attempted to treat a variety of topics in EM induction and electrical geophysics. We begin by reviewing the state-of-the-art in data collection, including new instrumentation. We continue by examining data analysis methods, with an emphasis on noise and bias reduction in the computation of' the magnetotelluric and magnetic variations response functions. We then treat forward modelling developments, especially for two-and three-dimensional induction problems. Recent progress has been made in EM induction inverse problems, and we assess the impact of this on the field. An overview of field measurements in North America is given, including the recent EMSLAB experiment which was carried out in 1985--1986 in the northwest US, southwest Canada, and contiguous offshore regions. This is followed by a review of developments in oceanic applications of EM principles. The reference list is believed to be complete through June 1986. In the interest of brevity, only refereed publications or works in press are included, and meeting abstracts or technical reports are generally not cited. Nevertheless, the number of references exceeds 600, attesting to the health of the discipline. Additional information on EM induction research may be found in the proceedings of the most recent semiannual Workshops on EM Induction held in
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 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.
Some Student Conceptions of Electromagnetic Induction
Research in Science Education, 2008
Introductory electromagnetism is a central part of undergraduate physics. Although there has been some research into student conceptions of electromagnetism, studies have been sparse and separated. This study sought to explore second year physics students' conceptions of electromagnetism, to investigate to what extent the results from the present study are similar to these results from other studies, and to uncover any new forms of alternative conceptions. Data for this study came from 15 in-depth interviews. Three previously unreported alternative conceptions were identified in the study: 1) induced current varies proportionately with current in solenoid; 2) there must be contact between magnetic flux and the external coil in order for any emf to be induced in the coil; 3) coulombic or electrostatic potential difference is present in an induced electric field. These alternative conceptions were manifested in these students' explanations of electromagnetic phenomena presented to them during the interviews.
Faraday's equation and law of electromagnetic induction - theory and practice
The Papers of Independent Authors, ISSN 2225-6717, 55, 59–66, 2022
It can be said that induction, discovered by Faraday, was the main reason for the emergence of Maxwell's system of equations. She entered this system as one of these equations. Based on this equation, the law of electromagnetic induction is formulated. It is shown that this law should not be applied in practical electrical engineering. Contents
Using a PC and external media to quantitatively investigate electromagnetic induction
Physics Education, 2011
In this article we describe an experimental learning path about electromagnetic induction which uses an Atwood machine where one of the two hanging bodies is a cylindrical magnet falling through a plexiglass guide, surrounded either by a coil or by a copper pipe. The first configuration (magnet falling across a coil) allows students to quantitatively study the Faraday-Neumann-Lenz law, while the second configuration (falling through a copper pipe) permits learners to investigate the complex phenomena of induction by quantifying the amount of electric power dissipated through the pipe as a result of Foucault eddy currents, when the magnet travels through the pipe. The magnet's fall acceleration can be set by adjusting the counterweight of the Atwood machine so that both the kinematic quantities associated with it and the electromotive force induced within the coil are continuously and quantitatively monitored (respectively, by a common personal computer (PC) equipped with a webcam and by freely available software that makes it possible to use the audio card to convert the PC into an oscilloscope). Measurements carried out when the various experimental parameters are changed provide a useful framework for a thorough understanding and clarification of the conceptual nodes related to electromagnetic induction. The proposed learning path is under evaluation in various high schools participating in the project 'Lauree Scientifiche' promoted by the Italian Department of Education.
IEEE Transactions on Geoscience and Remote Sensing, 2000
A finite-element analysis of electromagnetic induction (EMI) in the presence of multiple buried metal targets is undertaken for the purpose of unexploded ordnance (UXO) detection and discrimination. The effects of mutual coupling between metal targets and the host conductivity are shown to be important. At high frequencies, mutual coupling is strong, and effects of host conductivity are relatively minor. At lower frequencies near the resistive limit, EMI responses are very small, but the effect of host conductivity becomes important. This is due to the galvanic current flow in the host medium that dissipates charge accumulations on the host/target interfaces. Qualitative analysis of induced current patterns in metal targets demonstrates that mutual coupling is strongly affected by target orientation and skin depth. Rigorous forward modeling of EMI responses is essential to understanding UXO sensor signatures so that discrimination between live UXO items and harmless fragments and clutter may become possible.
Study of Electric charge induction with a three-dimensional model using the finite elements method
Revista Brasileira de Ensino de Física, 2018
One of the first subjects studied in Electricity and Magnetism classes is how one can make an electrically neutral object be an electrically charged object. There are three ways to do it: charging by friction, charging by contact and charging by induction. Induction charging is a method used to charge an object without actually touching the object to any other charged object. In order to illustrate the explanation of how the process of charging an electrically neutral body by induction, a 3D model was built using the finite elements method to show the increasing of the surface charge density in a initially neutral sphere when the distance between this sphere and a negatively charged bar decreases.