query: who discovered the magnetic field of electric current

pos: Magnetic field Siméon Denis Poisson (1781–1840) created the first successful model of the magnetic field, which he presented in 1824. In this model, a magnetic -field is produced by 'magnetic poles' and magnetism is due to small pairs of north/south magnetic poles. Three discoveries challenged this foundation of magnetism, though. First, in 1819, Hans Christian Ørsted discovered that an electric current generates a magnetic field encircling it. Then in 1820, André-Marie Ampère showed that parallel wires with currents attract one another if the currents are in the same direction and repel if they are in opposite directions. Finally, Jean-Baptiste Biot and Félix

pos: Magnetic moment not be taken too far because magnetic dipoles are associated with angular momentum (see Relation to angular momentum). Nevertheless, magnetic poles are very useful for magnetostatic calculations, particularly in applications to ferromagnets. Practitioners using the magnetic pole approach generally represent the magnetic field by the irrotational field , in analogy to the electric field . After Hans Christian Ørsted discovered that electric currents produce a magnetic field and André-Marie Ampère discovered that electric currents attract and repel each other similar to magnets, it was natural to hypothesize that all magnetic fields are due to electric current loops. In this model

pos: Magnetism the reason compasses pointed north (previously, some believed that it was the pole star (Polaris) or a large magnetic island on the north pole that attracted the compass). An understanding of the relationship between electricity and magnetism began in 1819 with work by Hans Christian Ørsted, a professor at the University of Copenhagen, who discovered by the accidental twitching of a compass needle near a wire that an electric current could create a magnetic field. This landmark experiment is known as Ørsted's Experiment. Several other experiments followed, with André-Marie Ampère, who in 1820 discovered that the magnetic field circulating in

pos: Electromechanics subsystems of parts, including electric typewriters, teleprinters, clocks, initial television systems, and the very early electromechanical digital computers. The first electric motor was invented in 1821 by Michael Faraday. The motor was developed only a year after Hans Christian Ørsted discovered that the flow of electric current creates a proportional magnetic field. This early motor was simply a wire partially submerged into a glass of mercury with a magnet at the bottom. When the wire was connected to a battery a magnetic field was created and this interaction with the magnetic field given off by the magnet caused the wire

pos: Electromagnet permanent magnet is that the magnetic field can be quickly changed by controlling the amount of electric current in the winding. However, unlike a permanent magnet that needs no power, an electromagnet requires a continuous supply of current to maintain the magnetic field. Electromagnets are widely used as components of other electrical devices, such as motors, generators, electromechanical solenoids, relays, loudspeakers, hard disks, MRI machines, scientific instruments, and magnetic separation equipment. Electromagnets are also employed in industry for picking up and moving heavy iron objects such as scrap iron and steel. Danish scientist Hans Christian Ørsted discovered in 1820 that

pos: Oersted's law plates, through which no current passes, from which the equation would give zero magnetic field. Ørsted's law was modified by Maxwell to cover the case of time-varying currents by adding a new source term called displacement current, giving the Ampere-Maxwell equation. Oersted's law In electromagnetism, Ørsted's law, also spelled Oersted's law, is the physical law stating that an electric current creates a magnetic field. This was discovered on 21 April 1820 by Danish physicist Hans Christian Ørsted (1777–1851), when he noticed that the needle of a compass next to a wire carrying current turned so that the needle was perpendicular

pos: Oersted's law Oersted's law In electromagnetism, Ørsted's law, also spelled Oersted's law, is the physical law stating that an electric current creates a magnetic field. This was discovered on 21 April 1820 by Danish physicist Hans Christian Ørsted (1777–1851), when he noticed that the needle of a compass next to a wire carrying current turned so that the needle was perpendicular to the wire. Ørsted investigated and found the physical law describing the magnetic field, now known as Ørsted's law. Ørsted's discovery was the first connection found between electricity and magnetism, and the first of two laws that link the two; the

pos: Fleming's left-hand rule for motors left in Britain". The rule for generators can be recalled by remembering that either the letters "g" and "r" is common to both "right" and "generator", or the phrase "Jenny is always right" ("Genny" being a common shortened version of Generator). When electrons, or any charged particles, flow in the same direction (for example, as an electric current in an electrical conductor, such as a metal wire) they generate a cylindrical magnetic field that wraps round the conductor (as discovered by Hans Christian Ørsted). The direction of the induced magnetic field is sometimes remembered by "Maxwell's corkscrew rule". That is,

pos: Electrical telegraph of acid. An electric current was sequentially applied by the sender through the various wires representing each digit of a message; at the recipient's end the currents electrolysed the acid in the tubes in sequence, releasing streams of hydrogen bubbles next to each associated letter or numeral. The telegraph receiver's operator would watch the bubbles and could then record the transmitted message. This is in contrast to later telegraphs that used a single wire (with ground return). Hans Christian Ørsted discovered in 1820 that an electric current produces a magnetic field which will deflect a compass needle. In the same

neg: Wiedemann effect Wiedemann effect The twisting of a ferromagnetic rod through which an electric current is flowing when the rod is placed in a longitudinal magnetic field. It was discovered by the German physicist Gustav Wiedemann in 1858 . The Wiedemann effect is one of the manifestations of magnetostriction in a field formed by the combination of a longitudinal magnetic field and a circular magnetic field that is created by an electric current. If the electric current (or the magnetic field) is alternating, the rod will begin torsional oscillation. In linear approach angle of rod torsion "α" does not depend on its

neg: Wiedemann effect disturbances. In order to avoid this the wire is connected to a mechanical damper that end. Wiedemann effect The twisting of a ferromagnetic rod through which an electric current is flowing when the rod is placed in a longitudinal magnetic field. It was discovered by the German physicist Gustav Wiedemann in 1858 . The Wiedemann effect is one of the manifestations of magnetostriction in a field formed by the combination of a longitudinal magnetic field and a circular magnetic field that is created by an electric current. If the electric current (or the magnetic field) is alternating, the rod will

neg: Magnetic field apart from each other as electric charges can, but always come in north/south pairs. If a magnetized object is divided in half, a new pole appears on the surface of each piece, so each has a pair of complementary poles. The magnetic pole model does not account for magnetism that is produced by electric currents. After Ørsted discovered that electric currents produce a magnetic field and Ampere discovered that electric currents attracted and repelled each other similar to magnets, it was natural to hypothesize that all magnetic fields are due to electric current loops. In this model developed by Ampere,

neg: Physics the particles of which a substance is composed; thermodynamics deals with the relationships between heat and other forms of energy. Electricity and magnetism have been studied as a single branch of physics since the intimate connection between them was discovered in the early 19th century; an electric current gives rise to a magnetic field, and a changing magnetic field induces an electric current. Electrostatics deals with electric charges at rest, electrodynamics with moving charges, and magnetostatics with magnetic poles at rest. Classical physics is generally concerned with matter and energy on the normal scale of observation, while much of modern

neg: Hall effect Hall effect The Hall effect is the production of a voltage difference (the Hall voltage) across an electrical conductor, transverse to an electric current in the conductor and to an applied magnetic field perpendicular to the current. It was discovered by Edwin Hall in 1879. For clarity, the original effect is sometimes called the ordinary Hall effect to distinguish it from other "Hall effects" which have different physical mechanisms. The Hall coefficient is defined as the ratio of the induced electric field to the product of the current density and the applied magnetic field. It is a characteristic of the

neg: Magnetic current Magnetic current Magnetic current is, nominally, a current composed of fictitious moving magnetic monopoles. It has the dimensions of volts. The usual symbol for magnetic current is formula_1 which is analogous to formula_2 for electric current. Magnetic currents produce an electric field analogously to the production of a magnetic field by electric currents. Magnetic current density, which has the units of V/m² (volts per square meter), is usually represented by the symbols formula_3 and formula_4. The superscripts indicate total and impressed magnetic current density. The impressed currents are the energy sources. In many useful cases, a distribution of electric charge

neg: Excitation (magnetic) Excitation (magnetic) An electric generator or electric motor consists of a rotor spinning in a magnetic field. The magnetic field may be produced by permanent magnets or by field coils. In the case of a machine with field coils, a current must flow in the coils to generate the field, otherwise no power is transferred to or from the rotor. The process of generating a magnetic field by means of an electric current is called excitation. Field coils yield the most flexible form of magnetic flux regulation and de-regulation, but at the expense of a flow of electric current. Hybrid

neg: Magnetic field the magnetic field generated by a steady current. Also in this work, Ampère introduced the term electrodynamics to describe the relationship between electricity and magnetism. In 1831, Michael Faraday discovered electromagnetic induction when he found that a changing magnetic field generates an encircling electric field. He described this phenomenon in what is known as Faraday's law of induction. Later, Franz Ernst Neumann proved that, for a moving conductor in a magnetic field, induction is a consequence of Ampère's force law. In the process, he introduced the magnetic vector potential, which was later shown to be equivalent to the underlying mechanism

neg: Electric current loses its magnetism immediately. Electric current produces a magnetic field. The magnetic field can be visualized as a pattern of circular field lines surrounding the wire that persists as long as there is current. Magnetism can also produce electric currents. When a changing magnetic field is applied to a conductor, an Electromotive force (EMF) is produced, and when there is a suitable path, this causes current. Electric current can be directly measured with a galvanometer, but this method involves breaking the electrical circuit, which is sometimes inconvenient. Current can also be measured without breaking the circuit by detecting the magnetic

neg: Maxwell's equations by a static (charge induced) electric field. This aspect of electromagnetic induction is the operating principle behind many electric generators: for example, a rotating bar magnet creates a changing magnetic field, which in turn generates an electric field in a nearby wire. Ampère's law with Maxwell's addition states that magnetic fields can be generated in two ways: by electric current (this was the original "Ampère's law") and by changing electric fields (this was "Maxwell's addition", which he called displacement current). In integral form, the magnetic field induced around any closed loop is proportional to the electric current plus displacement current

neg: Magnetic current can be mathematically replaced by an equivalent distribution of magnetic current. This artifice can be used to simplify some electromagnetic field problems. It is possible to use both electric current densities and magnetic current densities in the same analysis. The direction of the electric field produced by magnetic currents is determined by the left-hand rule (opposite direction as determined by the right-hand rule) as evidenced by the negative sign in the equation Magnetic displacement current or more properly the magnetic displacement current density is the familiar term where The electric vector potential, F, is computed from the magnetic current density,

neg: Excitation (magnetic) the shaft, such as the thyristor rectifiers and chopper interfaces . Excitation (magnetic) An electric generator or electric motor consists of a rotor spinning in a magnetic field. The magnetic field may be produced by permanent magnets or by field coils. In the case of a machine with field coils, a current must flow in the coils to generate the field, otherwise no power is transferred to or from the rotor. The process of generating a magnetic field by means of an electric current is called excitation. Field coils yield the most flexible form of magnetic flux regulation and de-regulation,

neg: Hall effect voltage. A radial current through a circular disc, subjected to a magnetic field perpendicular to the plane of the disc, produces a "circular" current through the disc. The absence of the free transverse boundaries renders the interpretation of the Corbino effect simpler than that of the Hall effect. Hall effect The Hall effect is the production of a voltage difference (the Hall voltage) across an electrical conductor, transverse to an electric current in the conductor and to an applied magnetic field perpendicular to the current. It was discovered by Edwin Hall in 1879. For clarity, the original effect is sometimes

neg: Galvanometer of measuring electric current. The earliest galvanometer was reported by Johann Schweigger at the University of Halle on 16 September 1820. André-Marie Ampère also contributed to its development. Early designs increased the effect of the magnetic field generated by the current by using multiple turns of wire. The instruments were at first called "multipliers" due to this common design feature. The term "galvanometer," in common use by 1836, was derived from the surname of Italian electricity researcher Luigi Galvani, who in 1791 discovered that electric current would make a dead frog's leg jerk. Originally, the instruments relied on the Earth's

neg: Skin effect charge carriers constituting that current, usually electrons, are driven by an electric field due to the source of electrical energy. An alternating current in a conductor produces an alternating magnetic field in and around the conductor. When the intensity of current in a conductor changes, the magnetic field also changes. The change in the magnetic field, in turn, creates an electric field which opposes the change in current intensity. This opposing electric field is called “counter-electromotive force” (back EMF). The back EMF is strongest at the center of the conductor, and forces the conducting electrons to the outside of the

neg: Electrical reactance the fact that an electric current produces a magnetic field around it. In the context of an AC circuit (although this concept applies any time current is changing), this magnetic field is constantly changing as a result of current that oscillates back and forth. It is this change in magnetic field that induces another electric current to flow in the same wire, in a direction such as to oppose the flow of the current originally responsible for producing the magnetic field (known as Lenz's Law). Hence, "inductive reactance" is an opposition to the change of current through an element. For

neg: Force mathematical character as Coulomb's Law with the proviso that like currents attract and unlike currents repel. Similar to the electric field, the magnetic field can be used to determine the magnetic force on an electric current at any point in space. In this case, the magnitude of the magnetic field was determined to be where formula_48 is the magnitude of the hypothetical test current and formula_49 is the length of hypothetical wire through which the test current flows. The magnetic field exerts a force on all magnets including, for example, those used in compasses. The fact that the Earth's magnetic

neg: Dynamo the metal, creating an electric current in the wire. On small machines the constant magnetic field may be provided by one or more permanent magnets; larger machines have the constant magnetic field provided by one or more electromagnets, which are usually called "field coils". The "commutator" is needed to produce direct current. When a loop of wire rotates in a magnetic field, the magnetic flux through it, and thus the potential induced in it, reverses with each half turn, generating an alternating current. However, in the early days of electric experimentation, alternating current generally had no known use. The few

neg: Magnetism field can be quickly changed by controlling the amount of electric current in the winding. However, unlike a permanent magnet that needs no power, an electromagnet requires a continuous supply of current to maintain the magnetic field. Electromagnets are widely used as components of other electrical devices, such as motors, generators, relays, solenoids, loudspeakers, hard disks, MRI machines, scientific instruments, and magnetic separation equipment. Electromagnets are also employed in industry for picking up and moving heavy iron objects such as scrap iron and steel. Electromagnetism was discovered in 1820. As a consequence of Einstein's theory of special relativity, electricity and

neg: Nonelectrostatic electric fields of induction, if the magnetic flux is changed through the loop, an emf will be induced in this. The magnetic flux may be changed by changing the area of the loop or by changing the magnetic field. Why a changing magnetic field produces current in the loop? The loop contains electrons, which don't feel magnetic field, but if the magnetic field changes, they feel it. It is customary to think that if in a given region magnetic field changes with time, an electric field is induced in this region, which causes motion of electrons in the loop. But, an electric

neg: Magnetic nozzle pressure being confined by the magnetic field gives rise to a diamagnetic drift, which is proportional to the pressure of electrons and inversely proportional to the magnetic field strength. Together with the formula_1 drift, the diamagnetic drift is responsible of the formation of an "azimuthal electric current" formula_2 in the plasma domain. This azimuthal electric current generates an induced magnetic field which opposes the applied one, generating a repulsive magnetic force formula_3 that pushes the plasma downstream. The reaction to this force is felt on the magnetic generator of the magnetic nozzle and is called magnetic thrust. This is the

neg: Johann von Lamont 1835, took his doctorate of philosophy in 1830 and became professor of astronomy in 1852 at Munich University. At the observatory he undertook the task of creating a star catalog that had about 35,000 entries. In 1845 he was elected an Honorary Fellow of the Royal Society of Edinburgh. His most important work was on the magnetism of the Earth. He performed magnetic surveys in Bavaria and northern Germany, France, Spain, and Denmark. He discovered a magnetic decennial period (ten-year cycle) and the electric current in the Earth closing the electric "circuit" creating the magnetic field in 1850. This roughly

neg: Eddy current the part of the sheet under the leading edge of the magnet "(left side)" the magnetic field through the sheet is increasing as it gets nearer the magnet, formula_1. From Faraday's law of induction, this creates a circular electric field in the sheet in a counterclockwise direction around the magnetic field lines. This field induces a counterclockwise flow of electric current "(I, red)", in the sheet. This is the eddy current. At the trailing edge of the magnet "(right side)" the magnetic field through the sheet is decreasing, formula_2, inducing a second eddy current in a clockwise direction in the

neg: Near-field electromagnetic ranging an electro-magnetic field ((E and H are the components E=electric and H=magnetic)) vary with distance around small antennas. This was first discovered by Heinrich Hertz and is formulated with Maxwell's field theory. Close to a small antenna, the electric and magnetic field components of a radio wave are 90 degrees out of phase. As the distance from the antenna increases, the EH phase difference decreases. Far from a small antenna in the far-field, the EH phase difference goes to zero. Thus a receiver that can separately measure the electric and magnetic field components of a near-field signal and compare their

neg: Equatorial electrojet in the E region of the Earth's ionosphere (100–130 km altitude), and a primary eastwards electric field near day-side magnetic equator, where the magnetic field is horizontal and northwards. This electric field gives a primary eastwards Pedersen current. E cross B drift results in a downwards Hall current, sustaining vertical charge separation across the depth of the ionosphere, giving an upwards secondary electric field and a secondary Pedersen current that is opposite to the primary Hall current. A secondary Hall current then reinforces the original Pedersen current. At about 110 km height, the integration of the current density gives a

neg: Electromagnetic coil Electromagnetic coil An electromagnetic coil is an electrical conductor such as a wire in the shape of a coil, spiral or helix. Electromagnetic coils are used in electrical engineering, in applications where electric currents interact with magnetic fields, in devices such as electric motors, generators, inductors, electromagnets, transformers, and sensor coils. Either an electric current is passed through the wire of the coil to generate a magnetic field, or conversely an external "time-varying" magnetic field through the interior of the coil generates an EMF (voltage) in the conductor. A current through any conductor creates a circular magnetic field around the

neg: Electricity at right angles to it. Ørsted's slightly obscure words were that "the electric conflict acts in a revolving manner." The force also depended on the direction of the current, for if the flow was reversed, then the force did too. Ørsted did not fully understand his discovery, but he observed the effect was reciprocal: a current exerts a force on a magnet, and a magnetic field exerts a force on a current. The phenomenon was further investigated by Ampère, who discovered that two parallel current-carrying wires exerted a force upon each other: two wires conducting currents in the same direction

neg: Displacement current ∂t" is necessary as a second source term which gives the correct magnetic field when the surface of integration passes between the capacitor plates. Because the current is increasing the charge on the capacitor's plates, the electric field between the plates is increasing, and the rate of change of electric field gives the correct value for the field B found above. In a more mathematical vein, the same results can be obtained from the underlying differential equations. Consider for simplicity a non-magnetic medium where the relative magnetic permeability is unity, and the complication of magnetization current (bound current) is absent,

neg: Magnetic particle inspection Magnetic particle inspection Magnetic particle Inspection (MPI) is a non-destructive testing (NDT) process for detecting surface and shallow subsurface discontinuities in ferromagnetic materials such as iron, nickel, cobalt, and some of their alloys. The process puts a magnetic field into the part. The piece can be magnetized by direct or indirect magnetization. Direct magnetization occurs when the electric current is passed through the test object and a magnetic field is formed in the material. Indirect magnetization occurs when no electric current is passed through the test object, but a magnetic field is applied from an outside source. The magnetic lines

neg: Electric machine are three types of transformers There are four types of transformers based on structure "Electromagnetic-rotor machines" are machines having some kind of electric current in the rotor which creates a magnetic field which interacts with the stator windings. The rotor current can be the internal current in a permanent magnet (PM machine), a current supplied to the rotor through brushes (Brushed machine) or a current set up in closed rotor windings by a varying magnetic field (Induction machine). "PM machines" have permanent magnets in the rotor which set up a magnetic field. The magnetomotive force in a PM (caused by

neg: Inductance Inductance In electromagnetism and electronics, inductance is the property of an electrical conductor by which a change in electric current through it induces an electromotive force (voltage) in the conductor. It is more accurately called "self-inductance". The same property causes a current in one conductor to induce an electromotive force in nearby conductors; this is called mutual inductance. Inductance is an effect caused by the magnetic field of a current-carrying conductor acting back on the conductor. An electric current through any conductor creates a magnetic field around the conductor. A changing current creates a changing magnetic field. From Faraday's law

neg: Bloch wave – MoM method the domain of the "i"-th current basis function, thereby completing the quadratic form) produces the "i"-th row of the matrix eigenvalue equation for a 3-dimensional array of PEC scatterers as: As in all MoM formulations, the reaction concept in electromagnetics (Rumsey [1954], Harrington [1961]) was used in obtaining this equation. The electric field boundary/continuity conditions are "tested" (or enforced) by being integrated against electric current basis functions (for dielectric structures, the magnetic field continuity conditions are additionally tested by being integrated against magnetic current basis functions), and this is how the electric (and magnetic) field boundary conditions are converted into

neg: Explosively pumped flux compression generator magnetic field surrounded by a correspondingly large electric current. The purpose of the flux generator can be either the generation of an extremely strong magnetic field pulse, or an extremely strong electric current pulse; in the latter case the closed conductor is attached to an external electric circuit. This technique has been used to create the most intense manmade magnetic fields on Earth; fields up to about 1000 teslas (about 1000 times the strength of a typical permanent magnet) can be created for a few microseconds. An external magnetic field (blue lines) threads a closed ring made of a perfect

neg: James Clerk Maxwell Foundation Electromagnetic Field, Maxwell defined electromagnetics in terms of 20 equations, later summarised in his 1873 book Treatise on Electricity and Magnetism. Hendrik Lorentz subsequently reinterpreted these as the fundamental equations of electrodynamics and Oliver Heaviside developed the notation we use today. The theory behind Maxwell's equations was the first grand unification theory of the forces of Nature as this theory united the electric and magnetic fields. A person who is stationary may experience only an electric field but a person who is in relative motion may experience an electric current and a magnetic field. Thus the one field (called the

neg: Electric field NMR Electric field NMR Electric field NMR (EFNMR) spectroscopy differs from conventional NMR in that a sample containing suitable nuclei is polarised by a strong dc electric field instead of a constant magnetic field. The nuclei are stimulated (perturbed) by means of an alternating magnetic field, generated by passing an alternating current through a set of coils. The resulting magnetic resonance signal is small, and as in conventional NMR is typically sensed using a second set of coils and an amplifier. The shifting and splitting of spectral lines of atoms and molecules due to the presence of an external static electric

neg: Magnetic field rotates to align itself with the first. In this example, the magnetic field of the stationary magnet creates a "magnetic torque" on the magnet that is free to rotate. This magnetic torque tends to align a magnet's poles with the magnetic field lines. A compass, therefore, turns to align itself with Earth's magnetic field. Magnetic torque is used to drive electric motors. In one simple motor design, a magnet is fixed to a freely rotating shaft and subjected to a magnetic field from an array of electromagnets. By continuously switching the electric current through each of the electromagnets, thereby flipping

neg: Induction hardening decreasing in the circuit. Faraday concluded that an electric current can be produced by a changing magnetic field. As there was no physical connection between the primary and secondary windings, the emf in the secondary coil was said to be "induced" and so Faraday's law of induction was born. Once discovered, these principles were employed over the next century or so in the design of dynamos (electrical generators and electric motors, which are variants of the same thing) and in forms of electrical transformers. In these applications, any heat generated in either the electrical or magnetic circuits was felt to

neg: Ampère's circuital law Ampère's circuital law In classical electromagnetism, Ampère's circuital law (not to be confused with Ampère's force law that André-Marie Ampère discovered in 1823) relates the integrated magnetic field around a closed loop to the electric current passing through the loop. James Clerk Maxwell (not Ampère) derived it using hydrodynamics in his 1861 paper "" and it is now one of the Maxwell equations, which form the basis of classical electromagnetism. The original form of Maxwell's circuital law, which he derived in his 1855 paper "On Faraday's Lines of Force" based on an analogy to hydrodynamics, relates magnetic fields to electric

neg: Electric field NMR field is referred to as the Stark effect. Electric field NMR Electric field NMR (EFNMR) spectroscopy differs from conventional NMR in that a sample containing suitable nuclei is polarised by a strong dc electric field instead of a constant magnetic field. The nuclei are stimulated (perturbed) by means of an alternating magnetic field, generated by passing an alternating current through a set of coils. The resulting magnetic resonance signal is small, and as in conventional NMR is typically sensed using a second set of coils and an amplifier. The shifting and splitting of spectral lines of atoms and molecules due

neg: Paleolightning charge is transferred to the ground via lightning channels, which carry a strong electric current. Because of the intensity of this electric current, when lightning hits the ground, it can produce a strong, albeit brief, magnetic field. Thus, as the electric current travels through soils, rocks, plant roots, etc., it locks a unique magnetic signature within these materials through a process known as lightning-induced remanent magnetization (LIRM). Evidence of LIRM is manifested in concentric magnetic field lines surrounding the location of the lightning strike point. LIRM anomalies normally occur close to the location of the lightning strike, usually encapsulated within

neg: Magnetic dipole Magnetic dipole A magnetic dipole is the limit of either a closed loop of electric current or a pair of poles as the dimensions of the source are reduced to zero while keeping the magnetic moment constant. It is a magnetic analogue of the electric dipole, but the analogy is not complete. In particular, a magnetic monopole, the magnetic analogue of an electric charge, has never been observed. Moreover, one form of magnetic dipole moment is associated with a fundamental quantum property—the spin of elementary particles. The magnetic field around any magnetic source looks increasingly like the field of a

neg: Neurostimulation not well understood. Developing DBS microelectrodes is still challenging. Compared to electrical stimulation that utilizes brief, high-voltage electric shock to activate neurons, which can potentially activate pain fibers, transcranial magnetic stimulation (TMS) was developed by Baker in 1985. TMS uses a magnetic wire above the scalp, which carries a sharp and high current pulse. A time variant magnetic field is induced perpendicular to the coil due to the applied pulse which consequently generates an electric field based on Maxwell's law. The electric field provides the necessary current for a non-invasive and much less painful stimulation. There are two TMS devices

neg: Magnetic field depicted in the figure. From outside, the ideal magnetic dipole is identical to that of an ideal electric dipole of the same strength. Unlike the electric dipole, a magnetic dipole is properly modeled as a current loop having a current and an area . Such a current loop has a magnetic moment of: where the direction of is perpendicular to the area of the loop and depends on the direction of the current using the right-hand rule. An ideal magnetic dipole is modeled as a real magnetic dipole whose area has been reduced to zero and its current increased to

neg: Fourier optics assumed that the unit vector in the z-direction points into the half-space where the far field calculations will be made. These equivalent magnetic currents are obtained using equivalence principles which, in the case of an infinite planar interface, allow any electric currents, J to be "imaged away" while the fictitious magnetic currents are obtained from twice the aperture electric field (see Scott [1998]). Then the radiated electric field is calculated from the magnetic currents using an equation similar to the equation for the magnetic field radiated by an electric current. In this way, a vector equation is obtained for the

neg: Magnetic field field combined with an electric field "can" distinguish between these, see Hall effect below. An alternative mnemonic to the right hand rule is Flemings's left hand rule. The formulas derived for the magnetic field above are correct when dealing with the entire current. A magnetic material placed inside a magnetic field, though, generates its own bound current, which can be a challenge to calculate. (This bound current is due to the sum of atomic sized current loops and the spin of the subatomic particles such as electrons that make up the material.) The -field as defined above helps factor out

neg: Electric generator electricity and frequently make acceptable manual generators. Electromagnetic generators fall into one of two broad categories, dynamos and alternators. Mechanically a generator consists of a rotating part and a stationary part One of these parts generates a magnetic field, the other has a wire winding in which the changing field induces an electric current The armature can be on either the rotor or the stator, depending on the design, with the field coil or magnet on the other part. Before the connection between magnetism and electricity was discovered, electrostatic generators were invented. They operated on electrostatic principles, by using moving

neg: Paleolightning several meters of the point of contact. The anomalies are generally linear or radial, which, just like actual lightning channels, branch out from a central point. It is possible to determine the intensity of the electric current from a lightning strike by examining the LIRM signatures. Since rocks and soils already have some preexisting magnetic field, the intensity of the electric current can be determined by examining the change between the "natural" magnetic field and the magnetic field induced by the lightning current, which generally acts parallel to the direction of the lightning channel. Another characteristic feature of an LIRM

neg: Inductance no ferromagnetic materials are nearby (no magnetic core). Inductance In electromagnetism and electronics, inductance is the property of an electrical conductor by which a change in electric current through it induces an electromotive force (voltage) in the conductor. It is more accurately called "self-inductance". The same property causes a current in one conductor to induce an electromotive force in nearby conductors; this is called mutual inductance. Inductance is an effect caused by the magnetic field of a current-carrying conductor acting back on the conductor. An electric current through any conductor creates a magnetic field around the conductor. A changing current

neg: Electron quasi-electrons—quasiparticles, which have the same electrical charge, spin, and magnetic moment as real electrons but might have a different mass. When free electrons—both in vacuum and metals—move, they produce a net flow of charge called an electric current, which generates a magnetic field. Likewise a current can be created by a changing magnetic field. These interactions are described mathematically by Maxwell's equations. At a given temperature, each material has an electrical conductivity that determines the value of electric current when an electric potential is applied. Examples of good conductors include metals such as copper and gold, whereas glass and Teflon

neg: Earth's magnetic field the core (planetary differentiation, the iron catastrophe) as well as decay of radioactive elements in the interior. The pattern of flow is organized by the rotation of the Earth and the presence of the solid inner core. The mechanism by which the Earth generates a magnetic field is known as a dynamo. The magnetic field is generated by a feedback loop: current loops generate magnetic fields (Ampère's circuital law); a changing magnetic field generates an electric field (Faraday's law); and the electric and magnetic fields exert a force on the charges that are flowing in currents (the Lorentz force). These

neg: Ampère's circuital law circuital equation is extended by including the polarization current, thereby remedying the limited applicability of the original circuital law. Treating free charges separately from bound charges, The equation including Maxwell's correction in terms of the -field is (the -field is used because it includes the magnetization currents, so does not appear explicitly, see -field and also Note): (integral form), where is the magnetic field (also called "auxiliary magnetic field", "magnetic field intensity", or just "magnetic field"), is the electric displacement field, and is the enclosed conduction current or free current density. In differential form, On the other hand, treating all

neg: Dipole there are magnetic dipoles in the form of the quantum-mechanical spin associated with particles such as electrons (although the accurate description of such effects falls outside of classical electromagnetism). A theoretical magnetic "point dipole" has a magnetic field of exactly the same form as the electric field of an electric point dipole. A very small current-carrying loop is approximately a magnetic point dipole; the magnetic dipole moment of such a loop is the product of the current flowing in the loop and the (vector) area of the loop. Any configuration of charges or currents has a 'dipole moment', which describes

neg: Inductance or helix of wire. The term "inductance" was coined by Oliver Heaviside in 1886. It is customary to use the symbol formula_1 for inductance, in honour of the physicist Heinrich Lenz. In the SI system, the unit of inductance is the henry ("H"), which is the amount of inductance which causes a voltage of 1 volt when the current is changing at a rate of one ampere per second. It is named for Joseph Henry, who discovered inductance independently of Faraday. Electric circuits which are located close together, so the magnetic field created by the current in one passes through

neg: Magnetic moment be a force, proportional to the magnetic field gradient, acting on the magnetic moment itself. There are two expressions for the force acting on a magnetic dipole, depending on whether the is a current loop or two monopoles (analogous to the electric dipole). The force obtained in the case of a current loop model is In the case of a pair of monopoles being used (i.e. electric dipole model), the force is And one can be put in terms of the other via the relation In all these expressions is the dipole and is the magnetic field at its position.

neg: Magnetic field magnetic field. It is often claimed that the magnetic force can do work to a non-elementary magnetic dipole, or to charged particles whose motion is constrained by other forces, but this is incorrect because the work in those cases is performed by the electric forces of the charges deflected by the magnetic field. The force on a current carrying wire is similar to that of a moving charge as expected since a current carrying wire is a collection of moving charges. A current-carrying wire feels a force in the presence of a magnetic field. The Lorentz force on a macroscopic

neg: Curie–Weiss law will experience in an external magnetic field. A loop of electric current, a bar magnet, an electron, a molecule, and a planet all have magnetic moments. The magnetization or magnetic polarization of a magnetic material is the vector field that expresses the density of permanent or induced magnetic moments. The magnetic moments can originate from microscopic electric currents caused by the motion of electrons in individual atoms, or the spin of the electrons or the nuclei. Net magnetization results from the response of a material to an external magnetic field, together with any unbalanced magnetic moment that may be present

neg: Magnetic potential is the four-current. The first equation is the Lorenz gauge condition while the second contains Maxwell's equations. The four-potential also plays a very important role in quantum electrodynamics. The scalar potential is another useful quantity in describing the magnetic field, especially for permanent magnets. In a simply connected domain where there is no free current, hence we can define a "magnetic scalar potential", "ψ", as Using the definition of H: it follows that Here, acts as the source for magnetic field, much like acts as the source for electric field. So analogously to bound electric charge, the quantity is called

neg: Critical field increases generally to a maximum at absolute zero. For a Type I superconductor the discontinuity in heat capacity seen at the superconducting transition is generally related to the slope of the critical field (formula_1) at the critical temperature (formula_2): There is also a direct relation between the critical field and the critical current - the maximum electric current density that a given superconducting material can carry, before switching into the normal state. According to Ampère's law any electric current induces a magnetic field, but superconductors exclude that field. On a microscopic scale the magnetic field is not quite zero at

neg: Electromagnet Electromagnet An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. The magnetic field disappears when the current is turned off. Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in the hole in the center of the coil. The wire turns are often wound around a magnetic core made from a ferromagnetic or ferrimagnetic material such as iron; the magnetic core concentrates the magnetic flux and makes a more powerful magnet. The main advantage of an electromagnet over a

neg: Electromagnetic field that any case that seems to consist of a "pure" static electric or magnetic field, can be converted to an EM field, with both E and M components present, by simply moving the observer into a frame of reference which is moving with regard to the frame in which only the “pure” electric or magnetic field appears. That is, a pure static electric field will show the familiar magnetic field associated with a current, in any frame of reference where the charge moves. Likewise, any new motion of a charge in a region that seemed previously to contain only a

neg: Current density to the net movement of electric dipole moments per unit volume, i.e. the polarization P: Similarly with magnetic materials, circulations of the magnetic dipole moments per unit volume, i.e. the magnetization M, lead to magnetization currents: Together, these terms add up to form the bound current density in the material (resultant current due to movements of electric and magnetic dipole moments per unit volume): The total current is simply the sum of the free and bound currents: There is also a displacement current corresponding to the time-varying electric displacement field D: which is an important term in Ampere's circuital law,

neg: Inductive discharge ignition around an iron magnetic core that more or less channels the magnetic field through the loop of wire. As the current flows, the wire loops develop their own magnetic field, which takes a certain amount of energy to form. The magnetic field is a type of potential energy. There is usually some sort of device that opens and closes the circuit called a contact breaker, points or an ignitor. As the points or ignitor open, the current ceases flowing, and the magnetic field collapses. The energy stored in the magnetic field is released in the form of increased electric voltage

neg: Transcranial magnetic stimulation Transcranial magnetic stimulation Transcranial magnetic stimulation (TMS) is a form of neurostimulation. TMS is a non-invasive procedure in which a changing magnetic field is used to cause electric current to flow in a small targeted region of the brain via electromagnetic induction. During a TMS procedure, a magnetic field generator, or "coil", is placed on the scalp. The coil is connected to a pulse generator, or stimulator, that delivers a changing electric current to the coil. TMS is used diagnostically to measure the connection between the central nervous system and skeletal muscle to evaluate damage in a wide variety of

neg: Electricity an electric field, and a time-varying electric field was a source of a magnetic field. Thus, when either field is changing in time, then a field of the other is necessarily induced. Such a phenomenon has the properties of a wave, and is naturally referred to as an electromagnetic wave. Electromagnetic waves were analysed theoretically by James Clerk Maxwell in 1864. Maxwell developed a set of equations that could unambiguously describe the interrelationship between electric field, magnetic field, electric charge, and electric current. He could moreover prove that such a wave would necessarily travel at the speed of light, and

neg: Magnetic field formed around an iron core may act as an "electromagnet", generating a strong, well-controlled magnetic field. An infinitely long cylindrical electromagnet has a uniform magnetic field inside, and no magnetic field outside. A finite length electromagnet produces a magnetic field that looks similar to that produced by a uniform permanent magnet, with its strength and polarity determined by the current flowing through the coil. The magnetic field generated by a steady current (a constant flow of electric charges, in which charge neither accumulates nor is depleted at any point) is described by the "Biot–Savart law": where the integral sums over

neg: Solar dynamo Solar dynamo The solar dynamo is the physical process that generates the Sun's magnetic field. A dynamo, essentially a naturally occurring electric generator in the Sun's interior, produces electric currents and a magnetic field, following the laws of Ampère, Faraday and Ohm, as well as the laws of hydrodynamics, which together form the laws of magnetohydrodynamics. The detailed mechanism of the solar dynamo is not known and is the subject of current research. A dynamo converts kinetic energy into electric-magnetic energy. An electrically conducting fluid with shear or more complicated motion, such as turbulence, can temporarily amplify a magnetic field

neg: Rotor (electric) to aid stamping conductor slots to specific shapes and sizes. As currents travel through the wire coil a magnetic field is created around the core, which is referred to as field current. The field current strength controls the power level of the magnetic field. Direct current (DC) drives the field current in one direction, and is delivered to the wire coil by a set of brushes and slip rings. Like any magnet, the magnetic field produced has a north and a south pole. The normal clockwise direction of the motor that the rotor is powering can be manipulated by using

neg: Covariant formulation of classical electromagnetism or particles: The signs in the following tensor analysis depend on the convention used for the metric tensor. The convention used here is +−−−, corresponding to the Minkowski metric tensor: The electromagnetic tensor is the combination of the electric and magnetic fields into a covariant antisymmetric tensor whose entries are B-field quantities. and the result of raising its indices is where E is the electric field, B the magnetic field, and "c" the speed of light. The four-current is the contravariant four-vector which combines electric charge density "ρ" and electric current density j: The electromagnetic four-potential is a covariant four-vector

neg: Transcranial magnetic stimulation the magnetic field pulse at a targeted area of the brain, one can either depolarize or hyperpolarize neurons in the brain. The magnetic flux density pulse generated by the current pulse through the coil causes an electric field as explained by the Maxwell-Faraday equation, formula_2 . This electric field causes a change in the transmembrane current of the neuron, which leads to the depolarization or hyperpolarization of the neuron and the firing of an action potential. The exact details of how TMS functions are still being explored. The effects of TMS can be divided into two types depending on the

neg: Photomagnetic effect Photomagnetic effect The magnetic effect is a theoretical quantum mechanical effect discovered by the researchers Samuel L. Oliveira and Stephen C. Rand at University of Michigan 2007–2011. The researchers have discovered a powerful magnetic interaction between the photons dynamic magnetic field – and certain isolator materials atoms magnetic moment, that is 100 million times stronger than formerly anticipated. Under the proper circumstances, the photons magnetic fields effect is as strong as their electric field – as e.g. in solar cells. The discovery is a surprise, because it is not straightforward to derive the strong magnetic effect from the physical equations,

neg: Biot–Savart law and Félix Savart, who discovered this relationship in 1820. The Biot–Savart law is used for computing the resultant magnetic field B at position r in 3D-space generated by a "steady" current "I" (for example due to a wire). A steady (or stationary) current is a continual flow of charges which does not change with time and the charge neither accumulates nor depletes at any point. The law is a physical example of a line integral, being evaluated over the path "C" in which the electric currents flow (e.g. the wire). The equation in SI units is In a "non"-magnetostatic situation,

neg: Electric machine by building up electric charge. Early types were friction machines, later ones were influence machines that worked by electrostatic induction. The Van de Graaff generator is an electrostatic generator still used in research today. "Homopolar machines" are true DC machines where current is supplied to a spinning wheel through brushes. The wheel is inserted in a magnetic field, and torque is created as the current travels from the edge to the centre of the wheel through the magnetic field. For optimized or practical operation of electric machines, today's electric machine systems are complemented with electronic control. Electric machine In electrical

neg: Magnetic circuit group of compatible analogies used to model systems across multiple energy domains. Magnetic reluctance, or magnetic resistance, is analogous to resistance in an electrical circuit (although it does not dissipate magnetic energy). In likeness to the way an electric field causes an electric current to follow the path of least resistance, a magnetic field causes magnetic flux to follow the path of least magnetic reluctance. It is a scalar, extensive quantity, akin to electrical resistance. The total reluctance is equal to the ratio of the MMF in a passive magnetic circuit and the magnetic flux in this circuit. In an

neg: Geomagnetically induced current Earth structure using magnetotellurics, but it also creates a hazard. This geomagnetic hazard is primarily a risk to technology under the Earth's protective atmospheric blanket. A time-varying magnetic field external to the Earth induces telluric currents—electric currents in the conducting ground. These currents create a secondary (internal) magnetic field. As a consequence of Faraday's law of induction, an electric field at the surface of the Earth is induced associated with time variations of the magnetic field. The surface electric field causes electrical currents, known as geomagnetically induced currents (GIC), to flow in any conducting structure, for example, a power or

neg: Electric-field integral equation Electric-field integral equation The electric-field integral equation is a relationship that allows the calculation of an electric field (E) generated by an electric current distribution (J). When all quantities in the frequency domain are considered, a time-dependency formula_1 that is suppressed throughout is assumed. Beginning with the Maxwell equations relating the electric and magnetic field an assuming linear, homogeneous media with permeability formula_2 and permittivity formula_3: Following the third equation involving the divergence of H by vector calculus we can write any divergenceless vector as the curl of another vector, hence where A is called the magnetic vector potential. Substituting

neg: Pulsed field magnet current, with time between the pulses to allow the heat to dissipate, stronger currents can be used and thus stronger magnetic fields can be generated. The magnetic field produced by pulsed field magnets can reach between 50 and 100 T, and lasts several tens of milliseconds. Pulsed field magnet A pulsed field magnet is a strong electromagnet which is powered by a brief pulse of electric current through its windings rather than a continuous current, producing a brief but strong pulse of magnetic field. Pulsed field magnets are used in research in fields such as materials science to study the

neg: Magnetism response of a paramagnet, but much larger. An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. The magnetic field disappears when the current is turned off. Electromagnets usually consist of a large number of closely spaced turns of wire that create the magnetic field. The wire turns are often wound around a magnetic core made from a ferromagnetic or ferrimagnetic material such as iron; the magnetic core concentrates the magnetic flux and makes a more powerful magnet. The main advantage of an electromagnet over a permanent magnet is that the magnetic

neg: Spin Hall effect of a sample carrying electric current. The opposing surface boundaries will have spins of opposite sign. It is analogous to the classical Hall effect, where "charges" of opposite sign appear on the opposing lateral surfaces in an electric-current carrying sample in a magnetic field. In the case of the classical Hall effect the charge build up at the boundaries is in compensation for the Lorentz force acting on the charge carriers in the sample due to the magnetic field. No magnetic field is needed for the SHE which is a purely spin-based phenomenon. The SHE belongs to the same family

neg: Electric motor monk Andrew Gordon and American experimenter Benjamin Franklin in the 1740s. The theoretical principle behind them, Ampère's force law, was discovered by André-Marie Ampère in 1820. The law described the production of mechanical force by the interactions of an electric current and a magnetic field. The conversion of electrical energy into mechanical energy by electromagnetic means was demonstrated by English scientist Michael Faraday in 1821. A free-hanging wire was dipped into a pool of mercury, on which a permanent magnet (PM) was placed. When a current was passed through the wire, the wire rotated around the magnet, showing that the

neg: Multipolarity of gamma radiation number. Electric and magnetic multipole radiations of the same order formula_1 (i.e., dipole, or quadrupole...) carry the same angular momentum formula_1 (in units of formula_6), but differ in parity. The following relations hold for formula_15: The designation ""electric" multipole radiation" seems appropriate since the major part of that radiation is produced by the charge density in the source; conversely, the ""magnetic" multipole radiation" is mainly due to the current density of the source. In electric multipole radiation, the electric field has a radial component; in magnetic multipole radiation, the magnetic field has a radial component. An example: in the simplified

neg: Heliospheric current sheet due to the magnetic tension force. During solar maximum the entire magnetic field of the sun flips, thus alternating the polarity of the field every solar cycle. The heliospheric current sheet rotates along with the Sun with a period of about 25 days, during which time the peaks and troughs of the skirt pass through the Earth's magnetosphere, interacting with it. Near the surface of the Sun, the magnetic field produced by the radial electric current in the sheet is of the order of 5×10 T. The magnetic field at the surface of the Sun is about 10 teslas. If

neg: Interplanetary magnetic field to the Earth-Sun line, though this angle varies with solar wind speed. The angle of the IMF to the radial direction reduces with helio-latitude, as the speed of the photospheric foot point is reduced. Depending on the polarity of the photospheric foot point, the heliospheric magnetic field spirals inward or outward; the magnetic field follows the same shape of spiral in the northern and southern parts of the heliosphere, but with opposite field direction. These two magnetic domains are separated by a two current sheet (an electric current that is confined to a curved plane). This heliospheric current sheet has

neg: Displacement current Displacement current In electromagnetism, displacement current density is the quantity appearing in Maxwell's equations that is defined in terms of the rate of change of , the electric displacement field. Displacement current density has the same units as electric current density, and it is a source of the magnetic field just as actual current is. However it is not an electric current of moving charges, but a time-varying electric field. In physical materials (as opposed to vacuum), there is also a contribution from the slight motion of charges bound in atoms, called dielectric polarization. The idea was conceived by James

neg: Electric motor The magnetizing current increases with the air gap. For this reason, the air gap should be minimal. Very small gaps may pose mechanical problems in addition to noise and losses. Windings are wires that are laid in coils, usually wrapped around a laminated soft iron magnetic core so as to form magnetic poles when energized with current. Electric machines come in two basic magnet field pole configurations: "salient-" and "nonsalient-pole" configurations. In the salient-pole machine the pole's magnetic field is produced by a winding wound around the pole below the pole face. In the "nonsalient-pole", or distributed field, or round-rotor,

neg: Electrification current, the distribution of alternating current soon became the most favored option. The main advantages of AC were that it could be transformed to high voltage to reduce transmission losses and that AC motors could easily run at constant speeds. Alternating current technology was rooted in Michael Faraday 1830–31 discovery that a changing magnetic field can induce an electric current in a circuit. The first person to conceive of a rotating magnetic field was Walter Baily who gave a workable demonstration of his battery-operated polyphase motor aided by a commutator on June 28, 1879 to the Physical Society of London.

neg: Condensed matter physics William Shockley developed the first semiconductor-based transistor, heralding a revolution in electronics. In 1879, Edwin Herbert Hall working at the Johns Hopkins University discovered a voltage developing across conductors transverse to an electric current in the conductor and magnetic field perpendicular to the current. This phenomenon arising due to the nature of charge carriers in the conductor came to be termed the Hall effect, but it was not properly explained at the time, since the electron was experimentally discovered 18 years later. After the advent of quantum mechanics, Lev Landau in 1930 developed the theory of Landau quantization and laid

neg: Geomagnetic storm Geomagnetic storm A geomagnetic storm (commonly referred to as a solar storm) is a temporary disturbance of the Earth's magnetosphere caused by a solar wind shock wave and/or cloud of magnetic field that interacts with the Earth's magnetic field. The increase in the solar wind pressure initially compresses the magnetosphere. The solar wind's magnetic field interacts with the Earth’s magnetic field and transfers an increased energy into the magnetosphere. Both interactions cause an increase in plasma movement through the magnetosphere (driven by increased electric fields inside the magnetosphere) and an increase in electric current in the magnetosphere and ionosphere. During

neg: Electromagnetic forming replacing the pusher in traditional forming. When the system releases its intense magnetic pulse , the coil generates a magnetic field which in turn accelerates the workpiece to hyper speed and onto the die. The magnetic pulse and the extreme deformation speed transforms the metal into a visco-plastic state – increasing formability without affecting the native strength of the material. See the magnetic pulse forming illustration for a visualization. A rapidly changing magnetic field induces a circulating electric current within a nearby conductor through electromagnetic induction. The induced current creates a corresponding magnetic field around the conductor (see Pinch (plasma

neg: Heliospheric current sheet the form of the field were a magnetic dipole, the strength would decrease with the cube of the distance, resulting in about 10 teslas at the Earth's orbit. The heliospheric current sheet results in higher order multipole components so that the actual magnetic field at the Earth due to the Sun is 100 times greater. The electric current in the heliospheric current sheet has a radial component (directed inward) as well as an azimuthal component, the radial circuit being closed by outward currents aligned with the Sun's magnetic field in the solar polar regions. The radial current in the circuit

neg: Hans Christian Ørsted and the German term "Gedankenversuch" in 1820. On 21 April 1820, during a lecture, Ørsted noticed a compass needle deflected from magnetic north when an electric current from a battery was switched on and off, confirming a direct relationship between electricity and magnetism. His initial interpretation was that magnetic effects radiate from all sides of a wire carrying an electric current, as do light and heat. Three months later he began more intensive investigations and soon thereafter published his findings, showing that an electric current produces a circular magnetic field as it flows through a wire. For his discovery, the

neg: Wireless power transfer Accelerating electric charges, such as are found in an alternating current (AC) of electrons in a wire, create time-varying electric and magnetic fields in the space around them. These fields can exert oscillating forces on the electrons in a receiving "antenna", causing them to move back and forth. These represent alternating current which can be used to power a load. The oscillating electric and magnetic fields surrounding moving electric charges in an antenna device can be divided into two regions, depending on distance "D" from the antenna. At large relative distance, the near-field components of electric and magnetic fields are