11/9/2022 0 Comments Fringe field effect![]() ![]() The magnetic coupling can be improved (but only by a small amount) by employing a “ magnetic reflector” in the form of magnetic core made typically out of soft ferrite or other suitable magnetic materials such as amorphous or nanocrystalline ribbon. k ≈ 0.2) 9), large magnetic reluctance, and large flux fringing between the coils. 8)īy the requirement of being “wireless” the coils have to be separated by some non-magnetic material (non-metallic casing of the device and the spacing through air) which contributes to significantly reduced magnetic coupling (e.g. In other words it can be said that the energy is transmitted in the near field (inductive coupling, rather than electromagnetic radiation in far field). Wireless charging can be accomplished by using magnetic coupling between the primary coil of the transmitter, and the secondary coil of the receiver. metal cases or supporting bars if placed within the space affected by the fringing flux. Similar losses will be developed in any other conductive parts, e.g. Eddy current loss is roughly proportional to the square of the thickness, so excessive losses can be produced by such high-amplitude planar eddy currents. Fringe field effect full#The amplitude of flux density is of the same order of magnitude as in the rest of the core, but for the perpendicular component of flux (normal to the surface) the active “thickness” of the lamination is equal to the full width of the strip. However, the fringing flux flows through all the sides, including those with large surface area of the laminations, as shown in Fig. The effective thickness of the laminations is usually chosen to produce manageable magnitude of eddy currents, to keep the total losses at acceptable level. On the edges of laminations the eddy currents will not exceed their normal amplitude, because the involved dimensions are the same and so is the flux density. Therefore, with the part of the winding placed away by approximately such distance the high-intensity magnetic field was not penetrating the windings any more, and the local copper loss was reduced drastically, so that the hot spot temperature decreased to almost the same as the rest of the winding. 4) This is visible in the simulation results in Fig. In practice, for a uniform air gap the high-intensity magnetic field due to the fringing flux is produced over a distance roughly equal to the length of the air gap. 2 the part of the winding subjected to the fringing flux operates at a temperature greater by 50☌ than the rest of the winding. The additional power loss might be small as compared to the total loss of the transformer or inductor, but it can locally create a high-temperature hot spot. 2, the part of the winding placed directly next to the air gap can be subjected to excessive heating caused only by the eddy currents in the copper wire. This also applies to windings which are made out of highly conductive materials like copper or aluminium. Such additional losses are exacerbated at higher frequencies - following the same principle as induction heating. Hence, there can be significant eddy currents generated in any conductive material placed in the volume of the fringing flux. The magnitude of fringing flux is relatively large, because of the concentration of the flux in the magnetic core. For simple cores it can be approximated by the following equation: 4) Relative permeability of air gap is $\mu_$ by which the inductance increases depends on the geometry of the magnetic core. The magnetic core is designed so that a well defined gap is placed in the magnetic circuit for storing energy in magnetic field.Īn air gap constitutes a magnetic discontinuity in the magnetic core. Flux fringing is especially pertinent to magnetic cores with an air gap, for instance in flyback transformers or PFC inductors. ![]()
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