Hysteresis loop of permalloy is very small and its related with losses. Magnetic Permeability of permalloy is very high and good heating can be obtained due to losses. Are there any other parameters that can influence the losses ?
What is the purpose of using hysteresis losses : heating means that you need a lot of losses. To make a transformer you need to reduce the losses?
Losses are related not only to the area of M-H hysteresis loop, but to eddy currents as well. This is why transformers' cores are not built from the single pieces but rather have a multilayer structure. Permalloy, in opposition to sintered ferrites, is a quite good electric conductor.
If you would like to melt a polymer by induction heating, you need heat by joule losses or magnetic hysteresis. so you need high losses to melt in less time
B-H loop as well as J-H loop or even M-H loop encompasses ALL the losses occuring in magnetic material, including the eddy current loss.
Any magnetic material can be heated up by magnetic losses provided that the magnetisation frequency is high enough. In the first approximation loss grows proportionally to the square of both flux density (B, J or M) and magnetisation frequency. So if high amplitude is maintained (e.g. close to the knee of the curve) then at high frequency all the materials will heat up, even soft ferrites which have very high resistivity (very small eddy currents).
For this reason the design of all HF transformers operating at frequencies higher than 100 kHz are loss limited (heating), not saturation limited.
Stan, your point of view may and should be contested. I was writing about hysteresis loop observed in quasitatic process, i.e. when the system remains in thermodynamic equilibrium. This is what is most often published (well, in practice the loops are almost equally frequently taken at 50 or 60 Hz excitation). There are no eddy curents then and the magnetization losses are perfectly equal to the area of M-H loop. Under excitation at non-zero frequency the system doesn't maintain the equlibrium state anymore, thus the classical thermodynamics (thermostatics) is no longer fully applicable. Even the shape of hysteresis loop changes and becomes frequency dependent then. In this situation you have many sources of losses, with eddy currents most easily coming to the mind. But there are other sources of losses, including acoustic emission strictly related to magnetostriction.
Besides, I would like to ask questioner to clarify his intention: is he interested in minimizing or maximizing the heating effects?
Marek, indeed in the strictest sense "hysteresis" should be applied under quasi-static conditions, but more often than not "hysteresis" is used by the non-purists to mean any B-H loop, also that under dynamic conditions.
The original question is not very precise...
It's really rather misty, what is the intention of the questioner. From his statement:
Magnetic Permeability of permalloy is very high and good heating can be obtained due to losses.
it seems that he really wants to exploit the high permeability of PY for heating - not very good idea, as losses are connected to the area of hysteresis loop (either dc or ac, see the above discussion of Stan and Marek) and not to directly to permeability. On the other hand PY is typical by low Hc (naturally connected to high permeability) and thus extremely low hysteresis losses. I recommend to consult any magnetician from the rather strong magnetic group at the University of Kaiserslautern for some basic information.
Your question is not easily comprehensible to say the least. Heating is due to losses, hysteresis, eddy current etc and this increases with the frequency employed. Permalloy was discovered exactly to get the opposite effects. So do not talk about this alloy and your problem- whatever it is?
The losses can be reduced to zero if one prepares a nanosintered ferrite block properly. I have observed 5 deggrees C of cooling with barium Ferrite.
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