Radio use inductors. Magnetic hysteresis and eddy current losses. - Page 1
Forum section: electronics / beginners

author: renzoms
author_rank: Regular Contributor
timestamp: November 24, 2019, 02:14:38 am
content: My textbook states “For radio use, inductors often have air cores to avoid losses caused by magnetic hysteresis and eddy current that occur within magnetic core-type inductors.” Then it doesn’t get into the topic, probably because it just introduced passive components and its entry stuff. I have questions about magnetic hysteresis and eddy currents.I have a graph of the typical hysteresis curve of a magnetic core. I get it. The core remains magnetized depending on what way it becomes saturated.And eddy current I could use some support with. Eddy currents arise when any conductor experiences a changing magnetic field and are created in any given loop in the conductor. The emf = dMagneticflux/dt. Then the eddy current I is equal to I = emf/R_loop_resistance.Questions: So if the iron core is like a permanent magnet after saturation and then the inductor sees a changing current the inductor experiences self induction equal to the sum of the cores alignment to the magnetic field created by the changing current seen by the inductor and the magnetic field created by the change in current. So it effects the self-induced voltage and the current passing through the circuit and so the power, current, and voltage everywhere in the circuit.Am i correct saying the rate of change of the magnetic flux experience by the inductor dM/dt is equal to the voltage across the inductor V_inductor = L dI/dt — like (emf = dMagneticFlux/dt)The self-induced voltage and its effect on the current passing through the inductor is proportional to the rate of change of magnetic flux that is now not aligning with the magnetic field created by the change in current like before2. What other losses are owed to magnetic hysteresis.Eddy currents: So there are losses due to heating because of the eddy currents? Materials with low resistivity experience higher eddy current losses.What are these losses i literally do not get it brain giving ou-Do they affect the current passing through the wire? the image I’m looking at shows them at the faces of the iron core of the inductor. Do they affect the self-induced voltage, the magnetic field created by the changing current seen by the inductorI don’t really get eddy currents. I see the pictures. I read some text and watched some videos. They still seem abstract and I don’t see where the losses are coming from and what they affect.Thank you for any help! I appreciate your effort.

author: unitedatoms
author_rank: Frequent Contributor
timestamp: November 24, 2019, 02:32:52 am
content: Eddy current losses are zero in ideal inductor. Now add secondary ideal coil, shorted, with finite resistance. This will work as transformer. There are two consequences, resistive loss and reduce of inductance of primary coil. For example in extreme case with fully coupled transformer and zero resistance, shorted secondary coil will subtract inductance completely, so the primary coil will become a zero ohm conductor with zero Henry.Now replace secondary ideal coil and resistor with simple resistor in series with single ideal primary coil. You will get equivalent circuit, depicting nature of losses. These are thermal losses.Another nonidealities is resistance of coil, even if it is an air coil. The reason Radio literature is talking about losses is not an energy concern, but the Q factor concern, because the filters made with lossy components will be more difficult to make as selective as ideal filters. Or perhaps if the topic is high power radio, then the losses are an energy concern too, together with selectivity.