Magnetic Flux Visualisations - Page 1
Forum section: electronics / beginners

author: John B
author_rank: Frequent Contributor
timestamp: July 06, 2017, 01:24:15 am
content: Hi, does anyone know of some good animations that show the expanding and collapsing magnetic fields in components such as in inductors, transformers etc. Most visualisations are either static, or show the north/south magnetic lines as rotating around a core (such as in a toroid). To me this was always an odd visualisation, as it did not represent the flux lines cutting through the conducting coil in a perpendicular manner.

author: cdev
author_rank: Super Contributor
timestamp: July 06, 2017, 01:27:43 am
content: ferrofluid is a liquid amalgamation of nanoscale particles of a magnetic material and some carrier, and it responds mechanically, physically to magnetic fields. So you may be able to have a physical demo of some concepts. I don't know if it would help you dramatize some concept. . Read up on it.Engineered nano-materials, including iron, are potentially hazardous.

author: Sceadwian
author_rank: Unknown
timestamp: July 06, 2017, 02:31:17 am
content: The construction of each device is so different there's very little to visualize, one of the things about those kind of magnetics is they're designed to have the flux confined to the core as much as is possible for RFI considerations as well as you want it coupled locally as much as you can rather than anything that actually 'gets out'

author: Circlotron
author_rank: Super Contributor
timestamp: July 06, 2017, 08:58:23 am
content: The flux stays confined to the core. It doesn't cut the wire. I think the varying flux created an electrostatic field that extends beyond the core. Someone else rather more skilled in the art will have to fill in the details.

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: July 06, 2017, 09:21:57 am
content: I don't have any pre-prepared animations to show you but many years ago now I was producing exactly this sort of thing for my final year uni project. I was designing fancy types of brushless motors. You can draw structures and simulate their magnetic behaviour with this free softwarehttp://www.femm.info/wiki/HomePageIt also has a scripting language so you can draw your system then have a script simulate it, output a picture of the field lines then move some part or change a current density somewhere then re-simulate and so on. Then you can compile these pictures in to an animated gif. It works really nicely.

author: Rerouter
author_rank: Super Contributor
timestamp: July 06, 2017, 09:34:38 am
content: It gets complex, you can treat magnetics like flux transmission lines, there can be reflections, dissipation losses, and other weird things like corner fringing,A magnetic feild does not immediatly form across the entire magnetic core, it builds much like a voltage down a transmission line, propagating through the core, expanding in flux density, like a voltage down a transmission line, instead of impedance, you have reluctance. which changes with temperature and frequency due to purity of materials. As the flux reaches a coil elsewhere on the core its much like a termination of the tranmission line, which can lead to a positive or negative reflection of the flux density, which can ring inside the core.Most of the math on these things varies with material combinations.Note that all wires on earth sit in its magnetic field, so its not like a bubble of field lines expanding and cutting the wires, rather the amount of field lines increases in density as the field strength in an area increases, this density change is what induces the current. effectively like changing electron density on a capacitor plate induces a voltage, changing the density of a magnetic field induces a current.A magnetic field never collapses, just is reduced to ambient density.

author: John B
author_rank: Frequent Contributor
timestamp: July 10, 2017, 03:48:24 am
content: I have taken on board the notion of changing flux density as being the mechanism by which current or voltage is induced (V= d Wb/ dt ). I have to query one of the above comments as stating the flux lines do not "cut" the wire, in fact my understanding is that only the perpendicular component of relative conductor/flux density motion is useful in inducing voltage. (Otherwise you only induce a slight voltage across the diameter of the wire, electrons sloshing side to side in the wire). Should flux lines be taken more like barometric pressure, or topological maps?It took me a while to respond as I thought it easiest to make a diagram. The last frame is like most diagrams where the flux lines are contained within the core, though I want to make sure my mental visualisations of the process is correct in transitions between increasing current, decreasing current, no current, then reversing current etc. For brevity I only represented one flux line. All the action seems to happen in the open middle of the core. As long as a wire goes through the middle, a varying magnetic field will induce the same voltage (same V= dWb/dt) whether the wire is in the middle of the hole or close to the core itself. (Again, another confusing aspect of common diagrams)I also think I have the polarity correct, the induced voltage must have an associated magnetic field that opposes the field that induces the current, in order to abide by the conservation of energy principle, and not to annoy Big Oil by tapping in the quantum vacuum energy of space

author: MrAl
author_rank: Super Contributor
timestamp: July 10, 2017, 05:55:16 pm
content: Hi,You should probably start from the basics. What that means is abandon the core constructions and turn to the single, straight wire where the operation becomes more apparent. Magnetic cores just complicate the issue. This is the way to start to learn any new theory. Start with the basics, then add complications later.With a single straight wire we have lines of flux encircling the wire. The circles would be symmetrical about the wire. From the time the first electron starts to move in the wire in classical theory the field emanates out to infinity, so the flux lines go out to infinity even though there is very little current right away. That means we have flux circles that are 1000's of meters in diameter, and some that are only nanometers in diameter. That means some circle are inside the wire and some circles are outside the wire.When we increase the current level, the density of these flux lines increases. That would be equivalent to generating more circles, and so we see a denser packing in the space around the wire. We can visualize this by thinking of circles that start at the center of the wire and get larger and larger. Although that's not yet the enire picture, it will suffice for now. So the circles get larger and larger but there are more smaller circles to take their place, and all having origin at the wire.So what happens when we decrease the current. When the current decreases, the circles start to collapse back onto the wire, and each line is said to 'cut' the wire in the way a knife might cut a loaf of bread. When a cricle gets small enough to match the diameter of the wire, it soon start to become smaller then the wire, and so it now resides again inside the wire, and that is considered "cutting' the wire. That is the point at which the back emf from that flux circle is generated.To get a slightly more clear picture of what is happening here we have to turn to the idea of a multi filament wire. That is a wire that is made up of a larger number of tiny filaments that run perfectly parallel to each other. Their total cross section matches the cross section of the original wire. This can be thought of as a simple multi strand wire, where each strand is in parallel to each other with no twisting.Now when the first circle falls back onto the wire, it first cuts the outer strands, and so only they generate a back emf. When they get even smaller then they cut the next smaller diameter of strands, and generate more back emf. This happens until they get back to a diameter of zero.There are some circles that are already inside the wire diameter, so they start generating back emf right away in the same manner.In this classical theory once current is applied to the wire the flux circles, with no other influence, would reach a diameter of infinity in zero time, but in real life it would take about 8 minutes for a flux ring to reach the Sun in our solar system. Since the field drops off so fast though as we get farther and farther away from the wire, it sometimes doesnt matter that much.The reaction of the current to the collapsing flux lines is known as "self inductance". It is equivalent to the number of flux lines that fall back onto the wire when the current is reduced to zero from a level of unity. Thus the self inductance is obtained by integrating all the flux lines from the axial center of the wire to infinity (and times a constant)