The terminology scientists use is that monopoles single magnetic poles do not exist. The magnetic field lines are closed loops and must be continuous between a north and a south pole. In the case of a bar magnet, think of field lines exiting from the north pole, radiating through space, and re-entering the bar magnet at the south pole, continuing through the magnet back to the north pole.
Since these field lines must be continuous, they must find a way back to their origin. They cannot be stopped and have nowhere to go. The field lines can however be redirected. Therefore, it is possible to design a region of space relatively void of magnetic field lines because they have been redirected around that region. Note that you have not stopped them, just redirected them.
The field lines still must be continuous and eventually close back on themselves. In order to redirect magnetic field lines, you offer them a preferred path.
Magnetic field lines prefer to travel in materials that have certain magnetic properties, namely materials with high permeability. By placing a material of high permeability or at least a permeability higher than the region in question around the region you wish to shield, you effectively offer the field lines a better path to travel. The magnetic lines take that path and stay out of the region you wanted to shield. The high permeability material will "conduct" the magnetic field lines better than its original path.
While it is not the same phenomenon, this reminds us of the fact that electricity takes the path of least resistance. The field lines choose the easiest path to travel. Thus, a shell of high permeability material built around an area will effectively keep most of the magnetic field lines in the actual shell itself and out of the area inside the shell. While lead blocks or stops radioactive emissions such as beta particles or gamma rays, it does nothing to block magnetic fields.
The permeability of lead is low and has basically no affect on magnetic fields. Why Union? Yes, it is possible to guide magnetic field lines using a shaped magnetic material. Just as field lines concentrate when entering the south pole of a magnet from a large area, an external magnetic field can be "gathered" using, for example, a cone-shaped piece of iron. The cone can be positioned such that the static field spread over a large area enters the wide end of the cone.
The iron confines the field and will guide it to the tip of the cone, where it will emerge with a much higher density and, therefore, a much higher magnetic field strength. This will, of course, reduce the field to the sides of the cone, since this method won't increase the total magnetic field present in the region. The field lines that used to occupy that space are now simply confined inside the cone.
This is basically what a solenoid does. You have multiple current rings, and "within" the solenoid the magnetic field loops are concentrated whereas outside they are very weak and actually divergent in the limiting case. A much more interesting questions is if one could design a solenoid or solenoid like structure which "minimizes" the magnetic fields and currents "within" the sources wire loops while maximizing it in the region "outside" of the "sources" interior of the solenoid without any currents or sources.
This would have practical implications, since there are limits to how much current and magnetic fields materials which hold the currents can tolerate before they breakdown. It would be great if one could generate very large fields outside of the sources to say confine a magnetic fusion plasma, without breaking down structure containing the generating currents.
It is a much more difficult problem because you have to treat the field within the conductors themselves. I have thought about it fruitlessly for a while and would love to find someone who might have worked on this more. Perhaps it could not easily be solved analytically, but just like they are doing with antennas these says, perhaps, since the equations are already there, the deux ex machina of genetic algorithms might be useful if one could define all the parameters.
Also, there is perhaps a completely different approach than the solenoid one, that is a dynamical electromagnetic field. Since these can be self-propagating in the vaccuum, and one could theoretically focus a magnetic field outside of a source.
Technically, there would be far-field radiation in such cases, but not all cases. For example, Schott in discovered non-radiating solutions for spherically charged objects rotating at relativistic velocities. To my knowledge, no one has designed an object which could do this without such high velocities, but these kinds of problems have been solved before by a more clever design.
This is a one-time-only device. Using a 4" square piece of steel we had the machinist turn a flat cone 4" at the base and 1" at the top. I think it is possible to bent magnetic force of line. If the solenoid is straight the magnetic force line emits both of the two sides.
But we need to focus magnetic force line at a point. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
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