If I lay a wide area, multi-turn loop coil on the floor and twist it over once into a figure 8, how does that affect the geometry and intensity of the radiated field?
Steve Randall
If I lay a wide area, multi-turn loop coil on the floor and twist it over once into a figure 8, how does that affect the geometry and intensity of the radiated field?
Steve Randall
It will make two adjacent loops with opposite directions of current flow, of course. You can work out the resulting magnetic field strength for yourself/
Chris
The radiated field is that of a dipole, and decreases rapidly with distance - IIRR as the fourth power of distance along the long axis of the 8 and even faster as you move away fro that axis.
-- Bill Sloman, Nijmegen
Not a dipole--the dipole moment cancels if the two loops are the same size. It's a quadrupole.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal
Third power.
Isn't the close-in field sort of toroidal?
John
Yes, although that's also true of a simple current loop. Putting two coils next to each other doesn't produce a very high coefficient of coupling, so it doesn't look much like a toroid toroid. The two opposing dipoles cancel out in the far field--all that's left is the quadrupole, which is two equal and opposite dipoles offset from each other.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal
r.
Maybe there are other, higher-order corrections; the figure-eight configuration doesn't have the exact symmetries of a pure quadrupole; that would require two figure-eights at right angles. The far-field will be dominated by quadrupole, but one cannot rule out some octopole or higher terms as small corrections.
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