I have two air coils. They both have diameter d. There is a distance D between their centres.
D is much greater than d (more than 10x greater)
Both coils are at different angles, a and b, relative to the line between their centers. There is an alternating current in one coil.
Is there some simple function which estimates the current induced in the second coil? I would be happy if the form of the function was:
k * f(D, a, b) (where k had to be measured)
For example: k * cos(a) * cos(b) * D^-2
Best Answer
I think you are looking for Ampere's law and Faraday's law, parts of Maxwell's equations.
For a distance D between coils much greater than the coil diameter, The voltage induced on the second coil from a given current on the input coil is something like
where
and in turn,
where
At long distances, the magnetic field (and hence the produced voltage) drops off with D^(-3).
"Microchip AN678: RFID Coil Design"
"Microchip microID(R) 125 kHz RFID System Design Guide"