field experts, which DD design is better

[Funfinder]

and why there isnt some kind of EM-shortcut
if the coils crosses each other?

[Funfinder]

Great job, guys.

Either you have forgotten this topic, all the Guru's are dissing me
or nobody here has the slightest clue about the important things!

[Carl-NC]

The one on the right side won't induction balance.

[IBGold]

Hi as Carl says the coils have to cross to get induction balance it is by varying the distance apart of the crossed loop that you achieve induction balance.

Regards, Ian.

[Davor]

Sorry Funfinder, I thought it was a trick question, but here are my 2 cents. Each coil has magnetic field inside going one way, say +, and outside field is going the other way, say -. While inside field is nicely concentrated, the outside field is dispersed. Encompassing the inside field is easy, while encompassing the outer field requires looooots of space. A balance is achieved when a larger portion of a Rx loop that is outside the Tx loop encompasses the same amount of field as the portion inside. In practice it is ~10% area.
Because coils are electrically insulated, and the magnetic portion is in antiseries, there is no EM shortcut but a nice balance.

[Skippy]

A simple way to understand the DD arrangement is to make one and play with it. Just slap together a pair of 6cm diameter circular coils, about 100 turns each. Feed 5KHz into one of them from a sig-gen, look at the output from the other on a scope, and move them around relative to each other.