what is astatical winding of inductors?

Question

inductors when placed together show mutual inductance.To prevent it, astatical winding is done...

Answer 1

You are quite right that adjacent inductors will couple into one another, much like a transformer. Furthermore, some manufacturers use a clockwise winding, whereas other manufacturers use a counterclockwise winding, such that the polarity of the coupling is unpredictable. I've had experience in an RF application where the effect was to detune the circuit. Our solution was to buy all the coils from the same manufacturer.

However, I believe that an inductor can be wound so that the net external field is canceled. Perhaps that is what you are referring to as an astatical winding. It's been awhile, and I don't recall the method. I don't think it is as simple as winding half the turns clockwise and half the turns counterclockwise, because it seems to me that the fields would cancel and the inductance would be much lower than desired.

Another solution to prevent mutual inductance, and one that we considered, is to use magnetically shielded coils. These coils have an outer sleeve of ferrite or iron that contain the magnetic field. We chose not to use them because of their higher cost.