AC resistance formula for bubble memory drive coils

A formula for the ac resistance of tightly wound, uniform field, multilayer coils is deduced. This type of coil is used to provide the drive field for bubble memories. The loading effects of the orthogonal coil and the enhancing effect of the bias magnet homogenizer found in these devices are not considered here. The formula is developed by first deriving an expression for the ac resistance of coils wound with square wire and then empirically adapting it to round wire. Agreement between the formula and ac resistances measured on one, two, and three layer coils is generally better than 10 percent. The formula is also found to agree with published data on single layer solenoids.