Demonstration of the lateral AC skin effect using a pickup coil

Abstract

We present a simple demonstration of the skin effect by observing the current distribution in a wide rectangular strip conductor driven at frequencies in the 0.25–5 kHz range. We measure the amplitude and phase of the current distribution as a function of the transverse position and find that they agree well with numerical simulations: The current hugs the edges of the strip conductor with a significant variation in phase across the width. The experimental setup is simple, uses standard undergraduate physics instructional laboratory equipment, and is easy to implement as a short in-class demonstration. Our study is motivated by modeling ac magnetic near fields in the vicinity of a rectangular trace on an atom chip.

Microwave Atom Chip Design

“…Numerical simulations are needed to obtain accurate estimates of the microstrip's near field mode. In particular, at high frequencies, the current tends to hug the trace edges due to the AC skin effect [20], which in turn tends to modify the near field at distances below the trace width. Furthermore, the proximity effect tends to modify the current distribution in neighboring traces (and image traces): in a single microstrip, the current hugs the bottom of the trace (it is attracted to the ground plane); for neighboring microstrips, in-phase currents tend to repel each other, while 180 • currents tend to attract.…”

“…For instance, thin wires are not good approximations for broad chip traces when traps are only one or two trace widths away. Additionally, the AC skin effect's adjustment of current density and phase within each trace [20] and the proximity effect between traces should be captured in proper near field calculations.…”