Investigation of Frequency-Dependent Effects in Inductive Coils for Implantable Electronics

In this paper, we investigated how frequency-related effects influence the resistance of inductive coils used in wireless links for implantable electronics. In particular, we studied proximity and skin effect by employing numerical simulation. In order to elicit these effects, simple three-turn coils with varying fill factors were studied. We found that proximity effect depends strongly on the fill-factor ratio. This is verified experimentally with a seven- and 17-turn coils of the same inner and outer diameter. We found that the coil with lower fill factor has better performance in terms of its quality factor at higher frequencies. A maximum Q increase of 29% was observed for the seven-turn coil compared to the 17-turn coil.