Skin Effect Estimation in Radiofrequency Coils for Nuclear Magnetic Resonance Applications

The design and development of dedicated radiofrequency (RF) coils is a fundamental task to maximize the signal-to-noise ratio (SNR) in nuclear magnetic resonance (NMR) applications. Coil resistance reduces the SNR and should be minimized by employing conductors of appropriate shape and cross section. At RF, the conductor resistance is increased due to the skin effect, which distributes the current primarily on the surface of the conductor instead of uniformly over the cross section. In particular, in rectangular shape conductors the current density is concentrated in the high-curvature area and increases the conductor resistance, while rounded conductors present lower resistance and demonstrate improvements in performance especially in low-frequency tuned coils. This paper summarizes the different methods for estimating conductor losses in RF coils for NMR applications, whose performance strongly affect quality data. Because the impact to coil loss from conductors with different cross-sectional area is not something generally recognized and nor addressed in many other coil design works, we believe the review could be interesting for researchers working in the field of NMR coil design and development.