Anomalous Losses in Thin Metal Shells Due to High-Frequency Magnetic Fields and Related Phenomena

Abstract

Losses in very thin metal shells induced by high-frequency electromagnetic fields have been analyzed. It has been shown, in addition to the existing literature, that the loss dependence on the shell thickness has both minima and maxima. The latter are attained at thicknesses two orders of magnitude smaller than skin depth, or at units of micrometers at several tens of kHz in aluminum and copper. In shielding applications, an inopportune choice of the shield may result in very high losses, bringing about shield overheat, melting, and even evaporation within fractions of a second. Both analytical and numerical analyses are presented, supported by an experimental demonstration. It is shown, in particular, that specific losses maximize with decreasing thickness, and remain independent of it after a certain threshold. It is also shown that even in moderate fields of the order of tens of kA/m specific losses can be so high that the energy of vaporization can be exceeded in milliseconds. Thus, useful applications of the noted effect can also be envisioned, especially in pulsed power, such as the controlled explosion of thin metal foils and films for circuit breaking, forming nanopowders, ultrafast local heating, etc. The obtained results are valid within the limitations of the macroscopic Maxwell equations.