Magnetic cloak from superconducting/ferromagnetic composite
Both the superconducting (SC) and ferromagnetic (FM) materials in form of layers or shells have been widely used for magnetic shielding. It was demonstrated directly from Maxwell equations that a properly designed cylindrical SC/FM bilayer shell can exactly cloak uniform static magnetic fields. This theoretical assumption was experimentally confirmed in a device with centimeter dimensions. Easily accessible commercial materials have been utilized for its manufacturing: FeNiCr transformer core sheet and coated conductor tape from high-temperature superconductor YBCO cooled by liquid nitrogen (77 K). Our results show that the right combination of materials with suitable geometry yields shielding with no external distortion of applied field thus the magnetic invisibility .
Fig.: Interaction of static magnetic field applied in horizontal direction with the objects of tubular shape made from a) superconductor, b) ferromagnet, c) suitable combination of superconductor (inner tube) and ferromagnet (outer tube) compared with the reference case d) non-magnetic and non-superconducting materials. Outside the tube the distributions in c) and d) are quite similar, i.e. the combination of superconducting and ferromagnetic tube can shield its inner space without being detected by a magnetic field sensor outside.
Gömöry, F., Solovyov, M., Šouc, J., Navau, C., Camps, J.P., and Sanchez, A.: Experimental realization of a magnetic cloak, Science 335 (2012) 1466-1468