Design of Magnetic Cloak for Experiments in AC Regime

The magnetic shielding device causing only negligible distortion of external magnetic field is called the magnetic cloak. We have designed and tested cloaks with a coaxial bilayer structure where a superconducting cylindrical layer is placed inside the tube from a ferromagnetic material. Such object when inserted in the bore of a coil generating ac magnetic field should not change the coil's impedance. This experiment is suitable for checking the cloak performance in the ac regime by measuring the voltage on the coil terminations, particularly the change in its amplitude and phase. The impact on signal amplitude comes from the nonzero magnetic moments of the cloak components. Then, the opposite character of ferromagnetic and diamagnetic material can be used to suppress the response, e.g., by modifying the thickness of the ferromagnetic layer. On the other hand, the shift in the phase comes from the hysteresis behavior of both constituents, and their impacts are additive. We achieved decent results using the ferrite powder/epoxy composite for the outer tube and REBCO superconducting tapes for the inner cylinder. Numerical simulations and experimental verification were used to investigate the electromagnetic response at various geometrical arrangements of the superconducting part of the cloak.