Non-Destructive Sensing Evaluations by Using a Passive Magnetic Metasurface

In this paper, we present a non-destructive sensing technique exploiting a response-controlled passive magnetic metasurface, excited by an active RF coil placed in its near-field region. We numerically designed a magnetic metasurface, working at 3 MHz, able to synthetize arbitrary magnetic field distributions, by modulating the currents (amplitude and phase) flowing on the metasurface unit-cells and on the exciting RF coil. In particular, the proposed configuration comprises a 5×5 matrix whose unit-cells are made of an 8-turn planar spiral coil, covering a 19 cm × 19 cm area. By performing accurate full-wave simulations, we demonstrated that by designing the metasurface so as to produce a focused field distribution, it is possible to detect and spatially identify a 1 cm radius ferromagnetic inclusion, in spite of the low-frequency herein employed. The findings suggest that response-controlled magnetic metasurfaces could be used in non-destructive sensing, also exploiting real-time reconfigurability to sequentially scan the region of interest.