Detunable Wire Metasurface for Applications in Magnetic Resonance Imaging

Abstract: We introduce a detunable wire metasurface that can electromagnetically couple to an external transmit coil to increase local magnetic resonance imaging (MRI) sensitivity while being almost transparent during excitation. The structure is implemented as an array of wires printed on a dielectric substrate inserted into high-permittivity dielectric blocks at both ends. Detuning is achieved by changing the effective electrical dimensions of the metasurface by inserting switchable nonmagnetic crossed diodes into each wire. We experimentally demonstrate that the metasurface is effectively passively switched off during the transmission by a high current flowing within the wires. During the reception, the currents are much lower; hence the metasurface remains switched on, increasing the local signal-to-noise ratio (SNR). Detuning the metasurface guarantees the patient’s safety and allows standard clinical calibration techniques. This nonlinear mechanism expands the functionalities of metasurfaces and is an essential step toward direct integration in MRI systems.