Performance Assessment of a Single-Layer Metasurface Resonator for 3 T MRI

Metamaterials, in particular 2D metasurfaces, offer great potential to advance measurement efficiency in magnetic resonance imaging (MRI) and to overcome some limitations due to physiological restrictions that hamper technically feasible developments. In particular, the signal-to-noise ratio in MRI can be improved significantly in many applications. One major drawback, however, of MRI-compatible metamaterials is their usually bulky structure, which limits possible applications and does not allow for flexible or conformally fitted metamaterial layers. This problem can be overcome by flat stripe-shaped resonator unit cells in linear metasurfaces. Such unit cells need to be coupled capacitively, which implies multilayer designs. Here, we take the next step and investigate the use of interdigital capacitors to electrically elongate the wires composing a single-layer metasurface resonator. A comprehensive study of the fundamental mode, which is of particular interest for MRI, is presented. To that end, the on-bench performance of three prototypes are compared, two of which are designed with the help of structural parallel-plate capacitors on two layers, and the last using the interdigital, single-layer approach. Although the adoption of interdigital capacitors simplifies prototyping, we observe that the quality factor drops significantly. However, MRI experiments show promising results, leading to significant enhancement of the signal-to-noise ratio in the region of interest. Ultimately, single-layer structures open the possibility of flexible and conformal designs to optimally adapt to the patient’s body in MRI.