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Metasurfaces are artificial electromagnetic boundaries or interfaces usuallyimplemented as two-dimensional periodic structures with subwavelengthperiodicity and engineered properties of constituent unit cells. Theelectromagnetic bandgap (EBG) effect in metasurfaces prevents all surface modesfrom propagating in a certain frequency band. While metasurfaces provide anumber of important applications in microwave antennas and antenna arrays,their features are also highly suitable for MRI applications. In this work wemanufacture and experimentally study finite samples based on mushroom-type EBGmetasurfaces and employ them for suppression of inter-element coupling indipole transmit coil arrays for body imaging at 7T. We show experimentally thatemployment of the samples EBG leads to reduction of coupling between adjacentclosely-spaced dipole antenna elements of a 7T transmit/receive body array,which reduces scattering losses in neighboring channels and thereby improvesthe B1+ efficiency. The setup consists of two fractionated dipole antennaspreviously designed by the authors for body imaging at 7 Tesla. These areplaced on top of a body-mimicking phantom and equipped with the manufacturedfinite-size sample of the metasurface tuned to have EBG properties at theLarmor frequency of 298 MHz. To improve the detection range of the B1+ fielddistribution of the top elements, four additional elements were positionedalong the bottom side of the phantom. Scattering matrix measurements show thatcoupling between the two top elements is indeed reduced while the measurementsperformed on a 7T MRI machine confirm the array's B1+ efficiency improvementdue to reduced scattering losses. This study provides a tool for the decouplingof dipole antennas in ultrahigh field transmit arrays, possibly resulting indenser element placement and/or larger subject-element spacing.

Element Decoupling of 7T Dipole Body Arrays by EBG Metasurface Structures: Experimental Verification