Wireless deep-subwavelength metamaterial enabling sub-mm resolution magnetic resonance imaging

A wireless deep-subwavelength metamaterial architecture is proposed, modeled and demonstrated for a high-resolution magnetic resonance imaging (HR-MRI) application that is miniaturized to be resonant at approximately lambda(0)/1500 dimensions. The proposed structure has the adjustable resonance frequency from 65 MHz to 5.5 GHz for the sub-cm footprint area (8 mm x 8 mm for this study) and provides a quality factor (Q-factor) of approximately 80 in free space for 123 MHz of operation. This structure consists of a cross-via metallized partial-double-layer metamaterial, sandwiching a dielectric thin film; this structure strongly localizes the electric field in this film and has a highly capacitive metal overlay that allows for a wide range of frequency adjustment. Although the achieved resonance frequencies enable a large number of applications, as a proof-of-concept demonstration, we experimentally showed the operation of this wireless metastructure in HR-MRI to highlight its precise frequency adjustment and signal-to-noise-ratio (SNR) improvement capabilities. The proposed metamaterial was found to maintains high Q-factors despite loading with a body-mimicking lossy phantom. The experimental results indicated that the proposed metastructure can be used as an SNR-enhancing device offering 15-fold SNR enhancements that allows for imaging of objects as small as 200 mu m in diameter in its vicinity, at an unprecedented level of resolution at the given DC field using standard head coils. As a result of its deep-subwavelength miniaturization accompanied by reasonable Q-factor with outstanding resonance frequency adjustment capability, this class of metastructure is proved to be an excellent candidate for in vivo medical applications. (C) 2018 Elsevier B.V. All rights reserved.