Auxetics-Inspired Tunable Metamaterials for Magnetic Resonance Imaging

TL;DR

This paper introduces auxetics-inspired, mechanically tunable metamaterials with negative Poisson's ratio, capable of frequency tuning and enhancing MRI signal-to-noise ratio through 3D-printed, deformable metallic helix arrays.

Contribution

It presents a novel design of auxetic metamaterials with tunable electromagnetic properties for MRI applications, demonstrated through experimental validation at clinical MRI frequencies.

Findings

Achieved ~20 MHz frequency shift during deformation.

Enabled ~4.5X increase in MRI SNR.

Validated in a 3.0 Tesla clinical MRI system.

Abstract

Auxetics refers to structures or materials with a negative Poisson's ratio, thereby capable of exhibiting counter-intuitive behaviors. Herein, auxetic structures are exploited to design mechanically tunable metamaterials in both planar and hemispherical configurations operating at megahertz (MHz) frequencies, optimized for their application to magnetic resonance imaging (MRI). Specially, the reported tunable metamaterials are composed of arrays of inter-jointed unit cells featuring metallic helices, enabling auxetic patterns with a negative Poisson's ratio. The deployable deformation of the metamaterials yields an added degree of freedom with respect to frequency tunability through the resultant modification of the electromagnetic interactions between unit cells. The metamaterials are fabricated using 3D printing technology and a ~20 MHz frequency shift of the resonance mode is enabled during deformation. Experimental validation is performed in a clinical (3.0 Tesla) MRI, demonstrating that the metamaterials enable a marked boost in radiofrequency (RF) field strength under resonance matched conditions, ultimately yielding a dramatic increase in the signal-to-noise ratio (SNR) (~ 4.5X) of MRI. The tunable metamaterials presented herein offer a novel pathway towards the practical utilization of metamaterials in MRI, as well as a range of other emerging applications.