Auxetics‐Inspired Tunable Metamaterials for Magnetic Resonance Imaging. Issue 6 (19th December 2021)

• Record Type: Journal Article
• Authors: Wu, Ke; Zhao, Xiaoguang; Bifano, Thomas G.; Anderson, Stephan W.; Zhang, Xin
• Is Part Of: Advanced materials. Volume 34:Issue 6(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-12-19
• Subjects: auxetics -- magnetic coupling -- magnetic resonance imaging -- signal‐to‐noise ratio -- tunable metamaterials; Materials -- Periodicals; Chemical vapor deposition -- Periodicals; 620.11
• DOI: 10.1002/adma.202109032
• Languages: English
• ISSNs: 0935-9648

Abstract

Abstract: Auxetics refers to structures or materials with a negative Poisson's ratio, thereby capable of exhibiting counterintuitive 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 interjointed 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 an ≈20 MHz frequency shift of the resonance mode is enabled during deformation. Experimental validation is performed in a clinical (3.0 T) MRI system, demonstrating that the metamaterials enable a marked boost in radiofrequency field strength under resonance‐matched conditions, ultimately yielding a dramatic increase in the signal‐to‐noise ratio (≈4.5×) of MRI. The tunable metamaterials presented herein offer a novel pathway toward the practical utilization of metamaterials in MRI, as well as a range of other emerging applications. Abstract : Auxetics refers to structures or materials identified by a negative Poisson's ratio and exhibiting a counterintuitive geometrical behavior. Inspired by auxetics, mechanically tunable magnetic metamaterials in both planar and hemispherical configurations operating at megahertz frequencies are proposed, which serve to enhance local magnetic fields and increase signal‐to‐noise ratio (≈4.5×) in their application to magnetic resonance imaging.