Metastructures: From physics to application

Capolino, Filippo; Khajavikhan, Mercedeh; Alù, Andrea

doi:10.1063/5.0084696

Cited by 10 publications

(1 citation statement)

References 52 publications

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“…Bulk MM made up of three-dimensional (3D) arrays of elements have been explored for their use in MRI in the form of RF magnetic flux guides and lenses 9 – 22 . Compared to bulk MM, metasurfaces (MS) made up of two-dimensional (2D) arrays are a desirable alternative, as they are thin and flexible structures that are easier to manufacture and can provide the same performance as bulk structures in certain applications 23 . In the literature, MS have been proposed for application in MRI to provide local enhancement of the signal-to-noise ratio (SNR) of MRI coils 24 – 28 (SNR is the main figure of merit that assesses the quality of MRI).…”

Section: Introductionmentioning

confidence: 99%

Metasurfaces of capacitively loaded metallic rings for magnetic resonance imaging surface coils

Freire

2023

Sci Rep

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This work investigates the use of a metasurface made up of a two-dimensional array of capacitively loaded metallic rings to enhance the signal-to-noise ratio of magnetic resonance imaging surface coils and to tailor the magnetic near-field radio frequency pattern of the coils. It is found that the signal-to-noise ratio is increased if the coupling between the capacitively loaded metallic rings in the array is increased. The input resistance and the radiofrequency magnetic field of the metasurface loaded coil are numerically analyzed by means of an efficient algorithm termed the discrete model to determine the signal-to-noise ratio. Standing surface waves or magnetoinductive waves supported by the metasurface introduce resonances in the frequency dependence of the input resistance. The signal-to-noise ratio is found to be optimal at the frequency corresponding to a local minimum existing between these resonances.The discrete model is used in an optimization procedure to fit the structural parameters of a metasurface to enhance the signal-to-noise ratio at the frequency corresponding to this local minimum in the input resistance. It is found that the signal-to-noise ratio can be greatly improved if the mutual coupling between the capacitively loaded metallic rings of the array is made stronger by bringing them closer or by using rings of squared shape instead of circular. These conclusions derived from the numerical results provided by the discrete model are double-checked by means of numerical simulations provided by the commercial electromagnetic solver Simulia CST and by experimental results. Numerical results provided by CST are also shown to demonstrate that the surface impedance of the array of elements can be adjusted to provide a more homogeneous magnetic near-field radio frequency pattern that ultimately leads to a more uniform magnetic resonance image at a desired slice. This is achieved by preventing the reflection of propagating magnetoinductive waves at the edges of the array by matching the elements arranged at the edges of the array with capacitors of suitable value.

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