An acoustic isolator-type metamaterial for ultrasound attenuation at MHz frequencies

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Stoakes, Rachel and Domingo-Roca, Roger and Feeney, Andrew and Windmill, James F.C. (2025) An acoustic isolator-type metamaterial for ultrasound attenuation at MHz frequencies. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. ISSN 0885-3010 (https://doi.org/10.1109/TUFFC.2025.3618617)

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Abstract

Acoustic metamaterials (AMMs) offer significant promise for ultrasound probe backing layers due to their capacity to enhance acoustic energy dissipation through tailored sub-wavelength structures. However, practical implementation remains challenging due to difficulties in reliably reproducing the micron-scale features required for MHz-frequency operation, and the lack of quality assurance processes linking design intent to fabricated performance. This work presents the evaluation of a 3D-printed acoustic isolator-type metamaterial (AI-MM) backing designed for MHz operation using a custom aluminum oxide resin. Directional transmission intensity measurements revealed frequency-dependent asymmetry in forward and backward wave propagation (in both experiments and simulations), consistent with passive acoustic isolator behavior. X-ray micro-CT imaging of AI-MM samples revealed dimensional deviations, apex rounding, and local density variation. Attenuation spectra showed that AI-MM backings consistently outperformed homogeneous controls in both simulation and experiment, with frequency-dependent trends indicating enhanced scattering and viscous losses. A local attenuation peak near 2.6 MHz was within the operational range estimated from the measured geometry (2.22–2.94 MHz), underscoring the importance of linking performance to real-world fabrication. These findings support the potential of AI-MMs as tunable passive components in ultrasound systems and highlight the need for integrated design, fabrication, and validation workflows.

ORCID iDs

Stoakes, Rachel, Domingo-Roca, Roger ORCID logoORCID: https://orcid.org/0000-0002-0557-5431, Feeney, Andrew and Windmill, James F.C. ORCID logoORCID: https://orcid.org/0000-0003-4878-349X;
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