Non-Hermitian complimentary acoustic metamaterials for imaging through skull

Abstract

Complimentary metamaterials are designed to facilitate full acoustic transmission through highly mismatched impedance barriers. Applied to biomedical acoustics, complimentary metamaterials theoretically enable unidirectional acoustic transmission through the skull to realize noninvasive brain imaging and facilitate neural ultrasound therapies. Previously designed complimentary acoustic metamaterials relied on the realization of negative material parameters opposite to that of the skull to cancel the impedance mismatch effect. However, much of the incident acoustic energy is dissipated due to the skull’s internal porosity, preventing full energy transmission. To resolve this issue, we propose to counteract the skull’s acoustic attenuating effects with a non-Hermitian complimentary metamaterial (NHCMM) having an active gain circuit to achieve high acoustic transmission at high frequencies. In addition to the full wave simulations showing near perfect transmission from either side of the skull, the NHCMM preserves imaging information for objects inside the skull, and enhances the focused acoustic energy used for focused ultrasound therapies. By facilitating two-way acoustic transmission through the skull with NHCMMs, we lay the foundation for noninvasive brain imaging and treatment for neural disorders.