Non-Hermitian complementary acoustic metamaterials for lossy barriers

Complementary materials are designed for the suppression of strongly mismatched potential barriers to enhance wave transmission and reduce wavefront distortion through the barriers. In acoustics, complementary materials enable noninvasive brain imaging and the treatment of neural disorders by overcoming the high impedance mismatch layer that prevents ultrasound transmission. However, the porous skull layer possesses intrinsic loss that prohibits the effective use of complementary metamaterials alone. Here, we propose to apply a non-Hermitian complementary metamaterial (NHCMM) to counteract the impedance mismatch and energy attenuation effect of the skull to achieve high acoustic transmission at high frequencies. Our numerical study shows a near perfect, unidirectional transmission through the skull when the NHCMM is applied while preserving the imaging information and enhancing the acoustic energy at the focal point needed for focused ultrasound used for noninvasive therapies. The proposed acoustic NHCMM lays the foundation for noninvasive ultrasonic brain imaging through an intact skull by stimulating in-vivo deep brain circuitry research and treatments for neural disorders such as brain tumors and strokes.