Experimental realization of aqueous double negative metamaterials in near-megahertz range

Abstract

Ultrasound is strongly attenuated and aberrated by the skull, principally due to the complex structure and acoustic impedance mismatch of skull which generates strong scattering. Analytical models and finite element methods have shown that negative index metamaterials matching skull properties can enable the transmission of US which enhances bidirectional transmission of ultrasonic signal for imaging. However, it is difficult to realize double-negative metamaterials in near-megahertz range experimentally because of the limitation of fabrication and characterization methods. Here we show the experimental realization of waterborne double negative acoustic metamaterials by coupling micrometer-size membrane-based negative density metamaterials with Helmholtz resonator-based negative modulus materials. Numerical simulation and experimental verification consistently exhibit the double negative behavior between 230 kHz and 410 kHz. We demonstrated the feasibility of creating ultrasonic-range metamaterials for non-invasive ultrasound imaging and neuron stimulation.