Acoustic metamaterial optimization for megahertz frequencies

Acoustic metamaterials (AMMs) exhibit unique acoustic properties not found in conventional materials. Despite extensive research, applying AMMs in practice remains difficult, especially when translating mathematical models into functional devices. The challenge stems from the required manufacturing resolution for high frequency operation, where unit cell sizes must be scaled down to micrometer level. However, AMMs hold significant potential for applications where material size can be minimized without compromising performance, such as in the backing layers of ultrasound probes, which are essential components in medical ultrasound devices. A 3D-printable resin containing 60%wt aluminum oxide was developed to create acoustic diode-type metamaterial backing layers. These backing layers were experimentally (through-transmission tests) and theoretically (finite element analysis) evaluated and their reflection and transmission coefficients were compared to those of a homogeneous backing layer. This study marks a significant step towards advancing the fabrication and testing of AMMs for megahertz frequency applications such as medical ultrasound imaging.