Acoustic Metamaterials

 Acoustic metamaterials are architected materials that have premade geometry that are designed to control the creation of acoustic or elastic waves through a medium. Scientists have studied acoustic materials through theory and complex computer models. Creation of these materials is restricted due to large size and low frequencies.

Carlos Portela ia the Robert N. Noyce Career Development Chair And the assistant professor of mechanical engineering at MIT. He reports, “ The multifunction of metamaterials, being simultaneously lightweight and strong while having tunable acoustic properties makes them great candidates for use in extreme condition engineering applications. But challenges in miniaturizing and characterizing acoustic metamaterials at high frequencies have hindered progress towards realizing advanced materials that have ultrasonic wave control capabilities.”

The paper was published in the journal, science advances, and entitled, “ Tailored ultrasound, propagation, and micro scale, metamaterials via inertia design.”

A large collaboration of scientists from MIT and others have created a framework for control of ultrasound, wave, propagation, and acoustic metamaterials.

Portela Works with the department of mechanical engineering at MIT. He reports, “ Our work proposes, a design frame work based on precisely positioning  microscale spheres, which tune how ultrasound waves travel through 3-D micro scale metamaterials. Specifically, we investigate how placing microscopic spherical masses within a metamaterial lattice affects how fast ultrasound waves travel throughout, ultimately leading to wave guiding or focusing responses.”

The team demonstrated tunable elastic wave velocities within microscale materials. This was through non-destructive, high through-put laser ultrasonic characterization. They use the different way velocities move to tune wave propagation in micro scale materials. Scientists also demonstrated an acoustic de-multiplexer. It is a device that separates one acoustic signal into multiple output signals.

Portela explains, “ Using simple, geometrical changes, this design framework expands the tunable, dynamic property space of metamaterials, enabling straightforward design, and fabrication of microscale, acoustic metamaterials and devices.

The framework is responsive to other fabrication techniques beyond the nano scale. It requires a single constituent material and one base 3-D geometry. This creates largely tunable properties.

Rachel Sun is the first author of the study. She summarizes, “ The beauty of this framework is that it fundamentally linked physical material properties to geometric features. By placing spherical masses on a spring like lattice, scaffold, we could create direct analogies for how mass affects quasi static stiffness and dynamic wave velocity. I realized that we could’ve obtained hundreds of different designs and corresponding material properties, regardless of whether we vibrated or slowly compressed the materials.”