Sonic Metamaterials for Acoustic Shaping (METASonic)

Virginia Commonwealth University   |  Jan 19, 2020

In this project students will develop sonic metamaterials and metastructures for the manipulation and shaping of acoustic waves. The focus of the project will be placed on broad spectrum acoustic focusing, acoustic impedance matching, and the exploration of resonant structures for impedance-matched acoustic cloaks, filters, and black holes. Students will design structures using simulation software (COMSOL Multiphysics) and then fabricate/test them in real-world conditions using 3-D printing technology. By using an acoustic platform for the project, students will be able to learn the principles of metamaterials and the sub-wavelength control of waves which can be directly related to microwaves and light without requiring expensive and time-consuming nanofabrication techniques.

Building from prior advances, students will finalize and test a design for an impedance matched acoustic lens designed using effective medium theory. This is accomplished by varying the ratios of two materials (plastic and air) within the lens body to manipulate the speed of sound propagation within the lens structure. However, due to the large impedance mismatch with air, the lens requires special matching which has been implemented in the form of impedance tapers. A prototype has been fabricated and will be tested using a custom build acoustics test stand. Moreover, students will begin the exploration of resonant acoustic metamaterial structures where the acoustic phase front is not varied adiabatically (e.g. through propagation) but abruptly at an interface. This is accomplished by properly engineering acoustic resonators which radiate with a phase shift based on their shape, position, and composition. Such metastructures can achieve exact impedance matching and facilitate a broader design space for acoustic shaping. Students will explore the design of acoustic filters for sound filtering, cloaks for sound isolation, as well as acoustic black holes for omnidirectional sound focusing.

This project will have a substantial impact upon our society as urbanization has created significant issues with noise pollution. Through this project we aim to develop new approaches for controlling sound waves which can stifle noise, re-direct it, or filter it to reduce the impact of unwanted sounds in our everyday lives. Of particular interest, will be the study of clear structures which could be implemented in windows or along roadways to block sound without impacting vision of scenery or the landscape. Furthermore, such structures may also find application in the areas of high quality sound such as recording studios and performance centers. By enabling the reduction of sound reflections and shaping of waves, an optimal acoustic environment can be created.

The project will include the analytic and numerical design of various acoustic meta-structures while also emphasizing the link between these designs and their implementations in the microwave and optical spectral regions. Students will also use the VCU machine shop and maker spaces to realize their sonic metamaterial designs and test them in real life environments.