MechE PhD Prospectus Defense: Ao Chen

TITLE: Acoustic Wavefront Modulation with Acoustic Metamaterials

ABSTRACT: Acoustic wave propagation in fluids is primarily governed by two key properties of the medium: mass density and bulk modulus. Typically, these properties are positive values and remain fixed as the wave propagation in most natural materials. Acoustic metamaterial (AMM), a subset of the metamaterial family, leverage their unique subwavelength artificial structures to achieve effective negative mass density, negative effective bulk modulus, or both. These unconventional effective properties open up a realm of possibilities for various applications, such as holography, invisibility cloaking, and precise wave focusing. In this study, fundamental physics principles were applied to investigate applications of acoustic wavefront modulation using AMMs. The research focused on two main directions: shaping acoustic waves in amplitude and phase. The primary application addressed was sound attenuation. To overcome the limited bandwidth of current ventilated acoustic silencers, a broadband ventilated labyrinthine acoustic insulator was theoretically analyzed, numerically simulated, and experimentally validated. Additionally, a composite design employing two AMMs was studied to further extend the bandwidth of acoustic attenuation while maintaining effective ventilation. To address the issue of fixed functionalities in existing AMMs, an angle-variant AMM was proposed and examined. The flexibility of this design was numerically studied, and its multifunctionality was demonstrated. Finally, the study identified a limitation in current AMM designs, which often focus solely on controlling either reflection or transmission waves, neglecting the coupling between amplitude and phase of acoustic waves. To address this, a metascreen design was proposed and experimentally validated. This design enabled arbitrary combinations of amplitude and phase for reflected and transmitted sound in a broadband manner.

COMMITTEE: ADVISOR/CHAIR Professor Xin Zhang, ME/ECE/BME/MSE; Professor Paul Barbone, ME/MSE; Professor Thomas Bifano, ME/MSE/BME/ECE; Professor Harold Park, ME/MSE; Professor Chuanhua Duan, ME/MSE