Surpassing the Diffraction Limit: Harnessing Nonlinear Acoustic Effects in Wavefront Shaping

Acoustic wavefront shaping is a technique for precisely controlling the sound field in space. This research project's novelties lie in investigating an approach to overcoming the diffraction limit in acoustic wavefront shaping using nonlinear acoustic effects, which can significantly advance acoustic imaging, therapeutic ultrasound, multizone sound field reproduction, and active noise control. The project's impacts are expected to create a paradigm shift in the vibrant research area of acoustic wavefront shaping, spurring more technological innovation and scientific knowledge in nonlinear acoustics, which possesses characteristics that transcend the limitations imposed by linear acoustics. This project aims to provide a deeper understanding and broader applications of nonlinear acoustic phenomena. This project is also expected to support research-integrated education and benefit society and national security through technological advancements. Acoustic wavefront shaping forms the fundamental basis for numerous applications. Three particularly noteworthy examples of novel approaches in acoustic wavefront shaping include acoustic vortex beams, holograms, and self-bending beams. This research project aims to investigate integrating nonlinear acoustics with advanced wavefront shaping to surpass the diffraction limit. Specifically, the project involves generating nonlinear vortex beams to explore their potential in long-range communication, achieving high-resolution acoustic holograms, and developing nonlinear self-bending beams to create a remote whispering beam. The project will start from the extended second-order nonlinear acoustic wave equation and establish an accurate and efficient numerical model based on the finite-difference time-domain method. The numerical model will be utilized to investigate fundamental physics pertaining to nonlinear acoustic wave propagation. The team will then experimentally demonstrate significantly enhanced acoustic wavefront shaping by leveraging nonlinear acoustic effects, focusing on the three aforementioned applications. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.