Sound absorption across a wide range of frequencies is a focus in contemporary acoustics. Recently, integral bounds of absorption or reflection coefficients were introduced as a guide of design optimization following the footsteps of electromagnetics, where integral relations were derived based on system causality considerations. This talk carefully examines the proper formulation of physical causality and its implications on the scattering properties of the system. Taking into consideration the effects of different physical boundary conditions and the bulk absorber material, a more generalized integral bound is derived. It becomes evident that, while the bound exists, it is governed by system stiffness rather than the causality constraint. By studying the effects of various approximations made during mathematical derivations, the physics of the bound is thoroughly discussed, and the limitations in utilizing integral bounds as reference for design optimization are highlighted. The findings are expected to have significant implications for the development of effective noise reduction strategies and the advancement of smart acoustic design.
Mr Zhe Zhang is a first-year PhD student in the Department of Mechanical Engineering at HKU, working under the supervision of Professor Lixi Huang. He completed his undergraduate degree in Aeronautical Engineering from Imperial College London, and his master’s degrees in Aeronautics and Astronautics and Mechanical Engineering from Stanford University. Prior to pursuing his PhD at HKU, he worked as a CFD engineer at CAS Space (中科宇航). Mr. Zhang’s current research is centered around the study of acoustics and aerodynamics, with a specific focus on developing theories and computational methods in these fields.
Clean water and clean air are vital for public health. This project focuses on developing high-efficiency and environmentally sustainable filters for removing harmful air/water pollutants. The team has developed novel architectures and functionalities for the filters to achieve high permeance, high removal efficiency, and excellent reusability.
