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Seminar - From Membrane- to Plate-Type Acoustic Metamaterials: Towards Large-Scale Noise Control Applications by Prof. Heow Pueh LEE
日期:2018 年 09 月 04 日 ( 星期二)
Time:11:00 am – 12:00 pm
Venue:EF305

Abstract:

Recent works have demonstrated the potential of small-scale membrane-type acoustic metamaterials for low-frequency noise control. Such metamaterials are characterised based on the resonant behaviour of the membrane. Considering industrial applications, it is imperative to investigate large-scale design and introduce additional feature to complement the acoustical performance of the membrane-type metamaterials.

The first part of this seminar presents a large-scale membrane-type acoustic metamaterial (or the meta-panel), which was evaluated and verified numerically. Experimental results show that a broadband sound transmission loss (STL) improvement could be achieved by the incorporated membrane (up to 7.4 dB at 380 Hz). Numerically, parametric studies show that the broadband STL performance of the meta-panel was due to not only the resonant behaviour of the overhanging membrane but also the resonant behaviour of the sandwiched membrane along the boundaries of the unit cells. If properly designed, this resonant behaviour of the sandwiched membrane could complement membrane-type acoustic metamaterials to achieve an extended good STL performance across a broader frequency bandwidth. The second part of this seminar focuses on the potential manufacturing issues if large-scale designs are considered. Examples include the spatial consistency of the platelet(s), the uniformity of the membrane pretension, and the durability of the membrane—not to mention stress relaxation. Hence, it is imperative to address the shortcomings for manufacturability. The conceptual design of a membrane-type acoustic metamaterial without the need for pretension and platelet(s) is presented. Additionally, experimental and numerical results show that the acoustical performance could be complemented by the coupling effect between two enclosed cavities via an orifice (i.e., resonator’s effect). The orifice diameter could serve as a tuning parameter for broadband or narrowband transmission loss at selected frequencies. Consequently, the proposed design could address the shortcomings of membrane-type acoustic metamaterials and complement their acoustical performance with the additional feature.

The last part of this seminar presents the study on the influence of the possible causes—geometrical accuracy and viscous loss—on the damping of the resonator’s effect observed experimentally by investigating the same specimen in greater detail. Numerical and experimental results show that the damping of the resonator’s effect was due to the viscous losses induced by the acoustic boundary layer developed within the orifice. Consequently, the study offers complementary insights into the design of plate-type, and even membrane-type, acoustic metamaterials with an internal resonator so that they can be tuned for low-frequency noise applications, if required.

Bio-sketch:

Heow Pueh LEE is currently the Deputy Head (Research) for the Department of Mechanical Engineering, National University of Singapore. He graduated with first class honours from Cambridge University. He obtained his PhD in Mechanical Engineering from Stanford University. He was seconded to the Institute of High Performance Computing (IHPC) under the Agency for Science, Technology and Research (A*STAR) in 2002, initially as the Deputy Director for Research and subsequently assumed the role of Deputy Executive Director for research since 2003 till the end of his full-time secondment in 2007. His early works focused on the mechanics of robotic manipulators, mechanism designs, as well as the vibration of structural elements and the mechanics of ultrasonic motors. Notable contributions include the application of “Structural Intensity” for the vibration study to various aspects of engineering disciplines from fracture mechanics to biomechanics. His more recent works focus on mechanics in medicine, numerical methods and noise and vibration.

Research Interests - Modeling and simulation, sound and vibration, noise mitigation, vibroacoustics, mechanics in medicine.