学术报告 （6月15日 下午 15:00-）

主持人： 董建文 教授

欢迎广大师生前来参与！

报告摘要：

The research of acoustic metamaterials has matured into a robust and active field driven by scientific discoveries and application potentials [1]. In this talk, I will discuss our recent progress in sound field control with membrane-type acoustic metamaterials. In the first part, I will show the way to reshape reverberating sound field in a room by building a “spatial sound modulator” which is based on a metasurface that is an array of actively controllable metamaterials. We show the functionality of the on-demand creation of quiet zones and acoustic hotspots at audio frequencies anywhere in a reverberating room. This is the first realization of the adaptive wavefield shaping for acoustic waves [2]. In the second part, I will show that by building a subwavelength absorber for spherical waves, the focal spot formed by an isotropic converging wave in 3D can become smaller than the diffraction limit. The idea is based on the observation that diffraction limit is the consequence of the interference between incoming and outgoing waves, therefore by removing a majority of the outgoing energy with a subwavelength absorber, the total field profile is drastically modified, leading to sub-diffraction focusing. This result can also be interpreted as the realization of a stand-alone anti-causal Green’s function up to the surface of the absorber. The absorber also plays an important role of an acoustic sink, which is the time-reversal counterpart of a source [3].

References

1. G. Ma and P. Sheng, Acoustic metamaterials: From local resonances to broad horizons. Science Advances 2, e1501595 (2016).

2. G. Ma, X. Fan, P. Sheng, and M. Fink, Shaping reverberating sound fields with an actively tunable metasurface. PNAS (2018).

3. G. Ma, X. Fan, F. Ma, J. de Rosny, P. Sheng, and M. Fink, Towards anti-causal Green’s function for three-dimensional sub-diffraction focusing. Nature Physics 14, 608 (2018).

报告人简介：

马冠聪博士，现于香港浸会大学物理系任职助理教授。2007年本科毕业于华南理工大学。2007至2012年就读于香港科技大学物理学系，取得物理学博士学位。博士期间主要从事声波超材料的研究。2012-2017年分别在香港科技大学物理系和高等研究院任博士后研究员。2018年起在香港浸会大学物理系担任助理教授。研究兴趣包括声波超材料，声子晶体，声拓扑，非厄米系统等相关的经典波现象。相继在国际著名期刊Nature Materials, Nature Physics, Nature Communications, Physical Review X, Physical Review Letters等发表文章15篇，并在Science Advances发表关于声波超材料的综述文章。在国际著名会议META，PIERS等做邀请报告6次，并两次担任META会议（2017年韩国仁川，2018年法国马赛）的声波超材料和声子晶体分会场的组织者和会场主席。

马博士的主要研究成果有：

1. 利用薄膜型声波超材料实现多种新颖现象，包括声波双负参数，声波全反射、全吸收、三维亚波长聚焦等；
2. 通过固态弹性波超材料实现流体的弹性波性质；
3. 利用声子晶体首次实现声波的拓扑相变；
4. 首次在实验上实现非厄密系统中的高阶奇异点(high-order exceptional points in non-Hermitian systems)；
5. 首次实现“声波空间调制器”，并实验上实现对混响声场的操控。