在声子晶体中人工操控弹性波和声波，以获得不同于传统均质材料的新型声学材料及功能器件，成为近年来的研究热点。本项目拟研究声子晶体波导型多模干涉耦合器的特性及应用。在完整声子晶体中，引入邻近的多个线缺陷，选择恰当的参数构建多模波导或多波导阵列，基于导模传输法和耦合模理论，采用平面波展开法和时域有限差分法等计算方法，探讨不同入射位置（对称或反对称）时，波导系统中的多模干涉效应和自映像原理，以获得成输入场的直接像、镜像、多重像的数值关系，得到弹性波在传输方向上的周期性传输行为，波导之间的耦合及解耦合特性，及多模区可能出现的一些物理新现象和新特性。基于该种多模波导理论研究的基础，设计具有优越功能特性的新型声学功能器件。本项目的研究旨在探索人工声学材料中的新物理现象，以实现高性能的声学功能器件，不仅在学术研究方面具有重要的科学意义，在实际工程应用中亦具有潜在的应用价值。

New kind of acoustic materials and devices other than traditional homogeneous materials would be achieved by modifying and controlling artificially the elastic and acoustic waves in phononic crystal (PC), which have been attracted much attention in the recent years.This program will investigate the characteristics and their applications of PC waveguide-based multimode interference (MMI) coupler. MMI coupler and waveguides arrays with appropriate paramaters are constructed by introducing some neighbouring line defects in a perfect PC. Based on guided mode propagation analysis and coupled mode theory, MMI effect and self-imaing principle in a multimode region with a different input position (symmetrical or asymmetrical) will be studied by the methods of the plane wave expansion and the finite difference time domain. The mathematical derivations of the positions of the direct images,the mirrored images,the multiple-fold images and the periodical propagation of elastic waves along the propagation direction, as well as the coupling and decoupling of waveguides will be achieved. And some new physical phenomenas and characteristics may be introduced. Some novel sonic devices will be designed, simulated and optimized based on the theorectical analysis above.The aim of this program is to explore new physical phenomena and sonic devices with good performance in the new kind of artifical sonic materials. The results will provide important scientific value and can find potential application for the real engineering design and applications.