二维声子晶体FDTD方法计算禁带宽度的例子,用平面波展开法计算二维声子晶体带隙,应用小区域方差对比，程序简单。- Dimensional phononic crystals FDTD method calculation examples band gap, Computation Method D phononic bandgap plane wave, Application of small area variance comparison, simple procedures.