说明：  EMD可以对一个信号同时将不同尺度（频率）的波动或趋势逐级分解开来，产生一系列具有不同特征尺度的数据序列称为本征模函数
(EMD can decompose the fluctuations or trends of different scales (frequencies) of a signal step by step, and generate a series of data sequences with different characteristic scales, called eigenmode functions.)