HHT变换，HHT就是先将信号进行经验模态分解（EMD分解），然后将分解后的每个IMF分量进行Hilbert变换，得到信号的时频属性的一种时频分析方法。(HHT is to first perform the empirical mode decomposition (EMD decomposition) of the signal, and then perform Hilbert transform on each decomposed IMF component to obtain a time-frequency analysis method for the time-frequency properties of the signal.)