An Improved EMD Method Based on Utilizing Certain Inflection Points in the Construction of Envelope Curves

Abstract

The empirical mode decomposition (EMD) algorithm is widely used as an adaptive time-frequency analysis method to decompose nonlinear and non-stationary signals into sets of intrinsic mode functions (IMFs). In the traditional EMD, the lower and upper envelopes should interpolate the minimum and maximum points of the signal, respectively. In this paper, an improved EMD method is proposed based on the new interpolation points, which are special inflection points (SIP n ) of the signal. These points are identified in the signal and its first ( n − 1 ) derivatives and are considered as auxiliary interpolation points in addition to the extrema. Therefore, the upper and lower envelopes should not only pass through the extrema but also these SIP n sets of points. By adding each set of SIP i ( i = 1 , 2 ,...,n ) to the interpolation points, the frequency resolution of EMD is improved to a certain extent. The effectiveness of the proposed SIP n -EMD is validated by the decomposition of synthetic and experimental bearing vibration signals.