“…Since the time-frequency window of traditional filters (such as Kalman) is fixed, the limited ability of acquiring the ultralow-frequency signal component in the NCV is one obstacle. In recent years, multiresolution analysis (MRA) theory has also been used in the field of cell voltage (or resistance) analysis, such as the discrete wavelet transform (DWT) [21] and the wavelet-packet transform (WPT) [22], [23]. These methods are also not very suitable for analyzing alumina concentration information from the NCV.…”