would be regarded as noise which should be deleted using noise
filters. Here we designed a band-pass filter (Rangayyan, 2001)
ranging from 00.5 to 23 Hz to isolate the disturbance from grid
electricity of 60 Hz. However, we realized that just a one-class
low-pass filter could not effectively avoid the noise, so we added
another low-pass filter of 19 Hz, and the output was better with
much better stability