Frequency domain features: PSD
As shown on Figure 1, we could see variances in the spectrum, but generally not a trend. A higher definition of a PSD of a waveform is shown in Figure 2. Due to the carrier frequency, we can see that there are harmonics of 60Hz on the spectrum. These harmonics made it impossible to extract other features out of the spectrum. The dimension also increased to 4000 which is 32 times bigger than the original data. After all, extracting features from frequency domain was not an appropriate approach for this case.