Figure 1: Wavelet
time-frequency graph for U1
Figure 2: Wavelet time-frequency graph for U2
From above two figures, we can discover that there is no band
around high frequency, which means that there is no high frequency components
for electrical signal. This result is agreement with that of Fast Fourier
Transform. For observing the characteristics of low frequency, we need to zoom
them in as shown in Figure 3, 4.
Figure 3: Zoom in wavelet time-frequency for U1
Figure 4: Zoom in
wavelet time-frequency for U2
We can observe that
main frequency is located at 150 Hz for U1 and U2, This is the power source
frequency, and its corresponding period is 6.67 ms. For finding the changing of
intensity of frequency related to the power supply, we need to zoom in Figure 3
and the input electrical signal U1 as shown in Figure 5, 6.
Figure 5: Detailed time-frequency from
0.03 to 0.032 s
Figure 6: Detailed input signal U1 from 0.03 to 0.032 s
The undulation of input signal U1 is not large
enough, the peak to peak value is under 1 V, the intensity of frequency changes
regularly. So the fluctuation of input signal U1 cannot affect the
intensity of frequency. This is different from Ar-N2 double plasma electrical
signal. However, the non-stationary of power supply is still main reason
to produce fluctuation of plasma jet.
