Fig. 11

Results of the noise parallel (NPI) test. From 10 kHz to 3 Hz, the E-field signals measured by the two types of electrodes show high homogeneity. The coherence is high above 3 Hz. Below 3 Hz, the difference in the power spectrum density (PSD) is larger and the coherence decreases. Because the signal to noise ratio (SNR) in the low-frequency bands is low, the data quality decreases. The coherence of the two types of electrodes is approximately 1, with a fluctuation less than 5% when the frequency ranges from 3 Hz to 10 kHz