Author Affiliations
College of Electronic and Optical Engineering & College of Microelectronics, Nanjing University of Posts and Telecommunications, Nanjing, Jiangsu 210023, Chinashow less
Fig. 1. Second harmonic signals. (a) Original second harmonic spectrum; (b) Fourier transform frequency distribution of original second harmonic curve; (c) second harmonic spectrum with noise; (d) Fourier transform frequency distribution of noisy second harmonic curve
Fig. 2. Relationship between balance parameter and SNR of the first mode component of the second harmonic signal with different noise intensity. (a) SNR of noise signal is -7.6300 dB; (b) SNR of noise signal is -4.7368 dB; (c) SNR of noise signal is -2.7133 dB; (d) SNR of noise signal is -0.3417 dB; (e) SNR of noise signal is 2.6703 dB; (f) SNR of noise signal is 4.7096 dB; (g) SNR of noise signal is 7.1441 dB; (h) SNR of noise signal is 10.1235 dB
Fig. 3. Intrinsic mode components of noisy signals and their corresponding spectra. (a) IMF1; (b) IMF2; (c) IMF3; (d) IMF4; (e) frequency distribution of IMF1; (f) frequency distribution of IMF2; (g) frequency distribution of IMF3; (h) frequency distribution of IMF4
Fig. 4. Effect graph of VMD-WTFD
Fig. 5. Denoising effects of different algorithms. (a) EMD-WTFD; (b) EEMD-WTFD; (c) CEEMDAN-WTFD; (d) WTFD
Fig. 6. Relationship between second harmonic amplitude and CO concentration before denoising
Fig. 7. Relationship between second harmonic amplitude and CO concentration after denoising
Intrinsic mode component | IMF1 | IMF2 | IMF3 | IMF4 |
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Correlation coefficient | 0.9769 | 0.0003 | 0.0001 | 0 |
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Table 1. Correlation coefficients between four modal components of noise signal and original signal
Index | Before denoising | EMD-WTFD | EEMD-WTFD | CEEMDAN-WTFD | WTFD | VMD-WTFD |
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| -7.4250 | 11.0453 | 11.0883 | 10.9678 | 10.6556 | 12.7601 | | -2.4867 | 15.0792 | 15.6581 | 14.8579 | 15.7112 | 16.0574 | SNR /dB | -0.0239 | 16.7035 | 16.7094 | 16.1546 | 18.2476 | 18.9942 | | 2.2782 | 18.2272 | 17.9743 | 18.4066 | 19.4693 | 21.2155 | | 7.4566 | 22.7098 | 23.5169 | 23.6043 | 23.9212 | 24.7941 | | 9.9647 | 26.0866 | 26.0904 | 26.1249 | 25.9836 | 26.9643 |
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Table 2. Comparison of denoising performance of various methods