Fig. 1. The waveform characteristics of PPG signal
a: Systolic peak; b: Tidal notch; c: Dicrotic peak; d: Dicrotic notch

Fig. 2. The wavelet coefficients of PPG signal at various scales after CWT decomposition

Fig. 3. The frequency spectrum of wavelet coefficients in PPG signal after CWT

Fig. 4. The changes of volunteer’s blood glucose level

Fig. 5. The changes of the amplitude of the spectral component of volunteer’s PPG signal

Fig. 6. The flow chart of non-invasive blood glucose detection system

Fig. 7. The Clarke error grid analysis of model
(a): Calibration set; (b): Prediction set