Pulse Oximetry Based on Quadrature Multiplexing of the Amplitude Modulated Photoplethysmographic Signals

Figures

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  Figure 1. The acquisition of a PPG signal using a commercial pulse oximeter. Adapted with permission from Ref [13]. Copyright 2018, the Institute of Electrical and Electronics Engineers, IEEE.

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  Figure 2. The general waveform of a PPG signal. Reprinted with permission from Ref [24]. Copyright 2018, the Institute of Electrical and Electronics Engineers, IEEE.

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  Figure 3. A block diagram of quadrature multiplexing.

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  Figure 4. The block diagram of the proposed system.

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  Figure 5. Flowchart of signal processing of the proposed system based on the microcontroller (ESP32).

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  Figure 6. Sinusoidal sequences generated by the ESP32 using a difference equation (top) 90 Hz cosine sequence and (bottom) 90 Hz sine sequence for controlling two light sources.

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  Figure 7. The AM-PPG signals (top) in the time domain and (bottom) in the frequency domain.

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  Figure 8. The demodulated PPG signals: red and infrared components for 70%, 85%, and 100% SpO2 levels.

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  Figure 9. The percentage of relative error of the determined SpO2 level based on the proposed technique.

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  Figure 10. Testing scenarios: (a) hand still, (b) shadow movement over the hand, and (c) hand shaking.

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  Figure 11. Example of the detected red (red line) and IR (blue line) PPG signals of each condition based on the proposed technique.

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  Figure 12. Example of the detected red (red line) and IR (blue line) PPG signals of each condition based on the conventional technique.