研究目的
To demonstrate an ambient light oximeter (ALO) that can measure photoplethysmography signals and SpO2 using various kinds of ambient light, avoiding the use of LEDs.
研究成果
The ALO design reduces system and mechanical complexity by eliminating the need for a controlled light source, i.e., LEDs. The sensors are compatible with low-cost large-area production and are soft and flexible, making healthcare products more conformable and affordable. The ALO can perform pulse oximetry with ambient light sources, with sunlight providing the best signal magnitudes.
研究不足
The OPDs need to face the light sources to get a measurement, restricting usage compared to conventional pulse oximetry. The setup is susceptible to motion artifacts, especially under indoor lighting conditions where the signal strength is weak.
1：Experimental Design and Method Selection
The ALO was designed using spectral filters combined with organic photodiodes to create sensitivity peaks at green (525 nm), red (610 nm), and near-infrared (740 nm) wavelengths. The methodology involved using ambient light sources instead of LEDs for measurements.
2：Sample Selection and Data Sources
PPG signals and SpO2 measurements were collected from the index finger of volunteers under different indoor and outdoor lighting conditions. The measurements were validated with commercial pulse oximeters.
3：List of Experimental Equipment and Materials
Organic photodiodes based on PCDTBT:PCBM70 and P3HT:O-IDTBR, spectral filters (Kodak 58, 25, 89b), multiplexer (Analog Devices ADG1608), analog front end (AFE4490), microcontroller (Arduino Due), and a solar simulator (Newport, 94021A).
4：Experimental Procedures and Operational Workflow
The ALO system involved connecting two OPDs to readout electronics, using a multiplexer to switch between the two spectrally selective OPDs, and processing the data with custom in-house software. PPG signals were collected at 100 Hz.
5：Data Analysis Methods
The PPG signals were processed to calculate heart rate and SpO2. The ratio of the ratios of PPG signals (Ros) was used to calculate oxygenation, and SpO2 was derived from Ros.
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