Design of Multi-Wavelength Optical Sensor Module for Depth-Dependent Photoplethysmography

Area of Science:

• Biomedical Engineering
• Optical Sensing Technologies

Background:

• Photoplethysmography (PPG) sensors measure blood volume changes using light.
• Wavelength influences light penetration depth, enabling depth-dependent blood volume assessment.
• Existing PPG sensors often lack multi-wavelength capabilities for comprehensive analysis.

Purpose of the Study:

• To develop and implement an omnidirectional optical sensor module for simultaneous multi-wavelength photoplethysmography.
• To evaluate the performance of the developed sensor for measuring depth-dependent blood volume.

Main Methods:

• Designed an omnidirectional sensor with concentric blue (460 nm), green (530 nm), red (660 nm), and infrared (940 nm) LEDs around a photodetector.
• Manufactured the sensor by integrating LEDs into a metal plate with a central aperture.
• Validated the sensor by measuring irradiation light intensity and simultaneous photoplethysmograms at various peripheral human body sites.

Main Results:

• The developed sensor module demonstrated a linear increase in irradiation light intensity with an increasing number of LEDs.
• Pulsatile waveforms were successfully observed across all four wavelengths (blue, green, red, IR) at all tested body locations.
• The sensor effectively captured photoplethysmograms, indicating its capability for depth-dependent blood volume measurement.

Conclusions:

• The novel omnidirectional optical sensor module is capable of simultaneous multi-wavelength photoplethysmography.
• The sensor shows promise for accurate and versatile depth-dependent blood volume monitoring in various physiological applications.
• This technology advances non-invasive optical sensing for biomedical applications.