Abstract:

Photoplethysmography (PPG) is a non-invasive method of measuring the change in blood volume in tissues using a light source and a detector. At present, PPG is widely used in various sensors for the continuous determination of human health, and from the measured data, it is possible to determine the possibility of impending disease. Two basic types of photoplethysmography are transmittance and reflectance. For the transmittance PPG, a light source is emitted into the tissue and a light detector is placed on the opposite side of the tissue to measure the resultant light. Due to the limited penetration depth of the light through organ tissue, mainly the finger or the ear lobe are applicable for the transmittance PPG. At the reflectance PPG, the light source and detector are both placed on the same side of a body part and can be used can be applied to any part of the human body. In either case, the detected light reflected from or transmitted through the body part will fluctuate according to the pulsatile blood flow caused by the beating of the heart. Calculation of transmittance and reflectance of light of various wavelengths through the surface of skin layers at the finger or the ear lobe or thin-film layers is essential for a correct understanding of the external and internal influences on the recorded light signal. Within the photonics course, the calculation of these parameters is one of the basics that students should master. In the article is shown several exercises where students use Matlab to numerically model the transmittance and reflectance of light for various skin layers configurations at of wide range of wavelengths. By varying the number of layers and their optical parameters, students learn how to adjust the transmission curves to tune a particular wavelength to suit for PPG sensor. However, we assume a larger number of layers with different optical parameters, the method of transfer matrix is used. The results of simulations are transmission curves of the transmission and reflection of light of various wavelengths, which also can be used in other applications.

Keywords:

STEM education, new sensors, simulations.