The effect of materials in photoplethysmography-enabled mouthguards
de Almeida e Bueno L., Bergmann JHM.
The monitoring of cardiac signals using photoplethysmography (PPG) provides valuable insights into the health state of a person, both in clinical and non-clinical settings. However, current technologies have yet to be deployed in contact sports settings. This study aims to evaluate the impact of placing dental-grade materials, frequently used in mouthguards, over PPG sensors. The effects of signal-to-noise ratio (SNR) of different light wavelengths in ethylene vinyl acetate (EVA) and polymethyl methacrylate (PMMA) samples of varying thickness were explored. The light signals were assessed using a setup of highly absorbing and highly reflective environments, which allows for the assessment of the effect of specific materials on the photodetector. Using non-parametric statistical tests, this research identified that SNR is significantly affected by light wavelength, material thickness and the material forming process. Infrared light going through 1 mm non-thermoformed PMMA resulted in the highest SNR. This research shows the need for careful consideration of material selection and signal processing for the application of PPG sensors in mouthguards.