The skin has emerge as a compelling subject for investigation owing to its accessibility and the relatively straightforward application of optical procedures to it. Diffusive reflection spectroscopy (DRS) was employed to study the influence of probe pressure on human skin. A comprehensive non-invasive study was conducted, which covers almost all the important body parts for in vivo measurements. Reflection spectra were measured for the fingertip, forearm, forehead, neck, and foot under a set of probe pressures (0-265 kPa). Importantly, each tissue type's unique composition and morphology influenced the shape, size, intensity, and position of the recorded peak, highlighting the tissue-specific responses to pressure. In addition, time-based reflection spectroscopy was also performed on the forearm under blood occlusion for 5 min to study the effect. DRS measurements were performed on volunteers of different skin tones, including dark, medium, and fair. Later, a change in the intensity of the oxyhemoglobin peak was confirmed using a green laser light of a wavelength of 532 nm. Besides the dermal studies, diffusive reflection spectroscopy was also employed to investigate the probe pressure effect on human nails. A probe pressure ranging from 0 to 385 kPa was applied for nail spectroscopy. The same trend of intensity change was observed following the previous measurements. The suggested sensing system may be crucial in applications requiring pressure sensing when the human body is subjected to varying pressures, such as exercise, weightlifting, and other sports.
Keywords: dermal studies; diffusive reflection spectroscopy; hemoglobin; optical fiber; pressure probe.