Photoacoustic depth profiling of a skin model for non-invasive glucose measurement

A measurable depth of the blood glucose level by using photoacoustic spectroscopy (PAS) was discussed experimentally in order to improve detection sensitivity. Since a measurable depth of the PAS depends on a modulation frequency of the chopped light irradiated to a sample, the relationship between modulation frequency and the thickness of a sample was evaluated. The photoacoustic detector used in these experiments consisted of an acoustic resonance pipe and an optical microphone, and a two-layer model composed of silicone sheets with the different optical absorption. The measurable depth was 2–3 mm with modulation frequency of 1000–2000 Hz. Furthermore, the reason for the measurable depth to be deeper than the thermal diffusion length of the sample was discussed theoretically. From these analyses of thermoelastic wave, the relation between the photoacoustic signal propagation and the measurable depth in a tissue was clarified.