Near-infrared spectroscopy has been recognized as a potential technology for noninvasive blood glucose sensing. However, the detected spectral signal is unstable mainly because of (1) the weak light absorption of glucose itself within NIR range, (2) the influence of temperature and individual differences of biotissue. Our previous results demonstrated that the synergistic effect of both transmittance and reflectance could enhance the strength of the detection signal. In this talk, we design a set of experiments to analyze the effect of earlobe thickness on Near Infrared spectroscopic measurement by using home-made optical fiber probe within the wavelength of 1000-1600nm. Firstly, we made a MC simulation of single-layer skin model and five-layer skin model to get the diffused transmittance spectra and diffused reflectance spectra under different optaical path lengths. And then we obtain the spectra of the earlobes from different volunteers by the same way. The experimental results showed that with the increase of the thickness,the light intensity of diffused transmittance decreases, and the light intensity of diffused reflectance remaines substantially unchanged.
Near Infrared Spectroscopy (NIRS) technology has been recognized as one of the most promising non-invasive blood glucose measurement methods due to its convenience, high efficiency, noninvasiveness, and real-time monitoring. We build a system to measure transmittance and reflectance within NIR range simultaneously. And contact measuring method has been performed in order to reduce the influence of specular reflectance of the measured skin tissue. However, in this way, the optical probe could press the skin tissue and make it distorted, which might make the internal structure and the constituent distribution of tissue changed and further the tissue optical parameter changed. This could eventually change the distribution of transmittance spectra and reflectance spectra. In this talk, we collect the transmittance spectra and the diffused reflectance spectra of human earlobe within the wavelength of 900-1700nm under the different contact pressures. The results show that the diffused reflectance spectra decrease and the diffused transmittance spectra increase with the increase of the contact pressure between the probe and the earlobe. In order to improve the precision and stability of NIRS, the contact position of the deformation of 0.75mm is determined to be an optimal contact state measurement position.