Experimental study on the influence of the contact pressure to transmittance and reflectance spectra by near infrared spectroscopy

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.