We report a method that uses near-infrared spectroscopy and multivariate analysis to measure the temperature of turbid aqueous solutions. The measurement principle is based on the fact that the peak wavelength of the water absorption band, with its center near 1440 nm, shifts with changes in temperature. This principle was used to measure the temperatures of 1 mm thick samples of aqueous solutions containing Intralipid (2%), which are often used as optical phantoms for biological tissues due to similar scattering characteristics. Temperatures of pure water and aqueous solutions containing glucose (100 mg/ml and 200 mg/ml) were also measured for comparison. For the turbid Intralipid solutions, the absorbance spectrum varied irregularly with time due to the change in scattering characteristics. However, by making use of the difference between the absorbance at 1412 nm and the temperature-independent absorbance at 1440 nm, we obtained SEPs (standard error of prediction) of 0.3 degrees C and 0.2 degrees C by univariate linear regression and partial least squares regression, respectively. These accuracies were almost the same as those for the transparent samples (pure water and glucose solution).
We have proposed a novel method of non-contact thermal type measurement for low flow rates using radiation heating and spectroscopy of water in the near-infrared wavelength range . We made a simulation for studying the performance of the flowmeter, and based on the simulation we conducted experiments using a prototype flowmeter. We obtained calibration curves between the estimated and true flow rates. From the experimental results , we can measure the flow rates from 0.3 to 9 ml/ min with the accuracy of about 10% of the flow rate . We also obtained agreement between the simulation and measurement results. Discussions are made to improve the measurement accuracy .
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