Optical sensing with a mobile phone applied to liquid solutions

• The use of a mobile phone with a front side camera for the classification of liquid samples is described. The classification is based on the observation that there are different regions of the image captured by the mobile camera, one containing specular reflected light and one due to diffuse reflected light with transmission through the liquid. The specular reflected light contains information about the refractive index of the liquid sample whereas the diffuse light contains information about the color and absorption properties of the liquid. The information in the specular light is first elucidated. It is found that the reflectance of the region with specular reflected light increases linearly with increasing refractive index, n, in the range 1.33 < n < 1.38 as expected from the Fresnel equations. The information in the specular light is then used together with the previously described diffuse light from another region of the image to analyze several types of liquid samples. It is shown that a combination of the two areas of the image improves the classification abilities of the mobile phone.

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