Two measurement modes for mobile phone optical sensing

Abstract

The use of a mobile phone for classification and quantification of liquid samples is described. The screen of the phone is used for controlled illumination and the front side camera for imaging. No additional optical equipment is needed. It is shown that there are different regions of the captured image containing different information about the sample. One region contains light that has been specular reflected at the air-liquid interface and one is dominated by light that has propagated through the liquid. The specular reflected light contains information about the refractive index of the liquid sample whereas the transmitted light contains information about color and absorption. It is found that the specular reflectance increases linearly with increasing refractive index, n, in the range 1.33 < n < 1.38, as expected from the Fresnel equations. A change of the refractive index of about 0.004 refractive units can be detected. The transmitted light intensity is well described by the Beer-Lambert law over a large absorption range. Light from the two different areas of the image is used to analyze several types of liquid samples. It is shown that a combination of the two measurement modes improves the classification abilities of the mobile phone.

A prototype of an optical sensor for the identification of diesel oil adulterated by kerosene

“…The trend regarding field measurements of liquids, including fuels, is to develop portable sensors that are based on the exploitation of spectroscopic techniques [6,7]. In principle, this can be realized, in some cases, with the aid of modern technology that is based on mobile telephones [8]. In the past, we have contributed to the development of various types of spectral measurements techniques for detecting the purity of transparent and turbid liquids that are present in process industry [9], and liquid products, such as red wine [10,11].…”