An optical and electrical layered sensor for the measurement of ingredients in liquid

• Published in: Measurement science & technology Vol. 18; no. 11; pp. 3523 - 3529
• Main Authors: Kimoto, A, Makisako, T, Shida, K
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.11.2007
• ISSN: 0957-0233; 1361-6501
• DOI: 10.1088/0957-0233/18/11/036

In this paper, an electrical and optical layered sensor is proposed as a new, non-invasive sensing method for the measurement of ingredients in liquid, particularly in the food industry. In the proposed sensor, the optical properties of the liquid are measured by a light-emitting diode (LED) and a photodiode, and the electrical properties are measured by indium tin oxide (ITO) film electrodes with the transparent conductive properties arranged on the surfaces of the LED and the photodiode. Thus, the electrical and optical properties in the same space of the liquid can be simultaneously measured at a single sensor. To test the sensor experimentally, two parameters of a liquid-such as concentrations of red color and sodium chloride (NaCl) between 0.1% and 0.5% in distilled water-were estimated using measurement values of the electrical and optical properties obtained with the proposed sensor. In addition, it was found that two other parameters of a liquid, such as coffee and milk concentrations between 0.1% and 1.0% in distilled water, could also be estimated with the proposed sensor. The measurement values of optical properties with and without the ITO film and those of electrical properties using an ITO film electrode and a stainless-steel film electrode were also compared. The results suggested that it is possible to measure both optical and electrical properties using the proposed sensor, although there are still some problems such as the surface resistance and transmittance of the ITO film that must be addressed.