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Millimeter-wave based contactless sensing of food moisture content Host Publication: 28th EFFoST International Conference Authors: G. Pandey, W. Vandermeiren and J. Stiens Publication Date: Nov. 2014
Abstract: Millimeter (mm) waves occupy the region of the electromagnetic spectrum between microwaves and the far infrared they offer a good compromise between lateral resolution and penetration depth in matter like food. The effectiveness of the mm-wave sensor has not yet been explored in monitoring production processes in the food industry. Determining accurate moisture content in food allows to deliver food with the highest (preservation) quality and to reduce the processing costs. At the considered mm-wave frequencies, the EM waves interact predominantly with water dipoles present in the food under study whose response is dependent on temperature and phase state of water molecules: bound, free, frozen, evaporated. As such the response of the incident EM wave is dependent on the amount of water in the food and its temperature. In this work we present experimental results on contactless monitoring of the full drying process of raw potato slabs. Simultaneous measurement of the reflection and transmission coefficient of incident EM waves is carried out with a mm-wave vector network analyzer. The mm-wave measurement system is integrated in a multi-sensor set up: particularly the potato mass, relative air humidity, air velocity and temperature is used to track the environmental conditions over time. It is shown that reflection and transmission spectra can be used to derive the absolute moisture content of the food product: the reflected signal is effective to determine moisture content in the beginning of the drying process, while the transmitted signal is effective in the preceding part of drying process. We show that the mm wave based sensor allows to perform volume-moisture measurements due to its relatively large penetration depth in dry matter. It is also proven that real time, precise and nondestructive moisture content measurements are possible with MM-wave sensors. The physical principle is discussed and experimental results are presented.
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