Abstract
Moisture content is an important index to assess the grain quality and food processing conditions. A measurement system based on the traveling–standing microwave attenuation method is designed for a fast and nondestructive grain moisture content determination. The proposed system consists of a microwave cavity oscillator, microwave transmitting and receiving horn antennas, microwave detector, slide rail, sample container, weight sensor, temperature sensor, and controller. The traveling–standing wave caused by free space microwave multiple reflection is discussed. The moisture content calibration functions eliminated the interference of bulk density and temperature are proposed based on the attenuation of the maximum field strength of the transmission traveling–standing wave. The moisture content of rice, which ranges from 10.75% to 27.62%, is obtained with a standard error of prediction (SEP) of 0.586% and a coefficient of determination ( R2) of 0.988, whereas the moisture content of corn, which ranges from 7.72% to 24.46%, is obtained with a SEP of 0.340% and R2 of 0.991. The main results might provide technical support for the development of accurate and intelligent grain quality detection equipment.
Highlights
An excessive moisture content will lead to grain germination and mildew, which in turn lead to difficult storage
The volume of corn kernels expands after absorbing water, thereby leading to an abnormal decrease in their bulk density along with an increasing moisture content
Calibration models are proposed based on the attenuation of the maximum field of the transmission traveling–standing wave at 10.5 GHz
Summary
Moisture content detection is important and essential in grain storage, trading, transportation, processing, and other processes.[1,2] An excessive moisture content will lead to grain germination and mildew, which in turn lead to difficult storage. A very low moisture content will destroy the physical structure of grains, reducing their nutritional value and making them easy to crush. Measuring the moisture of agricultural products requires a fast, efficient process to satisfy the requirements of high-precision and online nondestructive testing.[3] The methods for measuring grain moisture content can be divided into direct methods and indirect methods.[4,5] Oven-drying technique is the most commonly used direct method. The relative moisture content are obtained by measuring the weight difference before and after drying. This method is destructive, discontinuous, and both time and energy consuming
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