Influence of Moisture of Wheat on Acoustic Wave Propagation Characteristics

Acoustic methods have been widely used for the measurement of grain moisture content and temperature as well as for detecting the presence of insects in grain. Therefore, this study was conducted to understand the influence of wheat moisture content on acoustic wave propagation characteristics. A novel device was developed for measuring the acoustic wave propagation constant. The propagation constants of 12 samples of wheat were measured, with each sample having a different moisture content in the range from 1.1% to 21.2% (wet basis). The results showed that the acoustic wave velocity decreased slightly with an increase in moisture from 1.1% to 7.8%, while the attenuation coefficient increased slightly. When the moisture increased from 7.8% to 21.2%, the velocity increased gradually, while the attenuation coefficient decreased. A quadratic equation described the results well. In addition, a Johnson-Champoux-Allard (JCA) model was adopted to study the influence of moisture on the pore structure of wheat samples. With the increase in moisture from 1.1% to 21.2%, the average radius of interconnection between two adjacent pores decreased from 0.275 to 0.262 mm at moisture below 7.8% and then increased to 0.304 mm, and the average radius of the pores decreased from 0.773 to 0.481 mm at moisture below 7.8% and then increased to 1.2 mm.