Non‐destructive prediction of forage crop moisture contents using microwave transmitted signals with a microstrip transmission line sensor

Abstract

AbstractThis paper describes a non‐destructive method for using microwave transmitted signals to measure the moisture content of silage wrapped with plastic films. To collect measurements by a vector network analyzer, each bag of silage was placed on a microstrip transmission line without destruction of the films. Both rye and corn were tested. Significant linear relationships between the amplitude change (ΔA) and phase shift (Δφ) were obtained except for with fully dried corn, and the corresponding R2 values between ΔA and Δφ were 0.8 or greater. The slopes, which represent the ratio of phase shift to amplitude change (Δφ–ΔA ratio), depended on the frequency and moisture content. R2 values between the Δφ–ΔA ratio and moisture content of rye and corn were greater than 0.8 at the frequency of 3.6 GHz or above except for with fully dried corn samples. At 3.6 GHz, significant linear relationships between the Δφ–ΔA ratio and moisture content were obtained for rye and corn. Furthermore, the slope and intercept of the linear regression line between the Δφ–ΔA ratio and moisture content of rye were not significantly different from those of corn. These results illustrate the potential of the non‐destructive moisture content measurement method with microwave transmitted signals for silage materials with high moisture contents.