Nondestructive Wheat Moisture Detection System with Metasurface Plane Wave Antenna and De-Embedding Algorithm

The precise measurement of wheat moisture content is a key issue to ensure the quality and safety of wheat. However, high-precision, rapid, and nondestructive detection of wheat moisture content remains challenging. In this article, we proposed a system with single-layer low-frequency metasurface plane wave lens antenna (MPWLA) for nondestructive wheat moisture detection in the frequency range of 5.8-5.9 GHz. Based on the propagation characteristics of plane waves in multilayer dielectric, antenna and container error de-embedding algorithms are proposed to reduce the measurement errors introduced by the parameters of the antenna and container during the measurement process. According to the de-embedded scattering parameters of wheat, its dielectric constant and loss factor are obtained. The calculated dielectric constant and loss factor showed a good linear relationship with moisture content of wheat at 25.C (+/- 0.5 degrees C). Based on the relationship between the dielectric properties and moisture content of wheat, a linear regression equation is established to predict the moisture content of wheat. Experimental results show that the root-mean-square error (RMSE), mean absolute error (MAE), and maximum relative error (MRE) of the predicted values were 0.19%, 0.16%, and 4.0%, respectively.