Low-Terahertz Channel Performance in Falling Wheat for Moisture Sensing

Terahertz (THz) waves are highly sensitive to water and therefore offer a promising noncontact approach to wheat moisture sensing, but existing THz studies have been limited to static samples. This article investigates moisture sensing based on the performance of a THz channel in falling wheat, as encountered at grain intake. The channel power loss is measured at six frequencies from 120 to 320 GHz for three moisture contents and interpreted with a physics-based model that couples the double-Debye permittivity of water, Landau-Lifshitz-Looyenga mixing, and Lorenz-Mie extinction. The model reproduces the measured loss. Above the extinction maximum, the dielectric moisture response peaks where the wavelength approaches the kernel diameter, and that a two-frequency loss ratio removes the loading dependence. A channel-level analysis of QPSK and 16-QAM links shows that a 1 dB moisture-induced loss change alters the bit error rate (BER) by a factor of 3 to 30. THz communication channels at grain intake could therefore sense moisture as a byproduct of data transmission.