Rice Grain Moisture Determination Using Microstrip Wide-Ring and Microstrip Coupled-Line Sensors

Determining the Moisture Content (MC) inside rice grain is an important element for grain processesing such as harvesting, storage, quality control and transportation. A microstrip wide-ring sensor and a microstrip coupled-line sensor with low insertion loss were developed to operate at relatively low frequency to determine the MC and relative complex permittivity of rice grain. The complex permittivity for rice grain with various moisture levels was measured by the proposed sensors based on the resonance technique. Calibration equations for measurement of grain MC were obtained and validated with white rice for MC ranging from 10 to 28% wet basis. The coupled-line sensor showed better sensitivity to moisture measurement as compared to the wide-ring sensor. For a 1% change in MC, the changes of resonant frequency for the wide-ring and coupled-line sensors were 4.36 and 10.69 MHz respectively. Meanwhile, the wide-ring sensor had a higher accuracy in MC prediction than the coupled-line sensor. The average errors in moisture prediction for wide-ring and coupled-line sensors were 0.85 and 1.30% respectively.