A Differential Microstrip Resonator-ased Sensor for High-Sensitivity Moisture Detection in Wheat Grains

Abstract

Background and Objectives: Accurate measurement of moisture content (MC) in wheat grains is vital for quality control and storage management. This study presents the development of a differential microwave sensor with enhanced sensitivity for detecting MC in wheat grains, leveraging resonant techniques to improve detection precision. Methods: The proposed sensor utilizes two identical half-wavelength (λ/2) microstrip resonators symmetrically coupled to a standard 50Ω transmission line. One resonator serves as a reference with a relative permittivity (ζr) of 1, while the second is exposed to the sample under test (SUT), where ζr > 1. This differential structure enables the identification of dielectric property changes due to moisture variation. The operating principles are theoretically analyzed using even- and odd-mode techniques. Results: The proposed sensor exhibits three distinct transmission zeros (TZs) within the 0.1–2 GHz frequency range, which arise from the harmonic behavior of the resonators. A prototype was fabricated on a low-cost, compact substrate with dimensions of 6 × 4.5 × 0.16 cm³ and was experimentally tested, confirming the simulation results. The sensor demonstrates a high normalized sensitivity of 7.63%. Conclusion: The developed differential microwave sensor demonstrates strong potential for precise and reliable MC detection in wheat grains. Its compact design, cost-effectiveness, and high sensitivity make it a suitable candidate for practical agricultural and food monitoring applications.