Soil Hardness Measurement Using Fiber Bragg Grating Sensor: Combined Compression Forces Methodology

Accurate soil hardness measurement is essential for enhancing agricultural productivity and geotechnical stability. Conventional methods, such as cone penetrometers, offer limited precision as they only measure penetration resistance, without considering soil reaction forces. This study introduces a novel Fiber Bragg Grating (FBG) sensor system, which captures both downward penetration and upward push‐back forces, providing a more comprehensive evaluation of soil hardness. By combining theoretical modeling, simulations, and experimental validation, the relationship between soil moisture and penetration resistance is analyzed. Results show a nonlinear correlation between moisture content and force, with forces ranging from 1.2 × 10 4 N at 0.8 moisture content to 7.8 × 10 4 N at 0.2 moisture content, at a depth of 0.01 m. Additionally, the FBG‐embedded beam experiences a peak deformation of 1.25 × 10 −6 m at a depth of 0.25 m, confirming the sensor's high accuracy. The dual‐force measurement approach significantly enhances the precision of soil hardness evaluations, offering real‐time, high‐resolution data for sustainable soil management. Furthermore, new equations specific to FBG‐based soil resistance and Bragg wavelength shifts are proposed for dual‐force measurement addressing limitations of conventional methods. This study advances soil testing technologies, with potential applications in agriculture, geotechnical engineering, and environmental sustainability.