A Semi-Empirical Model for Predicting the Effects of Moisture on Microwave Signal Attenuation in Fouled Railroad Ballast

Monitoring moisture content in fouled railroad ballast is important for understanding the structural integrity of the ballast. A semi-empirical mixing model is developed in this work to understand microwave signal propagation in the heterogeneous and multi-dielectric structure of ballast to facilitate the future use of embedded wireless sensors. The model uses the measured dielectric properties and volumetric percent composition of the materials in the mixture to determine the dielectric properties of the composite. The attenuation data calculated from the model show good agreement with measured data at 1.2 GHz. The model thus shows promise in predicting moisture content in railroad ballast with the use of microwave propagation measurements.