Contactless Moisture Content Sensor Based on Wheeler Cap for Waste-to-Energy Plants

This paper presents a novel nondestructive, contactless moisture content sensor based on the Wheeler Cap measurement technique. The sensor comprises an electrically small antenna enclosed within a compact metallic cap, along with the material under test. The operating frequency of the sensor without material under test is 268.25 megahertz. By measuring the reflection coefficient at the input port of the antenna enclosed in the metallic cap, the moisture content of the material under test can be determined. The proposed sensor is aimed for moisture content measurement of the municipal solid waste, the primary feedstock for refuse-derived fuel utilized in waste-to-energy power plants. The moisture content of material under test can be determined using magnitude or frequency of the minimum reflection coefficient from the measured frequency response. Linear regression models are developed to establish the relationship between moisture content and the measured magnitude or frequency yielding coefficient of determination $R^{2}$ of 0.934 and 0.936, respectively. The sensor exhibits a sensitivity of 0.034 dBm decrease in magnitude and 0.097 MHz decrease in frequency per 1% increase in moisture content. This performance demonstrates the sensor’s potential as a reliable and accurate tool for moisture content measurement in WtE applications.