Dual-Frequency Microwave Moisture Sensor Based on Circular Microstrip Antenna

A dual-frequency sensor was developed to measure moisture content of lossy liquids. The experiment is based on measurements of far-field reflection at two frequencies in the X-band, 8.48 and 10.69 GHz. The replacement of the conventional open horn antenna with microstrip radiating patches makes the sensor more versatile and compact. The sensor is interfaced to a notebook computer using a multipurpose data acquisition board and few custom made circuits. Data collection, errors correction and calibration modules were written using LabVIEW^reg programming language. Three calibration methods were used to obtain an empirical equation, which is applied to obtain the moisture content of the rubber latex samples. Moisture content can be determined with a standard error 0.49%.