Radiowave sensor for measuring the properties of dielectric sheets: Application to veneer moisture content and mass per unit area measurement

A radiowave sensor for measuring the properties of thin dielectric sheets has been constructed. The sensor is an electromagnetic stripline resonator with two center conductors. The sensor is non-contacting, tolerates moderate perpendicular movements of the measurement object, and has high sensitivity even for thin sheets. Also, an array of several adjacent sensors and a fast measuring equipment have been developed for the real-time mapping of wide sheets on a fast transporter. The sensor has been applied to simultaneous measurement of the moisture content and mass per unit area of veneer sheets, both undried (green veneer) and dried. The resonance frequency of the sensors used was about 350 MHz. Results obtained in the laboratory and in the factory are reported.