Sensor for Measuring the Mass Per Unit Area of a Dielectric Layer

A sensor for non-contact measurements of the thickness or mass per unit area of a dielectric layer has been developed. It has been constructed for measuring a cake of wooden particles on a steel band in the particle board industry. The sensor is suspended at a distance above the layer of particles to form a strip line resonator together with the steel band. The resonant frequency and the quality factor are measured. The resonant frequency correlates well with the mass per unit area and the quality factor can be used to deduce the mean wetness in the layer. The sensor is insensitive to moderate variations in the distance between the sensor and the steel band.