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Abstract

A method for highly accurate, high speed, multi-slice density and moisture content measurements and calculations of homogeneous or non-homogeneous fibrous material, using a microwave resonator device and computer algorithms. The device is comprised of a cylindrical microwave resonator, including two cutoff waveguides, internal corrective pieces, a teflon tube, signal input and output ports, alternative microwave sources, alternative signal receivers, temperature sensor and optional moisture sensor, and computerized processing and display units. The method comprises passing fibrous material, located in-line of a production process, through the resonator, wherein the fibrous material is scanned with a sweeping range of microwave frequencies, in a continuous, real time, and multi-slice mode. The presence of the fibrous material causes resonance frequency shifts and changes in resonator quality, which are proportional to, and used in calculations of, material density and moisture content, respectively. Calculations of material density (and moisture content) are based on evaluation of density and moisture content arrays (of time samples), which are functions of resonator frequency shift and quality data, empirically determined density, moisture content, and structurally dependent correlation functions, and material temperature. Improved accuracy in values of density is obtained by compensating for moisture content. Density and moisture content values are used for real time quality control feedback of process parameters, including fiber density, moisture content, temperature, and incoming feed rate.

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