A mm-Wave Sensor for Remote Measurement of Moisture in Thin Paper Layers

We present the design and performance of a moisture sensor operating at 200 GHz for remote measurement of water content in paper. The system aims at industrial processes such as offset print and paper production. The moisture content in the paper is derived through an accurate measurement of the loss of a signal transmitted through the paper. The system is designed to achieve high accuracy in the measurement of the loss presented by the paper, not affected by 1/f or drift noise. The sensor is capable of resolving 0.005 dB loss achieving a moisture resolution of 0.1% for moisture content higher than 15%. The resolution can be improved if necessary in exchange for longer measurement times. The sensor is tested in offset print and paper production processes and measured values are compared to laboratory measured samples of the paper.