Research On Moisture Cotent Measurement Sensor Using Microwave Coaxial Resonant

The quality of materials such as crop, food and mineral is influeced by moisture content. The traditional measurement method using microwave transmission technique distributes electromagnetic fields in free space easily which makes it hard to improve measurement precision. Resonant cavity sensor is not suitable for on-line industry applications because the measured material is inside. It is necessary to develop an open-ended coaxial resonant sensor to obtain rapid and high precise measurement.In this study, some key technologies, related theories and methods on designing microwave coxial resonant moisture sensor, are adopted and researched. The main reaearch works are as follows:Firstly, high precise and rapid moisture content measurements have become the main problem that some industries face. On the base of analyzing existing moisture content measurement techniques, some disadvantages about infrared and free space microwave are presented. So open-ended coaxial resonant cavity as moisture content sensor are presented.An open-ended coaxial resonant cavity for moisture content sensor is presented and developed. On perturation theory resonant cavity model is built by FDTD dividing grids of resonant cavity space and solving them. On the base of the model, electromagnetic fields distribution inside and outside of resonant cavity, also noload resonance frequency and cover material's influences on measurement precision are analyzed. Otherwise installation manner and transfer system on line for resonant cavity sensor are designed. Simulation results show that taking 2.45GHz as resonance frequency balances measurement nonlinearity and resolution well, and cover material can infulence the measurement resolution. Last, samples prepared for experiment are introduced. Experiments of stability, resolution and repeatability on open-ended resonant cavity sensor are researched.