同轴腔微扰法测量颗粒状物料湿度

Determination of Humidity of Particulate Materials by the Method of Coaxial Cavity Perturbation

导出开路端外导体加长的λ／４同轴腔受颗粒状介质微扰的频偏近似计算公式，并在实验上测出不同湿度不同颗粒大小黄豆的频偏值．理论计算及实验均表明，如用上述腔体的过极限圆波导段做容器，由于过极限圆波导中电磁场沿纵向按指数率衰减，当选择合适的衰减系数α，在通常的黄豆等粮食颗粒的线度变化范围内，填充一层颗粒状介质所产生的频偏值随颗粒半径Ｒ的变化不大．应用此种腔体测量颗粒状介质湿度，可以在一定范围内消除粒度大小和形状的影响．

The approximate formula for calculating frequency shift by the perturbation method of coaxial cavity ,which has a extended outer conductor,is deduced ,and the experimental results for frequency shift measurement of soybeans with different radii under with different levels of humidity are presented.If the section of cut off circular waveguide above mentioned is used as a vessel,the electromagnetic field in it would attenuate exponentially along the longitudinal direction.When the attenuation constant is selected suitably ,the frequency shift caused by filling a layer of particulate material in it has little to do with the measured object′s radius R if soybeans,peanuts and so on were used as sample. For this reason,such a cavity can be used for measuring humidity of some particulate material ,which can eliminate the influence of its size and shape to some extent.