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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 of the frequency deviation of the λ / 4 coaxial cavity extended by the open end outer conductor by the perturbation of the granular medium is deduced and the frequency deviation of the soybeans with different particle sizes is experimentally measured. Theoretical calculations and experiments show that when using the cavity of the limit-limited circular waveguide section as a container, the electromagnetic field in the limit-limited circular waveguide attenuates exponentially in the longitudinal direction. When the appropriate attenuation coefficient α is selected, Of the linear variation range, filled with a layer of granular media generated frequency deviation value with the particle radius R little change. The use of such cavities to measure the wetness of the granular media eliminates the effects of particle size and shape within a certain range.