Ultrasensitive moisture content sensing in wood samples is demonstrated employing a modified cylindrical cavity resonator geometry. A vertical sensing channel is introduced at the middle section of the cavity for sample placement. Field homogeneity inside the sensing channel is improved by a thin hollow quartz inset. A relation between the moisture content of wood and the resonance frequency for the dominant TM${}_{010}$-mode is extracted for the operation frequency range. Full-wave simulations are used to characterize and optimize the sensing technique. For experimental verification, a wood sample with 24$\%$ moisture content is allowed to dry in the cavity at room temperature for 24 h and its resonance frequency is monitored. The experiment is repeated for a sample which partially fills the sensing channel. Finally, the variation of the moisture content of a freshly cut tree branch is monitored in vitro. The experiments and simulations reveal that the proposed technique offers a very high sensitivity for characterization of the moisture content of wood samples of different radii, owing to the very high quality factor of the cylindrical cavity resonator. The technique is thus a promising candidate for the non-destructive monitoring of the moisture content of trees towards the prevention of forest fires and for the evaluation of products made from wood in industry.

演示了采用改进的圆柱腔谐振器几何形状的木材样品中超灵敏的水分感测。在腔体的中间部分引入了一个垂直的感应通道，用于放置样品。感应通道内部的场均匀性通过薄的空心石英镶嵌得以改善。木材的水分含量与TM的共振频率之间的关系${}_{010}$-mode是针对工作频率范围提取的。全波模拟用于表征和优化传感技术。为了进行实验验证，用24$％$使水分在室温下在型腔中干燥24小时，并监测其共振频率。对部分填充传感通道的样品重复该实验。最后，在体外监测鲜切树枝的水分含量的变化。实验和仿真表明，由于圆柱腔谐振器的质量因数很高，所提出的技术为表征不同半径的木材样品的水分含量提供了很高的灵敏度。因此，该技术是用于无损监测树木的水分以防止森林火灾以及评估工业用木材产品的有前途的候选人。