Department of Mechanical and Aerospace Engineering, Sapienza University of Rome, 00184 Rome, Italy.
Department of Information Engineering, Electronics and Telecommunications, Sapienza University of Rome, 00184 Rome, Italy.
Sensors (Basel). 2022 Mar 10;22(6):2148. doi: 10.3390/s22062148.
In this work, the dielectric permittivity of four kinds of wood (Fir, Poplar, Oak, and Beech Tree), used in Italian Artworks and structures, was characterized at different humidity levels. Measurements were carried out using three different probes connected to a bench vector network analyzer: a standard WR90 X-band waveguide, a WR430 waveguide, and an open-ended coaxial probe. In particular, we investigated the dispersion model for the four wood species, showing how a log-fit model of the open-ended data presents a determination coefficient R2 > 0.990 in the 1−12 GHz frequency range. This result has proven helpful to fill the frequency gap between the measurements obtained at different water contents with the two waveguide probes showing an R2 > 0.93. Furthermore, correlating the log-fit vertical shift with the water content, it was possible to find a calibration curve with a linear characteristic. These experimental results will be helpful for on-site non-invasive water monitoring of wooden artworks or structures. Moreover, the final results show how the open-ended coaxial probe, with a measurement deviation lower than 7% from the waveguide measurements, may be used directly as a non-invasive sensor for on-site measurements.
在这项工作中，对四种用于意大利艺术品和结构的木材（冷杉、杨木、橡木和山毛榉木）的介电常数在不同湿度水平下进行了表征。使用连接到台式矢量网络分析仪的三个不同探头进行了测量：标准 WR90 X 波段波导、WR430 波导和开放式同轴探头。特别地，我们研究了四种木材的色散模型，表明开放式数据的对数拟合模型在 1-12GHz 频率范围内呈现出确定系数 R2>0.990。这一结果有助于填补使用两个波导探头在不同含水量下获得的测量值之间的频率间隙，显示出 R2>0.93。此外，将对数拟合垂直位移与含水量相关联，可以找到具有线性特征的校准曲线。这些实验结果将有助于对木质艺术品或结构进行现场非侵入式水监测。此外，最终结果表明，开放式同轴探头的测量偏差比波导测量低 7%，可直接用作现场测量的非侵入式传感器。
