活立木中的腐烂和空洞通常是造成树木倒塌的重要原因,通过检测活立木内部结构来判断木材内部的缺陷。针对此现状,提出基于微波层析成像的活立木内部缺陷检测方法。首先搭建由16个天线组成的微波层析成像系统,在1 GHz的频率下模拟健康木材和两种不同缺陷的木材模型,通过有限元分析软件模拟活立木内部的电场特性,得到用于图像重建的散射场,采用线性反投影图像重建算法重建木材内部的介电常数分布图。然后使用平均结构相似性指数分析重建图像。最后对不同的树干模型和重建图像进行定性和定量分析。仿真结果表明,微波层析成像技术可以利用重建介电常数分布图的可视化效果直接识别缺陷的位置和大小等。

The collapse of trees can be mainly attributed to the decay and hollow in standing timber. The internal structure of standing timber is verified to determine the internal defects. In this study, a method is proposed to detect the internal defects in standing timber based on microwave tomography. First, a microwave tomography system comprising 16 antennas is developed. Second, a healthy wood model and two wood models with different defects are simulated at a frequency of 1 GHz. Third, the finite element analysis software is used to simulate the internal electric field characteristics of the standing timber, based on which image reconstruction can be performed using the linear backprojection image reconstruction algorithm, thereby reconstructing the dielectric constant distribution map inside the wood. Then, the reconstructed image is analyzed based on the average structural similarity index. Finally, qualitative and quantitative analyses of the different trunk models and reconstructed image are conducted. Simulation results demonstrate that the position and size of a defect can be directly identified using the proposed microwave tomography system based on the visualization effect of the reconstructed permittivity distribution map.