The oil palm trees in Southeast Asia face a great challenge due to voids within tree trunks. Besides, both plantations and the palm oil industry suffered considerable losses due to ineffective inspection of defective trees. Several techniques such as ultrasound, X-ray, capacitive volume, gamma computed tomography, and microwave tomography were applied to detect and control the decay of a trunk. However, all the techniques showed substantial drawbacks (such as limited resolution, tedious processing time, and use of bulky equipment with limited mobility) except for microwave tomography which overtook the other techniques by using a method that distinguishes the dielectric properties of healthy and diseased trunks. This work proposes ultra-wide-band (UWB) signal transmission and reception using antenna sensor arrays that record reflections from affected regions in the trunk. Various factors have been considered, such as different cylindrical arrays of 4, 8, 12, and 16 antennas; different positions of hollows; a heterogeneous trunk; multiple targets; and larger trunk samples (16–30 cm). To validate the system’s capabilities, two cylindrical wood samples with different diameters of 100 mm and 140 mm and with one hollow and three hollows within are 3D-printed, investigated, and then measured. The authors recommended a robust time-reversal algorithm (RTR) to reconstruct 2D images that successfully identified and localized cavities with the smallest diameter of 3.5 mm. Furthermore, reconstructed images of measured data verified a practical and reliable oil palm trunk imaging and sensing system with a high structural similarity index and resolution.

中文翻译：

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超宽带天线在油棕主干中空洞的微波成像及鲁棒的时间逆转算法

由于树干中的空隙，东南亚的油棕树面临着巨大的挑战。此外，由于对不良树木的无效检查，种植园和棕榈油行业均遭受了可观的损失。诸如超声，X射线，电容性体积，伽马计算机断层扫描和微波断层扫描等多种技术被应用于检测和控制躯干的衰变。但是，所有技术均显示出重大缺陷（例如分辨率受限，繁琐的处理时间以及使用流动性有限的笨重设备），但微波层析成像技术通过使用区分健康和患病树干的介电特性的方法取代了其他技术。这项工作提出了使用天线传感器阵列的超宽带（UWB）信号发送和接收，该传感器记录了树干中受影响区域的反射。已经考虑了多种因素，例如4、8、12和16个天线的不同圆柱阵列。空心的不同位置；异类主干 多个目标；和较大的树干样本（16–30厘米）。为了验证系统的功能，对3个直径分别为100毫米和140毫米，内部有一个中空和三个中空的圆柱形木质样品进行3D打印，研究和测量。作者建议使用鲁棒的时间逆转算法（RTR）来重建2D图像，该图像可成功识别和定位最小直径为3.5毫米的腔体。此外，