基于微波热声成像的植物叶片水分含量分布无损检测技术研究

Detection of Water Distribution in Plant Leaves Using Thermoacoustic Imaging

目的植物叶片水分含量分布是衡量植物生理生化的重要指标,该指标也是农业科学领域中制定抗旱策略的重要依据。微波成像对水分含量分布和变化具有高对比度,超声成像对水分含量分布具有高分辨率。据此,本文提出兼具微波和超声成像优势的无损微波热声成像(thermoacoustic imaging,TAI)技术,并用此技术开展了植物叶片水分含量分布的无损检测研究,进行植物叶片水分含量分布的检测,对于实现精准灌溉、发展节水农业、提高水资源利用率有重要意义。方法本文构建了激发频率3.0 GHz、横向分辨率406μm的二维透射式TAI系统。基于主动加热技术(150℃热风,90 s),模拟3组曼陀罗叶片水分流失过程,对其TAI图像进行定量分析。结果加热导致叶片局部水分流失,微波热声信号降低(信号最大变化量为10%),验证了基于TAI技术实现植物叶片水分含量变化无损检测的可行性。实现了曼陀罗、野茼蒿和紫苏叶片水分含量分布的无损检测,检测结果与核磁共振成像吻合。结论本研究有助于实现精准灌溉,为植物在正常和胁迫环境下对环境的响应特性研究提供技术支撑。尤其是与非接触超声检测技术相结合,可以实现植物叶片水分含量的遥感成像,更具实用价值。

Objective The distribution of water content in plant leaves is an important indicator for measuring plant physiology and biochemistry,and it is also an important basis for formulating drought resistance strategies in the field of agricultural science.Microwave imaging has high contrast and sensitivity in the distribution and variation of water content,while ultrasound imaging has high resolution.Based on this,this paper proposes a nondestructive microwave thermoacoustic imaging(TAI)technology that combines the advantages of microwave and ultrasound imaging,and uses this technology to carry out non-destructive testing research on the distribution of plant leaf water content,which is of great significance for achieving precise irrigation,developing water-saving agriculture,and improving water resource utilization.Methods This study constructs a two-dimensional transmissive TAI system with an excitation frequency of 3.0 GHz and a lateral resolution of 0.406μm.Based on active heating technology(150℃ hot air,90 s),3 sets of mandala leaf moisture loss processes were simulated,and their TAI images were quantitatively analyzed.Results The results showed that heating caused local moisture loss and reduced thermoacoustic signals,verifying the feasibility of non-destructive detection of plant leaf water content changes based on TAI,which achieves non-destructive detection of water content distribution in leaves of Datura,Crassocephalum crepidioides and Perilla.The results are consistent with magnetic resonance imaging(MRI).Conclusion This study contributes to achieve precise irrigation and provides technical support for studying the response characteristics of plants to the environment under normal and stress environments.Especially when combined with non-contact ultrasound detection technology,remote sensing of plant leaf water content can be achieved,which has more practical value.