摘要
根据时域传输TDT法,设计了灌木茎体含水率测量装置。装置由高频信号源、同轴传输线、缠绕式探头及相位比较电路4部分组成。高频电磁波在不同介质中的传播速度不同,表现为在不同介质中的传播相位不同,而含水灌木介电常数的大小主要取决于其含水率的大小,因此通过测量电磁波在同轴电缆上A和缠绕于灌木茎体上探头B的相位差来获取灌木的含水率。选择吸水棉棒来模拟不同含水率的灌木,研究高频信号源工作频率、探头结构对相位差的影响。实验表明,当探针长度为60 cm,信号源频率为50 MHz和100 MHz时,A、B两路电磁波信号的相位差与棉棒吸水率变化呈单调性,且具有良好的相关性。
Based on time domain transmissometry （TDT）, measurement device for shrub stem water content was designed. This device consists of high frequency signal source, coaxial transmission lines, winding probe and phase comparison circuit. Propagation velocity of high frequency electromagnetic wave varies in different medium, and the propagation phase also changes. The dielectric constant of wet shrubs mainly depends on its moisture content. By measuring phase difference between the coaxial cable A and the winding stem probe B, the moisture content in shrubs was obtained. Absorbent cotton stick was choice to simulate shrubs with different moisture content. And the influence of the phase difference from frequency of high frequency signal source and the structure of the probe was studied. Experimental results show that under the conditions of 60cm probe length, 50MHz and 100MHz signal source frequency, the phase difference between the coaxial cable A and the winding stem probe B is monotonic with the change of water content, and there exists a good correlation between phase difference and moisture content.
出处
《农业机械学报》
EI
CAS
CSCD
北大核心
2014年第5期259-264,共6页
Transactions of the Chinese Society for Agricultural Machinery
基金
国家自然科学基金资助项目(31371537)
农业科技成果转化资金资助项目(2012GB23600634)
北京市教育委员会共建项目建设计划科学研究与科研基地建设资助项目(2008BJKY01)
国际科技合作专项(2010DFA34670)
