塿土介电特性与水分检测频率及温度影响

Dielectric properties of Lou soil and moisture content detection affected by frequency and temperature

为了确定基于介电特性的土壤含水率传感器的合适检测频率,并降低温度对介电参数的影响,以陕西关中地区的塿土为对象,利用矢量网络分析仪和同轴探头技术研究了信号频率(10～4 500 MHz)、土壤含水率(9%～25%)和温度(5～50℃)对土壤相对介电常数ε'和介质损耗因数ε″的影响,分析了介电参数变化的原因及频率、含水率和温度对电磁波穿透深度的影响规律.研究结果表明,在10～4 500 MHz频段内,随着频率的增大,土壤的ε'单调递减,而ε″先增大,后减小,进而再增大;ε'和ε″均随含水率和温度的增大而增大;穿透深度随频率、含水率和温度的增大而减小;频率、含水率和温度是影响土壤介电参数及穿透深度的主要因素.50～100MHz是基于介电特性检测土壤含水率的最佳频段.

To determine reasonable detecting frequency for developing soil′s moisture sensor based on dielectric properties and to reduce influence of temperature on permittivities,Lou soil in Guanzhong Plain,Shaanxi Province,was used to study the influence of frequency（10-4 500 MHz）,moisture content（9%-25%） and temperature（5-50 ℃） on relative dielectric constant and dielectric loss factor by network analyzer and coaxial-line probe technology.The reasons why permittivities changed with these factors were analyzed,and the frequency-,moisture content-and temperature-dependent penetration depth was determined.The results show that with the increasing of frequency from 10 MHz to 4 500 MHz,the relative dielectric constant decreases,while the dielectric loss factor changes from increasing to decreasing then to increasing.Both dielectric constant and loss factor increase with increasing moisture content and temperature over the detected ranges.The penetration depth decreases with increasing frequency,moisture content and temperature.Frequency,moisture content and temperature are major factors which influence dielectric permittivities and penetration depth of soil.The study indicates that the reasonable frequencies for detecting moisture content of soil based on dielectric properties are over the frequency range from 50 MHz to 100 MHz.