FDR探头结构对土壤介电谱测量的影响分析

为了研究FDR探头结构中探针间距和探针长度对土壤介电谱测量的影响,通过矢量网络分析仪分别对2种土壤的4个不同体积含水率进行了介电谱测量,通过28 mm长度下10 mm、14 mm探针间距探头和10 mm间距下28 mm、45 mm长度探头所测介电谱对比发现,在31.2 MHz以上频段探针间距对土壤介电谱测量影响很小,而探针长度在不同频段对土壤介电实部或虚部均有不同影响。研究表明,探针间距不是土壤介电谱测量的影响因素,根据测量需要可对其进行一定范围的调整;探针长度影响土壤介电谱弛豫频率值,探针越短其弛豫频率越大,探针长度是影响土壤介电谱测量的关键因素之一。FDR探头的探针应适当缩短以拓展介电谱平滑段的频率范围,这有利于FDR传感器测量精度和环境适应性的提高。

FDR Probe Structure Influence on the Soil Dielectric Spectrum Measurement

The soil dielectric spectrum are related to the soil physical properties, and those are affected by the structure of the probe too. In order to determine how the probe structure influence the soil dielectric spectrum measurement, the two kinds of soils were measured at four water content level by 10mm and 14mm spacing needle at 28mm probe length, 28mm and 45mm length needle at 10mm spacing. It has been confirmed that the probe spacing has no effect on the soil dielectric spectrum measurement above 31.2MHz by comparing the dielectric spectrums, and the length of the probe can affect the real or imaginary part of the soil dielectric spectrum in the range of 0.001~3GHz. The research shows that the spacing of needle is not the key factor to the soil dielectric property measurement within a certain spacing, and the length of the probe has a greater influence on the soil dielectric property measurement. The smaller of the probe length, the larger of the dielectric relaxation frequency. Therefore, the probe length is the important factor that affect soil dielectric measurements. The FDR probe should be shorter, it is good to improve the measurement accuracy and environmental adaptation.