Time domain reflectrometry measurements using a movable obstacle for the determination of dielectric profiles

[摘要] Microwave techniques for the measurement of the permittivity ofsoils including the water content of soils and other materials,especially TDR (time domain reflectometry), have become accepted asroutine measurement techniques. This summary deals with an advanceduse of the TDR principle for the determination of the water contentof soil along a probe. The basis of the advanced TDR technique is awaveguide, which is inserted into the soil for obtainingmeasurements of the effective soil permittivity, from which thewater content is estimated, and an obstacle, which can mechanicallybe moved along the probe and which acts as a reference reflectionfor the TDR system with an exactly known position. Based on theknown mechanical position of the reference reflection, the measuredelectrical position can be used as a measure for the effectivedielectric constant of the environment. Thus, it is possible todetermine the effective dielectric constant with a spatialresolution given by the step size of the obstacle displacement.

A conventional industrial TDR-system, operating in thebaseband, is used for the signal generation and for the evaluationof the pulse delay time of the obstacle reflection. Thus, a costeffective method for the acquisition of the dielectric measurementdata is available.

[学科分类] 电子、光学、磁材料