Characterization of Dielectric Profiles by Using Microwave Delay Time Measurements

Delay time measurements, e. g. time domain reflectometry (TDR), are a well-established method for the measurement of permittivity in various materials, especially soils. However, common measurement systems provide only one average value of the dielectric constant along the length of the TDR probe. This contribution presents two methods for the measurement of dielectric profiles independent of the structure of the material under test. The basis of these advanced delay time measurement technique is a waveguide, which is inserted into the material under test for obtaining measurements of the effective permittivity, and an obstacle, which can mechanically be moved along the probe. The obstacle serves as a discontinuity. Thus, by moving the obstacle the permittivity of the surrounding can be determined with a spatial resolution given by the step size of the obstacle displacement.