A time domain transmission method for the characterization of inhomogeneous dielectric materials

Delay time measurements, e.g. time domain transmission (TDT), are a well-established method for the measurement of permittivity in various materials, especially soils. However, common measurement systems only provide an average value of the dielectric constant along the length of the TDT probe. This contribution deals with an advanced use of the TDT principle for the determination of the water content of soil along the probe. The basis of the advanced TDT technique is a probe, realized by a combination of a waveguide and a dielectric obstacle, which can mechanically be moved along the probe. The probe is inserted into the soil for obtaining measurements of the effective soil permittivity. Thus, the water content along the probe can be estimated by means of the effective permittivity. Based on the known mechanical length of the probe and the position of the obstacle, the measured delay time can be used as a measure for the effective dielectric constant of the environment in the surrounding of the obstacle. Thus, it is possible to determine the effective dielectric constant with a spatial resolution given by the step size of the obstacle displacement.