A novel sensor design for the determination of dielectric profiles using time domain reflectometry

The measurement of dielectric profiles, for example for the determination moisture distributions in natural soils, gets more and more important. One common setup for dielectric measurements uses time domain reflectometry (TDR) techniques. Actually, standard measurement setups give only mean or point-wise results, but for many applications it is necessary to determine a dielectric profile. Two different basic setups for the determination of dielectric profiles with a resolution in a centimeter range are presented in this contribution. Both setups are based on time domain reflectometry (TDR) measurements. On the one hand an arbitrary spatial resolution is achieved by a movable dielectric obstacle, which causes a discontinuity along the sensor line. On the other hand a sensor based on remotely switched diodes allows the determination of a spatially resolved dielectric profile by discrete steps. Both setups have the advantage that the spatial resolution is independent of the material of interest. Thus it is even possible to determine a dielectric profile of a material with continuously varying permittivities.