  The spatial sensor characteristics of a 6cm TDR flat band cable sensor
section was simulated with finite element modelling (High Frequency Structure
Simulator-HFSS) under certain conditions: (i) in direct contact to the
surrounding material (air, water of different salinities, different synthetic
and natural soils (sand-silt-clay mixtures)), (ii) with consideration of a
defined gap of different size filled with air or water and (iii) the cable
sensor pressed at a borehole-wall. The complex dielectric permittivity or
complex electrical conductivity of the investigated saturated and unsaturated
soils was examined in the frequency range 50MHz-20GHz at room temperature and
atmospheric pressure with a HP8720D- network analyser. Three soil-specific
relaxation processes are assumed to act in the investigated
frequency-temperature-pressure range: one primary (main water relaxation) and
two secondary processes due to clay-water-ion interactions (bound water
relaxation and the Maxwell-Wagner effect). 3D finite element simulation is
performed with a 1/3 wavelength based adaptive mesh refinement at a solution
frequency of 1MHz, 10MHz, 0.1GHz, 1GHz and 12.5GHz. The electromagnetic field
distribution, S-parameter and step responses were examined.
