Отправлено: 12.07.17 12:48. Заголовок: Ultra-broad-band electrical spectroscopy of soils and sediments— a combined permittivity and conduct

GJI Marine geosciences and applied geophysics
Ultra-broad-band electrical spectroscopy of soils and sediments— a combined permittivity and conductivity model
M. Loewer,1 T. Gunther, ¨ 1 J. Igel,1 S. Kruschwitz,2 T. Martin3 and N. Wagner4

Geophys. J. Int. (2017) 210, 1360–1373 doi: 10.1093/gji/ggx242

SUMMARY
We combined two completely different methods measuring the frequency-dependent electrical
properties of moist porous materials in order to receive an extraordinary large frequency
spectrum. In the low-frequency (LF) range, complex electrical resistivity between 1 mHz and
45 kHz was measured for three different soils and sandstone, using the spectral induced polarization
(SIP) method with a four electrode cell. In the high-frequency (HF) radio to microwave
range, complex dielectric permittivity was measured between 1 MHz and 10 GHz for the same
samples using dielectric spectroscopy by means of the coaxial transmission line technique.
The combined data sets cover 13 orders of magnitude and were transferred into their equivalent
expressions: the complex effective dielectric permittivity and the complex effective electrical
conductivity. We applied the Kramers-Kronig relation in order to justify the validity of the data
combination. A new phenomenological model that consists of both dielectric permittivity and
electrical conductivity terms in a Debye- and Cole–Cole-type manner was fitted to the spectra.
The combined permittivity and conductivity model accounts for the most common representations
of the physical quantities with respect to the individual measuring method. A maximum
number of four relaxation processes was identified in the analysed frequency range. Among
these are the free water and different interfacial relaxation processes, the Maxwell-Wagner
effect, the counterion relaxation in the electrical double layer and the direct-current electrical
conductivity. There is evidence that free water relaxation does not affect the electrical response
in the SIP range. Moreover, direct current conductivity contribution (bulk and interface) dominates
the losses in the HF range. Interfacial relaxation processes with relaxations in the HF
range are broadly distributed down to the LF range. The slowest observed process in the LF
range has a minor contribution to the HF response.