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Spatial Retrieval of Broadband Dielectric Spectra
Jan Bumberger 1 , Juliane Mai 2 , Felix Schmidt 1 , Peter Lünenschloß 1 , Norman Wagner 3 , Hannes Töpfer 4
1  Department Monitoring and Exploration Technologies, Helmholtz Centre for Environmental Research—UFZ, Permoserstrasse 15, 04318 Leipzig, Germany;(F.S.);(P.L.)
2  Department of Computational Hydrosystems, Helmholtz Centre for Environmental Research—UFZ, Permoserstrasse 15, 04318 Leipzig, Germany
3  Institute of Material Research and Testing—MFPA at the Bauhaus-University Weimar, Coudraystrasse 9, 99423 Weimar, Germany
4  Department of Advanced Electromagnetics, Technische Universität Ilmenau, Helmholtzplatz 2, 98693 Ilmenau, Germany

Published: 23 August 2018 by MDPI in Sensors
MDPI, Volume 18; 10.3390/s18092780
Abstract: A broadband soil dielectric spectra retrieval approach (1 MHz–2 GHz) has been implemented for a layered half space. The inversion kernel consists of a two-port transmission line forward model in the frequency domain and a constitutive material equation based on a power law soil mixture rule (Complex Refractive Index Model—CRIM). The spatially-distributed retrieval of broadband dielectric spectra was achieved with a global optimization approach based on a Shuffled Complex Evolution (SCE) algorithm using the full set of the scattering parameters. For each layer, the broadband dielectric spectra were retrieved with the corresponding parameters thickness, porosity, water saturation and electrical conductivity of the aqueous pore solution. For the validation of the approach, a coaxial transmission line cell measured with a network analyzer was used. The possibilities and limitations of the inverse parameter estimation were numerically analyzed in four scenarios. Expected and retrieved layer thicknesses, soil properties and broadband dielectric spectra in each scenario were in reasonable agreement. Hence, the model is suitable for an estimation of in-homogeneous material parameter distributions. Moreover, the proposed frequency domain approach allows an automatic adaptation of layer number and thickness or regular grids in time and/or space.
Keywords: Modeling, Dielectric materials, microwave propagation, dielectric measurements, Soil Measurements, Electromagnetic Scattering Inverse Problems
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