Collaboration NAWA Pologne- Institut Fresnel

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Dans le cadre de la collaboration scientifique entre Institute of Agrophysics PAS (Lublin - Varsovie) - - et notre laboratoire nous recevrons une délégation de chercheurs polonais.
Trois d’entre eux nous présenterons leurs travaux lors de séminaires le mercredi 10 juillet 2019 à partir de 10h00 en salle Pierre Cotton.

 Wojciech Skierucha
 Arkadiusz Lewandowski
 Agnieszka Szypłowska

Wojciech Skierucha - Standardization of electromagnetic measurement of soil moisture
Abstract : Dielectric soil moisture sensors available currently on the market differ among each other in operating frequency and measurement accuracy. Yet, there is no widely accepted standard for verification and testing of sensors that would enable fair and reliable comparison of various devices. Therefore, the objective of the described project is to develop a comprehensive standardized testing procedure including reference soil dielectric spectrum measurement systems, soil dielectric spectrum modeling, reference materials for sensor calibration and verification and a reliable testing procedure. The presentation will describe the specific aims of the project, planned tasks and an outlook on the application of the research results.

Arkadiusz Lewandowski - One-Port Vector Network Analyzer Characterization of Soil Dielectric Spectrum
Abstract : The development of accurate soil moisture sensors and their verification require the knowledge of soil complex dielectric permittivity spectrum in a broad frequency range. Accurate wideband measurement of soil complex dielectric permittivity is possible with the use of large-diameter coaxial transmission-line cells connected to a vector network analyzer (VNA). We present a new laboratory system for soil dielectric spectrum characterization in the 0.05-3 GHz frequency range based on one-port VNA measurement. The key part of our approach is the use of an electronic calibration unit terminating the coaxial cell to extract the scattering parameters of the sample, which are then fed into a dielectric permittivity extraction algorithm. The system consists of six sample cells connected to the VNA by a six-channel multiplexer. The cells are placed in a temperature chamber extension in order to control the temperature of the samples from 0 to 40 degrees Celsius. We verify our methodology based on measurements of reference materials (polytetrafluoroethylene, isopropanol, and ethanol) and compare it to the classical two-port measurements. The measurement accuracy of the presented system is comparable to a two-port VNA setup for lossy materials, and higher than the two-port setup for low-loss materials like PTFE, due to the avoidance of the use of flexible cables. Also, the system is much more cost- and labour-efficient, enabling testing of up to six samples simultaneously at controlled temperatures.

Agnieszka Szypłowska - Reference dielectric measurement system as a tool for verification of soil moisture - dielectric permittivity calibration functions
Abstract : The accuracy of soil moisture measurement performed with the use of dielectric sensors depends not only on the accuracy of soil dielectric permittivity measurement, but also on the accuracy of the dielectric permittivity – soil moisture calibration curve and its selectivity to other factors like soil salinity and texture. The impact of these factors depends on the measurement frequency. The aim of the research is to examine the impact of salinity on dielectric permittivity – soil moisture calibration functions for ten soils of medium texture in the frequency range from 20 MHz to 3 GHz. Soil dielectric permittivity spectra were measured with the use of a coaxial transmission-line cell connected to a vector-network-analyzer. The obtained moisture – permittivity relations were compared to the calibration curves of several capacitance/impedance sensors operating at various frequencies. Based on the root-mean-square error analysis, the impact of salinity and texture was assessed and an optimal frequency range for soil moisture measurement was determined.