Development of a Resonant Microwave Sensor for Sediment Density Characterization.

R Mansour,B Lescop,S Rioual,M Abboud,P Talbot,W Farah,G Tanné

doi:10.3390/s20041058

Abstract

In this study, a sensor based on the development of a planar antenna immersed in sediments dedicated to water content monitoring in this type of material is proposed and experimentally validated. It is produced by a conventional Printed Circuit Board (PCB) manufacturing process on a double-sided metalized FR4 substrate. The sensitivity of the sensor is ensured by the variation of the real part of the complex dielectric permittivity of sediments with water content at around 1 GHz. As shown, in this frequency range, electrode polarization and Maxwell–Wagner polarization effects become negligible, leading to only a bulk water polarization sensitivity. The sensor operates in the reflection mode by monitoring the variation of the resonant frequency as a function of the sediment density through the S11 reflection measurements. An experimental sensitivity of was achieved. Despite the simplification of data interpretation at the considered frequency, the influence of ionic species such as NaCl in sediments on the real part of the relative complex dielectric permittivity is highlighted. This demonstrates the importance of considering a second parameter such as the S11 level at low frequency or the electrical conductivity to extract the density from the frequency measurements.

Highlights

The study of sedimentary systems and assessment of geological hazards associated with different external mechanisms requires a characterization of the physical and mechanical properties of the medium such as electrical conductivity and density
We propose to exploit the results depicted in Figure 9b where the S11 level at low frequency is shown to depend on c
The development of planar resonant radiofrequency sensors for water content monitoring in high loss dielectric materials such as sediments is feasible around 1 GHz due to the absence of polarization effects and to the presence of a minimum of the radiofrequency losses

Summary

Introduction

The study of sedimentary systems and assessment of geological hazards associated with different external mechanisms (earthquake, tsunami, etc.) requires a characterization of the physical and mechanical properties of the medium such as electrical conductivity and density. Acoustic profilers sensitive to the variation of the acoustic impedance have been used for decades to measure in-situ properties of subsurface sediments [5,6]. Optical backscattered sensors (OBS) are very popular for this purpose and measure the turbidity of water and suspended sediment concentrations [7]. Electromagnetic sensors are based on the variation of dielectric property of materials, i.e., the relative complex dielectric permittivity εr = ε0 − jε00. The latter is strongly correlated to the water volume content due to the high value of the real part of the relative dielectric permittivity (ε0 ) of water with respect to other species, about 5 for minerals and 80 for water. Extracting the water content by considering simple mixture models is a Sensors 2020, 20, 1058; doi:10.3390/s20041058 www.mdpi.com/journal/sensors

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Conclusion