Design and analysis of wideband antennas for borehole and surface ground penetrating radars: Application to soil moisture content measurements - Université Pierre et Marie Curie Accéder directement au contenu
Communication Dans Un Congrès Année : 2010

Design and analysis of wideband antennas for borehole and surface ground penetrating radars: Application to soil moisture content measurements

Résumé

In civil engineering, the non destructive sounding of underground infrastructures (embankment, roads, bridges…) allows to monitor the structural integrity or adequacy during construction, and the detection of degradations of construction materials (cement concrete, bituminous concrete, masonry, earthwork…) during the working life [1]. Ground Penetrating Radar (GPR) is a proven technique based on the propagation of transient electromagnetic (EM) waves in a soil or a man-made structure in a large frequency band ([0.1;2] GHz) to detect, localize and characterize dielectric discontinuities with a high resolution. The choice of the frequency range is a trade-off between resolution (close to the wavelength) and penetration depth (around 20 wavelengths). In order to enhance the dielectric characterization of underground structures and particularly to estimate the moisture content of a soil as a function of depth, we have designed several original wideband antennas (folded dipole, blade dipole and bowtie slot) dedicated either to a borehole or a surface GPR radar. As a surface radar relies on wave reflection and a borehole radar on wave transmission [5], the frequency band defined in the case of a surface radar will be lower than in the case of a borehole radar in order to obtain the penetration of EM waves at a depth close to 1 m; in the crosshole radar that considers narrow boreholes with diameter less than 60 mm, the distance between antennas are less than 70 cm. Thus, the frequency bands defined are [0.35;1] GHz and [0.5;1.5] GHz respectively. According to previous studies, the design of the antennas appears as a challenge as we had to reduce the width in the case of the borehole radars (d<60 cm), and the length in the case of the surface radar (l~52 cm). In this paper, we have used the FDTD method to simulate the complete GPR links associated with both types of GPR configuration. In particular, we have studied in details the response of the proposed antennas in the presence of a layered soil. The modeling has allowed to highlight the physical phenomena involved in the measurement data. Measurements made in the frequency domain using a VNA (Vector Network Analyzer) on a wet clay sand embankment. Their transformation in the time domain has highlighted the dielectric interfaces corresponding to the different moisture contents. Data processing has allowed to estimate the volumetric moisture and the attenuation coefficient as a function of the depth.
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Dates et versions

hal-01054361 , version 1 (06-08-2014)

Identifiants

  • HAL Id : hal-01054361 , version 1

Citer

Florence Sagnard, Fayçal Rejiba, Michel Froumentin. Design and analysis of wideband antennas for borehole and surface ground penetrating radars: Application to soil moisture content measurements. IEEE International Symposium on Antennas and Propagation, Jul 2010, Canada. 4p. ⟨hal-01054361⟩
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