KEYWORDS: General packet radio service, Antennas, Signal attenuation, Dielectrics, Radar, Nondestructive evaluation, Interfaces, Electromagnetism, Magnetism, Radio propagation
Ground-penetrating radar (GPR) is a high resolution surveying method applied to civil engineering, surface geology,
archaeology and other disciplines. Today, GPR is an effective technique for investigating the integrity of concrete
structures. As a non destructive technique, it is particularly suited for the assessment of large structures such as
prestressed concrete bridges, highways, railway tracks and tunnels. A significant parameter in GPR high frequency
surveys is the horizontal resolution. This parameter indicates the capability of the method to detect anomalies and to
discriminate between adjacent elements. In concrete structures analysis the horizontal resolution lead to determine the
exact position of reinforcing elements. This paper presents the basics of GPR, its limits, and the experimental
measurements and the signals post-processing performed in order to determine the horizontal resolution of a 1.6 GHz
antenna in concrete structures assessments.
KEYWORDS: Antennas, General packet radio service, Radar, Signal attenuation, Time metrology, Receivers, Radiation effects, Near field, Transmitters, Electromagnetism
Ground-Penetrating Radar has become a popular non-destructive and non-invasive tool in different kind of applications:
civil engineering, archaeology, concrete and masonry analysis, etc. The selection of the antenna frequencies depends on
the application, but each antenna has a radiation pattern and some characteristics that have influence in the final
interpretation and in the model obtained for the studied medium. The knowledge of these features and its coupling
effects with the medium could improve the results of the GPR prospecting studies. In this work, some experimental
procedures were carried out in order to obtain the 1.6 GHz centre frequency antenna characteristics in the air and in one
material medium and to compare them. First, the study of the attenuation due to geometrical spreading was performed.
This result was compared with the amplitude attenuation in a material medium, deduced from the GPR experimental
data. Second, the shape of the radiation pattern was estimated in laboratory for different distances between the target and
the antenna. Near field and far field were considered during the experimental data acquisition. Third, the relative
amplitude of the reflected wave (in dB) was obtained depending on the relative position of the antenna over the target.
The shape of the radiation pattern and the relative amplitudes obtained in the air were compared with those obtained in a
slow medium (water). This slow medium was characterized with the wave velocity and the attenuation factor of the GPR
signal.
Ground-penetrating radar (GPR) is a high resolution surveying method applied to civil engineering, surface geology,
archaeology and other disciplines. Mainly it is used solving the direct problem and obtaining a model of the studied
medium. Otherwise, the study of the inverse problem could provide other valuable information: the electromagnetic
properties of the medium. These parameters are obtained from the changes of the velocity, attenuation and frequency of
the recorded wave. The physical properties of the medium related to those wave parameters are, mainly, the water
content and the porosity. Several lab experiences are performed in order to obtain these parameters from different soil
samples. Porosity and water content are measured and controlled. Velocity is obtained by measuring the two-way travel
time of the reflected wave and comparing wave reflected amplitudes on the surface of the samples. Attenuation
coefficients are determined from the analysis of the amplitude of the wave traveling in different thickness samples.
Frequencies velocities and wave attenuation are analyzed in the different cases in order to characterize those different
media and to relate its water content and its porosity with these measured parameters. The experimental results were also
compared with the complex refraction index model (CRIM).
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