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|Title: ||Numerical modelling of high-frequency ground-penetrating radar antennas|
|Authors: ||Warren, Craig|
|Supervisor(s): ||Giannopoulos, Antonios|
Forde, Michael C.
|Issue Date: ||2009|
|Publisher: ||The University of Edinburgh|
|Abstract: ||Ground-Penetrating Radar (GPR) is a non-destructive electromagnetic investigative
tool used in many applications across the fields of engineering and
geophysics. The propagation of electromagnetic waves in lossy materials is
complex and over the past 20 years, the computational modelling of GPR has
developed to improve our understanding of this phenomenon.
This research focuses on the development of accurate numerical models of
widely-used, high-frequency commercial GPR antennas. High-frequency, highresolution
GPR antennas are mainly used in civil engineering for the evaluation
of structural features in concrete i. e., the location of rebars, conduits, voids
and cracking. These types of target are typically located close to the surface
and their responses can be coupled with the direct wave of the antenna. Most
numerical simulations of GPR only include a simple excitation model, such as an
infinitesimal dipole, which does not represent the actual antenna. By omitting
the real antenna from the model, simulations cannot accurately replicate the
amplitudes and waveshapes of real GPR responses.
Numerical models of a 1.5 GHz Geophysical Survey Systems, Inc. (GSSI) antenna
and a 1.2 GHz MALÅ GeoScience (MALÅ) antenna have been developed.
The geometry of antennas is often complex with many fine features that must be
captured in the numerical models. To visualise this level of detail in 3d, software
was developed to link Paraview—an open source visualisation application which
uses the Visualisation Toolkit (VTK)—with GprMax3D—electromagnetic simulation
software based on the Finite-Difference Time-Domain (FDTD) method.
Certain component values from the real antennas that were required for the
models could not be readily determined due to commercial sensitivity. Values
for these unknown parameters were found by implementing an optimisation
technique known as Taguchi’s method. The metric used to initially assess
the accuracy of the antenna models was a cross-corellation of the crosstalk
responses from the models with the crosstalk responses measured from the real
antennas. A 98 % match between modelled and real crosstalk responses was
Further validation of the antenna models was undertaken using a series of
laboratory experiments where oil-in-water (O/W) emulsions were created to
simulate the electrical properties of real materials. The emulsions provided
homogeneous liquids with controllable permittivity and conductivity and enabled
different types of targets, typically encountered with GPR, to be tested. The laboratory setup was replicated in simulations which included the antenna
models and an excellent agreement was shown between the measured and
modelled data. The models reproduced both the amplitude and waveshape of
the real responses whilst B-scans showed that the models were also accurately
capturing effects, such as masking, present in the real data. It was shown
that to achieve this accuracy, the real permittivity and conductivity profiles of
materials must be correctly modelled.
The validated antenna models were then used to investigate the radiation
dynamics of GPR antennas. It was found that the shape and directivity of
theoretically predicted far-field radiation patterns differ significantly from real
antenna patterns. Being able to understand and visualise in 3d the antenna
patterns of real GPR antennas, over realistic materials containing typical
targets, is extremely important for antenna design and also from a practical
|Keywords: ||ground-penetrating radar|
Geophysical Survey Systems, Inc.
|Appears in Collections:||Engineering thesis and dissertation collection|
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