Craig Warren

Creating FDTD models of commercial GPR antennas using Taguchi’s optimisation method

Very few researchers have developed numerical models of Ground-Penetrating Radar (GPR) that include realistic descriptions of both the antennas and the subsurface. This is essential to be able to accurately predict responses from near-surface, near-field targets. This paper presents detailed three-dimensional (3D) Finite-Difference Time-Domain (FDTD) models of two commercial GPR antennas—a Geophysical Survey Systems, Inc. (GSSI) 1.5 GHz antenna and a MALA Geoscience 1.2 GHz antenna—developed using simple analyses of the geometries and the main components of the antennas. Values for unknown parameters in the antenna models (due to commercial sensitivity) were estimated by using Taguchi’s optimisation method, resulting in a good match between the real and modelled crosstalk responses in free-space. Validation using a series of oil-in-water emulsions to simulate the electrical properties of real materials demonstrated that it was essential to accurately model the permittivity and dispersive conductivity. When accurate descriptions of the emulsions were combined with the antenna models the simulated responses showed very good agreement with real data. This provides confidence for use of the antenna models in more advanced studies.Very few researchers have developed numerical models of ground-penetrating radar (GPR) that include realistic descriptions of both the antennas and the subsurface. This is essential to be able to accurately predict responses from near-surface, near-field targets. We have developed a detailed 3D finite-difference time-domain models of two commercial GPR antennas — a Geophysical Survey Systems, Inc. (GSSI) 1.5-GHz antenna and a MALA Geoscience 1.2-GHz antenna — using simple analyses of the geometries and the main components of the antennas. Values for unknown parameters in the antenna models (due to commercial sensitivity) were estimated by using Taguchi’s optimization method, resulting in a good match between the real and modeled crosstalk responses in free space. Validation using a series of oil-in-water emulsions to simulate the electrical properties of real materials demonstrated that it was essential to accurately model the permittivity and dispersive conductivity. When accurate descriptions of the emu...

On the Use of Conformal Models and Methods in Dosimetry for Nonuniform Field Exposure

Numerical artifacts affect the reliability of computational dosimetry of human exposure to low-frequency electromagnetic fields. In the guidelines of the International Commission of Non-Ionizing Radiation Protection, a reduction factor of 3 was considered to take into account numerical uncertainties when determining the limit values for human exposure. However, the rationale for this value is unsure. The IEEE International Committee on Electromagnetic Safety has published a research agenda to resolve numerical uncertainties in low-frequency dosimetry. For this purpose, intercomparison of results computed using different methods by different research groups is important. In previous intercomparison studies for low-frequency exposures, only a few computational methods were used, and the computational scenario was limited to a uniform magnetic field exposure. This study presents an application of various numerical techniques used: different finite-element method (FEM) schemes, method of moments, and boundary-element method (BEM) variants, and, finally, by using a hybrid FEM/BEM approach. As a computational example, the induced electric field in the brain by the coil used in transcranial magnetic stimulation is investigated. Intercomparison of the computational results is presented qualitatively. Some remarks are given for the effectiveness and limitations of application of the various computational methods.

Foreword of IWAGPR2017 - the 9th International Workshop on Advanced Ground Penetrating Radar

It has been a great honour and pleasure to organise the 9th International Workshop on Advanced Ground Penetrating Radar (IWAGPR2017) in Edinburgh, UK from the 28th to the 30th June, 2017. This biennial event is one of the few international conferences dedicated solely to the dissemination of new research and best practice in ground penetrating radar (GPR). Its main aim is to be a productive forum where new research ideas can be discussed and new collaborations can be developed to advance further GPR research and technologies.

Performance of a Ground Penetrating Radar Antenna in Heterogeneous Environments

Understanding how energy is transmitted and received by Ground Penetrating Radar antennas is crucial to many areas of the industry: antenna design, data processing and inversion algorithms, usage of antennas in GPR surveys, and interpretation of GPR responses. The radiation characteristics of antennas are usually investigated by studying the radiation patterns and directivity. For GPR antennas it is important to study these characteristics when the antenna is in environments that would typically be encountered in GPR surveys. Physically measuring antenna radiation patterns in such environments presents many practical difficulties, and there have been very limited numerical studies that combine real GPR antenna models with realistic environments. This paper presents a numerical investigation of the radiation characteristics of a high-frequency GPR antenna in a realistic environment. An advanced modelling toolset has been developed that enables detailed models of GPR antennas to be used with realistic heterogeneous soil models. In this initial investigation small differences in directivity have been observed between a lossless dielectric environment and a more realistic environment featuring a heterogeneous soil model. These findings are part of an on-going full parametric study incorporating a range of different soils, fractal weightings and also the inclusion of rough surface modelling.

Numerical Modelling of Commercial GPR Antennas

The use of Ground Penetrating Radar (GPR) has become widespread in a range of fields - civil engineering, geophysics, environmental engineering, archaeology, and remote sensing. This has led to the development of increasingly sophisticated GPR models to help progress understanding of how to detect, interpret and identify buried objects. The transmitter and receiver antenna(s) are a key component of any GPR system, but are often not accurately described and therefore not well modelled in many GPR simulators. This research aims to improve understanding and interpretation of GPR signal attributes, by incorporating accurate descriptions of commercially used antennas into GPR models. A methodology is demonstrated for creating 3D FDTD models of two real GPR antennas. It is shown that when the, often complex, geometry is accurately represented in the FDTD model, a good agreement can be obtained between the simulated results and those measured directly using real GPR transducers.