Bernhard Lampe

A finite-difference time-domain simulation tool for ground-penetrating radar antennas

The generation and recording of electromagnetic waves by typical ground‐penetrating radar (GPR) systems are complex phenomena. To investigate the characteristics of typical GPR antennas operating in diverse environments, we have developed a versatile and efficient simulation tool. It is based on a finite‐difference time‐domain (FDTD) approximation of Maxwells equations that lets one simulate the radiation characteristics of a wide variety of typical surface GPR antenna systems. The accuracy of the algorithm is benchmarked and validated with respect to laboratory measurements for comparable antenna systems. Computed radiation patterns demonstrate that the illumination of the subsurface in the near‐ to intermediate‐field range varies significantly according to how the antenna is designed. Our models show the effects of varying the shapes of the antennas, adding shielding (metal box with and without absorbing material and with and without resistive loading), adding a receiver antenna, and changing the soil ...

Effects of fractal fluctuations in topographic relief, permittivity and conductivity on ground‐penetrating radar antenna radiation

Typical ground‐penetrating radar (GPR) transmitters and receivers are dipole antennas. These antennas have pronounced directivity properties and exhibit strong coupling to interfaces across which there are changes in electric material properties. Antenna coupling to the surface of idealized half‐space models has been the subject of intense research for several decades. In contrast, the behavior of antennas in the vicinity of interfaces with realistic topographic fluctuations and/or subsurface heterogeneities has been largely unexplored. To explore this issue, we simulate the responses of a typical surface GPR antenna system located on a suite of realistic fractal earth models using the finite‐difference time‐domain (FDTD) method. The models are characterized by topographic roughness of the air–soil interface and small‐scale heterogeneous distributions of permittivity and conductivity in the subsurface. Synthetic radiation patterns and input impedance values of the simulated GPR antenna system demonstrate ...

Resistively loaded antennas for ground-penetrating radar: A modeling approach

The design of surface ground-penetrating radar (GPR) antennas is inherently difficult, primarily because the presence of the air-soil interface greatly complicates both analytic and laboratory-based approaches aimed at characterizing the antennas. Versatile numerical simulation techniques capable of describing the key physical principles governing GPR antenna radiation offer new solutions to this problem. We use a finite-difference time-domain (FDTD) solution of Maxwells equations in three dimensions to explore the radiation characteristics of various bow-tie antennas (including quasi-linear antennas) operating in different environments. The antenna panels are either modeled as having an infinite conductivity [i.e., a perfect electrical conductor (PEC)], a constant finite conductivity, or a Wu-King finite-conductivity profile. Finite conductivities are accommodated through a subcell extension of the classical FDTD approach, with the model space surrounded by highly efficient generalized perfectly matched...

Numerical modeling of a complete ground-penetrating radar system

The generation and recording of electromagnetic waves by typical ground-penetrating radar (GPR) sounding systems is complex and the effects of the antennas on the recorded data are not well understood. To address this problem, we present a versatile and efficient GPR system simulation tool. This algorithm is based on a finite-difference time-domain (FDTD) approximation of Maxwells equations and allows us to model realistically the radiation characteristics of a wide variety of typical surface GPR antenna systems. The accuracy of the algorithm is benchmarked and validated with respect to extensive laboratory measurements for comparable antenna systems. Given the flexibility of this GPR modeling software, we anticipate that it will be useful not only for the design and interpretation of GPR surveys, but also for the design of novel GPR sounding systems.

Finite-difference modeling of ground penetrating radar antenna radiation

The interaction of high-frequency electromagnetic wave-fields with a typical ground-penetrating radar (GPR) antenna is complex and its effects on the recorded data are not well understood. Further distortions of the radiation pattern and pulse shape must be expected to arise in the presence of a shielding of the antenna. To address these issues, we present a three-dimensional finite-difference approximation of Maxwells equations that allows to model realistically the near-field radiation characteristic of a typical GPR system.

Realistic modelling of surface ground-penetrating radar antenna systems: where do we stand?

The generation and recording of electromagnetic waves by ground-penetrating radar (GPR) systems are complex phenomena. To investigate the characteristics of typical surface GPR antennas operating in realistic environments, we have developed an antenna simulation tool based on a finite-difference time-domain (FDTD) approximation of Maxwells equations in 3-D Cartesian coordinates. The accuracy of the algorithm is validated with respect to laboratory measurements for comparable antenna systems. Numerically efficient and accurate modeling of small antenna structures and high permittivity materials is achieved via subgridding. We simulate the radiation characteristics of a wide range of common surface GPR antenna types ranging from thin-wire antennas to bow tie antennas with arbitrary flare angles. Due to the modular structure of the algorithm, additional planar antenna designs can readily be added. Shielding is achieved by placing a metal box immediately above the antenna. Damping is accounted for by filling the shield with absorbing material, by connecting the antenna to the shield with resistors or by continuous resistive loading of the antenna panels. The effects that these features have on the radiative properties of the tested GPR systems and thus on the illumination of the subsurface are investigated for various half-space models.

Realistic modeling of surface georadar antenna systems

The generation and recording of electromagnetic waves by georadar systems are complex phenomena. To investigate the characteristics of typical surface georadar antennas operating in realistic environments, we have developed an antenna simulation tool based on a finite-difference timedomain (FDTD) approximation of Maxwells equations in 3-D Cartesian coordinates. The accuracy of the algorithm is validated with respect to laboratory measurements for comparable antenna systems. Numerically efficient and accurate modeling of small antenna structures and high permittivity materials is achieved via subgridding. The antenna panels are modeled either as perfect electrical conductors or as thin material sheets of finite, spatially variable electrical conductivity. We simulate the radiation characteristics of a wide range of common surface georadar antenna types ranging from thin-wire antennas to bow-tie antennas with arbitrary flare angles. In particular, we explore how the performance of surface georadar antennas is affected by topographic roughness and small-scale heterogeneity as well as by optimized resistive loading.

Effects of random heterogeneities and topographic fluctuations on ground-penetrating radar antenna radiation

Typical ground-pentrating radar (GPR) transmitters and receivers consist of dipole-type antennas. These antennas have pronounced directive properties and exhibit strong coupling to interfaces across which there are changes in electric material properties. Whereas coupling of antennas to smooth interfaces has been the subject of intense research for several decades, the behaviour of antennas in the vicinity of realistic small-scale heterogeneities is largely unexplored. To address this issue, we simulate the responses of a typical surface GPR antenna to a suite of scale-invariant earth models of increasing complexity. Finite-difference time-domain (FDTD) simulations demonstrate that roughness of the air-soil interface has a pronounced effect on radiation patterns. By comparison, small-scale fluctuations of permittivity only cause relatively minor local distortions of the radiation patterns.