Computer Simulation

The theoretical modelling of the radar tests on the wall will be carried out using a software package called GPRMAX 2D/3D written by Dr Antonis Giannopoulos.

All electromagnetic phenomena, on a macroscopic scale, are described by the well known Maxwells equations . These use first order partial differential equations which express the relations between the fundamental electromagnetic field quantities and their dependence on their sources.

In order to model the propagation of radar waves through a medium, GPRMAX2D/3D solves Maxwells equations using the finite difference time domain method (FDTD).

The FDTD method was originally pioneered by Kane Yee. The method is an iterative procedure in space and time domains utilising Maxwells Equations. The procedure uses a finite model, due to computational restraints, to represent infinite space. It accomplishes this by introducing an 'Absorbing Boundary Condition' at the edge of the model space. This ABC absorbs all simulated waves striking it, avoiding any reflections, and thereby modelling infinite space. This can be carried out in both 2D and 3D space.

Complex geometry can be modelled from component shapes, which in turn are individually assigned EM properties. This gives rise to a very flexible system.

Examples of the output from this program are shown below

The above movie shows the passage of a radar wave through a dual-leaf wall system with an air void.

The above movie shows the passage of a radar trace through a post-tensioned beam.