Electromagnetic tomography measuring bench for estimating the density of materials

In the laboratory, the density of pavement cores (cylindrical samples of hot mix asphalt (HMA) material taken from roads) is assessed using an electromagnetic (EM) bench consisting of two ultra-wideband (UWB) Vivaldi antennas and a vector network analyser (VNA). The main objective is to replace the nuclear gauge system currently used in the laboratory as the standard method for this purpose. Firstly, specific antipodal Vivaldi antennas have been adapted from the literature. Their dimensions are 7 × 7 cm with a bandwidth [1.5–15 GHz]. Secondly, a tomographic approach is compared with an analytical solution and a Finite-Difference Time Domain (FDTD) simulation, based on a time-domain estimation of the dielectric under test (DUT) with a single transmitter/receiver configuration. A laboratory validation is presented and the adapted antennas as well as the time domain approach show acceptable results for assessing the dielectric constant on known materials. Finally, to show that the proposed EM bench is a promising non-ionising solution, the density or equivalent compactness of HMA cylindrical samples is estimated and compared with nuclear gauge results.