In-material electromagnetic characterization of concrete using embedded monopole antennas: A Method of Auxiliary Sources approach

This study presents a minimally invasive electromagnetic method for distinguishing different types of concrete using two monopole antennas inserted into small holes drilled in the material. One antenna is used as the transmitter, while the electromagnetic response induced on the second antenna is analyzed as a function of frequency. Concrete specimens with different mixture ratios were prepared and experimentally characterized. Dielectric spectroscopy was used to determine their frequency-dependent complex permittivity, while compression tests provided the corresponding mechanical-strength values. The measured dielectric properties were incorporated into full-wave simulations to interpret the electromagnetic interaction between the embedded antennas and to identify the resonant behavior of the specimens. The simulations were performed using the Method of Auxiliary Sources (MAS) and validated with the commercial electromagnetic solver FEKO, showing close agreement in the calculated current distributions. The results demonstrate that the electromagnetic response of the embedded-monopole configuration is strongly influenced by the permittivity and dielectric losses of the concrete, producing specimen-dependent signatures governed primarily by its measured complex permittivity. However, within the limited dataset considered in this study, the resonant frequency alone is insufficient for reliably estimating compressive strength. Therefore, the proposed configuration should be regarded as a preliminary framework for electromagnetic signature-based concrete characterization that can be further refined and extended in future studies, with the MAS model serving as a complementary tool for interpreting the measured responses.